REST-FRAME OPTICAL EMISSION LINES IN FAR-INFRARED-SELECTED GALAXIES AT z < 1.7 FROM THE FMOS-COSMOS SURVEY

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.

A New Diagnostic Diagram of Ionization Sources for High-redshift Emission Line Galaxies

“…The use of the BPT diagram at higher redshift remains valid (Trump et al 2011b;Kashino et al 2013Kashino et al , 2017Kewley et al 2013bKewley et al , 2016Juneau et al 2014;Steidel et al 2014;Coil et al 2015;Kartaltepe et al 2015;Kriek et al 2015;Sanders et al 2016). However, a public database of NIR spectra for large samples of highredshift galaxies is not available.…”

“…Our sample include 10 galaxies (3 are AGNs) from Kriek et al (2007), 1 LBG from Teplitz et al (2000), 6 LBGs from Pettini et al (1998Pettini et al ( , 2001, and 2 gravitationally lensed star-forming galaxies from Hainline et al (2009). Samples of z∼2 galaxies with NIR spectra are increasing thanks to the deployment of NIR spectrographs such as FMOS on Subaru (Kashino et al 2013(Kashino et al , 2017Kartaltepe et al 2015) and MOSFIRE on Keck (Steidel et al 2014;Kriek et al 2015). These data, once they become public, will improve the calibration of the KEx diagram at z∼2 significantly.…”

A Spectroscopic Census of X-Ray Systems in the COSMOS Field

“…The mean redshift difference from zCOSMOS redshifts measured from 154 duplicated objects is 27 ± 10 km s −1 . Kartaltepe et al (2015): The FMOS-COSMOS survey published redshifts measured from the FMOS near-infrared spectrograph on the Subaru telescope. From this survey, we compile 116 redshifts within the range 0.5 < z < 1.7.…”

The NuSTAR Extragalactic Surveys: Unveiling Rare, Buried AGNs and Detecting the Contributors to the Peak of the Cosmic X-Ray Background

“…As a consequence, this source has an hardness ratio 0.68 (Civano et al 2016). In the optical band, cid_3570is associated with a galaxy at redshift z=1.244 (Kartaltepe et al 2015;Marchesi et al 2016a). We thus expect the NuSTAR detection to be real, and associated with a highly obscured AGN with a hard spectrum barely detected by Chandra and previously missed by NuSTAR.…”