The 2nd Shanghai Assembly on Cosmology and Structure Formation

Oct 30, 2023, 8:45 AM → Nov 3, 2023, 6:00 PM Asia/Shanghai

Conference Hall (TD Lee Library)

The Shanghai Assembly on Cosmology and Structure Formation (SHACS) is a biennial conference hosted by the Astronomy Department at SJTU and TDLI. The first one was successfully held in November 2019.  As the Covid19 is now cleared, we are resuming the SHACS meeting.

Recent and upcoming surveys including DESI, Euclid and CSST will provide rich data sets for probing cosmology and structure formation. The ever increasing computing power will allow us to simulate and model various galaxy formation processes to a much higher accuracy. We hope this conference will bring people working on theory, simulations, data and facilities together, highlighting recent progresses, providing an open and friendly forum for future works, and more importantly, trigger some interesting collaboration projects.

• Update: the final program can be viewed in the timetable menu. The talk slots are 12+3minutes, 15+5minutes and 20+5minutes (talk+questions) long.
• Abstract submission deadline: 20/Sep., 2023
• Registration deadline: 10/Oct., 2023 
  • Registration fee: 1000 RMB (to be collected on site). The registration fee covers reception/lunch/banquet.
  • The conference is limited to 150 participants and we may close the registration earlier if places run out.
  •  Accommodation is to be arranged by the participant herself/himself. A list of nearby hotels is available from the menu on the left.
• Reception: 29/Oct; Banquet: 1/Nov.

 

Confirmed Invited Speakers:

Fuyu Dong (SWIFAR/YNU)        
Vincent Desjacques (Technion)        
Willem Elbers (Durham)        
Elisa Ferreira (IPMU)
Jiaxin Han (SJTU)        
Fangzhou Jiang (Peking Univ.)        
Xi Kang (Zhejiang Univ.)             
Cheng Li (Tsinghua Univ.)        
Hui Li (Tsinghua Univ.)        
Yen-Ting Lin (ASIAA)        
Aaron Ludlow (ICRAR)        
Philip Mansfield (KIPAC)
Hironao Miyatake (Nagoya Univ.)       
Houjun Mo (UMass)        
Isabel Santos-Santos (Durham Univ.)        
Arman Shafieloo (KASI)        
Jubee Sohn (Seoul National Univ.)
Francisco Villaescusa-Navarro (Flatiron)       
Zvonimir Vlah (Cambridge/Zagreb)        
Huiyuan Wang (USTC)       
Jie Wang (NAOC) 
Xiaohu Yang (SJTU)      

Monday, October 30

9:00 AM → 9:10 AM Opening Remarks

9:10 AM → 10:25 AM Galaxy: formation & population

Convener: Xiaohu Yang (Shanghai JiaoTong University)

9:10 AM Two-stage assembly of dark matter halos, a key to understanding galaxy evolution and supermassive black hole growth

I will describe a scenario in which galaxy formation and the growth of supermassive black holes are regulated by the two-stage assembly of dark matter halos.

Speaker: Houjun Mo (U. Mass.)

9:35 AM The star formation of galaxies and halo mass accretion histories for the last 13 billion years.

In this talk I present the evolution of the star formation rates (SFRs) / stellar masses of galaxies and the dark matter halo mass accretion histories (MAHs) for the last 13 billion years of the Universe. The observed star formation rate-stellar mass (SFR-M*) relation and the "observed" cosmic star formation rate density (CSFRD) represent both important canvases for our current knowledge of galaxy formation and are both routinely used to constrain cosmological models. I employ cosmological simulations combined with radiative transfer and demonstrate that the adopted methodology / indicator (e.g. IR, UV, Ha, SED) to obtain the observed galaxy SFRs and stellar masses are bound to heavily affect the derived properties something that I further show by comparing results from different observational studies. In addition, I demonstrate that state-of-the-art simulations (EAGLE, TNG, Simba, semi-analytic models) are found to suffer from troubling limitations mostly connected to resolution effects and the adopted feedback prescriptions which have to be reconsidered. Last, I demonstrate that the observed star formation rate density and Cosmic Mass accretion History can be described by only two parameters and a function that resembles a Gamma growth, like numerous other physical processes in Nature (from Economy to Biology) while it has a plateau from z = 1-4 and not a strong peak at z = 2. I proceed to show that Dark matter halo growth follows the same Gamma growth pattern using an analysis of Mass accretion Histories that covers halos from 1 solar mass to 1000 trillion solar masses.

