Alma Observations of the Submillimeter Dense Molecular Gas Tracers in the Luminous Type-1 Active Nucleus of NGC 7469

ALMA HCN AND HCO+ J = 3 − 2 OBSERVATIONS OF OPTICAL SEYFERT AND LUMINOUS INFRARED GALAXIES: CONFIRMATION OF ELEVATED HCN-TO-HCO+ FLUX RATIOS IN AGNS

“…Interpretations of the observed HCN-to-HCO + flux ratios are less ambiguous than the flux comparison among molecules with largely different dipole moments (e.g., HCN vs. CO). Using ALMA, a similar enhancement of observed HCN-to-HCO + flux ratios was also found at J=4-3 for LIRGs that are infrareddiagnosed to be AGN-important (Imanishi & Nakanishi 2013a,b, 2014Iono et al 2013;Garcia-Burillo et al 2014;Izumi et al 2015Izumi et al , 2016. These observations suggest that elevated HCN-to-HCO + flux ratios could be used to identify AGNs, including deeply buried (= obscured in virtually all directions) ones.…”

“…Interferometric CO J=2-1 and HCN/HCO + J=4-3 observations of the NGC 7469 nucleus revealed that molecular emission lines at the nuclear position are narrow with a full width at 10% intensity <400 km s −1 (Davies et al 2004;Izumi et al 2015). Detailed results of ALMA Cycle 2 sub-arcsec spatial-resolution observations of NGC 7469 at HCN J=4-3 and HCO + J=4-3 were reported by Izumi et al (2015).…”

“…We did not detect HCN/HCO + v 2 =1f J=3-2 emission lines in these AGN-dominated Seyfert 1 nuclei, and this requires some quantitative consideration. For the NGC 7469 nucleus, the HCN v 2 =1f J=4-3 emission line was also undetected by ALMA observations (Izumi et al 2015).…”

“…Recent sensitive ground-based 8-13 µm spectroscopy has shown some signatures of an 11.3 µm PAH emission feature from the NGC 7469 nucleus (Honig et al 2010;Esquej et al 2014), but the estimated nuclear starburst luminosity is only ∼20% of the AGN luminosity (Esquej et al 2014;Genzel et al 1995). Interferometric CO J=2-1 and HCN/HCO + J=4-3 observations of the NGC 7469 nucleus revealed that molecular emission lines at the nuclear position are narrow with a full width at 10% intensity <400 km s −1 (Davies et al 2004;Izumi et al 2015). Detailed results of ALMA Cycle 2 sub-arcsec spatial-resolution observations of NGC 7469 at HCN J=4-3 and HCO + J=4-3 were reported by Izumi et al (2015).…”

“…Thus, the flux attenuation of the HCN and HCO + v=0 emission by line opacity is also expected to be smaller in unobscured AGNs. Izumi et al (2015) estimated the line opacity for the HCN v=0 J=4-3 emission to be <3.5 for the NGC 7469 nucleus. Even if unobscured AGNs and buried AGNs show intrinsically similar HCN v 2 =1f to v=0 flux ratios, the observed HCN v 2 =1f to v=0 flux ratios in buried AGNs can become larger due to higher HCN v=0 flux attenuation.…”