Kapteyn Institute Preprints (1996)

# 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.

## 1996 Preprints

Preprint 216 Interactions between Massive Dark Halos and Warped Disks Konrad Kuijken
Preprint 215 Comments on PN Evolution, Stuart R. Pottasch
Preprint 214 Radio Spectra of Gigahertz Peaked Spectrum Radio Sources, W.H. de Vries, P.D. Barthel, C.P. O'Dea
Preprint 213 The PLANET Collaboration: Probing Lensing Anomalies, M. Albrow, J.-P. Beaulieu, P. Birch, J.A.R. Caldwell, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R.M. Naber, J.-W. Pel, K. Pollard, P.D. Sackett, K.C. Sahu, P. Vreeswijk, R. Watson, A. Williams, M. Zwaan
Preprint 212 Solid Methane Toward Deeply Embedded Protostars, A.C.A. Boogert, W.A. Schutte, A.G.G.M. Tielens, D.C.B. Whittet, F.P. Helmich, P. Ehrenfreund, P.R. Wesselius, Th. de Graauw and T. Prusti
Preprint 211 Infrared Observations and Laboratory Simulations of Interstellar CH4 and SO2, A.C.A. Boogert, W.A. Schutte, F.P. Helmich, A.G.G.M. Tielens and D.H. Wooden
Preprint 210 HI Velocity Fields and the Shapes of Dark Matter Halos, R.H.M. Schoenmakers
Preprint 209 Anomalous Radio-Loudness of Cygnus A and other Powerful Radio Galaxies, P.D. Barthel and K.A. Arnaud
Preprint 208 The URSA Major Cluster of Galaxies. I. Cluster Definition and Photometric Data, R. Brent Tully, Marc A.W. Verheijen, Michael J. Pierce, Jia-Sheng Huang and Richard J. Wainscoat
Preprint 207 K and Evolutionary Corrections from UV to IR, B.M. Poggianti
Preprint 206 Beamed Radio and Far Infrared Emission in Quasars and Radio Galaxies H. Hoekstra, P.D. Barthel and R. Hes
Preprint 205 Does Low Surface Brightness Mean Low Density? W.J.G. de Blok and S.S. McGaugh
Preprint 204 A Search for Counter-Rotating Stars in S0 Galaxies, Konrad Kuijken, David Fisher and Michael R. Merrifield
Preprint 203 Molecular Hydrogen in the Central Regions of Southern Infrared Galaxies, Jan Koornneef and Frank P. Israel
Preprint 202 A New Chemo-Evolutionary Population Synthesis Model for Early-Type Galaxies. I. Theoretical Basis, A. Vazdekis, E. Casuso, R.F. Peletier, J.E. Beckman
Preprint 201 HI Observations of Low Surface Brightness Galaxies: Probing Low-Density Galaxies, W.J.G. de Blok, S.S. McGaugh and J.M. van der Hulst
Preprint 200 The Fundamental Plane in CL 0024+16 at z=0.4: Implications for the Evolution of the Mass-to-Light Ratio Pieter G. van Dokkum, and Marijn Franx
Preprint 199 Starbursts and the Butcher-Oemler Effect in Galaxy Clusters, B.M. Poggianti and G. Barbaro
Preprint 198A Optical Methane-band Observations of Jovian Shoemaker-Levy 9 Impact Debris, N.G. Douglas
Preprint 198 Emission Line Imaging of 3CR Quasars and Radio Galaxies, R. Hes, P.D. Barthel and R.A.E. Fosbury
Preprint 197 Measuring the Evolution of the M/L Ratio from the Fundamental Plane in CL 0024+16 at z=0.39, Marijn Franx and Pieter G. van Dokkum
Preprint 196 A Counter-Rotating Bulge in the Sb Galaxy NGC 7331, F. Prada, M. Gutierrez, R.F. Peletier, C.D. McKeith
Preprint 195 Scale Lengths in Disk Surface Brightness as Probes of Dust Extinction in 3 Spiral Galaxies: M 51, NGC 3631 and M 100, J.E. Beckman. R.F. Peletier, J.H. Knapen, R.L.M. Corradi, L.J. Gentet
Preprint 194 Ages of Galaxy Bulges and Disks from Optical and near Infra-red Colors, R.F. Peletier and M. Balcells
Preprint 193 Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. IV. Using color profiles to study stellar and dust content of galaxies, Roelof S. de Jong
Preprint 192 Neutral carbon in translucent regions of the dark cloud L183, Ronald Stark, Paul R. Wesselius, Ewine F. van Dishoeck, R.J. Laureijs
Preprint 191 The Ca+ Abundance of HVC Complex C, B.P. Wakker, H. van Woerden, U.J. Schwarz, R.F. Peletier, N.G. Douglas
Preprint 190 Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. III. The statistics of the disk and bulge parameters, Roelof S. de Jong
Preprint 189 Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. II. A two-dimensional method to determine bulge and disk parameters, Roelof S. de Jong
Preprint 188 The Fundamental Plane for Cluster E and S0 Galaxies, Inger Jorgensen, Marijn Franx, Per Kjaergaard

## Interactions between Massive Dark Halos and Warped Disks

Preprint No. 216

Accepted for publication in: "Dark and Visible Matter in Galaxies and Cosmological Implications" (eds. M. Persic & P. Salucci), A.S.P. Conf. Series

### Abstract

The normal mode theory for warping of galaxy disks, in which disks are assumed to be tilted with respect to the equator of a massive, flattened dark halo, assumes a rigid, fixed halo. However, consideration of the back-reaction by a misaligned disk on a massive particle halo shows there to be strong coupling leading to efficient damping (or in some circumstances excitation) of the misalignment, and hence the warp. We therefore discuss possible alternative explanations of the warp phenomenon, with emphasis on the effect of a responsive, gravitationally live massive galactic halo.

