The Physical Properties of Star-forming Galaxies with Strong [O III] Lines at z = 3.25

Abstract

We present an analysis of physical properties of 34 [O III] emission-line galaxies (ELGs) at z = 3.254 ± 0.029 in the Extended Chandra Deep Field South (ECDFS). These ELGs are selected from deep narrow H₂S(1) and broad K _s imaging of 383 arcmin² obtained with CFHT/WIRCam. We construct spectral energy distributions (SEDs) from U to K _s to derive the physical properties of ELGs. These [O III] ELGs are identified as starburst galaxies with strong [O III] lines of L _OIII ~ 10^42.6-10^44.2 erg s^-1 and have stellar masses of M _* ~ 10^9.0-10^10.6 M _⊙ and star formation rates of ~10-210 M _⊙ yr^-1. Our results show that 24% of our sample galaxies are dusty with A _V > 1 mag and EW([O III])_rest ~ 70-500 Å, which are often missed in optically selected [O III] ELG samples. Their rest-frame UV and optical morphologies from HST/ACS and HST/WFC3 deep imaging reveal that these [O III] ELGs are mostly multiple-component systems (likely mergers) or compact. And 20% of them are nearly invisible in the rest-frame UV owing to heavy dust attenuation. Interestingly, we find that our sample ELGs reside in an overdensity consisting of two components: one southeast (SE) with an overdensity factor of δ _gal ~ 41 over a volume of 13³ cMpc³, and the other northwest (NW) with δ _gal ~ 38 over a volume of 10³ cMpc³. The two overdense substructures are expected to be virialized at z = 0 with a total mass of ~ 1.1 × 10¹⁵ M _⊙ and ~ 4.8 × 10¹⁴ M _⊙ and probably merge into a Coma-like galaxy cluster.