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Monthly Notices of the Royal Astronomical Society, 378 (1), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Monthly Notices of the Royal Astronomical Society, 356 (4), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Monthly Notices of the Royal Astronomical Society, 390 (2), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

Bolton et al. (2007) have derived a mass-based fundamental plane using photometric and spectroscopic observations of 36 strong gravitational lenses. The lensing allows a direct determination of the mass-surface density and so avoids the usual dependence on mass-to-light ratio. We consider this same sample in the context of modified Newtonian dynamics (MOND) and demonstrate that the observed mass-based fundamental plane coincides with the MOND fundamental plane determined previously for a set of high-order polytropic spheres chosen to match the observed range of effective radii and velocity dispersions in elliptical galaxies. Moreover, the observed projected mass within one-half an effective radius is consistent with the mass in visible stars plus a small additional component of ``phantom dark matter'' resulting from the MOND contribution to photon deflection., Comment: Minor revisions in response to referee. Revised title. Accepted in MNRAS

We describe the HST ACS Coma Cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma Cluster (Abell 1656). The survey was designed to cover an area of 740 arcmin2 in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of 2007 January 27 leaves the survey 28% complete, with 21 ACS pointings (230 arcmin2) complete, and partial data for a further four pointings (44 arcmin2). The predicted survey depth for 10 σ detections for optimal photometry of point sources is g'=27.6 in the F475W filter and IC=26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g'=27.55 and IC=26.65. For extended sources, the predicted 10 σ limits for a 1 arcsec2 region are g'=25.8 mag arcsec-2 and IC=25.0 mag arcsec-2. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultracompact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well-known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO10861.

We describe the HST ACS Coma Cluster Treasury survey, a deep two-passband imaging survey of one of the nearest rich clusters of galaxies, the Coma Cluster (Abell 1656). The survey was designed to cover an area of 740 arcmin2 in regions of different density of both galaxies and intergalactic medium within the cluster. The ACS failure of 2007 January 27 leaves the survey 28% complete, with 21 ACS pointings (230 arcmin2) complete, and partial data for a further four pointings (44 arcmin2). The predicted survey depth for 10 σ detections for optimal photometry of point sources is g'=27.6 in the F475W filter and IC=26.8 mag in F814 (AB magnitudes). Initial simulations with artificially injected point sources show 90% recovered at magnitude limits of g'=27.55 and IC=26.65. For extended sources, the predicted 10 σ limits for a 1 arcsec2 region are g'=25.8 mag arcsec-2 and IC=25.0 mag arcsec-2. We highlight several motivating science goals of the survey, including study of the faint end of the cluster galaxy luminosity function, structural parameters of dwarf galaxies, stellar populations and their effect on colors and color gradients, evolution of morphological components in a dense environment, the nature of ultracompact dwarf galaxies, and globular cluster populations of cluster galaxies of a range of luminosities and types. This survey will also provide a local rich cluster benchmark for various well-known global scaling relations and explore new relations pertaining to the nuclear properties of galaxies. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO10861.

We combine high-resolution images in four optical/infrared bands, obtained with the laser guide star adaptive optics ( LGSAO) system on the Keck telescope and with the Hubble Space Telescope ( HST), to study the gravitational lens system SDSS J0737 + 3216 ( lens redshift 0.3223, source redshift 0.5812). We show that ( under favorable observing conditions) ground-based images are comparable to those obtained with HST in terms of precision in the determination of the parameters of both the lens mass distribution and the background source. We also quantify the systematic errors associated with both the incomplete knowledge of the PSF and the uncertain process of lens galaxy light removal and find that similar accuracy can be achieved with Keck LGSAO as with HST. We then exploit this well-calibrated combination of optical and gravitational telescopes to perform a multiwavelength study of the source galaxy at 0.01 '' effective resolution. We find the Sersic index to be indicative of a disklike object, but the measured half-light radius (r(e) = 0.59 +/- 0.007 stat +/- 0.1 sys kpc) and stellar mass (M* = 2.0 +/- 1.0 stat +/- 0.8 sys x 10(9) M(circle dot)) place it more than 3 sigma away from the local disk size-mass relation. The SDSS J0737 + 3216 source has the characteristics of the most compact faint blue galaxies studied and comparable size and mass to dwarf early-type galaxies in the local universe. With the aid of gravitational telescopes to measure individual objects' brightness profiles to 10% accuracy, the study of the high-redshift size-mass relation may be extended by an order of magnitude or more beyond existing surveys at the low-mass end, thus providing a new observational test of galaxy formation models.

A simple algorithm is employed to deproject the two-dimensional images of a pilot sample of 12 high-quality images of edge-on disc galaxies and to study their intrinsic three-dimensional (3D) stellar distribution. We examine the radial profiles of the stars as a function of height above the plane and report a general trend within our sample of an increasing radial scalelength with height outside of the dust lane. This could be explained by the widespread presence of a thick disc component in these galaxies. In addition, the 3D view allows the study of the vertical distribution of the outer disc, beyond the break region, where we detect a significant increase in scalelength with vertical distance from the major axis for the truncated discs. This could be regarded as a weakening of the ‘truncation’ with increasing distance from the plane. Furthermore, we conclude that the recently revised classification of the radial surface brightness profiles found for face-on galaxies is indeed independent of geometry. In particular, we find at least one example of each of the three main profile classes as defined in complete samples of intermediate to face-on galaxies: not-truncated, truncated and antitruncated. The position and surface brightness that mark the break location in the radial light distribution are found to be consistent with those of face-on galaxies.

