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Paper: Constraints on the Prevalence of Luminous, Dusty Starbursts at Very High Redshifts
Volume: 380, At the Edge of the Universe: Latest Results from the Deepest Astronomical Surveys
Page: 357
Authors: Ivison, R.J.
Abstract: At a conference devoted to ever deeper surveys hunting for ever more distant galaxies, I posed a question for which a concensus view has been difficult to reach: ‘Is there evidence for, or can we rule out, a significant popu- lation of dust-obscured starbursts at z > 3?’ If, as seems likely, submm-selected galaxies are proto-ellipticals, one of the biggest unanswered questions is whether a significant fraction form at very high redshift – perhaps by the collapse of single gas clouds – or whether the entire population forms over a range of red- shifts, primarily via merging. The latter scenario is favoured strongly by existing data for the majority of bright submm galaxies – mergers are common; typical spectroscopic redshifts are in the range 1–3. However, our reliance on radio imaging to pinpoint submm galaxies leaves open the possibility of a significant population of very distant, massive starbursts. To rule out such a scenario requires a completely unbiased redshift distribution for submm-selected galaxies and this is unlikely to be forthcoming using conventional optical/infrared spectroscopic techniques. Here, I summarise recent attempts to close that door, or pass through to an early Universe inhabited by a significant population of colossal, dust-obscured starbursts. I conclude that the door is only barely ajar; however, the idea of galaxies forming, near instantaneously, on a colossal scale is not dead: I show an SMG imaged by MERLIN+VLA for >1Ms – the deepest high-resolution radio image so far obtained. The data reveal a galaxy-wide starburst covering ≥10 kpc. Thus interpreting SMGs in terms of compact ULIRG-like events may not always be appropriate, as one might expect when considering the Eddington limit for ≥103-M yr−1 starbursts.
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