Tracing early structure formation with massive starburst galaxies and their implications for reionization

Abstract

Cosmological hydrodynamic simulations have significantly improved over the past several years, and we have already shown that the observed properties of Lymanbreak galaxies (LBGs) at z = 3 can be explained well by the massive galaxies in the simulations. Here we extend our study to z = 6 and show that we obtain good agreement for the LBGs at the bright-end of the luminosity function (LF). Our simulations also suggest that the cosmic star formation rate density has a peak at z = 5−6, and that the current LBG surveys at z = 6 are missing a significant number of faint galaxies that are dimmer than the current magnitude limit. Together, our results suggest that the universe could be reionized at z = 6 by the Pop II stars in ordinary galaxies.We also estimate the LF of Lyman-α emitters (LAEs) at z = 6 by relating the star formation rate in the simulation to the Lyα luminosity. We find that the simulated LAE LFs agree with the observed data provided that the net escape fraction of Lyα photon is f Lyα ≤ 0.1. We investigate two possible scenarios for this effect:(1) all sources in the simulation are uniformly dimmer by a factor of 10 through attenuation, and (2) one out of ten LAEs randomly lights up at a given moment. We show that the correlation strength of the LAE spatial distribution can possibly distinguish the two scenarios.

Lyα Emitters in Hierarchical Galaxy Formation

“…Nevertheless, the theoretical understanding of LAEs is still developing, and there are several different approaches to theoretical modeling: analytical calculations based on the halo mass function and on simple assumptions linking Ly emission to halo mass (Haiman & Spaans 1999;Thommes & Meisenheimer 2005;Dijkstra et al 2007b;Fernandez & Komatsu 2007;Mao et al 2007;Stark et al 2007b), cosmological hydrodynamic simulations (Barton et al 2004;Davé et al 2006;Nagamine et al 2006;Tasitsiomi 2006), and hierarchical clustering models of galaxy formation (so-called semianalytical models; Le Delliou et al 2005. A key ingredient in theoretical models is the escape fraction of Ly photons from their host galaxy, f Ly esc .…”

Escape of Ionizing Radiation from Star-forming Regions in Young Galaxies

“…z ! 6 the universe are thought to originate in Population II stars in normal ( ) galaxies (Nagamine et al 2006). …”

Photometric Properties of the Most Massive High‐Redshift Galaxies

“…At high redshifts (z k 6) the absorption is very strong near Ly (e.g., > 3; see Fig. 2 of Night et al 2006) and typical line-of-sight fluctuations will lead to strong spectral breaks. We therefore assume the mean IGM opacity calculated from the model since we are primarily concerned with high redshifts (z k 5), but we note that the calculated photometric trajectories could experience either small shifts in color-color space position or rate of change with redshift, owing to line-of-sight opacity fluctuations.…”

“…Theoretical calculations of the photometric properties of galaxies have been explored previously by hydrodynamical simulations of cosmological structure formation at redshifts z < 3 (Katz et al 1992;Davé et al 1999;Nagamine et al 2005aNagamine et al , 2005b, z $ 3 ( Weinberg et al 2002;Nagamine et al 2004Nagamine et al , 2006, z k 4 ( Harford & Gnedin 2003;Finlator et al 2006;Night et al 2006), and z k 6 ( Barton et al 2004;Davé et al 2006), and in semianalytic calculations (e.g., Baugh et al 1998;Kauffmann et al 1999;Somerville et al 2001). These calculations show that simulated galaxies, typically with maximum star formation rates of SFR P100 M yr À1 , can satisfy Lyman break color selection techniques.…”