We present rotation curves for 19, mostly luminous, early-type disk galaxies. Rotation velocities are measured from a combination of HI velocity fields and long-slit optical emission line spectra along the major axis. We find that the rotation curves generally rise rapidly in the central regions and often reach rotation velocities of 200 - 300 km/s within a few hundred parsecs of the centre. The detailed shape of the central rotation curves shows a clear dependence on the concentration of the stellar light distribution and the bulge-to-disk luminosity ratio: galaxies with highly concentrated stellar light distributions reach the maximum in their rotation curves at relatively smaller radii than galaxies with small bulges and a relatively diffuse light distribution. We interpret this as a strong indication that the dynamics in the central regions are dominated by the stellar mass. At intermediate radii, many rotation curves decline. The strength of the decline is correlated with the total luminosity of the galaxies, more luminous galaxies having on average more strongly declining rotation curves. At large radii, however, all declining rotation curves flatten out, indicating that substantial amounts of dark matter must be present in these galaxies too. A comparison of our rotation curves with the Universal Rotation Curve from Persic et al. (1996) reveals large discrepancies between the observed and predicted rotation curves; we argue that rotation curves form a multi-parameter family which is too complex to describe with a simple formula depending on total luminosity only. (abridged), 27 pages, 9 figures. Accepted for publication in MNRAS. A pdf-version with full resolution figures and the full atlas can be found at http://www.nottingham.ac.uk/~ppzen/rotcurs.accepted.pdf

We present a 2D kinematic analysis for a sample of simulated binary disc merger remnants with mass ratios 1:1 and 3:1. For the progenitor discs we used pure stellar models as well as models with 10 per cent of their mass in gas. A multitude of phenomena also observed in real galaxies are found in the simulations. These include misaligned rotation, embedded discs, gas rings, counter-rotating cores (CRCs) and kinematic misaligned discs. Using the 2D maps we illustrate projection effects and the change in properties of a merger remnant when gas is included in the merger. We find that kinematic peculiar subsystems are preferably formed in equal-mass mergers. Equal-mass collisionless remnants can show almost no rotation, regular rotation or strong kinematic misalignment. The inclusion of gas makes the remnants appear more round (1:1) and axisymmetric (3:1). CRCs are almost exclusively formed in equal-mass mergers with a dissipational component. 3:1 remnants show a much more regular structure. We quantify these properties by applying the kinemetric methods recently developed by Krajnovic et al. This work will help to understand observations of elliptical galaxies with integral field spectrographs, like SAURON.

We present deep B- and R-band surface photometry for a sample of 21 galaxies with morphological types between S0 and Sab. We present radial profiles of surface brightness, colour, ellipticity, position angle and deviations of axisymmetry for all galaxies, as well as isophotal and effective radii and total magnitudes. We have decomposed the images into contributions from a spheroidal bulge and a flat disk, using an interactive, 2D decomposition technique. We study in detail the relations between various bulge and disk parameters. In particular, we find that the bulges of our galaxies have surface brightness profiles ranging from exponential to De Vaucouleurs, with the average value of the Sersic shape parameter n being 2.5. In agreement with previous studies, we find that the shape of the bulge intensity distribution depends on luminosity, with the more luminous bulges having more centrally peaked light profiles. By comparing the ellipticity of the isophotes in the bulges to those in the outer, disk dominated regions, we are able to derive the intrinsic axis ratio q_b of the bulges. The average axis ratio is 0.55, with an rms spread of 0.12. None of the bulges in our sample is spherical, whereas in some cases, the bulges can be as flat as q_b = 0.3 - 0.4. The bulge flattening seems to be weakly coupled to luminosity, more luminous bulges being on average slightly more flattened than their lower-luminosity counterparts. Our finding that most bulges are significantly flattened and have an intensity profile shallower than R^{1/4} suggests that `pseudobulges', formed from disk material by secular processes, do not only occur in late-type spiral galaxies, but are a common feature in early-type disk galaxies as well. (abridged), Comment: 26 pages, 11 figures. Accepted for publication in MNRAS. A pdf-version with full resolution figures and the full atlas can be found at http://www.nottingham.ac.uk/~ppzen/surfphot.accepted.pdf

We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy (IFS) observations were performed using PMAS in the PPAK mode covering a field of view of similar to 74 x 64 arcsec(2) centred on the core of the cluster, in order to obtain spectroscopy of an unbiased flux-limited sample of cluster galaxies. 43 objects were detected in the IFS data, 31 of them with enough signal-to-noise ratio to derive the redshift, all of them brighter than I The morphologically segregated colour-magnitude diagram shows that the early-type galaxies cover the range of brighter and redder colours (the so-called 'red sequence'). A large fraction of spiral galaxies (similar to 50 per cent) is found, most of them fainter than the limit of previous studies. They cover a wide range in colours, from blue colours typical of Butcher-Oemler galaxies to red colours similar to those of early-type galaxies. This result indicates that early-type galaxies are more massive and have older stellar populations, while late-type galaxies are less massive and have a wider range of stellar populations. The distribution of luminosity-weighted ages as a function of metallicities and luminosity-weighted masses, and the distribution of Sersic indices as a function of the luminosity-weighted masses confirm these results. They in fact agree with a proposed two-step scenario for the evolution of galaxies in clusters, where the star formation is quenched first in the infalling spirals, after which a morphological transformation follows that requires larger time-scales. This scenario naturally explains the population faint late-type galaxies with old stellar populations observed in this cluster. In addition, an extremely blue merging galaxy system is found at the core, with the nominal redshift of the cluster.

SUMMARIZED ABSTRACT: We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy was obtained using PMAS/PPAK@3.5m CAHA to obtain a complete flux limited sample of cluster members within its field-of-view (~74"X64"). In addition of 31 galaxies with known redshifts in the outer regions, we built up a final sample of 59 spectroscopically confirmed cluster members. Multiban photometry and detailed morphologies were obtained using deep images taken with the HST/ACS camera in the BVRI and z-bands. The CM diagram shows that the E-type galaxies cover the range of brighter and redder colors. A large fraction of spiral galaxies ($\sim$50%) is found. They cover a wide range in colors. This result, together with the distributions of ages, metallicities and masses, indicates that E-type galaxies are more massive and have older stellar populations, while L-type galaxies are less massive and have a wider range of stellar Our results agree with a proposed two-step scenario for the evolution of galaxies in clusters. In addition, an extremely blue merging galaxy system is found at the core, with the nominal redshift of the cluster., Comment: 29 pages, 17 figures, accepted for publishing in MNRAS. (HST/ACS composite image: http://www.caha.es/sanchez/abell2218/BRI_big.jpg)

We discuss the colours of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 'main' spectroscopic sample (a flux-limited sample, r(Pet)

We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 'main' spectroscopic sample ( a flux-limited sample for 1360 deg(2)). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite ( IRAS), Green Bank GB6 survey ( GB6), Faint Images of the Radio Sky at Twenty-centimetres ( FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from

