The Star formation law in galactic disks

1989
8 pages
Published in:
  • Astrophys.J. 344 (1989) 685

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Abstract: (ADS)
Measurements of the distribution of H-alpha emission in galaxies are combined with published H I and CO data in order to reassess the dependence of the massive star formation rate (SFR) on the density and dynamics of the interstellar gas. The disk-averaged H-alpha surface brightness is correlated with the mean atomic and total gas surface densities, but is only weakly correlated with the mean molecular gas density inferred from CO emission. Radial profiles of gas and H-alpha emission in 15 galaxies are used to define the relationship between the SFR and gas surface density. In dense regions, the SFR and total gas density are well-represented by a Schmidt power-law relation. This Schmidt law breaks down, however, at densities below a critical threshold value. Massive star formation is completely suppressed at surface densities well below the threshold, while at densities near the threshold value the slope of the SFR-density relation is much steeper than a normal Schmidt law. A simple Toomre disk stability model predicts threshold densities and radii which are in excellent agreement with observations.
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