The Effect of Line of Sight Temperature Variation and Noise on Dust Continuum Observations

TL;DR

This paper examines how line of sight temperature variations and noise impact dust property measurements from continuum observations, highlighting limitations of common methods and proposing insights for more accurate temperature estimates.

Contribution

It analyzes the effects of temperature variations and noise on dust property determination methods, revealing their sensitivities and proposing improved approaches for accurate temperature estimation.

Findings

Flux fitting near the SED peak yields inaccurate temperature estimates due to temperature variations.

Longer wavelength fluxes can better recover the spectral index but are sensitive to noise.

Including shorter wavelengths reduces the threshold temperature for accurate estimates.

Abstract

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 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 micron 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.