### Stuart R. Pottasch

Preprint No. 215

Accepted for publication in: "Planetary Nebulae" (eds. H.J. Habing and H.J.G.L.M. Lamers), Proceedings of IAU Symposium 180, Groningen, August 1996

### Abstract

The improved distances given earlier in the symposium by Harris (parallaxes) and Terzian (expansion distances) are used to discuss the evolution of PN and their central stars. A critical note is given concerning the use of model nebulae to derive abundances and central star parameters.

### W.H. de Vries, P.D. Barthel, C.P. O'Dea

Preprint No. 214

Accepted for publication in: Astronomy and Astrophysics

### Abstract

A well defined sample of 72 Gigahertz Peaked Spectrum radio sources is compiled, having turnover frequencies in the range of 0.5 - 10 GHz. Using this sample, the canonical GPS radio spectrum is constructed, which is found to have a constant shape, independent of AGN type, redshift or radio luminosity. A possible deficiency of low turnover frequencies at high redshift is found, which may reflect a physical mechanism where turnover frequency and radio luminosity are correlated.

## The PLANET Collaboration: Probing Lensing Anomalies

### M. Albrow, J.-P. Beaulieu, P. Birch, J.A.R. Caldwell, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R.M. Naber, J.-W. Pel, K. Pollard, P.D. Sackett, K.C. Sahu, P. Vreeswijk, R. Watson, A. Williams, M. Zwaan

Preprint No. 213

Accepted for publication in: "Astrophysical Returns of Microlensing Surveys" (eds. R. Ferlet en J.-P. Maillard), Proceedings of the 12th Colloquium of the Institut d'Astrophysique de Paris

### Abstract

The Probing Lensing Anomalies NETwork (PLANET) is a worldwide collaboration of astronomers using semi-dedicated European, South African, and Australian telescopes to perform continuous, rapid and precise multi-band CCD photometric monitoring of on-going Galactic microlensing events. As well as providing important additional information on the nature, distribution and kinematics of Galactic microlenses, PLANET photometry is optimized for the detection of Jovian-mass planets orbiting several AU from Galactic lenses. The final PLANET database is expected to contain hundreds of variable stars sampled at hourly time scales with 1-5% precision.

## Solid Methane Toward Deeply Embedded Protostars

### A.C.A. Boogert, W.A. Schutte, A.G.G.M. Tielens, D.C.B. Whittet, F.P. Helmich, P. Ehrenfreund, P.R. Wesselius, Th. de Graauw and T. Prusti

Preprint No. 212

Accepted for publication in: Astronomy and Astrophysics Letters

### Abstract

We report on the detection of an absorption feature near 7.67 mu toward the deeply embedded protostellar objects W 33A and NGC 7538 : IRS9, using the ISO Short Wavelength Spectrometer. Comparison with laboratory spectra shows that this feature can be identified as the nu_4 (`deformation') mode of solid state CH4 embedded in polar molecules (i.e., H2O and/or CH3OH) in icy grain mantles. The solid CH4 column density relative to solid H2O is 0.4-1.9%. Unlike solid CO, solid CH4 does not seem to be subjected to out-gassing toward the warm source W 33A. The low gas-to-solid ratio for CH4 argues that CH4 is formed on grains either by hydrogenation of accreted C or by ultraviolet processing of CH3OH-rich ices.

## Infrared Observations and Laboratory Simulations of Interstellar CH4 and SO2 of the Mass-to-Light Ratio

### A.C.A. Boogert, W.A. Schutte, F.P. Helmich, A.G.G.M. Tielens and D.H. Wooden

Preprint No. 211

Accepted for publication in: Astronomy and Astrophysics

### Abstract

Interstellar CH4 may consume a fair amount of the carbon budget in dense molecular clouds, but probably less than CO, CH3OH, and CO2. However, it can only be observed at wavelength regions in the infrared that are heavily affected by the earth atmosphere. With new space and airborne missions (e.g. ISO, SOFIA) in mind we have studied the near infrared absorption spectra of solid and gaseous CH4. We obtained laboratory spectra of the nu4 deformation mode (1302 cm-1, 7.68 mu) of solid CH4 in astrophysically relevant mixtures. We found that the peak position and width of this absorption band vary strongly as a function of molecular environment, compared to temperature and particle shape effects. Hence, observations of this feature will provide a powerful probe of the molecular composition of interstellar ices. Also the gas phase CH4 ro-vibrational spectrum of the same band has been calculated. Using observed physical conditions around the protostar W 33A, we show that unresolved gaseous CH4 lines are detectable (at the 2-5% level) at a resolution >1000, when the column density N>1016 cm-2. An astrophysically relevant molecule with a very strong transition in the same wavelength regime, is SO2. We studied the nu3 asymmetric stretching mode (1319 cm-1, 7.58 mu) of solid SO2 in several mixtures, revealing that the peak position, width and detailed profile of this band are very sensitive to the molecular environment. Besides probing the composition of ice mantles, observations of solid SO2 will provide important information on the sulfur budget locked up in grain mantles, which is currently poorly known. We compare the laboratory and calculated spectra of CH4 and SO2 with previously published ground based spectra and new airborne observations of young stellar objects in the 7-8 mu region. W 33A, NGC 7538 : IRS1 and IRS9 show a feature near 7.68 mu that is consistent with absorption by solid CH4 or the Q-branch of gaseous CH4. The column density of solid CH4 would be 0.3-4% of solid H2O, indicating that solid CH4 consumes 0.5±0.3% of the cosmic carbon abundance. A gaseous origin would imply a column density of at least this amount, being highly dependent on the assumed temperature of the absorbing gas. A second absorption feature is detected toward W 33A and NGC 7538 : IRS1 at 7.58 mu. The peak position and width of this feature are consistent with the nu3 mode of solid SO2 in a matrix of solid CH3OH or pure SO2. The derived column density is 0.1-1% of solid H2O, indicating that solid SO2 locks up 0.6-6% of the cosmic sulfur abundance. This study shows that 7-8 mu spectroscopy of dense molecular clouds, using new airborne and space-based platforms, will provide valuable information on the composition of icy grain mantles and molecular cloud chemistry.

