About Galev

GALEV evolutionary synthesis models describe the spectral and chemical evolution of galaxies over cosmological timescales, i.e. from the onset of star formation (SF) to the present, in terms of time and redshift evolution for any cosmological model, including evolutionary and cosmological corrections, as well as attenuation by intergalactic hydrogen. With the stellar initial mass function (IMF) and the SFH of a model galaxy as the basic free parameters, GALEV follows the time and redshift evolution of its spectrum, luminosities and colours (currently UV - optical - NIR), gas content, stellar mass, gaseous and stellar abundances, SN rate, etc. The number of free parameters is kept to a minimum. GALEV doesn't yet incorporate the effects of galaxy dynamics, nor does it provide spatially resolved information.

What makes GALEV so special?

The prime feature that makes GALEV models stand out among other evolutionary synthesis models is the simultaneous treatment of the chemical evolution of the gas and the spectral evolution of the stellar content. This allows for what we call a chemically consistent treatment:

• use input physics (stellar evolutionary tracks, stellar yields and model atmospheres) for a large range of metallicities and consistently account for the increasing initial abundances of successive stellar generations.

• Accounting for stellar (sub-)populations with subsolar abundances is of prime importance in the context of low luminosity (and hence low metallicity) galaxies (late type galaxies and dwarfs) in the local universe. This becomes even more important when describing distant, younger and hence less chemically evolved galaxies (Shapley et al. 2005, Möller et al. 1997, Fritze 2001, Bicker et al. 2004).

• Lick stellar absorption indices as well as gaseous emission, both line and continuum, are included in GALEV as well. This is done in a consistent manner across the range of metallicities considered (Anders & Fritze 2003).

• SF indicators (emission lines, UV fluxes, etc.) have been carefully investigated on the basis of these models and significant metallicity dependencies have been found for all of them (Bicker & Fritze 2005, Weilbacher & Fritze 2001).

Comparison to models lacking the chemical consistency

Comparison with results obtained from earlier, i.e. not chemically consistent evolutionary synthesis models indicates that in many cases they 

1. overestimate SFRs by factors > 2
   
2. underestimate galaxy ages by factors > 2
   
3. overestimate photometric redshifts and misclassify galaxy types
   
4. overestimate photometric masses by factors of > 5.

The largest discrepancies are found for intrinsically low-luminosity and metal-poor galaxies.

More features

A cosmological model can be included to yield the redshift evolution of both gas phase abundances in terms of a large number of individual elements and of spectral properties including evolutionary and cosmological corrections as well as the effect of attenuation on the light from distant galaxies by intervening neutral hydrogen.

GALEV models can also include the effects of starbursts as well as of star formation truncation in galaxies, and, for the first time, follow their full evolution through post-starburst and post-star-formation phases.

Applications of GALEV models cover the range from local resolved stellar populations like star clusters and dwarf galaxies to analyses of observations of star clusters in integrated light in starburst galaxies to studies of the chemical and spectral properties of nearby galaxies of all kinds (including normal, dwarf, starbursting, and interacting ones, in the isolation, groups and clusters) all through studies of high-redshift galaxies.

Dust absorption is not yet included in the present set of GALEV models. Our first attempt to consistently include dust into the chemically consistent models for various types of galaxies accounting for the evolution in gas content and abundances and for geometry and projection effects (averaged over samples) gave promising results (M\"oller et al. 2001a, b). The effects of dust absorption and thermal reemission (stellar envelopes, PAH features, diffuse component) are currently being included in collaboration with C. Popescu (UCLan) and R. Tuffs (MPIK, Heidelberg) to extend the spectral range of the GALEV models into the mid- and far-IR.

A long-term project will couple GALEV with a cosmodynamical structure formation code including stars, gas, and Dark Matter, a SF criterium and appropriate feedback description. An early feasibility study for this is in Contardo et al. 1998.