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arXiv · 1505.03527

Rest-frame Optical Emission Lines in Far-Infrared Selected Galaxies at z<1.7 from the FMOS-COSMOS Survey

Jeyhan S. Kartaltepe·D. B. Sanders·J. D. Silverman·D. Kashino·J. Chu·H. Zahid·G. Hasinger·L. Kewley·K. Matsuoka·T. Nagao·L. Riguccini·M. Salvato·K. Schawinski·Y. Taniguchi·E. Treister·P. Capak·E. Daddi·K. Ohta
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Abstract

We have used FMOS on Subaru to obtain near-infrared spectroscopy of 123 far-infrared selected galaxies in COSMOS and obtain the key rest-frame optical emission lines. This is the largest sample of infrared galaxies with near-infrared spectroscopy at these redshifts. The far-infrared selection results in a sample of galaxies that are massive systems that span a range of metallicities in comparison with previous optically selected surveys, and thus has a higher AGN fraction and better samples the AGN branch. We establish the presence of AGN and starbursts in this sample of (U)LIRGs selected as Herschel-PACS and Spitzer-MIPS detections in two redshift bins (z~0.7 and z~1.5) and test the redshift dependence of diagnostics used to separate AGN from star-formation dominated galaxies. In addition, we construct a low redshift (z~0.1) comparison sample of infrared selected galaxies and find that the evolution from z~1.5 to today is consistent with an evolving AGN selection line and a range of ISM conditions and metallicities from the models of Kewley et al. (2013b). We find that a large fraction of (U)LIRGs are BPT-selected AGN using their new, redshift-dependent classification line. We compare the position of known X-ray detected AGN (67 in total) with the BPT selection and find that the new classification line accurately selects most of these objects (> 70%). Furthermore, we identify 35 new (likely obscured) AGN not selected as such by their X-ray emission. Our results have direct implications for AGN selection at higher redshift with either current (MOSFIRE, KMOS) or future (PFS, MOONS) spectroscopic efforts with near-infrared spectral coverage.

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Jeyhan S. Kartaltepe, D. B. Sanders, J. D. Silverman, D. Kashino, J. Chu, H. Zahid, G. Hasinger, L. Kewley, K. Matsuoka, T. Nagao, L. Riguccini, M. Salvato, K. Schawinski, Y. Taniguchi, E. Treister, P. Capak, E. Daddi, K. Ohta. 2015-05-15. Rest-frame Optical Emission Lines in Far-Infrared Selected Galaxies at z<1.7 from the FMOS-COSMOS Survey. https://arxiv.org/abs/1505.03527

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