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Galaxy Evolutionary Synthesis Models
help you understand your data on star clusters and galaxies from the early universe until today in terms of their relevant physical and chemical properties and their evolutionary state.


The following list is intended to give an impression of the manifold of projects that profit from our unique chemically consistent galaxy evolutionary synthesis code.

We are always looking for new collaborators. So if you are interested in any of the projects listed below and considering using GALEV for the analysis, or have an idea on how GALEV can be used for a project not listed below, we would be more than happy to hear from you. Just write us an email to contact at

Star Formation, Chemical Enrichment and Mass Assembly Histories of Galaxies: The Observational Cosmology Approach

R. Kotulla, U. Fritze
Comparison of
    spectroscopic and photometric redshifts
In this project we aim at deriving - for the first time simultaneously -
1. the Star Formation Histories (SFHs)
2. the Mass Assembly Histories (MAHs), and
3. the Chemical Enrichment Histories (CEHs)
of galaxies from the highest redshifts to the present time using two complemen- tary approaches (also see below). In the Observational Cosmology approach we analyse the evolution of the integrated light of galaxies over a wide range in wavelengths and over the full redshift range from the earliest epochs to the present.
Most previous results dealing with the SFHs, MAHs and CEHs of galaxies have been based on spectroscopic observations. Notwithstanding its merits, the spectroscopic approach is biased towards the most luminous - certainly not the typical - galaxies at any redshift, and limited to the actively star-forming ones which offer emission lines for redshift determinations. Instead, we use an approach based on multi-wavelength photometry of galaxies, analysed with dedicated tools and interpreted by comparing with results from our chemically consistent evolutionary synthesis code GALEV.

Star Formation, Chemical Enrichment and Mass Assembly
Histories of Galaxies: The Astro-Archaeological Approach

R. Kotulla, U. Fritze
in collaboration with P. Anders, R. de Grijs
Color-Color plot for SSPs of
      different metallicities
In the Astro-Archaeological approach we use star clusters, their ages and chemical abundances in local galaxies of various types/masses as fossil records of their parent galaxy SFH, CEH and MAH.
The Astro-Archaeological is an entirely new one. Its power has only recently been realised, partly thanks to our involvement. It has become clear that
1. star cluster formation is a major mode of all active star formation and the dominant mode in the strongest starbursts, i.e. those accompanying mergers of gas-rich spirals where, together with short-lived, low-mass clusters significant populations of long-lived, high-mass clusters are formed from gas pre-enriched in their parent galaxies, and that
2. since star clusters can be analysed one-by-one, after careful background subtraction, the age distribution of a population of clusters and their chemical abundances yield direct information about the (violent) star formation and chemical enrichment history, over cosmological time scales, of their parent galaxy.
read more

Young Star Cluster Systems:
Star Formation vs. Star Cluster Formation, violent vs normal SF

U. Fritze, P. Anders (Utrecht)
in collaboration with R. de Grijs, Sheffield; S. Larsen, H. Lamers, Utrecht;
Rich populations of massive, compact, long-lived star clusters (SCs) form in starbursts resulting from mergers of massive gas-rich galaxies (cf. Schweizer 2002, 2003, Fritze & Burkert 1995).
A good fraction of those SCs with radii and masses in the range of those  observed for globular cluster (GCs) are expected to survive for many Gyrs and turn into objects similar to GCs (Goudfrooij et al. 2001, 2004, Fritze 2004). These "secondary GCs" will stand out from GCs formed in the early universe, by their younger ages and enhanced metallicities since they were formed out of gas which was pre-enriched in spiral galaxies before a merger event. Provided their ages and metallicities can be disentangled, they will give testimony of the merger, of the epoch when it happened, and of the properties of the merging galaxies.
read more

Galaxy transformation in clusters

Ralf Kotulla, Uta Fritze, A. Falkenberg (Göttingen);
in collaboration with: P. Woudt, P. Kotze, Univ. Cape Town; T. Lisker, H. T. Meyer, Univ. Heidelberg; E. Brinks, T. Scott (UH).
B/W image of the Coma
      Galaxy Cluster
Galaxy populations in the field and in clusters are markedly different, and yet clusters keep forming and growing by the continuous infall of field galaxies. The field galaxy population is rich in spirals like our Milky Way with active star formation (=SF), while the inner parts of rich galaxy clusters are dominated by S0 and dwarf galaxies without any gas and SF. A variety of processes have been proposed, and indeed observed to work in individual cases, that can transform gas-rich SFing field spirals into gas-poor passive cluster S0s or dwarfs. Some processes are due to interactions of the infalling spirals with the hot and dense intracluster gas observed in X-rays in the central regions of rich clusters (ram pressure stripping/sweeping), others have to do with the frequent high-speed encounters between galaxies (harassment), or with the increased galaxy merger rate within infalling groups. All processes occur preferentially at different distances from the cluster center, probably have different timescales and transition stages (blue/red E+A/Hdelta-strong galaxies), and, partly, different end products (S0s, dEs, dSphs).
read more

