A hard x-ray test of hcn enhancements as a tracer of embedded black hole growth

DOI: 
10.3847/1538-4357/ab8015
Publication date: 
02/06/2020
Main author: 
Privon G.C.
IAA authors: 
Pérez-Torres, M.A.
Authors: 
Privon G.C., Ricci C., Aalto S., Viti S., Armus L., Díaz-Santos T., González-Alfonso E., Iwasawa K., Jeff D.L., Treister E., Bauer F., Evans A.S., Garg P., Herrero-Illana R., Mazzarella J.M., Larson K., Blecha L., Barcos-Muoz L., Charmandaris V., Stierwalt S., Pérez-Torres M.A.
Journal: 
Astrophysical Journal
Refereed: 
Yes
Publication type: 
Article
Volume: 
893.0
Pages: 
149
Number: 
149
Abstract: 
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 (NH > 1024 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 LAGN/LIR f 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. © 2020. The American Astronomical Society. All rights reserved
Database: 
SCOPUS
ADS
URL: 
https://ui.adsabs.harvard.edu/#abs/2020ApJ...893..149P/abstract
ADS Bibcode: 
2020ApJ...893..149P