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

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 $z\sim 8-9$ 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 ${\Sigma }_{min}(z)\sim 0.15-0.3$, with ${\Sigma }_{min}$ increasing with redshift as a consequence of shorter halo assembly periods at higher redshifts. Current observations ($m_{AB}\sim 27$) 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 $\Sigma \ge {\Sigma }_{min}$. Deeper future observations reaching $m_{AB}\sim 28.2-29$ 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.

12 pages, 7 figures, 1 table; accepted for publication in ApJ

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• A redshift-independent efficiency model: star formation and stellar masses in dark matter halos at z>4
• Inferences on the Timeline of Reionization at z~8 From the KMOS Lens-Amplified Spectroscopic Survey
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• The bright-end galaxy candidates at z ~ 9 from 79 independent HST fields
• The Impact of Scatter in the Galaxy UV Luminosity to Halo Mass Relation on Ly$\alpha$ Visibility During the Epoch of Reionization
• Breaking degeneracies in the first galaxies with clustering
• The Brightest Galaxies at Cosmic Dawn from Scatter in the Galaxy Luminosity versus Halo Mass Relation
• Effects of self-consistent rest-ultraviolet colours in semi-empirical galaxy formation models
• HOD modelling of high redshift galaxies using the BLUETIDES simulation
• Mapping reionization bubbles in the JWST era I: empirical edge detection with Lyman alpha emission from galaxies
• A semi-analytical perspective on massive galaxies at $z\sim 0.55$
• Probing Reionization-Era Galaxies with JWST UV Luminosity Functions and Large-Scale Clustering
• The Diversity of Environments Around Luminous Quasars at Redshift $z\sim 6$