Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...461..202h&link_type=abstract
Astrophysical Journal v.461, p.202
Astronomy and Astrophysics
Astronomy
21
Galaxies: Individual Ngc Number: Ngc 4449, Galaxies: Irregular, Galaxies: Ism, Ism: Molecules, Radio Lines: Galaxies
Scientific paper
We present observations of the CO (J = 1-0) molecular emission in the actively star-forming irregular galaxy NGC 4449. Observations of eight positions within the optical galaxy cover a variety of H I cloud locations and levels of star-formation activity. Within a beam of 1.7 kpc we detect 1-4 x 10^7^ M_sun_ of M_H_2__ in six positions, assuming conversion of CO emission to H_2_ as appropriate for irregular galaxies and a large beam size. The size of the telescope beam, the high masses of molecular material, and the relatively high velocity dispersions observed suggest that these are molecular cloud complexes, similar to some of those found in other nearby, late-type galaxies. Except for the center of the galaxy, the molecular mass, molecular and peak H I column densities, and the ratio M_H_2__/M_HI_ do not vary by more than a factor of 2 between the positions. The low molecular-to-atomic gas mass ratio and high H I column densities are consistent with the molecular material being the cores of dense atomic clouds, where it is protected from UV radiation. Regions with few or no bright H II regions have molecular gas masses and gas column densities similar to those in regions containing many sites of star formation. It is not clear whether these regions will become active in the future.
Hunter Deidre Ann
Thronson Harley A. Jr.
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