The evolution of the specific star formation rate of massive galaxies to z ~ 1.8 in the E-CDFS

TL;DR

This study investigates how the specific star formation rate of massive galaxies evolves up to redshift 1.8 using multi-wavelength data, revealing that higher mass galaxies have lower rates and the fraction of quiescent galaxies decreases with redshift.

Contribution

It provides new insights into the evolution of star formation activity in massive galaxies up to z ~ 1.8 using combined UV and IR data.

Findings

Specific star formation rates increase with redshift roughly as (1+z)^5.

Higher mass galaxies have substantially lower specific star formation rates.

The fraction of quiescent massive galaxies decreases to about 19% at z ~ 1.8.

Abstract

We study the evolution of the star formation rate (SFR) of mid-infrared (IR) selected galaxies in the extended Chandra Deep Field South (E-CDFS). We use a combination of U-K GaBoDS and MUSYC data, deep IRAC observations from SIMPLE, and deep MIPS data from FIDEL. This unique multi-wavelength data set allows us to investigate the SFR history of massive galaxies out to redshift z ~ 1.8. We determine star formation rates using both the rest-frame ultraviolet luminosity from young, hot stars and the total IR luminosity of obscured star formation obtained from the MIPS 24 um flux. We find that at all redshifts the galaxies with higher masses have substantially lower specific star formation rates than lower mass galaxies. The average specific star formation rates increase with redshift, and the rate of incline is similar for all galaxies (roughly (1+z)^{n}, n = 5.0 +/- 0.4). It does not seem to be a strong function of galaxy mass. Using a subsample of galaxies with masses M_*> 10^11 M_sun, we measured the fraction of galaxies whose star formation is quenched. We consider a galaxy to be in quiescent mode when its specific star formation rate does not exceed 1/(3 x t_H), where t_H is the Hubble time. The fraction of quiescent galaxies defined as such decreases with redshift out to z ~ 1.8. We find that, at that redshift, 19 +/-9 % of the M_* > 10^11 M_sun sources would be considered quiescent according to our criterion.