## HI Velocity Fields and the Shapes of Dark Matter Halos

### R.H.M. Schoenmakers

Preprint No. 210

Accepted for publication in: "Dark and Visible Matter in Galaxies and Cosmological Implications", eds. M. Persic and P. Salucci, A.S.P. Conf. Series.

### Abstract

I report on a new method for measuring deviations from axisymmetry in the velocity fields of gas disks. The method is an extension of the method that Franx, van Gorkom and de Zeeuw developed for a single orbit gas ring. The measurement is based upon a higher order harmonic expansion of the full velocity field. Epicyclic theory is used to calculate the effects of a perturbation in the potential on these harmonic terms. It is shown how the s_1 and s_3 harmonics can be used to measure epsilon_R sin(2 phi_{obs}), where epsilon_R is the elongation of the potential and phi_{obs} is an (unknown) viewing angle. The advantage of this method over previous attempts to derive the elongation of dark matter halos is that, by using HI, we can probe the potential at radii beyond the stellar disk, into the regime where the dark matter is thought to be the dominant dynamical component. As a demonstration, I applied this method to HI velocity fields of two spiral galaxies, NGC 2403 and NGC 3198. NGC 3198 shows a very small epsilon_R sin(2 phi_{obs}), which suggests that the galaxy is very nearly axisymmetric. NGC 2403 shows a larger epsilon_R sin(2\phi_{obs}), varying in a systematic way between 0 and 0.1 and is probably influenced by spiral arms. The current data suggests that spiral galaxies are close to axisymmetry, but a larger sample is needed to quantify this statement.

### P.D. Barthel and K.A. Arnaud

Preprint No. 209
Figure and Table are separated from the text:
Figure
Table

Accepted for publication in: Monthly Notices of the Royal Astronomical Society (Letters).

### Abstract

The nearby, extremely powerful radio galaxy Cygnus A stands out as having an atypically low far-infrared/radio luminosity ratio. It is demonstrated that in objects displaying such a low ratio the radio-loudness is anomalously high, which fact is connected to these objects inhabiting dense X-ray haloes. The enhanced radio emission is most likely due to strong radiation losses in the dense environment. It must be concluded that radio luminosity is not a good measure of AGN power.

## The URSA Major Cluster of Galaxies. I. Cluster Definition and Photometric Data

### R. Brent Tully, Marc A.W. Verheijen, Michael J. Pierce, Jia-Sheng Huang and Richard J. Wainscoat

Preprint No. 208

Accepted for publication in: The Astronomical Journal.

### Abstract

The Ursa Major Cluster has received remarkably little attention, although it is as near as the Virgo Cluster and contains a comparable number of HI-rich galaxies. In this paper, criteria for group membership are discussed and data are presented for 79 galaxies identified with the group. Of these, all 79 have been imaged at B,R,I bands with CCDs, 70 have been imaged at K' with a HgCdTe array detector, and 70 have been detected in the HI 21cm line. A complete sample of 62 galaxies brighter than M(B)=-16.5 is identified. Images and gradients in surface brightness and color are presented at a common linear scale. As has been seen previously, the galaxies with the reddest global colors are reddest at the centers and get bluer at large radii. However, curiously, among the galaxies with the bluest global colors there are systems with very blue cores that get redder at large radii

## K and Evolutionary Corrections from UV to IR

### B.M. Poggianti

Preprint No. 207

Figures can be requested by electronic mail (bianca@astro.rug.nl).

Accepted for publication in: Astronomy and Astrophysics Supplement Series.

### Abstract

K and evolutionary corrections are given for the E, Sa and Sc Hubble types for the U, B, V, R, I, J, H, K filters of the Johnson-Bessell & Brett photometric system and the gri filters of the modified Thuan & Gunn system up to the redshift z=3. Their dependence on the time scale of star formation in ellipticals is investigated. The corrections are computed according to an evolutionary synthesis model that reproduces the integrated galaxy spectrum in the range 1000-25000 A; such a model makes use of an infrared observed stellar library and its results are compared with nearby galaxies. Evolving spectral energy distributions of the various Hubble types, as well as optical-IR and IR-IR colour evolution and adopted filter response functions are also given.

