Chemically Consistent Evolutionary Synthesis Models

Any stellar system with a star formation history (SFH) more extended than a massive star's lifetime will be composite in metallicity. Our method of chemically consistent evolutionary synthesis tries to account for the increasing initial metallicity of successive generations of stars. Using various sets of input physics for a range of metallicities $10^{-4} \leq Z \leq 0.05$ we keep track of the ISM enrichment and follow successive generations of stars using stellar evolutionary tracks, yields, model atmosphere spectra, index calibrations, etc., appropriate for their respective initial metallicities. Since the SFH determines the evolution not only of the metallicity, but, in particular, of abundance ratios of specific elements, stellar evolution and galaxy evolution become intimately coupled. I review the concept of chemically consistent evolution, present results for the photometric, spectral, and chemical evolution of galaxies of various types in the local Universe and at high redshift, and discuss its advantages as well as its current limitations.Comment: 10 pages, using paspconf.sty, Invited Talk, Annapolis Conference ` Spectrophotometric Dating of Stars and Galaxies', April 199

The Evolution of Galaxies on Cosmological Timescales

I discuss the chemical and spectrophotometric evolution of galaxies over cosmological timescales and present a first attempt to treat both aspects in a chemically consistent way. In our evolutionary synthesis approach, we account for the increasing metallicity of successive generations of stars and use sets of stellar evolutionary tracks, stellar yields, spectra, etc. for various metallicities. This gives a more realistic description of nearby galaxies, which are observed to have broad stellar metalllicty distributions, as well as of young galaxies at high redshift. Selected results are presented for the chemo-cosmological evolution of galaxies as compared to QSO absorption line observations and for the spectrophotometric evolution of galaxies to very high redshifts. On cosmological timescales, intercations are important drivers of galaxy evolution. Neglecting dynamical aspects we study the effects of interaction-induced starbursts on the spectrophotometric and chemical evolution of galaxies and briefly discuss the formation of star clusters and Tidal Dwarf Galaxies in this context.Comment: 22 pages, 4 figs, Highlight Talk to appear in {\sl New Astrophysical Horizons}, Rev. Mod. Astron. {\bf 13

Predicting Spectral Properties of DLA Galaxies

Comparison of our chemically consistent models for spiral galaxies with observed DLA abundances shows that at high redshift DLA galaxies may well be the progenitors of normal spiral disks of all types from Sa through Sd. Towards lower redshifts z </= 1.5 however, early type spirals drop out of DLA samples due to low gas or/and high dust content. We use the spectrophotometric aspects of our unified spectral, chemical, and cosmological evolution models to predict expected luminosities in different bands for DLA galaxies at various redshifts and compare to the few optical identifications available.Comment: 5 pages, using LAMUPHYS LaTeX macro Springer, version 1.0, ESO Workshop "Chemical Evolution from Zero to High Redshift

Chemically Consistent Evolution of Galaxies on Cosmological Timescales and the DLA Galaxy Population

We describe the evolution of galaxies in a chemically consistent way accounting for the increasing initial metallicity of successive generations of stars. The enrichment of various types of model galaxies is compared with Damped Ly$\alpha$ (= DLA) abundances over the redshift range from ${\rm z \sim 0}$ through ${\rm z > 4.4}$. We discuss properties and composition of the galaxy population giving rise to DLA absorption. Beyond evolution of individual galaxies a change is found in the composition of DLA galaxy samples from high to low redshift. Spectrophotometric properties are predicted for optical identifications of DLA galaxies.Comment: 4 pages, using moriond.sty, Proceedings of the XIXth Moriond Astrophysics Meeting `Building Galaxies: from the Primordial Universe to the Present', Les Arcs, March 199

