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Published June 1, 2011 | Published
Journal Article Open

Extended Schmidt Law: Role of Existing Stars in Current Star Formation

Abstract

We propose an "extended Schmidt law" with explicit dependence of the star formation efficiency (SFE = SFR/M _(gas)) on the stellar mass surface density (Σ_(star)). This relation has a power-law index of 0.48 ± 0.04 and a 1σ observed scatter on the SFE of 0.4 dex, which holds over five orders of magnitude in the stellar density for individual global galaxies, including various types and especially the low-surface-brightness (LSB) galaxies that deviate significantly from the Kennicutt-Schmidt (KS) law. When applying it to regions of a sample of 12 spiral galaxies at sub-kiloparsec resolution, the extended Schmidt law not only holds for LSB regions but also shows significantly smaller scatters both within and across galaxies compared with the KS law. We argue that this new relation points to the role of existing stars in regulating the SFE, thus better encoding the star formation physics. Comparison with physical models of star formation recipes shows that the extended Schmidt law can be reproduced by some models including gas free fall in a stellar-gravitational potential and pressure-supported star formation. By implementing this new law into the analytic model of gas accretion in ΛCDM, we show that it can reproduce the observed main sequence of star-forming galaxies (a relation between the SFR and stellar mass) from z = 0 up to z = 2.

Additional Information

© 2011 The American Astronomical Society. Received 2010 December 8; accepted 2011 March 22; published 2011 May 9. We thank the anonymous referee for the detailed and constructive comments.We also thank Daniel Dale, Leslie K. Hunt, Eva Schinnerer, and Bruce G. Elmegreen for careful reading and comments. The work is supported through the Spitzer 5MUSES Legacy Program 40539. The authors acknowledge support by NASA through awards issued by JPL/Caltech. This work was based on observations made with the Spitzer Space Telescope, which is operated by JPL/Caltech under a contract with NASA. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web site is http://www.sdss.org/.

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August 22, 2023
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October 23, 2023