The estimated distances of elliptical galaxies, as determined by the Dn – σ technique, can be affected by stellar population variations and perhaps also dynamical effects due to mergers, leading to spuriously large positive peculiar velocities.

25 star systems were observed in 1983-1987 with the 80cm telescope on the board of astrophysical station “Astron”. Entrance diaphragms were 60″ and 10″. Spectrometer with the exit slit 28 A has measured fluxes in erg/sec cm2 A in the region 1600-3500 AA in regime of narrow band photometry. Exposures in every point were 2-5 min for bright objects and 10-30 min for week ones.

Suggestions for the source of the ultraviolet flux in elliptical galaxies and spiral bulges include young stars, post-asymptotic-giant-branch (PAGB) stars, hot-horizontal-branch stars, and accreting white dwarfs. Each candidate has different implications for the spectral evolution of galaxies. We review current understanding of the origin of the far-UV flux, with emphasis on recent results from the Hopkins Ultraviolet Telescope (HUT), flown on the Astro-1 space-shuttle mission in December 1990.

Faint object spectroscopy and deep infrared imaging is providing exciting opportunities to understand the astrophysical nature of normal galaxies up to ≃8-10 Gyr ago (Ho=50). Deep photometry of 10 distant clusters with 0.5< z <1 shows a systematic bluing of red members with look-back time, in good agreement with the view that the bulk of the early type population must be genuinely old (zf >2) and remarkably homogeneous. Statistically complete redshift surveys of the highly abundant population of faint blue field galaxies, however, indicate sizeable changes must have occurred in the galaxy luminosity functions as recently as z≃0.5. Possible explanations include widespread merging of star-forming sub-units of present day galaxies, or an entirely new population of sources whose present-day remnants are intrinsically faint. The contrast between the long term evolution of the spheroidal population and that seen in the faint counts is striking. I finally discuss some new opportunities to identifying field galaxies with z>l using gravitational lensing and QSO absorber identifications.

A brief and non-exhaustive review of the main research papers on Evolutionary Population Synthesis is presented. The degree up to which these studies obey well known astrophysical constrains, such as the Fuel Consumption Theorem, is analyzed. A summary of the most significant results from the Isochrone Synthesis Spectral Evolution Models of Bruzual and Charlot (1992) concludes this presentation.

We present models of chemical and photometric evolution of galaxies. We show that the onset of the AGB phase at a few 108yr causes a sudden change in the infrared colours of the galaxy. However, this powerful indicator of the time of galaxy formation is wiped out by cosmological effects.

The determination of the age of stellar populations in progressively more distant stellar systems requires successive calibrations which in some way remind the procedures followed in determining astronomical distances. A few exemplifications of this Age Ladder are schematically reviewed, such as the determination of the age of galactic globular clusters, of the youngest population in bulges and ellipticals, and of the most distant, high redshift radiogalaxies.

We review primeval galaxy searches based on the Lyα line emission. Simple arguments are given which suggest that primeval galaxies (interpreted here as ellipticals and bulges undergoing their first major bursts of star formation) should be detectable with present-day technology. Many active objects are now known at large redshifts, which may be plausibly interpreted as young galaxies, but there is so far no convincing detection of a field population of forming normal galaxies. This suggests that either primeval galaxies were obscured, and/or are to be found at higher redshifts, zgf > 5.

Galaxy formation is one of the central problems of modern cosmology. It touches on many different subfields of astrophysics: formation and evolution of large-scale structure, chemical evolution and star formation history of galaxies and stellar populations, physics of star formation, etc. Discovery of normal galaxies forming at large redshifts will be an important milestone and would open many new exciting problems and fields of inquiry.

The purpose of this review is to describe some of the observational issues involved, to describe the results from modern searches for primeval galaxies (hereafter PGs), and the future prospects. Previous reviews include those by Davis 1980, Koo 1986, Spinrad 1987, 1989, Cowie 1988, 1989, Djorgovski 1988a,b, 1992, and numerous excellent papers in the proceedings edited by Frenk et al. 1989 and Bergeron et al. 1988; and also in Hewitt et al. 1987, Thuan et al. 1988, Kron & Renzini 1988, Kron 1990, and many others.

The photometric (spectral) evolution is but one aspect of a more universal central question in modern astrophysics — the complex problem of formation and evolution of galaxies. The method used to follow the photometric evolution is straightforward, consisting in computing on the basis of adopted prescriptions for star formation the stellar populations present at various moments and summing up the contributions of all the multitude of stars of different ages and evolutionary stages. The usual strategy is to neglect the dynamics and chemical changes of matter, although during the initial collapse of a galaxy and rapid enrichment of its matter both processes should be important contributors shaping the forming stellar populations. Other widely used simplifications are the rejection of interstellar absorption and the restriction of models to the volume element with constant star formation time scale in its borders (so-called “one-zone models”, they stricly apply to the infinitely narrow ellipsoidal shells in real galaxies). An additional postulate that the region considered is closed and isolated, having not been subjected to interactions or mass exchange with the surroundings, is introduced in the simpliest closed “classical” or “canonical” models (Traat 1988), computed e.g. by Tinsley (1972), Searle et al. (1973), Traat and Einasto (1979), and others. Such assumption, however, is not always valid and some objects need to be modelled by burst models or more universal accretion models.

We discuss the results of a cosmological test involving mean colors of the early-type galaxy population in distant clusters for tracing the World model. A global approach to the cosmological problem is attempted deriving the allowed combinations for the fundamental parameters (Ho, qo, λo), and the redshift of galaxy formation (zf).

