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We present mass models of a sample of 19 low surface brightness (LSB) galaxies and compare the properties of their constituent mass components with those of a sample of high surface brightness (HSB) galaxies. We find that LSB galaxies are dark matter dominated, Their halo parameters are only slightly affected by assumptions on stellar mass-to-light ratios, Comparing LSB and HSB galaxies we find that mass models derived using the maximum disc hypothesis result in the discs of LSB galaxies having systematically higher stellar mass-to-light ratios than HSB galaxies of similar rotation velocity, This is inconsistent with all other available evidence on the evolution of LSB galaxies, We argue therefore that the maximum disc hypothesis does not provide a representative description of the LSB galaxies and their evolution, Mass models with stellar mass-to-light ratios determined by the colours and stellar velocity dispersions of galactic discs imply that LSB galaxies have dark matter haloes that are more extended and less dense than those of HSB galaxies. Surface brightness is thus related to the halo properties. LSB galaxies are slowly evolving, low-density and dark matter dominated galaxies.

Theories of stellar orbit diffusion in disk galaxies predict different rates of increase of the velocity dispersions parallel and perpendicular to the disk plane, and it is therefore of interest to measure the different velocity dispersion components in galactic disks of different types. We show that it is possible to extract the three components of the velocity ellipsoid in an intermediate-inclination disk galaxy from measured line-of-sight velocity dispersions on the major and minor axes. On applying the method to observations of the Sb galaxy NGC 488, we find evidence for a higher ratio of vertical to radial dispersion in NGC 488 than in the solar neighbourhood of the Milky Way (the only other place where this quantity has ever been measured). The difference is qualitatively consistent with the notion that spiral structure has been relatively less important in the dynamical evolution of the disk of NGC 488 than molecular clouds., 5 pages LaTex, including 2 figures, mn.sty, submitted to MNRAS

We present Very Large Array ({\sc vla}) and Westerbork Synthesis Radio Telescope ({\sc wsrt}) 21-cm H{\sc i} 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 H{\sc i} surface densities, about a factor of $\sim 3$ 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 increasing 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 $M_{\rm HI}/L_B$ and $M_{\rm dyn}/L_B$ 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., Accepted for MNRAS. Needs mn.sty. 20 pages, including figures. Figure 2 not included: available upon request from blok@astro.rug.nl or at http://www.astro.rug.nl/~blok/lsb.html

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 new four-image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All-Sky Survey. This system consists of four flat-spectrum radio images that are also seen on a Hubble Space Telescope (HST) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HST images. The light distribution of the tensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of similar to 1.33 for the lensed object the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four-image to two-image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies.

We present a luminosity function for low surface brightness (LSB) galaxies identified in the Automatic Plate Measuring Facility survey of Impey et al. These galaxies have central surface brightnesses [mu(0)] in B in the range 22.0 less than or equal to mu(0) less than or equal to 25.0. Using standard maximum likelihood estimators, we determine that the best-fit Schechter function parameters for this luminosity function (LF) are alpha = -1.42, M* = -18.34, and phi* = 0.0036, assuming H-0 = 100 h(100) km s(-1) Mpc(-1). We compare the luminosity and number densities derived from this luminosity function with those obtained from other recent field galaxy studies and find that surveys that do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the galaxies in the local universe. Under our most conservative estimates, our derivation of the LF for LSB galaxies suggests that the CfA Redshift Survey has missed at least one-third of the local galaxy population. This overlooked fraction is not enough by itself to explain the large number of faint blue galaxies observed at moderate redshift under no-evolution models, but it does help to close the gap between local and moderate-redshift galaxy counts.

We show that the gas mass fraction of spiral galaxies is strongly correlated with luminosity and surface brightness. It is not correlated with linear size. Gas fraction varies with luminosity and surface brightness at the same rate, indicating evolution at fixed size. Dim galaxies are clearly less evolved than bright ones, having consumed only similar to 1/2 of their gas. This resolves the gas consumption paradox, since there exist many galaxies with large gas reservoirs. These gas-rich galaxies must have formed the bulk of their stellar populations in the last half of a Hubble time. The existence of such immature galaxies at z = 0 indicates that either galaxy formation is a lengthy or even ongoing process, or the onset of significant star formation can be delayed for arbitrary periods in tenuous gas disks.

