Planck Observations of M33

TL;DR

This study analyzes M33's dust emission from radio to ultraviolet, revealing a single blackbody fit with radial gradients in dust properties and highlighting the importance of CMB fluctuations in accurate measurements.

Contribution

It provides the first detailed analysis of M33's dust emission across multiple wavelengths, including the effects of CMB fluctuations on derived dust parameters.

Findings

M33's dust emission is well-described by a single modified blackbody between 100 GHz and 3 THz.

Radial gradients in dust temperature and emissivity are observed across M33.

Ignoring CMB fluctuations leads to overestimating dust temperature by ~5 K and underestimating emissivity by ~0.4.

Abstract

We have performed a comprehensive investigation of the global integrated flux density of M33 from radio to ultraviolet wavelengths, finding that the data between $\sim$100 GHz and 3 THz are accurately described by a single modified blackbody curve with a dust temperature of $T_\mathrm{dust}$ = 21.67$\pm$0.30 K and an effective dust emissivity index of $\beta_\mathrm{eff}$ = 1.35$\pm$0.10, with no indication of an excess of emission at millimeter/sub-millimeter wavelengths. However, sub-dividing M33 into three radial annuli, we found that the global emission curve is highly degenerate with the constituent curves representing the sub-regions of M33. We also found gradients in $T_\mathrm{dust}$ and $\beta_\mathrm{eff}$ across the disk of M33, with both quantities decreasing with increasing radius. Comparing the M33 dust emissivity with that of other Local Group members, we find that M33 resembles the Magellanic Clouds rather than the larger galaxies, i.e., the Milky Way and M31. In the Local Group sample, we find a clear correlation between global dust emissivity and metallicity, with dust emissivity increasing with metallicity. A major aspect of this analysis is the investigation into the impact of fluctuations in the Cosmic Microwave Background (CMB) on the integrated flux density spectrum of M33. We found that failing to account for these CMB fluctuations would result in a significant over-estimate of $T_\mathrm{dust}$ by $\sim$5 K and an under-estimate of $\beta_\mathrm{eff}$ by $\sim$0.4.