Gas and dust in the inner region of the Galaxy are distributed in a flat, disklike structure. We model the dynamics of this material in the framework of an accretion disk approach, and thus determine the efficiency of the radial transport of mass and angular momentum in the inner ∼ 200 pc of the Galactic Plane. Moreover, this allows us to establish the location (coordinates: galactic longitude l and depth normal to the celestial sphere) of molecular clouds from the observed positions (l) and radial velocities (currently, we neglect details of the vertical structure). Ultimately this will yield a map of the distribution of molecular clouds about Sgr A∗.

Recent observations with ASCA (Mushotzky 94, New Horizon of X-Ray Astron.-1st Results from ASCA) have confirmed the prediction (Arnaud et al. 92, A&A 254, 49; Elbaz et al. 95, to appear in A&A) that the Fe present in the intra-cluster medium (ICM) is mainly due to SNII and not SNIa: α-elements (O, Ne, Si, S) are overabundant with respect to Fe. To account for the large Fe mass present in galaxy clusters as well as these abundances ratios, one must consider that the IMF was different in the past, favouring high-mass stars. Moreover, the simplest way to eject the enriched ISM into the ICM is to consider that the same high-mass stars that were responsible for the Fe enrichment have also driven a galactic wind in young E/SO's.

We present several pieces of evidence that there was an interaction between a bar, which is now dissolved (presumably by a small merger event - Emsellem 1995, A&A in press), and the interstellar medium (gas/dust) in the Sombrero Galaxy (M 104). This study has been achieved by combining new photometric and 2D spectroscopic data (HRCAM, TIGER - Fig. 1) with realistic models (a 3D spatial model of the dust distribution taking into account light scattering, and self consistent two-integral models). Such secular evolution of galaxies driven by bars may be a very common process (Friedli & Benz 1993, A&A 268, 65).

Edvardson et al 1993 demonstrated that rapid build up of oxygen in the inner Galaxy. Do these high [O/Fe] ratios prevail also for metal rich stars? We have obtained high resolution (R = 100 000) spectra with the 2D-Coude Spectrometer at the McDonald Observatory 2.7 m telescope for 50 metal rich F, G and K dwarfs. These stars where chosen to represent both an old stellar population which originates ‘inside’ the solar orbit and the young extreme Population I.

We have improved in the NIR the model of galaxy evolution developed by Guiderdoni & Rocca-Volmerange (A&A 186, 1) in the UV and the visible, allowing thus a multispectral analysis of the evolution of galaxies and of faint galaxy counts. Since evolutionnary effects should be low in the near-infrared, cosmological ones might be put in evidence.

Line strengths and their gradients in Mg, Fe, and Hβ have been determined for a sample of 20 S0 galaxies in order to study the stellar populations of their bulges and disks and to investigate their relationship to elliptical galaxies. The data were obtained with the Lick Observatory 3m telescope in the long-slit mode over the region 4215–5615 Å with resolution 3.1 Å.

Combining the results from Keck spectral and HST imaging data (Forbes et al. 1994), we have derived various quantitative parameters for 17 faint (I ∼ 21), distant (z ∼ 0.5) galaxies. Such redshifts correspond to a look–back time that is about half the age of the Universe and for which some scenarios predict significant galaxy evolution. We have measured disk scale lengths (with sizes ranging from 1–5 kpc) from fits to the surface brightness profiles and internal velocities with a rest frame resolution of σ = 55 to 80 km s–1 by fitting to the emission lines. The luminosity–disk size and luminosity–internal velocity relations for our moderate redshift galaxies are similar to the scaling relations seen for local galaxies, albeit with modest ΔMB ∼ 1m brightening. We do not see evidence for a dominant population of starbursting dwarf galaxies, that have disappeared by the present epoch. Further details of this study can be found in Forbes et al. (1995). When large samples of kinematic data on distant galaxies are available, we will be able to trace galaxy evolution by mass as distinct from light.

The high burst strengths and star formation efficiencies found with spectrophotmetric and chemical evolutionary synthesis for mergers of gas-rich spirals led us to expect the formation of a secondary population of globular clusters (GC) with enhanced metallicity (F. – v. A. & Gerhard 1994, A&A 285, 751 u.775). HST imaging of NGC 7252, NGC 4038/39 and NGC 1275 revealed rich populations of bright young star clusters (YSC).

