Massive Lyman Break Galaxies at z~3 in the Spitzer Extragalactic First Look Survey

TL;DR

This study analyzes a large sample of Lyman Break Galaxies at z~3, revealing their mass, dust content, and star formation rates, and demonstrating their significant contribution to the cosmic star formation history.

Contribution

It provides the first statistical analysis of massive LBGs at z~3 using wide-area multi-wavelength data, highlighting their role in galaxy evolution and star formation.

Findings

Massive LBGs are dusty and have high star formation rates.

Infrared-luminous LBGs are starburst galaxies with SFRs of 100-1000 Msun/yr.

Massive galaxies significantly contribute to the star formation rate density at z~3.

Abstract

We investigate the properties of 1088 Lyman Break Galaxies (LBGs) at z~3 selected from a ~2.63$ deg2 sub-region of the First Look Survey field using the ground-based multi-color data and the Spitzer Space Telescope mid-infrared data at 3--8 and 24 um. With the wide area and the broad wavelength coverage, we sample a large number of ``rare'' u-band dropouts which are massive (M* > 10^11 Msun), allowing us to perform a statistical analysis of these subsets of LBGs that have not been studied in detail. Optically bright (R(AB) < 24.5 mag) LBGs detected in mid-infrared (S_{3.6um} > 6 uJy) reside at the most massive and dusty end of the LBG population, with relatively high and tight $M/L$ in rest-frame near-infrared. Most infrared-luminous LBGs (S_{24um} > 100 uJy) are dusty star-forming galaxies with star formation rates of 100--1000 Msun/yr, total infrared luminosity of > 10^12 Lsun. By constructing the UV luminosity function of massive LBGs, we estimate that the lower limit for the star formation rate density from LBGs more massive than 10^11 Msun at z~3 is > 3.3 x 10^-3 Msun/yr/Mpc^3, showing for the first time that the UV-bright population of massive galaxies alone contributes significantly to the global star formation rate density at z~3. When combined with the star formation rate densities at z < 2, our result reveals a steady increase in the contribution of massive galaxies to the global star formation from z=0 to z=3, providing strong support to the downsizing of galaxy formation.