paper

ALMA Multiple-Transition Observations of High Density Molecular Tracers in Ultraluminous Infrared Galaxies

arXiv:1803.02408 · doi:10.3847/1538-4357/aab42f

Abstract

We present the results of our ALMA observations of eleven (ultra)luminous infrared galaxies ((U)LIRGs) at J=4-3 of HCN, HCO+, HNC and J=3-2 of HNC. This is an extension of our previously published HCN and HCO+ J=3-2 observations to multiple rotational J-transitions of multiple molecules, to investigate how molecular emission line flux ratios vary at different J-transitions. We confirm that ULIRGs that contain or may contain luminous obscured AGNs tend to show higher HCN-to-HCO+ flux ratios than starburst galaxies, both at J=4-3 and J=3-2. For selected HCN-flux-enhanced AGN-important ULIRGs, our isotopologue H13CN, H13CO+, and HN13C J=3-2 line observations suggest a higher abundance of HCN than HCO+ and HNC, which is interpreted to be primarily responsible for the elevated HCN flux in AGN-important galaxies. For such sources, the intrinsic HCN-to-HCO+ flux ratios after line opacity correction will be higher than the observed ratios, making the separation between AGNs and starbursts even larger. The signature of the vibrationally excited (v2=1f) HCN J=4-3 emission line is seen in one ULIRG, IRAS 12112-0305 NE. P Cygni profiles are detected in the HCO+ J=4-3 and J=3-2 lines toward IRAS 15250+3609, with an estimated molecular outflow rate of ~250-750 Mo/year. The SiO J=6-5 line also exhibits a P Cygni profile in IRAS 12112+0305 NE, suggesting the presence of shocked outflow activity. Shock tracers are detected in many sources, suggesting ubiquitous shock activity in the nearby ULIRG population.

59 pages, 32 Figures (emulateapj.cls). Accepted for publication in ApJS. Resolutions of some figures are degraded

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