We present H. observations of 68 early-type disk galaxies from the WHISP survey. They have morphological types between S0 and Sab and absolute B-band magnitudes between - 14 and - 22. These galaxies form the massive, high surface-brightness extreme of the disk galaxy population, few of which have been imaged in H. before. The H. properties of the galaxies in our sample span a large range; the average values of M-HI/L-B and D-HI/D-25 are comparable to the ones found in later-type spirals, but the dispersions around the mean are larger. No significant differences are found between the S0/S0a and the Sa/Sab galaxies. Our early-type disk galaxies follow the same H. mass-diameter relation as later-type spiral galaxies, but their effective H. surface densities are slightly lower than those found in later-type systems. In some galaxies, distinct rings of H. emission coincide with regions of enhanced star formation, even though the average gas densities are far below the threshold of star formation derived by Kennicutt ( 1989, ApJ, 344, 685). Apparently, additional mechanisms, as yet unknown, regulate star formation at low surface densities. Many of the galaxies in our sample have lopsided gas morphologies; in most cases this can be linked to recent or ongoing interactions or merger events. Asymmetries are rare in quiescent galaxies. Kinematic lopsidedness is rare, both in interacting and isolated systems. In the appendix, we present an atlas of the H. observations: for all galaxies we show H. surface density maps, global profiles, velocity fields and radial surface density profiles.

The stellar disc kinematics in a sample of fifteen intermediate- to late-type edge-on spiral galaxies are studied using a dynamical modeling technique. The sample covers a substantial range in maximum rotation velocity and deprojected face-on surface brightness and contains seven spirals with either a boxy- or peanut-shaped bulge. Dynamical models of the stellar discs are constructed using the disc structure from $I$-band surface photometry and rotation curves observed in the gas. The differences in the line-of-sight stellar kinematics between the models and absorption line spectroscopy are minimized using a least-squares approach. The modeling constrains the disc surface density and stellar radial velocity dispersion at a fiducial radius through the free parameter $\sqrt{M/L}$ $(\sigma_{\rm z}/\sigma_{\rm R})^{-1}$, where $\sigma_{\rm z}/\sigma_{\rm R}$ is the ratio of vertical and radial velocity dispersion and $M/L$ the disc mass-to-light ratio. For thirteen spirals a transparent model provides a good match to the mean line-of-sight stellar velocity dispersion. Models that include a realistic radiative transfer prescription confirm that the effect of dust on the observable stellar kinematics is small at the observed slit positions. We discuss possible sources of systematic error and conclude that most of these are likely to be small. The exception is the neglect of the dark halo gravity, which has probably caused an overestimate of the surface density in the case of low surface brightness discs., Comment: Accepted for publication by the Monthly Notices of the R.A.S

In earlier papers in this series we determined the intrinsic stellar disc kinematics of 15 intermediate- to late-type edge-on spiral galaxies using a dynamical modelling technique. The sample covers a substantial range in maximum rotation velocity and deprojected face-on surface brightness, and contains seven spirals with either a boxy or peanut-shaped bulge. Here we discuss the structural, kinematical and dynamical properties. From the photometry we find that intrinsically more flattened discs tend to have a lower face-on central surface brightness and a larger dynamical mass-to-light ratio. This observation suggests that, at a constant maximum rotational velocity, lower surface brightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from the dynamical modelling that at least 12 discs are submaximal. The average disc contributes 53 +/- 4 per cent to the observed rotation at 2.2 disc scalelengths (h(R)), with a 1 sigma scatter of 15 per cent. This percentage becomes somewhat lower when effects of finite disc flattening and gravity by the dark halo and the gas are taken into account. Since boxy and peanut-shaped bulges are probably associated with bars, the result suggests that at 2.2 h(R) the submaximal nature of discs is independent of barredness. The possibility remains that very high surface brightness discs are maximal, as these discs are underrepresented in our sample. We confirm that the radial stellar disc velocity dispersion is related to the galaxy maximum rotational velocity. The scatter in this sigma versus nu(max) relation appears to correlate with the disc flattening, face-on central surface brightness and dynamical mass-to-light ratio. Low surface brightness discs tend to be more flattened and have smaller stellar velocity dispersions. The findings are consistent with the observed correlation between disc flattening and dynamical mass-to-light ratio and can generally be reproduced by the simple collapse theory for disc galaxy formation. Finally, the disc mass Tully-Fisher relation is offset from the maximum-disc scaled stellar mass Tully-Fisher relation of the Ursa Major cluster. This offset, -0.3 dex in mass, is naturally explained if the discs of the Ursa Major cluster spirals are submaximal.

In earlier papers in this series we determined the intrinsic stellar disc kinematics of fifteen intermediate to late type edge-on spiral galaxies using a dynamical modeling technique. From the photometry we find that intrinsically more flattened discs tend to have a lower face-on central surface brightness and a larger dynamica mass-to-light ratio. This observation suggests that at a constant maximum rotational velocity lower surface brightness discs have smaller vertical stellar velocity dispersions.Although the individual uncertainties are large, we find from the dynamical modeling that at least twelve discs are submaximal. The average disc contributes 53$\pm$4 percent to the observed rotation at 2.2 disc scalelengths, with a 1$\sigma$ scatter of 15 percent. This percentage becomes somewhat lower when effects of finite disc flattening and gravity by the dark halo and the gas are taken into account. Since boxy and peanut-shaped bulges are probably associated with bars, the result suggests that at 2.2$h_{\rm R}$ the submaximal nature of discs is independent of barredness. The possibility remains that very high surface brightness discs are maximal.We confirm that the radial stellar disc velocity dispersion is related to the galaxy maximum rotational velocity. The scatter in this $\sigma-v_{\rm max}$ relation appears to correlate with the disc flattening, face-on central surface brightness and dynamical mass-to-light ratio. Low surface brightness discs tend to be more flattened and have smaller stellar velocity dispersions. The findings are consistent with the observed correlation between disc flattening and dynamical mass-to-light ratio., Comment: Accepted for publication by Mon. Not. R.A.S

Owing to the fact that the near future should see a rapidly expanding set of probes of the halo masses of individual early-type galaxies, we introduce a convenient parameter for characterizing the halo masses from both observational and theoretical results: del(l)Y the logarithmic radial gradient of the mass-to-light ratio. Using halo density profiles from Delta-cold dark matter (CDM) simulations, we derive predictions for this gradient for various galaxy luminosities and star formation efficiencies SF. As a pilot study, we assemble the available del(l)Y data from kinematics in early-type galaxies - representing the first unbiased study of halo masses in a wide range of early-type galaxy luminosities - and find a correlation between luminosity and del(l)Y, such that the brightest galaxies appear the most dark-matter dominated. We find that the gradients in most of the brightest galaxies may fit in well with the CDM predictions, but that there is also a population of fainter galaxies whose gradients are so low as to imply an unreasonably high star formation efficiency epsilon(SF) > 1. This difficulty is eased if dark haloes are not assumed to have the standard CDM profiles, but lower central concentrations.

