Gas accretion of intra cluster gas into the potential well of giant elliptical or cD galaxies can provide the material for both nuclear non-thermal activity and continuous, probably low mass, star formation (Fabian et al. 1982, Valentijn and Bijleveld 1983). In a few dozen cases it has been observed in the nearby universe that the hydrostatic equilibrium of X-ray emitting gaseous atmospheres around cD galaxies is disturbed by the thermal bremsstrahlung cooling in the central high density area, leading to an inflow of gas into the centrally located gE or cD galaxy (“cooling flows”, Jones and Forman 1984). This thermal instability is different from those studied in models of early galaxy formation (Gunn and Gott 1972, Rees and Ostriker 1972) only because of the assumed self-gravitation of the collapsing gas in the galaxy formation scenarios. If however, during early galaxy formation the collapsing gas is accreted by a pre-existing dark potential well, then the processes of early galaxy formation and the observed present epoch cooling flows are likely to be intimately related to each other. The cooling accretion flows could then lead to the original formation of the visible object, and subsequently govern its evolution through the fuelling of star formation and nuclear non-thermal activity.

Constraints on supernova-driven galactic winds from elliptical galaxies at the epoch of star formation are investigated. The occurrence of mass loss is found to depend critically on the supernova rate in the case of dwarf galaxies, while the depth of the potential well is the most important constraint for giant ellipticals. The smallest dwarf ellipticals must have evolved from significantly more massive progenitors in order to have sustained a wind that carried away most of their metal production.

We calculate the partial inflow of gas fuelled by stellar mass loss at an early epoch (109yr after the birth of the galaxy) during the evolution of an elliptical galaxy assuming a modified King model stellar distribution. The influence of the partial thermalization of stellar mass lost on the amount of gas which can be stored in the nucleus of a typical elliptical during the time of partial inflow is investigated. Masses up to 105M⊙ of cool (≤ 104K) material can be stored in the nucleus of the galaxy before the fast dissipation of the “kinetic bulk energy” of the nuclear gas cloud leads to “thermal” instability and subsequent collapse. A supermassive star can form. A detailed discussion of the model and the results is subject of a forthcoming paper (Kunze et al., 1986).

New, self–consistent energy distribution have been generated from 52 short – wavelength and 40 long–wavelength IUE spectra of 31 early–type galaxies, plus the bulge of M31. All galaxies in this sample have measurements of the absorption–line index Mg2 and central velocity dispersion, and a (1550–V) color is determined by combing the IUE data with photoelectrically–measured V magnitudes.

We have measured line-strength indices as a function of radius in several elliptical galaxies. All of them show strong radial gradients in Mg, but much weaker gradients in Fe and Hβ. The isophotes and contours of constant line-strength have the same flattening. More luminous galaxies have shallower gradients, contrary to the prediction of models of dissipative collapse. Most of the galaxies observed show weak central emission which can partially fill the Balmer absorption lines.

Dissipational formation theories (e.g. Larson 1974) predict a metallicity change with distance from the center in elliptical galaxies. Several authors have reported small color gradients in visual colors like B–V and B–R. The interpretation of these data is not easy, due to uncertainties caused by the short wavelength–baseline, and by the presence of a hot stellar population suggested by IUE–data (e.g. Burstein et al. 1986). Simultaneous measurements of visual and visual-infrared colors provide the means to determine both the average temperature of the giant branch and the turnoff–temperature of the main sequence. This allows to model fractional contributions of different populations, including age– and metallicity–effects. The required continuity of solutions at different radii provides a strong constraint in selecting a more unique overall population model, and relieves the ambiguous interpretation of single measurements.

We present a determination of the stellar luminosity function in luminous elliptical galaxies which includes all stars more massive than 0.15 M⊙. This limit corresponds to masses beyond the maximum in the solar neighbourhood stellar mass function, and therefore includes effectively all the luminous mass. Galaxies with X-ray evidence for current massive star formation, also show no evidence for enhanced low mass star formation in their central regions. All elliptical galaxies studied to date have stellar luminosity functions for masses above 0.15 solar masses which do not differ significantly from that in the solar neighbourhood. Elliptical galaxies have stellar bolometric mass-to-light ratios of 2.5< M/L <5.0.

The mass to light ratio of the inner parts of the Fornax system is 3.2 ± 1.1. Its major axis rotation is only 3.4 ± 2.4 km s-1 over ± 1 kpc, which argues against its origin as a stripped dwarf irregular.

By far the brightest and the most massive globular cluster in our Galaxy,ω Cen seems to be, in some of its properties, a kind of transition step between dwarf ellipticals and ordinary globular clusters. For this giant cluster, the comparison between observations and King-Michie multi-mass dynamical models appears possible only using models with strong anisotropy in the velocity dispersion. A more comprehensive description of this work is to be published (Meylan 1986).

With a velocity dispersion of 370 ± 50 km/sec the globular cluster system of M87 is kinematically hotter than the stars in the giant elliptical itself. This is consistent with the clusters' shallower density distribution for isotropic orbits. the mean metallicity of the 27 clusters in the sample analyzed here is no more than a factor of 2 more metal rich than the cluster system of the Milky Way, but considerably more metal poor than the integrated starlight in the field at a radius of 1' from the center of M87. There is no evidence for the existence of young clusters in the system. the mass-radius relation between 1' and 5' required to contain the globular clusters joins on to that required to contain the hot gas around M87.

