arXiv subjects

Bipradeep Saha

Publications and source records attributed to Bipradeep Saha.

3 recordsLinked to original sources

arXiv2026

Bulk vs. turbulent motions at the centres of galaxy clusters: AGN-driven turbulence according to TNG-Cluster

The highly dynamic intracluster medium (ICM) influences cluster thermodynamic evolution and probes key physical processes. Quantifying the non-thermal motions is therefore essential for understanding cluster physics and interpreting high spectral-resolution X-ray observations from telescopes like {\it XRISM}. We quantify bulk and turbulent gas motions in 352 galaxy clusters at $z=0$ (${\rm M_{200c}=10^{14.3-15.4}\, M_\odot}$) from the TNG-Cluster suite of magneto-hydrodynamical galaxy simulations. We use a multi-scale filtering Reynolds decomposition to separate total gas velocities into bulk (coherent) and turbulent (small-scale fluctuations) components. We primarily focus on the hot X-ray emitting gas in the central core regions. According to TNG-Cluster, majority of the ICM has subsonic turbulence but with broad velocity distributions reaching $\mathcal{M}_{\rm Turb}\sim 10$ and large cluster-to-cluster variations. In cluster centres, turbulence contributes less than half of the total velocity dispersion $(\sigma_{v\rm,Turb } \sim 0.5 ~\sigma_{v,\rm Total})$ for most clusters, with typical turbulent velocity dispersions of $50-75$ km s$^{-1}$ across the mass range, and with sub per cent levels of turbulent pressure support. Clusters that are strong cool cores, or have X-ray cavities, or experienced recent SMBH feedback energy injections exhibit systematically larger turbulent velocity dispersions and more prominent turbulent velocity tails. On average, the turbulent velocity dispersion peaks in cluster centres, decreases slightly to a minimum at $0.1-0.2 \, R_{\rm500c}$, then rises again. Our analysis shows that SMBH feedback is a key driver of turbulence in cluster cores, generating strong but short-lived motion alongside high-velocity outflows. It also calls for caution for interpreting {\it XRISM} observations.

astro-ph.GA↗

arXiv2026

A framework for modelling Population III stars in cosmological simulations

Population III (Pop III) stars are the first generation of stars to form in the universe, emerging from primordial gas composed mainly of hydrogen and helium. They play a crucial role in ending the cosmic dark ages and initiating reionization. In this work, we present a comprehensive framework for modelling Pop III stars in cosmological simulations. This includes three key components: (1) an enhanced thermochemical network that tracks the equilibrium abundances of key catalytic species such as $\rm{H_2^+}$ and $\rm{H^-}$, which are crucial for forming molecular hydrogen in primordial gas; (2) detailed stellar spectra of Pop III stars computed from MESA evolutionary tracks and TLUSTY atmosphere models; and (3) comprehensive supernova feedback, including both Core-Collapse and Pair-Instability supernovae, with detailed elemental yields. We implement these improvements in AREPO-RT and test them using cosmological zoom-in simulations of a $1.95 \times 10^9$ $\rm M_\odot$ halo at $z=3$. Our results show that Pop III stars form at $z > 13$ and continue forming until $z \sim 5$, significantly affecting early galaxy evolution through radiation and energetic supernova feedback. The enhanced thermochemistry enables more efficient gas cooling, while Pop III feedback creates photo-heated diffuse gas and drives distinct metal enrichment patterns at $10 < z < 6$. The choice of IMF for Pop III stars critically determines the balance between radiative and mechanical feedback, with top-heavy choices producing stronger feedback and more metals but retaining less metal-enriched gas within the halo. Finally, we show that high-energy radiation from Pop III stars is necessary to explain the recent high-equivalent-width observations of the $\rm HeII$ line from a galaxy at $z\sim11$.

astro-ph.GA↗

arXiv2024

Quantifying the impact of AGN feedback on the large-scale matter distribution using two- and three-point statistics

Feedback from active galactic nuclei (AGN) plays a critical role in shaping the matter distribution on scales comparable to and larger than individual galaxies. Upcoming surveys such as $\textit{Euclid}$ and LSST aim to precisely quantify the matter distribution on cosmological scales, making a detailed understanding of AGN feedback effects essential. Hydrodynamical simulations provide an informative framework for studying these effects, in particular by allowing us to vary the parameters that determine the strength of these feedback processes and, consequently, to predict their corresponding impact on the large-scale matter distribution. We use the EAGLE simulations to explore how changes in subgrid viscosity and AGN heating temperature affect the matter distribution, quantified via 2- and 3-point correlation functions, as well as higher order cumulants of the matter distribution. We find that varying viscosity has a small impact ($\approx 10\%$) on scales larger than $1 h^{-1}$ Mpc, while changes to the AGN heating temperature lead to substantial differences, with up to $70\%$ variation in gas clustering on small scales ($\lesssim 1 h^{-1}$ Mpc). By examining the suppression of the power spectrum as a function of time, we identify the redshift range $z = 1.5 - 1$ as a key epoch where AGN feedback begins to dominate in these simulations. The 3-point function provides complementary insight to the more familiar 2-point statistics, and shows more pronounced variations between models on the scale of individual haloes. On the other hand, we find that effects on even larger scales are largely comparable.

astro-ph.CO↗