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Date and Time of the Query: 2019-06-18 T17:45:32 PDT
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For refcode 2011ApJ...731...25K:
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2011ApJ...731...25K Which Phase of the Interstellar Medium Correlates with the Star Formation Rate? Krumholz, Mark R.; Leroy, Adam K.; McKee, Christopher F. Abstract. Nearby spiral galaxies show an extremely tight correlation between tracers of molecular hydrogen (H_2_) in the interstellar medium and tracers of recent star formation, but it is unclear whether this correlation is fundamental or accidental. In the galaxies that have been surveyed to date, H_2_ resides predominantly in gravitationally bound clouds cooled by carbon monoxide (CO) molecules, but in galaxies of low metal content the correlations between bound clouds, CO, and H_2_ break down, and it is unclear if the star formation rate (SFR) will then correlate with H_2_ or with some other quantity. Here, we show that star formation will continue to follow H_2_ independent of metallicity. This is not because H_2_ is directly important for cooling, but instead because the transition from predominantly atomic hydrogen (H I) to H_2_ occurs under the same conditions as a dramatic drop in gas temperature and Bonnor-Ebert mass that destabilizes clouds and initiates collapse. We use this model to compute how SFR will correlate with total gas mass, with mass of gas where the hydrogen is H_2_, and with mass of gas where the carbon is CO in galaxies of varying metallicity, and show that preliminary observations match the trend we predict. Key words: galaxies: star formation, ISM: atoms, ISM: clouds, ISM: molecules, stars: formation
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