Probing Star Formation in Galaxies at z ≈ 1 via a Giant Metrewave Radio Telescope Stacking Analysis

We report deep Giant Metrewave Radio Telescope (GMRT) 610 MHz continuum imaging of four subfields of the DEEP2 Galaxy Redshift Survey. We stacked the radio emission in the GMRT images from a near-complete (absolute blue magnitude M _B ≤ -21) sample of 3698 blue star-forming galaxies with redshifts 0.7 ≲ z ≲ 1.45 to detect (at ≈17σ significance) the median rest-frame 1.4 GHz radio continuum emission of the sample galaxies. The stacked emission is unresolved, with a rest-frame 1.4 GHz luminosity of L _1.4GHz = (4.13 ±0.24) ×10²² W Hz^-1. We used the local relation between total star formation rate (SFR) and 1.4 GHz luminosity to infer a median total SFR of (24.4 ±1.4) M _o yr^-1 for blue star-forming galaxies with M _B ≤ -21 at 0.7 ≲ z ≲ 1.45. We detect the main-sequence relation between SFR and stellar mass, M _∗, obtaining SFR = (13.4 ± 1.8) ×[(M _∗/10¹⁰ M _o)]^0.73±0.09 M _o yr^-1; the power-law index shows no change over z ≈ 0.7-1.45. We find that the nebular line emission suffers less extinction than the stellar continuum, contrary to the situation in the local universe; the ratio of nebular extinction to stellar extinction increases with decreasing redshift. We obtain an upper limit of 0.87 Gyr to the atomic gas depletion time of a subsample of DEEP2 galaxies at z ≈ 1.3; neutral atomic gas thus appears to be a transient phase in high-z star-forming galaxies.