The Star Formation Rate-Density Relation at 0.6<z<0.9 and the Role of Star Forming Galaxies
Abstract
We study the star formation rates (SFRs) of galaxies as a function of local galaxy density at 0.6<z<0.9. We used a low-dispersion prism in IMACS on the 6.5 m Baade (Magellan I) telescope to obtain spectra and measured redshifts to a precision of sigmaz/(1+z) 1% for galaxies with z<23.3 AB mag. We utilized a stellar mass-limited sample of 1000 galaxies above M=1.8x1010 Msun to conduct our analysis. With SFRs measured from (1) Spitzer MIPS 24 µm imaging, (2) SED fitting, and (3) [OII] 3727A emission, we find the median specific SFR (SSFR) and SFR to decline with increasing local galaxy density by roughly an order of magnitude, from the low-density field to the cores of groups and a cluster. We find a similar decline even after removing the cluster environment from our sample. Galaxies in clusters and groups at these redshifts therefore have lower overall star formation (SF) activity than galaxies in the field, as is the case at z 0. Using the rest-frame U-V and V-J colors to select star-forming galaxies (SFGs), including both unobscured (i.e., blue) and obscured (i.e., red), we find the SSFRs of SFGs to decline with increasing density by factors of 2-5 depending on the SFR indicator. The declining SFRs of SFGs with density is paralleled by a decline in the median AV, providing indirect evidence that the cold gas that fuels future SF is being removed from galaxies in higher density environments. The order of magnitude decline in the SSFR-density relation at 0.6<z<0.9 is therefore driven by a combination of declining SFRs of SFGs as well as a changing mix of SFGs and quiescent galaxies.
- Publication:
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American Astronomical Society Meeting Abstracts #217
- Pub Date:
- January 2011
- Bibcode:
- 2011AAS...21723306P