Speaker: Antonios Katsianis (Sun Yat-sen University)

S1-2-KATSIANIS.pdf

9:55 AM Formation of massive disc galaxies in the IllustrisTNG simulation

We investigate the formation history of massive disc galaxies in hydrodynamical simulation -- the IllustrisTNG, to study why massive disc galaxies survive through cosmic time. 83 galaxies in the simulation are selected with M$_{*,z=0}$ $>8\times10^{10}$ \Msun and kinematic bulge-to-total ratio less than $0.3$. We find that 8.4 percent of these massive disc galaxies have quiet merger histories and preserve disc morphology since formed. 54.2 percent have a significant increase in bulge components in history, then become discs again till present time. The rest 37.3 percent experience prominent mergers but survive to remain discy. While mergers and even major mergers do not always turn disc galaxies into ellipticals, we study the relations between various properties of mergers and the morphology of merger remnants. We find a strong dependence of remnant morphology on the orbit type of major mergers. Specifically, major mergers with a spiral-in falling orbit mostly lead to disc-dominant remnants, and major mergers of head-on galaxy-galaxy collision mostly form ellipticals. This dependence of remnant morphology on orbit type is much stronger than the dependence on cold gas fraction or orbital configuration of merger system as previously studied.

Speaker: Guangquan Zeng (NAOC)

S1-3-ZENG.pdf

10:10 AM Environmental effects on cold disk formation: Fornax cluster vs. TNG50 simulations

The removal/strangulating of gas in cluster environments cause the stop of star formation, especially on extended cold disks, while tidal shocking/stripping might destroy or heat the cold disks in galaxies formed before fell into the cluster. The cold disk fraction and stellar population provide fossil records on how the cluster environments impact on the galaxy structure formation.

In the context of the Fornax3D project, we analyzed 21 galaxies in the Fornax cluster observed with MUSE/VLT by applying a novel population-orbit superposition method.
By fitting the luminosity distribution, stellar kinematics, age and metallicity maps simultaneously, we obtained the internal stellar orbit distribution and stellar population distributions.
Based on the model, we decompose the dynamically cold disk (orbital circularity λz > 0.8) for each galaxy, and obtain its luminosity fraction, age and metallicity radial profiles. For galaxies in the Fornax cluster, we find that the luminosity fraction of cold disk in recent infallers are consistent with field galaxies from CALIFA, while the cold disk fractions in ancient infallers with tinfall > 8 Gyr are a factor of ∼ 4 lower, with control of stellar mass. Moreover, the stellar age of cold disk is highly correlated with galaxy infall time into the cluster, and we find positive age gradients in cold disks, with stars in the inner disk being younger than those in the outer disk, contrary to the expectation of inside-out growth.

We then directly compare our results with galaxies in Fornax-like clusters in TNG50 simulations, and find that they agree with each other remarkably well on cold disk fractions, stellar age, age gradients, and their dependence on galaxy’s infall time to the cluster. In the simulations, we find gas in the outer disk was partly removed and partly compacted into the inner regions when falling into the cluster, which leads to quick stop of star formation in the outer disk, but a long tail of star formation in the inner regions. The turnover of star formation radius from out to inner regions is highly correlated with the galaxy’s infall time. This process explains most of the above results. At the same time, tidal shocking partially heats the cold disk formed before infall, which further reduces the cold disk fraction in ancient infallers which bear the strongest tidal effects.

Speaker: Yuchen Ding (Shanghai Astronomical Observatory)

S1-4-DING.pdf

10:25 AM → 11:00 AM Conference Photo & coffee break

https://web.gravity.sjtu.edu.cn/event/4/images/3-group%20photo.JPG

11:00 AM → 12:05 PM Galaxy: formation & population

Convener: xi kang (zhejiang university)

11:00 AM Application of a Constrained Simulation in understanding Galaxy-Halo Connection: the case for Halo Assembly Bias

The halo assembly bias, a phenomenon referring to dependencies of the large-scale bias of a dark matter halo other than its mass, is a fundamental property of the standard cosmological model. By utilizing the constrained simulation Elucid that faithfully reproduces the observed structures larger than 2 Mpc in the local universe, for a sample of 634 massive clusters at z<0.12, we found their counterpart halos in Elucid and used the mass growth history of the matched halos to estimate the formation time of the observed clusters. This allowed us to construct a pair of early- and late-forming clusters, with a similar mass as measured via weak gravitational lensing, and large-scale biases differing at 3 sigma level, suggestive of the signature of assembly bias, which is further corroborated by the properties of cluster galaxies. Our study paves a way to further detect assembly bias based on cluster samples constructed purely on observed quantities.

Speaker: Yen-Ting Lin (ASIAA)

S2-1-LIN.pdf

11:25 AM The formation of the ultra-compact drawf galaxies

In this talk, I will present a study of ultracompact dwarf (UCD) galaxies in the Virgo cluster based mainly on imaging from the Next Generation Virgo Cluster Survey (NGVS). We have identified more than 600 candidate UCDs, from the core of Virgo out to its virial radius. Candidates have been selected through a combination of magnitudes, ellipticities, colors, surface brightnesses, half-light radii, and, when available, radial velocities. Candidates were also visually validated from deep NGVS images. Subsamples of varying completeness and purity have been defined to explore the properties of UCDs and compare to those of globular clusters and the nuclei of dwarf galaxies with the aim of delineating the nature and origins of UCDs. From a surface density map, we find the UCDs to be mostly concentrated within Virgo's main subclusters, around its brightest galaxies. We identify several subsamples of UCDs—i.e., the brightest, largest, and those with the most pronounced and/or asymmetric envelopes—that could hold clues to the origin of UCDs and possible evolutionary links with dwarf nuclei. We find some evidence for such a connection from the existence of diffuse envelopes around some UCDs and comparisons of radial distributions of UCDs and nucleated galaxies within the cluster.