We discuss the possible origin of the radial truncations in stellar discs, using measurements that we presented in an earlier paper (Kregel, van der Kruit & de Grijs, 2002). A tentative correlation is found with the de-projected face-on central surface brightness; lower surface brightness discs tend to have a smaller truncation radius in units of scalelength. This and our earlier finding that in smaller spirals the truncation tends to occur at a larger number of scalelengths are best reproduced when the truncation is caused by a constant gas density threshhold on star formation., Accepted for publication by Mon. Not. R.A.S

We present deep optical long-slit spectra of 17 edge-on spiral galaxies of intermediate to late morphological type, mostly parallel to their major axes and in a few cases parallel to the minor axes.The line-of-sight stellar kinematics are obtained from the stellar absorption lines using the improvedc ross-correlation technique. In general, the stellar kinematics are regular and can be traced well into the disc-dominated region. The mean stellar velocity curves are far from solid-body, indicating that the effect of dust extinction is not large. The line-of-sight stellar disc velocity dispersion correlates with the galaxy maximum rotational velocity, but detailed modeling is necessary to establish whether this represents a physical relation. In four spirals with a boxy- or peanut-shaped bulge we are able to detect asymmetric velocity distributions, having a common signature with projected radius in the mean line-of-sight velocity and the $h_{3}$ and $h_{4}$ curves. In two cases this kinematic asymmetry probably represents the `figure-of-eight' pattern synonymous of a barred potential. We emphasize, however, that the signatures seen in the $h_{3}$ and $h_{4}$ curves may also be due to the disc seen in projection., Comment: Accepted for publication by Mon. Not. R.A.S

thly notices of the Royal Astronomical Society, 346 (1), ISSN:0035-8711, ISSN:1365-2966

Results from numerical simulations of normal isolated late-type spiral galaxies are presented; specifically, the galaxy NGC 628 is used as a template. The method employs a TREESPH code including stellar particles, gas particles, cooling and heating of the gas, star formation according to a Jeans criterion and supernova feedback. A regular spiral disc can be generated as an equilibrium situation of two opposing actions: on the one hand, cooling and dissipation of the gas; on the other hand, gas heating by the far-ultraviolet field of young stars and supernova mechanical forcing. The disc exhibits small- and medium-scale spiral structure of which the multiplicity increases as a function of radius. The theory of swing amplification can explain, both qualitatively and quantitatively, the emerging spiral structure. In addition, swing amplification predicts that the existence of a grand-design m=2 spiral is only possible if the disc is massive. The simulations show that the galaxy is then unstable to bar formation, confirming the result of Ostriker & Peebles. The occurrence of this bar instability is further investigated. A general criterion is derived for the transition between a stable and an unstable bar, depending on the disc mass contribution and the on-disc thickness. It seems that bar stability barely depends on the presence of gas. A detailed quantitative analysis is made of the emerging spiral structure and a comparison is made with observations. This demonstrates that the structure of the numerical isolated galaxies is not as strong and has a larger multiplicity compared with the structure of some exemplary real galaxies. It is argued that the suggestion of Kormendy & Norman holds, i.e. that a grand design can only be generated by a central bar or by tidal forces resulting from an encounter with another galaxy.

A new method for the determination of the extinction in the Galaxy is proposed. The method uses surface brightnesses of external galaxies in the B and R-bands. The observational data have been taken from the ESO-LV galaxy catalog. As a first application of our model we derive the ratio of R-band to B-band extinction. We introduce two methods for computing the ratio which give: 0.62 +/- 0.05 (the first method) and 0.64 +/- 0.06 (the second method) which is in agreement with the recent literature value of 0.61. This agreement confirms the validity and efficiency of our model and is an independent verification for the standard value of the "total to selective extinction". The method of extinction determination introduced in this paper will be explored in subsequent publication.

[EN]We have carried out computer simulations to study the effect of merging on the Fundamental Plane (FP) relation. Initially, systems are spherical Jaffe models following a simple scaling relation (M/R2e= constant). They have been put on the FP by imposing different M/L values. Various orbital characteristics have been considered. Our results show that the merger remnants lie very close to the FP of the progenitors. Although non-homology is introduced by the merging process, mergers among homologous galaxies leave a pre-existing FP-relation intact. As a side result we find that variations in the point of view lead to non-negligible scatter about the FP.

As part of our program to map the large-scale distribution of galaxies behind the Milky Way, we used the Parkes 210 ft (64 m) radio telescope for pointed HI observations of a sample of low surface-brightness (due to heavy obscuration) spiral galaxies selected from the deep optical Zone of Avoidance (ZOA) galaxy catalog in the Hydra/Antlia region (Kraan-Korteweg 2000a). Searching a simultaneous velocity range of either 300 to 5500 km s(-1) or 300 to 10 500 km s(-1) to an rms level of typically 2-4 mJy resulted in detections in 61 of the 139 pointings, leading to a total of 66 detections (an additional detection was made in a reference position, and two other pointings revealed two and four independent signals respectively). Except for 2 strong HI emitters identified in the shallow Zone of Avoidance HI survey (Henning et al. 2000), all HI detections are new. An analysis of the properties of the observed and detected galaxies prove that pointed HI observations of highly obscured galaxies allow the tracing of a population of nearby, intrinsically large and bright spiral galaxies that otherwise would not be recovered. The new data identified a previously unrecognized nearby group at l similar to 287.degrees5; b similar to -9.degrees5, V similar to 1700 km s(-1), the continuation of the Hydra/Antlia filament on the opposite side of the Galactic plane, and helped to delimit a distinct void in the ZOA centered at 2000 km s(-1).

