Late-type dwarf galaxies in the Virgo cluster — I. The samples

We selected samples of late-type dwarf galaxies in the Virgo cluster with H  i information. The galaxies were observed at the Wise Observatory using several broad-band and Hα bandpasses. UV measurements were carried out with the IUE Observatory from VILSPA, and with the FAUST shuttle-borne UV telescope.   We describe the observations in detail, paying particular attention to the determination of measurement errors, and present the observational results together with published data and far-infrared information from IRAS . The sample will be analysed in subsequent papers, in order to study star formation mechanisms in galaxies.     

Nucleated dwarf elliptical galaxies in the Virgo cluster

Using images from a charge-coupled device survey with the Wide Field Camera on the Isaac Newton Telescope, we performed B - and I -band photometry on 156 Virgo cluster dwarf elliptical (dE) galaxies, 25 candidate new cluster dwarfs, and nine candidate field dwarfs. Galaxies were modelled with Sérsic profiles, using both 1D χ² and 2D cross-correlation methods, with nuclei modelled as point sources. The intensity profiles of 50 galaxies previously classified as dE, dE?, or ? are more accurately fitted if a nucleus is included, and this results in the majority of dwarfs now being classified as nucleated dwarf ellipticals (dE,N). Some faint galaxies with B magnitudes of 18–21 have particularly large relative nuclei, while a small number have apparent central dimmings. For cluster dE,N galaxies the nucleus magnitude is correlated with the magnitude of the host galaxy. The profile parameters of dE and dE,N galaxies are not significantly different, and there is no evident discontinuity in relative nucleus size between non-nucleated and nucleated dwarfs, suggesting that they may form a continuum. Nuclei are on average redder than their underlying galaxies, though a spread of relative colours was found, and two-fifths of nuclei are bluer. Formation mechanisms of nuclei are discussed: at least some appear to have formed in an already existing non-nucleated galaxy, though others may have formed simultaneously with their galaxies and subsequently evolved within them.     

The difference between the nearby galaxies and the Virgo cluster

The sample of galaxies within 7 Mpc has been compared with that of the Virgo cluster in order to find new and confirm already known differences which may be caused by the environment. The well-known morphology-density relation is found to be valid not only for luminous galaxies but also for faint objects. The differences in the global luminosity functions are mainly caused by the different composition of the samples, whereas the luminosity functions of narrow morphological subgroups, with the exception of the irregulars, probably are not dependent on the density or on other quantities. The already observed HI-deficiency of the interstellar medium of the Virgo cluster spirals has been confirmed. There is a steep drop of this quantity with increasing distance from the dominant galaxies M 87 and M 49. The interstellar dust masses of Virgo cluster spirals and irregulars have been estimated from far-infrared fluxes. These data have been combined with the HI masses in order to obtain the gas-to-dust ratios, which come out to be smaller by a factor of 4 for the Virgo cluster spiral galaxies than for the nearby systems, on the average. The gas-to-dust ratio is strongly correlated with the HI-deficiency. These results support the concept of the ram pressure of the intracluster medium on the spiral galaxies in the core of the Virgo cluster.     

Atomic and molecular gas components in spiral galaxies of the Virgo cluster

Based on two models, we investigate the molecular-to-atomic gas ratio in Virgo cluster galaxies in comparison with field galaxies. We show that the enhanced metallicity for cluster members and the ram pressure stripping of atomic gas from the disk periphery cannot fully explain the observed gas component ratios. The additional environmental factors affecting the interstellar medium and leading to an increase in the molecular gas fraction should be taken into account for cluster galaxies.     

The census of nuclear activity of late-type galaxies in the Virgo cluster

The first spectroscopic census of active galactic nuclei (AGNs) associated with late-type galaxies in the Virgo cluster was carried out by observing 213 out of a complete set of 237 galaxies more massive than   M _dyn > 10^8.5 M_⊙  . Among them, 77 are classified as AGNs [including 21 transition objects, 47 low-ionization nuclear emission regions (LINERs) and nine Seyferts] and comprise 32 per cent of the late-type galaxies in Virgo. Due to spectroscopic incompleteness, at most 21 AGNs are missed in the survey, so that the fraction would increase up to 41 per cent. Using corollary near-infrared observations that enable us to estimate galaxy dynamical masses, it is found that AGNs are hosted exclusively in massive galaxies, i.e.   M _dyn≳ 10¹⁰ M_⊙  . Their frequency increases steeply with the dynamical mass from zero at   M _dyn≈ 10^9.5 M_⊙  to virtually 1 at   M _dyn > 10^11.5 M_⊙  . These frequencies are consistent with those of low-luminosity AGNs found in the general field by the Sloan Digital Sky Survey. Massive galaxies that harbour AGNs commonly show conspicuous r -band star-like nuclear enhancements. Conversely, they often, but not necessarily, contain massive bulges. A few well-known AGNs (e.g. M61, M100, NGC 4535) are found in massive Sc galaxies with little or no bulge. The AGN fraction seems to be only marginally sensitive to galaxy environment. We infer the black hole masses using the known scaling relations of quiescent black holes. No black holes lighter than  ∼10⁶ M_⊙  are found active in our sample.     

Sizes of the stellar subsystems of galaxies and intracluster stars in the Virgo cluster

Stellar photometry for three fields in the Virgo cluster of galaxies has been performed on the basis of archival Hubble Space Telescope ACS/WFC images. The densely populated red giant branches belonging to cluster galaxies are seen on the constructed Hertzsprung–Russell diagrams. The distances to eight galaxies in the Virgo cluster have been determined by the TRGB method. The sizes of the stellar subsystems and the gradients in the number density of red giants along the galactic radius have been determined for the investigated galaxies. The stellar periphery of the galaxies has been found to extend to great distances and to cover the entire area of the images used. Therefore, the stars that have previously been thought to be intracluster stars actually belong to the periphery of neighboring galaxies.     