Speaker: Chengze Liu (Shanghai Jiao Tong University)

S2-2-LIU.pdf

11:45 AM Semi-Analytic Catalog For Next-Generation Surveys

In anticipation of the ongoing and upcoming next-generation surveys, we present galaxy catalog by the well-established LGalaxies semi-analytic model and galaxy emission line catalog by post-processing. We have made modifications to the models to solve the time convergence problem and re-calibrated the parameters to accurately reproduce the observed black hole mass function at z~0. Our catalog successfully reproduces various observational properties, such as the galaxy stellar mass function, red galaxy fraction, black hole mass function, and luminosity function of various emission lines at both local and high redshift. Based on our catalog, we have identified that different emission lines have different biases for tracing the matter distribution of the universe. We have developed a fitting formula that describes the bias as a function of luminosity and redshift for different emission line tracers. In addition, our models are applied to the largest cosmological N-body simulation, the Hyper-Millennium project, yielding self-consistent predictions of galaxy properties.

Speaker: Wenxiang Pei (NAOC)

S2-3-Pei Wenxiang.pdf

2:00 PM → 3:10 PM Galaxy: feedback

Convener: Huiyuan Wang (University of Science and Technology of China)

2:00 PM NIHAO-GIZMO: A Comparison of Simulated Disc Galaxies from GASOLINE and GIZMO

We utilize the public GIZMO code to simulate twelve disc galaxies from the NIHAO suite simulated with the GASOLINE code, then compare the corresponding galaxies in the two simulations. We find that while both codes with the same initial conditions and large-scale environments can successfully produce similar disc galaxies, significant differences are still seen in many properties of the galaxies, particularly in the circumgalactic medium (CGM) environment they reside. Specifically, the thermal feedback recipe used in GASOLINE results in ubiquitous long-lasting collimated outflows, primarily driven by high-density hot interstellar medium (ISM) from the galaxy center, and inflows of gas not aligned with the outflow cools rapidly and flows towards the galactic center. In contrast, galaxies from GIZMO code do not exhibit large-scale outflows at low redshifts, but instead display quasi-virialized hot gaseous halos that arise from the strong interaction between inflow of gas and feedback driven outflow. Therefore, the origins of mass and angular momentum of the cold disc in the two simulations are quite different, even though the final morphologies of corresponding galaxies are similar at $z\sim0$. The differences in the distribution of CGM gas are mainly due to different feedback models implemented in the two codes, thus future observations of CGM provide valuable insight into the physics governing the baryon cycle in disc galaxies.

Speaker: Xi Kang (zhejiang university)

S3-1-KangXi.pdf

2:25 PM Tracing the baryonic cycle in and around galaxies using radiation hydrodynamic simulations

Unraveling the gas cycling in and around galaxies is pivotal to understanding their evolution. To tackle this complex, nonlinear process, I introduce "RIGEL", a novel galaxy formation model that integrates radiative transfer with low-temperature cooling/heating, HII region modeling, and resolved supernova feedback from individual massive stars. In this talk, I will talk about some of RIGEL's key features and the impact of radiative transfer on star formation, interstellar medium, and galactic outflows. Finally, I will highlight how detailed modeling of fine-structure line cooling can significantly affect the star formation rate in low-metallicity dwarf galaxies.

Speaker: Hui Li (Tsinghua University)

S3-2-LIHui.pdf

2:50 PM Probing feedback processes in galaxy formation with simulations

AGN and stellar feedback processes strongly affect galaxy formation and are one central unsolved problem in contemporary astronomy. Galactic feedback processes mainly evolve in the circumgalactic medium (CGM), which is another hot research field in recent years. Here I will talk about a series of our recent and ongoing works on both AGN and stellar feedback in the Milky way and several nearby galaxies. By using idealized hydrodynamic simulations and detailed comparisons with multi-wavelength observations, we try to reveal the fundamental physics governing the evolution and impact of these feedback processes.

Speaker: Fulai Guo (Shanghai Astronomical Observatory)

S3-3-GuoFulai.pdf

3:10 PM → 3:40 PM coffee break

3:40 PM → 4:55 PM Galaxy: dynamics & archaeology

Convener: Alessandro Sonnenfeld

3:40 PM Spurious heating of stellar motions by dark matter particles in cosmological hydrodynamical simulations

Simulated galaxies and their dark matter (DM) halos are resolved by fewer particles than there are stars and DM particles in real galaxies and, as a result, are subject to spurious evolution due to gravitational scattering. I will present results from a suite of idealized simulations designed to study the effect of spurious collisional heating on the kinematics and morphologies of simulated galactic discs. I will then present results from two simulations from the EAGLE Project that differ only in the mass resolution of their DM component (one having and equal number of DM and baryonic particles, the other having a factor of seven more DM particles) but keep all other numerical and subgrid parameters fixed. These simulations indicate that a number of global properties of simulated galaxies and halos are unaffected by spurious collisional heating but, below a characteristic mass scale, their structural and kinematic properties are affected. A simple semi-empirical model rooted in analytic theory can be used to identify the characteristic halo mass above which the structural and kinematic properties of galaxies are robust to spurious collisional heating.

