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A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth

Privon, G. C. and Ricci, C. and Aalto, S. and Viti, S. and Armus, L. and Díaz-Santos, T. and González-Alfonso, E. and Iwasawa, K. and Jeff, D. L. and Treister, E. and Bauer, F. and Evans, A. S. and Garg, P. and Herrero-Illana, R. and Mazzarella, J. M. and Larson, K. and Blecha, L. and Barcos-Muñoz, L. and Charmandaris, V. and Stierwalt, S. and Pérez-Torres, M. A. (2020) A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth. Astrophysical Journal, 893 (2). Art. No. 149. ISSN 1538-4357.

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Enhanced emission from the dense gas tracer HCN (relative to HCO+) has been proposed as a signature of active galactic nuclei (AGN). In a previous single-dish millimeter line survey we identified galaxies with HCN/HCO+ (1–0) intensity ratios consistent with those of many AGN but whose mid-infrared spectral diagnostics are consistent with little to no (≾15%) contribution of an AGN to the bolometric luminosity. To search for putative heavily obscured AGN, we present and analyze NuSTAR hard X-ray (3–79 keV) observations of four such galaxies from the Great Observatories All-sky LIRG Survey. We find no X-ray evidence for AGN in three of the systems and place strong upper limits on the energetic contribution of any heavily obscured (N_H > ²⁴10 cm⁻²) AGN to their bolometric luminosity. The upper limits on the X-ray flux are presently an order of magnitude below what XDR-driven chemistry models predict are necessary to drive HCN enhancements. In a fourth system we find a hard X-ray excess consistent with the presence of an AGN, but contributing only ~3% of the bolometric luminosity. It is also unclear if the AGN is spatially associated with the HCN enhancement. We further explore the relationship between HCN/HCO⁺ (for several J_(upper) levels) and L_(AGN)/L_(IR) for a larger sample of systems in the literature. We find no evidence for correlations between the line ratios and the AGN fraction derived from X-rays, indicating that HCN/HCO⁺ intensity ratios are not driven by the energetic dominance of AGN, nor are they reliable indicators of ongoing supermassive black hole accretion.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Privon, G. C.0000-0003-3474-1125
Ricci, C.0000-0001-5231-2645
Viti, S.0000-0001-8504-8844
Armus, L.0000-0003-3498-2973
Díaz-Santos, T.0000-0003-0699-6083
Iwasawa, K.0000-0002-4923-3281
Jeff, D. L.0000-0003-0416-4830
Treister, E.0000-0001-7568-6412
Bauer, F.0000-0002-8686-8737
Evans, A. S.0000-0003-2638-1334
Garg, P.0000-0002-5923-2151
Herrero-Illana, R.0000-0002-7758-8717
Mazzarella, J. M.0000-0002-8204-8619
Larson, K.0000-0003-3917-6460
Blecha, L.0000-0002-2183-1087
Barcos-Muñoz, L.0000-0003-0057-8892
Charmandaris, V.0000-0002-2688-1956
Stierwalt, S.0000-0002-2596-8531
Additional Information:© 2020 The American Astronomical Society. Received 2019 August 20; revised 2020 March 9; accepted 2020 March 12; published 2020 April 24. The authors thank the anonymous referee for constructive comments that have improved the clarity and quality of the paper. The authors also thank Masatoshi Imanishi for comments on an earlier version of the manuscript. G.C.P. and D.L.J. acknowledge support from a NASA NuSTAR award 80NSSC17K0623. G.C.P. also acknowledges support from the University of Florida. C.R. acknowledges support from the CONICYT+PAI Convocatoria Nacional subvencion a instalacion en la academia convocatoria año 2017 PAI77170080. T.D-S. acknowledges support from the CASSACA and CONICYT fund CAS-CONICYT Call 2018. E.G.-A. is a Research Associate at the Harvard-Smithsonian Center for Astrophysics, and thanks the Spanish Ministerio de Economía y Competitividad for support under project ESP2017-86582-C4-1-R. K.I. acknowledges support by the Spanish MINECO under grant AYA2016-76012-C3-1-P and MDM-2014-0369 of ICCUB (Unidad de Excelencia "María de Maeztu"). L.B. acknowledges support from National Science Foundation grant AST-1715413. F.E.B. acknowledges support from CONICYT-Chile (Basal AFB-170002) and the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. E.T. acknowledges support from CONICYT-Chile grants Basal-CATA AFB-170002, FONDECYT Regular 1160999 and 1190818, and Anillo de ciencia y tecnologia ACT1720033. K.L.L. was supported by NASA through grants HST-GO-13690.002-A and HST-GO-15241.002-A from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. M.P.T. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and through grant PGC2018-098915-B-C21. A portion of this work was performed at the Aspen Center for Physics, which is supported by National Science Foundation grant PHY-1607611. The authors thank the Sexten Center for Astrophysics ( where part of this work was performed. This research has made use of the NASA/IPAC Extragalactic Database (NED) and NASA's Astrophysics Data System. Facility: NuSTAR. - Software: ipython (Pérez & Granger 2007), numpy (Van Der Walt et al. 2011), scipy (Virtanen et al. 2020), matplotlib (Hunter 2007), Astropy (The Astropy Collaboration et al. 2013, 2018), Aplpy (Robitaille & Bressert 2012), DESPOTIC (Krumholz 2014), UCLCHEM (Viti et al. 2004; Holdship et al. 2017), CLOUDY (Ferland et al. 2017).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
University of FloridaUNSPECIFIED
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)2017 PAI77170080
CAS South America Center for Astronomy (CASSACA)Call 2018
Harvard-Smithsonian Center for AstrophysicsUNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)ESP2017-86582-C4-1-R
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2016-76012-C3-1-P
Ministerio de Economía, Industria y Competitividad (MINECO)MDM-2014-0369
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1160999
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1190818
Anillo de Ciencia y TecnologiaACT1720033
Severo OchoaSEV-2017-0709
Severo OchoaPGC2018-098915-B-C21
Subject Keywords:Molecular gas ; Active galactic nuclei ; X-ray active galactic nuclei ; Luminous infrared galaxies ; Starburst galaxies
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Molecular gas (1073); Active galactic nuclei (16); X-ray active galactic nuclei (2035); Luminous infrared galaxies (946); Starburst galaxies (1570)
Record Number:CaltechAUTHORS:20200424-103341359
Persistent URL:
Official Citation:G. C. Privon et al 2020 ApJ 893 149
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102774
Deposited By: Tony Diaz
Deposited On:24 Apr 2020 17:57
Last Modified:24 Apr 2020 17:57

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