Nonthermal Emission from Star-Forming Galaxies

The detections of high-energy gamma-ray emission from the nearby starburst galaxies M82 & NGC253, and other local group galaxies, broaden our knowledge of star-driven nonthermal processes and phenomena in non-AGN star-forming galaxies. We review basic aspects of the related processes and their modeling in starburst galaxies. Since these processes involve both energetic electrons and protons accelerated by SN shocks, their respective radiative yields can be used to explore the SN-particle-radiation connection. Specifically, the relation between SN activity, energetic particles, and their radiative yields, is assessed through respective measures of the particle energy density in several star-forming galaxies. The deduced energy densities range from O(0.1) eV/cm^3 in very quiet environments to O(100) eV/cm^3 in regions with very high star-formation rates.Comment: 17 pages, 5 figures, to be published in Astrophysics and Space Science Proceeding

Australia telescope compact array observations of radio recombination lines toward 30 Doradus

Three hydrogen recombination lines-H90 alpha at 8.9 GHz, H92 alpha at 8.3 GHz, and H109 alpha at 5.0 GHz-have been observed with the Australia Telescope Compact Array toward the 30 Doradus Nebula, the giant H II region in the Large Magellanic Cloud. In this paper, emphasis is placed on the more sensitive H90 alpha observations, which also include the He90 alpha and H113 beta lines. A spatial resolution of 15 '' was obtained with a velocity resolution of 4.2 km s(-1) and an rms noise of 1.6 mJy. Typical line-to-continuum ratios were 0.04 for the H90 alpha and H92 alpha, and 0.03 for the H109 alpha data. The distributions of radial velocity and electron temperature have been determined. The heliocentric velocity of the ionized gas varies between 245 and 290 km s(-1) with a mean value of 262 km s(-1). In some places the line profile is double, suggesting that sections of expanding shells are being observed. The mean (LTE) electron temperature is dose to 7700 K over most of the nebula. The intensity ratio of H113 beta/H90 alpha is close to the expected LTE value of 0.28, implying that the calculated LTE electron temperatures are close to the true electron temperatures; in one area to the north the ratio is enhanced, 0.39 +/- 0.03. The helium abundance (Y+ = He+/H+) shows no significant variation across the source, with a mean value of 0.13 +/- 0.02

Культура и коммуникация: глобальные и локальные измерения

Conference paperNon peer reviewe