Variations of the Radio Synchrotron Spectral Index in M33

TL;DR

This study maps the spatial variation of the nonthermal radio spectral index in M33 by separating thermal and nonthermal emissions without assuming a constant spectral index, using multi-wavelength data and dust modeling.

Contribution

It introduces a method to determine the nonthermal spectral index variation in M33 without assuming constancy, utilizing FIR data and Hα de-reddening for thermal emission separation.

Findings

Mapped the nonthermal spectral index variation across M33.

Demonstrated the effectiveness of separating thermal and nonthermal components.

Provided insights into the spatial distribution of cosmic ray electrons.

Abstract

We determine the variation in the nonthermal radio spectral index in the nearby spiral galaxy M33. We separate the thermal and nonthermal components of the radio continuum emission without the assumption of a constant nonthermal spectral index. Using the Spitzer FIR data at 70 and 160 $\mu$m and a standard dust model, we de-redden the H$\alpha$ emission. The extinction-corrected H$\alpha$ emission serves as a template for the thermal free-free radio emission. Subtracting from the observed 3.6 and 20cm emission (Effelsberg and the VLA) this free-free emission, we obtain maps of the nonthermal intensity and spectral index.