The Calibration of Mid-Infrared Star Formation Rate Indicators
Abstract
With the goal of investigating the degree to which the mid-infrared emission traces the star formation rate (SFR), we analyze Spitzer 8 um and 24 um data of star-forming regions in a sample of 33 nearby galaxies with available HST/NICMOS images in the Paschen-alpha (1.8756 um) emission line. The galaxies are drawn from the Spitzer Infrared Nearby Galaxies Survey (SINGS) sample, and cover a range of morphologies and a factor ~10 in oxygen abundance. Published data on local low-metallicity starburst galaxies and Luminous Infrared Galaxies are also included in the analysis. Both the stellar-continuum-subtracted 8 um emission and the 24 um emission correlate with the extinction-corrected Pa-alpha line emission, although neither relationship is linear. Simple models of stellar populations and dust extinction and emission are able to reproduce the observed non-linear trend of the 24 um emission versus number of ionizing photons, including the modest deficiency of 24 um emission in the low metallicity regions, which results from a combination of decreasing dust opacity and dust temperature at low luminosities. Conversely, the trend of the 8 um emission as a function of the number of ionizing photons is not well reproduced by the same models. The 8 um emission is contributed, in larger measure than the 24 um emission, by dust heated by non-ionizing stellar populations, in agreement with previous findings. Two SFR calibrations, one using the 24 um emission and the other using a combination of the 24 um and H-alpha luminosities (Kennicutt et al. 2007), are presented. No calibration is presented for the 8 um emission, because of its significant dependence on both metallicity and environment. The calibrations presented here should be directly applicable to systems dominated by on-going star formation.
Keywords
Cite
@article{arxiv.0705.3377,
title = {The Calibration of Mid-Infrared Star Formation Rate Indicators},
author = {D. Calzetti and R. C. Kennicutt and C. W. Engelbracht and C. Leitherer and B. T. Draine and L. Kewley and J. Moustakas and M. Sosey and D. A. Dale and K. D. Gordon and G. X. Helou and D. J. Hollenbach and L. Armus and G. Bendo and C. Bot and B. Buckalew and T. Jarrett and A. Li and M. Meyer and E. J. Murphy and M. Prescott and M. W. Regan and G. H. Rieke and H. Roussel and K. Sheth and J. D. T. Smith and M. D. Thornley and F. Walter},
journal= {arXiv preprint arXiv:0705.3377},
year = {2010}
}
Comments
67 pages, 15 figures, accepted for publication on the Astrophysical Journal; replacement contains: correction to equation 8; important tweaks to equation 9; various typos corrected