SPITZER ANALYSIS OF H II REGION COMPLEXES IN THE MAGELLANIC CLOUDS: DETERMINING A SUITABLE MONOCHROMATIC OBSCURED STAR FORMATION INDICATOR

Journal Article · Thu Jun 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/716/1/453· OSTI ID:21450847

Lawton, B; Gordon, K D; Meixner, M; Sewilo, M; Shiao, B ^[1]; Babler, B; Bracker, S; Meade, M ^[2]; Block, M; Engelbracht, C W; Misselt, K ^[3]; Bolatto, A D ^[4]; Carlson, L R ^[5]; Hora, J L; Robitaille, T ^[6]; Indebetouw, R ^[7]; Madden, S C ^[8]; Oey, M S ^[9]; Oliveira, J M ^[10]

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1. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
2. Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter St., Madison, WI 53706 (United States)
3. Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721 (United States)
4. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
5. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD (United States)
6. Harvard-Smithsonian, CfA, 60 Garden St., MS 65, Cambridge, MA 02138-1516 (United States)
7. Department of Astronomy, University of Virginia, P.O. Box 3818, Charlottesville, VA 22903-0818 (United States)
8. Service d'Astrophysique, CEA/Saclay, l'Orme des Merisiers, 91191 Gif-sur-Yvette (France)
9. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042 (United States)
10. School of Physical and Geographical Sciences, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG (United Kingdom)

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 profiles. We derive an obscured SFR equation that is modified from the literature to use 70 {mu}m luminosity, SFR(M {sub sun} yr{sup -1}) = 9.7(0.7) x 10{sup -44} L {sub 70}(ergs s{sup -1}), which is applicable from 10 to 300 pc distance from the center of an H II region. We include an analysis of the spatial variations around H II regions between the obscured star formation indicators given by the IR and the unobscured star formation indicators given by UV and H{alpha}. We compute obscured and unobscured SFRs using equations from the literature and examine the spatial variations of the SFRs around H II regions.

• OSTI ID: 21450847
• Journal Information: Astrophysical Journal, Vol. 716, Issue 1; Other Information: DOI: 10.1088/0004-637X/716/1/453; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
BOLOMETERS
BRIGHTNESS
DUSTS
ENERGY SPECTRA
EQUATIONS
INFRARED SPECTRA
LUMINOSITY
MAGELLANIC CLOUDS
MONOCHROMATIC RADIATION
PHOTOMETRY
STARS
TELESCOPES
ULTRAVIOLET RADIATION
ELECTROMAGNETIC RADIATION
GALAXIES
MEASURING INSTRUMENTS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
RADIATIONS
SPECTRA