Kapteyn Institute Preprints (1995)

Kapteyn Institute Preprint Service.

Preprints of the Kapteyn Institute.
Paper copies can be ordered at:
Kapteyn Institute
P.O. Box 800
9700 AV Groningen
The Netherlands
All the preprints are compressed using gzip.

1995 Preprints

* Preprint 187 An HI Survey of the Bootes Void. II. The Analysis, A. Szomoru, J.H. van Gorkom, M.D. Gregg and M.A. Strauss
* Preprint 186 An HI Survey of the Bootes Void. I. The Data, A. Szomoru, J.H. van Gorkom and M.D. Gregg
* Preprint 185 Global HI Profiles of Spiral Galaxies, J.J. Kamphuis, D. Sijbring and T.S. van Albada
* Preprint 184 Structure Analysis of Edge-on Spiral Galaxies, R. de Grijs and P.C. van der Kruit
* Preprint 183 Neutral Hydrogen in the Nearby Galaxies Dwingeloo 1 and Dwingeloo 2, W.B. Burton, M.A.W. Verheijen, R.C. Kraan-Korteweg and P.A. Henning
* Preprint 182-3 Stellar Populations of Bulges and Disks: New Insights from Near-IR Colours, R.F. Peletier and M. Balcells
* Preprint 182-2 New Spectrophotometric Population Synthesis Models for Elliptical and Early Type Spirals, A. Vazdekis, R. Peletier, E. Casuso and J. Beckman
* Preprint 182-1 Ages of Galaxy Bulges and Disks from Optical and Near-Infrared Colours, R.F. Peletier and M. Balcells
* Preprint 181 Short WSRT HI Observations of Spiral Galaxies, M.H. Rhee and T.S. van Albada
* Preprint 180-2 The PLANET Collaboration: Probing Lensing Anomalies with a world-wide NETwork, M. Albrow, P. Birch, J. Caldwell, R. Martin, J. Menzies, J.-W. Pel, K. Pollard, P.D. Sackett, K. Sahu, P. Vreeswijk, A. Williams, M. Zwaan
* Preprint 180-1 The Distribution of Dark Mass in Galaxies, Techniques, Puzzles, and Implications for Lensing, Penny D. Sackett

The Distribution of Dark Mass in Galaxies: Techniques, Puzzles, and Implications for Lensing

Penny D. Sackett

Preprint No. 180
To appear in: "Astrophysical Applications of Gravitational Lensing" (eds. C. Kochanek and J. Hewitt), Proceedings IAU Symposium 173, Melbourne, July 1995.

Abstract

Gravitational lensing is one of a number of methodse a used to probe the distribution of dark mass in the Universe. On galactic scales, complementary techniques include the use of stellar kinematics, kinematics and morphology of the neutral gas layer, kinematics of satellites, and morphology and temperature profile of X-ray halos. These methods are compared, with emphasis on their relative strengths and weaknesses in constraining the distribution and extent of dark matter in the Milky Way and other galaxies. It is concluded that (1) the extent of dark halos remains ill-constrained, (2) halos need not be isothermal, and (3) the dark mass is probably quite flattened

The PLANET Collaboration: Probing Lensing Anomalies with a world-wide NETwork

M. Albrow, P. Birch, J. Caldwell, R. Martin, J. Menzies, J.-W. Pel, K. Pollard, P.D. Sackett, K. Sahu, P. Vreeswijk, A. Williams, M. Zwaan

Preprint No. 180
To appear in: "Astrophysical Applications of Gravitational Lensing" (eds. C. Kochanek and J. Hewitt), Proceedings IAU Symposium 173, Melbourne, July 1995.

Abstract

A newly-formed microlensing monitoring network, the PLANET collaboration, is briefly described.

Short WSRT HI Observations of Spiral Galaxies

M.H. Rhee and T.S. van Albada

Preprint No. 181
Accepted for publication in Astronomy and Astrophysics Supplement Series.

Abstract

We have obtained short HI observations of 60 late type spiral galaxies with the Westerbork Synthesis Radio Telescope (WSRT). Several HI properties are presented, including the radial surface density distribution of HI and a position-velocity map. When possible these are compared to those measured from single-dish observations. We confirm earlier results that there is no serious systematic difference between the WSRT and single-dish observations in total flux and linewidths.
Preprint 182

This preprint consists of 3 contributions to conference proceedings.

