The abstracts are not formatted and shown in the order in which they were submitted.
We present numerical simulations of the passage of clumpy gas through a galactic spiral shock and the
subsequent formation of giant molecular clouds (GMCs) and the triggering of star formation.
The spiral shock forms dense clouds while dissipating kinetic energy, producing
regions that are locally gravitationally bound and collapse to form stars. In addition
to triggering the star formation process, the clumpy gas passing through the
shock naturally generates the observed velocity dispersion size relation of molecular clouds.
The coupling
of the clouds' internal kinematics to their externally triggered formation
removes the need for the clouds to be self-gravitating. Globally unbound molecular clouds
provides a simple explanation of
the low efficiency of star formation. While dense regions in the shock become
bound and collapse to form stars, the majority of the gas disperses as it leaves the spiral arm.
The emerging conviction that thick disks are prevalent in disk
galaxies offers rich possibilities of new insights into the origin and
evolution of such galaxies. Disk galaxies simulated using our galaxy formation code
are shown to have a thick disk component (Brook et al 2004, ApJ, 612) . Thick disk
stars are formed from gas which is accreted to the galaxy during a chaotic
period of hierarchical clustering at high redshift. We show that our
scenario is consistent with a wide variety of observations, including the
age, metallicity and elemental abundance of the Milky Way thick disk
population, colours of photometrically imaged extra-galactic thick disks,
and vertical colour gradients from recent spectroscopic observations of
extra-galactic thick disk stars. We then follow the evolution of structural parameters
of the subsequently formed disk galaxy, from redshift $\sim$1 to present. Consistent
with observation, little evolution in the ratio of scale height to scale length is found
in our simulated galaxy, despite its somewhat chaotic origins.
If we are ever to understand the formation of the oldest stars in
our Galaxy, and the formation of our Galaxy itself, we must understand
how the chemical abundances of old globular clusters (GCs) and very
metal-poor stars originate. Our group has identified two issues
relevent to this problem that involve the element nitrogen, as seen in
the 3360A NH molecular feature (which originates in the main sequence
stars in the GCs). The integrated spectra of old M31 GCs and old
Galactic GCs show only nitrogen enhanced, with M31 GCs having it much
more strongly enhanced than do Galactic GCs of equivalent metallicity.
Furthermore, several very metal-poor stars show enhancements of 50-200
in C, N and O, in contrast to what we see in the old GCs. All of this
evidence points to what the first stars (the zero-metal stars)
produced, but models of such stars are still in their infancy. These
are the two nitrogen conundra facing us in understanding old
stellar populations.
Galaxy disks and bulges are thought to form and evolve by two distinct
mechanisms: mergers and accretion. Testing this fundamental feature of
galaxy formation models requires the bulge-disk decomposition of
large, well-defined samples. In this talk I will report results from
the decomposition of 10,000 galaxies drawn from the Millennium Galaxy
Catalogue (MGC). The MGC is a local survey (median $z = 0.12$)
spanning 31 deg$^2$, and it combines the size, depth (26 mag
arcsec$^{-2}$) and high redshift completeness (96\%) that are
necessary to avoid serious selection biases. In particular I will
present the joint luminosity and surface brightness distributions of
disks (and bulges). The aim is to provide a $z=0$ data point for
comparison with higher redshift observations and theory.
The Deep Extragalactic Evolutionary Probe (DEEP) is a long-term Keck spectroscopic survey program
that combines structural and photometric data from HST images with kinematic, star formation,
and stellar population data from Keck spectra of galaxies at redshifts up to z ~ 1.4. We present
highlights based on results, both on-going and completed, on our study of the luminosities, sizes,
colors, kinematics, B/T, masses, star formation rates, structure, and morphologies of distant young
disk-like galaxies, many of which are small, very blue, and luminous. We will also describe the
properties of their associated bulges of their luminosity and SED's in the near to mid-IR derived
from deep Spitzer IRAC images and of their neighbors and environment.
Central to the problem of star formation is the shape of the IMF.
Feedback effects on star-forming interstellar clouds are believed to play an
important role in the properties of the IMF. The ability of interstellar gas to
be compressed under the influence of hydrodynamics and gravity depends on a
variety of feedback parameters, e.g.: metallicity, turbulent motions, stellar
radiation, dust shielding. An overview is given of the impact of these various
forms of feedback on the IMF and the differences in feedback that exist between
normal and active star-forming galaxies.
The density profiles of dark matter haloes, as inferred from rotation curve
decompositions, depend critically on the adopted M/L of the disk component.
The maximum-disk hypothesis is an often used refuge to circumvent this disk-halo
degeneracy. However, a direct and absolute measurement of the M/L can be derived
from the vertical component of the stellar velocity dispersion ellipsoid. In
this talk, we will present our ongoing Disk Mass project in which we use a novel
technique to measure the stellar velocity dispersion in a statistically
significant sample of nearly face-on spiral galaxies. For this purpose, we have
designed and build two wide-field special-purpose Integral Field Units for the
WIYN and Calar Alto telescopes. We will describe these IFUs and present some
first results.
We have used long-slit spectra of 38 bulges with the ARC 3.5m telescope to obtain luminosity-weighted age and metallicity gradients as well as line-of-sight velocity distributions. We have also perfomed bulge-to-disk decomposition using images obtained with the same telescope to study the structural properties and to separate the bulge and disk contributions. We find that most Sa and Sab bulges have large SSP ages and super-solar metallicities [Mg/Fe]. Later-typed bulges exhibit more scatter in their stellar populations, with several resembling their disks. S0s fall into both categories. There are striking correlations between the stellar populations of bulges and their kinematics, particularly in the ratio of rotational to random velocities.
\documentclass{article}
\begin{document}
The wave theory of the spiral structure of galaxies with the rare
exception is developed on the basis of the spectral/modal theory of
hydrodynamic instability. The very exception represents works (cf.
Goldreich and Lynden-Bell 1965, Goldreich and Tremain 1978, Nakagawa
and Sekyia 1992) using so-called non-modal approach. In the 1990s it
was proved by the hydrodynamical community that in the study of
smooth shear flows (gaseous galactic disks represent an example of
such flows) the canonical/modal analysis lacks perfection: operators
existing in the mathematical formalism of the modal analysis of
shear flows (e.g. the plane Couette, the Poiseuille) are not normal
and corresponding eigenfunctions are consequently non-orthogonal and
strongly interfere (Reddy et al. 1993). As a result, instability may
set in even in spectrally/asymptotically stable shear flows(cf.
Reddy and Henningson 1993, Trefethen et al. 1993, Batler and Farrell
1992, Gustavsson 1991). This circumstance provoked a change in the
paradigm in hydrodynamic studies in favor of an approach -- the non
-modal analysis -- that takes into account the non-orthogonality of
shear flow systems. This method of analysis is extensively used and
is highly productive when accompanied by numerical calculations.
(cf. Criminale and Drazin 1990, Farrell and Ioannou 1993, 2000,
Chagelishvili et al. 1993, 1996, 1997). Following this path we apply
the non-modal approach in combination with numerical calculations to
the study of the dynamics of spiral density waves in gaseous
galactic disks. Our dynamical equation exhibits interesting
properties in wavenumber space (\textbf{k}-space) that determine the
whole peculiarities of the spiral density wave phenomena in real/physical
space. In particular, we can define a physical basis of corotation
and Lindblad resonances in \textbf{k}-space.
We first investigate the evolution of separate spatial Fourier
harmonics of spiral waves with time in the shearing sheet
approximation (Goldreich and Lynden-Bell 1965). The over-reflection
and over-transmission coefficients are computed numerically for
various values of the self-gravitation (Q) parameter and wavenumber.
A detailed physical/qualitative analysis of the numerical results is
presented.
Then we move on to analyzing the dynamics of localized (both in real
and \textbf{k}-spaces) packets of spiral density waves. For this
purpose we take a Gaussian packet of short leading waves in
\textbf{k}-space at the initial moment of time. It turns out that
the behavior and motion of such a packet of short leading waves in
real/physical space depend considerably on the location of its Fourier
transform in \textbf{k}-space. For example, the initial packet may
split into two packets of long leading waves which with time are
transformed into packets of long trailing waves. Subsequently, these
two packets join and eventually convert into two packets of short
trailing waves (numerically simulated movies of this phenomenon can
be viewed at \textbf{http://www.mamacashvili.pochta.ru}). Such
dynamics is realized if the center of the original packet Fourier
transform crosses certain regions in \textbf{k}-space. Some other
cases are also considered. The evolution of the localized packet
energy and the over-reflection and over-transmission coefficients
for the split (over-reflected and over-transmitted) parts/packets
are calculated.
\\
References:
\\
Goldreich, P. and Lynden-Bell, D., 1965, {\em Mon. Not. R. astr.
Soc.}, \textbf{130}, 125.
Goldreich, P. and Tremaine, S., 1978, {\em Ap.J.}, \textbf{222},
850.
Julian, W. H. and Toomre, A., 1966, {\em Ap.J.}, \textbf{146}, 810.
Nakagawa, Y. and Sekiya, M., 1992, {\em Mon. Not. R. astr. Soc.},
\textbf{256}, 684.
Toomre, A., 1964, {\em Ap.J.}, \textbf{139}, 1217.
Toomre, A., 1981, {\em The Structure and Evolution of Normal
Galaxies}, p. 111 eds. Fall, S. M. and Lynden-Bell, D., Cambridge
University Press, Cambridge.
Toomre, A., 1969, {\em Ap.J.}, \textbf{158}, 899.
Mark, J. W-K., 1976, {\em Ap.J.}, \textbf{205}, 363.
Mark, J. W-K., 1974, {\em Proc. IAU Symposium No. 58, Formation and
Dynamics of Galaxies} ed. J.R. Shakeshaft (Dordrecht: Reidel),p.417
Lin, C. C. and Shu, F. H., 1966, {\em Proc. Nat. Acad. Sci. USA},
\textbf{55}, 229.
Bertin, G. and Lin, C.C., 1996, {\em Spiral Structure in Galaxies:
A Density Wave Theory}, The MIT Press Cambridge, Massachusetts and
London, England.
Papaloizou, J. C. B. and Savonije, G. J., 1991, {\em Mon. Not. R.
astr. Soc.}, \textbf{248}, 353.
\\
References concerning the non-orthogonality of eigenfunctions in
shear flows and non-modal approach:
\\
Reddy, S. C., Schmid, P. J. and Henningson, D. S., 1993,
Pseudospectra of the Orr-Sommerfeld operator., {\em SIAM(Soc.
Ind-Appl. Math) J. Appl. Math.}, \textbf{53}, 15.
Reddy, S. C. and Henningson, D. S., 1993, Energy growth in viscous
channel flows., {\em J. Fluid Mech.}, \textbf{252}, 209.
Trefethen, L. N., Trefethen, A. E., Reddy, S. C. and Driscoll, T.
A., 1993, Hydrodynamic stability without eigenvalues. {\em Science},
\textbf{261}, 578.
Butler, K. M. and Farrel, B. F., 1992, Three-dimensional optimal
perturbations in viscous shear flows. {\em Phys. Fluids A},
\textbf{4}, 1637.
