AzTEC Survey of the Central Molecular Zone: Increasing Spectral Index of Dust with Density

TL;DR

This study uses a combined millimeter and far-IR survey to analyze dust properties in the Galactic Center's extreme environment, revealing that dust spectral index increases with density, affecting temperature estimates.

Contribution

It introduces a novel Bayesian modeling approach that incorporates PSFs and foreground/background contributions, providing detailed spatial analysis of dust in the CMZ.

Findings

Dust spectral index increases from 2.0 to 2.4 in dense regions

Large grains are deficient or dust properties change in dense areas

Dust temperature estimates could be underestimated by 10-50% in dense regions

Abstract

The Central Molecular Zone (CMZ) of our Galaxy hosts an extreme environment analogous to that found in typical starburst galaxies in the distant universe. In order to understand dust properties in environments like our CMZ, we present results from a joint SED analysis of our AzTEC/Large Millimeter Telescope survey, together with existing \textit{Herschel} far-IR data on the CMZ, from a wavelength range of $160$ $\mu m$ to $1.1$ $mm$. We include global foreground and background contributions in a novel Bayesian modeling that incorporates the Point Spread Functions (PSFs) of the different maps, which enables the full utilization of our high resolution ($10.5''$) map at 1.1 $mm$ and reveals unprecedentedly detailed information on the spatial distribution of dusty gas across the CMZ. There is a remarkable trend of increasing dust spectral index $\beta$, from $2.0-2.4$, toward dense peaks in the CMZ, indicating a deficiency of large grains or a fundamental change in dust optical properties. This environmental dependence of $\beta$ could have a significant impact on the determination of dust temperature in other studies. Depending on how the optical properties of dust deviate from the conventional model, dust temperatures could be underestimated by $10-50\%$ in particularly dense regions.