The Characteristic Star Formation Histories of Galaxies from z~2-7

Colloquium: Astronomy Colloquia | September 27 | 4 p.m. | 2 LeConte Hall

Speaker/Performer: Naveen Reddy, UC Riverside

Sponsor: Department of Astronomy

We use a large spectroscopic sample of L* galaxies at redshifts 1.5 < z < 3.4 with Keck, Hubble, and Spitzer observations, to study the average star formation history of galaxies at z~2. We first perform a detailed comparison between the bolometric SFRs of z~2 galaxies and those obtained from SED-fitting. This comparison suggests that exponentially-declining models are, in general, a poor representation of the star formation histories at z~2. Taking into account a number of systematic biases, we find a near unity relationship between SFR and stellar mass for z~2 galaxies. The median specific SFR of our sample, when placed in context with the median specific SFRs found for higher redshift dropout samples, suggests a scenario where SFRs rise roughly exponentially with time. We find that the net cold gas accretion rate, as inferred from the specific SFR and the K-S relation, is typically 2-3 times larger than the SFR at z>4. However, if we evolve to higher redshift the star formation histories and the masses of the halos that are expected to host L* galaxies at z~2, then we find that 4 actually contribute to star formation at those epochs. These results highlight the relative inefficiency of star formation even at early cosmic times when galaxies were first assembling.

Event Contact: rhelgens@astro.berkeley.edu, 510-642-5275