Expanding the boundaries of dark matter halo

May 26, 2025, 9:00 AM → May 30, 2025, 5:00 PM Asia/Shanghai

C204, Student Center (Shanghai Jiao Tong University)

Dark matter halos have long served as fundamental units in our understanding of structure and galaxy formation. However, the classical picture of a virialized dark matter halo is undergoing significant revision, with recent research emphasizing the importance of the non-equilibrium outer regions. New definitions of halo boundaries, such as the splashback radius, depletion radius, and related boundaries in phase-space, are emerging alongside the classical virial radius. Together, these boundaries are shaping a more nuanced picture of a heterogeneous halo structure. This refined framework promises more physical modelling of structure formation with higher precision and finer detail, competing with while also complemented by machine learning approaches. At the same time, detecting new halo boundaries has become an important goal for observational surveys.

This workshop aims to highlight recent progress in expanding our understanding of dark matter halos, bringing together cutting-edge theoretical advancements, computational innovations, and observational breakthroughs. By fostering collaboration across these diverse developments, the event seeks to strengthen the prospects for a unified, physical understanding of structure formation in the Universe.

See detailed list of topics & invited speakers.

Updates: 

• 14/Apr: final program.
• 26/Mar: Draft program available.
•  20/Feb: Registration is now open.
   

Key Dates

• Abstract submission deadline: 9/Mar., 2025
• Registration: 
  • closes on 20/Apr.  
  • Registration fee: 1000 RMB (to be collected on site). 
  • The workshop is limited to ~60 participants and we may need to moderate the registration if places run out.
• Program: 26-30, May
• Banquet: 28/May (Wednesday)

Monday, May 26

9:00 AM → 10:20 AM Halo Theory: Boundary dynamics

9:00 AM The depletion radius of dark matter halo

I will report our recent development of the depletion radius, which is a new but fundamental halo boundary stemming from the macroscopic physics of halo growth. I will show that the depletion radius is both an important physical probe of halo evolution and a concise geometric boundary for halo models of the large scale structure, capable of overcoming major limitations of the classical halo in a systematic way. I will also present our observational measurements of the depletion radius for both our Milky Way halo and DESI galaxy groups.

Speaker: Jiaxin Han (Shanghai Jiao Tong University)

9:30 AM The Dependence of Depletion Radius on Mass Accretion Rate

We determine the depletion radius from the stacked mass flow rate (MFR) profiles of dark matter haloes in a cosmological simulation and explore its dependence on halo properties. We find that the MFR profiles exhibit near self-similarity for haloes with different masses. The primary factor that determines the depletion radius is still the mass accretion rate, and the relation is similar to that of splashback radius. However, their evolution trends are opposite, while the depletion radius following the self-similar spherical collapse model. By analysing the structure of haloes in phase space, we find that this dependence arises from the overdensity definition of halo.

Speaker: Jiale Zhou (Shanghai Jiao Tong University)

9:50 AM Splashback radius as a probe of cosmology and astrophysics

Splashback radius is a physically motivated boundary of halos, formed at the first apocenters of orbiting matter. Due to its strong correlation to the recent mass accretion history, especially that over the last one dynamical time, the splashback radius could be used to study the cosmic evolution, as well as astrophysics within halos. In this talk, I will briefly summarize the recent progress on theories and observations of splashback radius, then present the (preliminary) result from the galaxy clusters detected by the eROSITA X-ray survey.

Speaker: Tae-hyeon Shin (Carnegie Mellon University)

10:20 AM → 10:45 AM Coffee Break

10:45 AM → 11:45 AM Halo Theory: Boundary dynamics

10:45 AM Splashback radius of nonspherical dark matter halos and the cosmological implications

We investigate the splashback features of nonspherical dark-matter halos in phase space, namely based on cosmic density and velocity fields. Besides the density correlation function binned by the halo orientation angle, which was used in the literature, we introduce the corresponding velocity statistic, alignment velocity correlation function, to consider halo's asphericity. Using large-volume, high-resolution $N$-body simulations, we measure the density and velocity alignment statistics. On halo scales, $\sim 1 h^{-1} {\rm mpc}$, we detect a sharp steepening in the velocity correlation associated with the physical halo boundary, or the splashback feature, which is found more prominent than in the density correlation. We also find that the splashback radius determined from the density correlation becomes $\sim 3.5\%$ smaller than that from the momentum correlation. Moreover, the orientation-dependent splashback feature due to halo asphericity is measured when the density profile is determined by dark-matter particles, which can be used as a test of collisional cold dark matter since the halo shape is predicted to be rounder in such a model.

Speaker: Prof. Teppei Okumura (ASIAA)

11:15 AM The splashback radius and the radial velocity profile of galaxy clusters in IllustrisTNG

Clusters of galaxies are massive bound systems. At a large radius of 5 Mpc or more, massive clusters of galaxies decouple from the Hubble flow. Within this turnaround radius, galaxies are still accreting onto the cluster in the outer portion, the infall region. In the dense central regions with radii < 2 Mpc, clusters are dynamically relaxed. We use the radial velocity profile of cluster member galaxies from IllustrisTNG to derive two new dynamically determined radii that mark the transition from the region where galaxies are infalling to the inner virialized region. Both of these dynamical radii lie within $1\sigma$ of the splashback radius, the first apocenter of newly accreted galaxies. The dynamically determined radii provide a complementary physical view of the splashback radius as the inner boundary of the infall region.

Speaker: Michele Pizzardo (Saint Mary's University)

11:45 AM → 12:10 PM discussions

12:10 PM → 2:00 PM Lunch

2:00 PM → 3:20 PM Halo Theory: profile formation

2:00 PM Outskirts of Galaxy Clusters beyond a Self-similar Picture

The self-similar spherical collapse model provides an insightful framework for understanding the formation and evolution of galaxy clusters in an expanding Universe. However, cosmological simulations have revealed significant deviations of the cluster outskirts and their evolution from the self-similar prediction. In this talk, I will discuss intriguing physics behind this problem and introduce our novel idealized simulations designed to understand structures in the outskirts of galaxy clusters, including dark matter splashback, accretion shocks, and etc. Our findings indicate distinguished behaviors of the gas and dark matter boundaries driven by merger processes. I will further discuss the concept of total and smooth mass accretion rates and their role in determining the cluster boundaries.

