Other
Scientific paper
Jan 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912201t&link_type=abstract
American Astronomical Society, 189th AAS Meeting, late abstracts, #122.01; Bulletin of the American Astronomical, Vol. 29, p. 73
Other
Scientific paper
We present (12) CO 1->0 of seven HI rich dwarf galaxies which currently have active star formation. Four of them are HII galaxies with bursts of star formation, while the remaining three are magellanic irregulars with lower levels of star formation. We detect four galaxies, and have low upper limits for the non--detections. The CO emission for a given mass of molecular gas is believed to depend upon the galaxy metal abundance. Combining our data with CO observations of HII galaxies and dwarf irregulars in the literature, we find evidence suggesting that low abundance galaxies (12 + log (O/H) < 8.0) have a lower average ratio of CO luminosity-to-HI mass than do higher abundance galaxies (12 + log (O/H) >= 8.0). However, there may be an explanation for this result other than a dependence of CO emission on abundance. Nearly all of the detected galaxies are HII galaxies, and because of their vigorous star formation they are likely to have warmer molecular gas than the dwarf irregulars, thereby having higher CO luminosities for a given amount of H_2. Most of the HII galaxies we used are high abundance systems; most of the dwarf irregulars (which are undetected with poor upper limits) are low abundance systems. Thus combining only HII galaxies with high abundances and dwarf irregulars with low abundances could give rise spuriously to the trend we identified. We do find evidence that the CO luminosity is dependent on the star formation rate as measured by Hα luminosity. Observations of both HII galaxies and dwarf irregulars over a wide range of metal abundances and star formation rates will be necessary to disentangle and confirm the trends of CO luminosity with metal abundance and star formation rate.
Kobulnicky Henry
Skillman Evan
Taylor Charles
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