arXiv subjects

Tian-Cheng Luan

Publications and source records attributed to Tian-Cheng Luan.

4 recordsLinked to original sources

arXiv2026

Universal Fitting Formulae for the Peak Concentration of Dark Matter Halos

The prediction of the structural properties of dark matter halos is crucial for studies in modern cosmology and galaxy formation. Utilizing a comprehensive suite of N-body simulations spanning diverse cosmologies and box sizes, we derive a universal halo concentration prescription aligned with the excursion set theory framework. The halo peak-height parameter is revised to incorporate the linear growth factor at the halo formation epoch, enhancing its physical relevance to assembly history tracking. For fixed halo mass, we fit the distributions of the halo concentration and revised peak height to lognormal functions to extract their peak values. We find that these peaks follow a universal, tight relation invariant to redshift, box size, initial power spectrum, and cosmology, exhibiting remarkably small scatter. In particular, the relation flattens systematically with increasing revised peak height, approaching an asymptotic value of ~2.54, consistent with previous reports of a concentration floor. The fitting formula consistently describes both the mass-concentration and peak height-concentration relations, easily quantifying how these relations depend on redshift and cosmological parameters. This universal framework enables robust prediction of the most probable (peak) halo concentration using our fitting formula or theoretical/semianalytical mass assembly histories. A software package for calculating peak concentrations is publicly available online.

astro-ph.CO↗

arXiv2026

Hermes - Towards an Optimal High-Performance Algorithm for Cosmic Statistics of Large Data Sets

We present Hermes, an in situ multiresolution framework for efficient and flexible measurements of cosmic large-scale-structure statistics from discrete catalogues. Hermes reconstructs a catalogue as a continuous density field in a compact scaling-function basis and replaces explicit counting of particle tuples with algebraic operations among window-filtered fields. Standard binning schemes for counts-in-cells, two-point and higher-order correlation functions are thereby expressed through choices of window functions, while new statistics can be constructed by modifying the kernels without redesigning the estimator. We introduce PyHermes, an open-source Python implementation combining multiresolution reconstruction, FFT-based convolution, MPI/thread parallelism, and GPU acceleration. It supports isotropic and anisotropic two-point statistics, marked correlations, standard and multipole three-point functions, filtered statistics, and differential operators for derived physical fields. Tests with cosmological N-body halo catalogues demonstrate a range of clustering measurements and quantify the computational efficiency and scalability of the approach. By separating field representation from statistical windows, a single reconstructed field can be reused for many standard and customised measurements, making Hermes well suited to large data sets from current and future galaxy surveys.

astro-ph.CO↗

arXiv2025

Impact of cosmic web on the properties of galaxies in IllustrisTNG simulations

We investigate the influence of the cosmic web on galaxy properties in the IllustrisTNG simulations. To disentangle the effects of galaxy groups and cosmic filaments, we classify the cosmic web environment into four categories: group, group-dominated, filament-dominated, and field. By controlling for stellar mass, we reveal evident differences in specific star formation rates (sSFR), quenched fraction, gas fractions, local density, and stellar ages among central galaxies in different cosmic web environments, particularly for lower-mass galaxies. However, these differences largely diminish when the effect of local overdensity is further accounted for, indicating its dominant role. Additionally, we observe distinct differences in these properties among satellite galaxies across environments, mainly driven by stellar mass, halo mass, and overdensity. Notably, residual differences between satellites in field and filament-dominated region persist even after controlling for these factors, suggesting a stronger susceptibility of satellite galaxies to filaments compared to centrals. Our findings highlight the importance of differentiating between central and satellite to accurately assess the environmental effects of the cosmic web. Our analysis suggests that the relationship between galaxy properties and their distance from filaments arises from a combination of factors, including stellar and halo mass, groups, overdensity, and the intrinsic influence of the cosmic web. Additionally, we find that the effect of the cosmic web on galaxy properties is reduced at $z=0.5$, compared to $z=0$. Furthermore, central galaxies near thick filaments tend to exhibit slightly to moderately lower sSFR and cold gas fractions compared to those near thin filaments.

astro-ph.GA↗

arXiv2025

Recovering Cosmic Structure with a Simple Physical Constraint

Radio observation of the large-scale structure (LSS) of our Universe faces major challenges from foreground contamination, which is many orders of magnitude stronger than the cosmic signal. While other foreground removal techniques struggle with complex systematics, methods like foreground avoidance emerge as effective alternatives. However, this approach inevitably results in the loss of Fourier modes and a reduction in cosmological constraints. We present a novel method that, by enforcing the non-negativity of the observed field in real space, allows us to recover some of the lost information, particularly phase angles. We demonstrate that the effectiveness of this straightforward yet powerful technique arises from the mode mixing from the non-linear evolution of LSS. Since the non-negativity is ensured by mass conservation, one of the key principles of the cosmic dynamics, we can restore the lost modes without explicitly expressing the exact form of the mode mixing. Unlike previous methods, our approach utilizes information from highly non-linear scales, and has the potential to revolutionize the analysis of radio observational data in cosmology. Crucially, we demonstrate that in long-baseline interferometric observations, such as those from the Square Kilometre Array (SKA), it is still possible to recover the baryonic acoustic oscillation (BAO) signature despite not directly covering the relevant scales. This opens up potential future survey designs for cosmological detection.

astro-ph.CO↗