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Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey

Chen, C.-T. J. and Brandt, W. N. and Reines, A. E. and Lansbury, G. and Stern, D. and Alexander, D. M. and Bauer, F. and Del Moro, A. and Gandhi, P. and Harrison, F. A. and Hickox, R. C. and Koss, M. J. and Lanz, L. and Luo, B. and Mullaney, J. R. and Ricci, C. and Trump, J. R. (2017) Hard X-Ray-selected AGNs in Low-mass Galaxies from the NuSTAR Serendipitous Survey. Astrophysical Journal, 837 (1). Art. No. 48. ISSN 1538-4357. doi:10.3847/1538-4357/aa5d5b.

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We present a sample of 10 low-mass active galactic nuclei (AGNs) selected from the 40-month Nuclear Spectroscopic Telescope Array (NuSTAR) serendipitous survey. The sample is selected to have robust NuSTAR detections at 3-24 keV, to be at z < 0.3, and to have optical r-band magnitudes at least 0.5 mag fainter than an L_★ galaxy at its redshift. The median values of absolute magnitude, stellar mass, and 2–10 X-ray luminosity of our sample are 〈 M_★〉 = -20.03, M_r〉 = 4.6 x 10^9 M_⊙, and 〈L_(2-10 keV)〉 = 3.1 x 10^(42) erg s^(−1), respectively. Five objects have detectable broad Hα emission in their optical spectra, indicating black hole masses of (1.1--10.4) x 10^6 M_⊙. We find that 30_(-10)^(+17)% of the galaxies in our sample do not show AGN-like optical narrow emission lines, and one of the 10 galaxies in our sample, J115851+4243.2, shows evidence for heavy X-ray absorption. This result implies that a non-negligible fraction of low-mass galaxies might harbor accreting massive black holes that are missed by optical spectroscopic surveys and < 10 keV X-ray surveys. The mid-IR colors of our sample also indicate that these optically normal low-mass AGNs cannot be efficiently identified with typical AGN selection criteria based on Wide Field Infrared Survey Explorer colors. While the hard (> 10 keV) X-ray-selected low-mass AGN sample size is still limited, our results show that sensitive NuSTAR observations are capable of probing faint hard X-ray emission originating from the nuclei of low-mass galaxies out to moderate redshift (z > 0.3), thus providing a critical step in understanding AGN demographics in low-mass galaxies.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper ItemOnline Figure Set (Github)
Chen, C.-T. J.0000-0002-4945-5079
Brandt, W. N.0000-0002-0167-2453
Lansbury, G.0000-0002-5328-9827
Stern, D.0000-0003-2686-9241
Alexander, D. M.0000-0002-5896-6313
Bauer, F.0000-0002-8686-8737
Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Hickox, R. C.0000-0003-1468-9526
Koss, M. J.0000-0002-7998-9581
Lanz, L.0000-0002-3249-8224
Luo, B.0000-0002-9036-0063
Mullaney, J. R.0000-0002-3126-6712
Ricci, C.0000-0001-5231-2645
Additional Information:© 2017. The American Astronomical Society. Received 2016 October 11; revised 2017 January 24; accepted 2017 January 27; published 2017 March 1. We thank the referee for carefully reading the manuscript and providing helpful comments. This work was supported under NASA contract no. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). C.-T.J.C. and W.N.B. acknowledge support from Caltech NuSTAR subcontract 44A-1092750. Support for A.E.R. was provided by NASA through Hubble Fellowship grant HST-HF2-51347.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. D.M.A. gratefully acknowledges support from Science and Technology Facilities Council (ST/L00075X/1). F.E.B. and C.R. acknowledge support from NASA NuSTAR A01 Award NNX15AV27G, CONICYT-Chile grants Basal-CATA PFB-06/2007, FONDECYT Regular 1141218 and 1151408, China-CONICYT Fellowship, and the Ministry of Economy, Development, and Tourisms Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics, MAS. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III Web site is This research has made use of the "Aladin sky atlas" developed at CDS, Strasbourg Observatory, France (Bonnarel et al. 2000). This work has also made use of observations made with the Spitzer Space Telescope, obtained from the NASA/IPAC Infrared Science Archive, both of which are operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Facilities: NuSTAR - The NuSTAR (Nuclear Spectroscopic Telescope Array) mission, Chandra - , XMM-Newton - Newton X-Ray Multimirror Mission satellite, Swift/BAT - Swift Gamma-Ray Burst Mission, Swift/XRT - , WISE - Wide-field Infrared Survey Explorer, Keck - , NTT - New Techology Telescope, Palomar - . Software: Astropy, CIAO, HEAsoft, XMMSAS, XSPEC.
Group:Space Radiation Laboratory, NuSTAR, Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Caltech NuSTAR subcontract44A-1092750
NASA Hubble FellowshipHST-HF2-51347.001-A
NASANAS 5-26555
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1151408
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Science and Technology Facilities Council (STFC)ST/L00075X/1
Alfred P. Sloan FoundationUNSPECIFIED
Participating InstitutionsUNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: dwarf; X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20170201-075210760
Persistent URL:
Official Citation:C.-T. J. Chen (陳建廷) et al 2017 ApJ 837 48
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73908
Deposited By: Joy Painter
Deposited On:01 Feb 2017 17:04
Last Modified:11 Nov 2021 05:23

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