Gustavsson, L. H., 1991, Energy growth of three--dimensional
disturbances in plane Poiseuille flow., {\em J. Fluid Mech.},
\textbf{224}, 241.
Criminale, W. O. and Drazin, P. G., 1990, {\em Studies in Appl.
Math.}, \textbf{83}, 123.
Farrell, B. F. and Ioannou, P. J., 1993, {\em Phys. Fluids A},
\textbf{5}, 1390.
Farrel, B. F. and Ioannou, P. J., 2000, {\em Phys. Fluids},
\textbf{12}, 3021.
Chagelishvili, G. D., Chanishvili, R. G., Khristov, T. S. and
Lominadze, J. G., 1993, {\em Phys. Rev. E}, \textbf{47}, 366.
Chagelishvili, G. D., Rogava, A. D., Tsiklauri, D. G., 1996, {\em
Phys. Rev. E}, \textbf{53}, 6028.
Chagelishvili, G. D., Tevzadze, A. G., Bodo, G. Moiseev, S. S.,
1997, {\em Phys. Rev. Lett.}, \textbf{79}, 3178.
\end{document}
The chemical evolution of the thin and thick disk
of our Galaxy was investigated in framework of the opened model with gas inflow.
It was supposed that the thin and thick disks separate chemically and spatially
and have different evolution timescales.
The Galactic evolution of alpha elements (Mg, Si, O) was investigated for the
thin and thick disk.
The obtained results allow us that the star formation history
of the thin disk is more smooth and quiet than its for the thick disk of our
Galaxy.A gas infall plays an important role
in an appearance of chemical distinctions of relative abundances
between the thin and thick disk -
a inflow rate is more intensive for the thick disk.
The outer halo of M31 has been the subject of many a study over the last
decade. The stellar population studies fall into three broad categories:
(1) ground-based wide-field imaging and photometry, most recently with
CFHT/MegaCam and Subaru/Suprime-Cam (2) deep Hubble Space Telescope imaging,
including ultradeep imaging reaching below the main-sequence turnoff and
(3) spectroscopy of individual luminous red giant branch stars with
Keck/DEIMOS. In this talk, I will focus on the first and third categories
of studies touching upon subjects such as: bulge versus extended outer halo,
orbit and progenitor of the giant southern stream, outer disk-halo interface,
halo dynamics, and chemical abundance constraints.
We study the effects of the UV radiation from the first stars and quasars on the formation of
primordial bound objects in the Universe. We trace the evolution of a spherically symmetric
density perturbation in the Lambda Cold Dark Matter model, solving the frequency-dependent
radiative transfer equation, non-equilibrium chemistry, and one-dimensional gas
hydrodynamics. We concentrate on the destruction and formation processes of the H2
molecule, which is the main coolant in the primordial objects. Although the UV radiation can
destroy H2 molecules and suppress collapsing of the primordial clouds, we find that for
plausible radiation intensities and spectra, the collapsing gas can cool efficiently to
temperatures well below 10^4 K. Our results imply that that star formation can take place in
low mass objects collapsing in the UV background.
We study the vertical density distribution of stars and gas (HI and
H_2) in a galactic disk which is embedded in a dark matter halo. The
new feature of this work is the inclusion of gas, and the gravitational
coupling between stars and gas, which has led to a more realistic
treatment of a multi-component galactic disk. The gas gravity is shown
to be crucially important despite the low gas mass fraction. This
approach physically explains the observed scaleheight distribution of
all the three disk components, including the long-standing puzzle
(Oort 1962) of a constant HI scaleheight observed in the inner Galaxy.
The above model is applied to two external galaxies: NGC 891 and
NGC 4565, and the stellar disk is shown to be not strictly flat as was
long believed but rather it shows a moderate flaring with radius. This
result is in a good agreement with the recent observations of a large
sample of edge-on spiral galaxies by de Grijs & Peletier (1997).
The mass and dark matter fraction of the Milky Way remain among the major
unsolved problems about our home galaxy. The masses of other spiral
galaxies can be determined from their rotation curves, through long-slit
spectroscopy. For the Milky Way obtaining the complete rotation
curve is a more complex problem. By obtaining the 3-dimensional motions of
tracer objects outside the solar circle, the rotation curve and
Galactic mass distribution can be derived. Therefore, we present the first
findings from a project to definitively measure the motions of disk
tracers, both inside and outside the solar circle. Our tracer of choice is
the open cluster population of the Galactic disk, a tracer that has
numerous advantages over other, previously tried types. We have collected
a near uniform sample of spectroscopic data for large numbers of stars in
over 100 open clusters. Each measured member star has an accurate radial
velocity ($\sigma_v \sim$1 km/s) and proper motion (from Tycho2),
permitting accurate cluster membership determination. By averaging over
the ensemble of cluster members, we obtain a very accurate determination
of the complete space velocity vector. From this sample, we present new
measurements of the Galactic rotation curve from $0.7 R_{Sun}$ to $2 R_{Sun}$.
The stellar velocity data in the central regions of the Large Magellanic Cloud
shows the presence of counterrotation. This region and the secondary bar of the
LMC have the same location and position angle. We also propose that the
velocity data can be matched with a model where the inner LMC has two disks with
different LON and velocity profile. Two disks with different LON
and velocity profiles can create regions which are kinematically and spatially
separated. Predicted such locations are found to match the observed locations
where the HI clouds are found to have two velocities. The possibility of
an accretion or merger event for the formation of counterrotating core will be
presented. We also discuss whether the two disks and the counterrotation
happened together. (This paper in the process of getting accepted in ApJ letters,
after the first revision.)
Fully self-consistent N-body simulations of a disc galaxy show that
there is a strong dynamical interaction between the bar, the halo and
the central mass concentration (CMC), whenever all three components are
present. In particular, in some cases the CMC can cause a weakening of
the bar, while, in other cases, it can destroy the bar
completely. This depends not only on the CMC properties (mass and
central concentration), but also on the properties of the bar and of the
halo. I examine what types of bars are more prone to destruction and
what types of haloes favour this process, relying strongly on orbital
structure studies. I also examine the bar remnants to establish
whether this mechanism can explain the formation of bulges and/or
lenses.
N-body simulations argue that the inner haloes of barred galaxies
should not be axisymmetric, but rather triaxial and prolate-like. The
departure from sphericity is strongest near the center and decreases
outwards. The length of this inner structure, which I call a halo bar,
increases with time, but always stays shorter than the disc bar. It is
roughly aligned with the disc bar, i.e. it turns with the same pattern
speed. The bisymmetric component in the halo continues outside the
halo bar, trailing behind the disc bar in the form of an open
spiral. The inner parts of the halo display some rotation, and a
velocity field characteristic of ovals. There are correlations between
the properties of the halo bar and those of the disc bar.
We present preliminary results of our research in radial velocity and proper
motion measurements in the galactic bulge. Radial velocity spectra have been
taken in the VLT's integral field spectrograph VIMOS/IFU in four low extinction
``windows" while proper motion mesurements come from HST imaging. The procedure
to extract each star spectrum from the fiber-spectra cube combines the IFU data
with the HST positions and it has not been used before. These preliminary results
show that we can measure radial velocities for $\sim 80$ stars in a
$30"\times 30"$ field. The goal in this project is to find a description
in the gravitational potential, the bar shape and velocity distributions
according to our observations and previous work.
We present results and progress notes from an investigation into the
rotation curves of spiral galaxies at high and low redshift. We discuss
the rotation curves of spirals at z~1 from the DEEP projects that have HST
imaging. We show the science that the DEEP team is doing with them,
and highlight a pilot Tully-Fisher study of 15 cluster disk galaxies at z~0.4.
For this project, we carefully choose a local field comparison sample
resembling our own and closely match our velocity and luminosity
measurement techniques to those used locally and find that the distant
cluster sample is 0.5 mag underluminous as compared to local field galaxies.
With a local sample of bright spirals, we discuss dark matter scaling
relations and the galaxies' integrated and radial angular momentum content.
These data are compared to theories for dark matter distributions in
galactic halos with and without taking into account the mechanism of
adiabatic contraction, and theories for the integrated and radial
distribution of angular momentum in dark matter halos.
Solution of the classical gas consumption puzzle in normal
luminous galaxies could lie in the presence of "dark" baryons
hidden in their haloes. Discovery of the low-redshift population
of Lymann-alpha absorbers and first steps made in understanding of
the transition between the high-redshift intergalactic and the
low-redshift predominantly galactic population of QSO absorption
systems, as well as improved understanding of the nature of
so-called high-velocity clouds point in that direction, reviving
the old idea of Spitzer about the infall from gaseous galactic
haloes. These indications are naturally followed by different
hypotheses about the ultimate fate of baryons - for spiral
galaxies, they are bound to fall in the gravitational potential of
the dark halo and coalesce with the rotationally supported disk.
Such aggregates also present a potential reservoir of gas for
fuelling future star formation. We study the impact of different
models of global gas infall into "normal" spiral disks on their
gas consumption and star-forming time scales using two different
samples : 61 "normal" spiral galaxies with values of gas and star
formation rate (SFR) surface densities averaged over the optical
disk (Kennicutt 1998) and 16 disk galaxies for which azimuthally
averaged quantities were computed (Boissier et al. 2003). Adopting
the Schmidt star formation law with index n=1.3 (the average value
of a sample of observational surveys), we compare the consumption
time scales of the galaxies from the former sample for two
scenarios of their evolution: "naive" model with neither recycling
of interstellar gas nor gas infall from galactic haloes, and a
more realistic one with parameters that control the recycling and
infall of gas. The later sample is used for analysis of the impact
that different values of the star formation threshold have on the
resulting star-forming time scales.
Intervening absorption lines found in the spectra of bright background
quasars are powerful probes of galaxies at all redshifts. The highest HI column
density absorbers, damped Ly-alpha systems (DLAs), dominate the neutral gas
mass density of the universe. However, the optical identification of
the galaxies associated with the DLAs has proven to be difficult,
despite the large effort that has gone into finding these
systems. This seems confusing since in the local universe blind 21-cm
surveys such as HIPASS have shown that the bulk of the neutral
hydrogen mass density resides in L* galaxies, which should be easily
identifiable. To resolve this paradox we have used the WHISP data
base of 21-cm HI maps of local galaxies to calculate in detail the
expected properties of z=0 DLA systems. We found that the properties
and incident rate of DLA absorption systems are in good agreement with
DLAs originating in gas disks of galaxies like those in the z=0
population. This analysis includes the redshift number density
$dN/dz$, the frequency distribution of column densities $f(N)$, and
also extends to the impact parameters relative to the centres of
optically identified hosts, their luminosties and even to the
distribution of DLA metallicities.
We present a summary of the results of blind extragalactic 21-cm
surveys and make a comparison with the results from DLA studies, use
the WHISP analysis to argue that the local galaxy population can
explain all DLA properties, and discuss the implications for our understanding
of DLAs and their host galaxies.
We will present results from a moderate (R=10,000) spectral resolution
integral field spectroscopic survey of 39 nearly face-on disk galaxies.