We analyse the global structure of the old stellar discs in 34 edge-on spiral galaxies. The radial and vertical exponential scale parameters of the discs are obtained by applying an improved two-dimensional decomposition technique to our I-band photometry. We find a clear increase in the disc scaleheight with maximum rotational velocity, in accordance with observations of the stellar velocity dispersions in galaxy discs. The range and maximum of the intrinsic flattening of the disc light seem to increase with both maximum rotational velocity and total HI mass. We use the disc flattening to estimate the disc contribution to the maximum rotational velocity, resulting in an average of 57+-22 percent. The disc light distributions are further investigated for the presence of radial truncations. We find that the radial light distributions of at least 20 spirals are truncated, corresponding to 60 percent of the sample. For small scalelength spirals, which are the most numerous in the local Universe, the results suggest that the average ratio of disc truncation radius to disc scalelength is at least four., 25 pages, 7 figures, appendix, Accepted for MNRAS (April 4 2002)

We measure the z=0 B-band optical luminosity function (LF) for galaxies selected in a blind HI survey. The total LF of the HI selected sample is flat, with Schechter parameters M*=-19.38_{-0.62}^{+1.02} + 5 log h mag and alpha=-1.03_{-0.15}^{+0.25}, in good agreement with LFs of optically selected late-type galaxies. Bivariate distribution functions of several galaxy parameters show that the HI density in the local Universe is more widely spread over galaxies of different size, central surface brightness, and luminosity than is the optical luminosity density. The number density of very low surface brightness (>24.0 mag/arcsec^2) gas-rich galaxies is considerably lower than that found in optical surveys designed to detect dim galaxies. This suggests that only a part of the population of LSB galaxies is gas rich and that the rest must be gas poor. However, we show that this gas-poor population must be cosmologically insignificant in baryon content. The contribution of gas-rich LSB galaxies (>23.0 mag/arcsec^2) to the local cosmological gas and luminosity density is modest (18_{-5}^{+6} and 5_{-2}^{+2} per cent respectively); their contribution to Omega_matter is not well-determined, but probably < 11 per cent. These values are in excellent agreement with the low redshift results from the Hubble Deep Field., Accepted for publication in MNRAS, 12 pages 6 figures

We discuss strong gravitational lensing by multiple objects along any line of sight. The probability for strong gravitational lensing by more than one lens is small, but a number of strong lens systems in which more than one separate lens contribute significantly to the lensing potential will be detected in the large sample of lens systems compiled with new instruments. Using multi-lens ray-tracing, we estimate the likelihood for gravitational lensing by two lenses at different redshifts and investigate typical image geometries and magnification cross sections. We find that, for a cosmology with Omega_M=0.3 and Omega_Lambda=0.7, about one in twenty lens systems consist of two lenses with merging caustics. Multiple lens systems differ from single lenses. They have a larger multiple imaging cross section and significantly differ in the image configuration. The external shear induced by a nearby galaxy, group or cluster can affect image positions even for more widely separated lens pairs. Both of these effects must be accounted for in lens modelling. We also show how the presence of aligned discs in the pair of lensing galaxies can lead to very large high-magnification cross sections. Multiple lens systems will be important in future, both for constraining lens models of individual systems and for statistical lensing., Comment: 9 pages, 12 figures. MNRAS, submitted. Changed format of figures to jpg. A ps file of the paper including all figures can be obtained from http://www.astro.rug.nl/~ole/papers/double/paper.ps.gz

In this data paper we present the results of an extensive 21 cm-line synthesis imaging survey of 43 spiral galaxies in the nearby Ursa Major cluster using the Westerbork Synthesis Radio Telescope. Detailed kinematic information in the form of position-velocity diagrams and rotation curves is presented in an atlas together with HI channel maps, 21 cm continuum maps, global HI profiles, radial HI surface density profiles, integrated HI column density maps, and HI velocity fields. The relation between the corrected global HI linewidth and the rotational velocities V-max and V-flat as derived from the rotation curves is investigated. Inclination angles obtained from the optical axis ratios are compared to those derived from the inclined HI disks and the HI velocity fields. The galaxies were not selected on the basis of their HI content but solely on the basis of their cluster membership and inclination which should be suitable for a kinematic analysis. The observed galaxies provide a well-defined, volume limited and equidistant sample, useful to investigate in detail the statistical properties of the Tully-Fisher relation and the dark matter halos around them.

We investigate the star formation history and chemical evolution of low surface brightness (LSB) disk galaxies by modelling their observed spectro-photometric and chemical properties using a galactic chemical and photometric evolution model incorporating a detailed metallicity dependent set of stellar input data. For a large fraction of the LSB galaxies in our sample, observed properties are best explained by models incorporating an exponentially decreasing global star formation rate (SFR) ending at a present-day gas fraction M-gas/(M-gas + M-stars) = 0.5 for a galaxy age of 14 Gyr. For some galaxies small amplitude star formation bursts are required to explain the contribution of the young (5-50 Myr old) stellar population to the galaxy integrated luminosity. This suggests that star formation has proceeded in a stochastic manner. The presence of an old stellar population in many late-type LSB galaxies suggests that LSB galaxies roughly follow the same evolutionary history as HSB galaxies, except nl a much lower rate. In particular, our results imply that LSB galaxies do not form late, nor have a delayed onset of star formation, but simply evolve slowly.

We have obtained integrated spectra and multifilter photometry for a representative sample of similar to 200 nearby galaxies. These galaxies span the entire Hubble sequence in morphological type, as well as a wide range of luminosities (M(B) = -14 to -22) and colors (B-R = 0.4-1.8). Here we describe the sample selection criteria and the U, B, R surface photometry for these galaxies. The spectrophotometric results will be presented in a companion paper. Our goals for the project include measuring the current star formation rates and metallicity of these galaxies, and elucidating their star formation histories, as a function of luminosity and morphology. We thereby extend the work of Kennicutt to lower luminosity systems. We anticipate that our study will be useful as a benchmark for studies of galaxies at high red-shift. We discuss the observing, data reduction, and calibration techniques and show that our photometry agrees well with previous work in those cases in which earlier data are available. We present an atlas of images, radial surface brightness profiles, and color profiles as well as tables of derived parameters. The atlas and tables of measurements will be made available electronically. We study the correlations of galaxy properties determined from the galaxy images. Our findings include the following: (1) colors determined within the effective radius correlate better with morphological type than with M(B) and (2) 50% of the low-luminosity galaxies are bluest in their centers.

