Abstract
We investigate the relation between star formation rates and local galaxy environment for a stellar mass selected galaxy sample in the redshift range 1.5 < z < 3. We use near-infra-red imaging from an extremely deep Hubble Space Telescope survey, the GOODS-NICMOS Survey (GNS) to measure local galaxy densities based on the nearest neighbour approach, while star-formation rates are estimated from rest-frame UV-fluxes. Due to our imaging depth we can examine galaxies down to a colour-independent stellar mass completeness limit of log M\ast = 9.5 M\odot at z ~ 3. We find a strong dependence of star formation activity on galaxy stellar mass over the whole redshift range, which does not depend on local environment. The average star formation rates are largely independent of local environment apart from in the highest relative over-densities. Galaxies in over-densities of a factor of > 5 have on average lower star formation rates by a factor of 2 - 3, but only up to redshifts of z ~ 2. We do not see any evidence for AGN activity influencing these relations. We also investigate the influence of the very local environment on star-formation activity by counting neighbours within 30 kpc radius. This shows that galaxies with two or more close neighbours have on average significantly lower star formation rates as well as lower specific star formation rates up to z ~ 2.5. We suggest that this might be due to star formation quenching induced by galaxy merging processes.
Highlights
Observational studies have shown that up to half of the currently existing stellar mass was already in place by z ∼ 1 (Brinchmann & Ellis 2000; Drory et al 2004; Bundy et al 2006; Perez-Gonzalez et al 2008; Mortlock et al 2011)
In the following we investigate the relations between star formation rates (SFR), specific SFR (SSFR) and local density
We investigate the connection to the colour-density relation found in the same sample by Grutzbauch et al (2011b) and the effect of dust extinction (Section 3.2) as well as the role of stellar mass in the SFRdensity relation (Section 3.3)
Summary
Observational studies have shown that up to half of the currently existing stellar mass was already in place by z ∼ 1 (Brinchmann & Ellis 2000; Drory et al 2004; Bundy et al 2006; Perez-Gonzalez et al 2008; Mortlock et al 2011). It is clear that the main epoch of galaxy formation occurs at z > 1, but it is still unclear which processes trigger or suppress star formation, and what are the most important factors in determining galaxy properties Is it primarily galaxy mass (i.e. a galaxy’s gravitational potential), is it galaxy merging on local scales or is it the large scale environment that drives galaxy evolution?. Balogh et al (2004) show that the correlation between local density and star formation rate extends beyond the dense cluster environment to galaxies in the field They argue that shortterm local processes like galaxy merging at high redshift causes this dependence. This effect is observed in the cores of the most massive galaxy clusters as early as z ∼ 1.4 (Lidman et al 2008; Bauer et al 2011b), while in less massive clusters at similar redshifts star formation in the cluster core was found to be enhanced (Hayashi et al 2010; Tran et al 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
