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