The Calibration of Monochromatic Far-Infrared Star Formation Rate Indicators

• Published in: The Astrophysical journal Vol. 714; no. 2; pp. 1256 - 1279
• Main Authors: Calzetti, D, Wu, S.-Y, Hong, S, Kennicutt, R. C, Lee, J. C, Dale, D. A, Engelbracht, C. W, van Zee, L, Draine, B. T, Hao, C.-N, Gordon, K. D, Moustakas, J, Murphy, E. J, Regan, M, Begum, A, Block, M, Dalcanton, J, Funes, J, Gil de Paz, A, Johnson, B, Sakai, S, Skillman, E, Walter, F, Weisz, D, Williams, B, Wu, Y
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 10.05.2010; IOP
• Subjects: ABUNDANCE; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CALIBRATION; DUSTS; Earth, ocean, space; ELECTROMAGNETIC RADIATION; ELEMENTS; EMISSION; Exact sciences and technology; GALAXIES; LUMINOSITY; MONOCHROMATIC RADIATION; NONLINEAR PROBLEMS; NONMETALS; OPACITY; OPTICAL PROPERTIES; OXYGEN; PHYSICAL PROPERTIES; RADIATIONS; STARS; stars: formation; galaxies: starburst; infrared: galaxies; Star formation; Starburst galaxies; galaxies: ISM; galaxies: interactions; Infrared galaxies; Formation rate; Infrared star; ISM: structure
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/714/2/1256

Spitzer data at 24, 70, and 160 {mu}m and ground-based H{alpha} images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160 {mu}m. We compare recently published recipes for SFR measures using combinations of the 24 {mu}m and observed H{alpha} luminosities with those using 24 {mu}m luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70 {mu}m and 160 {mu}m luminosity are found for L(70) {approx_gt} 1.4 x 10{sup 42} erg s{sup -1} and L(160) {approx_gt} 2 x 10{sup 42} erg s{sup -1}, corresponding to SFR {approx_gt} 0.1-0.3 M{sub sun} yr{sup -1}, and calibrations of SFRs based on L(70) and L(160) are proposed. Below those two luminosity limits, the relation between SFR and 70 {mu}m (160 {mu}m) luminosity is nonlinear and SFR calibrations become problematic. A more important limitation is the dispersion of the data around the mean trend, which increases for increasing wavelength. The scatter of the 70 {mu}m (160 {mu}m) data around the mean is about 25% (factor {approx}2) larger than the scatter of the 24 {mu}m data. We interpret this increasing dispersion as an effect of the increasing contribution to the infrared emission of dust heated by stellar populations not associated with the current star formation. Thus, the 70 (160) {mu}m luminosity can be reliably used to trace SFRs in large galaxy samples, but will be of limited utility for individual objects, with the exception of infrared-dominated galaxies. The nonlinear relation between SFR and the 70 and 160 {mu}m emission at faint galaxy luminosities suggests a variety of mechanisms affecting the infrared emission for decreasing luminosity, such as increasing transparency of the interstellar medium, decreasing effective dust temperature, and decreasing filling factor of star-forming regions across the galaxy. In all cases, the calibrations hold for galaxies with oxygen abundance higher than roughly 12 +log(O/H) {approx} 8.1. At lower metallicity, the infrared luminosity no longer reliably traces the SFR because galaxies are less dusty and more transparent.