AGES OF GALAXY BULGES AND DISKS FROM OPTICAL AND NEAR-INFRARED COLOURS

R.F. Peletier and M. Balcells

Preprint 182-1.
To be published in: "Evolutionary Phenomena in Galaxies" (eds. R. Bender and R.L. Davies), Reidel, Dordrecht

Abstract.

For a sample of bright nearby early-type galaxies we have obtained surface photometry in bands ranging from U to K. Since the galaxies have inclinations larger than 50 degrees it is easy to separate bulges and disks. By measuring the colours in special regions, we minimize the effects of extinction, and by looking at B-K colour gradients we can show that for these type of spirals the colours mainly give information about stellar populations, and not extinction. We find that the differences between bulges and disks in all colours is very small, and using simple population models we can show that on the average the age difference between the bulge and the disk at 2 scale length is smaller than 30%, and much smaller if part of the difference is caused by a gradient in metallicity.

NEW SPECTROPHOTOMETRIC POPULATION SYNTHESIS MODELS FOR ELLIPTICAL AND EARLY TYPE SPIRALS

A. Vazdekis, R. Peletier, E. Casuso and J. Beckman

Preprint 182-2.
To be published in: "Spiral Galaxies in the Near-Infrared" (ed. D. Minitti), ESO, Garching, Germany.

Abstract

We have developed a model calculating colours and absorption line indices for composite stellar systems. The model can synthesize observations for single age, single metallicity stellar populations, but can also incorporate chemical evolution, following the evolution of a galaxy from an initial gas cloud to the present time. We have obtained accurate observations in many colours and line indices of three famous galaxies: NGC 3379, NGC 4472 and NGC 4594, and have used those to calibrate our models.

STELLAR POPULATIONS OF BULGES AND DISKS: NEW INSIGHTS FROM NEAR-IR COLOURS

R.F. Peletier and M. Balcells

Preprint 182-3.
To be published in: "Spiral Galaxies in the Near-Infrared" (ed. D. Minitti), ESO, Garching, Germany.

Abstract.

Colours of spiral galaxies generally are affected by the underlying old stellar population, younger stars, and extinction by dust. Old and young populations generally can be disentangled using a combination of blue and near-infrared colours. Extinction effects are very hard to take into account, except for galaxies with special orientations. In this paper we give some results of one of the first studies of galactic bulges and disks in various optical and near-infrared bands, and its implications for the stellar populations of spirals.

Neutral Hydrogen in the Nearby Galaxies Dwingeloo 1 and Dwingeloo 2

W.B. Burton, M.A.W. Verheijen, R.C. Kraan-Korteweg and P.A. Henning

Preprint No. 183
Accepted for publication in Astronomy and Astrophysics.

Abstract

We present observations made with the Westerbork Synthesis Radio Telescope of HI emission from Dwingeloo 1, a nearby barred spiral discovered during the Dwingeloo Obscured Galaxies Survey for galaxies hidden in the Zone of Avoidance, and of Dwingeloo 2, a small galaxy discovered in the beam of these WSRT observations. The WSRT data reveal the position of the dynamical center of Dw1, its systemic LSR velocity, its total (projected) width in velocity, its inclination on the sky, and its integrated HI flux, as well as details of the velocity field and gas distribution. Dw1 is the nearest grand-design barred spiral system, and is probably amongst the ten largest galaxies closer than about 5 Mpc. We report here also the discovery of Dwingeloo 2, a small galaxy located within the WSRT primary beam as pointed to Dw1. In view of its angular and kinematic proximity to Dw1, Dw2 may well be a companion to the larger system. The two galaxies are probably both members of the group containing Maffei 1 & 2 and IC342 and may influence the peculiar motions within that group and the morphology of its individual members.

Structure Analysis of Edge-on Spiral Galaxies

R. de Grijs and P.C. van der Kruit

Preprint No. 184
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Accepted for publication in Astronomy and Astrophysics Supplement Series.

