ALMA Sub-arcsecond-resolution 183 GHz H2O and Dense Molecular Line Observations of Nearby Ultraluminous Infrared Galaxies
Abstract
We present the results of ALMA ~2 mm, ≲1″-resolution observations of 10 (ultra)luminous infrared galaxies ([U]LIRGs; infrared luminosity ≳1011.7 L ⊙) at z < 0.15, targeting dense (>104 cm-3) molecular (HCN, HCO+, and HNC J = 2-1) and 183 GHz H2O 31,3-22,0 emission lines. Active galactic nucleus (AGN)-important ULIRGs tend to show higher HCN/HCO+ J = 2-1 flux ratios than starburst-classified sources. We detect 183 GHz H2O emission in almost all AGN-important ULIRGs, and elevated H2O emission is found in two sources with elevated HCN J = 2-1 emission, relative to HCO+ J = 2-1. Except one ULIRG (the Superantennae), the H2O emission largely comes from the entire nuclear regions (~1 kpc), rather than an AGN-origin megamaser at the very center (≪1 kpc). Nuclear (~1 kpc) dense molecular gas mass derived from HCO+ J = 2-1 luminosity is ≳ a few × 108 M ⊙, and its depletion time is estimated to be ≳106 yr in all sources. Vibrationally excited J = 2-1 emission lines of HCN and HNC are detected in a few (U)LIRGs, but those of HCO+ are not. It is suggested that in mid-infrared-radiation-exposed innermost regions around energy sources, HCO+ and HNC are substantially less abundant than HCN. In our ALMA ~2 mm data of 10 (U)LIRGs, two continuum sources are serendipitously detected within ~10″, which are likely to be an infrared-luminous dusty galaxy at z > 1 and a blazar.
- Publication:
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The Astrophysical Journal
- Pub Date:
- February 2022
- DOI:
- 10.3847/1538-4357/ac3a68
- arXiv:
- arXiv:2111.09338
- Bibcode:
- 2022ApJ...926..159I
- Keywords:
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- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 50 pages, 16 Figures. ApJ accepted