Dependence of the outer density profiles of halos on their mass accretion rate (1401.1216v2)

Abstract: We present a systematic study of the density profiles of LCDM halos, focusing on the outer regions, 0.1 < r/Rvir < 9. We show that the median and mean profiles of halo samples of a given peak height exhibit significant deviations from the universal analytic profiles discussed previously in the literature, such as the Navarro-Frenk-White and Einasto profiles, at radii r > 0.5 R200m. In particular, at these radii the logarithmic slope of the median density profiles of massive or rapidly accreting halos steepens more sharply than predicted. The steepest slope of the profiles occurs at r ~ R200m, and its absolute value increases with increasing peak height or mass accretion rate, reaching slopes of -4 and steeper. Importantly, we find that the outermost density profiles at r > R200m are remarkably self-similar when radii are rescaled by R200m. This self-similarity indicates that radii defined with respect to the mean density are preferred for describing the structure and evolution of the outer profiles. However, the inner density profiles are most self-similar when radii are rescaled by R200c. We propose a new fitting formula that describes the median and mean profiles of halo samples selected by their peak height or mass accretion rate with accuracy < 10% at all radii, redshifts and masses we studied, r < 9 Rvir, 0 < z < 6 and Mvir > 1.7E10 Msun/h. We discuss observational signatures of the profile features described above, and show that the steepening of the outer profile should be detectable in future weak-lensing analyses of massive clusters. Such observations could be used to estimate the mass accretion rate of cluster halos.

• The paper demonstrates that outer halo density profiles steepen near r ≈ 0.5–1 in direct relation to high mass accretion rates.
• The paper introduces a new fitting formula combining an inner Einasto profile, a transition term, and a power-law outer region with fit accuracy under 10%.
• The paper highlights observational implications for weak-lensing analyses by linking profile steepening to halo mass accretion histories.

Dependence of the Outer Density Profiles of Halos on Their Mass Accretion Rate

This paper presents a comprehensive paper of the outer density profiles of $\Lambda$CDM halos, focusing on the interplay between these profiles and the halos' mass accretion rates. The authors investigate the deviations from established analytic profiles, such as the Navarro-Frenk-White (NFW) and Einasto profiles, in the outer regions of halos. They propose a new fitting formula, revealing significant deviations from universal behavior in halo profiles, especially at high radii. This paper sheds light on the traits governing halo structure and their ramifications amidst the dynamic environment stemming from accreting mass.

Key Findings

1. Profile Steepening: An important discovery is the steepening of the slope of mass profiles around $r \approx 0.5-1$, dependent on peak height $\nu$ or mass accretion rate $\Gamma$. This steepening signifies that the outer profiles of halos, particularly those with high accretion rates, cannot be described accurately by the classic NFW and Einasto profiles.
2. Self-Similarity: The paper reveals that the outer regions at $r \gtrsim$ exhibit self-similarity when radii are rescaled using $$, suggesting optimal scaling with respect to the mean density. This observation contrasts with the inner profiles, which demonstrate the most self-similarity when scaled using radii tied to the critical density. 3. **Accretion Rate Correlation**: It is evident from the research that the halo mass accretion rate$$\Gamma$$, rather than major mergers alone, predominantly drives variations in the outer profile shapes. Higher$$\Gamma$results in a steeper slope at radii around$.
3. Observational Implications: The implications of these findings extend to observational signatures in weak-lensing analyses. The steepening of profiles provides a method to gauge mass accretion rates in massive clusters, which might open new horizons in observational cosmology.
4. Fitting Formula: The authors propose a fitting formula characterized by an inner Einasto profile, a transition term, and a power-law outer profile, that fits halos across a range of redshifts, masses, and accretion rates. This new formula achieves a remarkable fit accuracy of $\lesssim 10\%$.

Implications and Speculations

The findings hint at significant practical and theoretical implications:

• Halo Model Revisions: The insights necessitate reconsideration in models used to describe the halo-matter correlation function and the specifics governing structural transitions in halos.
• Cosmological Simulations: Future simulations can leverage these nuanced observations to improve realism in mass distribution models, especially in environments marked by dynamic accretion activities.
• Weak-Lensing Applications: On the observational front, these results highlight the potential for utilizing weak-lensing techniques to estimate halo growth rates, providing a more profound understanding of structure formation dynamics.

Concluding Remarks

This paper marks a pivotal step in elucidating the intricate dependence of halo profiles on mass accretion rates. The discovered self-similarity principles and the proposed fitting formula set the foundation for future explorations, potentially refining theoretical and observational methods in astrophysical research. The assertion that halo profiles are fundamentally indicative of their accretion histories conveys a broader message about galactic evolution, tying cosmic structures intimately to their formative dynamics. Such understanding not only enhances the accuracy of current models but also steers forthcoming inquiries into the realms of galaxy dynamics and cosmological evolution.