Speaker: Aaron Ludlow (ICRAR-UWA)

S4-1-LUDLOW.pdf

4:05 PM Uncover galaxies’ merger history through the chemo-dynamical structures

Deriving galaxies’ past merger history is challenging, albeit possible with their 3D internal chemical-dynamical structures illustrated by the MW with resolved single stars. Modern IFU spectrographs offer the ability to map the spatial distribution of the motions, ages, and chemical abundances of stars for many nearby galaxies. But the information is still blended along the line-of-sight. To further uncover the intrinsic 3D chemo-dynamical structures, we developed a novel population-orbit superposition method, which fit all the aforementioned data simultaneously. This allows us to quantify the mass and stellar populations of hot inner stellar halo, a structure as relic of ancient mass mergers like the MW Gaia-Enceladus-sausage, thus uncover the merger history of many nearby galaxies in a comparable way.

By applying the method to the Fornax cluster galaxies observed by MUSE/VLT through the Fornax3D project, we find two of them, NGC1380 and NGC1427, have massive inner stellar halo components. By comparing to analogues from the cosmological galaxy simulation TNG50 and EAGLE, we find that the formation of the inner stellar halo of NGC1380 and NGC1427 requires a merger with stellar mass of ~4e10 Msun and ~1.4e10 Msun, respectively. We further constrain their merger time by the stellar age distributions in different structures, and find the last massive merger should be happened at ~10 Gyr ago for NGC 1380 and <8 Gyr ago for NGC 1427.

On the other hand, we provide decisive evidence for finding the extreme `merger-free’ relic galaxies, which are taken as the survived z~2 red nugget galaxies not experienced any subsequent mergers. Compact ETGs in the nearby universe are usually taken as candidates as they are massive, extremely compact and with old stellar populations, which, however, could also be result of tidal stripping to a normal ETG. By applying our method to a sample of 16 compact ETGs in the nearby universe, we find seven of them have extremely low fraction of hot inner stellar halo, and with a survived cold disk, which strongly support them as true relic galaxies. This is consistent with the high fraction of red disky galaxies found by JWST at hight-z.

Speaker: Ling Zhu (Shanghai Astronomical observatory)

S4-2-ZHU Ling.pdf

4:25 PM Quantifying the stellar ages of dynamically-separated bulges and disks of CALIFA spiral galaxies

We employ a recently-developed population-orbit superposition technique to simultaneously fit the stellar kinematic and age maps of 82 CALIFA spiral galaxies, and obtain the ages of stars in different dynamical structures. We first evaluate the capabilities of this method on CALIFA-like mock data created from the Auriga simulations. The recovered mean ages of dynamically cold, warm and hot components match the true values well, with up to $20\%$ observational error in the mock age maps. For CALIFA spiral galaxies, we find that the stellar ages of the cold, warm and hot components all increase with galaxies' stellar mass, from $\overline{t_{\rm cold}}\sim2.2$ Gyr, $\overline{t_{\rm warm}}\sim2.3$ Gyr and $\overline{t_{\rm hot}}\sim2.6$ Gyr for galaxies with stellar mass $M_*<10^{10}\,\rm M_{\odot}$, to $\overline{t_{\rm cold}}\sim4.0$ Gyr, $\overline{t_{\rm warm}}\sim5.1$ Gyr and $\overline{t_{\rm hot}}\sim5.9$ Gyr for galaxies with $M_*>10^{11}\,\rm M_{\odot}$. About $80\%$ of the galaxies in our sample have $t_{\rm hot}>t_{\rm cold}$, and the mean values of $t_{\rm hot}-t_{\rm cold}$ also increase with stellar mass, from $0.7_{-0.2}^{+0.6}$ Gyr in low-mass galaxies ($10^{8.9}\,\rm M_{\odot}

Speaker: Yunpeng Jin

S4-3-JIN.pdf

4:40 PM Constraining dark matter content of galaxies by combining IFU stellar kinematics and integrated HI spectrum

Dark matter content within a few Re of galaxies can provide important test of hydrodynamical cosmological simulations, but we are still lacking of reliable measurements of dark matter content in a large number of galaxies across the Hubble types. IFU surveys have provide stellar kinematics for thousands of nearby galaxies, but they usually only cover the inner 1-2Re of galaxies. To strongly constrain the dark matter mass, we need kinematic tracers at the outer regions of galaxy. In this talk, I will introduce a new method combining stellar kinematics from IFU observations and integrated HI spectrum. Although with no spatial resolution of the HI gas kinematics, we can constrain the dark matter fraction within 5Re with a relative uncertainty of ~40%, which is significantly reduced comparing to the uncertainty of ~100% with IFU only. Such integrated HI spectrum can be obtained efficiently for large sample of nearby galaxies from such as HI-MaNGA survey and FAST observations. This will allow us to constrain dark matter content accurately in a large sample of nearby galaxies.