Chemical Evolution of Spiral Galaxies from Redshift 4 to the Present

We use our unified chemical and spectrophotometric evolutionary synthesis code to describe galaxies of various Hubble types. With stellar evolutionary tracks and element yields for 5 different metallicities we follow the spectrophotometric evolution of composite stellar populations and the chemical evolution of ISM abundances in a chemically consistent way, i.e., accounting for the increasing initial metallicities of successive generations of stars. Evolutionary galaxy models are required to give agreement with template nearby galaxies of various Hubble types in terms of SEDs, stellar absorption indices or HII region abundances, respectively. Within the framework of a given cosmological model the redshift evolution of ISM abundances and abundance ratios is compared to damped Lyman $\alpha$ abundances. This provides information about the early star formation and nucleosynthesis history of the absorber galaxies and, at the same time, our models predict their spectral energy distributions. Optically identified DLA absorbers, with their spectral and chemical properties, provide, of course, the strongest constraints for the model parameters.Comment: 5 pages Latex, 2 POSTSCRIPT figures, using psfig and crckapb.sty To appear in the proceedings of IAU Symposium 187 `Cosmic Chemical Evolution', August 26-30, 1997, Kyoto, Japa

Multi-color observations of Young Star Clusters

We present a new set of evolutionary synthesis models of our GALEV code, specifically developed to include the gaseous emission of presently forming star clusters, in combination with an advanced tool to compare large model grids with multi-color broad-band observations of YSC systems. Tests and first applications are presented.Comment: 1 page, conference proceeding IAU General Assembly 2003, Sydney, Joint Discussion 0

Young star clusters: Progenitors of globular clusters!?

Star cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.Comment: 3 pages, 2 eps-figures, conference proceeding IAU General Assembly 2003, Sydney, Joint Discussion 1

Young star clusters: Clues to galaxy formation and evolution

Young clusters are observed to form in a variety of interacting galaxies and violent starbursts, a substantial number resembling the progenitors of the well-studied globular clusters in mass and size. By studying young clusters in merger remnants and peculiar galaxies, we can therefore learn about the violent star formation history of these galaxies. We present a new set of evolutionary synthesis models of our GALEV code specifically developed to include the gaseous emission of presently forming star clusters, and a new tool that allows to determine individual cluster metallicities, ages, extinction values and masses from a comparison of a large grid of model Spectral Energy Distributions (SEDs) with multi-color observations. First results for the newly-born clusters in NGC 1569 are presented.Comment: 2 pages, 1 ps-figure, conference proceeding IAU General Assembly 2003, Sydney, Symposium 21

Dwarf Galaxies of Tidal Origin -- Relevant for Cosmology ?

Evolutionary synthesis models for Tidal Dwarf Galaxies (TDGs) are presented that allow to have varying proportions of young stars formed in the merger-induced starburst and of stars from the merging spirals' disks. The specific metallicities as well as the gaseous emission of actively star forming TDGs are consistently accounted for. Comparison of models with observational data (e.g. Duc, this volume) gives information on the present evolutionary state and possible future luminosity evolution of TDGs. The redshift evolution of merger rates and of the gas content and metallicities of spiral galaxies are used to estimate the number of TDGs at various redshifts and to investigate their contribution to magnitude limited surveys.Comment: 4 pages Latex, using moriond.sty To appear in Dwarf Galaxies and Cosmology, eds. T. X. Thuan, C. Balkowski, V. Cayatte, J. Tran Thanh Van, Editions Fronti\`ere

On the Nature and Redshift Evolution of DLA Galaxies

We extend our spiral galaxy models that successfully describe nearby template spectra as well as the redshift evolution of CFRS and HDF spirals to include - in a chemically consistent way - the redshift evolution of a series of individual elements. Comparison with observed DLA abundances shows that DLAs might well be the progenitors of present-day spiral types Sa through Sd. Our models bridge the gap between high redshift DLA and nearby spiral HII region abundances. The slow redshift evolution of DLA abundances is a natural consequence of the long SF timescales for disks, the scatter at any redshift reflects the range of SF timescales from early to late spiral types. We claim that while at high redshift all spiral progenitor types seem to give rise to DLA absorption, towards low redshifts, the early type spirals seem to drop out of DLA samples due to low gas and/or high metal and dust content. Model implications for the spectrophotometric properties of the DLA galaxy population are discussed in the context of campaigns for the optical identifications of DLA galaxies both at low and high redshift.Comment: 8 pages, using kluwer LaTeX macro, Proceedings "The Evolution of Galaxies on Cosmological Timescales