The Average Star Formation Histories of Galaxies in Dark Matter Halos from z=0-8 (1207.6105v2)

Abstract: We present a robust method to constrain average galaxy star formation rates, star formation histories, and the intracluster light as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates, and cosmic star formation rates from z=0 to z=8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, star formation rates, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z=8. We also provide new compilations of cosmic and specific star formation rates; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 10^12 Msun are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for star formation histories that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the star formation history of galaxies into a self-consistent framework based on the modern understanding of structure formation in LCDM. Constraints on the stellar mass-halo mass relationship and star formation rates are available for download at http://www.peterbehroozi.com/data.html .

• The paper introduces an advanced empirical method combining abundance matching with large-scale simulations to derive average star formation and stellar mass histories from z=0 to 8.
• The paper finds that dark matter halos around 10^12 M☉ exhibit peak baryon conversion efficiency, which notably declines in more massive halos post z~2.5.
• The paper distinguishes central galaxy growth from intracluster light accumulation, providing robust constraints for galaxy evolution models and future high-redshift observations.

Overview of "The Average Star Formation Histories of Galaxies in Dark Matter Halos from $z=0-8$"

The academic paper titled "The average star formation histories of galaxies in dark matter halos from $z=0-8$" by Behroozi et al. presents an advanced empirical method for assessing galaxy formation histories within the standard $\Lambda$CDM cosmological paradigm. The authors aim to deduce the average star formation rates (SFRs), stellar mass accumulation histories, and the intracluster light (ICL) distribution as functions of dark matter halo mass from redshift $z=0$ to $z=8$. The paper employs a robust analytical framework that integrates various empirical models with comprehensive N-body simulation data to evaluate the cosmic star formation history consistent with observational data on galaxy stellar mass functions, specific star formation rates, and the cosmic star formation rate.

Methodology and Findings

Behroozi et al. utilize a sophisticated approach combining abundance matching techniques with large-scale cosmological simulations to populate halos with realistic galaxy properties over time. Their results adhere to observational galaxy data across multiple epochs, with intrinsic uncertainties being systematically addressed. Their method involves:

• Star Formation and Mass Relationships: They propose a functional form for the stellar mass-halo mass relationship, incorporating variable efficiency parameters that shift with redshift. Their findings suggest an evolutionary function wherein accumulation efficiency peaks at masses around $10^{12} M_\odot$ consistently across time.
• Efficient & Inefficient Halos: Their analysis indicates that halos near $10^{12} M_\odot$ maintain peak efficiency in converting baryonic matter into stellar content throughout cosmic history. The baryon conversion efficiency for halos larger than this value declines prominently post-$z \sim 2.5$, aligning with theoretical dynamics of cold-mode accretion cessation.
• ICL and Halo Accretion Dynamics: The breakdown of stellar mass distribution into intracluster light is significant for massive galaxies, traced out to redshift $z\sim 1-1.5$. The paper also reveals that galactic merger remnants contribute minimally to central galaxies' stellar masses in massive halos, resonating with observational concerns about numerically inflated stellar mass growth previously unaccounted for in other models.
• Dwarfs and High Redshift Galaxies: Findings show that dwarf galaxies at low redshift have surprisingly efficient star formation histories and higher stellar mass to halo mass ratios than certain theoretical predictions suggested—contrasting historical models which underrepresented late-forming stellar populations.

Implications and Future Directions

The implications of these findings extend to multiple areas of galaxy evolution and cosmology. Firstly, the identification of the peak baryon conversion efficiency around $10^{12} M_\odot$ provides constraints on feedback and cooling processes. The notable decline of efficiency in massive halos post-$z \sim 2.5$ can inform theories on the thermal regulation of galactic environments and the transition away from cold-mode accretion.

Secondly, their refined mapping of ICL growth and merger dynamics underscores the need to distinguish between central galaxy and intracluster light in massive galaxies accurately. The work points to evolutions in the bulk properties of massive galaxies in a hierarchical universe, providing a framework for isolating the effects of star formation versus merger-driven growth.

Finally, the paper establishes potential avenues for further exploration, particularly in the detailed statistical properties of high-redshift galaxies and the cosmic dawn era. The proposed methodology allows for predictions that can be tested with next-generation observational surveys, like those anticipated from the James Webb Space Telescope, further refining our understanding of early star formation periods.

Conclusion

This comprehensive paper by Behroozi et al. presents a coherent narrative linking the buildup of stellar components within halos across cosmic history under the $\Lambda$CDM framework. By integrating rigorous theoretical modeling with empirical observation, the research contributes essential insights into the dynamic processes governing galaxy formation and paves the way for future advancements in deciphering the universe's star formation chronicle.