Recent improvements of spectrophotometric evolutionary models are described. New stellar libraries in the near-infrared (JHK) allow extension of the synthetic spectral Atlas of galaxies down to 10μm. From analyses in the far-UV and visible, observed colors and counts of faint galaxies are fitted by modelling a standard luminosity evolution and a low value of ωo(≃ 0.1) while, in a ωo=1 Universe, models only fit data with a standard luminosity evolution and a number density evolution ≃ (1 + z)1.8: such a modelling is simulating a merging process. Another solution would be a tidally triggered star formation rate in a model in which galaxies form by hierarchical clustering of a dominant dark matter component. From evolution of M/L ratio, these models allow to link observed luminosity functions with mass distributions predicted from galaxy formation models and then to significantly connect evolution to formation models. Nevertheless these two models are not sufficient to fit some observational data such as the Hubble diagrams and faint galaxy counts in the near-infrared, the bright galaxy counts in visible and the Extragalactic Background Light. So new evolution scenarios are needed implying other constraints for cosmological parameters.

After summarizing the evidence for dark baryonic matter in various environments, I review theoretical considerations relevant to the nature of such a component of the universe in regions where it is the dominant mass fraction. Phenomenological constraints are given on the primordial stellar initial mass function. The primordial rate of star formation is evaluated during the early stages of galaxy formation, utilizing simple theoretical considerations motivated by present day star formation rates. Applications are given to predominantly dark objects whose existence is inferred from galaxy formation theory, including low surface brightness giant and dwarf galaxies. Prospects for detection of dark populations that dominate our own galactic halo are described.

Properties of neutron stars are discussed and their density in Galaxy is roughly estimated. Their input in average galactic density is not large and they cannot be a reasonable dark matter candidates.

The chemical composition of 86 planetary nebulae from the Strasbourg-ESO survey are analysed (Acker et al., 1989; Köppen et al., 1991). Strong correlations between O, S, Ar, as well as between N and N/O are found. Galactic radial gradients for the abundances of He, S, and Ar in the old disk nebulae are found in accord with the results of Faúndez-Albans and Maciel (1986). The S gradient is steeper than that of O, and the S/O ratio decreases with increasing distance from the galactic centre, which is quite different from the result deduced from HII regions.

New methods for displaying radial velocities of pulsating stars are presented. The profiles of weak spectral lines in Cepheids are observed to be asymmetric during the inward velocity part of the pulsation cycle but not the outward velocity part. A prescription is given for standardising the method of measuring radial velocity. New projection factors are calculated for Cepheid variables using this method and p=1.37 is recommended as a constant value. This should lead to a systematic error in radius determinations of ~1% from this source.

Orbits for 615 halo and high-velocity disk stars have been numerically integrated in two different models for the galactic mass distribution, both satisfying recent observational constraints for the rotation curve and the perpendicular force (Allen and Martos 1986, Allen and Santillán 1991). In spite of major differences in the mathematical form of both models for the galactic potential, the orbital parameters of most of the computed orbits do not change appreciably. The greatest differences are found in the apogalactic distances reached by weakly bound stars, in the heights above galactic plane, and most importantly, in the total fraction of chaotic as opposed to semiperiodic orbits found for each galactic potential model.

Recently, Alfaro et al. (1991) [ApJ, 378, 106] have noted and stressed the clear spatial connection between the vertical structure of the galactic disk, defined by the young open cluster distribution (YOC), and the large scale star-forming activity in the Milky Way. In this context the estimate and study of the vertical pattern displayed by the Wolf-Rayet (WR) star population, as representative of the formation places of massive stars, could provide new insights on the connection between the morphological properties and the stellar-formation processes in our Galaxy.

With this aim in mind we have estimated a set of Z values for a grid of points on the X-Y plane from a sample of WR stars with measured Z, X, and Y coordinates (Vacca & Conti 1990 [AJ, 100, 431]) by using Automatic Cartography techniques (Kriging) (Cabrera-Caño et al. 1990 [in Bias, Errors and Uncertainties in Astronomy, Cambridge University Press, p. 101], Alfaro et al. 1991). The obtaining of this grid of points has allowed us to construct contour-maps and/or three-dimensional pictures of the galactic disk, as defined by this component, in the neighborhood of the Sun.

A comparative analysis between the two vertical patterns displayed by the YOC and WR distributions, has lead us to the following conclusions:

1.- At distances from the Sun lower than ≍ 1.5 kpc, both stellar populations show a very similar vertical behaviour.

2.- The WR distribution appears to be shifted down, ≍ 20 pc in average, with respect to the YOC Z-structure.

3.- The existence of a large and deep depression (Big Dent) in the galactic third quadrant (Alfaro et al. 1991), is corroborated by the distribution of the WR stars.

4.- At distance from the Sun larger than 1.5 kpc, both population show clear differences in their vertical patterns. Whether these discrepancies are mainly due to large errors in the distances of the remote WR stars or to actual differences in the Z-structure for both populations remains as an open question.

We show that in a scenario of isothermal density perturbations, stars ≥50M (Population III) at a redshift z ≫ zgal (redshift of galaxy formation) can be formed. We take into account in the calculation the expansion of the Universe and a series of physical processes relevant to the primordial plasma: photon-drag, photon-cooling, recombination, collisional ionization, photoionization, Lyman-α cooling and molecular hydrogen cooling.

The galaxy M82 has in its central region ongoing a giant burst of star formation. Van van den Bergh (1971) first separated the bright semistellar objects in central region of M82, which in fact are young star clusters. Using subsecond seeing, Artamonov et al. (1990) managed to distinguish about 70 semistellar objects in M 82 in colour ‘V’.