We present a study of the radio properties of 870 μm-selected
submillimetre galaxies (SMGs), observed at high resolution with Atacama
Large Millimeter Array (ALMA) in the Extended Chandra Deep Field South.
From our initial sample of 76 ALMA SMGs, we detect 52 SMGs at
>3σ significance in Karl G. Jansky Very Large Array 1400 MHz
imaging, of which 35 are also detected at >3σ in new 610 MHz
Giant Metre-Wave Radio Telescope imaging. Within this sample of
radio-detected SMGs, we measure a median radio spectral index α
_{610}^{1400} = -0.79 ± 0.06, (with inter-quartile range α
= [-1.16, -0.56]) and investigate the far-infrared/radio correlation via
the parameter qIR, the logarithmic ratio of the rest-frame
8-1000 μm flux and monochromatic radio flux. Our median
qIR = 2.56 ± 0.05 (inter-quartile range qIR
= [2.42, 2.78]) is higher than that typically seen in single-dish 870
μm-selected sources (qIR ˜ 2.4), which may reflect
the fact that our ALMA-based study is not biased to radio-bright
counterparts, as previous samples were. Finally, we search for evidence
that qIR and α evolve with age in a codependent manner,
as predicted by starburst models: the data populate the predicted region
of parameter space, with the stellar mass tending to increase along
tracks of qIR versus α in the direction expected,
providing the first observational evidence in support of these models.