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

Wu, Po-FengPo-FengWuVAN DER WEL, ARJENARJENVAN DER WELGALLAZZI, Anna RitaAnna RitaGALLAZZIBezanson, RachelRachelBezansonPacifici, CamillaCamillaPacificiStraatman, CarolineCarolineStraatmanFranx, MarijnMarijnFranxBarišić, IvanaIvanaBarišićBell, Eric F.Eric F.BellBrammer, Gabriel B.Gabriel B.BrammerCalhau, JoaoJoaoCalhauChauke, PriscillaPriscillaChaukevan Houdt, JoshaJoshavan HoudtMaseda, Michael V.Michael V.MasedaMuzzin, AdamAdamMuzzinRix, Hans-WalterHans-WalterRixSobral, DavidDavidSobralSpilker, JustinJustinSpilkervan de Sande, JesseJessevan de Sandevan Dokkum, PieterPietervan DokkumWild, VivienneVivienneWild2020-10-232020-10-2320180004-637Xhttp://hdl.handle.net/20.500.12386/27958Drawing 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.STAMPAenStellar Populations of over 1000 z ̃ 0.8 Galaxies from LEGA-C: Ages and Star Formation Histories from D n 4000 and HδArticle10.3847/1538-4357/aab0a62-s2.0-85044045343000427362600001https://iopscience.iop.org/article/10.3847/1538-4357/aab0a62018ApJ...855...85WFIS/05 - ASTRONOMIA E ASTROFISICA