Work

Star Formation in Isolated Disk Galaxies. II. Schmidt Laws and Efficiency of Gravitational Collapse

Year: 2006

Type: article

Abstract: We model gravitational instability in a wide range of isolated disk galaxies, using GADGET, a three-dimensional, smoothed particle hydrodynamics code. The model galaxies include a dark matter halo and a disk of stars and isothermal gas. Absorbing sink particles are used to directly measure the mass of gravitationally collapsing gas. Below the density at which they are inserted, the collapsing gas is fully resolved. We make the assumption that stars and molecular gas form within the sink particle once it is created and that the star formation rate is the gravitational collapse rate times a constant efficiency factor. In our models, the derived star formation rate declines exponentially with time, and radial profiles of atomic and molecular gas and star formation rate reproduce observed behavior. We derive from our models and discuss both the global and local Schmidt laws for star formation: power-law relations between surface densities of gas and star formation rate. The global Schmidt law observed in disk galaxies is quantitatively reproduced by our models. We find that the surface density of star formation rate directly correlates with the strength of local gravitational instability. The local Schmidt laws of individual galaxies in our models show clear evidence of star formation thresholds. The variations in both the slope and the normalization of the local Schmidt laws cover the observed range. The averaged values agree well with the observed average and with the global law. Our results suggest that the nonlinear development of gravitational instability determines the local and global Schmidt laws and the star formation thresholds. We derive from our models the quantitative dependence of the global star formation efficiency on the initial gravitational instability of galaxies. The more unstable a galaxy is, the quicker and more efficiently its gas collapses gravitationally and forms stars.

Source: The Astrophysical Journal

DOI: 10.1086/499350

Authors: Yuexing Li, Mordecai‐Mark Mac Low, Ralf S. Klessen

Institutions: American Museum of Natural History, Smithsonian Astrophysical Observatory, Center for Astrophysics Harvard & Smithsonian, Columbia University, Leibniz Institute for Astrophysics Potsdam

Language: English

Topic: Galaxies: Formation, Evolution, Phenomena

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: bronze

Funders: National Science Foundation, National Aeronautics and Space Administration, American Museum of Natural History, Deutsche Forschungsgemeinschaft

Awards: Collaborative Research: Fireworks at the Ballet: Globular Cluster Formation, Bulge Dynamics and the Role of Central Black Holes in Galaxy Mergers, CAREER: Structure Formation and Support by Magnetized, Supersonic Turbulence in the Interstellar Medium and Star-Forming Regions, TRAIN THE NEXT GENERATION AND TO ENHANCE THE INFRA STRUCTURE FOR EDUCA- TION AND RESEARCH AT THE FR