Probing Galaxy Evolution in Massive Clusters Using ACT and DES: Splashback as a Cosmic Clock
Authors: Adhikari Susmita , Shin Tae-hyeon , Jain Bhuvnesh , Hilton Matt , Baxter Eric , Chang Chihway , Wechsler Risa H. , Battaglia Nick , Bond J. Richard , Bocquet Sebastian , Choi Steve K. , DeRose Joseph , Devlin Mark , Dunkley Jo , Evrard August E. , Ferraro Simone , Hill J. Colin , Hughes John P. , Gallardo Patricio A. , Lokken Martine , MacInnis Amanda , Madhavacheril Mathew S. , McMahon Jeffrey , Nati Frederico , Newburgh Laura B. , Niemack Michael D. , Page Lyman A. , Palmese Antonella , Partridge Bruce , Rozo Eduardo , Rykoff Eli , Salatino Maria , Schillaci Alessandro , Sehgal Neelima , Sifón Cristóbal , To Chun-Hao , Wollack Ed , Wu Hao-Yi , Xu Zhilei , Aguena Michel , Allam Sahar , Amon Alexandra , Annis James , Avila Santiago , Bacon David , Bertin Emmanuel , Bhargava Sunayana , Brooks David , Burke David L. , Rosell Aurelio C. , Kind Matias Carrasco , Carretero Jorge , Castander Francisco Javier , Choi Ami , Costanzi Matteo , da Costa Luiz N. , Vicente Juan De , Desai Shantanu , Diehl Thomas H. , Doel Peter , Everett Spencer , Ferrero Ismael , Ferté Agnès , Flaugher Brenna , Fosalba Pablo , Frieman Josh , García-Bellido Juan , Gaztanaga Enrique , Gruen Daniel , Gruendl Robert A. , Gschwend Julia , Gutierrez Gaston , Hartley Will G. , Hinton Samuel R. , Hollowood Devon L. , Honscheid Klaus , James David J. , Jeltema Tesla , Kuehn Kyler , Kuropatkin Nikolay , Lahav Ofer , Lima Marcos , Maia Marcio A. G. , Marshall Jennifer L. , Martini Paul , Melchior Peter , Menanteau Felipe , Miquel Ramon , Morgan Robert , L. C. Ogando Ricardo , Paz-Chinchón Francisco , Malagón Andrés Plazas , Sanchez Eusebio , Santiago Basilio , Scarpine Vic , Serrano Santiago , Sevilla-Noarbe Ignacio , Smith Mathew , Soares-Santos Marcelle , Suchyta Eric , E. C. Swanson Molly , Varga Tamas N. , Wilkinson Reese D. , Zhang Yuanyuan , Austermann Jason E. , Beall James A. , Becker Daniel T. , Denison Edward V. , Duff Shannon M. , Hilton Gene C. , Hubmayr Johannes , Ullom Joel N. , Lanen Jeff Van , Vale Leila R. ,   (DES Collaboration),   (ACT Collaboration)
Published: December 2021

Abstract
We measure the projected number density profiles of galaxies and the splashback feature in clusters selected by the Sunyaev–Zel’dovich effect from the Advanced Atacama Cosmology Telescope (AdvACT) survey using galaxies observed by the Dark Energy Survey (DES). The splashback radius is consistent with CDM-only simulations and is located at

2.4

−
0.4

+
0.3

Mpc

h

−
1

. We split the galaxies on color and find significant differences in their profile shapes. Red and green-valley galaxies show a splashback-like minimum in their slope profile consistent with theory, while the bluest galaxies show a weak feature at a smaller radius. We develop a mapping of galaxies to subhalos in simulations and assign colors based on infall time onto their hosts. We find that the shift in location of the steepest slope and different profile shapes can be mapped to the average time of infall of galaxies of different colors. The steepest slope traces a discontinuity in the phase space of dark matter halos. By relating spatial profiles to infall time, we can use splashback as a clock to understand galaxy quenching. We find that red galaxies have on average been in clusters over 3.2 Gyr, green galaxies about 2.2 Gyr, while blue galaxies have been accreted most recently and have not reached apocenter. Using the full radial profiles, we fit a simple quenching model and find that the onset of galaxy quenching occurs after a delay of about a gigayear and that galaxies quench rapidly thereafter with an exponential timescale of 0.6 Gyr.