UV Luminosity Functions atz∼4, 5, and 6 from the Hubble Ultra Deep Field and Other DeepHubble Space TelescopeACS Fields: Evolution and Star Formation History

Abstract

We use the ACS BV iz data from the HUDF and all other deep HST ACS fields (including the GOODS fields) to find large samples of star-forming galaxies at z ∼ 4 and z ∼ 5 and to extend our previous z ∼ 6 sample. These samples contain 4671, 1416, and 627 B, V , and i dropouts, respectively, and reach to extremely low luminosities (0.01 − 0.04L * z=3 or M UV ∼ −16 to −17), allowing us to determine the rest-frame U V luminosity function (LF) and faint-end slope α at z ∼ 4 − 6 to high accuracy. We find faint-end slopes α of −1.73 ± 0.05 at z ∼ 4, −1.66 ± 0.09 at z ∼ 5, and −1.74 ± 0.16 at z ∼ 6 -suggesting that the faint-end slope is very steep and shows little evolution with cosmic time. We find that M * UV brightens considerably in the 0.7 Gyr from z ∼ 6 to z ∼ 4 (by ∼ 0.7 mag from M * UV = −20.24 ± 0.19 to M * UV = −20.98 ± 0.10). The observed increase in the characteristic luminosity over this range is almost identical to that expected for the halo mass function -suggesting that the observed evolution is likely due to the hierarchical coalescence and merging of galaxies. The evolution in φ * is not significant. The U V luminosity density at z ∼ 6 is modestly lower (0.45 ± 0.09×) than that at z ∼ 4 (integrated to −17.5 AB mag) though a larger change is seen in the dust-corrected star-formation rate density. We thoroughly examine published LF results and assess the reasons for their wide dispersion. We argue that the results reported here are the most robust available. The extremely steep faint-end slopes α found here suggest that lower luminosity galaxies play a significant role in reionizing the universe. Finally, recent search results for galaxies at z ∼ 7 − 8 are used to extend our estimates of the evolution of M * from z ∼ 7 − 8 to z ∼ 4.

Modeling high-redshift galaxies: what can we learn from high and ultra-high resolution hydrodynamical simulations?

“…This strong evolution is a direct consequence of the rapid decrease of the cosmic star formation rate density from z = 4 to 7 in our simulation and is, to a large extent, unaffected by resolution effects. At z > 6, recent analyses of the HUD and the GOODS fields (Bouwens et al 2007(Bouwens et al , 2008) suggest a slightly steeper faint-end slope of α 1.74 again in good agreement with our simulation as we find that the faint-end slope of our LF does steepen slowly with redshift. Finally, at the bright end of the LF, our two dust extinction models yield different results.…”

First light: exploring the spectra of high-redshift galaxies in the Renaissance Simulations

“…In its initial 2005 HUDF campaign, the Hubble Advanced Camera for Surveys (ACS) used four optical filters to identify galaxies with redshifts up to 7.5, showing that the galaxy number density further declines with redshift (e.g. Malhotra et al 2005;Bouwens et al 2007;Oesch et al 2007).…”

Understanding the non-linear clustering of high-redshift galaxies

“…J13 then incorporate a physically motivated model for the total star formation rate in a dark matter halo to compute the UV luminosity of the LBGs hosted by the halo. The parameters of the model are constrained by fitting the observed UV luminosity functions of LBGs from Bouwens et al (2007), Reddy et al (2008) and Bouwens et al (2012). Thus J13 constrains the relation between the UV luminosity and halo mass of high-z LBGs from which the HOD of LBGs brighter than a given luminosity is computed.…”