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Extinction and nebular line properties of a Herschel-selected lensed dusty starburst AT z=1.027

N. Timmons, A. Cooray, H. Nayyeri, C. Casey, Jae Calanog, B. Ma, H. Messias, M. Baes, R. S. Bussmann, L. Dunne, S. Dye, S. Eales, H. Fu, R. J. Ivison, S. J. Maddox, M. J. Michałowski, I. Oteo, D. A. Riechers, E. Valiante, J. Wardlow

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 $E(B-V)=0.8pm 0.5$. The Hα-based star formation rate (SFR), when corrected for extinction, is 60 ± 50 ${{M}_{odot }}$ yr−1, lower than the instantaneous SFR of 390 ± 90 ${{M}_{odot }}$ 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 $zsim 1$ for a galaxy with a stellar mass of $sim 2	imes {{10}^{11}}$ ${{M}_{odot }}$. 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.

Keywords
cosmology: observations – galaxies: evolution – infrared: galaxies – submillimeter: galaxies

The Astrophysical Journal
Volume 805, Number 2, Page 140
2015 June

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia