Simulating high-redshift galaxies

Abstract

Recent observations have gathered a considerable sample of high redshift galaxy candidates and determined the evolution of their luminosity function (LF). To interpret these findings, we use cosmological SPH simulations including, in addition to standard physical processes, a detailed treatment of the Pop III-Pop II transition in early objects. The simulated high-z galaxies match remarkably well the amplitude and slope of the observed LF in the redshift range 5<z<10. The LF shifts towards fainter luminosities with increasing redshift, while its faint-end slope keeps an almost constant value, \alpha ~-2. The stellar populations of high-z galaxies have ages of 100-300 (40-130) Myr at z=5 (z=7-8), implying an early (z>9.4) start of their star formation activity; the specific star formation rate is almost independent of galactic stellar mass. These objects are enriched rapidly with metals and galaxies identified by HST/WFC3 (M_UV < -18) show metallicities ~0.1 Zsun even at z=7-8. Most of the simulated galaxies at z~7 (noticeably the smallest ones) are virtually dust-free, and none of them has an extinction larger than E(B-V) = 0.01. The bulk (50%) of the ionizing photons is produced by objects populating the faint-end of the LF (M_UV < -16), which JWST will resolve up to z=7.3. PopIII stars continue to form essentially at all redshifts; however, at z=6 (z=10) the contribution of Pop III stars to the total galactic luminosity is always less than 5% for M_UV < -17 (M_UV < -16). The typical high-z galaxies closely resemble the GRB host galaxy population observed at lower redshifts, strongly encouraging the use of GRBs to detect the first galaxies.Comment: 14 pages, 10 figures, MNRAS in pres

Essential physics of early galaxy formation

“…The exact value of this slope and its redshift-evolution is important, given that it is the galaxies occupying the faint-end of the UV LF that provide most of the photons for cosmic reionization (e.g. Choudhury & Ferrara 2007;Salvaterra et al 2011). As explained in Sec.…”

“…Finlator et al 2007;Dayal et al 2009;Nagamine et al 2010;Dayal et al 2010;Forero-Romero et al 2011;Salvaterra et al 2011;Dayal & Ferrara 2012;Jaacks et al 2012;Dayal et al 2013). Although these studies can shed light on important physical properties of galaxies (halo/stellar/gas masses, metallicities), their assembly, and their clustering, running simulations necessarily involves a number of assumptions regarding the star-formation density threshold, gas ejection, metal pollution and fraction of SN energy that can power winds, to name a few.…”

GRB 100219A with X-shooter – abundances in a galaxy at z =4.7

“…Galaxy data are from Erb et al (2006) for z ∼ 2.3 and from Mannucci et al (2009) for z ∼ 3.1. Salvaterra et al (2011) studied the redshift evolution of the mass-metallicity relation from redshift 5 to 10 using galaxy evolution simulations with the GADGET code (Springel, 2005). They found considerable enrichment even of the smallest galaxies of up to 1/10 already at redshifts 7 − 8 and probably even higher.…”

Probing the first galaxies with the Square Kilometer Array

“…While the James Webb Space Telescope (JWST 1 ) will be able to detect galaxies at z ≤ 10 (e.g., Stiavelli et al 2004), it will not image all of the sources responsible for the reionization of the Universe. If current estimates in the literature are correct, even deep fields with JWST will only detect ∼30% of the sources responsible for reionization or maintaining reionization at z ∼ 12 (Salvaterra et al 2010). At z ∼ 20, direct emission from stars will be below the threshold of JWST observations and new techniques will be required to probe the onset of reionization.…”