Herschel-Astrophysical Terahertz Large Area Survey: detection of a far-infrared population around galaxy clusters
Rodighiero, G.; Ivison, R. J.; Clements, D. L.; de Zotti, G.; Scott, D.; Smail, Ian; Fritz, J.; Cooray, A.; Ibar, E.; Negrello, M.; Auld, R.; Baes, M.; Cava, A.; Dariush, A.; Dunne, L.; Dye, S.; Eales, S.; Hopwood, R.; Maddox, S.; Michałowski, M. J.; Serjeant, S.; van der Werf, P.; Pohlen, M.; Edge, A. C.; Geach, J. E.; Pascale, E.; Coppin, K. E. K.; Buttiglione, S.; Smith, D. J. B.; Temi, P.; Jarvis, M.; Rigby, E.; Murphy, D. N. A.
Canada, United Kingdom, Belgium, Italy, Spain, United States, Iran, South Africa, Netherlands
Abstract
We report the detection of a significant excess in the surface density of far-infrared sources from the Herschel-Astrophysical Terahertz Large Area Survey within ∼1 Mpc of the centres of 66 optically selected clusters of galaxies in the Sloan Digital Sky Survey with <z>∼ 0.25. From the analysis of the multiwavelength properties of their counterparts we conclude that the far-infrared emission is associated with dust-obscured star formation and/or active galactic nuclei (AGN) within galaxies in the clusters themselves. The excess reaches a maximum at a radius of ∼0.8 Mpc, where we find 1.0 ± 0.3 S250 > 34 mJy sources on average per cluster above what would be expected for random field locations. If the far-infrared emission is dominated by star formation (as opposed to AGN) then this corresponds to an average star formation rate of ∼7 M⊙ yr-1 per cluster in sources with LIR > 5 × 1010 L⊙. Although lensed sources make a negligible contribution to the excess signal, a fraction of the sources around the clusters could be gravitationally lensed, and we have identified a sample of potential cases of cluster-lensed Herschel sources that could be targeted in follow-up studies. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.