Title: The ISM in z~2.5 starbursting galaxies: dust, synchrotron emission and cold molecular 
gas

Abstract:
I will present key results from two recent studies in to the ISM conditions in z~2.5 submillimetre 
galaxies (SMGs). In the first, I will present the radio properties of submillimetre sources 
identified in single-dish LABOCA imaging of ECDFS, and followed up at high-resolution with 
ALMA. From the initial sample of 76 ALMA SMGs, we detect 52 SMGs at > 3σ significance in 
VLA 1.4GHz imaging, of which 35 are also detected at > 3σ in new 610MHz GMRT imaging. 
Within this sample of radio-detected SMGs, we measure a median radio spectral index that is 
consistent with star formation (α ~ -0.8), but with a large spread reflecting the heterogeneity of 
the SMG population. We investigate the far-infrared/radio correlation via the parameter qIR, the 
logarithmic ratio of the rest-frame 8–1000μm flux and monochromatic radio flux, and search 
for evidence that qIR  and α evolve with age in a co-dependent manner, as predicted by 
theoretical starburst models: the data populate the predicted region of parameter space, with 
the stellar mass tending to increase along tracks of versus α versus qIR in the direction 
expected, providing the first observational evidence in support of these models. In the second 
study, I present an insight in to the spatially-resolved ISM physics of the strongly-lensed z=2.3 
SMG, “The Eyelash”. Using high-resolution VLA imaging of the CO(1-0) line – and 
exploiting the ~37.5x magnification by the foreground cluster – we identify ~100pc molecular 
gas clumps, which we find to have densities log[n(H_2)/cm^3] ~ 3.8 and temperatures T_k ~ 
70K, whose star formation rate (ΣSFR) and molecular gas mass (Σgas) surface densities probe 
the highest-density region of the Schmidt-Kennicutt plot.