We present new results on the fundamental plane of galaxies in two rich clusters, Cl 1358+62 at z = 0.33 and MS 2053-04 at z = 0.58, based on Keck and Hubble Space Telescope observations. Our new data triple the sample of galaxies with measured fundamental plane parameters at intermediate redshift. The early-type galaxies in these clusters define very clear fundamental plane relations, confirming an earlier result for Cl 0024+16, at z = 0.39. This large sample allows us to estimate the scatter reliably. We find it to be low, at +/-0.067 in log r(e), or 17% in r(e), similar to that observed in comparable low-redshift clusters. This suggests that the structure of the older galaxies has changed little since z = 0.58. The M/L(V) ratios of early-type galaxies clearly evolve with redshift; the evolution is consistent with Delta log (M/L(V)) similar to -0.3z. The M/L(V) ratios of two E+A galaxies in Cl 1358+62 are also lower by a factor of similar to 3, consistent with the hypothesis that they underwent a starburst 1 Gyr previously. We conclude that the fundamental plane can therefore be used as a sensitive diagnostic of the evolutionary history of galaxies. Our data, when compared with the predictions of simple stellar population models, imply that the oldest cluster galaxies formed at high redshift (z > 2). We infer a different evolutionary history for the E+A galaxies, in which a large fraction of stars formed at z

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 greater than or equal to 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.

Data are presented for 693 galaxies identified in a large new survey for low surface brightness galaxies in the nearby universe (z less than or similar to 0.1). The survey covers 786 square degrees centered on the equator, and it extends significantly the surface brightness range of galaxy surveys in which there are a substantial number of galaxies with redshifts. The data are derived from the Automated Plate Measuring machine scans of survey plates from the UK Schmidt Telescope and from follow-up observations at radio and optical wavelengths. Accurate positions, total B magnitudes, surface brightness parameters, and angular sizes are tabulated for each galaxy. Radial velocities, optical luminosities, and neutral hydrogen masses are listed for a subset of the sample. Finding charts are also presented for those objects having a large enough angular size that the scans from survey plates provide some morphological information. The selection function and the luminosity function that can be derived from the survey are discussed in two companion papers.

Central velocity dispersions, Mg-2 line indices and radial velocities for 220 E and SO galaxies are derived on the basis of intermediate resolution spectroscopy. Galaxies in the following clusters have been observed: Abell 194, Abell 539, Abell 3381, Abell 3574, S639, S753, Doradus, HydraI (Abell 1060) and Grm 15. For 151 of the galaxies, the velocity dispersion has not previously been measured. 134 of the Mg-2 determinations are for galaxies with no previous measurement. The spectra cover either 500 or 1000 Angstrom, centred on the magnesium triplet at 5177 Angstrom. The observations were obtained with the Boiler & Chivens spectrograph at the ESO 1.5-m telescope and with OPTOPUS, a multi-object fibre-fed B&C spectrograph, at the ESO 3.6-m telescope. The data are part of our ongoing study of the large-scale motions in the Universe and the physical background for the Fundamental Plane. The Fourier fitting method was used to derive the velocity dispersions and radial velocities. The velocity dispersions have been corrected for the effect of the size of the aperture. The correction was established on the basis of velocity dispersion profiles available in the literature. A comparison with results from Davies et al. shows that the derived central velocity dispersions have an rms error of 0.036 in log sigma. There is no offset relative to the velocity dispersions from Davies et al. The offset relative to data from Lucey & Carter is - 0.017 +/- 0.011 in log sigma, with our velocity dispersions being the smallest. The velocity dispersions derived from the B&C and the OPTOPUS observations, as well as the velocity dispersions published by Davies et al., Dressier, Lucey & Carter and Lucey et al., can be brought on a system consistent within 3 per cent. The Mg-2 line indices have been corrected for the size of the apertures, transformed to the Lick system, and corrected for the effect of the velocity dispersion. From comparison with data from Davies et al. and from Faber, we find that the rms error of Mg-2 is 0.013. Comparisons of the radial velocities with data from the literature show that our determinations are accurate to within approximate to 35 km s(-1). The accuracies reached for these observations are adequate for the study of the large-scale motions in the Universe and for investigations of the Fundamental Plane.

