Detection of [O III] at z~3: A Galaxy above the Main Sequence, Rapidly Assembling its Stellar Mass

Abstract

We detect bright emission in the far infrared fine structure [O III] 88$\hat{I}¼$m line from a strong lensing candidate galaxy, H-ATLAS J113526.3-014605, hereafter G12v2.43, at z=3.127, using the $2^{\mathrm{nd}}$ generation Redshift (z) and Early Universe Spectrometer (ZEUS-2) at the Atacama Pathfinder Experiment Telescope (APEX). This is only the fifth detection of this far-IR line from a sub-millimeter galaxy at the epoch of galaxy assembly. The observed [O III] luminosity of $7.1\times 10^9(\frac{10}{\hat{\mathrm{I}}}¼){\mathrm{L}}_{\odot }$ likely arises from HII regions around massive stars, and the amount of Lyman continuum photons required to support the ionization indicate the presence of $(1.2-5.2)\times 10^6(\frac{10}{\hat{\mathrm{I}}}¼)$ equivalent O5.5 or higher stars; where $\hat{I}¼$ would be the lensing magnification factor. The observed line luminosity also requires a minimum mass of $\sim 2\times 10^8(\frac{10}{\hat{\mathrm{I}}}¼){\mathrm{M}}_{\odot }$ in ionized gas, that is $0.33\%$ of the estimated total molecular gas mass of $6\times 10^{10}(\frac{10}{\hat{\mathrm{I}}}¼){\mathrm{M}}_{\odot }$. We compile multi-band photometry tracing rest-frame UV to millimeter continuum emission to further constrain the properties of this dusty high redshift star-forming galaxy. Via SED modeling we find G12v2.43 is forming stars at a rate of 916 $(\frac{10}{\hat{\mathrm{I}}}¼){\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ and already has a stellar mass of $8\times 10^{10}(\frac{10}{\hat{\mathrm{I}}}¼){\mathrm{M}}_{\odot }$. We also constrain the age of the current starburst to be $⩽$ 5 million years, making G12v2.43 a gas rich galaxy lying above the star-forming main sequence at z$\sim$3, undergoing a growth spurt and, could be on the main sequence within the derived gas depletion timescale of $\sim$66 million years.

11 pages, 3 figures, accepted for publication in The Astrophysical Journal