## Beamed Radio and Far Infrared Emission in Quasars and Radio Galaxies

### H. Hoekstra, P.D. Barthel and R. Hes

Preprint No. 206

Accepted for publication in: Astronomy and Astrophysics.

### Abstract

Simple orientation model predictions for the radio to far infrared spectral energy distributions of radio-loud AGN are confronted with observations at various radio frequencies. This model is subsequently used to investigate 60 $\mu$m far-infrared data. The results are supportive of the unified scheme for Fanaroff-Riley class II radio galaxies and quasars. The relative strength of the beamed component is derived as a function of frequency, and it is found that the higher far infrared fluxes of quasars, as compared to radio galaxies, can be explained invoking moderately beamed nonthermal far-infrared emission.

## Does Low Surface Brightness Mean Low Density?

### W.J.G. de Blok and S.S. McGaugh

Preprint No. 205
Figures are separated from the text:
Figure 1
Figure 2
Accepted for publication in: Astrophysical Journal Letters.

### Abstract

We compare the dynamical properties of two galaxies at identical positions on the Tully-Fisher relation, but with different surface brightnesses. We find that the low surface brightness galaxy UGC 128 has a higher mass-to-light ratio, and yet has lower mass densities than the high surface brightness galaxy NGC 2403. This is true for the gas surface density, the stellar surface density, and the total mass density.

## A Search for Counter-Rotating Stars in S0 Galaxies

### Konrad Kuijken, David Fisher and Michael R. Merrifield

Preprint No. 204

Figure 2 is separated from the text:
Figure 2a
Figure 2b

Accepted for publication in Monthly Notices of the Royal Astronomical Society.

### Abstract

We have obtained high signal-to-noise spectra along the major axes of 28 S0 galaxies in order to search for the presence of disk stars on retrograde orbits. Full line-of-sight velocity distributions were extracted from the data, and the velocity distributions were modelled as arising from the superposition of populations of stars on prograde and retrograde orbits. We find no new cases in which a significant fraction of disk stars lie on retrograde orbits; an identical analysis of NGC~4550 does reveal the previously-known counter-rotating stellar disk in this system. Upper limits determined for each object indicate that no more than about 5% of the observed disk star light could arise from counter-rotating stellar components. These results suggest that previously-discovered disk galaxies with counter-rotating stars are exceptional and that (at 95% confidence) at most 10% of S0 galaxies contain significant counter-rotating populations. The most likely value for the fraction of such S0 galaxies lies closer to 1%. This result contrasts with the prevalence of counter-rotating gas in these systems; combining our new observations with existing data, we find that 24+/-8% (1-sigma error) of the gas disks in S0 galaxies counter-rotate relative to their stellar components.

## Molecular Hydrogen in the Central Regions of Southern Infrared Galaxies

### Jan Koornneef and Frank P. Israel

Preprint No. 203
To appear in: New Astronomy

### Abstract

An extensive set of molecular hydrogen observations of centers of southern infrared galaxies is presented. We combine our data with published infrared and radio observations to investigate the relationship between nuclear and circumnuclear activity. We convert the observational data to absolute luminosities, by applying the known distances. The resulting dataset covers several decades in luminosity for the various parameters, which observe fairly tight correlations. The parameters of our (power law) fits are, at the level of accuracy achieved, not dependent on the type of nuclear activity: while the dataset comprises a mixture of alleged Seyfert, Liner & Starburster galaxies, single fits match the complete sample well enough. In particular, non-thermal nuclei (AGN) present in some of the galaxies in the current sample, do not stand out in the parameters we investigated. The absence of a significant dependence on the nuclear type is consistent with the idea that the ever present starbursts energetically dominate a possible 'AGN in a dusty environment'-component in galaxy nuclei with infrared excesses.
The size of the H_2 emitting region is found to be proportional to the square root of the 21 cm radio continuum luminosity. The excitation of the circumnuclear H_2 is dominated by shocks. If the H_2 extent marks the size of an inner cavity in the dense molecular material surrounding a galaxy nucleus and the radio luminosity is proportional to the mechanical luminosity of (circum-)nuclear winds. This result then indicates that the cavity size occurs at constant pressure in the sample galaxies, in accordance with the superwind model by Heckman, Armus & Miley (1990). Our results, together with those obtained by others, thus suggest that luminosities and size scales of excited gas and dust around active nuclei are dominated by the mechanical energy input. Given the difficulties of uniquely establishing the presence of an AGN, we cannot exclude that (a large fraction of the) infrared luminous galaxies procure part of their radiated energy through accretion onto a massive dark object.

