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




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 & 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.

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Copyright © 2015 IOP Publishing. This article first appeared in The Astrophysical Journal Letters 799, no. 1 (January 19, 2015): L10. doi:10.1088/2041-8205/799/1/L10.

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