# GTC Observations of an Overdense Region of LAEs at z=6.5

## TL;DR

This study uses deep GTC imaging to identify a significant overdensity of Lyman Alpha Emitters at redshift 6.5, indicating a potential early protocluster that could evolve into a massive galaxy cluster.

## Contribution

First deep imaging survey targeting an overdense region at z=6.5, revealing a candidate protocluster with 45 LAE candidates and implications for early structure formation.

## Key findings

- Overdensity factor of about 2 compared to the field
- Identification of 45 LAE candidates in the region
- Potential discovery of an early universe protocluster

## Abstract

We present the results of our search for the faint galaxies near the end of the Reionisation Epoch. This has been done using very deep OSIRIS images obtained at the Gran Telescopio Canarias (GTC). Our observations focus around two close, massive Lyman Alpha Emitters (LAEs) at redshift 6.5, discovered in the SXDS field within a large-scale overdense region (Ouchi et al. 2010). The total GTC observing time in three medium band filters (F883w35, F913w25 and F941w33) is over 34 hours covering $7.0\times8.5$ arcmin$^2$ (or $\sim30,000$ Mpc$^3$ at $z=6.5$). In addition to the two spectroscopically confirmed LAEs in the field, we have identified 45 other LAE candidates. The preliminary luminosity function derived from our observations, assuming a spectroscopic confirmation success rate of $\frac{2}{3}$ as in previous surveys, suggests this area is about 2 times denser than the general field galaxy population at $z=6.5$. If confirmed spectroscopically, our results will imply the discovery of one of the earliest protoclusters in the universe, which will evolve to resemble the most massive galaxy clusters today.