## A New Chemo-Evolutionary Population Synthesis Model for Early-Type Galaxies. I. Theoretical Basis

### A. Vazdekis, E. Casuso, R.F. Peletier, J.E. Beckman

Preprint No. 202
To appear in: The Astrophysical Journal Supplement

### Abstract

We have developed a new stellar population synthesis model designed to study early-type galaxies. It provides optical and near-infrared colors, and line indices for 25 absorption lines. It can synthesize single age, single metallicity stellar populations or follow the galaxy through its evolution from an initial gas cloud to the present time. The model incorporates the new isochrones of the Padova group and the latest stellar spectral libraries. We have applied our model to new data for a set of three early-type galaxies, to find out whether these can be fitted using single-age old metal-rich stellar populations, as is normal practice when one uses other stellar models of this kind. The model is extensively compared with previous ones in the literature to establish its accuracy as well as the accuracy of this kind of models in general.
Using the evolutionary version of the model we find that we cannot fit the most metal-rich elliptical galaxies if we keep the IMF constant and do not allow infall of gas. We do however reproduce the results of Arimoto & Yoshii (1986) for the evolution of the gas, and produce colors, and, for the first time with this type of models, absorption line-strengths. It is in fact possible to fit the data for the elliptical galaxies by varying the IMF with time. Our numerical model is in good broad agreement with the analytical simple model. We prefer however to calculate the evolution of the gas numerically instead of using the simple model, since it offers more flexibility, and even improved insight, when comparing with observations. In the present paper we describe the model, and compare a few key observables with new data for three early-type standard galaxies. However the data, as well as our fits, will be discussed in much more detail in a second paper (Vazdekis et al. 1996), where some conclusions will be drawn about elliptical galaxies on the basis of this model.

## HI Observations of Low Surface Brightness Galaxies: Probing Low-Density Galaxies

### W.J.G. de Blok, S.S. McGaugh and J.M. van der Hulst

Preprint No. 201
Figure 2 is separated from the text:
Figure 2 (1st part)
Figure 2 (2nd part)

Accepted for publication in Monthly Notices of the Royal Astronomical Society.

### Abstract

We present Very Large Array (VLA) and Westerbork Synthesis Radio Telescope (WSRT) 21-cm HI observations of 19 late-type low surface brightness (LSB) galaxies. Our main findings are that these galaxies, as well as having low surface brightnesses, have low HI surface densities, about a factor of ~3 lower than in normal late-type galaxies. We show that LSB galaxies in some respects resemble the outer parts of late-type normal galaxies, but may be less evolved. LSB galaxies are more gas-rich than their high surface brightness counterparts. The rotation curves of LSB galaxies rise more slowly than those of HSB galaxies of the same luminosity, with amplitudes between 50 and 120 km s^{-1}, and are often still ncreasing at the outermost measured point. The shape of the rotation curves suggests that LSB galaxies have low matter surface densities. We use the average total mass surface density of a galaxy as a measure for the evolutionary state, and show that LSB galaxies are among the least compact, least evolved galaxies. We show that both M_{HI}/L_B and M_{dyn}/L_B depend strongly on central surface brightness, consistent with the surface brightness-mass-to-light ratio relation required by the Tully-Fisher relation. LSB galaxies are therefore slowly evolving galaxies, and may well be low surface density systems in all respects.

## The Fundamental Plane in CL 0024+16 at z=0.4: Implications for the Evolution of the Mass-to-Light Ratio

### Pieter G. van Dokkum, and Marijn Franx

Preprint No. 200
Figure 3 is separated from the text:
Figure 3

Accepted for publication in Monthly Notices of the Royal Astronomical Society.

### Abstract

We present results on the Fundamental Plane of early-type galaxies in the rich cluster CL 0024 +16 at z=0.391. The internal velocity dispersions of the galaxies have been measured from a 19 hour integration at the MMT. The photometric parameters of the galaxies have been measured from deep HST images. The galaxies satisfy a tight Fundamental Plane relation which is similar to that at low redshift. The scatter is 15% in log r_e, also very similar to that at low redshift. The data show that massive early-type galaxies existed at z=0.4, and extend earlier studies of the luminosities and colors of early-types in rich clusters. The evolution of the M/L ratio is derived from the Fundamental Plane, by a comparison with Coma. The M/L ratio increases by 31 ± 12% between z=0.391, and z=0.023. The evolution is low when compared to models for stellar populations. The expected evolution depends on the IMF, q_0, and the formation redshift of the galaxies. The data are in agreement with high formation redshifts. The modeling is still uncertain, however, because of various possible biases. The most serious bias may be the progenitor bias: if the progenitors of some current day early-types are spirals at z=0.4, they would not be included in the sample, and the sample would be biased towards the oldest galaxies. More data are needed to measure the evolution of the Fundamental Plane more precisely, and its scatter. There is a hint that the form of the Fundamental Plane changes with redshift, and this needs to be determined better. Deeper samples on more clusters would be valuable. Studies of the richest nearby clusters may help to test the underlying hypothesis that the Fundamental Plane is identical in all clusters.

## Starbursts and the Butcher-Oemler Effect in Galaxy Clusters

### B.M. Poggianti and G. Barbaro

Preprint No. 199

Figures can be requested by electronic mail (bianca@astro.rug.nl).

Accepted for publication in Astronomy and Astrophysics.

### Abstract

In order to explain the spectroscopic observations of most of the galaxies in the intermediate redshift clusters, bursts of star formation superimposed to the traditional scenario of galactic evolution are needed.
The analysis of spectral lines and colours by means of an evolutionary synthesis model, including both the stellar contribution and the emission of the ionized gas, allows in most of the cases the determination of the time elapsed since the end of the burst and the fraction of galactic mass involved in it. In the four clusters considered (AC103, AC114, AC118 at z = 0.31 and Cl1358+6245 at z = 0.33), the theoretical analysis demonstrates that the bursts affect substantial galactic mass fractions, typically 30% or more.
The observations can be equally well reproduced by either elliptical+burst models or by spiral+burst models in which the star formation is truncated at the end of the burst. A way to determine the galactic original type is suggested.

