Abstract

We analyze the multifrequency radio spectral properties of 41 6 GHz-detected Atacama Large Millimeter/submillimeter Array (ALMA)-identified, submillimeter galaxies (SMGs), observed at 610 MHz, 1.4 GHz, and 6 GHz with the Giant Metrewave Radio Telescope and the Very Large Array. Combining high-resolution (similar to 0 ''.5) 6 GHz radio and ALMA 870 mu m imaging (tracing rest frame similar to 20 GHz, and similar to 250 mu m dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio q(IR), measuring < q(IR)> = 2.20 +/- 0.06 for our sample. We show that the high-frequency radio sizes of SMGs are similar to 1.9 +/- 0.4 x (similar to 2-3 kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on similar to 10 kpc scales at 1.4 GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample shows evidence of a spectral break, with a median - 0.60 +/- 0.06, but = -1.06 +/- 0.04-a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields (B similar to 35 mu G) and young ages (t(SB) similar to 40-80 Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts, and we are observing these systems roughly halfway through their current episode of star formation, this implies starburst durations of less than or similar to 100 Myr, in reasonable agreement with estimates derived via gas depletion timescales.