A multivariate statistical analysis of data measuring the optical and X-ray properties of the Einstein sample of early-type galaxies (Eskridge et al. 1995) showed that: 1) on average S0s have lower X-ray luminosity LX at fixed optical luminosity LB than do Es; 2) at fixed LB the X-ray brightest galaxies are also the roundest; this correlation holds for both morphological subsets of Es and S0s. We investigate whether a flat and partially rotationally supported galaxy is expected to host a different gas flow phase (and so a largely different amount of hot gas) with respect to a spherical pressure supported galaxy of the same LB. This is accomplished using the global energetic balance of the hot gas flows, and axisymmetric two-component galaxy models (Ciotti and Pellegrini 1995).

Recent redshift surveys (eg. Colless et al. 1993) have shown that the excess galaxies seen in faint B band number counts are not evolved giants at high redshift, but low to moderate luminosity objects at modest redshifts. This led to the suggestion (eg. Cowie et al. 1991) that there was once an extra population of dwarfs which has now disappeared, ie. there is nonconservation of galaxy number. We have investigated a picture in which the dwarfs have merely faded to become very low surface brightness galaxies like those now turning up in nearby clusters (eg. Turner et al. 1993).

We present detailed velocity field of NGC 1052 in [NII]6583Å line obtained with scanning Perot-Fabry. Extended ionized gas was studied by Davies et al. (1986) showing a clear counter-rotation between ionized gas and stars. It is an E4 galaxy type with ‘Boxy’ isophotes (Nieto et al. 1991). Taking benefit from high spectral resolution and 2D mapping of Scanning PF, we have discovered several components in our profiles (Plana 1995). Their study shows two main gaseous components: a first one with a Major Axis at PA=45° and a second one at PA=30°. The ionized gas extension is approximately 40″ for the first component and 20″ for the second. The main component contains 100 times more gas than the second one.

A significant evolution has been detected in intermediate redshift clusters (z < 0.9), first by photometric studies ([1], [2]), which showed an excess of blue objects; subsequent spectroscopic studies revealed anomalies in most of the galaxies, mainly consisting of excessively strong Balmer lines. In order to explain the spectroscopic observations, bursts of star formation superimposed to the traditional scenario of galactic evolution are needed. The analysis of spectral lines and colours by means of an evolutionary synthesis model ([3]), including both the stellar contribution and the emission of the ionized gas, allows in most of the cases the determination of the time elapsed since the end of the burst and the fraction of galactic mass involved in it. In the clusters considered (AC103, AC114, AC118 at z = 0.31, [4]), the theoretical analysis demonstrates that the bursts affect substantial galactic mass fractions, typically 30 % or more. The observations can be equally well reproduced by either elliptical+burst models or by spiral+burst models in which the star formation is truncated at the end of the burst. The analysis of an UV colour such as (1550-V) is proposed as a valid method to distinguish between the two cases for Hδ strong red galaxies.

Recent redshift surveys of galaxies (e.g. the Center for Astrophysics Survey (CfA)), revealed that bright galaxies are distributed in sheet-like structures which surround large voids. Still under debate is the question whether all galaxies follow such a distribution or if less luminous galaxies are more equally distributed. Given the limitation of the actual surveys, the observed emptiness of the voids may be a result of observational bias.

We present the analysis of a new set of radio and optical observations of a large sample of Byurakan Blue Compact Galaxies. HI spectra were obtained with the Nançay 300-m and Green Bank 43-m radio telescopes. CCD-images were taken with the KPNO 0.9-m and Whipple Observatory 1.2-m telescopes. Dark Matter (DM) to luminous mass ratios in these BCGs were found to vary from about less than 0.5 up to 14. Recent data taken from the literature indicate this same range. This result has important consequences on models of dwarf galaxy formation, indicating possibly different formation mechanisms. The standard CDM model of dwarfs formation requires large DM halos. However the formation of dwarfs as tidal debris resulting from strong interactions of massive spirals leads naturally to dwarfs with low content of DM. On Fig.1 we show DM to luminous mass ratio versus rotational velocity for our BCGs and some other galaxies.

In a series of papers (see Rakos & Schombert 1995, ApJ 439, 47), we have carried out CCD photometry of galaxies in rich clusters at various redshifts. We use a modified Strömgren system, modified in the sense that the filter set is “redshifted” to the cluster of galaxies in consideration (i.e., λobs = λ(1 + z), therefore no k-correction). We call it uz, vz, bz, yz to distinguish it from the original zero redshift system.

