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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Hine, N. K., Geach, J. E., Matsuda, Y., Lehmer, B. D., Michałowski, M. J., Farrah, D., Spaans, M., Oliver, S. J., Smith, D. J. B., Chapman, S. C., Jenness, T., Alexander, D. M., Robson, I. & van der Werf, P. (2016). The average submillimetre properties of Lyman α blobs at z = 3. Monthly Notices of the Royal Astronomical Society 460(4): 4075-4085.

Author(s) from Durham


Ly α blobs (LABs) offer insight into the complex interface between galaxies and their circumgalactic medium. Whilst some LABs have been found to contain luminous star-forming galaxies and active galactic nuclei that could potentially power the Ly α emission, others appear not to be associated with obvious luminous galaxy counterparts. It has been speculated that LABs may be powered by cold gas streaming on to a central galaxy, providing an opportunity to directly observe the ‘cold accretion’ mode of galaxy growth. Star-forming galaxies in LABs could be dust obscured and therefore detectable only at longer wavelengths. We stack deep Submillimetre Common User Bolometer Array 2 (SCUBA-2) observations of the Small Selected Area 22h field to determine the average 850 μm flux density of 34 LABs. We measure S850 = 0.6 ± 0.2 mJy for all LABs, but stacking the LABs by size indicates that only the largest third (area ≥1794 kpc2) have a mean detection, at 4.5σ, with S850 = 1.4 ± 0.3 mJy. Only two LABs (1 and 18) have individual SCUBA-2 >3.5σ detections at a depth of 1.1 mJy beam−1. We consider two possible mechanisms for powering the LABs and find that central star formation is likely to dominate the emission of Ly α, with cold accretion playing a secondary role.