## Optical Methane-band Observations of Jovian Shoemaker-Levy 9 Impact Debris

### N.G. Douglas

Preprint No. 198A
Figures are separated from the text:
Figures 1-4
Accepted for publication in Astronomy and Astrophysics.

### Abstract

During the encounter of comet Shoemaker-Levy 9 with Jupiter in July 1994, narrow-band imaging was used to detect changes in methane opacity in the upper atmosphere resulting from the impacts. Of nine debris clouds visible in the data, seven show clear evidence of a significant change, when compared with nearby parts of the disk, between the opacity in the optical methane band and that in a near-lying part of the continuum. Typical opacity enhancement is of the order of 30%. The result is found to be corroborated by related data from other sources. Possible reasons for the observed effect are discussed.

## Emission Line Imaging of 3CR Quasars and Radio Galaxies

### R. Hes, P.D. Barthel and R.A.E. Fosbury

Preprint No. 198
Accepted for publication in Astronomy and Astrophysics.

### Abstract

Optical emission line images and spectra of sixteen 3CR powerful radio galaxies and quasars are presented. Extended line emission is detected in both radio galaxies and quasars. We show that line luminosities, derived from the spatially integrated [OII]lambda3727 narrow emission line, are on average similar for radio galaxies and quasars of the same radio power and redshift. This result supports the unified model of these powerful radio sources, and indicates that the narrow line region contains dust.

## Measuring the Evolution of the M/L Ratio from the Fundamental Plane in CL 0024+16 at z=0.39

### Marijn Franx and Pieter G. van Dokkum

Preprint No. 197
To appear in: "New Light on Galaxy Evolution" (eds. R. Bender and R. Davies), IAU Symposium 171, Kluwer, Dordrecht, 1996.

### Abstract

The existence of the Fundamental Plane of early-type galaxies implies that the M/L ratios of early-types are well behaved. It provides therefore an important tool to measure the evolution of the M/L ratio with redshift. These measurements, in combination with measurements of the evolution of the luminosity function, can be used to constrain the mass evolution of galaxies.
We present the Fundamental Plane relation measured for galaxies in the rich cluster CL 0024+16 at z=0.391. The galaxies satisfy a tight Fundamental Plane, with relatively low scatter (15%). The M/L is 31+/-12% lower than the M/L measured in Coma, which is consistent with simple evolutionary models. Hence, galaxies with very similar dynamical properties existed at a z=0.4.
More, and deeper data are needed to measure the evolution of the slope and the scatter of the Fundamental Plane to higher accuracy. Furthermore, data on the richest nearby clusters would be valuable to test the hypothesis that the Fundamental Plane is independent of cluster environment.

## A Counter-Rotating Bulge in the Sb Galaxy NGC 7331

### F. Prada, M. Gutierrez, R.F. Peletier, C.D. McKeith

Preprint No. 196
Accepted for publication in the Astrophysical Journal Letters.

### Abstract

We have found that the bulge of the large, nearby Sb galaxy NGC 7331 rotates retrograde to its disk. Analysis of spectra in the region of the near-IR Ca II triplet along the major axis shows that, in the radial range between 5'' and ~20'', the line of sight velocity distribution of the absorption lines has two distinct peaks, and can be decomposed into a fast-rotating component with v/sigma > 3, and a slower rotating, retrograde component with v/sigma between 1-1.5. The radial surface brightness profile of the counter-rotating component follows that of the bulge, obtained from a 2-dimensional bulge-disk decomposition of a near-infrared K-band image, while the fast rotating component follows the disk. At the radius where the disk starts to dominate the isophotes change from being considerably boxy to very disky.
Although a number of spiral galaxies have been found that contain cold, couter-rotating disks, this is the first galaxy known to have a boxy, probably triaxial, fairly warm, counter-rotating component, which is dominating in the central regions. If it is a bar seen end-on, this bar has to be thicker than the disk. We find that NGC 7331, even though it is a fairly early-type spiral, does not have a conventional, co-rotating bulge. The fact that the inner component is retrograde makes us believe that it was formed from infalling material, in either stellar or gaseous form (e.g. Balcells & Quinn 1990). Another possibility however is that the structure has been there since the formation of the galaxy. In this case it will be a challenge to explain the large change in orientation of the angular momentum when going outward radially.

## Scale Lengths in Disk Surface Brightness as Probes of Dust Extinction in 3 Spiral Galaxies: M 51, NGC 3631 and M 100

### J.E. Beckman. R.F. Peletier, J.H. Knapen, R.L.M. Corradi, L.J. Gentet

Preprint No. 195
Accepted for publication in the Astrophysical Journal.

### Abstract

We have measured the radial brightness distributions in the disks of three nearby face-on spirals: M 51, NGC 3631, and NGC 4321 (M 100) in the photometric bands B through I, with the addition of the K band for M 51 only. The measurements were made by averaging azimuthally, in three modes, the two-dimensional surface brightness over the disks in photometric images of the objects in each band: (a) over each disk as a whole, (b) over the spiral arms alone, and (c) over the interarm zones alone. From these profiles scale-lengths were derived for comparison with schematic exponential disk models incorporating interstellar dust. These models include both absorption and scattering in their treatment of radiative transfer. The model fits show that the arms exhibit greater optical depth in dust than the interarm zones. The average fraction of emitted stellar light in V which is extinguished by dust within 3 scale-lengths of the center of each galaxy does not rise above 20% in any of them. We show that this conclusion is also valid for models with similar overall quantities of dust, but where this is concentrated in lanes. These can also account for the observed scale-lengths, and their variations.

