Stellar Populations of over 1000 z ̃ 0.8 Galaxies from LEGA-C: Ages and Star Formation Histories from D n 4000 and Hδ

Journal
Date Issued
2018
Author(s)
Wu, Po-Feng
•
•
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Bezanson, Rachel
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Pacifici, Camilla
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Straatman, Caroline
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Franx, Marijn
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Barišić, Ivana
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Bell, Eric F.
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Brammer, Gabriel B.
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Calhau, Joao
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Chauke, Priscilla
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van Houdt, Josha
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Maseda, Michael V.
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Muzzin, Adam
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Rix, Hans-Walter
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Sobral, David
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Spilker, Justin
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van de Sande, Jesse
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van Dokkum, Pieter
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Wild, Vivienne
DOI
Abstract
Drawing from the LEGA-C data set, we present the spectroscopic view of the stellar population across a large volume- and mass-selected sample of galaxies at large look-back time. We measure the 4000 Å break (D n 4000) and Balmer absorption line strengths (probed by Hδ) from 1019 high-quality spectra of z = 0.6-1.0 galaxies with M * = 2 × 1010 M ☉ to 3 × 1011 M ☉. Our analysis serves as a first illustration of the power of high-resolution, high signal-to-noise ratio continuum spectroscopy at intermediate redshifts as a qualitatively new tool to constrain galaxy formation models. The observed D n 4000-EW(Hδ) distribution of our sample overlaps with the distribution traced by present-day galaxies, but z ̃ 0.8 galaxies populate that locus in a fundamentally different manner. While old galaxies dominate the present-day population at all stellar masses >2 × 1010 M ☉, we see a bimodal D n 4000-EW(Hδ) distribution at z ̃ 0.8, implying a bimodal light-weighted age distribution. The light-weighted age depends strongly on stellar mass, with the most massive galaxies >1 × 1011 M ☉ being almost all older than 2 Gyr. At the same time, we estimate that galaxies in this high-mass range are only ̃3 Gyr younger than their z ̃ 0.1 counterparts, at odds with purely passive evolution given a difference in look-back time of >5 Gyr; younger galaxies must grow to >1011 M ☉ in the meantime, or small amounts of young stars must keep the light-weighted ages young. Star-forming galaxies at z ̃ 0.8 have stronger Hδ absorption than present-day galaxies with the same D n 4000, implying larger short-term variations in star formation activity.
Volume
855
Issue
2
Start page
85
Uri
Url
Issn Identifier
0004-637X
Ads BibCode
2018ApJ...855...85W
Rights
open.access
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