The aim of our project is to measure the metallicity gradient in the spheroid of the Andromeda galaxy (M31). Deep KPNO 4-m UBRI images of a 15′ × 15′ field in the outer spheroid of M31 are being used to isolate a sample of red giant branch (RGB) stars. These stars are distinguished from the more numerous distant field galaxies on the basis of broadband colors and image morphology. The color technique uses UBRI photometry for isolating faint stars while rejecting 97% of the background galaxies (Gould et al. 1992). This yields a sample of candidate RGB stars in M31's spheroid, located about 20 kpc from its center (in projection). The shape of the M31 RGB will be compared to those of Galactic globular clusters spanning a wide range of (known) metallicities. The metallicity of the M31 outer spheroid will be derived by interpolation. Combined with the metallicity measurement at 8.6 kpc in M31's spheroid (Pritchet & van den Bergh 1988), our new measurement will permit determination of the metallicity gradient of M31. This quantity is important for understanding galactic evolution as it provides a means to distinguish between the dissipational collapse model (Larson 1974) and the accretion model (Searle & Zinn 1978).

We present V and I photometry of the globular cluster systems of the early-type galaxies NGC 1374, NGC 1379, NGC 1387, NGC 1427, and NGC 1399, obtained with the 100 inch telescope of Las Campanas Observatory.

Using theoretical models of the planetary nebula populations in galaxies, we investigate whether the current oxygen abundances in bright planetary nebulae can be used to predict the oxygen abundance that persisted in the interstellar medium when star formation stopped. In all galaxies, these models predict that a gap develops between the abundances observed in bright planetary nebulae and those that persisted in the interstellar medium when star formation stopped. This abundance gap depends primarily upon the oxygen abundance achieved in the interstellar medium when star formation stopped, though it also has some sensitivity to the history of star formation. The gap is always less than 0.5dex in these models. For the Milky Way, the predicted abundance gap, 0.14dex, is identical to that observed. The abundance gap magnifies the abundance-related differences between diffuse ellipticals and dwarf irregulars found by Richer & McCall (1995, ApJ, 445, 642). Diffuse ellipticals are confirmed to have larger oxygen abundances than similarly luminous dwarf irregulars, and to have larger [O/Fe] ratios than dwarf irregulars with the same oxygen abundance. The simplest explanation for both of these observations is that diffuse ellipticals formed on shorter time scales than dwarf irregulars. Given this difference in the history of star formation, diffuse ellipticals cannot be the faded remnants of dwarf irregulars.

H and K band imaging spectroscopy of the central 12″ (4.2 kpc) of NGC1275 using the Max-Planck-Institut für extraterrestrische Physik imaging spectrometer “3D” maps the gas density and temperature in the core and separates the contribution of Seyfert emission to the core light.

We compute synthetic spectra in the region around 1 μm, including the Wing-Ford band (WFB) of Iron Hydride (FeH) in the calculations. This band is known to be a good indicator of surface gravities of M stars. Employing Kurucz model atmospheres, we study the response of the intensity of the WFB to atmospheric parameters and check our results against observations of M dwarfs. This study is part of an ongoing project which aims to investigate the M dwarf-to-giant ratio in galaxies, through a population synthesis method, exploring a number of spectral indicators in the near infrared, such as the WFB, the NaI, CaII and CO near infrared features.

The most puzzling observations concerning the LISM (distance < 100 pc) can be explained by a fast adiabatically cooled gas in the cavity of an old superbubble. The ultrasoft X-ray background and contributions to the C- and M-bands are due to the continuum emission of delayed recombination [1]. In contrast to collisional ionization equilibrium (CIE) models, but consistent with recent observations [2], our model predicts a lack of emission lines and a low emissivity in the EUV range. In the figure below we compare the emissivities resulting from CIE at T = 106 K and those from our model at T = 4.2 × 104 K. The basic feature of our model is a thermally self-consistent approach of the time-dependent evolution.

We recently completed two-color CCD photometry of resolved stars in 11 dwarf irregular galaxies (Hopp & Schulte-Ladbeck, 1995, A&AS 111, 527), selected because of their relative isolation from massive galaxies in the Kran-Korteweg – Tammann sample (1979, AN 300, 181). The B-R color magnitude diagrams (CMD) show that all galaxies studied had star formation activity in the last ∼ 108 yr. Several of them continue to form stars, the most active being UGC 5272 A (see Hopp & Schulte-Ladbeck, 1991, A&A 248, 1) while others, like DDO 210 (Hopp & Schulte-Ladbeck, 1994, ESO Conf. Workshop Proc. 49, 511), are pausing in their star formation activity. The CMDs enable us to select the brightest blue supergiants in these galaxies and to estimate their distances, D. Our values agree with the estimates based on the Virgo inflow model of Kran-Korteweg (1986, A&AS 66, 255) at the 30%-level. Prelimanary values are given in the table below.