We argue that the physical reason for the success of the Fundamental Plane and the D-n-sigma relation as distance estimators for elliptical galaxies is the existence of a relation between luminosity and mass with small intrinsic scatter. Therefore a better understanding of the luminosity and mass variables, and of the mass-luminosity relation, is needed to improve distance estimation for elliptical galaxies. We propose a distance indicator in the form of a mass-luminosity relation and use it to derive modifications to the Fundamental Plane and to the D-n-sigma relation. Note that distances estimated with these modified Fundamental Plane and D-n-sigma relations may, in practice, turn out to be less precise than those estimated with the standard relations when the added terms have large observational errors.

We have used the Tremaine-Weinberg method to measure the angular speed of rotation for the bar in the SBO galaxy NGC 936. With this technique, the bar's pattern speed, Omega(p), can be derived from the luminosity and stellar-kinematic information in long-slit spectral observations taken parallel to the major axis of the galaxy. The kinematic measurement required is the mean line-of-sight velocity of all stellar light entering the slit. This quantity can only be calculated reliably if any asymmetry in the shape of the broadening function of the spectral lines is also measured, and so we present a method which allows for such asymmetry. The technique also returns a true measure of the rms uncertainty in the estimate. Application of the analysis to a set of long-slit spectra of NGC 936 returns four separate measures of Omega(p) which are mutually consistent. Combination of these data produces a best estimate for the bar pattern speed of Omega(p), = 60 +/- 14 km s(-1) kpc(-1) (assuming a distance of 16.6 Mpc). This result refines the only previous attempt to make this measurement, which yielded an estimate for Omega(p), in NGC 936 of 104 +/- 37 km s(-1) kpc(-1) The new measurement places the co-rotation radius just beyond the end of the bar, in agreement with theoretical calculations.

We present the B band Tully-Fisher relation for Low Surface Brightness (LSB) galaxies. These LSB galaxies follow the same Tully-Fisher relation as normal spiral galaxies. This implies that the mass-to-light ratio (M/L) of LSB galaxies is typically a factor of 2 larger than that of normal galaxies of the same total luminosity and morphological type. Since the dynamical mass of a galaxy is related to the rotation velocity and scale length via M \propto V^2 h, at fixed linewidth LSB galaxies must be twice as large as normal galaxies. This is confirmed by examining the relation between scale length and linewidth for LSB and normal galaxies. The universal nature of the Tully-Fisher relation can be understood if LSB galaxies are galaxies with low mass surface density, \sigma. The mass surface density apparently controls the luminosity evolution of a galaxy such as to keep the product \sigma M/L constant., Comment: 9 pages, PostScript. Accepted for publication in Monthly Notices of the Royal Astronomical Society

Differences and similarities of E and SO galaxies have been studied based on CCD surface photometry in Gunn r for a magnitude limited sample of E and SO galaxies in the Coma cluster. Spectroscopy is available for about half the sample. Our analysis of the relative disk luminosities, the Fundamental Plane, and the Mg-2-log sigma relation implies that E and SO galaxies fainter than M(BT) = -22(m) belong to the same class of galaxies, instead of two separate classes.

We present short 21-cm line observations of about 50 spiral galaxies, made with the Westerbork Synthesis Radio Telescope. They form the first stage of a two-stage project to study the relation between the shape of extended rotation curves and galaxy properties, such as luminosity and morphological type. In this first stage, one-dimensional information has been obtained about the kinematics and spatial distribution of the neutral hydrogen (H I) along the major axis of each galaxy. The primary goal of these observations was to find galaxies with extended neutral hydrogen disks that have regular spatial and velocity distributions. In the second stage (Broeils, in preparation, see also Broeils 1992a,b), H I synthesis observations of twelve regular systems thus selected are analysed, in order to obtain full two-dimensional information on the H I distributions and velocity fields. The results of the first stage ace presented in Fig. A1, as position-velocity maps of the neutral hydrogen distribution of all galaxies in our sample. Global H I profiles and H I strip integrals are formed by integrating these maps, respectively in the position and in the velocity directions, The strip integrals are deprojected to face-on radial surface density distributions. For each galaxy a number of global H I properties, like diameters, fluxes, hydrogen masses, profile widths and systemic velocities are determined, In a future paper these properties and their relation to optical properties will be discussed, and representative rotation velocities from the position-velocity maps will be derived in order to investigate the influence of using these velocities instead of the profile widths on the scatter and slope of the Tully-Fisher relation.