Pixel-by-pixel analysis of starburst galaxies

R. Kotulla, U. Fritze
in collaboration with: J. Gallagher, Madison; R. de Grijs, Sheffield
Image of the Tadpole galaxy
         with overlaid ages
Pixel-by-pixel analyses of the ACS Early Release data for the Tadpole and Mice interacting galaxy systems with GALEV models have revealed the spatial   distribution of stars of various ages and, surprisingly, found star formation (SF) and even star cluster formation (SCF) all along the ~200 kpc long tidal tails. Other instances of extragalactic SF are found in deep H-alpha imaging (Ferguson+98), in the UV with Galex (Thilker+05). In collaboration with J. Gallagher (Madison) and E. Wehner (Canada) we investigate SF in low surface brightness structures around galaxies, the extremely low SFR density regime (Wehner+06).
read more

Tidal Dwarf Galaxies

in collaboration with: P.-A. Duc (Paris); P. Weilbacher (Potsdam); Elias Brinks (Hertfordshire)
The Dentist chair, showing
      the slit positions
An intriguing feature of strong galaxy interactions is the formation of so-called Tidal Dwarf Galaxies (TDGs) in the extended tidal tails thrown out of spiral disks. P. Weilbacher analysed the first sample of TDGs in his Diploma and PhD theses in Göttingen. Combining optical and NIR data, he investigated the ratio of stars formed in situ and stars inherited from the spiral and could, for the first time, show by means of VLT tilted slit commissioning spectra that some of these systems already show rotation, i.e. dynamical decoupling from their surrounding tail, in combination with infall (still in formation) (Weilbacher+00, 01, 02, 03). The cosmological implications of this recycling mode of dwarf galaxy formation still going on in the local universe are being explored in collaboration with P. Weilbacher (now Potsdam).
read more

QSO Absorption Lines, Attenuation and the Cosmic Baryon Content

in collaboration with: T. Tepper Garcia, P. Richter, Potsdam
Two QSO spectra showing the Lyman-Alpha forest
During his PhD in Göttingen, T. Tepper Garcia has investigated the stochastic effects in the attenuation by intergalactic HI, mostly in the form of Lyman-alpha clouds, on the luminosities and colours of distant galaxies. Using recent observed distributions for the number densities of clouds as a function of redshift, their column densities and Doppler parameters, he performed Monte Carlo realisations  of thousands of lines of sight with hundreds to thousands of Lyman-alpha clouds each. His results for the 1-, 2-, 3-sigma scatter around the mean attenuation are included in the GALEV models and used in our interpretation of high-z galaxies.
read more

Cosmo-chemical Evolution of Galaxies

U. Fritze
Sketch showing the origin of the Lyman Alpha forest
Several years ago, we have used our chemically consistent GALEV models for the chemical evolution of galaxies in terms of a large number of individual elements in comparison to observed abundances of Damped Ly-alpha Absorbers (DLAs) in the redshift range from z>4 to z~1.5. Our results indicated that the DLA abundances and their redshift evolution could well be explained by our spiral galaxy models, i.e. these DLAs could be the high-z progenitors of present-day spirals (Lindner & Fritze 99). We predicted that these galaxies should already be very massive at these high redshifts with at least half of their present mass, albeit largely in the form of gas, and we also predicted very faint luminosities.
read more

Resolved stellar populations vs. integrated light:
Accuracies and limitations in the recovery of Star Formation Histories

T. Lilly, U. Fritze
in collaboration with D. Alloin, ESO Santiago; P. Demarque, Yale; C. Gallart, IAC; S. Yi, Oxford/Korea;
     of an observed CMD with GALEV
An important methodological study - that is only possible with GALEV as the only evolutionary synthesis code that can describe the evolution of a resolved stellar population in terms of CMDs and, at the same time, the evolution of its integrated light - is the comparison to what accuracy and how far back in time the SFH of a composite stellar population can be reconstructed using these different approaches. While CMD analyses are limited to low stellar density systems in the local group, integrated light studies are the only approach to SFHs of distant galaxies.
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