We give a detailed description of the dynamical interaction of the stellar and gaseous components of a galactic disk. The stability of the two-component system against axisymmetric density perturbations is analyzed and the critical velocity dispersions of the stars and the gas, which control the instability, are determined. By comparison with the observed velocity dispersions it is shown that NGC 6946, a typical Sc galaxy, seems to be stable in the outer parts of the disk, but is dynamically unstable in the inner parts. The transition occurs exactly at the HII region disk boundary, so that the onset of gravitational instability appears to be related to the threshold of massive star formation (Kennicutt 1989). We study the dynamical evolution of the instability by numerical simulations using a code (cf. Casoli & Combes 1982), which implements both the stellar and gaseous components. It is shown that the gas forms after a short initial period of growing ring–like perturbations large cloud complexes, which induce by ‘swing-amplification’ (Toomre 1990) multi-armed spiral structures in the stellar and gas disks, exactly as observed.

We investigated how the encounters between galaxies change their mass M and velocity dispersion σ. We carried out a series of direct N-body simulation of encounters of two spherical galaxies. In Figure 1, the relative change of energy ΔE/E are plotted against that of mass ΔM/M for various initial conditions. The filled and open symbols correspond to the cases of Plummer model and relaxed Hernquist model, respectively. Here β ≡ (ΔE/E)/(ΔM/M).

We present the first self-consistent 3D barred model of the Milky Way including gas, as an evolved stage of an unsymmetrised N-body simulation with axisymmetric initial conditions (fig.1). The corotation lies at about 4 kpc and the central gas particles have condensed into a nuclear ring/disc. Distortions of the bar and other odd modes in the stellar distribution (a) affect the gas flow by producing one-side gas voids (b) and instabilities of the nuclear component like tilting, warping and off-centering (c-d). These peculiarities may help to reproduce the intriguing asymmetries and densely populated “forbidden” regions in the Galactic HI and CO (l – v) maps (e-f). More details are given in the proc. of IAU Coll. 157 “Barred Galaxies”.

The Universidad Complutense de Madrid survey is a long-term project with the aim of finding and analyzing star forming galaxies using the Hα line as the tracer for star formation processes. In order to obtain a representative and complete sample of the population detected, spectroscopic observations were carried out for the full sample of Hα emission-line galaxy (ELG) candidates of the UCM lists 1 and 2. The ELGs types most commonly found (47%) are intermediate to low-luminosity objects with a very intense star-formation region which dominates the optical energy output of the galaxy. This kind of ELGs is similar to the galaxy population detected in the blue objective-prism surveys. And what is more important, a second population (43%) of star-forming galaxies with low ionization or high extinction properties has been found. This ELGs group is detected neither in the blue (University of Michigan survey, Case survey) nor in other surveys (Kiso, IRAS, Markarian) using other selection techniques.

Recent observational evidence for steep dwarf galaxy luminosity functions in several rich clusters has led to speculation that their precursors, via supernovae (SNe)-driven galactic winds, may be the source of the majority of gas and metals inferred from intracluster medium (ICM) x-ray observations (Trentham 1994). Utilising a fully self-consistent photo-chemical evolution package (Gibson 1995), and insisting that the post-galactic wind dwarfs obey the observed colour-luminosity-metallicity relations, we demonstrate that the bulk of the ICM gas does not originate within their precursors (Gibson & Matteucci 1995).

We present the results of a spectroscopic study in which we have measured line-strength indices in a sample of 5 dwarf and 2 compact elliptical galaxies (mostly from Virgo). Some conclusions about the stellar populations in dwarf E's are derived by comparing the sample with classical E galaxies. In the adjacent figure, we plot in the Hβ-[MgFe] plane the central indices of our sample of dwarf and compact E's together with data from González (1993, PhD Thesis). The grid represents the predictions of single-burst stellar population models from Worthey (1994, ApJS, 95, 107). The main conclusion is that, whilst the central regions of giant, intermediate and compact ellipticals span, according to stellar population models, a wide range in mean stellar ages, bright dwarf ellipticals are found to be old, compatible with a ∼ 10 Gyr old stellar population. This means that the dichotomy found in the Fundamental Plane between dwarf ellipticals and the gE-iE-cE sequence (Bender, Burstein & Faber 1992, ApJ, 399, 462) is also observed in the stellar populations.