The H$\alpha$, [SII] and N[II] emission lines reveal clues about the state
of the ionized instellar medium in external galaxies. Ionized line flux
ratios yield the distribution of electron temperature and the ionization
state of the gas. Velocity dispersions measured perpendicular to the
plane allow us to explore the feedback mechanism that balances gas
dissipation and gravitational instabilities. We will compare our
observations of the ionized medium in a relatively large sample of
galaxies to the ionized medium in our own Milky Way.
IC 2602 is a rich loose clustering, 1.5 degrees in diameter, located
some 5 degrees south of the Galactic equator. This is one of the
nearest young open clusters and has gained the attention for two main
reasons: 1) it is a very suitable object for studying the chromospheric
activity and rotation evolution among the late type stars, and 2)it
is a possible member of the Local Sco-Cen Association. Being one of the
most prominent concentrations in the southern section of Local
Association, the cluster plays an important role in our understanding of
the Galactic structure in the Solar vicinity. This contribution presents
new results about the structure of the field of IC 2602 based on
homogeneous Stroemgren-H$\beta$ photometry of O-B9 stars. The precise
photometry and reliable calibrations allow four spatially coherent
groupings to be clearly separated in this direction: a low reddened
clustering located at 166 pc (IC 2602) and background layers at 500 pc,
1000 pc and 2500 pc. A region free of massive luminous stars is clearly
distinguished between 1.2 and 2.4 kpc and can be associated with
inter-arm space between the Local Association and the distant spiral
structures toward Carina.
We present the results of both Bulge-disk decomposition, and single component
Sersic fits for $\sim$10,000 galaxies from the 37.5 square degrees of the
Millennium Galaxy Catalogue (MGC). The MGC provides a view of the local Universe
that is deeper, of higher resolution, and higher completeness than SDSS
and represents the highest quality sample of galaxy structural parameters
in the local Universe. We demonstrate the recovery of disk parameters to an
accuracy of 10\%, and present measurements of the distribution in disk sizes,
and photometric parameters, including the disk luminosity function. The results
are compared to the expectations of models and high redshift samples.
Finally, the distribution of absolute magnitudes and surface brightnesses, as
a function of inclination, are used to derive an empirical dust law, which is
compared to physical models.
The dust opacity of foreground spiral disks can be probed from the number of
distant galaxies seen thorough it. To calibrate this number for effects other
then the dust extinction, Gonzalez et al. (1998) developed the ``Synthetic
Field Method". A synthetic field is an extincted Hubble Deep Field added to
the science field. The relation between the dimming and the number of retrieved
synthetic galaxies calibrates the number found in the science field.
Here I present results from counts in 32 HST/WFPC2 fields. The relations
between opacity and radius, Hubble type, arm/disk regions, surface brightness
and HI are presented. The opacity is found to be caused by a clumpy and flat
distribution of clouds in the disk. The brighter parts of the disk, centre
and spiral arms, are also the more opaque ones.
The dust distribution in spiral disks is found to be more extended then
stellar disk, a result corroborated by the few overlapping SCUBA observations
available. From the compariton with SCUBA and Spitzer emission, it seems
likely that this extended disk is very cold material. The ratio between he HI
column densities and opacity are compared to the literature. It seems to
point towards more dust in the disk then the previous studies which used warm
dust emission.
The ``Synthetic Field Method" is very well characterised now and the counts of
distant galaxies in recent HST/ACS imaging of M101 and M51 should reveal more
on the extent and relative importance of this cold dust disk.
I will report results from the SAURON 2D integral-field survey of the
stellar and ionized gas kinematics of a representative sample of nearby Sa
bulges.
In this talk I will focus on the relationship between the stellar and gas
distribution and kinematics of the different structures (bulge, disk, central
disks,...) found in our sample of galaxies. Using the stellar kinematics I will
review the frequency of central disks, kinematically decoupled cores and bars
and examine their relevance in the context of the formation of (pseudo-)bulges
and in the framework of secular evolution. I will use gas distribution and
kinematics, together with emission-line diagnostic tools, to discuss the origin
and triggers of the ionized gas, and their relation with the presence of dust in
Sa galaxies. Finally, I will highlight the individual case of NGC5953 to
illustrate the influence of mergers/interactions on the observed stellar and gas
properties of Sa galaxies.
We have examined the Tully-Fisher relations (TFRs) of distant cluster
and field disk galaxies, in order to investigate their evolution with
redshift and environment.
From 'matched' samples of 58 field and 22 cluster galaxies, with $0.25
< z < 1$ and $M_B < -19.5$ mag, we find that such cluster galaxies are
systematically brightened with respect to the field by $0.7\pm0.2$
mag, at a given rotation velocity. We suggest that this is due to
enhanced star-formation during the early stages of an interaction with
the cluster environment.
In the field we find a modest increasing offset from the local TFR
with redshift, reaching a brightening of at most $1.0\pm0.5$ mag, for
a given rotation velocity, by a redshift of 1. Interpreting this in
terms of star-formation rate (SFR) suggests that the recent rapid
decline in the SFR density of the universe is not driven by the
evolution of SFR in individual bright spiral galaxies.
We also present the latest TFR results from the ESO Distant Clusters
Survey.
Measurement of the vertical stellar velocity dispersion ($\sigma_z$)
in galactic disks is the limiting factor in directly obtaining the
disk mass-to-light ratio, $(M/L)_d$. Indeed, this measurement has
only recently become technically reasonable in normal or high surface
brightness disks. Yet, knowledge of $(M/L)_d$ is critical for
understanding the true, {\it unique} form of the dark matter (DM) halo
as opposed to an {\it allowable} form derived based on, say, a maximal
disk. Low surface brightness (LSB) galaxies are often used to
characterize DM halos since their baryonic content is nearly
insignificant however, the disk-halo degeneracy still persists. To
circumvent the observational difficulties entailed, we devise a method
of indirectly measuring $\sigma_z$ from the observed asymmetric drift
(AD). Under basic galactic disk dynamical assumptions including the
epicyclic approximation, the AD can be related to $\sigma_R$ and
$\sigma_z$. Previously-determined, empirical relations such as the
ratio of scale height to scale length or the disk stability criterion,
$Q$, can be used to isolate $\sigma_z$. Compared to directly
measuring $\sigma_z$ from absorption lines, measurement of the AD is
observationally less difficult and can, in principle, be detected at
lower signal levels. We present a test application of this method by
comparing absorption line measurements of $\sigma_z$ in NGC 3982 to
that determined by the AD. We also discuss the extension of the
method to the LSB and high-redshift regimes.
Galaxies do not spend their whole lifes in isolation. In fact, interactions
and merger events seem to be very important in galaxy evolution, even more so
at high redshift, where the volume-density of galaxies was considerably
higher than it is today. To develope a more general understanding of this
phenomenon it is necessary to study nearby examples in great detail.
The nearby merger NGC4038/39, the Antennae, forms a unique laboratory for this
purpose. Our focus is on the individual coeval young stellar populations that
formed when the system was triggered into starbursting mode by the interaction.
Recently high spatial resolution mid-infrared data were obtained with VISIR:
imaging tracing the distribution of PAHs in the overlap region plus low
resolution N-band spectrscopy of several of the youngest star clusters
(< 10 Myr). The combination of mid-infrared VISIR and near-infrared ISAAC
data gives us a better understanding of the physical conditions in these
superstarclusters. Here we present the first results on the properties of the
upper main sequence and the evolutionary state of the clusters.
The formation and evolution scenarios that led to the existence of
Low Surface Brightness (LSB) galaxies are not well understood yet.
Although LSBs have HI components with low surface densities,
they can be regarded as gas-rich in general.
Hence, the key in understanding LSBs lies in the answer to the question
what prevented them from sufficient star formation.
Using the public data releases of the Sloan Digital Sky Survey (SDSS),
we investigated the galaxy density around LSBs in comparison to High
Surface Brightness (HSB) galaxies. We performed a number
counting analysis in three dimensions
within spheres of several radii on a sample of HSBs and
LSBs with well measured SDSS redshifts.
On scales between 2 and 5\,Mpc our results show significantly lower galaxy
densities in the vicinity of LSBs compared to HSBs. At
larger scales than 5\,Mpc LSBs and HSBs share the same clustering
properties but on scales below 2\,Mpc the galaxy densities in the
neighbourhood of LSBs lie systematically (but only with a slight
significance) below that of HSBs.
In the pie slice diagrams LSBs favour the outer
rims of the filaments of the Large Scale Structure and
some LSBs are even found in voids.
These results give strong evidence to a formation and evolution
scenario where LSBs were formed in low density environments. Hence,
the lack of tidal interactions with companions must have caused the absence
of an effective trigger for a sufficient starburst.
The Deep Extragalactic Evolutionary Probe (DEEP) is a long-term Keck
spectroscopic survey program that combines structural and photometric data
from HST images with kinematic, star formation, and stellar population
data from Keck spectra of galaxies at redshifts up to z ~ 1.4. We present
highlights based on results, both on-going and completed, from our studies of
the luminosities, sizes, colors, star formation rates, stellar masses, structure (B/D), and morphologies of distant disk-like galaxies. We include our study of the relative colors, luminosities, and sizes of the bulges associated with the disks such data are relevant for exploring secular and other evolution models. Preliminary results from deep Spitzer IRAC and MIPS observations of our distant disks may also be in hand.
Recent observations have shown that the disks of spiral galaxies are
surrounded by thick layers of both neutral and ionized gas, which
extend out to large distances (up to 10-15 kpc)
and have peculiar kinematics.
Rotation curves at different heights have been derived from HI
observations of the edge-on galaxy NGC891 and a vertical decrease
in rotation velocity (about 15 km/s/kpc) has been found.
In non-edge-on galaxies (for instance NGC2403), large non-circular
motions have been detected of up to more than 100 km/s.
The origin and nature of this extra-planar gas are still a matter of
debate. It can be the result of superbubble outflows from the
galactic disk and/or of cosmological accretion from intergalactic space.
The extra-planar gas in nearby galaxies is likely to be the analogue
of the so-called Intermediate and High Velocity Clouds of the
Milky Way.
We present a study to determine how star formation contributes to
galaxy growth since redshift $z=1.5$. Using galaxies from the MUnich
Near-Infrared Cluster Survey (MUNICS) and the FORS Deep Field (FDF),
we investigate the specific star formation rate (SSFR, star formation
rate [SFR] per unit galaxy stellar mass) as a function of galaxy
stallar mass and redshift. We find that at all redshifts, the SSFR
decreases as galaxy stellar mass increases, suggesting that star
formation contributes more to the growth of low-mass galaxies than
high-mass galaxies during this epoch. We also find a ridge in the
SSFR that runs parallel to lines of constant SFR, which decreases by
an order of magnitude from $z=1$ to today. The ridge evolves
independently of galaxy stellar mass to a particular turnover mass at
the high mass end. Galaxies above the turnover mass show a sharp
decrease in SSFR compared to the average at that epoch, and the
turnover mass increases with redshift. We also show low redshift SSFR
results from independent longslit, drift-scanning observations of 100
Sloan Digital Sky Survey galaxies in an attempt to quantify any
aperture affects at $z<0.1$.
I will present results from a new set of multi million particles
simulations of the formation of individual disk galaxies in a
cosmological context. Galaxies span a significant range of masses.
