Stellar populations of over one 1000 z ∼ 0.8 galaxies from LEGA-C : ages and star formation histories from Dn4000 and Hδ
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 4000Å 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 x 1010M⊙−3×1011M⊙. Our analysis serves as a first illustration of the power of high-resolution, high-S/N 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 x 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 x 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 odd with pure passive evolution given a difference in lookback time of > 5 Gyr; younger galaxies must grow to > 1011M⊙ in the meantime, and/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.
Citation
Wu , P-F , van der Wel , A , Gallazzi , A , Bezanson , R , Pacifici , C , Straatman , C , Franx , M , Barišić , I , Bell , E F , Brammer , G B , Calhau , J , Chauke , P , van Houdt , J , Maseda , M V , Muzzin , A , Rix , H-W , Sobral , D , Spilker , J , van de Sande , J , van Dokkum , P & Wild , V 2018 , ' Stellar populations of over one 1000 z ∼ 0.8 galaxies from LEGA-C : ages and star formation histories from D n 4000 and Hδ ' , Astrophysical Journal , vol. 855 , no. 2 , 85 . https://doi.org/10.3847/1538-4357/aab0a6
Publication
Astrophysical Journal
Status
Peer reviewed
ISSN
0004-637XType
Journal article
Description
Funding: VW acknowledges funding from the ERC (starting grant SEDmorph, PI. Wild).Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.