The Young and the Dustless: Interpreting Radio Observations of Ultraviolet-Luminous Galaxies

Abstract

Ultraviolet-luminous galaxies (UVLGs) have been identified as intensely star-forming nearby galaxies. A subset of these, the supercompact UVLGs, are believed to be local analogs of high-redshift Lyman break galaxies. Here we investigate the radio continuum properties of this important population for the first time. We have observed 42 supercompact UVLGs with the VLA, all of which have extensive coverage in the UV/optical by GALEX and SDSS. Our analysis includes comparison samples of multiwavelength data from the Spitzer First Look Survey and from the SDSS-GALEX matched catalogs. In addition we have Spitzer MIPS data for 24 of our galaxies and find that they fall on the radio-FIR correlation of normal star-forming galaxies. We find that our galaxies have lower radio to UV ratios and lower Balmer decrements than other local galaxies with similar (high) star formation rates. Optical spectra show they have lower D_n(4000) and Hδ_A indices, higher Hβ emission-line equivalent widths, and higher [O III]5007/Hβ emission-line ratios than normal star-forming galaxies. Comparing these results to galaxy spectral evolution models we conclude that supercompact UVLGs are distinguished from normal star-forming galaxies firstly by their high specific star formation rates. Moreover, compared to other types of galaxies with similar star formation rates, they have significantly less dust attenuation. In both regards they are similar to Lyman break galaxies. This suggests that the process that causes star formation in the supercompact UVLGs differs from other local star-forming galaxies, but may be similar to Lyman break galaxies.

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