The clustering of massive galaxies at z~0.5 from the first semester of BOSS data (1010.4915v2)

Abstract: We calculate the real- and redshift-space clustering of massive galaxies at z~0.5 using the first semester of data by the Baryon Oscillation Spectroscopic Survey (BOSS). We study the correlation functions of a sample of 44,000 massive galaxies in the redshift range 0.4<z<0.7. We present a halo-occupation distribution modeling of the clustering results and discuss the implications for the manner in which massive galaxies at z~0.5 occupy dark matter halos. The majority of our galaxies are central galaxies living in halos of mass 10^{13}Msun/h, but 10% are satellites living in halos 10 times more massive. These results are broadly in agreement with earlier investigations of massive galaxies at z~0.5. The inferred large-scale bias (b~2) and relatively high number density (nbar=3e-4 h^3 Mpc^{-3}) imply that BOSS galaxies are excellent tracers of large-scale structure, suggesting BOSS will enable a wide range of investigations on the distance scale, the growth of large-scale structure, massive galaxy evolution and other topics.

• The paper measures clustering of ~44,000 massive galaxies from BOSS, establishing baseline bias (b ≈ 2) and spatial distribution metrics.
• It applies real- and redshift-space correlation functions to reveal that ~90% of galaxies are centrals in ~10^13 h⁻¹ M☉ dark matter halos.
• The study employs a Halo Occupation Distribution model to connect galaxy observations with cosmological large-scale structure analyses.

An Examination of Massive Galaxy Clustering at Redshift 0.5

The paper, "The clustering of massive galaxies at $z \sim 0.5$ from the first semester of BOSS data" by Martin White et al., delivers a detailed analysis of the spatial distribution of massive galaxies at intermediate redshifts using initial data from the Baryon Oscillation Spectroscopic Survey (BOSS). This research is pivotal for understanding the large-scale structure of the universe and offers insights into the occupation of dark matter halos by galaxies.

Overview of the BOSS Data and Objective

The BOSS initiative, part of the Sloan Digital Sky Survey-III (SDSS-III), aims to probe cosmic large-scale structure focusing on Luminous Red Galaxies (LRGs). The paper utilizes a substantial dataset of approximately 44,000 galaxies within the redshift range $0.4 < z < 0.7$, acquired from observing luminous galaxies whose high mass light profiles facilitate reliable spectroscopic measurements. This effort constitutes a pivotal component of the evolution of galaxy surveys following predecessors like the SDSS-I/II.

Technical Methodologies and Results

Clustering Measurement

The paper measures galaxy clustering in real- and redshift-space, employing correlation functions to interpret the spatial distribution:

• Real-space Clustering: The projected correlation function, $w_p(R)$, reveals clustering strength across spatial scales. The data indicate that massive galaxies predominantly occupy dark matter halos of mass around $10^{13}\,h^{-1}M_\odot$, with a subset residing as satellites within substantially larger halos. The clustering amplitude at large scales was reported to bias around $b \approx 2$, aligning with typical expectations for massive galaxies, suggesting they are reliable tracers of large-scale structure.
• Redshift-space Clustering: The analysis of angle-averaged redshift space correlation function, $\xi(s)$, is consistent with expectations showing suppression due to virial motions on small scales and enhancement due to coherent infall on larger scales.

Halo Occupation Distribution (HOD) Model

The authors utilize a Halo Occupation Distribution model to analyze the galaxy-dark matter halo connection:

• They find that about 90% of the galaxies are central in their dark matter halos, while roughly 10% are in satellite galaxies in more massive halos ($\sim 10$ times bigger).
• This robust agreement with earlier samples is validating for current theoretical models of galaxy formation and distribution.

Implications and Future Prospects

The results confirm that BOSS galaxies serve as excellent tracers for multiple cosmological investigations, including the cosmic distance scale, structure growth, and galaxy evolution. The statistics provided in the paper will become key in fine-tuning our understanding of the galaxy-halo connection and the growth of cosmic structures over time.

Potential Developments in AI and Processing

Going forward, advancements in AI and machine learning could streamline the data analysis processes of such spatial surveys, providing deeper insights into complex cosmological patterns. These machine-driven models may offer enhanced capabilities in real-time data processing, anomaly detection, and predictive analysis, thus significantly impacting future surveys' efficiency and depth of analysis.

Concluding Remarks

This paper establishes baseline measurements for future studies using BOSS data, playing a crucial role in the context of ongoing and future large-scale cosmological surveys. It enhances our comprehension of galaxy distribution at redshifts around 0.5 and leverages collaboration between observational data and sophisticated models to further unravel the universe's large-scale structure. Such foundational work lays groundwork for refining our cosmological models significantly and bridges observational astronomy with theoretical physics in ever more rigorous ways.