1997/10/21 by G. Petitpas, G. R. Petitpas, C. D. Wilson · 2 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Atomic and Molecular Physics #Dwarf galaxy #Galaxy #Irregular galaxy #Lenticular galaxy #Line (geometry) #Local Group #Mean kinetic temperature #Metallicity #Molecular cloud #Physics #Star formation #Stars #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/305351
20 pages with 6 ps figures, accepted for publication in The Astrophysical Journal
arxiv created 1997/10/21 · openalex publication_date 1998/03/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
We have observed the 12 CO J = 2-1 and J = 3-2 lines at a few locations in the dwarf irregular galaxies IC 10 and NGC 6822 using the James Clerk Maxwell Telescope. In addition, we have observed the 13 CO J = 2-1 line for IC 10 and the first detection of the 13 CO J = 3-2 transition in a Local Group galaxy. The CO line ratios in IC 10 are uniform and are consistent with the average line ratios observed in M33 at the 1 σ level. These low-metallicity environments appear to be porous to UV radiation and allow for more efficient heating of molecular gas by nearby H II regions. The 12 CO J = 3-2/ J = 2-1 ratio for the molecular cloud in NGC 6822 is higher than those found for IC 10 and M33 and suggests that the 12 CO emission is optically thin in this region. This high line ratio is likely the result of its location inside a large H II region with low metallicity and low gas content, and requires a hydrogen density greater than 10 4 cm -3 and a kinetic temperature greater than 100 K. The 12 CO/ 13 CO J = 3-2 line ratio in one of the molecular clouds in IC 10 indicates that the gas must have a rather high kinetic temperature of about 100 K. In IC 10 we observe structures on a variety of size scales that all appear to be gravitationally bound. This effect may help explain the rather high star formation rate in IC 10.