Speaker: yu lei (SHAO)

S4-4-LEI.pdf

Tuesday, October 31

9:00 AM → 10:15 AM halo: assembly & clustering

Convener: Jie Wang

9:00 AM The depletion radius of dark matter halo

I will talk about different boundaries of a dark matter halo focusing on our recently proposed depletion boundary. I will explain its physics and measurements, and illustrate how this new boundary could help us to gain new insights into halo evolution and to provide much improved description of the cosmic structure.

Speaker: Jiaxin Han (Shanghai Jiao Tong University)

S1-1-Han Jiaxin.pdf

9:25 AM A physical and concise halo model based on the depletion radius

We develop a self-consistent and accurate halo model by partitioning matter according to the depletion radii of haloes. Unlike conventional models that define haloes with the virial radius while relying on a separate exclusion radius or ad-hoc fixes to account for halo exclusion, our model distributes mass across all scales self-consistently and accounts for both the virialized and non-virialized matter distribution around each halo. Using a cosmological simulation, we show that our halo definition leads to very simple and intuitive model components, with the one-halo term given by the Einasto profile with no truncation needed, and the halo-halo correlation function following a universal power-law form down to the halo boundary. The universal halo-halo correlation also allows us to easily model the distribution of unresolved haloes as well as diffuse matter. Convolving the halo profile with the halo-halo correlation function, we obtain a complete description of the halo-matter correlation across all scales, which self-consistently accounts for halo exclusion at the transition scale. Mass conservation is explicitly maintained in our model, and the scale dependence of the classical halo bias is easily reproduced. Our model can successfully reconstruct the halo-matter correlation function within an accuracy of $9\%$ for halo virial masses in the range of $10^{11.5}h^{-1}{\rm M}_{\odot}

Speaker: Yifeng Zhou (SJTU)

S1-2-Zhou Yifeng.pdf

9:40 AM Characterize the assembly of dark matter halos with protohalo size histories

We propose a novel method to quantify the assembly histories of dark matter halos with the redshift evolution of the mass-weighted spatial variance of their progenitor halos, i.e. the protohalo size history. We find that the protohalo size history for each individual halo at z~0 can be described by a double power-law function. The amplitude of the fitting function strongly correlates to the central-to-total stellar mass ratios of descendant halos. The variation of the amplitude of the protohalo size history can induce a strong halo assembly bias effect for massive halos. This effect is detectable in observation using the central-to-total stellar mass ratio as a proxy of the protohalo size. The correlation to the descendant central-to-total stellar mass ratio and the halo assembly bias effect seen in the protohalo size are much stronger than that seen in the commonly adopted half-mass formation time derived from the mass accretion history. This indicates that the information loss caused by the compression of halo merger trees to mass accretion histories can be captured by the protohalo size history. Protohalo size thus provides a useful quantity to connect protoclusters across cosmic time and to link protoclusters with their descendant clusters in observations.

Speaker: Kai Wang (Kavli Institute for Astronomy and Astrophysics at Peking University)

S1-3-WANG Kai.pdf

10:00 AM Dependence of dark halo assembly bias on halo definition and orientation

High-resolution N-body simulations have shown that the large-scale clustering of dark halos is predominantly but not purely dependent on their dark matter mass. At fixed halo mass, the bias factor of halo clustering depends on a variety of secondary properties of halos such as formation time, concentration, spin and shape, an effect known as “assembly bias” which should be related to the variance of the assembly history of halos of a given mass. Both the mass-dependent halo bias and the assembly bias should have an important impact on galaxy formation and evolution. In this work, we use the IllustrisTNG300 dark matter-only simulation to investigate the dependence of the assembly bias on both the definition and the spatial orientation of dark matter halos. We find the long-standing controversial results reported in the literature on spin bias are caused by the different halo definitions adopted in different studies. Furthermore, we find strong anisotropy of the assembly bias when the halo spin or the axis-ratio of halos is considered as the secondary property. The spin bias becomes rather weak when the clustering measurement is limited to the direction along the major axis of halos, and this result depends only weakly on halo mass. A similar but weaker anisotropic effect is found for halo concentration, while no anisotropy is found for either halo formation time or halo shape. We discuss the link of these findings with the spatial alignment of galaxies that has been observed from low-z redshift surveys.

Speaker: Qinglin Ma (Tsinghua U.)

S1-4-MA Qinglin.pdf

10:15 AM → 10:45 AM coffee break

10:45 AM → 12:05 PM halo: assembly & clustering

Convener: Houjun Mo (U. Mass.)

10:45 AM Elucidating the impact of massive neutrinos on halo assembly bias

Massive neutrinos have a minimal impact on large-scale structure formation but suppress cosmic growth at small, nonlinear scales. We examine small-scale discrepancies between simulations with and without massive neutrinos from the Quijote simulation. Employing a one-to-one halo matching approach based on the initial peaks of haloes, where the initial positions of cold dark matter particles are identical, we compare matched halo pairs. Our results reveal weak correlations among halo initial peak curvature $\hat{s}$, concentration $\hat{c}$, and relative neutrino excess $\epsilon_{\nu}$. We also investigate the dependency of halo bias $\hat{b}$ on $\epsilon_{\nu}$, $\hat{s}$, and $\hat{c}$. While the first two parameters show notable correlations with halo bias, the latter does not. In conclusion, while massive neutrinos do influence halo formation, our findings suggest that constraining neutrino mass solely through observable halo properties is challenging.

