Eduardo Bañados, Bram Venemans, Fabian Walter, Jaron Kurk, Roderik Overzier, Masami Ouchi
High-redshift quasars are believed to reside in massive halos in the early Universe and should therefore be located in fields with overdensities of galaxies, which are thought to evolve into galaxy clusters seen in the local Universe. However, despite many efforts, the relationship between galaxy overdensities and z~6 quasars is ambiguous, which can possibly be attributed to the difficulty of finding galaxies with accurate redshifts in the vicinity of z~6 quasars. So far, overdensity searches around z~6 quasars are based on studies of Lyman break galaxies (LBGs), which probe a redshift range of Delta z ~ 1. This range is large enough to select galaxies which may not be physically related to the quasar. Here we use deep narrow- and broad-band imaging to study the environment of the z=5.72 quasar ULAS J0203+0012. The redshift range probed by our narrow band selection of Lyman alpha emitters (LAEs) is Delta z ~ 0.1, significantly narrower than LBG searches. This is the first time that LAEs are searched for near a z~6 quasar, to provide clues on the environments of quasars at the end of the Epoch of Reionization. We find no enhancement of LAEs in the surroundings of ULAS J0203+0012 in comparison with blank fields. We explore different explanations and interpretations for this non-detection of a galaxy overdensity, including that a) the strong ionization from the quasar may prevent galaxy formation in its immediate vicinity and b) that high-redshift quasars may not reside in the center of the most massive dark matter halos.
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http://arxiv.org/abs/1306.6642
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