%0 Generic %1 schruba2017physical %A Schruba, Andreas %A Leroy, Adam K. %A Kruijssen, J. M. Diederik %A Bigiel, Frank %A Bolatto, Alberto D. %A de Blok, W. J. G. %A Tacconi, Linda %A van Dishoeck, Ewine F. %A Walter, Fabian %D 2017 %K dwarf galaxy gas high molecular resolution %T Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way %U http://arxiv.org/abs/1701.02748 %X We present the ALMA survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0.9 arcsec ~ 2 pc) spatial resolution while covering large area: four 250 pc x 250 pc regions that encompass ~2/3 of NGC 6822's star formation. In these regions, we resolve ~150 compact CO clumps that have small radii (~2-3 pc), narrow line width (~1 km/s), and low filling factor across the galaxy. This is consistent with other recent studies of low metallicity galaxies, but here shown with a 15 times larger sample. At parsec scales, CO emission correlates with 8 micron emission better than with 24 micron emission and anti-correlates with Halpha, so that PAH emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and CO-to-H2 ratio ~1-2 times the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular cloud. Using dust to trace H2 for the entire complex, we find CO-to-H2 to be ~20-25 times the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H2-to-HI ratio is low globally and only mildly above unity within the complexes. The SFR-to-H2 ratio is ~3-5 times higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.

@misc{schruba2017physical, abstract = {We present the ALMA survey of CO(2-1) emission from the 1/5 solar metallicity, Local Group dwarf galaxy NGC 6822. We achieve high (0.9 arcsec ~ 2 pc) spatial resolution while covering large area: four 250 pc x 250 pc regions that encompass ~2/3 of NGC 6822's star formation. In these regions, we resolve ~150 compact CO clumps that have small radii (~2-3 pc), narrow line width (~1 km/s), and low filling factor across the galaxy. This is consistent with other recent studies of low metallicity galaxies, but here shown with a 15 times larger sample. At parsec scales, CO emission correlates with 8 micron emission better than with 24 micron emission and anti-correlates with Halpha, so that PAH emission may be an effective tracer of molecular gas at low metallicity. The properties of the CO clumps resemble those of similar-size structures in Galactic clouds except of slightly lower surface brightness and CO-to-H2 ratio ~1-2 times the Galactic value. The clumps exist inside larger atomic-molecular complexes with masses typical for giant molecular cloud. Using dust to trace H2 for the entire complex, we find CO-to-H2 to be ~20-25 times the Galactic value, but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state. The H2-to-HI ratio is low globally and only mildly above unity within the complexes. The SFR-to-H2 ratio is ~3-5 times higher in the complexes than in massive disk galaxies, but after accounting for the bias from targeting star-forming regions, we conclude that the global molecular gas depletion time may be as long as in massive disk galaxies.}, added-at = {2017-01-12T10:28:39.000+0100}, author = {Schruba, Andreas and Leroy, Adam K. and Kruijssen, J. M. Diederik and Bigiel, Frank and Bolatto, Alberto D. and de Blok, W. J. G. and Tacconi, Linda and van Dishoeck, Ewine F. and Walter, Fabian}, biburl = {https://www.bibsonomy.org/bibtex/210752968cb75e07d727e5db06deda8a5/miki}, description = {[1701.02748] Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way}, interhash = {48fd486fb64e1ed12970062f913eabbc}, intrahash = {10752968cb75e07d727e5db06deda8a5}, keywords = {dwarf galaxy gas high molecular resolution}, note = {cite arxiv:1701.02748Comment: Accepted for publication in The Astrophysical Journal; 22 pages, 10 figures, 7 tables}, timestamp = {2017-01-12T10:28:39.000+0100}, title = {Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way}, url = {http://arxiv.org/abs/1701.02748}, year = 2017 }