Stellar Populations of over 1000 z ∼ 0.8 Galaxies from LEGA-C: Ages and Star Formation Histories from Dn4000 and Hδ

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 break (Dn4000) and Balmer absorption line strengths (probed by Hδ) from 1019 high-quality spectra of...

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Bibliographic Details
Published in:The Astrophysical journal 2018-03, Vol.855 (2)
Main Authors: Wu, Po-Feng, Wel, Arjen van der, Gallazzi, Anna, Bezanson, Rachel, Pacifici, Camilla, Straatman, Caroline, Franx, Marijn, Bariši, Ivana, Bell, Eric F., Brammer, Gabriel B., Calhau, Joao, Chauke, Priscilla, Houdt, Josha van, Maseda, Michael V., Muzzin, Adam, Rix, Hans-Walter, Sobral, David, Spilker, Justin, Sande, Jesse van de, Dokkum, Pieter van, Wild, Vivienne
Format: Article
Language:English
Subjects:
Absorption
Astronomical models
Astrophysics
Galactic evolution
Galaxies
galaxies: evolution
galaxies: high-redshift
galaxies: stellar content
Galaxy distribution
Signal to noise ratio
Spectroscopy
Spectrum analysis
Star & galaxy formation
Star formation
Stars & galaxies
Stellar age
Stellar mass
Stellar populations
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Summary: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 break (Dn4000) and Balmer absorption line strengths (probed by Hδ) from 1019 high-quality spectra of z = 0.6-1.0 galaxies with M* = 2 × 1010M to 3 × 1011M . 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 Dn4000-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 × 1010M , we see a bimodal Dn4000-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 × 1011M 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 >1011M 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 Dn4000, implying larger short-term variations in star formation activity.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aab0a6