Speaker: Congyao Zhang (Masaryk University)

2:30 PM Inner structure of dark matter halos

The inner regions of dark matter halos exhibit a rich dynamical structure shaped by multi-streaming and phase-space mixing. In this talk, I will present our recent investigations into the multi-streaming region, characterized by the number of apocenter passages or the radial action of dark matter particles. Our results reveal a remarkable universality: when categorized by their number of apocenter passages, particles follow a distribution that aligns closely with the NFW profile (i.e., $\rho\propto r^{-1}$) in the innermost regions. This trend was observed to be established at an early stage of halo formation. I will also discuss how this behavior compares between cold dark matter (CDM) and warm dark matter (WDM) scenarios, shedding light on the impact of free-streaming on inner halo dynamics. These findings provide new insights into the fundamental processes governing halo structure and evolution.

Speaker: Takahiro Nishimichi (Kyoto Sangyo University)

3:00 PM The Evolution of Dark Matter Halo: from Prompt Cusps to NFW Halos

Dark matter halos are self-gravitating objects seeded from small density perturbations in the early universe. Their structure can be described by a universal spherical averaged density profile across the scale of nearly all astronomical objects - the NFW profile - whose physical origin is not well understood. In recent N-body simulations, halos forming density profile as power-law with index -1.5 are found near the cut-off scale of the density perturbations, while analytical self-similar solution gives a power-law index of -12/7. 
In this work, we investigate the evolution of the density profiles of 8 halos at high redshifts with 8 different cut-off scales in order to provide a more comprehensive picture of the relationship between halo structures and their initial perturbations, and tested the results against the theoretical predictions. Special attention is given to the validity of the self-similar assumption and attempts are made to understand the later convergence to NFW profile.

Speaker: Yuchan Wang (Durham University)

3:20 PM → 3:45 PM Coffee Break

3:45 PM → 4:35 PM Halo Theory: profile formation

3:45 PM Understanding the Cusp-Core Transition and Characteristic Radius in Dark Matter Halos

Scaling relations between dark matter halos provide profound insights into dark matter properties, revealing empirical correlations across cosmic structures. Many studies suggest that the mass surface density of dark matter halos remains remarkably constant over a wide range of total masses (Burkert 1995; Spano et al. 2008; Donato et al. 2009; Salucci et al. 2012; Kormendy & Freeman 2016; Salucci et al. 2019). While the physical origins of this phenomenon remain uncertain, Kaneda et al. (2024) recently identified the radius of maximum circular velocity, $R_\mathrm{max}$, as a key parameter. At this radius, the surface density $\Sigma_{R_\mathrm{max}}$ aligns well with both observational data and CDM model predictions across a broad mass spectrum (see also Ogiya et al. 2014).

In low-mass galaxies, however, the $R_\mathrm{max}(M_{200})$ relation in the CDM model exhibits a significant discrepancy with observational results. Observations indicate that the virial mass of $10^{11} M_\odot$ serves as a critical boundary, below which $R_\mathrm{max}$ becomes larger than theoretical predictions. Assuming this discrepancy shares the same physical origin as the cusp-core problem, where models predict a cusp-like profile but observations show a core-like distribution, we developed an analytical model in which supernova feedback drives the transition from the NFW profile (Navarro et al. 1996) to the Burkert profile (Burkert 1995) and applied it to the $R_\mathrm{max}(M_{200})$ relation. Our results show that this cusp-to-core transition is effective for dark matter halo masses below $10^{11} M_\odot$, corresponding to a critical stellar mass, $M_\mathrm{∗, crit}$, which defines a "forbidden region" where systems with stellar masses beyond $M_\mathrm{∗, crit}$ cannot form cores through supernova feedback alone. Most individual galaxies lie outside this forbidden region, allowing the cusp-core transition, while galaxy groups, clusters, and extremely low-mass systems such as ultra-faint galaxies remain within it, making the transition physically impossible. The diversity in low-mass galaxy density profiles likely arises from variations in star formation efficiency, which influence supernova feedback strength and modulate the intensity and timing of baryonic mass ejection.

The radius $R_\mathrm{max}$ is related to the classical virial radius and mass as $R_\mathrm{max} = x\ r_{200}/c(M_{200})$, where $x$ is a coefficient set by the mass distribution function (e.g., 2.16 for the NFW profile and 3.24 for the Burkert profile), and $c$ is the concentration parameter as a function of the virial mass. During the cusp-core transition, significant mass ejection shifts $R_\mathrm{max}$ outward, altering $c$ and potentially expanding the outer boundary of the dark matter halo. We examine how halo boundaries respond to this transition, combining theoretical models with observational data to elucidate the complex interplay between baryonic feedback processes and dark matter dynamics.

Speaker: Michi Shinozaki (University of Tsukuba)

4:05 PM Boundaries of the Milky Way Halo and Tidal Evolution of Satellites

I will present our work on measuring the Milky Way (MW)’s halo edges and modeling the tidal stripping of satellite galaxies, addressing two key aspects of halo dynamics and boundaries: (1) halo growth and (2) environmental effects, respectively.

(1) Using the kinematics of nearby dwarf galaxies within 3 Mpc, we measured the depletion radius and the turnaround radius of the MW, along with their enclosed masses. The depletion radius separates a growing halo from the draining environment, while the turnaround radius marks the outer edge of the infalling region, quantifying the ongoing evolution of the MW outer halo.

(2) We developed the first general analytic model that incorporates tidal truncation and the subsequent re-virialization via violent relaxation. This model accurately reproduces the density profiles and tidal edges of simulated galaxies. We demonstrate that dark matter-deficient galaxies may form due to the differential tidal loss of dark matter and stars, with applications to ultra-diffuse galaxies both within and beyond the MW.

Speaker: Zhaozhou Li (The Hebrew University of Jerusalem)

4:35 PM → 5:00 PM discussions

Tuesday, May 27

9:00 AM → 10:20 AM Halo finding & statistics

9:00 AM Connecting theory and observations of halo boundaries

Whether we try to observe the splashback, edge, or depletion radius (as well as sub-definitions thereof), the vast majority of experimental inferences are based on some type of spherically averaged, projected density profile. Commonly, the radius where the density slope is steepest is taken as the halo boundary, but this definition is particularly sensitive to the observational tracer and to methodological details. In this talk, I propose a new parameter space that includes a so-called truncation radius. This scale can be measured more robustly via a novel fitting function, exhibits fewer degenracies than previous parameters of the same kind, and correlates tightly with theoretical definitions of the halo boundary such as the splashback radius. This new framework has already been successfully applied to data.

