Bibcode
Twite, Jonathan W.; Conselice, Christopher J.; Buitrago, Fernando; Noeske, Kai; Weiner, Benjamin J.; Acosta-Pulido, J. A.; Bauer, Amanda E.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 420, Issue 2, pp. 1061-1078.
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2
2012
Citations
17
Refereed citations
17
Description
We present a near-infrared spectroscopic study of a stellar mass
selected sample of galaxies at z˜ 1 utilizing the Long-slit
Intermediate Resolution Infrared Spectrograph multi-object spectrograph
on the William Herschel Telescope. We detect continuum, and the Hα
line for our sample, which is one of the better direct tracers of star
formation in external galaxies. We spectroscopically measure the
Hα emission from 41 massive (M* > 1010.5
M&sun;) galaxies taken from the POWIR Survey with
spectroscopic redshifts 0.4 < zspec < 1.4. We correct
our Hα fluxes for dust extinction by using multiwavelength data,
and investigate star formation rate (SFR) trends with mass and colour.
We find a drop in the fraction of massive galaxies with M*
> 1011 M&sun; which are detected in Hα
emission at z < 0.9. We furthermore find that the fraction of
galaxies with Hα emission drops steadily and significantly with
redder (U-B) colours at z˜ 1, and that the specific SFR (SSFR)
drops with increasing (U-B) colour for galaxies at all masses. By
investigating the SFR-mass relation, we find that the SFR is roughly
constant with mass, in possible contrast to previous work, and that the
SSFR is lower in the most massive galaxies. The scatter in the SFR
versus mass relationship is very small for those systems with ongoing
star formation, which suggests that star formation in the most massive
galaxies at z˜ 1 shuts off rather abruptly over <1 Gyr, without
an obvious gradual decline. We furthermore investigate the SFR as a
function of (U-B) colour divided into different mass bins, revealing a
tracer of the epoch of transition from star forming to passive, as a
form of star formation 'downsizing'. This suggests that the shut off of
star formation occurs before the change in a galaxy's colour. We find
that galaxy stellar mass is the primary driving mechanism behind the
star formation history for these galaxies and discuss several possible
mechanisms for regulating this process.
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