Color gradients in elliptical galaxies are commonly interpreted as being due to stellar population gradients (e.g., Davies et al. 1993, MNRAS 262, 650). Here, I show that elliptical galaxies should generally contain a diffusely distributed component of dust, in addition to the “visible” component which is in the form of dust lanes or patches (see Fig. 1a). Employing a multiple scattering model for the dust, the presence of this newly postulated dust component is found to imply significant radial color gradients (see Fig. 1b). This should be taken seriously in the interpretation of color gradients in elliptical galaxies. This poster paper is based upon a (much!) more elaborate article by Goudfrooij & de Jong (1995, A&A 298, 784).

The nature of faint field galaxy evolution remains controversial. While many workers advocate exotic theories, such as rapid merging or disappearing populations, we have found that it is possible to explain the published counts and redshift data with traditional luminosity evolution models which derive an optimal set of local luminosity functions for different galaxy types (Gronwall & Koo 1995). Recently, there has been a tremendous amount of new data addressing this question, including 1) the measurement of the galaxy luminosity function vs. redshift from faint redshift surveys down to B = 24 and I = 22 (Colless 1995; Lilly et al. 1995), 2) morphological and angular size data from the HST Medium Deep Survey (Driver et al. 1995; Phillips et al. 1995), and 3) redshift measurements with Keck for a small sample of galaxies with I > 22 (Koo 1995). We have explored these new data and have found that while our model continues to provide an excellent match to the faintest observed redshift and angular size distributions, it underpredicts the faint counts and luminosity function evolution for very blue late-type galaxies. Since our current model includes only minimal evolution of these galaxies, the new observations suggest a need for additional evolution, perhaps through a starbursting or mild merging component.

The nature of evolution in faint field galaxies remains a mystery. The Tully-Fisher relation, empirically relating the intrinsic luminosity of a spiral galaxy to its rotation speed, is an important tool for constraining the amount of luminosity evolution in distant field galaxies. Studying the luminosity-vs-linewidth relation for distant galaxies allows one to compare the luminosity of local and distant galaxies. The customary measure of a galaxy's rotation speed is the width of an emission line. It is important, however, to test whether the linewidth is a reliable measure of the galaxy's rotation speed or if it is dominated by turbulent motion within HII regions. In order to do this, we study the spatially-resolved kinematics and distribution of 0[III] gas in about ten 〈B〉∼21 field galaxies at 〈z〉≈0.3.

Three galaxies from Second Byurakan Sky Survey have been studied. The spectra of these galaxies were obtained at 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. For these objects line widths and emission line ratios were measured and ionization mechanism and chemical abundances were determined.

Line strength gradients in luminous ellipticals show changes in metallicity of roughly a factor of two out to an effective radius (Worthey, Faber & Gonzalez, 1992; Davies, Sadler & Peletier (DSP), 1993; Gonzalez, 1993). The observed decline in Mg2 line strength with increasing radius, while Hβ remains roughly constant, has been interpreted to indicate an age gradient with the central parts of ellipticals being younger than the outer regions.

We present absorption line profile analysis of NGC 474, an elliptical with prominent, irregular shells. Profiles are parameterized with Gauss-Hermite polynomials (van der Marel & Franx ApJ 407 1993; Rix & White MNRAS 254 1992). The fastest rotation (∼ 50 km s–1) and steepest central velocity gradient along the intermediate photometric axis rules out the possibility that NGC 474 is a face-on S0 (Schombert & Wallin AJ 94 1987) and suggests that it is triaxial. The asymmetry of the LOSVDs (h3 up to 0.08) indicates the presence of a subsystem with rapid, ordered rotation. The minor axis velocity curve shows a kinematic feature at 3–4″ east of the nucleus, with no associated h3 or h4 features. Non-parametric LOSVD analysis (unresolved Gaussian decomposition, Kuijken & Merrifield MNRAS 264 1993) reveals a double-peaked profile at that location. In all position angles line-profiles are distinctly pointy for radii up to 2″, and are consistent with zero further out. We have found similar central positive h4 terms in the shell galaxy NGC 2865 (Hau et al. MNRAS in prep). Cores with pointy LOSVDs are uncommon in ellipticals (Bender, Saglia & Gerhard MNRAS 269 1994). Positive h4 terms might contain important clues on the shell-formation mechanism in ellipticals.