Star Formation Law in the Milky Way

Abstract

The Schmidt law (SF law) in the Milky Way was investigated using 3D distribution maps of HII regions, HI and molecular (\Htwo) gases with spatial resolutions of $\sim 1$ kpc in the Galactic plane and a few tens of pc in the vertical direction. HII regions were shown to be distributed in a star-forming (SF) disk with nearly constant vertical full thickness 92 pc in spatial coincidence with the molecular gas disk. The vertically averaged volume star formation rate (SFR) ${\rho }_{\mathrm{SFR}}$ in the SF disk is related to the surface SFR ${\Sigma }_{\mathrm{SFR}}$ by ${\rho }_{\mathrm{SFR}}/[{\mathrm{M}}_{\odot }{\mathrm{y}}^{-1}\mathrm{kp}{\mathrm{c}}^{-3}]=9.26\times {\Sigma }_{\mathrm{SFR}}/[{\mathrm{M}}_{\odot }{\mathrm{y}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}]$. The SF law fitted by a single power law of gas density in the form of ${\Sigma }_{\mathrm{SFR}}\propto {\rho }_{\mathrm{SFR}}\propto {\rho }_{\mathrm{gas}}^{\alpha }$ and $\propto {\Sigma }_{\mathrm{gas}}^{\beta }$ showed indices of $\alpha =0.78\pm 0.05$ for ${\rho }_{{\mathrm{H}}_2}$ and $2.15\pm 0.08$ for ${\rho }_{\mathrm{total}}$, and $\beta =1.14\pm 0.23$ for ${\Sigma }_{\mathrm{total}}$, where $\rho$ and $\Sigma$ denote volume and surface densities, respectively. The star formation rate is shown to be directly related to the molecular gas, but indirectly to HI and total gas densities. The dependence of the SF law on the gaseous phase is explained by the phase transition theory between HI and H${}_2$ gases.

arXiv comment7 pages, 8 figures, 1 table, to appear in PASJ

References in corpus (18)

• Star Formation in Galaxies Along the Hubble Sequence
• The Global Schmidt Law in Star Forming Galaxies
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Star Formation in the Milky Way and Nearby Galaxies
• The Milky Way in Molecular Clouds: A New Complete CO Survey
• The Star Formation Law in Nearby Galaxies on Sub-Kpc Scales
• The Star Formation Rate and Gas Surface Density Relation in the Milky Way: Implications for Extragalactic Studies
• Star Formation Rates in Molecular Clouds and the Nature of the Extragalactic Scaling Relations
• The observed spiral structure of the Milky Way
• Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: II. The Molecular Gas Disk
• Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: I. The HI Disk
• Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: III. The Total Neutral Gas Disk
• The rate and latency of star formation in dense, massive clumps in the Milky Way
• Molecular Gas, Kinematics, and OB Star Formation in the Spiral Arms of the Southern Milky Way
• The Schmidt Law at High Molecular Densities
• A Schmidt-Kennicutt law for star formation in the Milky Way disk
• Three-Dimensional Distribution of the ISM in the Milky Way Galaxy: IV. 3D Molecular Fraction and Galactic-Scale HI-to-H${}_2$ Transition
• Threshold between Spontaneous and Cloud-Collisional Star Formation

Cited by in corpus (2)

• Optical Thickness, Spin Temperature, and Correction Factor for Density of the Galactic HI Gas
• Radial Variations of the Volume- and Surface-Star Formation Laws in the Galaxy