The Cosmic Web Around The Brightest Galaxies During The Epoch Of Reionization

TL;DR

This study investigates the clustering around the brightest high-redshift galaxies during the epoch of reionization, using advanced modeling to understand how galaxy luminosity relates to halo mass and the implications for early universe structure formation.

Contribution

It introduces a novel modeling approach incorporating a scatter parameter in the luminosity-halo mass relation, extending low-redshift frameworks to high-redshift galaxy clustering analysis.

Findings

Larger luminosity scatter reduces the likelihood that bright galaxies reside in the most massive halos.

Derived a minimum scatter value increasing with redshift, indicating more stochastic galaxy formation at earlier times.

Current observations are consistent with models including significant luminosity scatter, suggesting weaker clustering than previously assumed.

Abstract

The most luminous galaxies at high-redshift are generally considered to be hosted in massive dark-matter halos of comparable number density, hence residing at the center of overdensities/protoclusters. We assess the validity of this assumption by investigating the clustering around the brightest galaxies populating the cosmic web at redshift $z\sim8-9$ through a combination of semi-analytic modeling and Monte Carlo simulations of mock Hubble Space Telescope WFC3 observations. The innovative aspect of our approach is the inclusion of a log-normal scatter parameter $\Sigma$ in the galaxy luminosity versus halo mass relation, extending to high-$z$ the conditional luminosity function framework extensively used at low redshift. Our analysis shows that the larger the value of $\Sigma$, the less likely that the brightest source in a given volume is hosted in the most massive halo, and hence the weaker the overdensity of neighbors. We derive a minimum value of $\Sigma$ as a function of redshift by considering stochasticity in the halo assembly times, which affects galaxy ages and star formation rates in our modeling. We show that $\Sigma_{min}(z)\sim0.15-0.3$, with $\Sigma_{min}$ increasing with redshift as a consequence of shorter halo assembly periods at higher redshifts. Current observations ($m_{AB}\sim27$) of the environment of spectroscopically confirmed bright sources at $z>7.5$ do not show strong evidence of clustering and are consistent with our modeling predictions for $\Sigma\geq\Sigma_{min}$. Deeper future observations reaching $m_{AB}\sim28.2-29$ would have the opportunity to clearly quantify the clustering strength, and hence to constrain $\Sigma$, investigating the physical processes that drive star formation in the early Universe.