Speaker: Benedikt Diemer (University of Maryland)

9:30 AM Rebuilding the Foundation of Large-Scale Structure: Defining Halo Substructure with Dynamics

Conventionally, halos are considered subhalos if their center lies within the radius of their hosts. However, definitions of the halo boundary vary throughout the literature, such that some halos are not consistently labeled as standalone structures or subhalos. What structures are considered discrete impacts quantities critical to our halo models, such as the halo mass or correlation function. To resolve this issue, we will discuss a new proposed definition for subhalos grounded in dynamics: a halo is a subhalo if and only if it has had a pericenter around a larger halo. We apply this definition to an N-body simulation and compare the halo mass function, subhalo-to-halo mass ratios, and subhalo radial distributions between our proposed and conventional definitions. We also employ particle-tracking techniques to examine how this definition changes the mass and spatial distributions of the subhalos lost by conventional halo finders. Furthermore, we show that the proposed definition removes artifacts like "backsplash" halos from these important quantities, demonstrating the strengths of defining subhalos in this way.

Speaker: Calvin Osinga (University of Maryland)

9:50 AM An ORIGAMI and Lagrangian view of halo and cosmic-web boundaries

I will discuss some benefits of using caustics (boundaries of stream/shell crossing) to delineate cosmic web components. Our original ORIGAMI (Order-ReversIng Gravity, Apprehended Mangling Indices) algorithm explicitly looks for particle crossings, but much of the tagging works simply by looking for out-of-order particles along orthogonal axes, and then filling in holes. It is also important to identify differences between this approach and others; e.g. Friends-of-Friends haloes viewed in Lagrangian initial coordinates often have holes near their edges.

Speaker: Mark Neyrinck (Blue Marble Space Institute of Science (BMSIS))

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 11:50 AM Halo finding & statistics

10:50 AM Probing halo boundary and properties with satellite radial distribution

Satellite galaxies are observable tracers of the dark matter subhalos, and are subject to the same gravitational influence of the main halo. Hence, the radial distribution of the satellite galaxies can probe the main halo’s density profile and the associated physical boundary. In this talk, I will discuss the observed satellite radial profiles of Milky Way-mass systems from the SAGA Survey, and how this result connects to our theoretical understanding. In addition, at a fixed host halo mass, it is well known that the number of subhalos is correlated with other secondary halo properties such as the halo formation time and the concentration parameter. We found such correlation varying with the radial ranges of the selected subhalos, and showing an interesting connection to the physical halo boundary. This result can inform future observations on satellite systems to better probe the physical halo boundary and unobservable halo properties.

Speaker: Yao-Yuan Mao (University of Utah)

11:20 AM Self-similar decomposition of the hierarchical merger tree of dark matter halos

We show that the merger tree of dark matter halos is approximately self-similar by investigating the universality of the subhalo peak mass function (PMF) describing the mass distribution of progenitor halos. Using a set of cosmological simulations and identifying subhalos of different merger levels with HBT+, we verify that the level-1 subhalo PMF is close to universal across halo mass, redshift, and cosmology. This approximate self-similarity allows us to analytically derive the subhalo PMF for subhalos accreted at any level (i.e., for sub-sub...halos) through self-convolutions of the level-1 PMF, and the resulting model shows good agreement with simulation measurements. We further derive a number of analytical properties on the hierarchical origin of subhalos, including the level distribution, accretion rate at each level, initial merger ratio distribution, and accretion redshift distribution. We find that higher-level subhalos dominate at progressively lower peak mass in the PMF and are more likely to originate from major mergers than lower-level ones. Among the top 100 subhaloes, both level 1 and level 2 populations contribute about 40 percent. At a given mass ratio at accretion time, the subhalo accretion rates at each level track the growth rate of the host halo. At a fixed final mass ratio, however, the accretion redshift distribution of subhalos depends on the subhalo level, peak mass, and host mass. Higher-level and higher-mass-ratio subhalos tend to be accreted more recently, and more massive halos also accrete their subhalos more recently. Finally, we claim that a well-defined halo boundary, which aligns with the orbits of particles and subhalos during mergers, is essential to preserve the self-similarity observed in halo merger trees.

Speaker: Mr Wenkang Jiang (Shanghai Jiao Tong University)

11:35 AM Can blue-tilted primordial power spectrum save the small scale crisis in MW? – From the perspective of Zoom-In simulation for MW host size dark matter halo

Based on [arxiv:2412.16072] Recent observations from the James Webb Space Telescope revealed a surprisingly large number of galaxies formed at high redshift. Along with strong lensing studies and nearby galaxy observations, these could challenge the standard Lambda Cold Dark Matter cosmology with a power-law primordial power spectrum. In this study, we conduct high-resolution cosmological zoom-in dark matter-only simulations of Milky Way host size halos with a blue, tilted primordial power spectrum (P(k)∝k^m_s with m_s>1 at small scales >1 Mpc^{−1}). We find that the blue-tilted subhalo mass functions can be enhanced by more than a factor of two for subhalo masses Msub≲10^10 M⊙, whereas the subhalo Vmax functions can be enhanced by a factor of four for maximum circular velocities Vmax≲30 km/s. The blue-tilted scaled cumulative substructure fraction can be an order of magnitude higher at ∼10\% of the virial radius. The blue-tilted subhalos also have higher central densities, since the blue-tilted subhalos reach the same Vmax at a smaller distance Rmax from the center. We have also verified these findings with higher-resolution simulations.

Speaker: Jianhao WU (The Chinese University of Hong Kong)

11:50 AM → 12:10 PM discussions

12:10 PM → 2:00 PM Lunch

2:00 PM → 3:05 PM Halo finding & statistics

2:00 PM The extent of a cluster’s environment based on galaxy properties

Clusters present an excellent laboratory for studying influences on galaxy evolution due to their extreme environments that alter the evolutionary pathways of galaxies. However, the cluster does not have a clear boundary, which has motivated a number of studies proposing and identifying boundary definitions that capture various aspects of a halo’s properties. For example, the standard overdensity criteria identifies the boundary of a halo that encloses the necessary mass to virialize a halo and the splashback radius incorporates information on the orbital dynamics of halos. In this talk, I will discuss a study in which we classify galaxies as “field” or “cluster” galaxies based on intrinsic properties like star formation rate and stellar to halo mass ratio and relate this to their spatial distribution in the universe. We then obtain a probability that a galaxy is within a cluster’s influence based on its distance to the cluster center and compare this to various boundary definitions to identify which might capture the extent of a galaxy cluster’s environment on galaxy evolution. This can help inform cluster boundary decisions as well as indicate observational signatures and galaxy selections that can measure boundaries like the splashback radius.