I will show how improved resolution and a physically motivated
description of energy feedback produce galaxies with realistic angular
momentum content, the correct abundance of satellites and an ISM
structure similar to what observed in nearby galaxies. Feedback
significantly delay star formation in smaller galaxies, easily reproducing the
observed antihierarchical age-mass relation.
I will then focus on the structure and evolution of galaxy disks
over cosmic ages, exploring the mechanisms that lead to the formation of
the Hubble sequence and showing that massive disks can form at redshift
higher than one, usually shortly after the last major merger event of
their parent halo. Animations will highlight some the results
presented.
We study the morphology of the halo of some one hundred
Galactic globular clusters with 2MASS Point Source Catalog.
Morphological parameters such as flattening and average radius
of the halo of each globular cluster
were estimated by fitting the effective density contour with ellipses.
The globular clusters in our sample in general have spherical halos,
with a median flattening (f=1-b/a) of 0.1. Those that are closer
to the Galactic bulge show more circularized shapes and have smaller
physical sizes. Furthremore, intrinsically more luminous clusters,
hence perhaps more massive, tend to be more circularized.
Remarkably, among the most 6 elongated globular clusters with f > 0.3
(1) Arp 2 and Pal 12 are known to be associated with the streamer of the
Sagittarius dwarf galaxy, (2) Pal 5 is being cannibalized by the Milky Way,
(3) UKS1 and NGC 6355 are known bulge
globular clusters, and (4) NGC 2419 is a halo member with a Galactocentric
distance ~90 kpc. We will discuss possible mechanisms which might have
caused the flattening of the globular clusters.
[revised abstract]
To better understand bulge formation, we use long-slit spectroscopy and imaging from the ARC 3.5m telescope to obtain luminosity-weighted SSP ages and abundances, line-of-sight velocity distributions, and bulge-to-disk decomposition for 38 spiral galaxies. Since previous studies have mostly found that bulges are old and metal-rich, we specifically included several blue bulges to see if these would have more disk-like stellar populations. Red bulges of all morphological types have stellar populations that are different from their disks and similar to ellipticals. Blue bulges of type S0-Sab have metallicity gradients but are similar to their disks in SSP age and [Mg/Fe]. Blue Sb-Sc bulges are identical to their disks in their stellar populations. Age gradients, with the central regions being younger, are found frequently and almost exclusively in barred galaxies. We identify galaxies in which secular processes were important based on different properties including the lack of stellar population gradients, structural and morphological properties, and kinematics. We discuss the degree of overlap among galaxies that meet the different criteria and what that implies for the formation scenarios.
We present the results of our HI survey of six loose groups of galaxies
analogous to the Local Group. The survey was conducted using the Parkes
telescope and the Australia Telescope Compact Array to produce a census
of all the gas-rich galaxies and analogs to the high-velocity clouds (HVCs)
within these groups down to M$_{HI}$< 10$^7~$M$_\odot$ as a test of models of
galaxy formation. We present the HI mass function and halo mass function
of the loose groups and show that they are consistent with those of the Local
Group. We demonstrate that our non-detection of HVC analogs in these groups
implies that they must have low HI masses and be clustered tightly around
galaxies, including around our own Milky Way. Finally, we discuss the
implications of these results for galaxy formation and evolution within loose
groups.
Recent HST imaging surveys have revealed the presence of central star
clusters in a majority of spiral galaxies. These clusters may provide
important clues to the central structure and secular evolution of disk
galaxies. However, their origin and nature remain poorly understood.
We therefore performed a spectroscopic survey with HST/STIS of 40 nuclear
clusters in early- and late-type spiral galaxies. To study the ages and
physical properties of the clusters we performed stellar population
synthesis modeling by fitting single- and mixed-population Bruzual-Charlot
template spectra. We augmented this with studies of broad-band colors and
the 4000 Angstrom break strength. The luminosity-weighted ages of the
clusters have a large spread, with ages between 10 million and 10 billion
years. Approximately half of the clusters have populations younger than
1 Gyr. This indicates that star formation in these clusters is an ongoing
process as gaseous material is driven to the center through dynamical
processes in the disk. We discuss the results in terms of scenarios for the
overall secular evolution of galactic disks and their nuclei.
The physics of the formation of Giant Molecular Clouds (GMC) is one of
the major unsolved problems of the interstellar medium. Although much
work have been done on the subject it is not yet known what the dominant
formation mechanism is, or even what the relative importance of gravity,
shocks, and magnetic fields are in the cloud formation process. A study
of GMCs in external galaxies can address the fundamental questions of
whether the molecular ISM in external galaxies is organized differently
than in the Milky Way and whether GMCs play the same central role in
massive star formation as in the Milky Way, and are then responsible for
galaxy evolution. Using the technique of mapping of dust column density
through a molecular cloud in the nearby radio-galaxy NGC5128 (Centaurus
A) we can easily disentangle molecular clouds and assess their basic
properties and star forming status, as opposed to the confused ``inside
view" of Galactic molecular clouds.
Using HST data, disc scalelengths in the ultraviolet, optical and near-infrared
wavelength regions are used to study age and metallicity gradients and dust
extinction in disc galaxies in the Hubble Deep Field North. The sample galaxies
are chosen from two redshift intervals: 0.3 < z < 0.6, and 0.8 < z < 1.1. The
observed colour gradients are compared to model calculations of dusty disc
galaxies. First results indicate that the age and metallicity gradients in the
HDF galaxies differ from the age and metallicity gradients found in local spiral
galaxies.
Theoretical predictions of spontaneous and triggered bar formation,
bar evolution, and bar dissolution will be reviewed and compared with
the available evidence from bars and disks out to redshifts of z~2. Blue
and irregular bars at high redshifts suggest that some bars form during
starbursts in the gas phase, rather than from dynamical instabilities in
existing cold stellar disks. Predictions of bar dissolution are difficult
to prove observationally as the bar fraction seems constant back to at
least z~1. Direct evidence for long-lived bars will be summarized, as
will the proposed evidence for dissolved bars. The morphology of spirals
at high redshift will also be summarized, using a recent catalog of 269
spiral galaxies in the Hubble Ultra Deep Field.
Galaxy disks, at least populations of stars in the far UV and star forming material in Halpha, have
now been found to extend to several optical radii in many galaxies. I will discuss the search for dust
at large radii, including the presentation of Spitzer data, and measurements of the kinematics of the
outer disks of galaxies. In edge-on galaxies we have extended Halpha rotation curves by a factor of
two using multi-hour obsevations on 6-8m class telescope. Finally, we will discuss whether we have
reached radii where counterrotating disk material is found.
Galaxies in the Hubble Ultra Deep Field (UDF) larger than 10 pixels (0.3 arcsec) have been classified
according to morphology. There are 884 galaxies, including spirals, ellipticals, chains, clump-clusters,
double-clumps, and tadpoles. Linear structures dominate at faint magnitudes. Radial profiles are
measured for the disk galaxies, and distributions of axial ratios for elliptical and spiral galaxies are
compared to nearby samples. Ten percent of the ellipticals are clumpy, and spiral and clump-cluster
galaxies are dominated by giant clumps. Galaxy redshifts, star formation histories, and masses are
modeled by comparing photometric colors and magnitudes with redshifted stellar population models.
Observing the star formation rate since the earliest times in the
universe is crucial to understanding galaxy formation and evolution.
Metallicity is intricately related to star formation because metals are
injected into the interstellar medium by stellar mass-loss processes.
Theory suggests that metallicity changes less rapidly than star
formation rate as a function of redshift, but until now, there has been
no solid observational foundation for the cosmic metallicity history of
star-forming galaxies. I will present results of our new
investigation into the metallicity history of galaxies. Our local
comparison samples include the Nearby Field Galaxy Survey and an
objectively selected sample of galaxy pairs. We find that the galaxy
pairs contain a broader range of star formation and metallicity
properties than observed in the NFGS, providing an important local
benchmark for comparisons with high-z samples. I compare the
metallicity properties of our local samples with a large sample of
galaxies from the GOODS field and with the Lyman Break Galaxies. This
analysis provides insight into the metallicity evolution of disk
galaxies spanning the redshift range 0 < z <3.
N-body simulations of bars are compared to both stellar kinematics and
near-infrared images of 30 edge-on spiral galaxies with a boxy bulge,
and a consistent picture of the influence of bars on the inner parts
of disks is presented. The N-body simulations allow to construct
stellar kinematic bar diagnostics for edge-on systems and to quantify
the expected vertical structure of bars. Long-slit spectra of the
sample galaxies show characteristic double-hump rotation curves,
dispersion profiles with secondary peaks and/or flat maxima, and
correlated h3 and V profiles, indicating that they indeed harbor
edge-on bars. The stellar kinematics also reveals the presence of
cold, quasi-axisymmetric central stellar disks. The ionized-gas
distribution and kinematics suggest that these likely formed through
bar-driven gaseous inflow and subsequent star formation, as often
suggested. Minimally affected by dust and dominated by Population II
stars, K-band imaging of the same galaxies spectacularly highlights
the varying scaleheight of bars, as expected from vertical disk
instabilities. The light profiles also vary in shape but never
approach a classical deVaucouleurs law. Filtering of the images
further isolates the specific orbit families at the origin of the boxy
structure, which can be directly related to periodic orbit
calculations in barred potentials. Bars are thus shown to contribute
substantially to the formation of both large-scale (triaxial) bulges
and embedded central disks, and our results support a picture where
the bulge and large-scale disk are not intrinsically distinct (either
structurally or kinematically), but both rather emerge from the rapid
radial variation of the scaleheight of the disk material (due to
bar-related vertical resonances).
I will present results from a recent survey of
late-type, low surface brightness (LSB)
spiral galaxies in the CO(1-0) and CO(2-1) lines.
In total, our group has now detected CO emission from six LSB
spirals, demonstrating that despite their typical low metallicities
and low mean gas surface densities,
at least some LSB disks contain a molecular
medium that is traced by CO. Moreover, our results indicate that
a bulge is not a prerequisite for the presence of
molecular gas at their centers. Comparing our new data
with galaxy samples
from the literature, several interesting trends emerge. We find that
CO-detected LSB spirals adhere to the same M_H2-FIR correlation as
brighter and more massive galaxies. In addition, we find that
among moderate-to-low surface brightness spirals, mass is
correlated with CO detectability to date, no moderate-to-low
surface brightness
spiral with V_rot<~90 km/s has been detected in CO to very sensitive
limits. It appears metallicity alone cannot explain this trend. I will discuss the
implications of these results for understanding the ISM structure and
dominant modes of star formation in low-mass and low surface
brightness disk galaxies.
The field of statistical studies of galaxy properties has matured well beyond
the calculation of luminosity functions, and by simultaneously analyzing a large
number of parameters, such as star formation rates, morphology, and environment,
new insights into the mechanisms that drive the evolution of galaxies can be
gained.
I present a study of the photometric and and spectroscopic properties of galaxies
in six nearby, rich clusters. The primary issues that I address are:
1) variations of the luminosity function between the field, groups, and
clusters, and their implications for the question of which environments most
strongly affect the evolution of galaxies, 2) luminosity functions for bulge
and disk components of galaxies, how they vary with morphology andenvironment,
and what this implies for the mechanisms are by which early-type galaxies are
formed in dense environments, and 3) the question whether residual correlations
between star formation and environment exist after taking into account the
fundamental differences in morphology, stellar mass, and stellar age that
already exist between galaxy populations in different environments, and what
this implies for the mechanisms that influence star formation.
