Shetty, Rahul and Kauffmann, Jens and Schnee, Scott and Goodman, Alyssa A. and Ercolano, Barbara (2009) The Effect of Line-of-Sight Temperature Variation and Noise on Dust Continuum Observations. Astrophysical Journal, 696 (2). pp. 2234-2251. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090821-130236801
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We investigate the effect of line-of-sight temperature variations and noise on two commonly used methods to determine dust properties from dust-continuum observations of dense cores. One method employs a direct fit to a modified blackbody spectral energy distribution (SED); the other involves a comparison of flux ratios to an analytical prediction. Fitting fluxes near the SED peak produces inaccurate temperature and dust spectral index estimates due to the line-of-sight temperature (and density) variations. Longer wavelength fluxes in the Rayleigh-Jeans part of the spectrum (≳ 600 μm for typical cores) may more accurately recover the spectral index, but both methods are very sensitive to noise. The temperature estimate approaches the density-weighted temperature, or "column temperature," of the source as short wavelength fluxes are excluded. An inverse temperature-spectral index correlation naturally results from SED fitting, due to the inaccurate isothermal assumption, as well as noise uncertainties. We show that above some "threshold" temperature, the temperatures estimated through the flux ratio method can be highly inaccurate. In general, observations with widely separated wavelengths, and including shorter wavelengths, result in higher threshold temperatures; such observations thus allow for more accurate temperature estimates of sources with temperatures less than the threshold temperature. When only three fluxes are available, a constrained fit, where the spectral index is fixed, produces less scatter in the temperature estimate when compared to the estimate from the flux ratio method.
|Additional Information:||© 2009 The American Astronomical Society. Received 2008 October 14; accepted 2009 February 23; published 2009 April 29. We thank P. Myers, D. Johnstone, J. Foster, J. Pineda, E. Rosolowsky, and S. Chakrabarti for useful discussions. We also thank N. Wright for help in executing MOCASSIN. In our analysis, we have made extensive use of NEMO software (Teuben 1995). S.S. acknowledges support from the Owens Valley Radio Observatory, which is supported by the National Science Foundation through grant AST 05-40399. R.S., J.K., and A.G. acknowledge support from the Harvard Initiative in Innovative Computing, which hosts the Star-Formation Taste Tests Community at which further details on these results can be found and discussed (see http://www.cfa.harvard.edu/ ∼agoodman/tastetests).|
|Subject Keywords:||dust, extinction; infrared: ISM; ISM: clouds; methods: miscellaneous; stars: formation|
|Official Citation:||The Effect of Line-of-Sight Temperature Variation and Noise on Dust Continuum Observations Rahul Shetty, Jens Kauffmann, Scott Schnee, Alyssa A. Goodman, and Barbara Ercolano 2009 ApJ 696 2234-2251 doi: 10.1088/0004-637X/696/2/2234.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||24 Aug 2009 17:21|
|Last Modified:||26 Dec 2012 11:14|
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