Publication Date:
2016-12-21
Description:
Synchrotron emission pervades the Galactic plane at low radio frequencies, originating from cosmic ray electrons interacting with the Galactic magnetic field. Using a low-frequency radio telescope, the Murchison Widefield Array (MWA), we measure the free–free absorption of this Galactic synchrotron emission by intervening H ii regions along the line of sight. These absorption measurements allow us to calculate the Galactic cosmic ray electron emissivity behind and in front of 47 detected H ii regions in the region 250° 〈 l 〈 355°, | b | 〈 2°. We find that all average emissivities between the H ii regions and the Galactic edge along the line of sight ( b ) are in the range of 0.39 ~ 1.45 K pc –1 with a mean of 0.77 K pc –1 and a variance of 0.14 K pc –1 at 88 MHz. Our best model, the two-circle model, divides the Galactic disc into three regions using two circles centring on the Galactic Centre. It shows a high emissivity region near the Galactic Centre, a low emissivity region near the Galactic edge, and a medium emissivity region between these two regions, contrary to the trend found by previous studies.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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