http://arxiv.org/abs/1407.5482
Diffuse radio emission in the interstellar medium of dwarf spheroidal (dSph) galaxies is an important aspect of the role of dwarf galaxies in the magnetization of the intracluster and inter-galactic medium in the early universe, competing with AGNs and starburst galaxy activity. The current quiescent phase of Local Group dSphs has so far dampened the possibility of measuring their non-thermal emissions and in turn of fully understanding connected aspects of dSph properties and evolution. Deep observations are required in order to probe the emission associated to the very-low level of dSph star formation or, possibly, to particle dark matter annihilating or decaying in the dSph halo. In this work, we employ radio observations of six local dSphs to test the presence of a diffuse component over typical scales of few arcmin. The dSph targets require wide-field low-frequency observations which were conducted with the Australia Telescope Compact Array in the frequency band 1.1-3.1 GHz. The achieved rms sensitivity is below 0.05 mJy/beam. We observed the dSph fields with both a compact array and long baselines. The high-resolution data were used to map small-scale background sources which were then subtracted to significantly reduce the confusion limit of the short-baseline maps. The latter were used for the extended emission search and have a synthesized beam of about 1 arcmin. We found no significant detection of a diffuse radio continuum component. After a detailed discussion on the modeling of the cosmic-ray (CR) electron distribution and on the dSph magnetic properties, we present bounds on several physical quantities related to the dSphs, such that the total radio flux, the angular shape of the radio emissivity, the equipartition magnetic field, and the injection and equilibrium distributions of CR electrons. Finally, we discuss the connection to far-infrared and X-ray observations.
M. Regis, L. Richter, S. Colafrancesco, et. al.
Tue, 22 Jul 14
34/45
Comments: 23 pages, 12 figure panels
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