A Large Number of z > 6 Galaxies around a QSO at z = 6.43: Evidence for a Protocluster?
Yousuke Utsumi (1, 2), Tomotsugu Goto (3, 4), Nobunari Kashikawa,, Satoshi Miyazaki, Yutaka Komiyama (1, 2), Hisanori Furusawa (2), Roderik, Overzier (5) ((1) The Graduate University for Advanced Studies (2) National, Astronomical Observatory of Japan (3) Institute for Astronomy

TL;DR
This study presents evidence of a significant overdensity of z~6.4 Lyman break galaxies around a quasar, indicating the quasar resides in a massive, possibly protocluster environment, with galaxy distribution showing a ring-like pattern.
Contribution
First large-field survey around a z=6.4 QSO revealing a potential protocluster with galaxy overdensity and unique spatial distribution.
Findings
Seven LBGs found around the QSO, compared to one in the control field.
Significant overdensity with less than 0.4% probability of occurring by chance.
Galaxies are distributed in a ring-like pattern, avoiding the QSO center.
Abstract
QSOs have been thought to be important for tracing highly biased regions in the early universe, from which the present-day massive galaxies and galaxy clusters formed. While overdensities of star-forming galaxies have been found around QSOs at 2<z<5, the case for excess galaxy clustering around QSOs at z>6 is less clear. Previous studies with HST have reported the detection of small excesses of faint dropout galaxies in some QSO fields, but these surveys probed a relatively small region surrounding the QSOs. To overcome this problem, we have observed the most distant QSO at z=6.4 using the large field of view of the Suprime-Cam (34' x 27'). Newly-installed CCDs allowed us to select Lyman break galaxies (LBG) at z~6.4 more efficiently. We found seven LBGs in the QSO field, whereas only one exists in a comparison field. The significance of this apparent excess is difficult to quantify…
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