Speaker: Yunjia Song

S2-1-Song Yunjia.pdf

11:00 AM Galaxy-Halo Spin Alignment and Conservation in the IllustrisTNG Simulation

Recent studies illustrate the correlation between the angular momenta of cosmic structures and their Lagrangian properties. However, only baryons are observable and it is unclear whether they reliably trace the cosmic angular momenta. We study the Lagrangian mass distribution, spin alignment, and conservation of dark matter (DM), gas, and stellar components of galaxy–halo systems using IllustrisTNG. We show that their protoshapes are similar in terms of the statistics of moment of inertia tensors. Under the common gravitational potential they are expected to be exerted the same tidal torque and generate strong spin direction and magnitude correlations. These correlations are not destroyed by the nonlinear evolution and complicated baryonic effects, except for the spin magnitude of stars, which is correlated with ex situ stellar mass fraction f_acc. We further show that the late-time angular momenta traced by total gas, stars, or the central galaxies, can be reliably reconstructed by the initial perturbations. These results suggest that baryonic angular momenta can potentially be used in reconstructing the parameters and models related to the initial perturbations.

Speaker: Mingjie Sheng (Xiamen University)

S2-2-Sheng Mingjie.pdf

11:15 AM Cosmic filament spin, boundary, and its impact on galaxy spin.

Cosmic filaments are one of the most important structures in the universe and have a significant influence on the formation and evolution of galaxies. Research involving both observation and simulation has demonstrated that the direction of a galaxy's spin is associated with the cosmic filament: low-mass galaxies tend to be aligned, while high-mass galaxies are usually perpendicular. However, only a few studies have looked at the properties of filaments, such as their dynamic properties and boundaries. In this talk, we will present our recent work on filament spin, filament radius, and its effect on galaxy spin. We are the first to detect the filament spin signal using SDSS data, and the signal has been repeated in simulations. We will also show how the filament spin affects the galaxy spin. Furthermore, by using the DisPerSE filament finder, we have defined the filament boundary (radius) in the TNG and MTNG simulations and SDSS data. We have also found the dependence of filament radius on multiple properties and their evolution pattern.

Speaker: Peng Wang (SHAO)

S2-3-WANG Peng.pdf

11:35 AM Anisotropic Distribution of Satellites around Pairs of Dark Matter Halos

Satellite galaxies tend to occupy the region in between pairs of massive galaxies, as seen in both the Local Group (between the Milky Way and M31) and distant galaxy pairs in SDSS. Possible origins include local gravity between paired halos and the large-scale filamentary environment. We investigate the anisotropic distribution of satellites around pairs of galaxy groups in SDSS/DR7 as well as pairs of dark matter halos in the ELUCID simulation. We construct mock catalogs based on the TNG300 hydrodynamic simulation to make a direct comparison between our observational and simulation results. The results from both the mock catalogs and the simulation agree quite well with SDSS. Our results and tests on the mocks suggest that the anisotropic distribution of satellites around paired halos can be naturally explained by the alignment of the galaxy distribution within dark halos with large-scale filamentary structures, rather than the local gravity as proposed by previous studies.

Speaker: Yanhan Guo (Tsinghua U.)

S2-4-GUO Yanhan.pdf

11:50 AM Size—spin relation and angular momentum evolution of disc galaxies in hydrodynamical simulation

In the standard disk galaxy formation model, the sizes of galactic disks are tightly related to the spin parameters of their dark matter haloes. The model has been wildly adopted by various semi--analytic galaxy formation models which have been extremely successful to interpret a large body of observational data. However, the size-$\lambda$ correlation was rarely seen in most modern hydrodynamical simulations of galaxy formation. We found galactic sizes correlate with spin parameters of their dark matter haloes in the simulations developed by the IllustrisTNG collaborations, albeit the relation does not always agree with prediction of MMW98 model overall stellar mass range we examined. Further, We explored how different AURIGA and APOSTLE sub-grid models, especially for stellar feedback, influence angular momentum evolution of disc galaxies, by comparing two suits of zoom-in simulations with identical initial conditions. Our results demonstrate that the gas recycling process has a significant impact on the evolution of angular momentum after the gas fall into the galaxy. Specifically, we find that the higher baryon recycling efficiency in the AURIGA simulation leads to galaxies with higher angular momentum magnitude and alignment than in the APOSTLE simulation.

