A massive proto-cluster of galaxies at a redshift of z {\approx} 5.3 (1101.3586v1)

Abstract: Massive clusters of galaxies have been found as early as 3.9 Billion years (z=1.62) after the Big Bang containing stars that formed at even earlier epochs. Cosmological simulations using the current cold dark matter paradigm predict these systems should descend from "proto-clusters" - early over-densities of massive galaxies that merge hierarchically to form a cluster. These proto-cluster regions themselves are built-up hierarchically and so are expected to contain extremely massive galaxies which can be observed as luminous quasars and starbursts. However, observational evidence for this scenario is sparse due to the fact that high-redshift proto-clusters are rare and difficult to observe. Here we report a proto-cluster region 1 billion years (z=5.3) after the Big Bang. This cluster of massive galaxies extends over >13 Mega-parsecs, contains a luminous quasar as well as a system rich in molecular gas. These massive galaxies place a lower limit of >4x10^11 solar masses of dark and luminous matter in this region consistent with that expected from cosmological simulations for the earliest galaxy clusters.

• The paper identifies a proto-cluster with over 11 times the expected density of Lyman Break galaxies, confirmed at >9σ using spectroscopic redshifts.
• The paper finds that the core galaxy, COSMOS AzTEC-3, contains over 5.3 billion solar masses of molecular gas and a star formation rate exceeding 1500 solar masses per year.
• The paper supports hierarchical structure formation theories by matching multiwavelength observations with simulations of early universe massive cluster development.

Overview of a Massive Proto-Cluster of Galaxies at Redshift z ≈ 5.3

The paper at hand presents significant observational findings concerning a massive proto-cluster of galaxies at a redshift of z ≈ 5.3, approximately one billion years post-Big Bang. This proto-cluster extends over more than 13 mega-parsecs and includes a luminous quasar and molecular gas-rich galaxy systems. The paper draws on extensive data within the COSMOS field, utilizing the entire electromagnetic spectrum, and marks a substantial contribution to understanding the early universe's large-scale structures.

Key Findings

The researchers identified an over-density in galaxy spots indicative of a proto-cluster by using optical and near-infrared data combined with Keck-II telescope spectroscopic redshifts. A key area of focus is around the galaxy COSMOS AzTEC-3, which, with over 5.3 x 10⁹ solar masses of molecular gas and a dynamical mass exceeding 1.4 x 10¹¹ solar masses, serves as a core of intense activity. The paper provides strong evidence for over 11 times the expected density of Lyman Break galaxies within this region, confirmed at the >9σ level.

Numerical Results and Implications

COSMOS AzTEC-3 exhibits a star formation rate exceeding 1500 solar masses per year, highlighting the active nature of the proto-cluster's core regions. The system showcases a notable baryonic mass, predominated by its gas component, indicating a chemical and dynamic youth in galactic evolution. The quasar, found within a short distance of the starburst, demonstrates X-ray luminosity at 1.9 x 10¹³ solar luminosities, embodying the expected phenomena in over-dense high-redshift environments.

Theoretical and Cosmological Insights

This paper reinforces theoretical frameworks surrounding early galactic over-densities and subsequent hierarchical structure formation. The observed proto-cluster's properties align with cosmological simulations of large-scale structure and cluster progenitors, predicting massive galaxy mergers leading to modern-day galaxy clusters. These observations position the identified proto-cluster as a potential analog to contemporary high-mass clusters dominantly formed via hierarchical Coalescence.

Future Directions

The findings presented in this paper open avenues for further exploration into high-redshift galactic environments. Increased sensitivity in infrared and optical measurements could refine estimates of age and mass distributions of proto-cluster galaxies. Expanded studies using emerging astronomical facilities could provide deeper insights into the influence of various environmental factors on galaxy evolution at this critical juncture of the universe's history.

Overall, this research delineates an observational cornerstone that aligns with existing theoretical models for galaxy and massive structure formation in the nascent universe, bridging observational astronomy with cosmological simulation frameworks. Through its multi-wavelength approach and robust statistical analysis, this paper remains a vital resource for astronomers and cosmologists examining the interplay of matter that defines the cosmic web.