arXiv subjects

Parsa Ghafour

Publications and source records attributed to Parsa Ghafour.

5 recordsLinked to original sources

arXiv2026

Cosmic Environment as the Primary Driver of Dwarf Satellite Statistics

Context: Satellite dwarf galaxies provide key constraints on galaxy formation and evolution, since their abundance and spatial distribution reflect both the host properties and the large-scale environment. Aims: This study quantifies the dependence of satellite populations on the host stellar mass, morphology, and star formation activity across different environments, and traces their evolution with cosmic time within the $\Lambda$CDM framework. Methods: The Millennium-II simulation combined with the G11 semi-analytic model is used to construct consistent samples of host galaxies brighter than $M_{r}<-16$ and their satellites ($M_{\ast}\geq 3\times10^{5}\,M_{\odot}$, $M_{r}<-9$) within the virial radius. Satellite abundance and radial profiles are analysed in cluster, group, and void environments, and their evolution is traced from $z=2$ to $z=0$ across three host stellar mass bins. Results: Satellite abundance is correlated strongly with host stellar and bulge mass, whereas host morphology has little independent effect once stellar mass is accounted for. Dense environments suppress satellite populations relative to voids. Correlations between satellite abundance, specific star formation rate, and disk scale length become evident only in groups and clusters. At $z=0$, radial profiles show strong central concentrations in voids, flattened distributions in clusters, and intermediate trends in groups. Their redshift evolution reveals progressive flattening for low- and intermediate-mass hosts in dense environments, stability for massive hosts, and increasing central concentration in voids. The cosmic evolution of satellite abundance further highlights distinct pathways: gradual accumulation in voids, mass-dependent trends in groups, and strong late-time suppression in clusters.

astro-ph.GA↗

arXiv2025

The Filament Rift: $\Lambda$CDM's Structural Challenge Against Observation

This study presents the first extended comparison of cosmic filaments identified in SDSS DR10 observations ($z < 0.05$) and the IllustrisTNG300-1 $\Lambda$CDM simulation ($z = 0$), utilizing the novel GrAviPaSt filament-finder method. The analyses are performed on both macro- and micro-filaments, each characterized by their length, thickness, and contrast in mass density. In addition to total sample comparisons, two subcategories of micro-filaments, GG (linking galaxy groups) and CC (linking galaxy clusters), are introduced to further analyze discrepancies between the $\Lambda$CDM model and observation. While $\Lambda$CDM produces extended macro-filaments, such structures are largely absent in SDSS, and where present, they exhibit higher densities than their simulated counterparts. Micro-filaments also show notable density discrepancies: at fixed length and thickness, observational filaments are significantly denser than those in the simulation. Employing radial density profiles reveal that micro-filaments in the $\Lambda$CDM simulation exhibit higher contrasts in mass density relative to the background compared to their observational counterparts. Notably, CC type micro-filaments displayed enhanced density contrasts over GG types in the simulation, while observational data showed the opposite trend. Furthermore, SDSS galaxies in both GG and CC micro-filaments exhibit lower specific star formation rates (sSFR) and older stellar populations, while TNG300-1 micro-filaments host more actively star-forming galaxies within the intermediate stellar mass range. These results reveal persistent discrepancies between observational data and the $\Lambda$CDM reconstruction of cosmic filaments, pointing to possible tensions in our current understanding of large-scale structures and their environmental effects on galaxy evolution.

astro-ph.CO↗

arXiv2025

From Voids to Clusters: Mergers and Evolutionary Pathways of Star-Forming and Quenched Low-Mass Galaxies

The evolution of low-mass galaxies is shaped by both internal processes and environmental factors, yet the role of environment and mergers in regulating their growth and star formation rates remains poorly understood, especially in the low-density regime. This study aims to compare the evolutionary pathways and merger histories of star-forming and quenched galaxies in dense (cluster) and under-dense (void) environments, focusing on galaxies with stellar masses in the range $10^{8.5} \leq M_\star/M_\odot \leq 10^{10.5}$. It presents the first statistical analysis within this stellar mass range, explicitly distinguishing between mini, minor, and major mergers across varying environments. Using the high-resolution TNG300-1 simulation from the IllustrisTNG project, we classify galaxies as star-forming and quenched based on sSFR and UVJ criteria. We track their physical properties over the last $\sim 10.5$ Gyr ($z < 2$), follow their complete merger histories, distinguishing between major, minor, and mini mergers, and assess the statistical impact of these mergers on star formation and gas content.

astro-ph.GA↗

arXiv2025

GrAviPaSt's Lens to the Past: Unveiling the Evolution of Filamentary Structures

This paper examines the evolution of cosmic filaments across redshifts 1, 0.5, and 0 using the IllustrisTNG100-1 magneto-hydrodynamical simulation. To achieve this, we introduce GrAviPaSt, a simple, efficient and parameter-free filament identification method that leverages gravitational potential, an A*-like path-finding algorithm, and spanning trees. Applying this method to galaxy distributions at different redshifts allows us to analyze various filament properties, including their length, thickness, mass density contrast, and radial profile. Additionally, we investigate dynamic characteristics such as the mean distance of filament galaxies from the skeleton, their weighted mean velocity, and velocity trends normalized by their positions within the filaments. Our findings reveal the evolution of cosmic filaments from redshift 1 to 0, highlighting key differences across classifications. In particular, we examine the mass density contrast radial profile of filaments connecting two galaxy groups and those linking two galaxy clusters, identifying distinct differences in profile shape between these categories. Furthermore, in the context of weighted mean velocity, we analyze cosmic filaments exhibiting either negative or positive weighted mean velocity, demonstrating their differing evolutionary trends in terms of the mean distance of filament galaxies from the skeleton.

astro-ph.CO↗

arXiv2025

Star-Forming vs. Quenched Galaxies in Voids: Insights into the Role of Mergers

Cosmic voids, the largest under-dense structures in the Universe, are crucial for exploring galaxy evolution. These vast, sparsely populated regions are home to void galaxies -- predominantly gas-rich, star-forming, and blue -- that evolve more slowly than those in denser environments. Additionally, the correlation between galaxy mergers and specific properties of galaxies, such as the star formation rate (SFR), is not fully understood, particularly in these under-dense environments. Quenched void galaxies exhibit high SFRs at high redshifts, significantly decreasing at lower redshifts (z < 0.5). These galaxies have higher dark matter halos than star-forming galaxies across all redshifts, leading to rapid gas consumption. They formed earlier and experienced more major mergers in earlier epochs but fewer recent mergers, resulting in a lack of fresh gas for sustained star formation. Also, star-forming and high-mass quenched void galaxies show higher SFRs in mergers compared to non-merger galaxies. This study highlights that formation time, merger rates, and dark matter halos play a crucial role in the star formation history of void galaxies. Rapid and earlier gas consumption due to earlier formation time and the absence of recent mergers could lead to quenched void galaxies at lower redshifts, providing valuable insights into galaxy evolution in low-density environments.

astro-ph.GA↗