The Effect of Noise on the Dust Temperature - Spectral Index Correlation

TL;DR

This paper examines how measurement uncertainties can create an apparent inverse correlation between dust temperature and spectral index in spectral energy distribution fits, highlighting the influence of noise on observational interpretations.

Contribution

It demonstrates that noise can produce an inverse T - beta correlation in SED fits, challenging previous assumptions about the physical nature of this relation.

Findings

Inverse T - beta correlation can arise from noise in flux measurements.

Noisy fits in the Rayleigh-Jeans regime yield unreliable T and beta estimates.

Noise may primarily cause the observed inverse T - beta relation in dust observations.

Abstract

We investigate how uncertainties in flux measurements affect the results from modified blackbody SED fits. We show that an inverse correlation between the dust temperature T and spectral index (beta) naturally arises from least squares fits due to the uncertainties, even for sources with a single T and beta. Fitting SEDs to noisy fluxes solely in the Rayleigh-Jeans regime produces unreliable T and beta estimates. Thus, for long wavelength observations (lambda >~ 200 micron), or for warm sources (T >~ 60 K), it becomes difficult to distinguish sources with different temperatures. We assess the role of noise in recent observational results that indicate an inverse and continuously varying T - beta relation. Though an inverse and continuous T - beta correlation may be a physical property of dust in the ISM, we find that the observed inverse correlation may be primarily due to noise.