Dependence of Star Formation Activity On Stellar Mass and Environment From the Redshift One LDSS-3 Emission Line Survey (ROLES)

TL;DR

This study investigates how star formation rates depend on stellar mass and environment at redshift around 1, revealing that low-mass galaxies in denser regions have higher star formation activity, contrasting with local universe trends.

Contribution

It provides new observational evidence that environment influences star formation in low-mass galaxies at z~1, highlighting the evolving role of density in galaxy evolution.

Findings

Low-mass galaxies show increased SFR with higher density at z~1.

Star formation correlates strongly with stellar mass, less so with environment at low redshift.

Environmental effects on star formation are more significant for low-mass galaxies at z~1.

Abstract

Using the sample from the \it Redshift One LDSS3 Emission line Survey \rm (ROLES), we probe the dependence of star formation rate (SFR) and specific star formation rate (sSFR) as a function of stellar mass $M_*$ and environment as defined by local galaxy density, in the CDFS field. Our spectroscopic sample consists of 312 galaxies with $K_{AB}<24$, corresponding to stellar mass $\log(M_*/M_{\sun})>8.5$, and with [OII] derived star-formation rates SFR$>0.3M_{\sun}/$yr, at $0.889\leq z \leq 1.149$. The results have been compared directly with the Sloan Digital Sky Survey Stripe 82 sample at $0.032\leq z \leq 0.05$. For star-forming galaxies, we confirm that there is little correlation between SFR and density at $z\sim 0$. However, for the lowest mass galaxies in our $z\sim 1$ sample, those with $\log(M_*/M_{\sun})<10$, we find that both the median SFR and specific SFR {\it increase} significantly with increasing local density. The "downsizing" trend for low mass galaxies to be quenched progressively later in time appears to be more pronounced in moderately overdense environments. Overall we find that the evolution of star-formation in galaxies is most strongly driven by their stellar mass, with local galaxy density playing a role that becomes increasingly important for lower mass galaxies.