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Durham University

Department of Physics

Staff profile

Publication details for Professor Ian Smail

Simpson, J. M. , Smail, I., Swinbank, A. M., Almaini, O., Blain, A. W., Bremer, M. N., Chapman, S. C., Chen, C.-C., Conselice, C., Coppin, K. E. K., Danielson, A. L. R., Dunlop, J. S., Edge, A. C., Farrah, D., Geach, J. E., Hartley, W. G., Ivison, R. J., Karim, A., Lani, C., Ma, C.-J., Meijerink, R., Michalowski, M. J., Mortlock, A., Scott., D., Simpson, C. J., Spanns, M., Thomson, A. P., van Kampen, E. & van der Werf, P. P. (2015). The SCUBA-2 Cosmology Legacy Survey: ALMA Resolves the Rest-frame Far-infrared Emission of Sub-millimeter Galaxies. The Astrophysical Journal 799(1): 81.

Author(s) from Durham


We present high-resolution (0.''3) Atacama Large Millimeter Array 870 μm imaging of 52 sub-millimeter galaxies (SMGs) in the Ultra Deep Survey field to investigate the size and morphology of the sub-millimeter (sub-mm) emission on 2-10 kpc scales. We derive a median intrinsic angular size of FWHM = 0.''30 ± 0.''04 for the 23 SMGs in the sample detected at a signal-to-noise ratio (S/N) >10. Using the photometric redshifts of the SMGs we show that this corresponds to a median physical half-light diameter of 2.4 ± 0.2 kpc. A stacking analysis of the SMGs detected at S/N <10 shows they have sizes consistent with the 870 μm bright SMGs in the sample. We compare our results to the sizes of SMGs derived from other multi-wavelength studies, and show that the rest-frame ~250 μm sizes of SMGs are consistent with studies of resolved 12CO (J = 3-2 to 7-6) emission lines, but that sizes derived from 1.4 GHz imaging appear to be approximately two times larger on average, which we attribute to cosmic ray diffusion. The rest-frame optical sizes of SMGs are around four times larger than the sub-millimeter sizes, indicating that the star formation in these galaxies is compact relative to the pre-existing stellar distribution. The size of the starburst region in SMGs is consistent with the majority of the star formation occurring in a central region, a few kiloparsecs in extent, with a median star formation rate surface density of 90 ± 30 M ☉ yr–1 kpc–2, which may suggest that we are witnessing an intense period of bulge growth in these galaxies.