Dense Molecular Gas in the Nearby Low-metallicity Dwarf Starburst Galaxy IC 10

作者：Kepley Amanda A; Bittle Lauren; Leroy Adam K; Jimenez Donaire Maria J; Schruba Andreas; Bigiel Frank; Gallagher Molly; Johnson Kelsey; Usero Antonio

来源：Astrophysical Journal, 2018, 862(2): 120.

DOI：10.3847/1538-4357/aacaf4

• galaxies: individual (IC 10)
• galaxies: irregular
• galaxies: ISM
• galaxies: star formation
• ISM: molecules
• radio lines: galaxies

Dense molecular gas and star formation are correlated in galaxies. The effect of low metallicity on this relationship is crucial for interpreting observations of high-redshift galaxies, which have lower metallicities than galaxies today. However, it remains relatively unexplored because dense molecular gas tracers like HCN and HCO+ are faint in low-metallicity systems. We present Green Bank Telescope observations of HCN(1-0) and HCO+(1-0) on giant molecular cloud (34 pc) scales in the nearby low-metallicity (12 + log(O/H) = 8.2) starburst IC 10 and compare them to those in other galaxies. We detect HCN and HCO+ in one and three of five pointings, respectively. The I-HCN/I-HCO(+) values are within the range seen in other galaxies, but are most similar to those seen in other low-metallicity sources and in starbursts. The detections follow the fiducial L-IR-L-HCN and L-IR-L-HCO(+) relationships. These trends suggest that HCN and HCO+ can be used to trace dense molecular gas at metallicities of 1/4 Z(circle dot), to first order. The dense gas fraction is similar to that in spiral galaxies, but lower than that in U/LIRGs. The dense molecular gas star formation efficiency, however, is on the upper end of those in normal galaxies and consistent with those in U/LIRGs. These results suggest that the CO and HCN/HCO+ emission occupy the same relative volumes as they do at higher metallicity, but that the entire emitting structure is reduced in size. Dense gas mass estimates for high-redshift galaxies may need to be corrected for this effect.

• 出版日期2018-8-1