Spitzer Analysis of H II Region Complexes in the Magellanic Clouds: Determining a Suitable Monochromatic Obscured Star Formation Indicator

• Published in: The Astrophysical journal 2010-06, Vol.716 (1), p.453-473
• Main Authors: Lawton, B, Gordon, K. D, Babler, B, Block, M, Bolatto, A. D, Bracker, S, Carlson, L. R, Engelbracht, C. W, Hora, J. L, Indebetouw, R, Madden, S. C, Meade, M, Meixner, M, Misselt, K, Oey, M. S, Oliveira, J. M, Robitaille, T, Sewilo, M, Shiao, B, Vijh, U. P, Whitney, B
• Format: Article
• Language: English
• Subjects: Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BOLOMETERS; BRIGHTNESS; DUSTS; Earth, ocean, space; ELECTROMAGNETIC RADIATION; ENERGY SPECTRA; EQUATIONS; Exact sciences and technology; GALAXIES; INFRARED SPECTRA; LUMINOSITY; MAGELLANIC CLOUDS; MEASURING INSTRUMENTS; MONOCHROMATIC RADIATION; OPTICAL PROPERTIES; PHOTOMETRY; PHYSICAL PROPERTIES; RADIATIONS; SPECTRA; STARS; TELESCOPES; ULTRAVIOLET RADIATION
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/716/1/453

H II regions are the birth places of stars, and as such they provide the best measure of current star formation rates (SFRs) in galaxies. The close proximity of the Magellanic Clouds allows us to probe the nature of these star forming regions at small spatial scales. To study the H II regions, we compute the bolometric infrared flux, or total infrared (TIR), by integrating the flux from 8 to 500 {mu}m. The TIR provides a measure of the obscured star formation because the UV photons from hot young stars are absorbed by dust and re-emitted across the mid-to-far-infrared (IR) spectrum. We aim to determine the monochromatic IR band that most accurately traces the TIR and produces an accurate obscured SFR over large spatial scales. We present the spatial analysis, via aperture/annulus photometry, of 16 Large Magellanic Cloud (LMC) and 16 Small Magellanic Cloud (SMC) H II region complexes using the Spitzer Space Telescope's IRAC (3.6, 4.5, 8 {mu}m) and MIPS (24, 70, 160 {mu}m) bands. Ultraviolet rocket data (1500 and 1900 A) and SHASSA H{alpha} data are also included. All data are convolved to the MIPS 160 {mu}m resolution (40 arcsec full width at half-maximum), and apertures have a minimum radius of 35''. The IRAC, MIPS, UV, and H{alpha} spatial analysis are compared with the spatial analysis of the TIR. We find that nearly all of the LMC and SMC H II region spectral energy distributions (SEDs) peak around 70 {mu}m at all radii, from {approx}10 to {approx}400 pc from the central ionizing sources. As a result, we find the following: the sizes of H II regions as probed by 70 {mu}m are approximately equal to the sizes as probed by TIR ({approx}70 pc in radius); the radial profile of the 70 {mu}m flux, normalized by TIR, is constant at all radii (70 {mu}m {approx} 0.45TIR); the 1{sigma} standard deviation of the 70 {mu}m fluxes, normalized by TIR, is a lower fraction of the mean (0.05-0.12 out to {approx}220 pc) than the normalized 8, 24, and 160 {mu}m normalized fluxes (0.12-0.52); and these results are the same for the LMC and the SMC. From these results, we argue that 70 {mu}m is the most suitable IR band to use as a monochromatic obscured star formation indicator because it most accurately reproduces the TIR of H II regions in the LMC and SMC and over large spatial scales. We also explore the general trends of the 8, 24, 70, and 160 {mu}m bands in the LMC and SMC H II region SEDs, radial surface brightness profiles, sizes, and normalized (by TIR) radial flux pr