We have obtained integrated and nuclear spectra as well as U, B, R surface photometry for a representative sample of 196 nearby galaxies. These galaxies span the entire Hubble sequence in morphological type, as well as a wide range of luminosities (M(B) = -14 to -22). Here we present the spectrophotometry for these galaxies. The selection of the sample and the U, B, R surface photometry is described in a companion paper. Our goals for the project include measuring the current star formation rates and metallicities of these galaxies, and elucidating their star formation histories, as a function of luminosity and morphology. We thereby extend the work of Kennicutt to lower luminosity systems. We anticipate that our study will be useful as a benchmark for studies of galaxies at high redshift. We describe the observing, data reduction, and calibration techniques and demonstrate that our spectrophotometry agrees well with that of Kennicutt. The spectra span the range 3550-7250 Angstrom, at a resolution (FWHM) of similar to 6 Angstrom and have an overall relative spectrophotometric accuracy of similar to +/- 6%. We present a spectrophotometric atlas of integrated and nuclear rest-frame spectra as well as tables of equivalent widths and synthetic colors. The atlas and tables of measurements will be made available electronically. We study the correlations of galaxy properties determined from the spectra and images. Our findings include: (1) galaxies of a given morphological class display a wide range of continuum shapes and emission-line strengths if a broad range of luminosities are considered, (2) emission-line strengths tend to increase and continua tend to get bluer as the luminosity decreases, and (3) the scatter on the general correlation between nuclear and integrated H alpha emission-line strengths is large.

We have obtained integrated and nuclear spectra, as well as U, B, R surface photometry, for a representative sample of 196 nearby galaxies. These galaxies span the entire Hubble sequence in morphological type, as well as a wide range of luminosities (M_B=-14 to -22). Here we present the spectrophotometry for these galaxies. The selection of the sample and the U, B, R surface photometry is described in a companion paper (Paper I). Our goals for the project include measuring the current star formation rates and metallicities of these galaxies, and elucidating their star formation histories, as a function of luminosity and morphology. We thereby extend the work of Kennicutt (1992a) to lower luminosity systems. We anticipate that our study will be useful as a benchmark for studies of galaxies at high redshift. We describe the observing, data reduction and calibration techniques, and demonstrate that our spectrophotometry agrees well with that of Kennicutt. The spectra span the range 3550--7250 A at a resolution (FWHM) of ~6 A, and have an overall relative spectrophotometric accuracy of +/- 6 per cent. We present a spectrophotometric atlas of integrated and nuclear rest-frame spectra, as well as tables of equivalent widths and synthetic colors. We study the correlations of galaxy properties determined from the spectra and images. Our findings include: (1) galaxies of a given morphological class display a wide range of continuum shapes and emission line strengths if a broad range of luminosities are considered, (2) emission line strengths tend to in- crease and continua tend to get bluer as the luminosity decreases, and (3) the scatter on the general correlation between nuclear and integrated H_alpha emission line strengths is large., Comment: Accepted for publication in ApJS (scheduled for Vol.127, 2000 March); 63 pages, LateX, 9 figures and 6 tables included, a spectrophotometric atlas is provided as GIF images, fig 1 as a JPEG image, in a single tar-file; a full 600 dpi version is available at http://www.astro.rug.nl/~nfgs/

We present optical and near-infrared colour maps of the central regions of bulges of S0 and spiral galaxies obtained with WFPC2 and NICMOS on the Hubble Space Telescope (HST). By combined use of HST and ground-based data, the colour information spans a region from a few tens of pc to a few kpc. In almost all galaxies, the colour profiles in the central 100-200 pc become more rapidly redder. We attribute the high central colour indices to a central concentration of dust. We infer an average extinction at the centre of A(V)=0.6-1.0 mag. Several objects show central dust rings or discs at subkpc scales similar to those found by others in giant ellipticals. For galactic bulges of types S0 to Sb, the tightness of the B-I versus I-H relation suggests that the age spread among bulges of early-type galaxies is small, at most 2 Gyr. Colours at 1R(eff), where we expect extinction to be negligible, are similar to those of elliptical galaxies in the Coma cluster, suggesting that these bulges formed at the same time as the bright galaxies in Coma. Furthermore, the galaxy ages are found to be independent of their environment. As it is likely that Coma was formed at redshift z > 3, our bulges, which are in groups and in the field, must also have been formed at this epoch. Bulges of early-type spirals cannot be formed by secular evolution of bars at recent epochs, because such bulges would be much younger. There are three galaxies of type Sbc and later; their bulges are younger and could perhaps arise from secular evolution of transient bars. Our results are in good agreement with semi-analytic predictions, which also predict that bulges, in clusters and in the field, are as old as giant ellipticals in clusters.

We present results of broad band BVRI observations of a sample of galaxies with a low surface brightness (LSB) disk and a bulge. These galaxies are well described as exponential disks and exponential bulges with no preferred value for either scale length or central surface brightness. The median B band disk scale length is 12.6 kpc (H-0 = 75 km s(-1) Mpc(-1)) which is much larger than scale lengths of typical (disk dominated) LSB or high surface brightness (HSB) galaxies. Furthermore, the disk and bulge scale lengths are correlated, suggesting a coupling in the formation. Bulge dominated LSB galaxies are observed to be redder than disk dominated LSB galaxies and their bulge-to-disk ratios are increasing towards redder wavelengths. We find colors that are comparable to or bluer than HSB galaxies of the same morphological types. Bulge dominated LSB galaxies are therefore not faded HSB galaxies with no current star formation. We find that bulge dominated LSB galaxies fit in with the general trends defined by the HSB galaxies. The properties of these bulge dominated LSB galaxies show that LSB galaxies do not just come in two varieties. They cover the entire range in optical and morphological properties between late-type disk dominated LSBs and giant Malin-1-like LSBs. LSB galaxies thus also form a LSB Hubble sequence, parallel to the classical HSB one.