Speaker: Hang Yang (NAOC)

S2-5-YANG Hang.pdf

2:00 PM → 3:05 PM halo: dark matter profile

Convener: Jiaxin Han (Shanghai Jiao Tong University)

2:00 PM Self-interacting dark matter and its role in the structural diversity issue of dwarf galaxies

One of the most persistent small-scale challenges to the LCDM paradigm is the striking structural diversity of dwarf galaxies. Cosmological simulations struggle in reproducing the full range of galaxy size or the inner dark-matter distribution as inferred from kinematics observations. While there have been efforts resorting to fine-tuning baryonic feedback and environmental effects, simple modifications on the dark sector may provide a clean solution, via making the dark matter self-interacting. We develop a simple analytical procedure for computing the density profile of self-interacting dark matter (SIDM) halos, incorporating gravitational influence of inhabitant galaxies and show that the model reproduces cosmological SIDM simulation results remarkably well. We show that the halo response to baryons is more diverse in SIDM than in CDM, a desirable feature in the context of the structural diversity problem. Using this new model, we discuss constraining the SIDM cross section using observations of dwarf galaxies and satellite galaxies. Finally, we show preliminary results towards developing a full semi-analytical frame work for SIDM satellite evolution, incorporating dark ram-pressure and facilitation of gravothermal core-collapse by tidal truncation.

Speaker: Fangzhou Jiang (Peking University)

2:25 PM Is the Core-cusp Problem a Matter of Perspective?

Mock member stars for dwarf galaxies are constructed from the cosmological AURIGA simulation, which reflects the dynamical status of realistic stellar tracers. Axisymmetric Jeans Anisotropic Multi-Gaussian Expansion (JAM) modeling is applied to each system to recover the underlying matter distribution. The stellar or dark matter component individually is poorly recovered, but the total profile is constrained more reasonably. The mass within the half-mass radius of tracers is recovered the tightest, and the mass between 200 and 300 pc, M(200-300 pc), is an unbiasedly constrained ensemble. Quiescent Saggitarius dSph-like systems and star-forming systems with strong outflows show distinct features, with M(200-300 pc) mostly underestimated for the former, and likely overestimated for the latter. The biases correlate with the dynamical status, which is a result of contraction motions due to tidal effects in quiescent systems or galactic winds in star-forming systems, driving them out of equilibrium. By extrapolating the actual density profiles and the dynamical constraints down to scales below the resolution, we find the mass within 150 pc can be an unbiasedly constrained ensemble, with a scatter of ~0.255 dex. We show that the contraction of member stars in nearby systems is detectable based on Gaia DR3 proper motion errors. In the end, we discuss the effect of binary orbital motions upon dynamical modelings of ultra faint dwarfs. In particular, the inner densities are mostly deflated due to the negative gradients in the velocity dispersion profiles, rather than inflated in the traditional recognition.

Speaker: Wenting Wang (SJTU)

S3-2-WANG Wenting.pdf

2:45 PM A strong lensing view of the core-cusp problem

Mapping the dark matter distribution in the Universe is of fundamental importance for both galaxy evolution and cosmology.
Observationally, one of the outstanding questions regarding dark matter is the so-called "core vs. cusp problem": how steep is the inner dark matter density profile of galaxies? The answer to this question can give us important insight on the relative importance of baryonic physics processes at play during galaxy formation, and on the nature of dark matter itself.
Strong gravitational lensing can provide unique constraints on the dark matter distribution in massive galaxies. Although current measurements are still scarce, future surveys will enable us to answer the core vs. cusp question. I will present a strategy to reach this goal, based on the statistical combination of a large sample of strong lenses.

Speaker: Alessandro Sonnenfeld (SJTU)

S3-3-SONNENFELD.pdf

3:05 PM → 3:35 PM coffee break

3:35 PM → 4:55 PM halo: stellar & gas

Convener: Peng Wang (SHAO)

3:35 PM Dynamical friction on bound orbits

In cosmological structure formation, objects ranging from compact binaries to satellite galaxies evolve on bound orbits while they interact gravitationally with the surrounding matter distribution. In this talk, I will present an analytic approach to the dynamical friction acting on circularly moving point masses in a gaseous medium. I will show how it can be extended to dark matter backgrounds and to eccentric orbits. Some astrophysical implications will also be discussed.

Speaker: Vincent Desjacques

4:00 PM Tracing the Dynamical Evolution of Cluster Galaxies in HectoMAP and Illustris-TNG

We use a 500 cluster sample from the HectoMAP redshift survey combined with the IllustrisTNG 300-1 simulation to explore the evolution of cluster members and their host clusters. We use the central stellar velocity dispersions, a fundamental observable that links galaxies with their dark matter subhalos. For a fair comparison with observed stellar velocity dispersions, we carefully examine the central velocity dispersion measurements for subhalos in IllustrisTNG-300. Based on the observed and simulated velocity dispersions, we explore the co-evolution of the brightest cluster galaxies (BCGs) and clusters based on their dynamical scaling relations. The observed ratio between the BCG velocity dispersion and cluster velocity dispersion declines as a function of cluster velocity dispersion for redshift $z < 0.6$, indicating that the BCG mass fraction decreases as a function of cluster mass. The simulated relation is consistent with the observed relation with a larger scatter. We also investigate the redshift evolution of the dynamical scaling relation, which can be a direct test for the structure formation model. These predictions that probe the evolution of the most massive galaxies and their host structures are useful tests for JWST and dense, deep future spectroscopic surveys.

