Large Scale Environment of a $z=6.61$ Luminous Quasar Probed by Ly$\alpha$ Emitters and Lyman Break Galaxies

TL;DR

This study investigates the large-scale environment of a luminous quasar at redshift 6.61 using LAE and LBG galaxy candidates, revealing complex clustering patterns and large-scale structures that suggest the quasar resides in a moderately massive halo.

Contribution

It provides the first large-area (700 arcmin$^2$) analysis of LAEs and LBGs around a high-redshift quasar, uncovering significant large-scale structures and environmental variations.

Findings

LAEs show underdensity near the QSO but clustering on larger scales.

LBGs form large-scale structures with high-density clumps.

The QSO is likely in a moderately massive halo, not the most massive one.

Abstract

Quasars (QSOs) hosting supermassive black holes are believed to reside in massive halos harboring galaxy overdensities. However, many observations revealed average or low galaxy densities around $z\gtrsim6$ QSOs. This could be partly because they measured galaxy densities in only tens of arcmin$^2$ around QSOs and might have overlooked potential larger scale galaxy overdensities. Some previous studies also observed only Lyman break galaxies (LBGs, massive older galaxies) and missed low mass young galaxies like Ly$\alpha$ emitters (LAEs) around QSOs. Here we present observations of LAE and LBG candidates in $\sim700$ arcmin$^2$ around a $z=6.61$ luminous QSO using Subaru Telescope Suprime-Cam with narrow/broadbands. We compare their sky distributions, number densities and angular correlation functions with those of LAEs/LBGs detected in the same manner and comparable data quality in our control blank field. In the QSO field, LAEs and LBGs are clustering in 4-20 comoving Mpc angular scales, but LAEs show mostly underdensity over the field while LBGs are forming $30\times60$ comoving Mpc$^2$ large scale structure containing 3-$7\sigma$ high density clumps. The highest density clump includes a bright (23.78 mag in the narrowband) extended ($\gtrsim 16$ kpc) Ly$\alpha$ blob candidate, indicative of a dense environment. The QSO could be part of the structure but is not located exactly at any of the high density peaks. Near the QSO, LAEs show underdensity while LBGs average to $4\sigma$ excess densities compared to the control field. If these environments reflect halo mass, the QSO may not be in the most massive halo, but still in a moderately massive one.