Environmental effects on subhalo abundance and internal density profiles
Abstract
In the study of structure formation, properties of dark matter subhalos offer clues to galaxy evolution and indirect dark matter detection. Using the high-resolution COLOR N-body simulation and a multiscale web classification algorithm based on NEXUS+, we examine how subhalo abundance and internal properties depend on the large-scale environment of host halos. Our findings reveal that hosts in filaments contain 5 to 20\% more subhalos than the cosmic mean, while those in voids show a 25\% deficit. Across all environments, the subhalo mass function shows an exponential cutoff at the high subhalo mass end. Subhalo internal properties vary with environment; subhalos in filaments tend to be up to 10\% more concentrated, whereas those in voids are less concentrated. These results show that cosmic web location significantly influences subhalo populations and dynamics, emphasising the need to include environmental effects in modelling small-scale galaxy formation.
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LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Environmental effects on subhalo abundance and internal density profiles Feven Markos Hunde Center for Theoretical Physics PAS (CFT PAS) PhD Supervisors: Wojciech Hellwing(CFT PAS), Maciej Bilicki(CFT PAS), with Oliver Newton(CFT PAS) and Krishna Naidoo(UoP) LSST@Europe7 September 19, 2025 Image credit: Hahn (2014)
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms The cosmic web ●A complex weblike pattern in which matter, gas, and galaxies aggregate in ●Elongated filaments, dense nodes or knots, flattened walls, and underdense voids Walls Voids Filaments Cluster or node Credit: Illustris TNG Walls Voids Filaments Cluster or node Springel et al. 2006
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Subhalos ●LCDM predicts hierarchical structure formation across all scales ●Galaxies are embedded in larger DM halos teeming with self-bound substructure → subhalos ●Simulations predicts a myriad of subhaloes are expected to orbit the Galaxy (CDM case: at least 20 subhalos with mass > 106 M ☉ within <= 30 kpc) (see e.g. Barry et al. 2023) Giocoli et al. 2010
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Haloes and galaxies in the cosmic web Cosmic Web - Halo & galaxy relation Cautun et al. 2013 Halo mass function Hellwing et al. 2021 Concentration Jaber et al. 2024 SHM relation ●Halo and galaxy properties vary across cosmic web environments ●The specific impact on observable properties is still unknown
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Haloes and galaxies in the cosmic web Cosmic Web - Halo & galaxy relation Environmental effect is stronger for haloes with masses below 1012 M ☉ Cautun et al. 2013 Halo mass function Jaber et al. 2024 SHM relation Hellwing et al. 2021 Concentration ●Halo and galaxy properties vary across cosmic web environments ●The specific impact on observable properties is still unknown
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Subhaloes in the context of the cosmic web Why subhalos? ●Subhalos can host satellite galaxies ●Subhalo statistics is a powerful discriminator between proposed DM models (cold, warm, self-interacting?) ●Subhalos are dense regions where dark matter annihilation may be boosted, making them relevant for indirect dark matter search
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Subhaloes in the context of the cosmic web Why subhalos? ●Subhalos can host satellite galaxies ●Subhalo statistics is a powerful discriminator between proposed DM models (cold, warm, self-interacting?) ●Subhalos are dense regions where dark matter annihilation may be boosted, making them relevant for indirect dark matter search Our approach ●We want to understand how the cosmic web environments influence subhalo populations ●Data: COCO simulation suite (Hellwing et al. 2016) with a resolution ~ 6.19×106M ☉ h−1 ●Cosmic web segmentation: CaCTus - the adapted version of the NEXUS+ (Cautun et al. 2013) algorithm ●Using eigenvalues of density Hessian matrix ●Multiscale detection Excluded subhalos with less than 100 particles
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Environmental Dependence I: Mass function Hunde, et al. 2025, A&A, 700, A65 ●The solid lines show the exponential power-law fitting given by: ...Giocoli et al. 2008a ●Higher subhalo abundance in denser environments ●Beta (𝛽) value shows dependence on the cosmic web location Best β values for M200 = 1010 M ☉ h−1 Filaments 48 ± 1 Walls 54 ± 2 Voids 60 ± 2
LSST@Europe7 | Poznań, Poland | September 15th-19th, 2025 Glossary & Acronyms Environmental Dependence II: Vmax-Rmax relation Hunde, et al. 2025, A&A, 700, A65 ●The characteristic density or concentration of subhalos Vmax = maximum circular velocity of subhalo , Rmax = the radius at which Vmax is attained