Speaker: Stephanie O'Neil (University of Pennsylvania)

2:30 PM Strawberry: Binding particles to haloes using the full potential field

Dark matter haloes are the end product of cosmological structure formation. Produced through the gravitational collapse of initial density perturbations, these objects are considered to be self gravitating and virialised. Nonetheless, standard methods, used to both detect and analyse these structures in simulations, produce objects that are not virialised requiring the inclusion of an additional external pressure to ensure their stability. The need for this term has been shown to simply be a selection artefact, and only arises due to the inclusion of newly accreted particles that are not yet bound to haloes.
Recently, it has been proposed that a more physical description of dark matter haloes could simplify observations and models that rely upon this definition, most notably the halo mass function, the halo profile, or the halo model for the non-linear two-point correlation function. However, due to the relatively large computational cost of current methods to perform this binding check, these studies have been limited to studying only small samples of haloes.
Here, we present a novel, physically motivated approach based on the boosted gravitational potential (Stücker et al. 2021). In practice, after directly reconstructing the effective local potential landscape felt by particles inside and surrounding a halo, the question of binding simply becomes: does a certain particle have a sufficient energy to escape this potential? As a result, this computationally inexpensive technique allows the production of large catalogues of virialised haloes, paving the way for future large sample studies of these objects and their properties.

Speaker: Tamara Richardson (Donostia International Physics Center)

2:50 PM Subhalo abundance matching with satellite fraction

Subhalo abundance matching (SHAM) is a widely used empirical model for linking galaxies to (sub)halos and predicting galaxy clustering. It assigns galaxies to subhalos by matching the cumulative number density of galaxies above a luminosity (or stellar mass) threshold to the corresponding number density of subhalos above a mass threshold. Scatters in the stellar-to-halo mass relation can also be incorporated into the model. Compared to the halo occupation distribution (HOD) model, SHAM offers distinct advantages: it requires far fewer free parameters and naturally reproduces galaxy distributions across a broad luminosity range.. However, the simplest SHAM struggles to fit galaxy clustering in small scales accurately. To address this limitation, previous studies have explored improvements such as using peak maximum circular velocity (Vpeak​) instead of subhalo mass and introducing orphan galaxies to account for tidally disrupted subhalos. We propose a new SHAM model including new parameters to describe the satellite fraction as function of stellar mass. This modification enables tuning of galaxy clustering on small scales. We test this SHAM using mock galaxies, SAM, and hydrodynamic simulation, demonstrating that it simultaneously achieves reasonable fits to galaxy clustering and recovers the underlying true satellite fraction. This new SHAM model provides a powerful tool for interpreting observed galaxy clustering and generating realistic mock galaxy catalogs from large-volume N-body simulations.

Speaker: Xiaoju Xu (上海交通大学)

3:05 PM → 3:35 PM Coffee Break

3:35 PM → 4:35 PM Halo finding & statistics: case studies

3:35 PM Can the splashback radius be an observable boundary of galaxy clusters

The splashback radius was proposed as a physically motivated boundary of clusters as it sets the limit between the infalling and the orbitally dominated regions. However, galaxy clusters are complex objects connected to filaments of the cosmic web from which they accrete matter that disturbs them and modifies their morphology. In this context, estimating the splashback radius and the cluster boundary becomes challenging. We used a constrained hydrodynamical simulation of the Virgo cluster's replica embedded in its large-scale structure to investigate the impact of its local environment on the splashback radius estimate. We identify the splashback radius from 3D radial profiles of dark matter density, baryons density, and pressure in three regions representative of different dynamical states: accretion from spherical collapse, from filaments, and matter outflow. We also identify the splashback radius from 2D-projected radial profiles of observation-like quantities: mass surface density, emission measure, and Compton-y. We show that the splashback radius mainly depends on the dynamics in each region and the physical processes traced by the different probes. Consequently, caution is required when using the splashback radius as a boundary of clusters, particularly in the case of highly disturbed clusters like Virgo.

Speaker: Théo Lebeau (Institut d'Astrophysique Spatiale, Université Paris-Saclay)

3:55 PM Local Group Analogs in a cosmological context: Relating the velocity structure to the cosmic web

The Local Group (LG), as a gravitationally bound system of the Milky Way and Andromeda, as well as their satellites, is a cornerstone of near-field cosmology. However, its utility as a cosmological probe requires understanding how it is related to the cosmic web. Using the ABACUSSUMMIT simulation, we identify LG analogues and quantify their environmental dependence. We find that the coupling energy of LG-analogue systems strongly correlates with large-scale overdensity, revealing a secondary bias effect. Crucially, we demonstrate that the LG-analogues are aligned to the anisotropic part of the cosmic web, and the alignment pattern is dependent on the coupling energy of the system. Our results underscore the role of non-local environmental effects in shaping LG-like systems and argue against treating the LG as an isolated system. Instead, we advocate for integrating the large-scale cosmic web into studies of LG analogues.

Speaker: Kai Wang (Durham University)

4:15 PM The Hierarchical Structure Around the Supercluster Abell 2029

The Blooming Tree (BT) algorithm is an optimized hierarchical clustering method designed to identify clusters, groups, and substructures. We evaluate the performance of this method using a compiled wide-field ($10° \times 10°$) spectroscopic dataset centered on a supercluster of galaxies, A2029. This algorithm effectively identifies all X-ray luminous clusters, many groups, and even filaments around clusters within the field. By adjusting the detection threshold, this algorithm can identify superclusters with explicit membership. It also provides hierarchical relationships between clusters and groups that make up superclusters. This capability could be helpful for understanding the inner structure of superclusters and the evolution of large-scale structures. Our results show that the BT method is a powerful tool for fully utilizing spectroscopic redshift survey data to analyze the hierarchical universe.

Speaker: Dr Heng Yu (Beijing Normal University)

4:35 PM → 4:55 PM discussions

Wednesday, May 28

9:00 AM → 10:20 AM Observational measurements

9:00 AM Splashback radius in observations: Challenges and opportunities

The detection of the boundary of a dark matter halo (splashback radius) combined with the measure of its halo mass allows a direct access to its mass accretion history. Given the importance of mass accretion rates to cosmology and to the formation and evolution of galaxies within the halo, accurate detection of splashback radius is important. I will present the challenges in the detection of these boundaries using samples of optically selected galaxy clusters, and how the inference of the such boundaries can be affected by choices of background subtractions carried out during the optical selection. I will also present our recent efforts to use galaxy clusters in SZ and X-rays and first efforts to translate these measurements in to the accretion rates of galaxy clusters.