## Ages of Galaxy Bulges and Disks from Optical and near Infra-red Colors

### R.F. Peletier and M. Balcells

Preprint No. 194
Accepted for publication in the Astronomical Journal.

### Abstract

We compare optical and near-infrared colors of disks and bulges in a diameter-limited sample of inclined, bright, nearby, early-type spirals. Color profiles along wedge apertures at 15 degrees from the major axis and on the minor axis on the side of the galaxy opposite to the dust lane are used to assign nominal colors for the inner disks (at 2 scale length) and for the bulges (~0.5 r_eff), respectively. We estimate that the effects of dust reddening and the cross-talk between the colors of the two components is negligible. We find that color differences (bulge - disk) are very small: Delta(U-R)=0.126 +/- 0.165, Delta(R-K)=0.078 +/- 0.165. Disks tend to be bluer by an amount three times smaller than that reported by Bothun & Gregg (1990) for S0's. Color variations from galaxy to galaxy are much larger than color differences between disk and bulge in each galaxy. Probably, the underlying old population of disks and bulges is much more similar than the population paradigm would lead us to believe. Implied age differences, assuming identical metallicities, are less than 30%.

## Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. IV. Using color profiles to study stellar and dust content of galaxies

### Roelof S. de Jong

Preprint No. 193
Accepted for publication in Astronomy and Astrophysics.

### Abstract

The stellar and dust content of spiral galaxies as function of radius has been investigated using near-infrared and optical broadband surface photometry of 86 face-on spiral galaxies. Colors of galaxies correlate with the azimuthally averaged local surface brightness both within and among galaxies, with the lower surface brightness regions being bluer. The colors formed from different passband combinations correlate strongly indicating that they probably arise from the same physical process.
A 3D radiative transfer model was developed to calculate the effect of dust absorption and scattering on the luminosity and color profiles of galaxies. Stellar synthesis models were used to investigate the effects of the star formation history and the metallicity on the broadband color profiles. Combining all optical and near-infrared data shows that the color gradients in this sample of face-on galaxies are best explained by a combined stellar age and metallicity gradient across the disk, with the outer regions being on average younger and of lower metallicity. Dust reddening probably plays only a minor role, as the dust models cannot produce reddening profiles that are compatible with the observations.
The observed color differences implicate substantial M/L_\lambda differences, both within galaxies and among galaxies. The variations are such that the "missing light" problem derived from rotation fitting becomes even worse. Late-type galaxies (T>6) have lower metallicities and are often of younger average age than earlier types and have therefore an entirely different M/L_\lambda in most passbands. The near-infrared passbands are recommended for studies where the M/L_\lambda ratios should not vary too much.

## Neutral carbon in translucent regions of the dark cloud L183

### Ronald Stark, Paul R. Wesselius, Ewine F. van Dishoeck, R.J. Laureijs

Preprint No. 192
Accepted for publication in Astronomy and Astrophysics.

### Abstract

Observations of the CI ^{3}P_{1}-^{3}P_{0} 492 GHz fine structure line and isotopic CO(2-1, 3-2) rotational lines have been made at six positions along an east-west strip through the centre of the high-latitude dark cloud L183 using the James Clerk Maxwell Telescope. The CI spectra have line strengths varying between T_{MB} = 0.8-3.4 K. The lines appear broad due to a blend of two kinematically different components around V \simeq 1 km s^{-1} and V \simeq 2.3 km s^{-1} which can be resolved at some positions. If the CI emission originates in the warmer, translucent envelopes (A_{V} \simeq 1-5 mag) of L183 we derive total column densities in both components in the range 7 x 10^{15}-3 x 10^{17} cm^{-2}. In case it would come primarily from the cold dark core (A_{V} > 5 mag) we calculate lower limits of about 10^{16}-10^{17} cm^{-2}. The component around V \simeq 1 km s^{-1} is most likely entirely translucent. We argue that most of the observed CI emission from the V \simeq 2.3 km s^{-1} component also originates in the translucent regions of L183 and has an optical depth in the range \tau = 0.1-6. We find a good correlation between the CI and ^{13}CO(3-2, 2-1) measurements but not with C^{18}O(2-1). The derived C/CO column density ratio along the cut varies between 0.08-0.7 and remains constant within the uncertainty. Chemical model calculations are used to study the CI column density as well as the C/CO ratio as a function of density and total hydrogen column density. A close inverse correlation is found between N(C)/N(CO) and A_{V} for N(H_{2}) ~ 10^{20}- 5 x 10^{21} cm^{-2}, which is consistent with the generally observed correlation between C and CO from diffuse clouds to dense photon dominated regions.

## The Ca+ Abundance of HVC Complex C

### B.P. Wakker, H. van Woerden, U.J. Schwarz, R.F. Peletier, N.G. Douglas

Preprint No. 191
Figures are separated from the text:
Figure 1
Figure 2
Accepted for publication in Astronomy and Astrophysics.

### Abstract

We report the first detection of CaII H and K absorption in the high-velocity cloud complex C, the largest HVC. Absorption is detected in the spectra of the quasar PG 1351+640 and of the Seyfert galaxy Mark 290, at velocities of -163 and -137 km s^{-1} (see Fig. 2). The implied Ca+ abundances are about 2 x 10^{-8}, or about 0.01 times the total solar Calcium abundance. This value lies near the middle of the range of values found for other HVCs. The measured abundance will allow firm conclusions about the distance of complex C from the presence or absence of its absorption in stellar spectra.

## Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. III. The statistics of the disk and bulge parameters

### Roelof S. de Jong

Preprint No. 190
Accepted for publication in Astronomy and Astrophysics.

### Abstract

The statistics of the fundamental bulge and disk parameters of galaxies and their relation to the Hubble sequence were investigated by an analysis of optical and near-infrared observations of 86 face-on spiral galaxies. The availability of near-infrared K passband data made it possible for the first time to trace fundamental parameters related to the luminous mass while hardly being hampered by the effects of dust and stellar populations. The observed number frequency of galaxies was corrected for selection effects to calculate volume number densities of galaxies with respect to their fundamental parameters. The main conclusions of this investigation are:
1) Freeman's law has to be redefined. There is no single preferred value for the central surface brightnesses of disks in galaxies. There is only an upper limit to the central surface brightnesses of disks, while for lower central surface brightnesses the number of galaxies per volume element decreases only slowly as function of the central surface brightness.
2) The Hubble sequence type index correlates strongly with the effective surface brightness of the bulge, much better than with the bulge-to-disk ratio.
3) The disk and bulge scalelengths are correlated.
4) These scalelengths are not correlated with Hubble type. Hubble type is a lengthscale-free parameter and each type therefore comes in a range of magnitudes (and presumably a range of total masses).
5) Low surface brightness spiral galaxies are not a separate class of galaxies. In a number of aspects they are a continuation of a trend defined by the high surface brightness galaxies. Low surface brightness galaxies are in general of late Hubble type.

## Near-Infrared and optical Broadband Surface Photometry of 86 Face-on Disk Dominated Galaxies. II. A two-dimensional method to determine bulge and disk parameters

### Roelof S. de Jong

Preprint No. 189
Accepted for publication in Astronomy and Astrophysics Supplement Series.

### Abstract

In this paper I present a new two-dimensional decomposition technique, which models the surface photometry of a galaxy with an exponential light profile for both bulge and disk and, when necessary, with a Freeman bar. The new technique was tested for systematic errors on both artificial and real data and compared with widely used one-dimensional decomposition techniques, where the luminosity profile of the galaxy is used. The comparisons indicate that a decomposition of the two-dimensional image of the galaxy with an exponential light profile for both bulge and disk yields the most reproducible and representative bulge and disk parameters.
An extensive error analysis was made to determine the reliability of the model parameters. If the model with an exponential bulge profile is a reasonable description of a galaxy, the maximum errors in the derived model parameters are of order 20%. The uncertainties in the model parameters will increase, if the exponential bulge function is replaced by other often used bulge functions as the de Vaucouleurs law.
All decomposition methods were applied to the optical and near-infrared data set presented by de Jong & van der Kruit (1994), which comprises 86 galaxies in six passbands.

## The Fundamental Plane for Cluster E and S0 Galaxies

### Inger Jorgensen, Marijn Franx, Per Kjaergaard

Preprint No. 188
Accepted for publication in Monthly Notices of the Royal Astronomical Society.

### Abstract

We have analyzed the shape of the Fundamental Plane (FP) for a sample of 226 E and S0 galaxies in ten clusters of galaxies. We find that the distribution of galaxies is well approximated by a plane of the form

log r_e = 1.24 log \sigma - 0.82 log I _e + \gamma

for photometry obtained in Gunn r. This result is in good agreement with previous determinations. The FP has a scatter of 0.084 in log r_e. For galaxies with velocity dispersion larger than 100 km/s the scatter is 0.073. If the FP is used for distance determinations this scatter is equivalent to 17% uncertainties on distances to single galaxies.
We find that the slope of the FP is not significantly different from cluster to cluster. Selection effects and measurement errors can introduce biases in the derived slope. The residuals of the FP correlate weakly with the velocity dispersion and the surface brightness. Some of the coefficients used in the literature give rather strong correlations between the residuals and absolute magnitudes. This implies that galaxies need to be selected in a homogeneous way to avoid biases of derived distances on the level of 5-10% or smaller.
The FP has significant intrinsic scatter. No other structural parameters like ellipticity or isophotal shape can reduce the scatter significantly. This is in contradiction to simple models, which predict that the presence of disks in E and S0 galaxies can introduce scatter in the FP. It remains unknown what the source of scatter is. It is therefore unknown whether this source produces systematic errors in distance determinations.
The Mg_2-\sigma relation for the cluster galaxies differs slightly from cluster to cluster. Galaxies in clusters with lower velocity dispersions have systematically lower Mg_2. The effect can be caused by both age and metallicity variations. With the current stellar population models, it is in best agreement with our results regarding the FP if the offsets are mainly caused by differences in metallicity.
Most of the distances that we derive from the FP imply small peculiar motions (<1000 km/s). The zero point of the FP must therefore be quite stable. Only for one cluster, located 28 degr from the direction towards the "Great Attractor", we find a peculiar motion of 1300 km/s. This motion is reduced to 890 km/s if we use the FP corrected for the offset of the Mg_2-\sigma relation. This confirms earlier suggestions that the residuals from the Mg_2-\sigma relation can be used to flag galaxies with deviant populations, and possibly to correct the distance determinations for the deviations.

 Maintained by:  Gineke Alberts