Axial Ratio of Edge-On Spiral Galaxies as a Test For Extended Bright Radio Halos

TL;DR

This study investigates whether extended bright radio halos are common in edge-on spiral galaxies by analyzing their surface brightness contours, challenging a recent model suggesting a widespread Galactic halo of uniform emissivity.

Contribution

The paper provides observational evidence against the prevalence of extended bright radio halos in normal spiral galaxies, testing and challenging a recent theoretical model.

Findings

No evidence for bright, extended radio halos in the sample

Galactic halos may be atypical or high-latitude emission has different origins

Surface brightness contours do not support the uniform halo model

Abstract

We use surface brightness contour maps of nearby edge-on spiral galaxies to determine whether extended bright radio halos are common. In particular, we test a recent model of the spatial structure of the diffuse radio continuum by Subrahmanyan and Cowsik which posits that a substantial fraction of the observed high-latitude surface brightness originates from an extended Galactic halo of uniform emissivity. Measurements of the axial ratio of emission contours within a sample of normal spiral galaxies at 1500 MHz and below show no evidence for such a bright, extended radio halo. Either the Galaxy is atypical compared to nearby quiescent spirals or the bulk of the observed high-latitude emission does not originate from this type of extended halo.