Galaxy Formation and Evolution - IAP Research Group

Date

Subject

Presented by

7 february 2013

Star-forming galaxies as seen through emission lines

In my talk, I first present star-forming (SF) galaxies in the SDSS that show nebular He II 4686 emission. I use this He II emitters to investigate the origin of this high ionization line in SF galaxies where the ionizing continua come from massive stars. I show that He II 4686 is not associated with Wolf-Rayet (WR) stars in most of He II emitters at low metallicities while current models for massive stars predict that WR stars are the main sources of ionization. I discuss possible explanations for this discrepancy.

In the second part of my talk, I compare the physical properties of SF galaxies in the local and high-redshift (high-z) Universe. To do this, I use local analogs of 14 high-z galaxies in the SDSS. These analogs have comparable specific star formation (sSFR) rates or EW(Ha) and masses to that of high-z SF galaxies. I show the ionization parameters for these high-z galaxies are higher than that of their low-z analogs. This implies that high-z SF galaxies have higher electron densities than low-z analogs. From this, I conclude that star formation takes place in denser HII regions at high-z.

Maryam Shirazi
Sterrewacht Leiden, Netherlands

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