We have obtained CCD images in R and V of Malin's “jet” in the weakly radio and X-ray active E0 galaxy M89 (NGC4552). the luminosity of this feature is approximately 1/4% of the total luminosity of the galaxy; its color is bluer than that of the whole galaxy with a V-R value smaller by about 0.15 magnitudes. the likely explanation of the feature, which looks more like a proboscis than a jet, is that it is, in the words of the Toomres (1972), a “tidal relic of a close encounter”, seen from a perspective that may hide a drawn out tail.

We present the results of an observational study of the dwarf galaxies in the Fornax cluster of galaxies.

We obtained the luminosity function (LF) for samples of galaxies from the CfA North catalogue (Huchra, Davis, Latham and Tonry, 1983). the criteria of selection of samples were the local density (range—more than 2 orders of magnitude) and/or the morphology. No difference in the combined LF for all morphological types is found for subsamples of different density. the LF of elliptical galaxies is found to be less steep at the faint end than the LFs for S and SO galaxies. E galaxies are on the average brighter than the other morphological types. the LFs measured for early–type galaxies (E + S0) in high and low density regions show marginal difference—the low density LF has a steeper faint end slope. (Such a difference is not found for S galaxies). If this feature is maintained for larger samples it may indicate that the LF determined at the moment of galaxy formation is only weakly influenced by the phenomena present in dense regions. This is because these phenomena would rather leave the opposite imprint on the LF—the tidal stripping in dense regions would populate them with faint remnants of disrupted, bright, low angular momentum galaxies. Mergers could not reverse this trend because they act mainly on the bright galaxies.

The luminosity functions of inner and outer regions of six Abell clusters (A569, A1656, A2147, A2151, A2199, and A2634) were compared. These clusters have a single, reasonably symmetric central concentration of galaxies within the central Mpc. For three other clusters with irregular spatial distributions of galaxies (A779, A1367, and A2197) luminosity functions for high and low density regions were compared. For three of the clusters in the first group (A1656, A2147, and A2199) there is a deficit of bright galaxies, according to the Kolmogorov-Smirnov and Wilcoxon rank-sum nonparametric tests, in a region of radius 0.5 Mpc about the cluster center compared to a concentric annular region with bounds of 0.5 and 1.0 Mpc.

Originally the luminosity function of galaxies was derived by E. Hubble (1936). Later studies are by Holmberg (1950), Zwicky (1957, 1964), Kiang (1961), Neyman and Scott (1962), Van den Bergh (1961), Pskovsky (1965), Nezhinsky and Osipkov (1967, 1969), Genkina (1969), Popov (1980), Tammann (1984), and others.

Low dispersion spectra of two shell galaxies, NGC 3923 and NGC 3051, have been obtained covering the 5300Å to 10000Å spectral range. These long-slit spectra go through the nucleus of each galaxy and also through 12 shells in NGC 3923 and through 3 shells in NGC 3051. the main results are:

1) In NGC 3051 the surface brightness of the 2 inner shells is nearly constant with radius. These plateaus of luminosity have very abrupt outer cutoffs but have no detectable inner limits.

Shells may be the result of the disruption of a small companion in the potential of a much larger galaxy (e.g., Hernquist & Quinn, 1986; Dupraz & Combes, 1985), the disturbance of a disk system in a tidal encounter (Toomre, 1972), an accumulation of resonant stellar orbits (Binney, pers.comm.) or the result of some shock phenomenon in a hot galactic atmosphere (e.g., Williams & Christiansen, 1985; Wilkinson & Bailey, 1985;). To distinguish between these formation mechanisms, CCD direct images in B and R have been obtained at the Anglo-Australian 3.8m telescope for 66 of the 74 galaxies in the range 01h 40′ α < 13h 46' in the Malin-Carter (1983) catalogue of shell galaxies.

A new method for probing the distribution of matter in elliptical galaxies surrounded by shell systems is described. As an illustration we have applied this technique to the giant elliptical galaxy NGC 3923. If the potential is modeled as the sum of an r1/4 law and a non–singular isothermal halo, then the best fit to the shell number and shell distribution gives a halo mass (within the shell system ~ 100h−1 kpc) ~ 40 times the mass of the elliptical and a halo core radius ~ 3 times the effective radius of the luminous material.

In previous articles (Dupraz & Combes, 1985, 1986a), we showed that shells form with different geometries around prolate and oblate galaxies. However, theory and observations suggest that some ellipticals could be tumbling bars (Miller & Smith 1980; Müllenhoff & Marenbach 1986). Here we simulate the accretion of a small galaxy by a tumbling bar; the tumble period T& is kept free. Let Tp be the typical period of motion of a particle in the potential of the elliptical galaxy. Then we find (Dupraz & Combes, 1986b):

a) When Tt > 3TP (Figure l a), shells form with the geometry of a static prolate potential, i.e., aligned with the major axis.

When Tb < 3Tp (Figure lc), the particles feel the time-averaged potential, which is oblate: the shells display the typical oblate geometry. But there is no confusion with a static oblate shell galaxy, because the tumbling bars must be seen edge -on for the shells to appear.

c) When Tb ~ 3Tp (Figure lb), the outer shells form with the oblate geometry, the inner shells with the prolate geometry. In between, no shells form, because particles follow resonant (non-radial) motions.

Sharp edged features have been observed by Malin and Carter (1980), Schweizer (1980) and others in the envelopes of many elliptical galaxies. the most promising of current models involves the disruption of a low mass galaxy penetrating close to the centre of a considerably larger ellipsoidal galaxy (Schweizer, 1980, Quinn, 1984, Hernquist and Quinn, 1986, Dupraz and Combes, 1986). the release of stars having a range of energies and with a definite relationship between velocity and position at the point of release generates sharp features by the “phase wrapping” mechanism.