Speaker: Surhud More (IUCAA)

9:30 AM Galaxy Cluster Properties using Weak Gravitational Lensing

I will present a comprehensive analysis of weak gravitational lensing data to assess mass biases in galaxy clusters and characterize their splashback radius, with implications for precision cluster cosmology.
Systematic assessments using state-of-the-art hydrodynamical simulations reveal that weak lensing mass biases depend on cluster mass, redshift, and orientation, with biases as high as 30% for specific projections but reducing to <10% through stacking.
I will discuss that the mass bias decreases for clusters more massive than 1015𝑀sun, with relaxed systems being less biased than unrelaxed ones. In refining the richness-mass relation, I will show that the zero-point parameter is redshift-independent but sensitive to the stellar mass threshold, with the slope evolving quadratically -- relatively constant up to z=0.55 -- and scatter increasing linearly with redshift. By modeling the projected matter density profiles, I will illustrate that splashback radius marking sharp transitions in cluster profile slopes, align closely with theoretical predictions but suggest a bias in optically selected clusters. These findings will provide a framework for improving mass-observable relations, essential for achieving the percent-level accuracy required in upcoming wide-field surveys.

Speaker: Carlo Giocoli (INAF - OAS Bologna)

10:00 AM Splashback radius from lensing and correlation function in KiDS

The splashback radius is a physically motivated boundary of galaxy clusters, offering a unique window into the cluster's mass accretion rate and the interplay between dark matter and baryonic processes. Consequently, accurate measurements of the splashback radius are crucial for testing cosmological models and advancing our understanding of structure formation. With the advent of large-scale surveys like Euclid and LSST, there is a growing need to develop robust and innovative methods to measure the splashback radius, as these data sets will offer unprecedented precision and depth.

In this presentation, I will provide an overview of our analyses based on galaxy clusters detected in the Kilo Degree Survey (KiDS) using the AMICO (Adaptive Matched Identifier of Clustered Objects) cluster finder. First, I will discuss the splashback radius constraints obtained from stacked cluster weak-lensing measurements based on KiDS-DR3 data, covering an effective area of 377 square degrees and extending up to redshift z = 0.6. Then, I will delve into the weak-lensing mass calibration of AMICO KiDS-1000 clusters, covering more than double the area of KiDS-DR3 and extending up to z = 0.8. Using this data set, we determine the splashback radius through both weak-lensing profiles and cluster-galaxy projected correlation function. We propose an innovative method for measuring the cluster-galaxy correlation function and modelling the profiles, incorporating corrections for photometric selection effects.

Speaker: Dr Giorgio Francesco Lesci (University of Bologna)

10:20 AM → 10:50 AM Coffee Break

10:50 AM → 11:45 AM Observational measurements

10:50 AM The Measurement of the Splash-back Radius of Dark Matter Halos

To avoid the pseudo-evolution problem of the traditionally defined halo mass and radius, we measure the splash-back radius (Rsp), a physically defined halo radius for many halos, using the shear catalog of the DECaLS DR8. The dark matter halos cover the mass of 10^13 - 3 × 10^15Msun and the redshift of 0.08–0.65. Our finding reveals a trend wherein massive halos demonstrate a larger Rsp, and the normalized Rsp (Rsp/R200m) shows a U-shaped mass evolution. The upturn in these relations mainly comes from the contribution of massive halos with low redshifts. We further find the Rsp increases with the peak height, while the normalized Rsp has a negative relation with the peak height. We also find that Rsp >~ R200m for most halos, indicating their low accretion rates. Our result is consistent with previous literature across a wide range of mass, redshift, and peak height, as well as the simulation work from More et al.

Speaker: Dr Weiwei Xu (National Astronomical Observatories, Chinese Academy of Sciences)

11:10 AM Indefinitely large galactic dark matter halos from a new weak-lensing method and applications to galaxy clusters

Weak gravitational lensing is a crucial tool to measure the mass profiles of dark matter halos. I will discuss a recent weak-lensing analysis of isolated galaxies in KiDS DR4 that finds flat circular velocities out to very large galactocentric radii (at least 300kpc), suggesting that the dark matter halos of galaxies are more extended than expected. Futhermore, these dark matter profiles exhibit scaling relations such as the Baryonic Tully-Fisher Relation that highlight a strong connection between between the visible and dark matter. These results apply to both early and late type galaxies, indicating a common universal behavior. This analysis is enabled by a novel non-parametric deprojection technique that, unlike many existing methods, does not assume a specific mass profile. I show how this non-parametric technique can be extended to galaxy clusters, enabling mass measurements that significantly reduce major sources of bias such as biases from miscentering and baryonic effects. With future observations, this may enable direct, non-parametric measurements of the splashback radius, allowing to discriminate between different models of dark matter and modified gravity.

Speaker: Tobias Mistele (Case Western Reserve University)

11:30 AM Detection of a non-evolving ''splashback'' radius of cosmic filaments across 0 < z < 1.2

Cosmic filaments represent the sites where the majority of galaxies in the universe form. However, the structure of filaments themselves, and the link between physical properties of galaxies and their spatial distribution within the filaments remain unclear. Here based on deep multi-wavelength data in the COSMOS and SDSS surveys, we characterize projected radial profiles (2-dimension) of cosmic filaments at 0 < z < 1.2, which are traced by both the stellar mass and number densities of galaxies within the filaments. We reveal that the average slope of the radial profiles of filaments changes with the distance to the filament spine, and exhibit a minimum at ∼ 0.4 Mpc (Rmin), with no obvious
evolution with redshifts. This characteristic distance mimics the splashback radius of dark matter halos, which defines a natural boundary for cosmic filaments. Identical results are obtained in the TNG300 simulations with the same process of filaments identification applied. Moreover, we further study the density profiles of filaments in 3-dimension in simulations, yielding a larger Rmin ∼ 1Mpc compared to ∼ 0.4 Mpc seen in the 2-dimension projection. The lack of evolution of Rmin with redshifts suggests a universal density profiles of cosmic filaments, which is at least valid during the last 8 Gyrs of cosmic time.

Speaker: Qiaoyang Hao (南京大学)

11:45 AM → 12:05 PM discussions

12:05 PM → 1:30 PM Lunch

1:30 PM → 5:30 PM free afternoon

The banquet venue is close to the bund, the Yu garden, people square, nanjing road market, and Jing'an temple. You may choose to have a tour at some of these places before the banquet.

5:30 PM → 7:30 PM Banquet

Thursday, May 29

9:00 AM → 10:20 AM Halo model of LSS

9:00 AM The next-generation halo model based on the depletion radius

The halo model is a powerful tool for understanding the non-linear evolution of the Universe. Conventionally, a dark matter halo is defined as a virialized object according to the virial radius. However, this definition does not completely partition all mass into halos, as the halo is much more extended beyond the virial radius and grows continuously. Consequently, there is a well-known limitation of the classical halo model in the transition region between the halo edge and the large-scale environment (for about 0.1<k<1 hMpc^-1). A more accurate and explicit halo model requires a better understanding of the dark matter halo and its boundary.

