# No Ly$\alpha$ emitters detected around a QSO at z=6.4: Suppressed by the QSO?

## TL;DR

This study used a custom narrow-band filter on Subaru to investigate Ly$ ext{alpha}$ emitters around a z=6.4 QSO, finding none and suggesting QSO UV radiation suppresses nearby galaxy formation, especially in low-mass halos.

## Contribution

First high-redshift narrow-band survey around a luminous QSO at z=6.4, revealing a significant deficit of Ly$ ext{alpha}$ emitters likely due to QSO UV radiation.

## Key findings

- No Ly$ ext{alpha}$ emitters detected around the QSO.
- The upper limit on LAE density is much lower than in blank fields.
- UV radiation from the QSO may suppress star formation in nearby low-mass halos.

## Abstract

Understanding how QSO's UV radiation affects galaxy formation is vital to our understanding of reionization era. Using a custom made narrow-band filter, $NB906$, on Subaru/Suprime-Cam, we investigated the number density of Ly$\alpha$ emitters (LAE) around a QSO at z=6.4. To date, this is the highest redshift narrow-band observation, where LAEs around a luminous QSO are investigated. Due to the large field-of-view of Suprime-Cam, our survey area is $\sim$5400~cMpc$^2$, much larger than previously studies at z=5.7 ($\sim$200 cMpc$^2$). In this field, we previously found a factor of 7 overdensity of Lyman break galaxies (LBGs). Based on this, we expected to detect $\sim$100 LAEs down to $NB906$=25 ABmag. However, our 6.4 hour exposure found none. The obtained upper limit on the number density of LAEs is more than an order lower than the blank fields. Furthermore, this lower density of LAEs spans a large scale of 10 $p$Mpc across. A simple argument suggests a strong UV radiation from the QSO can suppress star-formation in halos with $M_{vir}<10^{10}M_{\odot}$ within a $p$Mpc from the QSO, but the deficit at the edge of the field (5 $p$Mpc) remains to be explained.