We review the status of current observations of the fundamental parameters of intermediate redshift (0.2 < z < 1.2) spiral gal
axies. Advances in instrumentation of 8-10m class telescopes have made possible detailed measurements of galaxy luminosity, m
orphology, kinematics and mass, in both the optical and the infrared passbands. By studying such well known star formation in
dicators as [OII]3727A (in the optical) and H-alpha (redshifted to the infrared), the internal velocity structure and star for
mation rates of galaxies can be traced through this entire redshift regime. The combination of throughput and optimum seeing
conditions yields spectra which can be combined with high resolution multiband imaging to explore the evolution of galaxies of
various morphologies, and to place constraints on current models of galaxy formation and star formation histories.
Out to redshifts of z = 1, these data form a high redshift Tully-Fisher relation that spans four magnitudes and extends to wel
l below L*, with no obvious change in shape or slope with respect to the local relation. A comparison of disk surface brightn
ess between local and high redshift samples yields an offset in accordance with distance-dependent surface brightness selectio
n effects, as can the apparent change in disk size with redshift for disks of a given mass. These results support low Omega0
models of formation, and provide further evidence for modest increases in luminosity with lookback time for the bulk of the fi
eld spiral galaxy population.
We present results on the ionized phase of the interstellar medium of
many nearly face-on spiral galaxies based on integral-field echelle
observations. Emission-line fluxes and line-widths of H-alpha, [SII]
and N[II] reveal several puzzling characteristics of the ionized
gas. These include subtle variations of the line-widths between
galaxies and with galactic radius, but constancy between ions gross
similarity of HI and HII line-widths and a correlation of line-width
to emission line-flux. These measures provide estimates for
temperature, density, and energy source for the kinematic heating, as
well as insight on the possible feedback mechanisms balancing the
heating with gas dissipation and gravitational instabilities. All of
these points reveal clues about the state of the ionized interstellar
medium in external galaxies, and the extent to which the ionized gas
can be used to estimate the circular speed of the disk. We place our
observations of the ISM in this relatively large sample of galaxies in
the context of the ISM in our own Milky Way and in our recent
observations of the ISM in high-redshift galaxies.
Recent large surveys of galaxies have advanced morphological studies tremendously, moving this field
from the subjective art of morphological classification to a quantitative science of physical morphology.
The Hubble Space Telescope (HST), and in particular, the Hubble Deep Fields, have provided a vast
resource of photometric, spectroscopic, and morphological data on high redshift galaxies, and the
challenge now is to link these high redshift observations with their low redshift counterparts. Systematic
studies have been initiated to quantify galaxy morphology and extend the structural parameters that
form the basis of the Hubble sequence to higher redshifts. The comparative study of low and high
redshift morphology, however, is not straightforward. Complications arise in interpreting observations
due to redshift-dependent selection effects, biases, and incompleteness. The most fundamental
difficulty has been the lack of a good, complete, digital sample of nearby galaxies.
This presentation describes efforts to address the previously mentioned deficiencies. Using the Sloan
Digital Sky Survey (SDSS) as a local galaxy sample, we are conducting a fair comparison between low
(SDSS) and high redshift (HST/GOODS) galaxies while accounting for the systematics related to
redshift-dependent selection effects introduced by luminosity evolution, reduced apparent size,
under-sampling, bandpass shifting, and cosmological dimming.
The evidence for the link between gaseous galactic halos and star-formation in
the underlying disk is reviewed. Special emphasis will be given to the disussion
of H$^+$ halos, since the diffuse ionized gas is a good and easy to obserserve
tracer.
In addition, new results from X-ray observations with XMM and from
radio-continuum polarization observations with the VLA will be presented.
I will review the properties of the stellar disks of disk galaxies, with
some emphasis on the outermost regions
I will assess the similarities and differences between the
star-formation modes in quiescent spiral galaxies versus that in
violent starburst regions. As opposed to the quiescent star-formation
mode in spiral galaxies, such as the Milky Way, current empirical
evidence on the star-formation processes in the extreme, high-pressure
environments induced by galaxy encounters (mostly based on
high-resolution Hubble Space Telescope observations) strongly suggests
that star {\it cluster} formation is an important and perhaps even the
dominant mode of star formation in such starburst events. The sizes,
luminosities, and mass estimates of the young massive star clusters
(YMCs) are entirely consistent with what is expected for young Milky
Way-type globular clusters (GCs). Recent evidence lends support to the
scenario that GCs, which were once thought to be the oldest building
blocks of galaxies, are still forming today. One of the key unanswered
questions in this field relates to their possible survival chances for
a Hubble time, and thus to the potential evolutionary connection
between YMCs and GCs.
Within the context of a LCDM-like cosmology, a galaxy like the Milky Way is expected to have accreted
and tidally destroyed ~100 dwarf-size galaxies over its history. Most of the stars associated with these
accreted, destroyed dwarfs should end up a stellar halo, extending ~100 kpc from the galaxy center.
The search for streams and substructure in the halos of the Milky Way and nearby galaxies offers an
important test of hierarchical structure formation on small scales -- scales where the theory is facing
its most difficult challenges. The nature this substructure-- in real space, phase-space, and
metallicity space -- offers a window into low-mass galaxy formation at the earliest epochs.
This talk is about the relationship between damped
Lyman-alpha systems and the interstellar contents
of disk galaxies, including molecular and atomic
hydrogen, heavy elements, and dust.
Although there is strong evidence for the existence of pseudobulges from
stellar observations and evidence of concentrations of gas in the centers
of galaxies, there hasn't been any direct connection between the two.
In this talk I will present observations of spiral galaxies from the SINGS
survey that shows a correlation between galaxies with excess ISM in the
nuclear region and galaxies with pseudobulge light profiles.
The evolution of disks in various environments can be studied
in the local universe. I will review observational hints of disk
(re)formation after mergers in low density environments, of
fading and destruction in high density environments.
After a brief historical overview of the properties of rotation curves I
concentrate on the rotation curves of dwarf and low surface brightness
galaxies and what they can tell us about the dark matter distribution
in galaxies. I review both sides of the so-called cusp-core debate, and
conclude by showing some new data and analyses that may contribute
towards settling this debate.
I will review recent developments in bar dynamics. Part of the talk will focus on the bar-halo friction controversy, and show that the existence of strong, fast bars still requires near minimal dark matter densities. I will also discuss quantitive measures of bar strength and their implications.
New results from disk galaxy formation simulations will be presented,
with emphasis on the high-z Tully Fisher relation, X-ray emission
from disk galaxy haloes, and the Lyman-alpha properties of forming
disk galaxies. One or two computer animations will be shown.
Our understanding of star formation in disks is in the midst of an
observational revolution, with Spitzer, GALEX, and a host of groundbased
surveys providing complete inventories of star formation in nearby galaxies,
and the first truly multi-wavelength and spatially-resolved datasets.
The same data provide detailed information on the structure of the cold
interstellar medium on <<100 pc scales, and thus offer the promise of
understanding the complex interplay between the star formation rate and the
ISM, down to the physical scales where star formation events are triggered.
This talk will present highlights from these new observations, and describe
some of the new insights that have emerged from the surveys.
We investigate, through numerical hydrodynamic calculations, the behaviour of a
galactic disk subject to an external spiral potential. As the gas passes
through the potential, shocks occur in the spiral arms, and significant
secondary perturbations of the disk develop. We present detailed images
illustrating feathering of the spiral arms and spur-like structures extending
over arm and interarm regions. These features arise solely from the kinematics
of the gas: our model does not include magnetic fields or self gravity.
This substructure is only present at low (100K) temperatures, whereas the gas
is largely smoothed with higher pressures. Previous simulations of spiral
galaxies typically assume a much higher temperature, of the order $10^4K$
corresponding instead with the warm part of the ISM.
The evolution of molecular hydrogen has also been determined (calculated
\textit{after} simulations are completed). For the lower temperature
calculations, gas becomes sufficiently dense to become molecular when
compressed by a shock. The location of molecular 'clouds' are displayed as
they form in spiral arms. Most of these clouds are subsequently destroyed by
photodissociation, although a few survive to emerge into interarm regions.
We present the evolution of the luminosity-size and stellar mass-size
relations of luminous (L_V>3.4x10^{10}h_{70}^{-2}L_sun) and of massive
(M*>3x10^{10}h_{70}^{-2}M_sun) galaxies in the last ~11 Gyr. We use very deep near-infrared images of the Hubble Deep Field-South and the MS1054-03 field in the J_s, H and K_s bands from FIRES to retrieve the sizes in the optical rest-frame for galaxies with z>1. We combine our results with those from GEMS at 0.2
stellar mass was ~1.5 times smaller at z~2.5. Simple scaling relations
between dark matter halos and baryons in a hierarchical cosmogony predict a
stronger than observed evolution of the stellar mass-size relation. The
observed luminosity-size evolution out to z~1.7 matches well recent infall
model predictions for Milky-Way type objects. For disk galaxies, the weak
redshift-dependence of the stellar mass-size relation would follow naturally if
the individual galaxies grow inside-out, evolving ``along" the relation.
Galactic warps represent an old unresolved problem, since the discovery,
at the end of the fifties, of the HI warp of the Milky Way.
In this talk, we propose a new scenario explaining a large fraction of the observed
optical warps. Based on N-body simulations, we show that realistic galactic disks,
where the dark matter is essentially distributed in a disk, are subject
to bending instabilities. S, U-shaped, as well as asymmetric warps are
spontaneously generated and in some cases are long-lived.
While this scenario presents the advantage of explaining the three observed
types of warps, it also brings new constraints on the dark matter distribution
in spiral galaxies. Finally, it gives us a unified picture of galaxies where galactic
asymmetries, like bars, spirals and warps result from gravitational instabilities.
We present and interpret new integral field spectroscopic data,
obtained using the SAURON instrument, of the bar and circumnuclear
region of the barred disk galaxy M100. We have derived maps of the
mean velocity and velocity dispersion of both the gas and the stars,
and have produced emission line intensity and absorption line strength
maps. The gas and stellar velocity fields appear to be decoupled in
the inner region. While the stars are travelling on approximately
circular orbits, the gas shows strong kinematic signatures of
bar-induced streaming. The gas velocity dispersion is notably smaller,
presumably due to the inflow of cold gas, in an annular zone around
the centre, where massive star formation occurs in a nuclear ring.
The intensity and line strength maps all confirm the existence of a
younger population of stars within this ring.
In contradiction to a single but well-known claim in the literature,
imaging with ACS on the Hubble Space Telescope has led to the
conclusion that the the fraction, as well as the properties, of bars
in galaxies have not changed much from a redshift of about unity to
the present day. In this presentation, I will briefly review the
results on which this conclusion is based, and will then continue to
discuss some of the implications of bars for the evolution of
galaxies. Specifically, I will discuss the role of bars in fuelling
gas from the disk to the nuclear regions, where non-stellar or
starburst activity may ensue the possible role of secondary or nested
bars in such gas trabsport scenarios and the relations of bars with
the specific but important class of low-luminosity starbursts known as
nuclear rings.
