arXiv subjects

Zixiang Jia

Publications and source records attributed to Zixiang Jia.

5 recordsLinked to original sources

arXiv2026

Halo assembly bias in the early Universe: a clustering probe of the origin of the Little Red Dots

The clustering of galaxies encodes key information about the structure and assembly history of their host dark matter (DM) haloes, providing a powerful probe of the origin of extreme high-redshift systems. While halo assembly bias has been extensively studied at low redshift, its behavior in the early Universe remains poorly explored. Using the large-volume, high-resolution Shin-Uchuu cosmological $N$-body simulation, we characterize halo assembly bias associated with formation time, concentration, and angular momentum across a wide range of halo masses and redshifts. We find that the sign and amplitude of assembly bias depend on halo mass for both concentration and spin. High-concentration and low-spin haloes are more strongly clustered below characteristic peak heights of $ν\sim 1.5$ and $\sim 0.75$, respectively, while the trends weaken or reverse at higher masses. Halo age bias persists at all redshifts but decreases toward higher masses and earlier cosmic times. We apply these results to assess whether clustering can distinguish competing formation scenarios for the Little Red Dots (LRDs). We find that the direct-collapse-black-hole (DCBH) scenario predicts the strongest large-scale bias and enhanced pair fractions, the self-interacting-dark-matter (SIDM) core-collapse scenario and low-spin compact-galaxy scenarios yield weaker clustering due to lower characteristic halo masses and spin-related secondary bias, and a primordial-black-hole (PBH) scenario predicts unbiased clustering. Our results demonstrate that halo assembly bias and characteristic host masses provide powerful diagnostics for constraining the physical origin of LRDs, offering testable predictions for upcoming clustering measurements with JWST and future deep surveys.

astro-ph.CO↗

arXiv2026

Testing the isothermal Jeans model for self-interacting dark matter halos in the collapse phase

We benchmark the semi-analytical isothermal Jeans model against a high-resolution isolated N-body simulation that follows a self-interacting dark matter (SIDM) halo into deep core collapse. The model accurately reproduces the density evolution through much of the collapse phase, although it does not capture the sharp rise in central velocity dispersion during collapse. When applied to strong gravitational lensing observables, such as the projected mass and logarithmic density slope of SIDM halos, the Jeans model tracks the simulated evolution more closely than the parametric approach in the deep collapse regime. Our results demonstrate that the isothermal Jeans model provides a reliable and computationally efficient description of SIDM halo evolution.

astro-ph.CO↗

arXiv2026

An Enhanced Isothermal Jeans Approach to Constraining Dark Matter Self-Interactions from Galactic Kinematics

We present an improved semi-analytical model to predict density profiles of self-interacting dark matter (SIDM) halos and apply it to constrain the self-scattering cross section using SPARC galaxy rotation curves. Building on the isothermal Jeans approach, our model incorporates (i) velocity-dependent cross sections, (ii) an empirical treatment of core collapse, and (iii) enhanced robustness for identifying solutions. These advances allow us to fit a large sample of galaxies, including systems with baryon-dominated centers often excluded in earlier studies. We find that roughly 1/6 of galaxies admit both a core-growth and a core-collapse solution, while the rest favor a unique evolutionary state. Joint constraints across the sample reveal clear velocity dependence: the allowed parameter space forms an L-shaped degeneracy, where both nearly constant, low cross sections ($σ_0\sim2\,{\rm cm}^2$/g, $ω\gtrsim500\,$km/s) and strongly velocity-dependent models ($σ_0\sim100\,{\rm cm}^2$/g, $ω\sim60\,$km/s) are viable. Adopting the core-growth interpretation yields best-fit values $σ_0\simeq5\,{\rm cm}^2$/g and $ω\simeq250\,$km/s. Our constraints are remarkably consistent with previous results derived from a variety of independent probes. Compared to cold dark matter (CDM) models, SIDM outperforms simple adiabatic-contraction profiles and rivals empirical feedback-based CDM profiles, yet shows no correlation with stellar-to-halo mass ratio, a proxy for feedback strength, offering a distinct explanation for dwarf galaxy diversity. Moreover, SIDM does not affect galaxy-halo scaling relations significantly and makes concentration systematically lower. Our results highlight SIDM as a compelling framework for small-scale structure, while future low-mass kinematic data will be crucial for breaking degeneracies in velocity-dependent cross-section models.

astro-ph.GA↗

arXiv2025

The "Little Dark Dot": Evidence for Self-interacting Dark Matter in the Strong Lens SDSS J0946+1006?

Previous studies, based on precise modeling of a gravitationally lensing image, have identified what may be an extremely compact, dark perturber in the well-known lensing system SDSS J0946+1006 (the "Jackpot"). Its remarkable compactness challenges the standard cold dark matter (CDM) paradigm. In this paper, we explore whether such a compact perturber could be explained as a core-collapse halo described by the self-interacting dark matter (SIDM) model. Using the isothermal Jeans method, we compute the density profiles of core-collapse halos across a range of masses. Our comparison with observations indicates that a core-collapse halo has an inner density profile and mass enclosed within 1 kpc that fit the data well, but only if the halo has a total mass $\sim10^{11}~{\rm M_{\odot}}$. While a halo of this mass should host a detectable galaxy, the current observational upper limit on the perturber's luminosity remains uncertain. Resolving whether or not the data support the presence of a core-collapse SIDM halo therefore requires future deep observations to measure its luminosity.

astro-ph.GA↗

arXiv2025

Formation of the Little Red Dots from the Core-collapse of Self-interacting Dark Matter Halos

We present a statistical study of black hole (BH) formation and growth seeded by gravothermal core collapse of self-interacting dark matter (SIDM) halos at high redshift, using a cosmological semi-analytical framework based on Monte Carlo merger trees. We demonstrate that gravothermal collapse naturally leads to BH formation in high-concentration halos at a characteristic mass scale set by the SIDM cross section, and occurs predominantly in the early Universe. This mechanism is particularly promising for explaining the abundance of the little red dots (LRDs) -- a population of early, apparently galaxy-less active galactic nuclei hosting supermassive BHs. By incorporating this seeding process with simple models of BH growth and assuming a 100% duty cycle, we reproduce the observed LRD mass function for velocity-dependent cross sections of $σ_{0m} \sim 30\,\mathrm{cm}^2\,\mathrm{g}^{-1}$ and $ω\sim 80\,\mathrm{km}\,\mathrm{s}^{-1}$, which are consistent with independent constraints from local galaxies. While higher values of $σ_{0m}$ (or $ω$) would overpredict the low-mass (or high-mass) end of the BH mass function, such deviations could be reconciled by invoking a reduced duty cycle or lower Eddington ratio. Our results suggest that the demographics of high-redshift BHs can serve as a novel and complementary probe of SIDM physics.

astro-ph.GA↗