In:
The Astrophysical Journal, American Astronomical Society, Vol. 936, No. 1 ( 2022-09-01), p. 58-
Abstract:
Both Galactic and extragalactic studies of star formation suggest that stars form directly from dense molecular gas. To trace such high volume density gas, HCN and HCO + J = 1 → 0 have been widely used for their high dipole moments, relatively high abundances, and often being the strongest lines after CO. However, HCN and HCO + J = 1 → 0 emission could arguably be dominated by the gas components at low volume densities. The HCN J = 2 → 1 and HCO + J = 2 → 1 transitions, with more suitable critical densities (1.6 × 10 6 and 2.8 × 10 5 cm −3 ) and excitation requirements, would trace typical dense gas closely related to star formation. Here we report new observations of HCN J = 2 → 1 and HCO + J = 2 → 1 toward 17 nearby infrared-bright galaxies with the APEX 12 m telescope. The correlation slopes between the luminosities of HCN J = 2 → 1 and HCO + J = 2 → 1 and total infrared emission are 1.03 ± 0.05 and 1.00 ± 0.05, respectively. The correlations of their surface densities, normalized with the area of radio/submillimeter continuum, show even tighter relations (slopes: 0.99 ± 0.03 and 1.02 ± 0.03). The eight active galactic nucleus (AGN)–dominated galaxies show no significant difference from the 11 star-formation–dominated galaxies in the above relations. The average HCN/HCO + ratios are 1.15 ± 0.26 and 0.98 ± 0.42 for AGN- and star-formation–dominated galaxies, respectively, without obvious dependencies on infrared luminosity, dust temperature, or infrared pumping. The Magellanic Clouds roughly follow the same correlations, expanding to 8 orders of magnitude. On the other hand, ultraluminous infrared galaxies with AGNs systematically lie above the correlations, indicating potential biases introduced by AGNs.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/ac82eb
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2022
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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