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The Star Formation Law at Low Surface Density

Wyder, Ted K. and Martin, D. Christopher and Barlow, Tom A. and Foster, Karl and Friedman, Peter G. and Morrissey, Patrick and Neff, Susan G. and Neill, James D. and Schiminovich, David and Seibert, Mark and Bianchi, Luciana and Donas, José and Heckman, Timothy M. and Lee, Young-Wook and Madore, Barry F. and Milliard, Bruno and Rich, R. Michael and Szalay, Alex S. and Yi, Sukyoung K. (2009) The Star Formation Law at Low Surface Density. Astrophysical Journal, 696 (2). pp. 1834-1853. ISSN 0004-637X.

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We investigate the nature of the star formation law at low gas surface densities using a sample of 19 low surface brightness (LSB) galaxies with existing H I maps in the literature, UV imaging from the Galaxy Evolution Explorer satellite, and optical images from the Sloan Digital Sky Survey. All of the LSB galaxies have (NUV – r) colors similar to those for higher surface brightness star-forming galaxies of similar luminosity indicating that their average star formation histories are not very different. Based upon four LSB galaxies with both UV and far-infrared (FIR) data, we find FIR/UV ratios significantly less than 1, implying low amounts of internal UV extinction in LSB galaxies. We use the UV images and H I maps to measure the star formation rate (SFR) and hydrogen gas surface density within the same region for all the galaxies. The LSB galaxy star formation rate surface densities lie below the extrapolation of the power law fit to the SFR surface density as a function of the total gas density for higher surface brightness galaxies. Although there is more scatter, the LSB galaxies also lie below a second version of the star formation law in which the SFR surface density is correlated with the gas density divided by the orbital time in the disk. The downturn seen in both star formation laws is consistent with theoretical models that predict lower star formation efficiencies in LSB galaxies due to the declining molecular fraction with decreasing density.

Item Type:Article
Related URLs:
URLURL TypeDescription
Martin, D. Christopher0000-0002-8650-1644
Foster, Karl0000-0001-5800-5531
Morrissey, Patrick0000-0001-8177-1023
Neill, James D.0000-0002-0466-1119
Seibert, Mark0000-0002-1143-5515
Bianchi, Luciana0000-0001-7746-5461
Madore, Barry F.0000-0002-1576-1676
Rich, R. Michael0000-0003-0427-8387
Additional Information:© 2009 The American Astronomical Society. Received 2008 October 2; accepted 2009 February 24; published 2009 April 27. We thank Joannah Hinz, Samuel Boissier, Robert Kennicutt, and Mark Krumholz for helpful discussions. GALEX is a NASA Small Explorer, launched in 2003 April. We gratefully acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with the Centre National d'Etudes Spatiales of France and the Korean Ministry of Science and Technology.
Group:Space Astrophysics Laboratory
Funding AgencyGrant Number
Subject Keywords:galaxies: evolution; galaxies: irregular; galaxies: ISM; galaxies: spiral; ultraviolet: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20090904-124126138
Persistent URL:
Official Citation:The Star Formation Law at Low Surface Density Ted K. Wyder, D. Christopher Martin, Tom A. Barlow, Karl Foster, Peter G. Friedman, Patrick Morrissey, Susan G. Neff, James D. Neill, David Schiminovich, Mark Seibert, Luciana Bianchi, José Donas, Timothy M. Heckman, Young-Wook Lee, Barry F. Madore, Bruno Milliard, R. Michael Rich, Alex S. Szalay, and Sukyoung K. Yi 2009 ApJ 696 1834-1853 doi: 10.1088/0004-637X/696/2/1834.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15619
Deposited By: Tony Diaz
Deposited On:15 Sep 2009 16:37
Last Modified:09 Mar 2020 21:00

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