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

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 ∼1042.6-1044.2 erg s-1 and have stellar masses of M ∗ ∼109.0-1010.6 M ⊙ and star formation rates of 1/410-210 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.