We examine the role of mergers in the formation and statistics of galaxies and clusters of galaxies. First steps in this direction were carried out by Shaviv & Shaviv (1993, ApJ.Lett., 412, L25) where the OD case was treated. The work is extended to examine the effect of self gravity. Thus, we essentially explore the combined effect of violent relaxation and mergers on the resulting structure and mass distribution of galaxies in clusters of galaxies. We developed a numerical method to treat the spherical 2D problem (radial position and velocity) of the evolution of a collapsing cluster of gas clouds (Shaviv & Shaviv, 1995, ApJ., 448, 514).

Star-forming viscous disk model was proposed by Lin & Pringle (1987) as an ubiquitous mechanism to form the exponential stellar disk of spiral galaxies. To clarify whether the viscous evolution models can explain the chemical properties of general spiral galaxies, we have studied the chemical evolution of star-forming viscous disks under the several physical conditions in relation to the possible processes of the disk formation, and compared with the observed gas and metallicity distributions of spiral galaxy disks.

We have developed a catalog of local low surface brightness galaxies (LSBGs) which is selected by objective criteria. We present here a luminosity function (LF) for LSBGs based on that catalog. This LF includes the effects of the completeness corrections to the LSBG catalog, and includes only galaxies with surface brightnesses (22.25 ≤ μB (0) ≤ 24.5) fainter than those included in the CfA Redshift Survey (see Marzke et al. 1994, AJ 108, 437). The best-fitting Schechter function has parameters α = –1.42, M∗B = −18.34, and Φ∗ = 0.0036 h 3 Mpc–3 mag–1. Thus, surveys which do not take account of the observational selection bias imposed by surface brightness are missing a substantial fraction of the local galaxies, but, this missed fraction is not large enough to explain the counts of faint blue galaxies observed at moderate redshift.

Improved and reliable profile fitting codes have made it recently possible to calculate reliable column densities of gas producing QSO absorption lines. Even using intermediate to low resolution spectra, the obtained column densities are very accurate, as has been extensively proved by Jenkins (1986). We applied this technique to the 131 CIV absorption systems in the survey by Sargent Boksenberg and Steidel (1988) and Steidel (1990). Since several lines were saturated, many CIV column densities, N(CIV), are only lower limits, and a survival analysis (Avni et al. 1980) is required to obtain the underlying redshift distribution of CIV column densities, which we present in Figure 1. Together with the number density distribution of strong (log N(CIV) ≥ 14.2) and weak systems shown in Figure 2, we have found that i. Both strong and weak systems become generally weaker below z ∼ 2, and II. Weak systems become less numerous below z ∼ 2, whereas the stronger systems grow steadily in number density down the lowest redshifts sampled. For details of the analysis, and on how this fits into a model for the CIV absorption systems see Stengler-Larrea et al. (1995, in preparation).

NGC6119 and NGC6120 have been listed in Kiso catalog (Takase et al., 1987) as Sc and Irr galaxies. They have been selected by their clumpy features in order to investigate their nature and star formation history using slit spectroscopy. They have similar systemic velocities (respectively 9215 and 9200 km ·s–1) and seem to be members of a low gravitational interacting system of 4 galaxies (with MCG-6-36-30 and NGC6122).

A multiband CCD-survey of 355 UGC galaxies in our local cosmological neighbourhood is undertaken in collaboration with S.D.M. White (MPI-fAstrophysik Garching), S. McGaugh (IoA, Cambridge), M. Dennefeld (IAP Paris), H. Ferguson (STScI), M. Rieke, A. Grauer (Steward Obs. Arizona). Optical observations are obtained on Calar Alto (MPIA Heidelberg) and at La Palma (RGO) – with data 40% complete at the moment. The selection criterion is diameter 1.5′ < D25 < 2.5′. A database of local galaxy properties is being established (including total luminosities, mean SB, diameters, colours, colour gradients, D/B-ratios, present SFRs). Using theoretical evolution models we can predict the bona fide appearance of the galaxy population at any given redshift and thus provide a secure reference point to interpreting galaxies observed at intermediate and high z (e.g. faint galaxy counts).