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 arcmin(2) 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 ) similar to 10(42.6)-10(44.2) erg s(-1) and have stellar masses of M (*) similar to 10(9.0)-10(10.6) M (circle dot) and star formation rates of similar to 10-210 M (circle dot) yr(-1). Our results show that 24% of our sample galaxies are dusty with A (V) > 1 mag and EW([O iii])(rest) similar to 70-500 angstrom, 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 delta (gal) similar to 41 over a volume of 13(3) cMpc(3), and the other northwest (NW) with delta (gal) similar to 38 over a volume of 10(3) cMpc(3). The two overdense substructures are expected to be virialized at z = 0 with a total mass of similar to 1.1 x 10(15) M (circle dot) and similar to 4.8 x 10(14) M (circle dot) and probably merge into a Coma-like galaxy cluster.