In this talk, I will present an improved halo model that accounts for the unresolved mass component. Based on a new characterization of the halo boundary called depletion radius, we find the model ingredient (halo mass function, halo profile, and halo-halo correlation) can be expressed simply and naturally. I will also show how to solve for the matching halo profiles to completely decompose the matter field for any given halo catalogue. Our results show that the matching profile of the depletion-radius-based halo catalogue can be well described by the Einasto profile. Coupling the Einasto profile with the depletion-radius-based catalogue, our model accurately predicts the multiple statistics of the halo and matter field without any ad hoc fix. Finally, I will compare our model to other existing halo models, and highlight the advantages of our model in terms of clarity, interpretability, and versatility.

Speaker: Yifeng Zhou (Shanghai Jiao Tong University)

9:30 AM Compensated Halo Profiles and Mass Conservation

The standard halo model of large-scale structure provides an empirically-informed framework for describing nonlinear structures in the universe. However, this model does not enforce conservation laws, which can significantly hinder observable predictions on large scales. Examples of these observables include weak lensing, as the power spectrum is overpredicted by $\geq 8\%$ on scales larger than 20 degrees due to the absence of mass conservation, and the kinematic Sunyaev-Zel'dovich effect, where momentum conservation must be satisfied. We propose a solution to the mass conservation problem by amending the halo model to explicitly separate linear perturbations from compensated halo profiles. This amendment ensures that conservation laws are inherently satisfied and linear theory predictions are replicated on large scales. We also provide a simple fitting function for the compensated halo profiles and discuss the modified predictions for both 1-halo and 2-halo terms in the matter auto power spectrum, as well as other cosmological observables such as the weak lensing power spectrum. The results of this work are shown in more detail in https://arxiv.org/abs/1912.04872. Time permitting, I can also discuss how this model extends to the halo-mass cross power spectrum, particularly in the context of two-point halo correlations beyond the halo virial radius (https://arxiv.org/abs/2210.11499).

Speaker: Alice Chen (University of Waterloo/Perimeter Institute)

10:00 AM The anisotropic secondary bias of dark matter halo in N-body simulation

Secondary bias reflects the fact that large-scale clustering of haloes at a given mass varies significantly with their secondary properties. Recent studies identify tidal anisotropy, defined on intermediate scales, as the primary driver of secondary bias. Essentially, the tidal field is tightly intertwined with the large-scale matter distribution. In this work, we investigate the intricate relationships between secondary bias, matter anisotropy, and tidal anisotropy. Firstly, to depict the relation between secondary bias and matter anisotropy. we quantify the anisotropic secondary bias (ASB), exploring how secondary bias relates to halo orientation. We find that ASB is insignificant for concentration, formation time, and triaxiality but is pronounced for spin and the minor-to-major axis ratio. This indicates that halos with slower rotation or more elongated shapes tend to align with filaments, while other halo properties show no such correlation with alignment. Furthermore, we find that matter anisotropy (alignment) itself cannot explain the secondary bias. Moreover, tidal anisotropy emerges as the primary driver of secondary bias, including the alignment bias, but it plays a negligible role in the ASB. These findings underscore the complex interplay between the cosmic web and internal halo properties. Moreover, we observe that the halo definition partially influences secondary bias, particularly spin bias at the low-mass end, offering deeper insights into the physical origins of spin bias. Nevertheless, the halo definition has minimal impact on anisotropic secondary bias. Our findings emphasize the significant influence of halo anisotropy and definitions of secondary bias, related to the halo statistics, galaxy-halo models, and cosmological measurement.

Speaker: Qinglin Ma (Tsinghua Univ.)

10:20 AM → 10:40 AM Coffee Break

10:40 AM → 11:50 AM Halo model of LSS

10:40 AM The Dynamical Halo Model

I will introduce the dynamical halo model, a re-imagining of the traditional halo model built on the orbiting/infall dichotomy of particles around halos. We will introduce the basic ideas behind the dynamical halo model, some of the physical insights it provides that can improve our descriptions of large scale structure, and new tools we are developing to make the use of dynamical halos simpler for the community, including a new dynamical halo finder.

Speaker: Eduardo Rozo (University of Arizona)

11:10 AM The Relation Between Particle-Based and Galaxy-Based Measurements of the Halo Radius

Building on a dynamics-based halo model proposed by Salazar [Edgar M. Salazar et al., arXiv:2406.04054], we compare the halo radius derived from the halo-mass correlation function with that from the halo-galaxy correlation function. The discrepancy between these two radii shows a strong dependence on halo mass and galaxy mass. To explain this relationship, we have developed a dynamical friction model. Using this model, we can predict the halo radius measured from galaxies when given the halo radius measured from particles. Consequently, this model provides a valuable framework for connecting the theoretical dark matter halo model with observational galaxy data.

Speaker: Cheng Wu

11:30 AM Galaxy Cluster Mass Estimation Through The Splashback Radius

We present an analysis of the splashback radius ($R_{\text{sp}}$) and the associated splashback mass ($M_{\text{sp}}$) for a sample of galaxy clusters using SDSS spectroscopic data and mock simulations. $R_{\text{sp}}$ marks a physical boundary between the virialized core and the outer infall regions of clusters, providing a robust measure of cluster mass accretion history without being affected by pseudo-evolution. We model the cumulative galaxy number profile of clusters, testing different halo density models and considering the impact of cluster properties, such as center definitions, magnitude limits, galaxy colors, and field contamination, on the estimation of splashback features. Our results show that observed splashback radii are consistently smaller than predicted by dark matter simulations, with $R_\text{sp}/R_{200m} \approx 1$, supporting previous discrepancies in the literature. We also explore the relationship between $M_{\text{sp}}$ and $R_{\text{sp}}$, proposing a new scaling relation for future cosmological studies, as $R_{\text{sp}}$ is easily observable. Our findings indicate that splashback masses strongly correlate with radii, with a dispersion of $\approx 0.15$ dex, competitive with other mass-observable relations. However, the fitted relation diverges from the constant density expectations of galaxy clusters around $R_\text{sp}$. Additionally, the $M_{\text{sp}}-R_{\text{sp}}$ relation shows significant redshift evolution, though the predominantly low-redshift range of our sample limits our ability to confirm this trend conclusively. The approach developed here may play a key role in cluster characterization and cosmology in the era of large galaxy surveys.

