The Stellar Populations of Lyman Break Galaxies at z~5

TL;DR

This study analyzes the stellar populations of z~5 Lyman Break Galaxies using SED fitting, revealing their smaller stellar masses and younger ages compared to lower redshift counterparts, and estimating their stellar mass density.

Contribution

It provides the first large sample SED analysis of z~5 LBGs, deriving their stellar masses, ages, and mass function, and compares these properties with models and other redshifts.

Findings

Stellar masses range from 10^8 to 10^11 M_sun with median 4.1x10^9 M_sun.

z~5 LBGs are systematically less massive and younger than z=2-3 LBGs.

Stellar mass density at z~5 is (0.7-2.4)x10^7 M_sun Mpc^-3, consistent with the trend of increasing mass density over time.

Abstract

We present the results of Spectral Energy Distribution(SED) fitting analysis for Lyman Break Galaxies(LBGs) at z~5 in the GOODS-N and its flanking fields (the GOODS-FF). With the publicly available IRAC images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of sample LBGs. The derived stellar masses range from 10^8 to 10^11M_sun with a median value of 4.1x10^9M_sun. The comparison with z=2-3 LBGs shows that the stellar masses of z~5 LBGs are systematically smaller by a factor of 3-4 than those of z=2-3 LBGs in a similar rest-frame UV luminosity range. The star formation ages are relatively younger than those of the z=2-3 LBGs. We also compared the results for our sample with other studies for the z=5-6 galaxies. Although there seem to be similarities and differences in the properties, we could not conclude its significance. We also derived a stellar mass function of our sample by correcting for incompletenesses. Although the number densities in the massive end are comparable to the theoretical predictions from semi-analytic models, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 10^8 M_sun, the stellar mass density at z~5 is calculated to be (0.7-2.4)x10^7M_sun Mpc^-3. The stellar mass density at z~5 is dominated by massive part of the stellar mass function. Compared with other observational studies and the model predictions, the mass density of our sample is consistent with general trend of the increase of the stellar mass density with time.