I discuss results of thick disk formation in a multi-million particle
simulation created by the U Washington's "N-body Shop" with sub-kpc
resolution. This simulation forms a realistic disk galaxy
in a fully cosmological (Lambda CDM) context. Observational evidence suggests
that merging makes the main contribution to the formation of a
thick disk, but the question of whether mergers contribute directly to
thick disk material or dynamically heat a pre-existing thin disk remains.
This evolution of the disk in this simulation is free of numerical effects.
We incorporate a realistic star formation and feedback recipe that reproduces
a galaxy luminosity function in agreement with observations. Since other
simulations have previously overproduced low mass halos, they have been
unable to accurately explore the contribution of mergers to thick disk
formation at any epoch.
We present an initial look at the FIR-radio correlation within the
star-forming disks of four nearby, nearly face-on galaxies (NGC~2403,
NGC~3031, NGC~5194, and NGC~6946) using {\it Spitzer} MIPS imaging,
observed as part of the {\it Spitzer} Infrared Nearby Galaxies Survey
(SINGS, P.I. Kennicutt, R. C.), and WSRT radio continuum data taken
for the WSRT SINGS radio continuum survey (P. I. Braun, R).
At each galaxy's estimated distance, we are able to probe the
variations in the logarithmic 24$\mu$m/22cm ($q_{24}$) and
70$\mu$m/22cm ($q_{70}$) ratios across each disk at sub-kpc scales.
We have confirmed that the trend of $q_{24}$ and $q_{70}$
decreasing with declining surface brightness and increasing radius
to be a general property within galaxy disks when observed nearly
face-on.
We also find that the dispersion measured in $q_{24}$ is generally a
bit larger than what is found for $q_{70}$ within galaxies, and both are
comparable to what is measured {\it globally} among galaxies at around
0.2 dex.
Such moderate scatter in the IR/radio ratios across each disk suggests
that we have yet to probe physical scales small enough to observe a
breakdown in the correlation.
The residual dispersion around the trend of IR/radio ratios versus
surface brightness is significantly smaller than the residual
dispersion around the trend of IR/radio ratios versus radius
indicating star-formation sites are more important in determining
disk appearance than the underlying exponential disks.
We have also performed preliminary modeling of CR$e^{-}$ diffusion
using the smearing technique of Bicay $\&$ Helou (1990) and find that
this phenomenological model of smoothing the IR maps with a
parameterized kernel to match the morphology of the radio maps
improves the correlation.
In our analysis we use simple Gaussian and exponential kernels
oriented in the plane of the sky and galaxy varying in scale-length.
We find that exponential kernels work marginally better than Gaussian
type kernels independent of projection for these face-on galaxies.
The two more quiescent galaxies (NGC~2403 and NGC~3031) are better fit
using kernels having much larger scale-lengths compared with what best
fits the more active star-forming galaxies (NGC~5194 and NGC~6946).
This result may be due to the relative deficit of recent CR$e^{-}$
injection into the ISM for the more quiescent galaxies.
E. J. M. would like to acknowledge support for this work provided by
the Spitzer Science Center Visiting Graduate Student program.
As part of the Spitzer Space Telescope Legacy Science Program,
support was provided by NASA through Contract Number 1224769 issued
by the Jet Propulsion Laboratory, California Institute of Technology
under NASA contract 1407.
A new method of measuring distances using the parallax due to the Sun's offset from the galactic
centre tests whether a high velocity cloud stream traces an orbit around the Galaxy. The Magellanic
stream and other cloud complexes are considered.
We use a large new study to (try to) comprehend the complexity of the thick disk:
Metal weak or not, small or large asymmetric drift, short or long scale length,
`single' poplation or 'complex'.
In this talk I'll give a brief overview of the last 8-10 billion years
of disk galaxy evolution as seen in the GEMS and FIRES survey, reporting
also on some recent results from surveys with Spitzer's MIPS instrument.
We find:
i) The stellar mass density in disks is roughly constant, or slightly
increasing, from z=1 to the present day.
ii) Massive disks at intermediate redshift are forming stars intensely
40% of intermediate and high-mass disks at z~0.7 are forming stars at
greater than their past-averaged star formation rates.
iii) The stellar mass--size relation of disk galaxies does not
evolve strongly with redshift.
These observations are naturally interpreted in a scenario where disks
rapidly grow inside-out from z=1 to the present day, and where a
substantial number of disks are destroyed/disrupted in major galaxy
mergers during this epoch.
We use N-body dark matter simulations to test the idea of group infall
of satellites onto Milky Way (Lynden-Bell \& Lynden-Bell 1996). We
find that the infall pattern of substructures is clumpy, and this is
reflected, for example, in an excess of small scale power in the
two-point correlation function defined by the direction of their
orbital angular momenta. If the dynamical behavior of dark
substructures is related to tat of the bright satellites, our results
suggest that the similar orbital planes shared by several Milky Way
satellites might be a result of group infall while the Galaxy was
undergoing the hierarchical formation.
I shall review recent results from imaging and spectroscopic surveys
of galaxies at redshifts from z = 1 to 4, and assess what information
their number densities, clustering properties, chemical abundances,
and star-formation histories provide on the links between different
galaxy populations at high redshift and today's disk galaxies.
We have in recent years come to view the outer parts of galaxies
as a vital clue to study their formation and evolution. Here, I
would like to present our results on a complete sample of nearby,
late-type, spiral galaxies, using data from the SLOAN survey,
especially focused on the stellar light distribution in the outer
disk. Our study shows that only the minority of late-type galaxies
show a classical, exponential Freeman TypeI profile down to the
noise limit, whereas the majority exhibit either a downbending
(stellar truncation as introduced 1979 by Piet) or upbending profile.
I will discuss these properties in the context of current formation
and evolution scenarios.
I will present the first evidence for stellar disk truncation at high
redshift, based on surface photometry of a sample of high redshift (0.
6~$<$~z$~<$~1.0) disk galaxies from the GOODS HST/ACS data. This study
opens the ground for observing directly disk evolution through the
study of the truncation radius as a function of redshift. I will
present the radial profiles and properties of the sample galaxies. And
finally, I will discuss the implications of the results for the origin
of the truncation radius and disk evolution.
We present the results of multi-line observations of the
central region of Maffei2 with Nobeyama Millimeter Array(NMA).
Maffei2 is a nearby barred spiral galaxy behind the Galactic plan.
We made a CO map of Maffei2 with NRO 45-m telescope and found that
the distribution of the molecular gas shows structures often seen
in barred spiral galaxies strong central peak, offset ridges,
condensations at the bar end, and spiral arm.
Furthermore, we made high resolution observations with NMA and
found that the offset ridges continue toward the center
as two-arm spiral structure.
Early farinfrared to submillimeter continuum imaging results of cold dust and the
general ISM in a small sample of nearby (<60Mpc) elliptical galaxies with dusty
gas disks that we are currently studying will be presented. The results of these
dusty gas disks will be discussed in the context of the galaxies structure and
evolution and compared to the analysis of disk galaxies in general.
We study influence of a galactic central massive black hole binary
on gas dynamics and star formation activity
in the galactic central region
by making three-dimentional Tree+SPH simulations.
Due to orbital motion of each massive black hole,
there are various resonances
between gas motion and massive black hole binary.
We show that these resonances trigger
the large amount of gas fueling into the galactic central region
and huge star burst.
Moreover,
in high eccentric binary orbit case,
due to strong change of gravitational potential
in the galactic center,
gas is strongly influenced
and duration time of active star formation is much longer.
The formation and evolution of galaxies is one of the great
outstanding problems of astrophysics. The current paradigm for the
formation of structure in the Universe postulates that galaxies grow
in a hierarchical fashion, through the mergers of smaller
subunits. Even within this broad context, we have only a crude picture
of how galaxies like our own came into existence.
This contribution focuses on the formation of what seems to be one of
the most ubiquitous components of late-type galaxies: the thick disk.
We have carried out a series of N-body simulations of minor mergers
which include an exponential disk and satellite immersed in a 'live'
dark halo. Our initial conditions are consistent with being drawn
from cosmological simulations, and in this context we have explored a
region of parameter space embracing satellites with different
densities and orbits of various eccentricities. We will present our
first results aimed at characterizing the present-day spatial and
kinematic distribution of thick disks resulting from such events.
A substantial fraction of the light in the Universe comes from disk
galaxies, and we are lucky enough to live in one. Yet the dynamics of these
systems involve several major puzzles. I'll review our current
understanding of disk dynamics and evolution, much of which derives from
studies of the Milky Way, and ask how seriously the picture that emerges
conflicts with current cosmological theory.
In some external edge-on spirals, the azimuthal velocity of halo gas is observed
to decrease with height above the midplane ($z$). This effect has been observed
in both the neutral and ionized components of halos. Models of the disk-halo
interaction which consider the effects of moving gas out of the disk and into
the halo predict such a velocity gradient as a consequence of the conservation
of angular momentum. In order to observationally test the predictions of such
models, high spectral resolution emission line data with two-dimensional
coverage are required to first estimate the form of the radial density profile
in the halo, and subsequently extract the azimuthal velocities as a function
of $z$. We present high spectral resolution WIYN SparsePak observations of the
diffuse ionized gas (DIG) in NGC 891. Preliminary results of an analysis of
the azimuthal velocity field will also be summarized. This work is part of an
ongoing project to investigate the vertical azimuthal velocity gradient of the
ionized halo gas in a select sample of edge-on spirals with a range of DIG
halo morphology.
This material is based on work partially supported by the National Science
Foundation under Grant No. AST 99-86113.
We discuss the location of the Milky Way with respect to the Tully-Fisher
relation defined by external galaxies, based on an updated estimate of the local
surface brightness and stellar Mass-to-Light ratio in the Solar Neighbourhood.
We discuss implications for the Initial Mass Function in disc galaxies.
In order to study formation and evolution interstellar clouds,
we simulate multi phase of interstellar matter
in a disk galaxy by using SPH code, considering
radiative cooling, cloud formation and heating by star formation process.
We show that cloud mass function can be approximated by a power law function of cloud mass
and it is similar function form of observed cloud mass function in our galaxy.
By calculating various cases of total mass of interstellar mass and UV background radiation, we study
how cloud mass function depends on them. We show that the power index, $¥alpha$, of cloud mass function becomes small for large amount of interstellar medium and strong UV radiation case.
Our results suggest that cloud mass function is a good indicater of these
interstellar processes.
We have compiled a new sample of 241 halo objects with accurate
distance and radial velocity measurements, including globular
clusters, satellite galaxies, field blue horizontal branch stars and
red giant stars from the Spaghetti survey. The new data
lead to a significant increase in the number of known objects for
Galactocentric radii beyond 50 kpc, which allows a reliable
determination of the radial velocity dispersion profile out to very
large distances. The radial velocity dispersion shows an almost
constant value of 120 km/s out to 30 kpc and then continuously declines
down to 50 km/s at about 120 kpc. This fall-off puts
important constraints on the density profile of the Milky Way
dark matter halo. It rules out an isothermal profile with constant velocity
anisotropy, while it is consistent both with
a dark halo following a truncated flat model of mass
1.2^{+1.8}_{-0.5}* 10^{12} M_sun, and with an NFW profile of mass
0.8^{+1.2}_{-0.2}* 10^{12} M_sun and c=18.