Results are presented of spectroscopic emission and absorption line observations along the major axis of the Sb galaxy NGC 7331. The kinematics of the ionized gas and stellar component are derived, being regular and symmetric with respect to the centre of the galaxy. Contrary to what may be expected, for R less than or similar to 40 " the emission line gas appears to rotate slower than the stars. A likely explanation for this phenomenon is an inclined and warped gas layer in those inner regions. In the bulge dominated region the absorption line profiles are asymmetric in the sense that they have a shallow extension towards the systemic velocity. No counterrotating stellar component is observed, which is contrary to previous claims. As demonstrated, these claims might be based on a wrong interpretation of the employed analysis method. Outside the bulge dominated region the stellar radial velocities are in agreement with the neutral hydrogen dynamics and the stellar velocity dispersion decreases towards larger radii. A detailed bulge/disc light decomposition has been made. This has been used to construct a kinematical model of NGC 7331 from which model absorption line profiles were calculated. These profiles have been compared with the observations and model parameters have been adjusted to obtain a good match. It appeared necessary to combine a rapidly rotating disc having a radially decreasing velocity dispersion with a slowly rotating constant dispersion bulge. Then, simultaneously, the observed stellar radial velocities, the velocity dispersions and the observed asymmetry of the line profile could be explained satisfactorily. An even better fit to the data can be achieved when the disc is relatively thinner and colder inside the bulge region. For the disc the stellar velocity dispersions and photometry result in a mass-to-light ratio of 1.6 +/- 0.7 M./L.(I). This value agrees with previous determinations for other discs using observed velocity dispersions. A rotation curve analysis allows the calculation of the mass-to-light ratio of the bulge which amounts to 6.8 in the I-band; considerably larger than the disc value. It appears that the mass distribution of NGC 7331 is completely dominated by the combination of bulge and dark halo at all radii. Comparing well determined mass-to-light ratios of a number of bulges with disc values (M/L)(bulge) is, on average, three times as large as (MIL)di,, in the I-band. For the B-band this ratio goes up to 7.2, a fact which should have cosmological consequences.

We present spectroscopic observations of a sample of faint gigahertz peaked-spectrum (GPS) radio sources drawn from the Westerbork Northern Sky Survey (WENSS), Redshifts have been determined for 19 (40 per cent) of the objects. The optical spectra of the GPS sources identified with low-redshift galaxies show deep stellar absorption features. This confirms previous suggestions that their optical light is not significantly contaminated by active galactic nucleus-related emission, but is dominated by a population of old (>9 Gyr) and metal-rich (>0.2 [Fe/H]) stars, justifying the use of these (probably) young radio sources as probes of galaxy evolution. The optical spectra of GPS sources identified with quasars are indistinguishable from those of flat-spectrum quasars, and clearly different from the spectra of compact steep-spectrum (CSS) quasars. The redshift distribution of the GPS quasars in our radio-faint sample is comparable to that of the bright samples presented in the literature, peaking at z similar to 2-3, It is unlikely that a significant population of low-redshift GPS quasars is missed as a result of selection effects in our sample. We therefore claim that there is a genuine difference between the redshift distributions of GPS galaxies and quasars, which, because it is present in both the radio-faint and bright samples, cannot be caused by a redshift-luminosity degeneracy. It is therefore unlikely that the GPS quasars and galaxies are unified by orientation, unless the quasar opening angle is a strong function of redshift. We suggest that the GPS quasars and galaxies are unrelated populations and just happen to have identical observed radio spectral properties, and hypothesize that GPS quasars are a subclass of flat-spectrum quasars.

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity - the Tremaine-Weinberg method - has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Omega(p) = 52 +/- 13 km s(-1) kpc(-1). This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.

We present modified Newtonian dynamics (MOND) fits to 15 rotation curves of low surface brightness (LSB) galaxies. Good fits are readily found, although for a few galaxies minor adjustments to the inclination are needed. Reasonable values for the stellar mass-to-light ratios are found, as well as an approximately constant value for the total (gas and stars) mass-to-light ratio. We show that the LSB galaxies investigated here lie on the one, unique Tully-Fisher relation, as predicted by MOND. The scatter on the Tully-Fisher relation can be completely explained by the observed scatter in the total mass-to-light ratio. We address the question of whether MOND can fit any arbitrary rotation curve by constructing a plausible fake model galaxy. While MOND is unable to fit this hypothetical galaxy, a normal dark-halo fit is readily found, showing that dark matter fits are much less selective in producing fits. The good fits to rotation curves of LSB galaxies support MOND, especially because these are galaxies with large mass discrepancies deep in the MOND regime.

We have determined a dust-free colour-magnitude (CM) relation for spiral galaxies, by using I - K colours in edge-on galaxies above the plane. We find that the scatter in this relation is small and approximately as large as can be explained by observational uncertainties. The slope of the near-IR CM relation is steeper for spirals than for elliptical galaxies. We suggest two possible explanations. First, the difference could be caused by vertical colour gradients in spiral galaxies. In that case these gradients should be similar for all galaxies, on average similar to 0.15 dex in [Fe/H] per scaleheight, and should increase for rater galaxy types. The most likely explanation, however, is that spirals and ellipticals have intrinsically different CM relations. This means that the stars in spirals are younger than those in ellipticals. The age, however, or the fraction of young stars in spiral galaxies would be determined solely by the luminosity of the galaxy, and not by its environment.

We have determined a dust-free colour-magnitude (CM) relation for spiral galaxies, by using I - K colours in edge-on galaxies above the plane. We find that the scatter in this relation is small and approximately as large as can be explained by observational uncertainties. The slope of the near-IR CM relation is steeper for spirals than for elliptical galaxies. We suggest two possible explanations. First, the difference could be caused by vertical colour gradients in spiral galaxies. In that case these gradients should be similar for all galaxies, on average similar to 0.15 dex in [Fe/H] per scaleheight, and should increase for rater galaxy types. The most likely explanation, however, is that spirals and ellipticals have intrinsically different CM relations. This means that the stars in spirals are younger than those in ellipticals. The age, however, or the fraction of young stars in spiral galaxies would be determined solely by the luminosity of the galaxy, and not by its environment.

