Privon, GC;
Ricci, C;
Aalto, S;
Viti, S;
Armus, L;
Díaz-Santos, T;
González-Alfonso, E;
... Pérez-Torres, MA; + view all
(2020)
A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth.
The Astrophysical Journal
, 893
(2)
, Article 149. 10.3847/1538-4357/ab8015.
Preview |
Text
Privon_2020_ApJ_893_149.pdf - Published Version Download (1MB) | Preview |
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 Jupper levels) and LAGN/LIR 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.
| Type: | Article |
|---|---|
| Title: | A Hard X-Ray Test of HCN Enhancements As a Tracer of Embedded Black Hole Growth |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/ab8015 |
| Publisher version: | https://doi.org/10.3847/1538-4357/ab8015 |
| Language: | English |
| Additional information: | This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | Molecular gas; Active galactic nuclei; X-ray active galactic nuclei; Luminous infrared galaxies; Starburst galaxies |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10097372 |
Archive Staff Only
 |
View Item |
