Stellar populations of over one 1000 z ∼ 0.8 galaxies from LEGA-C : ages and star formation histories from Dn4000 and Hδ
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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.
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
© 2018 The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://doi.org/10.3847/1538-4357/aab0a6
DescriptionFunding: VW acknowledges funding from the ERC (starting grant SEDmorph, PI. Wild).
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