A Hard X-ray Test of HCN Enhancements as a Tracer of Embedded Black Hole Growth. (arXiv:2004.02884v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Privon_G/0/1/0/all/0/1">G. C. Privon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ricci_C/0/1/0/all/0/1">C. Ricci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aalto_S/0/1/0/all/0/1">S. Aalto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Viti_S/0/1/0/all/0/1">S. Viti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Armus_L/0/1/0/all/0/1">L. Armus</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Diaz_Santos_T/0/1/0/all/0/1">T. Díaz-Santos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gonzalez_Alfonso_E/0/1/0/all/0/1">E. González-Alfonso</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iwasawa_K/0/1/0/all/0/1">K. Iwasawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jeff_D/0/1/0/all/0/1">D. L. Jeff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Treister_E/0/1/0/all/0/1">E. Treister</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bauer_F/0/1/0/all/0/1">F. Bauer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Evans_A/0/1/0/all/0/1">A. S. Evans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Garg_P/0/1/0/all/0/1">P. Garg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Herrero_Illana_R/0/1/0/all/0/1">R. Herrero-Illana</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mazzarella_J/0/1/0/all/0/1">J. M. Mazzarella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Larson_K/0/1/0/all/0/1">K. Larson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blecha_L/0/1/0/all/0/1">L. Blecha</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barcos_Munoz_L/0/1/0/all/0/1">L. Barcos-Muñoz</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Charmandaris_V/0/1/0/all/0/1">V. Charmandaris</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stierwalt_S/0/1/0/all/0/1">S. Stierwalt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_Torres_M/0/1/0/all/0/1">M. A. Pérez-Torres</a>
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 ( $lesssim15% $)
contribution of an AGN to the bolometric luminosity. To search for putative
heavily obscured AGN, we present and analyze nustar hard X-ray (3-79 keV)
observations of four such galaxies from the Great Observatories All-sky LIRG
Survey. We find no X-ray evidence for AGN in three of the systems and place
strong upper limits on the energetic contribution of any heavily obscured ($N
_{rm H}>10^{24}$ cm$^{-2}$) AGN to their bolometric luminosity. The X-ray flux
upper limits are presently an order of magnitude below what XDR-driven
chemistry model 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 $sim3%$ 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 $mathrm{J}_mathrm{upper}$
levels) and $L_mathrm{AGN}/L_mathrm{IR}$ 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 whether SMBH accretion is ongoing.
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 ( $lesssim15% $)
contribution of an AGN to the bolometric luminosity. To search for putative
heavily obscured AGN, we present and analyze nustar hard X-ray (3-79 keV)
observations of four such galaxies from the Great Observatories All-sky LIRG
Survey. We find no X-ray evidence for AGN in three of the systems and place
strong upper limits on the energetic contribution of any heavily obscured ($N
_{rm H}>10^{24}$ cm$^{-2}$) AGN to their bolometric luminosity. The X-ray flux
upper limits are presently an order of magnitude below what XDR-driven
chemistry model 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 $sim3%$ 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 $mathrm{J}_mathrm{upper}$
levels) and $L_mathrm{AGN}/L_mathrm{IR}$ 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 whether SMBH accretion is ongoing.
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