Modelling and Interpretation
(Fritze and Kotulla)
What is 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.
What makes GALEV so special?
The prime feature that makes GALEV models stand out among other evolutionary synthesis models for galaxies 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:
- GALEV models 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 and
- account 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.
- 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.
Applications
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.
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. Models using solar metallicity input physics only significantly
- overestimate SFRs
- underestimate galaxy ages
- overestimate photometric redshifts and misclassify galaxy types
- overestimate photometric masses.
The chemically consistent treatment is of particular importance for the interpretation of Deep-Field data reaching down to intrinsically faint luminosities.
We use deep multiband imaging from a variety of Deep-Fields to study the Star Formation, Chemical Enrichment, and Mass Assembly Histories of huge numbers of individual galaxies.
Star Clusters and Globular Clusters in particular have recently been identified as prime tracers of their parent galaxies violent star formation history back to the very onset of star formation in the early universe. We have developed a powerful tool to largely automatically derive accurate star cluster ages, metallicities, (extinctions) and masses including their respective 1-sigma uncertainties from multiband imaging (UV through NIR).