Extinction and Nebular Line Properties of a Herschel-selected Lensed Dusty Starburst at z = 1.027
Ivison, R. J.; Baes, Maarten; Fu, Hai; Dunne, Loretta; Cooray, Asantha; Oteo, I.; Nayyeri, Hooshang; Michałowski, Michał J.; Dye, Simon; Riechers, Dominik A.; Eales, Steve; Valiante, Elisabetta; Messias, Hugo; Bussmann, R. Shane; Maddox, Steve; Ma, Brian; Timmons, Nicholas; Calanog, Jae; Wardlow, Julie; Casey, Caitlin
United States, Portugal, Belgium, New Zealand, United Kingdom, Germany, Denmark
Abstract
We present Hubble Space Telescope Wide Field Camera 3 (WFC3) imaging and grism spectroscopy observations of the Herschel-selected gravitationally lensed starburst galaxy HATLASJ1429-0028. The lensing system consists of an edge-on foreground disk galaxy at z = 0.218 with a nearly complete Einstein ring of the infrared luminous galaxy at z = 1.027. The WFC3 spectroscopy with G102 and G141 grisms, covering the wavelength range of 0.8-1.7 μm, resulted in detections of Hα + [Nii], Hβ, [Sii], and [Oiii] for the background galaxy from which we measure line fluxes and ratios. The Balmer line ratio Hα/Hβ of 7.5 ± 4.4, when corrected for [Nii], results in an extinction for the starburst galaxy of E(B-V)=0.8+/- 0.5. The Hα-based star formation rate (SFR), when corrected for extinction, is 60 ± 50 {{M}⊙ } yr-1, lower than the instantaneous SFR of 390 ± 90 {{M}⊙ } yr-1 from the total IR luminosity. We also compare the nebular line ratios of HATLASJ1429-0028 with other star-forming and sub-millimeter bright galaxies. The nebular line ratios are consistent with an intrinsic ultra-luminous infrared galaxy with no evidence for excitation by an active galactic nucleus (AGN). We estimate the metallicity, 12 + log(O/H), of HATLASJ1429-0028 to be 8.49 ± 0.16. Such a low value is below the average relation for stellar mass versus metallicity of galaxies at z∼ 1 for a galaxy with a stellar mass of ∼ 2× {{10}11} {{M}⊙ }. The combination of high stellar mass, the lack of AGN indicators, low metallicity, and the high SFR of HATLASJ1429-0028 suggest that this galaxy is currently undergoing a rapid formation.