MOSFIRE Spectroscopy of Quiescent Galaxies at 1.5 < z < 2.5. II. Star Formation Histories and Galaxy Quenching

We investigate the stellar populations for a sample of 24 quiescent galaxies at 1.5 < z < 2.5 using deep rest-frame optical spectra obtained with Keck MOSFIRE. By fitting templates simultaneously to the spectroscopic and photometric data and exploring a variety of star formation histories, we...

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Bibliographic Details
Published in:The Astrophysical journal 2019-03, Vol.874 (1), p.17
Main Authors: Belli, Sirio, Newman, Andrew B., Ellis, Richard S.
Format: Article
Language:English
Subjects:
Astrophysics
Emission lines
Galactic evolution
Galaxies
galaxies: evolution
galaxies: formation
galaxies: high-redshift
galaxies: stellar content
Photometry
Quenching
Red shift
Spectroscopy
Spectrum analysis
Star & galaxy formation
Star formation
Star formation rate
Stars & galaxies
Stellar age
Stellar populations
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Summary:We investigate the stellar populations for a sample of 24 quiescent galaxies at 1.5 < z < 2.5 using deep rest-frame optical spectra obtained with Keck MOSFIRE. By fitting templates simultaneously to the spectroscopic and photometric data and exploring a variety of star formation histories, we obtain robust measurements of median stellar ages and residual levels of star formation. After subtracting the stellar templates, the stacked spectrum reveals the H and [N ii] emission lines, providing an upper limit on the ongoing star formation rate of 0.9 0.1 M yr−1. By combining the MOSFIRE data with our sample of Keck LRIS spectra at lower redshift, we analyze the quiescent population at 1 < z < 2.5 in a consistent manner. We find a tight relation (with a scatter of 0.13 dex) between the stellar age and the rest-frame U − V and V − J colors, which can be used to estimate the age of quiescent galaxies, given their colors. Applying this age-color relation to large photometric samples, we are able to model the number density evolution for quiescent galaxies of various ages. We find evidence for two distinct quenching paths: a fast quenching that produces compact post-starburst systems and a slow quenching of larger galaxies. Fast quenching accounts for about a fifth of the growth of the red sequence at z ∼ 1.4 and half at z ∼ 2.2. We conclude that fast quenching is triggered by dramatic events, such as gas-rich mergers, while slow quenching is likely caused by a different physical mechanism.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab07af