Photometric catalogue of Shakhbazian compact groups of galaxies. I

Compact groups of galaxies are fruitful laboratories to study such processes as dynamical friction, tidal interaction, collision, and galaxy mergers. The largest survey of compact galaxy groups is the one of Shakhbazian, Petrosian, Baier, Tiersch. A programme to evaluate photometrical properties of the galaxies in the Shakhbazian groups has been started using the COSMOS/UKST catalogue of the Southern sky with δ ≤ + 2°30′. About a quarter of the Shakhbazian groups lie south of this declination limit. A list of 24 groups (Shkh 21, 24, 27, 30, 32, 33, 35, 81, 82, 83, 140, 141, 143, 144, 145, 146, 147, 148, 151, 152, 154, 261, 262, 263) is our first result.     

Evolution of dwarf early-type galaxies – I. Spatially resolved stellar populations and internal kinematics of Virgo cluster dE/dS0 galaxies

Understanding the origin and evolution of dwarf early-type galaxies remains an important open issue in modern astrophysics. Internal kinematics of a galaxy contains signatures of violent phenomena which may have occurred, e.g. mergers or tidal interactions, while stellar population keeps a fossil record of the star formation history; therefore studying connection between them becomes crucial for understanding galaxy evolution. Here, in the first paper of the series, we present the data on spatially resolved stellar populations and internal kinematics for a large sample of dwarf elliptical (dE) and lenticular (dS0) galaxies in the Virgo cluster. We obtained radial velocities, velocity dispersions, stellar ages and metallicities out to 1–2 half-light radii by reanalysing already published long-slit and integral-field spectroscopic data sets using the nbursts full spectral fitting technique. Surprisingly, bright representatives of the dE/dS0 class (   M_B =−18.0  to −16.0 mag) look very similar to intermediate-mass and giant lenticulars and ellipticals: (1) their nuclear regions often harbour young metal-rich stellar populations always associated with the drops in the velocity dispersion profiles; (2) metallicity gradients in the main discs/spheroids vary significantly from nearly flat profiles to −0.9 dex   r ⁻¹_e  , i.e. somewhat three times steeper than for typical bulges; (3) kinematically decoupled cores were discovered in four galaxies, including two with very little, if any, large-scale rotation. These results suggest similarities in the evolutionary paths of dwarf and giant early-type galaxies and call for reconsidering the role of major mergers in the dE/dS0 evolution.     

Markarian's chain of galaxies in Virgo

On the basis of a random number generator given by MAC LAREN and MARSAGLIA it is demonstrated that MARKARIAN'S chain of galaxies in Virgo is not accidental in its inner structure.     

Galaxy photometry in the Virgo cluster. II

For two fields of the Virgo cluster of galaxies a photometry in B, V, and R has been performed. A total of 72 galaxies has been identified and their magnitudes and diameters have been determined.     

Optical observations of bright elliptical galaxies in the Virgo cluster: stellar population and distance analysis

The analysis of deep imaging data of bright elliptical galaxies is capable of providing fundamental information on the stellar content and the distance of the target, via the Surface Brightness Fluctuation method (SBF hereafter). Here, I present the study of the properties of two ellipticals in the Virgo cluster, NGC 4621 and NGC 4374, based on deep BVR imaging data obtained with the FORS2 camera at the VLT.     

Strongly flattened galaxies in the abastumani merged catalogue of galaxies

1200 strongly flattened galaxies with axis ratio b/a ≤ 0.15 were selected from the UGC catalogue, contained in the Abadumani Merged Catalogue of Galaxies, and their properties were studied. The possibility of using strongly flattened galaxies and several other samples of galaxies according to their morphological type as a distance indicator has been examined by the Tully-Fisher relation. The investigation has shown that angular diameters of strongly flattened as well as flat, seen edge-on galaxies designated as F and L in the MCG catalogue can be used for the estimation of distance moduli with accuracy O.^m7. The distribution of absolute magnitudes of strongly flattened galaxies was approximated by analytic Schechter expression with main parameters M* = -21.^m2 and α = -1.0. The statistical method of the nearest companion applied to the apparent distribution of strongly flattened galaxies has shown that these galaxies are considerably more frequently found in mixed pairs and multiple systems than spirals. Published in Astrofizika, Vol. 41, No. 1, pp. 23–34, January-March, 1998.     

Luminous early-type field galaxies at z∼0.4– I. Observations and redshift catalogue of 581 galaxies

We have compiled a sample of ∼ 9600 bright, i ≤18.95 , red, b _J− r >2 , candidate galaxies in an area of 220 deg². These are luminous, L > L * , field early-type galaxies with redshifts 0.3≲ z ≲0.6 . We present a redshift catalogue of a subsample of 581 targets. The galaxies were selected according to their broad-band b _J ri colours from United Kingdom Schmidt Telescope plates, and have a surface density on the sky of only ∼ 50 deg⁻². Such luminous field galaxies are virtually absent from published redshift surveys and the catalogue provides a large sample of the most luminous normal galaxies, at cosmological distances. The statistical properties of the galaxy spectra, including absorption-line and emission-line measures, are presented and a composite spectrum constructed. The nature of the sample, combined with the relatively bright apparent magnitudes, makes the galaxies suitable targets for several key investigations in galaxy evolution and cosmology.