Speaker: Lucas Gabriel Silva (IAG/USP)

11:50 AM → 12:10 PM discussions

12:10 PM → 2:00 PM Lunch

2:00 PM → 3:00 PM Probing cosmology

2:00 PM Iterative mean-field approach to the spherical collapse of dark matter haloes

We propose an 'iterative mean-field approach' to compute the solutions of the gravitational collapse dynamics. This approach iteratively searches for the evolution of the interaction field ϕ(t) - in this case the enclosed mass profile M(r, t) - that is consistent with the dynamics, thus that ϕ(t) is the fix-point of the iterative mapping, H(ϕ)=ϕ. The formalism replaces the N-body interactions with one-body interactions with the coarse-grained interaction field, and thus shares the spirit of the mean-field theory in statistical physics. This 'iterative mean-field approach' combines the versatility of numerical simulations and the comprehensiveness of analytical solutions, and is particularly powerful in searching for and understanding intermediate asymptotic states in a wide range of dynamical systems where the solutions can not be obtained through the traditional self-similar analysis. For the study of dark matter halos, it provides a way to do spherical collapse for LCDM Universe and arbitrary halo MAH, and can work as a minimalistic model that captures the universality and diversity of outer profiles.

Speaker: Xun Shi

2:30 PM Edges of Dark Matter Halos: Boundaries of Massive Galaxy Clusters and Cosmological Constraints

Dark matter serves as the hidden framework shaping the universe, driving the formation, growth, and clustering of galaxies on cosmic scales. One key feature of dark matter halos, the splashback radius, represents a physical boundary that offers a more direct and fundamental description of halo structure compared to the traditional spherical overdensity approach. Using the deep, high-resolution imaging of the Hyper Suprime-Cam (HSC) survey, we can probe large-scale structures across a vast sky area. By combining weak lensing and galaxy clustering techniques, we aim to map the distribution of dark matter around massive galaxy clusters. Our study will provide the tightest constraints on the splashback radius using X-ray-selected clusters from eROSITA-eFEDS and HSC photometric galaxy data. We will then compare these results with $\Lambda$CDM predictions, contrast them with previous studies, and explore how the splashback radius can serve as a novel tool for resolving key tensions in modern cosmology.

Speaker: Dr Divya Rana (Leiden Observatory)

3:00 PM → 3:25 PM Coffee Break

3:25 PM → 4:45 PM Probing cosmology

3:25 PM Galaxy Clusters: Cosmology via the Infall Zone

Many of our strongest constraints on the cosmological model come from analysis of the Cosmic Microwave Background formed at high redshift in the early universe. Low-redshift cosmological tests are fundamentally important, however, as they test different regimes of time, scale and curvature. The abundance of galaxy clusters is one such test, constraining the product of the amplitude of fluctuations present in the matter distribution at early times, and the amount by which this amplitude has grown down to the present day. The degeneracy between these two factors limits the precision of abundance constraints. A few years ago, we pointed out that measurements of the instantaneous growth rate of clusters could break this degeneracy. Recently, we have proposed and implemented one way of doing this in practice, using weak gravitational lensing measurements of the “infall zone”. I will discuss this test and other recent work on cluster structure and evolution based on data from the UNIONS and Euclid-Wide surveys.

Speaker: Dr James Taylor (Waterloo Centre for Astrophysics)

3:55 PM The infall region of galaxy clusters as a complementary probe to cluster abundance

Galaxy cluster abundance measurements provide a classic test of cosmology. However, they exhibit a strong degeneracy between the amplitude of density fluctuations σ8, and the matter density Ωm, as do other similar low-redshift tests such as cosmic shear. The mass distribution in the infall region around galaxy clusters, where material is being accreted from the surrounding field, exhibits an orthogonal cosmological dependence in the Ωm-σ8 plane, making it highly complementary to halo abundance or cosmic shear studies. We explore how weak lensing measurements of the infall region might be used to complement abundance studies, producing forecasts for two weak lensing surveys: UNIONS and Euclid. We then perform this test in practice using UNIONS weak lensing profiles of galaxy clusters in three publicly available catalogues. Comparing profiles from the most complete catalogue to a suite of cosmological simulations with different combinations of Ωm and σ8, we find Ωm = 0.29 +/- 0.05 and σ8 = 0.80 +/- 0.04.

Speaker: Charlie Mpetha (University of Edinburgh)

4:15 PM Turnaround-scale probes of cosmology

The turnaround scale represents the largest non-expanding boundary of a dark matter halo. It is sensitive to cosmology, behaving as an evolving standard ruler, and it imprints on the galaxy distribution around cluster centers. I will discuss how the turnaround feature can be identified in simulated observations, and how it can be exploited to devise novel cosmological tests

Speaker: Vasiliki Pavlidou (University of Crete and IA-FORTH)

4:45 PM → 5:10 PM discussions

Friday, May 30

9:00 AM → 10:10 AM Boundaries in different tracers

9:00 AM Shock and Splash: Gas and Dark Matter Halo Boundaries around Galaxy Clusters

Recent advances in simulations and observations of galaxy clusters suggest the existence of a physical outer boundary for massive cluster-sized dark matter (DM) halos. Large-scale structures, including halo and cosmic-web boundaries, significantly influence splashback and shock phenomena. Using the Omega500 zoom-in hydrodynamical cosmological simulations, we found that the accretion shock radius is offset from the DM splashback radius, challenging predictions of self-similar models. Specifically, the accretion shock radius exceeds all definitions of the splashback radius in the literature by 20−100%. Identified by the steepest drop in entropy and pressure profiles, the accretion shock radius is roughly twice as large as the splashback radius defined by the steepest slope in the DM density profile and about 1.2 times larger than the edge of the DM phase space structure.

In this talk, we examine how large-scale structures influence the shock and splashback radii of DM halos and the roles of halo boundaries and cosmic-web structures in accretion shock phenomena. We explore the relationship between the gas accretion shock and splashback radius, highlighting challenges in defining these locations. We discuss the aspherical distributions of gas and DM, the critical roles of penetrating filaments, and the need to move beyond spherical assumptions in halo models. Our roadmap for improving these models, such as incorporating a halo+filament model, aims to better represent cosmic structures. This is crucial for understanding galaxy evolution and quenching mechanisms and interpreting recent SZ profile measurements while exploring prospects for measuring the shock radius.

