ALMA Observations of the Molecular Clouds in NGC 625
Abstract
We present the highest-resolution (1″) 12CO observations of molecular gas in the dwarf starburst galaxy NGC 625 to date, obtained with Atacama Large Millimeter/submillimeter Array. The molecular gas, which is distributed in discrete clouds within an area of 0.4 kpc2, does not have well-ordered large-scale motions. We measure a molecular mass in NGC 625 of 5.3 × 106 ${M}_{\odot }$ , assuming a Milky Way CO-to- ${{\rm{H}}}_{2}$ conversion factor. We use the CPROPS package to identify molecular clouds and measure their properties. The 19 resolved CO clouds have a median radius of 20 pc, a median linewidth 2.5 $\mathrm{km}\,{{\rm{s}}}^{-1}$ , and a median surface density of 169 ${M}_{\odot }\,{{\rm{pc}}}^{-2}$ . Larson scaling relations suggest that molecular clouds in NGC 625 are mostly in virial equilibrium. Comparison of our high-resolution CO observations with a star formation rate map, inferred from ancillary optical observations, suggests that about 40% of the molecular clouds coincide with the brightest H II regions. These bright H II regions have a range of molecular gas depletion timescales, all within a factor of ∼3 of the global depletion time in NGC 625 of 106-134 Myr. The highest surface density molecular clouds toward the southwest of the galaxy, in a region we call the Butterfly, do not show strong star formation activity and suggest a depletion timescale longer than 5 Gyr.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2020
- DOI:
- 10.3847/1538-4357/ab8883
- arXiv:
- arXiv:2002.09498
- Bibcode:
- 2020ApJ...895...21I
- Keywords:
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- Dwarf galaxies;
- Galaxies;
- Star formation;
- Interstellar medium;
- Giant molecular clouds;
- Molecular gas;
- Interstellar molecules;
- Starburst galaxies;
- Metallicity;
- Interferometry;
- Submillimeter astronomy;
- Molecular clouds;
- 416;
- 573;
- 1569;
- 847;
- 653;
- 1073;
- 849;
- 1570;
- 1031;
- 808;
- 1647;
- 1072;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- doi:10.3847/1538-4357/ab8883