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 \approx 2 pc ) spatial resolution while covering large area : four 250 pc \times 250 pc regions that encompass { \sim } 2 / 3 of NGC 6822 ’ s star formation .
In these regions , we resolve { \sim } 150 compact CO clumps that have small radii ( \sim 2 { - } 3 pc ) , narrow line width ( { \sim } 1 km s ^ { -1 } ) , 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 H \alpha , 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-H _ { 2 } ratio { \sim } 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 H _ { 2 } for the entire complex , we find CO-to-H _ { 2 } to be { \sim } 20 { - } 25 \times the Galactic value , but with strong dependence on spatial scale and variations between complexes that may track their evolutionary state .
The H _ { 2 } -to-H i ratio is low globally and only mildly above unity within the complexes .
The SFR-to-H _ { 2 } ratio is { \sim } 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 .