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

Abstract

We present the results of our ALMA observations of three AGN-dominated nuclei in optical Seyfert 1 galaxies (NGC 7469, I Zw 1, and IC 4329 A) and eleven luminous infrared galaxies (LIRGs) with various levels of infrared estimated energetic contributions by AGNs at the HCN and HCO + J=3-2 emission lines. The HCN and HCO + J=3-2 emission lines are clearly detected at the main nuclei of all sources, except for IC 4329 A. The vibrationally excited (v 2 =1f) HCN J=3-2 and HCO + J=3-2 emission lines are simultaneously covered, and HCN v 2 =1f J=3-2 emission line signatures are seen in the main nuclei of two LIRGs, IRAS 12112+0305 and IRAS 22491−1808, neither of which show clear buried AGN signatures in the infrared. If the vibrational excitation is dominated by infrared radiative pumping, through the absorption of infrared 14 µm photons, primarily originating from AGN-heated hot dust emission, then these two LIRGs may contain infrared-elusive, but (sub)millimeter-detectable, extremely deeply buried AGNs. These vibrationally excited emission lines are not detected in the three AGN-dominated optical Seyfert 1 nuclei. However, the observed HCN v 2 =1f to v=0 flux ratios in these optical Seyferts are still consistent with the intrinsic flux ratios in LIRGs with detectable HCN v 2 =1f emission lines. The observed HCN-to-HCO + J=3-2 flux ratios tend to be higher in galactic nuclei with luminous AGN signatures compared with starburst-dominated regions, as previously seen at J=1-0 and J=4-3.

Disentangling the Circumnuclear Environs of Centaurus A. III. An Inner Molecular Ring, Nuclear Shocks, and the CO to Warm H2 Interface

“…In the regions where these dense tracers are detected in Cen A, all R HCN/HCO + ratios lie well below those of the AGN dominated galaxies (Imanishi et al 2016) and within the range found for starburst galaxies ). Given our low R HCN/HCO + ratios we can discard that conditions as in other AGN dominated galaxies apply in the circumnuclear environments of Cen A.…”

Resolving the Interstellar Medium in Ultraluminous Infrared QSO Hosts with ALMA

“…ALMA HCN (3−2) and HCO + (3−2) imaging of I ZW 1 with a comparable angular resolution (0 .69×0 . 63) to our CO observations, show that the source is marginally resolved in dense molecular gas emission with a deconvolved size of ∼0 .4 (Imanishi et al 2016). Compared to the total molecular gas as traced by CO emission, both HCN and HCO + lines with high critical densities probe the dense molecular gas (i.e., n(H 2 ) 10 4 cm −3 ), of which the mass is observed to have a tight linear correlation with the SF rate in galaxies, suggesting that the dense gas is likely the direct fuel for star formation (e.g., Gao & Solomon 2004).…”

Complex molecular gas kinematics in the inner 5 kpc of 4C12.50 as seen by ALMA

“…8 for the momenta maps). The rotation is clearly seen for the inner 2 kpc, and it agrees with the results of Imanishi et al (2016Imanishi et al ( , 2018 for comparable or smaller scales. Counter-rotating blobs or high-velocity dispersion regions are also seen in the momenta maps, for example to the west of the nucleus.…”