Speaker: Daisuke Nagai (Yale University)

9:30 AM Stirring up the intracluster medium with substructures

The origin of turbulent motion of the intracluster medium (ICM) has been a longstanding open question, and X-ray observations of the new generation, such as XRISM and eROSITA, shed further light on it. Stirring by substructures (member galaxies and dark matter subhaloes) orbiting within a galaxy cluster is a possible mechanism to generate and maintain the ICM turbulence. We develop a semi-analytic model considering three processes of energy transfer from substructures to the ICM (dynamical friction, ram pressure and sloshing), and propagation and dissipation of the deposited energy. The model reproduces the gas velocity structure derived from hydrodynamical simulations. We find that dynamical friction and ram pressure are responsible to explain the significant turbulence (> 1000 km/s) in the cluster outskirts (> 1 Mpc), while sloshing explains the mild turbulence (~100 km/s) in the cluster centre. In the talk, we will also argue the role of substructures infalling toward the cluster for the first time from outside the virial radius of the dark matter halo of the cluster.

Speaker: Go Ogiya (Zhejiang University)

9:50 AM Kinetic Morphology around Halos

After shell-crossing, cosmic flows exhibit diverse rotational morphologies driven by stream-mixing processes. Vorticity generation is intricately linked to the large-scale structure of the universe, with distinct flow patterns emerging around halos, filaments, and voids. A detailed analysis of flow morphology around halos reveals a sharp transition in the logarithmic derivative of the volume fraction of one particular morphology, which aligns with the splashback radius. This feature encodes critical phase space information, offering new insights into the dynamical evolution of halos. Furthermore, hydrodynamic simulations reveal that gas flows also exhibit rich morphological signatures. Using the IllustrisTNG dataset, we uncover additional kinematic structures that reflect the impact of feedback processes. These findings provide a novel perspective on the interplay between cosmic flows, large-scale structure, and halo evolution.

Speaker: Prof. Xin Wang (Sun Yat-sen University)

10:10 AM → 10:30 AM Coffee Break

10:30 AM → 12:00 PM Boundaries in different tracers

10:30 AM Baryon Pasting the X-ray and SZ Universe

We present the latest development of "Baryon Pasting", a novel framework that adopts a physics-based approach for forward-modeling SZ and X-ray observations of galaxy clusters and groups. Baryon Pasting enables efficient exploration of the vast astrophysical and cosmological parameter space required for current and upcoming millimeter-wave surveys, such as the Simons Observatory and CMB-S4, while maintaining the physical accuracy of modern hydrodynamical simulations. This makes Baryon Pasting particularly powerful for disentangling the impact of cluster and group astrophysics from cosmology. Using the half-sky Baryon Pasted Uchuu lightcone simulation, we demonstrate significant map-level systematic effects that were previously difficult to quantify. Application of the Baryon Pasting model to the eRASS1 X-ray angular power spectrum has also yielded precise cosmological constraints, shedding new light on the ongoing S8 tension, as well as constraints on cluster astrophysics of feedback, non-thermal pressure, and the accretion shock radius. We also introduce a differentiable model of Baryon Pasting that captures the effect of halo mass accretion histories on the properties of the intracluster medium and their distinctive observational signatures in X-ray and SZ, such as assembly bias in the X-ray and SZ angular power spectra. Finally, we discuss how integrating Baryon Pasting with state-of-the-art cosmological simulations and cutting-edge generative AI models will fully unlock the potential of next-generation multiwavelength Stage IV surveys through efficient and interpretable modeling of the observable universe.

Speaker: Erwin Lau

11:00 AM The tracers of splashback in galaxy clusters

The relationship between the visible and dark components of galaxies is a complex function of mass, accretion history, and galaxy formation physics. Nevertheless, recent work using simulated galaxy clusters has shown that stars can be an accurate tracer of the splashback boundary of the dark matter halo, potentially providing a robust way to infer the dark matter in observations. Building on this, in this talk I will present results on the relationship between the dark matter splashback and the stellar and gas components of 324 simulated galaxy clusters from the Three Hundred suite. By isolating the orbiting and infalling material, I show how the splashback of the dark matter and stars is related to the first and second caustics in the density profile, and examine the prospects of using this to estimate the accretion rate.

Speaker: Kris Walker (The International Centre for Radio Astronomy Research, University of Western Australia)

11:20 AM Tracing Halo Boundaries Through the Metal Absorption Lines in Circumgalactic Medium: Insights from DESI

The Circumgalactic Medium (CGM), as a key interface connecting galaxies to the cosmic web, has its metal distribution and evolution directly reflecting the dynamical processes of halo boundaries. Using early data from the Dark Energy Spectroscopic Instrument (DESI), we analyze the equivalent widths (W) of 33 metal absorption lines to reveal the spatiotemporal evolution of the CGM and its implications for the definition of halo boundaries. This work covers a redshift range of 0.3 < z < 5.5 and a projected distance of D < 6.5 Mpc for galaxies (and QSOs), with a focus on absorption lines from elements such as Mg II, Fe II, and C IV. Result shows that the distribution of Mg exhibits a radial break at 100–200 kpc (depending on stellar mass), which can serve as a method for defining the Edge Radius. Additionally, we observe that star formation influences Mg II absorption primarily within 50 kpc,whcih could partially reflect the size of the outflows. Furthermore, This size may decrease with increasing stellar mass, as we find a significant reduction in absorption along the minor axis in more massive galaxies, suggesting that outflows are confined within deeper gravitational potential wells.

Speaker: Mr Zeyu Chen (中国科学技术大学)

11:40 AM Kept at Bay: Probing the Global Impact of Radio Jet Feedback at the Virial Radii of Galaxies

Relativistic jets are an essential channel accreting SMBHs release feedback energy to the host galaxies. Observationally, the radio lobes inflated by AGN jets extend to megaparsec scales, far beyond the virial radii of the hosts to interact with nearby galaxies. Theoretically, the magnetic field within the radio lobes can impact the growth and the dynamical evolution of galaxies, especially in more overdense environments where multiple generations of jet feedback join efforts synergistically. We therefore use magneto-hydrodynamic cosmological simulations to explore the impact of radio jet feedback in overdense regions. By injecting magnetic jet feedback at cosmic noon around accreting SMBHs, we find that the baryon fraction is significantly reduced for halos <1e12 solar masses in their subsequent evolution. Additionally, jet feedback alone is capable of populating the intracluster environment with micro-Gauss level magnetic fields, providing an alternative channel, in addition to primordial origins, to generate intergalactic magnetic fields.

Speaker: Yu Qiu (Center for Cosmology and Computational Astrophysics, Institute for Advanced Study in Physics, Zhejiang Univeristy)

12:00 PM → 12:30 PM discussions: Discussion & Concluding remarks

12:30 PM → 2:20 PM Lunch