The stellar populations of Lyman break galaxies at z ∼ 5

Abstract

We present the results of spectral energy distribution (SED) fitting analysis for Lyman break galaxies (LBGs) at z ∼ 5 in the Great Observatories Origins Deep Survey North (GOODS-N) and its flanking fields (the GOODS-FF). With the publicly available Infrared Array Camera (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 the sample LBGs. The derived stellar masses range from 10[superscript 8] to 10[superscript 11] M[subscript circled dot] with a median value of 4.1 × 10[superscript 9] M[subscript circled dot]. 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 semianalytic models involving active galactic nucleus feedback, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 10[superscript 8] M[subscript circled dot], the stellar mass density at z ∼ 5 is calculated to be (0.7–2.4) × 10[superscript 7] M[subscript circled dot] Mpc[superscript −3]. The stellar mass density at z ∼ 5 is dominated by the 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.