Abstract

The stellar distribution of a small sample of edge-on spiral galaxies is examined in B, V, R, and I by fitting model distributions to the light profiles, both perpendicular to the galaxy planes and along the major axes. We have developed a method to compare the fits for the models obtained for different galaxies by introducing a global goodness-of-fit parameter P_{ij}. In general, the best fitting vertical model is more peaked than expected for an isothermal sheet distribution, i.e. it is either an exponential light distribution or a sech(z)-model. The most likely explanation for the deviations from an exponential or a sech(z) distribution at small z is dust extinction, whereas the excess light detected at large z for a few early-type spirals could be due to a thick disk component. The constancy of the exponential scale height of both the thin and the thick disks as a function of position along the major axis is confirmed, although it seems to lose strength in the radial outer parts. It is found that the vertical scale parameters for both the thin and the thick disks are confined within narrow ranges. We show that the scale lengths vary as a function of z-distance from the galaxy planes. The smallest scale lengths were measured in the galaxy planes. This can be explained by a combination of absorption effects and a young stellar population, that is supposed to be present in the galaxy planes. The mean ratio of the radial to the vertical scale parameter, h_R/z_0, is 5.9 \pm 0.4.

Global HI Profiles of Spiral Galaxies

J.J. Kamphuis, D. Sijbring and T.S. van Albada

Preprint No. 185
Accepted for publication in Astronomy and Astrophysics Supplement Series.

Abstract

In this paper we present short HI synthesis observations of 57 galaxies without HI information in the RC3. These are a by-product of a large survey with the WSRT of the neutral hydrogen gas in spiral and irregular galaxies. Global profiles and related quantities are given for the 42 detected galaxies and upper limits for the remaining 15. A number of galaxies have low values of HI mass-to-blue luminosity ratio.

An HI Survey of the Bootes Void. I. The Data

A. Szomoru, J.H. van Gorkom and M.D. Gregg

Preprint No. 186
Accepted for publication in The Astronomical Journal.

Abstract

We present the results of a neutral hydrogen survey of the Bootes void carried out with the VLA (Napier et al. 1983) in D-array. The survey covers about 1100 Mpc^{3}, about 1% of the volume of the void as defined by Kirshner et al. 1987. We observed 24 fields, centered on known void galaxies;16 of these were detected in HI. Eighteen uncataloged companion galaxies were discovered directly in the HI line at distances of 45" to 14.5' from the target galaxies. We also present the results of follow-up optical imaging observations and discovery of one additional Bootes void galaxy, found through spectroscopy of a number of apparent companions to known void members. Our angular resolution is about 1' (45 kpc) each field has a size of about 1 degree (2.7 Mpc). The detected HI masses range from 8 x 10^{8} to 1 x 10^{10} M_sun. Typically our 2 sigma HI column density sensitivity is 2 x 10^{19} cm^{-2}. The radio and optical data are analyzed and discussed in the following companion article (Paper2, Szomoru, van Gorkom, Gregg and Strauss 1995).

An HI Survey of the Bootes Void. II. The Analysis

A. Szomoru, J.H. van Gorkom, M.D. Gregg and M.A. Strauss

Preprint No. 187
Accepted for publication in The Astronomical Journal.

Abstract

We discuss the results of a VLA (Napier et al. 1983) HI survey of the Bootes void and compare the distribution and HI properties of the void galaxies to those of galaxies found in a survey of regions of mean cosmic density. The Bootes survey covers 1100 Mpc^{3}, or about 1% of the volume of the void and consists of 24 cubes of typically 2 Mpc x 2 Mpc x 1280 km s^{-1}, centered on optically known galaxies. Sixteen targets were detected in HI; 18 previously uncataloged objects were discovered directly in HI. The control sample consists of 12 cubes centered on IRAS selected galaxies with FIR luminosities similar to those of the Bootes targets and located in regions of 1 to 2 times the cosmic mean density. In addition to the 12 targets 29 companions were detected in HI. We find that the number of galaxies within 1 Mpc of the targets is the same to within a factor of two for void and control samples, and thus that the small scale clustering of galaxies is the same in regions that differ by a factor of about 6 in density on larger scales.
A dynamical analysis of the galaxies in the void suggests that on scales of a few Mpc the galaxies are gravitationally bound, forming interacting galaxy pairs, loose pairs and loose groups. One group is compact enough to qualify as a Hickson compact group (hereafter HCG) (Hickson 1982).
The galaxies found in the void are mostly late-type, gas rich systems. A careful scrutiny of their HI and optical properties shows them to be very similar to field galaxies of the same morphological type. This, combined with our finding that the small scale clustering of the galaxies in the void is the same as in the field, suggests that it is the near environment that mostly affects the evolution of galaxies.


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