Differences and similarities of E and SO galaxies have been investigated on basis of new CCD surface photometry in Gunn r for 171 galaxies within the central square degree of the Coma Cluster; 146 of the galaxies are classified as E or SO. The galaxies form a magnitude-limited sample with Gunn r less-than-or-equal-to 15.3 mag. Together with the sample of Virgo galaxies compiled by Caon et al. (1993), this sample is one of the first volume-limited samples. The isophotal shapes of the galaxies have been studied in terms of ellipticity, c4 and c6. The sample is deficit of apparently round SO galaxies. The distribution of the apparent ellipticities for the SO galaxies cannot be fitted satisfactorily with any simple distribution of the intrinsic ellipticities. This suggests that face-on SO galaxies have been classified as ellipticals. It is shown that the ellipticity-c4 diagram can be used for determination of relative disk luminosities, L(D)/L(tot). The distribution of L(D)/L(tot) for galaxies fainter than M(BT) = -22 mag is very broad (H-0 = 50 km s-1 Mpc-1 is used). The distribution is best fitted by a model where 10% of the galaxies are diskless and 90% of the galaxies are drawn from a distribution which is uniform from zero to one. This model also predicts distributions of apparent ellipticities, c4, and inclinations which are in agreement with the data. E galaxies brighter than M(BT) = -22 mag do not show any evidence of disks and may form another class. The sample contains no SO galaxies brighter than M(BT) = -22 mag. Our analysis implies that the E and SO galaxies fainter than M(BT) = -22 mag form one class of galaxies with a continuous change in L(D)/L(tot). Face-on members of this class are mostly classified as E galaxies while more edge-on members are classified as SO galaxies. Further, it is found that only 12% of all the galaxies in the sample are truly diskless systems. The diskless systems contribute almost-equal-to 30% to the total luminosity of the sample, most of this originates from the six brightest galaxies. It is estimated that almost-equal-to 60% of the total luminosity of the sample originates from bulges.

We present accurate surface photometry in the B, V, R, I, H and K passbands of 86 spiral galaxies. The galaxies in this statistically complete sample of undisturbed spirals were selected from the UGC to have minimum diameters of 2' and minor over major axis ratios larger than 0.625. This sample has been selected in such a way that it can be used to represent a volume limited sample. The observation and reduction techniques are described in detail, especially the not often used driftscan technique for CCDs and the relatively new techniques using near-infrared (near-IR) arrays. For each galaxy we present radial profiles of surface brightness. Using these profiles we calculated the integrated magnitudes of the galaxies in the different passbands. We performed internal and external consistency checks for the magnitudes as well as the luminosity profiles. The internal consistency is well within the estimated errors. Comparisons with other authors indicate that measurements from photographic plates can show large deviations in the zero-point magnitude. Our surface brightness profiles agree within the errors with other CCD measurements. The comparison of integrated magnitudes shows a large scatter, but a consistent zero-point. These measurements will be used in a series of forthcoming papers to discuss central surface brightnesses, scalelengths, colors and color gradients of disks of spiral galaxies.

Near-infrared images confirm that the Hubble classification of spiral galaxies does not constrain the morphology of their stellar Population H disk, since galaxies on opposite ends of the spiral sequence can display remarkably similar evolved disk morphologies. Thus, the gas dominated Population I component determines the types (a, b, c), decoupled from the Population II. The underlying mass distributions observed in the infrared are exceptionally regular, suggesting that large scale spiral structure is principally intrinsic, as argued by the modal theory. Moreover, single arms, bisymmetric arms, lopsidedness and/or bars dominate the old stellar disk. The absence of infrared multiple-armed structure is attributed to the efficiency of Inner Lindblad Resonance absorption in the evolved Population II disk. These observations support a coherent framework for galaxy classification based on three parameters: stellar disk 'temperature', gas content and active disk mass.

We show that the D(n)-sigma relation, used for estimating distances to elliptical galaxies, needs a surface brightness correction. This correction follows from the universality of the R1/4 law, and can be derived analytically. It resolves the surface brightness bias problem of the D(n)-sigma relation noted earlier.