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Abstract: We studied the radio properties of very young massive regions of starformation in HII galaxies, with the aim of detecting episodes of recent starformation in an early phase of evolution where the first supernovae start toappear. The observed radio spectral energy distribution SED covers abehaviour range; 1 there are galaxies where the SED is characterized by asynchrotron-type slope, 2 galaxies with a thermal slope, and 3 galaxies withpossible free-free absorption at long wavelengths. The latter SED represents asignature of massive star clusters that are still well inside the progenitormolecular cloud. Based on the comparison of the star formation rates SFRdetermined from the recombination lines and those determined from the radioemission we find that SFRHa is on average five times higher than SFR1.4GHz. These results suggest that the emission of these galaxies is dominated bya recent and massive star formation event in which the first supernovae SNjust started to explode. We conclude that the systematic lack of synchrotronemission in those systems with the largest equivalent width of Hb can only beexplained if those are young starbursts of less than 3.5Myr of age, i.e. beforethe first type II SNe emerge.

Author: Daniel Rosa-Gonzalez INAOE, Henrique Schmitt Naval Research Laboratory, Elena Terlevich INAOE, Roberto Terlevich INAOE

Source: https://arxiv.org/


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