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The Star Formation and Enrichment Histories of Galaxies

Final Report Summary - SFEHG (The Star Formation and Enrichment Histories of Galaxies)

The objective of the project SFEHG is to carry out research in astronomy, specifically on the star formation and enrichment histories of galaxies. This means studying the populations of stars they contain in order to derive their ages and element abundances. As our Milky Way is a galaxy and as our sun is a star, we thus study the origin of our cosmological habitat. Some of the research is being carried out relying on the Calar Alto Legacy Integral Field Area Survey (CALIFA), which uses a state of the art technique called imaging spectroscopy to obtain information on the galaxies under study. The technique is particularly useful because it allows to derive physical quantities such as velocities, or abundances of heavy elements for many points in a galaxy. This is in contrast to earlier studies, which had to treat galaxies as a single entity due to observational restrictions. During this funding period the paper describing the sample of galaxies used in CALIFA has been written. In summary, this paper states that the CALIFA sample is useful to describe the galay population in general, thus fulfilling one of the main requirements to be able to use CALIFA for learning about galaxy evolution. Much work has also gone into understanding and summarizing the results of CALIFA for a wide audience of astronomers in Europe, Australia and the US (ca. 20 talks given at different occasions).

Another significant area of research being carried out has concentrated on providing information on distant galaxies that would be detailed enough to allow comparison to the Milky Way. Specifically, the enrichment of material in galaxies with time can be studied in the Milky Way on a star-by-star basis. Distant galaxies cannot be resolved into single stars so the same analysis is not possible. However, we have now shown that one can obtain information on subpopulations of stars within distant galaxies from the integrated spectropscoy. Comparison to the Milky Way then shows that massive galaxies grow in a way that is fundamentally different. While in the Milky Way, subsequent generations of stars are made out of the gas reservoir of the Galaxy, in massive galaxies, the stars being added have no relaton to the stars already present. They have been added by merging of smaller, independent galaxies into the already present massive galaxy. Following onto this work, we have been able to use the same data to extend our knowledge on the stars that create heavy elements in galaxies. With precisely determined ages and element abundances in those massive galaxies, we were able to determine on what timescale supernova explosions occur after the creation of a new stellar generation.

Method development is a more long term activity, but in particular the method of spectroscopy surface brightness fluctuations and methods to compare simulations to actual observations have been improved and will lead to results in the next years.
At the host institution (AIP) one bachelor student and three PhD students work in the fellows group, with one bachelor and one master thesis already successfully defended. Also, two undergraduate students were hired as research assistants, one of whom has found a position in industry based on the skills learned at AIP. During the funding period the fellow has transited from a normal postdoc position to a permanent staff position, in accordance with the goals of the Career Integration Grant.
Several outreach activities were undertaken, in particular, an outreach image for the CALIFA survey was created and retweeted, shared on facebook and just generally acknowledged by the wide astronomical community. It is available from