THE EFFECT OF NOISE ON THE DUST TEMPERATURE-SPECTRAL INDEX CORRELATION

We investigate how uncertainties in flux measurements affect the results from modified blackbody spectral energy distribution (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 greater than or similar to 200 mu m), or for warm sources (T greater than or similar to 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 interstellar medium, we find that the observed inverse correlation may be primarily due to noise.