Furthermore the significant increase
in the number of tracers combined with the large extent of the region probed
by these has allowed
a more precise determination of the Milky Way mass in comparison
to previous works.
Galaxies are are not simple superpositions of disks and
spheroids. Instead, most disk galaxies host multiple faint stellar
components. Studies within the Milky Way suggest that these
additional components are old and chemically unevolved, and that they
trace distinct epochs in the early history of the Galaxy. I will
discuss recent work on the structure, kinematics, and stellar
populations of thick disks and stellar halos, and the important
constraints that they place on the assembly of disk galaxies.
We introduce 11HUGS (11Mpc Halpha and Ultraviolet Galaxy Survey), an
outgrowth of the recently completed 11MPC Survey, a ground-based H-alpha
and R-band imaging program of a volume-limited sample of 340 spiral and
irregular galaxies within a distance of 11 Mpc. As such, the 11HUGS
galaxies are a complete subset of the 11MPC Survey catalog which avoid the
Galactic plane ( b >30) and are observable by GALEX.
The goal of 11HUGS is to characterize the demographics and star formation
properties of nearby galaxies, with an emphasis on the dwarf galaxies
which dominate the sample population. The data also provide a foundation
for follow-up studies of the HII region populations, star formation,
chemical abundance, and ISM properties of the galaxy sample. The
combination of Halpha imaging, which provides snapshots of the ongoing
star formation, and UV imaging, which traces star formation over a much
longer timescale, will yield powerful constraints on the systematic errors
in the inferred star formation related quantities.
Star forming regions in galaxies consist of a number of components, the evolving young stellar clusters
and their HII regions, isolated OB stars embedded in compact HII regions, older non-ionising stars,
the pre-existing old stellar population, all these are surrounded by a complex, turbulent, and fractal
foreground screen of gas and dust. I will describe how self-consistent dynamical and radiative transfer
modelling of these various components is now leading to synthetic pan-spectral energy distributions
from the Lyman Limit through to the millimetre range. These models provide excellent fits to real
objects, and also provide a new diagnostic tool to allow us to derive the fundamental physical
parameters of star forming galaxies in both the local universe as well as for distant objects such as
the sub-mm galaxies and the high redshift radio galaxies.
The properties of local star forming galaxies, in both clusters and the field,
can aid understanding of the environmental dependence of galaxy formation and
evolution. We present initial results from an H$\alpha$ survey of all Sa --- Sc
CGCG galaxies, with velocities within 3$\sigma$ of the cluster mean, in six local
Abell clusters, down to a limiting magnitude of M$_{B}=-18.5$. A more extended
sample of all emission line galaxies, in a total of eight clusters, identified
within these limits, by an objective prism survey carried out by Moss and
collaborators, is also included. Comparison of the cluster data with a substantial
field sample from the recent H$\alpha$ Galaxy Survey (James et al. 2004) allows
us to study of the effect of environment on amount, distribution amd morphological
dependence of star formation in the local Universe and provide vital clues
towards a better understanding of galaxy formation and evolution. In particular,
we examine the concentration of H$\alpha$ emission, across both samples, to
establish whether circumnuclear star formation preferentially occurs in the
cluster environment.
Kinematic and metallicity measurements are now possible for large
numbers of stars in the Local Group dwarf galaxies, which allows
us to study their stellar populations to retrace their evolution.
Detailed elemental abundances of these stars from high resolution
spectroscopy are also becoming available. These results can be
used to (1) search for evidence of the merging history of similar
small, isolated pre-galactic fragments in the formation of our Galaxy,
and (2) examine our assumptions about stellar nucleosynthesis,
particularly when contrasted with the metal-poor stars in our Galaxy.
The most detailed and direct constraints on galaxy formation come from
studies of the spatial distribution, ages, metallicities and kinematics of
resolved stellar populations. Populations in the far outer regions of galaxies are of particular interest since theory predicts many important clues about galaxy assembly should lie buried in these parts. I will summarise recent results from ground-based and HST studies of stars in the outskirts of our nearest large neighbours, M31 and M33, focusing on the properties of their stellar halos and outer disks.
T.B.D.
Does the tidal debris of minor mergers contribute to structures in the
halo of spiral galaxies or in the intergalactic medium? While major
mergers are known to create structures such as tidal dwarf galaxies
and star clusters within their tidal debris, not much is known about
minor mergers (mass ratios between a disk galaxy and dwarf galaxy of
less than one-third) and their tidal debris. This work surveys 15
minor mergers in optical and infrared to gain insight into
characterizing the clumps within their tidal debris in terms of size,
location, number, mass, and age. One example from this study of
nearby minor mergers, NGC 2782, will be presented here. The peculiar
spiral, NGC 2782, is the result of a merger between a large disk
galaxy and a lower mass disk galaxy with a mass ratio of 0.25
occurring $\sim200$ Myr ago. This merger produced an HI-poor, optically
bright Eastern tail and an HI-rich, optically faint Western tail. Deep
optical and near-infrared images in UBVRJHK reveal the presence of
blue ($B-V \sim -0.3$) clusters along both tails, suggesting that they are
young and possibly formed within the tail. The presence of young
clusters in the Western tail is unexpected due to the lack of
molecular gas observed in previous studies and the lack of $H\alpha$
emission. These results suggest that star cluster formation is a
common outcome of minor mergers regardless of gas content in the tidal
debris.
We present the highest angular resolution (~ 0.5 arcsec) and
most sensitive CO(2-1) and (1-0) observations ever made of the
nuclear region of the nearby late type (Scd) spiral galaxy NGC 6946.
The data - obtained with the Plateau de Bure interferometer in
its AB configuration - allow a study of the kinematics of the
elongated molecular gas disk. The disk - which has a size of
~ 12 arcsec - is unresolved in existing data. The kinematic
information is crucial to identify the mechanism(s) that funnel
large amounts of molecular gas into the very nucleus of
NGC 6946, as evidenced by two recent intense and short-lived starburst
episodes. The observations provide a test of models which
suggest nuclear gas spirals inside the inner Lindblad resonance (ILR)
as a possible funneling mechanism, and constrain on the
frequency of nuclear starbursts in NGC 6946.
A long-standing question in galaxy evolution involves
the role of nature (self-regulation) vs nurture (environment)
on the observed properties (and evolution) of galaxies. A
collaboration centered at the Instituto de Astrofisica de Andalucia
(Granada, Spain) is trying to address this question by producing a
observational database for a sample of 1050 isolated galaxies
from the catalog of Karachentseva (1973) with the overarching goal
being the generation of a "zero-point" sample against which effects
of environment on galaxies can be assessed. The AMIGA
(Analysis of the Interstellar Medium of Isolated Galaxies) database
(see www.iaa.es/~AMIGA) will include optical, IR and radio line and
continuum measures. The database and goals of the AMIGA collaboration
will be presented together with the most recent results with respect
to the optical and FIR properties of the sample.
We present our progress on a detailed study of M81 in the radio, ultraviolet and infrared wavelengths, in which we attempt to use HI produced in photodissociation regions (PDRs) as a tracer for molecular hydrogen.
By assuming that HI is a photodissociation product of star formation, it can be used independently from the popular CO(1-0) tracer. In many instances, patches of HI are found close to bright FUV-sources, as is expected for PDRs. These complexes of young, hot stars create a 'blanket' of dissociated HI around them. Together with the incident UV flux on the HI, and the local dust-to-gas ratio, the associated volume density of molecular hydrogen can be derived from the local HI column density.
How do we know that the HI is being produced in PDRs? Recent publications suggest that 8 micron PAH emission from star-forming regions can be used to trace PDRs. Matching regions of HI emission to PAH emission would support our approach.
Radio (VLA), UV (Galex) and IR (Spitzer) data are all available at about 6 arcsec resolution or better, corresponding to a linear scale of little over 100 parsec.
We expect to pursue the viability of the use of HI as a tracer for H$_2~$ across a variety of nearby galaxies, including NGC2403, M33 and M83, using VLA and GALEX data as a major extension to the existing studies of e.g. M101 and M81 in this context.
In order to investigate the correlation between the circular velocity
(Vc) and the central velocity dispersion of the spheroidal component
(sigma) we analyzed these quantities for a sample of 40 high surface
brightness disc galaxies (HSB), 8 giant low surface
brightness spiral galaxies (LSB), and 24 elliptical galaxies
characterized by flat rotation curves. We find that the Vc-sigma
relation is described by a linear law out to velocity dispersions as
low as sigma~50 km/s, while in previous works a power law was adopted
for galaxies with sigma>80 km/s. Elliptical galaxies with Vc derived
from HI data and LSB galaxies were not considered in previous studies.
Elliptical galaxies with Vc based on dynamical models or directly
derived from the HI rotation curves follow the same relation as the
HSB galaxies in the Vc-sigma plane. On the contrary, the LSB galaxies
follow a different relation, since most of them show either higher Vc
(or lower sigma) with respect to the HSB galaxies. This argues
against the relevance of baryon collapse in the radial density profile
of the DM haloes of LSB galaxies. Moreover, if the Vc-sigma relation
is equivalent to one between the mass of the DM halo and that of the
SMBH, these results suggest that the LSB galaxies host a SMBH with a
smaller mass compared to HSB galaxies of equal DM halo.
The vertical profiles of disk galaxies are build by the material
trapped around stable periodic orbits, which form their
"skeletons". Thus, the knowledge of the evolution of the stability of
the orbits of the main families as a function of the energy, gives all
possibilities of morphologies that can be encountered in a disk galaxy
when viewed side-on. The orbital structures which lead to the
appearance of boxy "bulges" and "X"-like features are presented, and
the importance of the barred or spiral perturbations for their
morphology is discussed.
Examples of galaxies are given where profiles foreseen by the
orbital theory are encountered in images of disk galaxies observed
edge-on.
I will review theories of galaxy formation with emphasis on the formation
and evolution of disk galaxies in a cosmological context.
We investigate, through numerical hydrodynamic calculations, the behaviour of a
galactic disk subject to an external spiral potential. As the gas passes
through the potential, shocks occur in the spiral arms, and significant
secondary perturbations of the disk develop. Feathering of the arms and
spur-like structures evolve which extend over arm and interarm regions.
These features arise solely from the kinematics of the gas and are only
present at low (100K) temperatures, whilst the gas is largely smoothed with
higher pressures.
The evolution of molecular hydrogen has also been determined (calculated
\textit{after} simulations are completed). For the lower temperature
calculations, gas becomes sufficiently dense to become molecular when
compressed by a shock. The location of molecular 'clouds' are displayed as
they form in spiral arms. Most of these clouds are subsequently destroyed by
photodissociation, although a few survive to emerge into interarm regions.
Finally we look at how a velocity dispersion can be generated as gas passes
through a spiral shock.
I will review the observational evidence for big disks and spiral structure (and for structural evolution
generally) as a function of cosmic epoch. In an attempt to be a bit different, I will pay special
attention to z>1, where much of the action seems to be happening, but where our
painful ignorance is particularly acute. Emphasis will be given to studies which try to
place morphological evolution in a modern context, and which try to capitalize on the
interplay in knowledge that comes about from combining information on individual objects
with information on the bulk properties of volume averaged samples (such as the evolving
star-formation rate density and stellar mass density functions).