A statistical study of global galaxy parameters can help to improve our understanding of galaxy formation processes. In this paper we present the analysis of global galaxy parameters based on optical and near-infrared observations of a large sample of edge-on disc galaxies. We found a correlation between the ratio of the radial to vertical scale parameter and galaxy type: galaxies become systematically thinner when going from S0's to Sc's, whereas the distribution seems to level off for later types. The observed scale length ratios (and thus the radial colour gradients) largely represent the galaxies' dust content. On average the colour gradients indicated by the scale length ratios increase from type Sa to at least type Sc. For galaxy types later than Sc, the average colour gradient seems to decrease again. The distribution of K-band (edge-on) disc central surface brightnesses is rather flat, although with a large scatter. However, the latest-type sample galaxies (T > 6) show an indication that their average disc central surface brightnesses may be fainter than those of the earlier types. This effect is probably not the result of dust extinction., 17 pages, LaTex, 11 figures, accepted for publication in MNRAS

We report on the detection of weak gravitational lensing of faint, distant background objects by Cl 1358+62, a rich cluster of galaxies at a redshift of z = 0.33. The observations consist of a large, multicolor mosaic of Hubble Space Telescope WFPC2 images. The number density of approximately 50 background objects arcmin(-2) allows us to do a detailed weak lensing analysis of this cluster. We detect a weak lensing signal out to similar to 1.5 Mpc from the cluster center. The observed distortion is consistent with a singular isothermal sphere model with a velocity dispersion of 780 +/- 50 km s(-1). The total projected mass within a radius of 1 Mpc corresponding to this model is (4.4 +/- 0.6) x 10(14) M.. The errors given here represent the random error due to the ellipticities of the background galaxies. The uncertainty in the redshift distribution introduces an additional systematic error of similar to 10% in the weak lensing mass. The weak lensing mass is slightly lower than dynamical estimates and agrees well with X-ray mass estimates. The mass distribution is elongated in a similar way as the light. The axis ratio of 0.30 +/- 0.15 and position angle of -21 degrees +/- 7 degrees were measured directly from the observations and agree very well with a previous strong lensing determination. A two-dimensional reconstruction of the cluster mass surface density shows that the peak of the mass distribution coincides with the peak of the light distribution. We find a value of (90 +/- 13)h(50) M. L-V.(-1) for the mass-to-light ratio, consistent with being constant with radius. The point-spread function of HST is highly anisotropic at the edges of the individual chips. This systematically perturbs the shapes of objects, and we present a method for applying the appropriate correction.

In a recent paper, Hawkins (1997) argues on the basis of statistical studies of double-image gravitational lenses and lens candidates that a large population of dark lenses exists and that these outnumber galaxies with more normal mass-to-light ratios by a factor of 3:1. If correct, this is a very important result for many areas of astronomy including galaxy formation and cosmology. In this paper we discuss our new radio-selected gravitational lens sample, JVAS/CLASS, in order to test and constrain this proposition. We have obtained ground-based and HST images of all multiple-image lens systems in our sample and in 12 cases out of 12 we find the lensing galaxies in the optical and/or near infrared. Our success in finding lensing galaxies creates problems for the dark lens hypothesis. If it is to survive, ad hoc modifications seem to be necessary: only very massive galaxies (M greater than or similar to 9 x 10(11) M.) can be dark, and the cutoff in mass must be sharp. Our finding of lens galaxies in all the JVAS/CLASS systems is complementary evidence which supports the conclusion of Kochanek et al. (1997) that many of the wide-separation optically-selected pairs are physically distinct quasars rather than gravitational lens systems.

In a recent paper, Hawkins (1997) argues on the basis of statistical studies of double-image gravitational lenses and lens candidates that a large population of dark lenses exists and that these outnumber galaxies with more normal mass-to-light ratios by a factor of 3:1. If correct, this is a very important result for many areas of astronomy including galaxy formation and cosmology. In this paper we discuss our new radio-selected gravitational lens sample, JVAS/CLASS, in order to test and constrain this proposition. We have obtained ground-based and HST images of all multiple-image lens systems in our sample and in 12 cases out of 12 we find the lensing galaxies in the optical and/or near infrared. Our success in finding lensing galaxies creates problems for the dark lens hypothesis. If it is to survive, ad hoc modifications seem to be necessary: only very massive galaxies (M greater than or similar to 9 x 10(11) M.) can be dark, and the cutoff in mass must be sharp. Our finding of lens galaxies in all the JVAS/CLASS systems is complementary evidence which supports the conclusion of Kochanek et al. (1997) that many of the wide-separation optically-selected pairs are physically distinct quasars rather than gravitational lens systems.

We combine high-resolution images in four optical/infrared bands, obtained with the laser guide star adaptive optics ( LGSAO) system on the Keck telescope and with the Hubble Space Telescope ( HST), to study the gravitational lens system SDSS J0737 + 3216 ( lens redshift 0.3223, source redshift 0.5812). We show that ( under favorable observing conditions) ground-based images are comparable to those obtained with HST in terms of precision in the determination of the parameters of both the lens mass distribution and the background source. We also quantify the systematic errors associated with both the incomplete knowledge of the PSF and the uncertain process of lens galaxy light removal and find that similar accuracy can be achieved with Keck LGSAO as with HST. We then exploit this well-calibrated combination of optical and gravitational telescopes to perform a multiwavelength study of the source galaxy at 0.01 '' effective resolution. We find the Sersic index to be indicative of a disklike object, but the measured half-light radius (r(e) = 0.59 +/- 0.007 stat +/- 0.1 sys kpc) and stellar mass (M* = 2.0 +/- 1.0 stat +/- 0.8 sys x 10(9) M(circle dot)) place it more than 3 sigma away from the local disk size-mass relation. The SDSS J0737 + 3216 source has the characteristics of the most compact faint blue galaxies studied and comparable size and mass to dwarf early-type galaxies in the local universe. With the aid of gravitational telescopes to measure individual objects' brightness profiles to 10% accuracy, the study of the high-redshift size-mass relation may be extended by an order of magnitude or more beyond existing surveys at the low-mass end, thus providing a new observational test of galaxy formation models.

We discuss the colours of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 'main' spectroscopic sample (a flux-limited sample, r(Pet)