UniverseMachine: The Correlation between Galaxy Growth and Dark Matter Halo Assembly from z=0-10 (1806.07893v2)

Abstract: We present a method to flexibly and self-consistently determine individual galaxies' star formation rates (SFRs) from their host haloes' potential well depths, assembly histories, and redshifts. The method is constrained by galaxies' observed stellar mass functions, SFRs (specific and cosmic), quenched fractions, UV luminosity functions, UV-SM relations, IRX-UV relations, auto- and cross-correlation functions (including quenched and star-forming subsamples), and quenching dependence on environment; each observable is reproduced over the full redshift range available, up to 0<z\<10. Key findings include: galaxy assembly correlates strongly with halo assembly; quenching at z\>1 correlates strongly with halo mass; quenched fractions at fixed halo mass decrease with increasing redshift; massive quenched galaxies reside in higher-mass haloes than star-forming galaxies at fixed galaxy mass; star-forming and quenched galaxies' star formation histories at fixed mass differ most at z<0.5; satellites have large scatter in quenching timescales after infall, and have modestly higher quenched fractions than central galaxies; Planck cosmologies result in up to 0.3 dex lower stellar mass-halo mass ratios at early times; and, nonetheless, stellar mass-halo mass ratios rise at z>5. Also presented are revised stellar mass-halo mass relations for all, quenched, star-forming, central, and satellite galaxies; the dependence of star formation histories on halo mass, stellar mass, and galaxy SSFR; quenched fractions and quenching timescale distributions for satellites; and predictions for higher-redshift galaxy correlation functions and weak lensing surface densities. The public data release (DR1) includes the massively parallel (>10^5 cores) implementation (the UniverseMachine), the newly compiled and remeasured observational data, derived galaxy formation constraints, and mock catalogues including lightcones.

• The paper presents a novel empirical framework that correlates galaxy star formation with dark matter halo properties over a vast redshift range.
• It demonstrates a strong link between galaxy assembly and halo growth, shaping star formation and quenching dynamics.
• The study reveals evolving stellar mass–halo mass ratios and distinct assembly histories between central and satellite galaxies.

Overview of "UniverseMachine: The Correlation between Galaxy Growth and Dark Matter Halo Assembly from $z=0-10$"

The paper under discussion introduces the UniverseMachine framework, providing insights into the correlation between galaxy growth and dark matter halo assembly over a substantial redshift range ($z=0-10$). This paper addresses a fundamental question in astrophysics: how do galaxies evolve in connection with their host dark matter halos? The authors, Behroozi et al., have leveraged an ambitious modeling approach that merges empirical data with dark matter simulations to discern patterns that govern star formation rates (SFRs) and galaxy quenching.

Methodology and Innovations

The UniverseMachine method introduces a sophisticated suite of empirical models developed to derive galaxy SFRs based on halo properties—specifically focusing on potential well depths and assembly histories. The authors bypass the challenges typically associated with directly simulating complex baryonic physics by correlating observable galaxy properties with dark matter halo metrics from N-body simulations. This approach is profound because it circumvents detailed baryonic modeling, instead empirically fitting observational data to predict galaxy behaviors over cosmic time.

Key Findings

1. Galaxy and Halo Assembly Correlation: One of the primary revelations is the strong correlation between galaxy assembly and halo assembly. The paper demonstrates that star formation histories and quenched fractions at different halo masses and redshifts can be consistently modeled, concluding that galaxy growth is inherently linked to halo growth patterns.
2. Quenching Dynamics: Their work reveals a robust correlation between quenching—when galaxies cease to form stars—and halo mass, particularly at high redshifts. This insight emphasizes the role halo mass and environmental factors play in influencing galaxy star formation activity over time.
3. Evolving Stellar Mass–Halo Mass Relationships: The paper observes that stellar mass–halo mass ratios demonstrate minimal evolution from $z=0$ to $z=4$, indicating a consistent efficiency in galaxy formation across this redshift range. However, a marked evolution is observed beyond $z=4$, suggesting a shift in galaxy formation efficiencies in the early universe.
4. Satellite and Central Galaxy Differences: The paper provides evidence for different evolutions and assembly scenarios between central and satellite galaxies. Satellite galaxies, being subject to additional physical processes such as tidal stripping, exhibit different star formation and quenching histories compared to central galaxies.

Implications and Future Directions

This research elucidates important implications for understanding galaxy formation. By linking galaxy growth to halo properties, it provides a predictive framework that could guide future observational campaigns and improve interpretations of large-scale structure surveys. The findings also stress the necessity for continued acquisition and refinement of high-redshift data to constrain the models further.

Moreover, the methodology posed by UniverseMachine represents a significant advancement in how empirical models are constructed and could foster developments in understanding other complex aspects of galaxy evolution, such as metallicity and morphological changes. As observational capabilities improve, especially with next-generation telescopes such as the James Webb Space Telescope, behaviors at the high redshift frontier will be elucidated, potentially validating or refuting aspects of the current models.

Conclusion

Behroozi et al.'s UniverseMachine stands as a pivotal development in astrophysical modeling, providing clarity to the intricate relationships between galaxies and their dark matter hosts. With robust constraints derived from observed data, this model adeptly handles the empirical complexities involved in galactic evolution. It not only advances our understanding of galaxy formation and quenching but also fosters a pathway forward for empirical paper methodologies in cosmology.