The distribution of visual matter in ~100 spiral galaxies was estimated
from NIR K-band maps observed with SOFI/NTT, ESO. Decomposing
the maps into standard components (e.g. disk and bulge) and using
HI line width data with a maximum disk assumption, synthetic rotation
curves were estimated for the sample. Morphological features of the
spiral pattern in the galaxies (e.g. size of bar, extent of spiral arms) were
estimated and compared with possible locations of stellar resonances
as derived from the synthetic rotation curves. The Poster describes the
general method and presents first results.
We present observations of highly inclined, HI deficient, Virgo
cluster spiral galaxies. Our high-resolution VLA HI and radio
continuum observations of edge-on galaxies allow us to distinguish
extraplanar gas from disk gas. All of our galaxies have truncated
H$\alpha$ disks, with little or no disk gas beyond a truncation
radius. While all the gas disks are trucated, the observations show
evidence for a continuum of stripping states: symmetric, undisturbed
truncated gas disks indicate galaxies that were stripped long ago,
while more asymmetric disks suggest ongoing or more recent
stripping. We compare these timescale estimates with results obtained
from two-dimensional stellar spectroscopy of the outer disks of
galaxies in our sample. One of the galaxies in our sample, NGC 4402,
also shows distinct evidence for an asymmetric extraplanar radio
continuum halo, and marginal evidence for extraplanar
HI. Additionally, we have high-resolution BVR images of NGC 4402,
showing a remarkable dust lane morphology: at half the optical radius,
the dust lane of the galaxy curves up and out of the disk, matching
the HI morphology. The optical images also show evidence for ongoing
dense cloud ablation at the leading edge of the interaction. These
observations, which suggest strong ongoing pressure, show that NGC
4402 is in a different environment than the galaxies located at larger
cluster radii. Our observations at a range of cluster radii allow us
to better understand the role that clusters play in the structure and
evolution of disk galaxies.
We present first results of a long-term study of the large-scale stellar population and evolutionary properties of nearby galaxies. We have acquired deep Gemini/GMOS spectra for 8 nearby late-type spiral galaxies and measured a suite of 24 Lick/IDS line indices in the bulge and inner disk, including the age-sensitive higher-order Balmer-line indices. The line indices are compared with stellar population synthesis models to characterize the luminosity-weighted ages and metal abundances in star-forming galaxies and place constraints on basic formation scenarios of spiral bulges. Careful attention is paid to nebular contamination and anomalous abundance ratios. Preliminary results reveal that i) late-type bulges and inner disks are generally young (<=1 to 6 Gyr) with little or no age gradients (out to ~r_d), and ii) late-type spirals have metallicities close to solar at their center decreasing rapidly outward (with gradients of -0.3 to - 0.7 dex per r_d). Disk contamination into the bulge is an issue but the young inferred ages exclude the interpretation of early rapid collapse or merger origin of late-type bulges. While secular evolution processes are likely the predominant mechanism for the (late-type) bulge build-up, the strong observed metallicity gradients are not currently supported by such models.
We present the results from our optical survey of 15.5 deg$^{2}$
targeted at a part of the the Arecibo HI Strip Survey (AHISS). We used
this survey in an automatic search for nearby galaxies -- especially for
low surface brightness (LSB) galaxies -- and found 306 galaxies using
SExtractor (Bertin \& Arnouts, 1996). We fitted each detected galaxy
with an exponential profile using the automated fitting program GALFIT
(Peng et al. 2002). A comparison of our survey with other optical
surveys shows that automated object detection and analytical size
estimation by using a fitting program provides an explicit rise in the
number density. Searches by eye result in a significant lower number
density. Furthermore, we have compared our results with the AHISS
itself to check whether optical or HI surveys suffer less from selection
effects. Our optical survey shows an estimated volume density which is
approximately 7 times as high as the one from the AHISS. We ascribe
this back to the stronger selection effects for HI surveys.
From our results we conclude that LSB galaxies provide a substantial
contribution to the local galaxy number density.
We present the discovery of an inhomogenous, low-surface brightness,
extended disk-like structure around the Andromeda galaxy (M31) based on a
large kinematic survey with the Keck/DEIMOS multi-object spectrograph. The
structure spans radii from 15 kpc out to 70 kpc.
Given the huge scale of the structure, this means that ~30\% of the total
angular momentum of Andromeda resides in the extended disk component. This
finding indicates that at least some galactic disks are vastly larger than
previously thought and are formed, at least in their outer regions,
primarily by accretion.
The origin of HI at anomalous velocities and at large distances above the disk,
detected in a few spiral galaxies, is still a puzzle. To improve on our
understanding of this extra-planar gas we have started a study of nearby
edge-on galaxies. In this poster, we will present the observations and
preliminary analysis of the extraplanar gas of UGC 1281 and NGC 7814.
NGC 7814 and UGC 1281, have been observed with the WSRT for 4 $\times$ 12 hours.
In UGC 1281 there are clear indications that this dwarf galaxy posesses a halo.
Preliminary analysis of NGC 7814 shows no halo however, we have detected
extra-planar gas at velocities higher than the systemic velocity in the center
of this galaxy. Here, we will try to prove that this gas is related to the bar
of NGC 7814.
A fundamental consequence of the theory of stellar evolution is that once
formed the subsequent life history of a star is a pre-determined function of
essentially one parameter, its birth mass. Consequently, detailed knowledge of
the initial distribution of stellar masses at birth (known as the initial mass
function or IMF) and how this quantity varies through time and space is
necessary to predict and understand the evolution of stellar systems, such as
clusters and galaxies. Unfortunately stellar evolution theory cannot predict
the form of this critical function and the origin of the stellar IMF remains
one of the major unsolved problems of modern astrophysics and star formation
research. Stars form in the cold dense cores of interstellar molecular clouds.
Detailed knowledge of the spectrum of masses of such cores within a
star-forming cloud is clearly a key piece of information necessary for the
development of a physical picture of the origin of the stellar IMF. To date,
observations have presented somewhat contradictory evidence relating to this
issue. In this poster we present a new and more robust determination of the dense core
mass function within an individual molecular cloud, derived from infrared dust
extinction measurements. These measurements of a statistically significant
sample of cores spanning a relatively wide and interesting range of mass reveal
a cloud mass spectrum that, apart from a simple scale factor in mass, is
surprisingly similar to that of the stellar IMF. This in turn suggests that
the distribution of stellar birth masses over essentially the entire range of
the IMF is a direct product of the fragmentation/coalescence process in a
molecular cloud, modified by a characteristic star formation efficiency of
about 30\%.
The correlation between far-infrared and radio emission in galaxies is
remarkably strong considering the very different emission mechanisms
which are thought to be responsible. Recently Murgia et al. have shown
that the correlation of CO and radio emission is comparably strong in a
sample of nearby disk galaxies observed at $\sim$5" resolution with the
VLA and BIMA. We analyze the CO-radio correlation as a function of size
scale, using a wavelet-based method. In some galaxies the correlation
begins to break down significantly on a scale of 1-2 kpc, while in
others it seems to hold down to scales an order of magnitude smaller.
We discuss the role of systematic errors and AGN contamination in
interpreting these results. We also compare the CO and radio images
with 24 $\mu$m Spitzer Space Telescope imaging of these galaxies from
the SINGS project. Finally, we contrast the results with a parallel
study of the LMC which probes the correlations down to a scale of
$\sim$50 pc.
Wide area ground based imaging surveys of M31 have discovered
several sub-structures in its outer regions, and recent spectroscopic
follow-up uncovered the suprising result that these sub-structures
belong to an extended disk, which is detected out to ~40 kpc. How this
extended disk formed is still unclear.
Constraints on the formation of the sub-structures should be provided
by their stellar populations and star formation histories. We are
probing these using colour-magnitude diagrams created from HST-ACS
images. Here I compare and discuss the CMDs for several fields close
to the major axis of M31, at projected distances of ~25 kpc.
Owing to the achievement of high-resolution interferometry, recent radio
observations of nearby spiral galaxies have revealed the centrally-condensed
profile of gas disks within ~500pc, in addition to the global 1/e radius of
several kilo-pc. The central condensation is often attributed to the global fueling process in
gas disks, which is due to angular momentum transfer with stellar bar potential
or environmental effect.
To examine the strength of of angular momentum transfer mechanisms,
we compared the degree of central gas condensation between barred and non-barred
galaxies, and between cluster member and other galaxies. The data is taken from
recent surveys with NMA (Nobeyama Millimeter array): Virgo CO Survey (ViCS) and
nearby Seyfert survey.
We show that the majority of these galaxies show centrally-condensed profile.
The degree of central condensation is larger in barred galaxies than in non-barred,
whereas it shows no clear difference between cluster members and other galaxies.
We present high resolution two-dimensional velocity fields from
integral field spectroscopy along with derived rotation curves for nine
low surface brightness galaxies. This is a positive step forward in terms
of both data quality and number of objects studied. We fit NFW and
pseudo-isothermal halo models to the observations. One galaxy is well fit
by the NFW halo, five prefer the isothermal halo, and three have no clear
preference. Cusps can clearly be detected by this method when they are
present and the data are of high quality. Yet only one of our six best
cases is consistent with a cusp.
We have imaged the object VIRGOHI 21 at Westerbork.It has all the
appearence of a dark edge-on disc weighing more than dex 10 solar
masses.It collided with NGC 4254 about dex 8 years ago leaving a clear
bridge of material behind.Simulations of NGC4252 had previously
suggested that a galactic mass collided with it 3 dex8 years ago,though no
visible candidiate could be found .VIRGOHI 21 is obviously the perturber
and we thake thw simulations as independent evidence of the large mass
of VIRGOHI21.The internal dynamics of VIRGOHI21 definitely cannot be
explained as tidal debris.
Spiral galaxies displaying molecule-dominated ISMs are potential candidates
for pattern speed determination by the Tremaine-Weinberg method (1984) the
molecular gas of such galaxies, as traced by CO emission, is argued to
approximately obey the continuity equation on orbital timescales—-a key
requirement of the method. We continue our work on this application of the
Tremaine-Weinberg method with pattern speed determinations of several galaxies
using CO emission data cubes from the BIMA SONG survey. Because the reliability
of a method such as this depends on the presence of a pattern, we select the
galaxies in our sample by visual inspection and by the use of Fourier
decompositions of deprojected surface brightness intensities as a means of
examining whether a large-scale pattern exists. For three of the galaxies in
our sample (NGC 5457, 5033, and 5055), molecular dominance is established using
radial profiles of Wong and Blitz (2002). We also consider their finding that
HI column densities are generally $\lesssim 10 M_{\sun}/pc^{2}$ as evidence for,
or against, molecule-dominated ISMs in the case of NGC 628, both CO and HI data are
required for the Tremaine-Weinberg calculation, as the dominance of one
component over another cannot be established over the extent of the CO
emission alone, and so both components must be considered in order to insure
that continuity is obeyed. Our analysis includes using the combined molecular
and atomic data to investigate the ability of the method to handle multiple
components and possibly multiple patterns.
1 July 2005