2004ApJ...606..853H -
Astrophys. J., 606, 853-861 (2004/May-2)
The radio continuum of the metal-deficient blue compact dwarf galaxy SBS 0335-052.
HUNT L.K., DYER K.K., THUAN T.X. and ULVESTAD J.S.
Abstract (from CDS):
We present new Very Large Array observations at five frequencies, from 1.4 to 22 GHz, of the extremely low metallicity blue compact dwarf SBS 0335-052. The radio spectrum shows considerable absorption at 1.49 GHz and a composite thermal plus nonthermal slope. After fitting the data with a variety of models, we find the best-fitting geometry to be one with free-free absorption homogeneously intermixed with the emission of both thermal and nonthermal components. The best-fitting model gives an emission measure EM∼8x107 pc/cm6 and a diameter of the radio-emitting region D~17 pc. The inferred density is ne∼2000r/cm3. The thermal emission comes from an ensemble of ∼9000 O7 stars, with a massive star formation rate (≥5 M☉) of 0.13-0.15/yr and a supernova (SN) rate of 0.006/yr. We find evidence for ionized gas emission from stellar winds, since the observed Brα line flux significantly exceeds that inferred from the thermal radio emission. The nonthermal fraction at 5 GHz is ∼0.7, corresponding to a nonthermal luminosity of ∼2x1020 W/Hz. We derive an equipartition magnetic field of ∼0.6-1 mG and a pressure of ∼3x10–8 to 1x10–7 dynes/cm2. Because of the young age and compact size of the starburst, it is difficult to interpret the nonthermal radio emission as resulting from diffusion of SN-accelerated electrons over 107-108 yr timescales. Rather, we attribute the nonthermal radio emission to an ensemble of compact SN remnants expanding in a dense interstellar medium. If the radio properties of SBS 0335-052 are representative of star formation in extremely low metallicity environments, derivations of the star formation rate from the radio continuum in high-redshift primordial galaxies need to be reconsidered. Moreover, photometric redshifts inferred from ``standard'' spectral energy distributions could be incorrect.
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Journal keyword(s):
Galaxies: Dwarf - Galaxies: Individual: Alphanumeric: SBS 0335-052 - Galaxies: Starburst - Radio Continuum: Galaxies - ISM: Supernova Remnants
Simbad objects:
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