The Inhomogeneous Reionization Times of Present-day Galaxies

Abstract

Today's galaxies experienced cosmic reionization at different times in different locations. For the first time, reionization (50% ionized) redshifts, z R , at the location of their progenitors are derived from new, fully coupled radiation-hydrodynamics simulation of galaxy formation and reionization at z>6, matched to N-body simulation to z=0. Constrained initial conditions were chosen to form the well-known structures of the local universe, including the Local Group and Virgo, in a (91 Mpc)3 volume large enough to model both global and local reionization. Reionization simulation CoDa I-AMR, by CPU-GPU code EMMA, used (2048) 3 particles and (2048) 3 initial cells, adaptively refined, while N-body simulation CoDa I-DM2048, by Gadget2, used (2048) 3 particles, to find reionization times for all galaxies at z=0 with masses M(z=0)10 8 M e . Galaxies with M z M 0 10 11  =  ( ) reionized earlier than the universe as a whole, by up to ∼500 Myr, with significant scatter. For Milky Way-like galaxies, z R ranged from 8 to 15. Galaxies with M z M 0 10 11  =  ( ) typically reionized as late or later than globally averaged 50% reionization at z 7.8 R á ñ = , in neighborhoods where reionization was completed by external radiation. The spread of reionization times within galaxies was sometimes as large as the galaxy-to-galaxy scatter. The Milky Way and M31 reionized earlier than global reionization but later than typical for their mass, neither dominated by external radiation. Their most-massive progenitors at z>6 had z R = 9.8 (MW) and 11 (M31), while their total masses had z R =8.2 (both).

The suppression of star formation on the smallest scales: what role does environment play?

“…Our results are consistent with recent hydrodynamical simulations of galaxy formation, which find that suppression of star formation by reionization is commonplace below a mass scale of M 10 5 M (Benítez-Llambay et al 2015;Fitts et al 2017;Jeon, Besla & Bromm 2017;Aubert et al 2018;Dawoodbhoy et al 2018). While reionization halts the infall of new gas in low-mass haloes, Figure 5.…”

Cosmic Reionization On Computers: Reionization Histories of Present-day Galaxies

“…Note that our highest neutral fraction threshold is the same as the single definition used in Aubert et al (2018). This results in a consistent reionization redshift in both high and low halo mass bins.…”

“…In this paper, we use the "Cosmic Reionization On Computers" (CROC) project to build upon and extend the work of Aubert et al (2018). CROC produces numerical simulations of reionization that self-consistently model relevant physical processes, providing a physically plausible (though, of course, not perfect) model for cosmic reionization.…”

Suppression of star formation in low-mass galaxies caused by the reionization of their local neighbourhood

“…Fortunately, a simple temporal re-scaling, z → 1.3z, 2 Towards this end, these same CLUES I.C. 's were recently used by another CoDa simulation, CoDa I-AMR, based on the hybrid CPU-GPU, AMR radiation-hydrodynamics code EMMA, as described by Aubert et al (2018), where objects in the Local Universe at z = 0 were matched to their progenitors during the EOR at z ≥ 6, to study the inhomogeneous reionization times of present-day galaxies. serves to align the data from CoDa I with many independent observational constraints, as shown in Ocvirk et al (2016), so it is useful to use this re-scaling when relating CoDa I to those observables.…”