Formation and Evolution of
Galaxy Clusters Across Cosmic Time

Theoretical models predict that quasars at z > 6 should be found in the most massive halos of the underlying dark matter distribution. However, observations have so far shown both scenarios of high-redshift quasars living in overdensities, environments consistent with blank fields, or even underdense. We investigate the ~1 proper Mpc environment of J1342+0928, a luminous quasar at redshift z = 7.54, e.g. well into the Epoch of Reionization. We use deep data from the Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3) onboard the Hubble Space Telescope (HST) to look for galaxy candidates in the vicinity of the quasar J1342+0928 and assess if it is immersed in a protocluster of galaxies as predicted by theory. For this purpose, we rely on imaging of a 1.1 x 1.1 pMpc area surrounding the quasar in the HST filters F814W, F105W, and F125W. We will use a combination of the Lyman-break technique redshift probability and color-color criteria to select the galaxy candidates. Available Spitzer/IRAC observations at 3.6 and 4.5 micrometers will complement the spectral energy distribution of the candidates in mid-infrared wavelengths to help differentiate the high-redshift galaxy candidates from lower-redshift contaminants. We will compare the number density of the galaxy candidates found to what is expected in a field without a quasar, both from deep field observations and the predictions from the galaxy rest-frame ultraviolet luminosity function at z ~ 7.5. The galaxy candidates resulting from this research will be excellent targets for follow-up observations with e.g. the James Webb Space Telescope (JWST) or the Atacama Large Millimeter/sub-millimeter Array,(ALMA), to confirm the redshift of these galaxies and study their physical properties.