Speaker: Jubee Sohn (Seoul National University)

S4-2-Sohn Jubee.pdf

4:25 PM Connecting stellar distribution of galaxy cluster to halo mass assembly in hydro-simulations

Massive central galaxies ($M_\star>10^{11.2}M_\odot$) in clusters and their satellites offer insights into the assembly history of their host massive dark matter halos that are crucial for cosmology. Therefore, it is necessary to establish a clear picture of their galaxy-halo connection. Recent works using deep image and weak lensing suggest that the stellar mass in the outskirt of massive central galaxies at low-redshift is a good halo mass proxy. Besides, massive halos with similar mass but different concentration show different distribution on the central galaxy stellar mass - richness plane. These intriguing results need more investigation due to they have important implications for the cluster cosmology and the study of assembly bias of massive halos. In this study, we check whether the hydro-simulations can reproduce the results and provide some insights. With the massive galaxies from Illustris and IllustrisTNG simulation, we confirm that the outskirt mass of massive central galaxies is a promising halo mass proxy in three simulations with different resolution and physical recipes for galaxy formation, outperforming the total accreted stellar mass (ex-situ). Additionally, we explore the TNG300 massive galaxies distribution on the outskirt mass - richness plane. We identify massive halos missed by the richness-based selection and uncover a systematic halo concentration trend over this parameter space. These results could help us to understand the assembly bias of massive halos in the era of DESI and better utilize the cosmological potential in massive halos.

Speaker: Shuo Xu (Department of Astronomy, Tsinghua University)

S4-3-XU Shuo.pdf

4:40 PM The evolution of physical baryon profiles in galaxy clusters

The distribution of baryons provides a significant way to understand the formation of galaxy clusters by revealing the details of its internal structure and changes over time. I will present theoretical studies on the scaled profiles of physical properties associated with the baryonic components, including gas density, temperature, metallicity, pressure and entropy as well as stellar mass, metallicity and satellite galaxy number density in galaxy clusters from z = 4 to z = 0 by tracking their progenitors. These mass-complete simulated galaxy clusters are coming from THE THREE HUNDRED with two runs: GIZMO-SIMBA and GADGET-X. The comparisons between the two runs, as well as with observed profiles that are generally available at low redshift, are discussed.

Speaker: Qingyang Li (SJTU)

S4-4-LI Qingyang.pdf

Wednesday, November 1

9:00 AM → 10:05 AM halo: satellite distribution

Convener: Fangzhou Jiang (Peking University)

9:00 AM Symfind: The Durability of Subhalos and Fragility of Subhalo Finders

A major question in ΛCDM is what this theory truly predicts for the properties of subhalo populations. Subhalos are difficult to simulate and to find within simulations, and this propagates into uncertainty in theoretical predictions for satellite galaxies. I present Symfind, a new particle-tracking-based subhalo finder, and demonstrate that it can track subhalos to orders-of-magnitude lower masses than the commonly used halo-finding tools, Rockstar and consistent-trees. These longer survival times allow Symfind to find tens-to-hundreds of percent more subhalos, depending on simulation resolution and the specifics of the subhalo population. We perform extensive numerical testing and comparisons against high-resolution idealized simulations. We combine these tests together into a new system for evaluating the performance of subhalo finders and show that Symfind is able to track subhalos until the point of likely galaxy disruption without orphan modeling, while Rockstar cannot and converges to a false solution. This allows for the elimination of a substantial source of systematic uncertainty in clustering measurements, galaxy models, and subhalo-based cosmological tests.

Speaker: Philip Mansfield (Stanford University)

S1-1-MANSFIELD.pdf

9:25 AM The true radial distribution of satellite galaxies around MW-mass halos in LCDM

The Milky Way (MW) galaxy presents a larger number of satellites within 40 kpc than predicted by cosmological simulations of MW halos. If we believe simulation results, one implication is that halos as small as Vpeak~7 km/s should harbour galaxies, which is in contrast to the expectations of most galaxy formation models. On the other hand, idealized simulations predict that the cuspy NFW density profile of cold dark matter halos never fully disrupts, and show that cosmological N-body simulations suffer from artificial disruption of subhalos near the centers of MW-mass halos after tidal stripping. This is a numerical limitation due to the finite mass resolution currently achievable in these simulations.
In this work we use the Aquarius simulations of MW-mass halos, combined with the Galform semi-analytical galaxy formation model, to account for these sub-resolution subhalos (commonly known as “type-2s/orphans”) and estimate the true radial distribution of satellite galaxies predicted by LCDM. We carry out a convergence study of the number of type-2s versus surviving satellites by comparing 5 different resolution levels and we characterize the population of type-2s. Our results show that the observed population of nearby ultrafaint MW satellites can be readily accommodated within LCDM models where galaxy formation occurs in halos with masses above the Hydrogen-cooling limit.

Speaker: Isabel Santos-Santos (Institute for Computational Cosmology, Durham University)

S1-2-SANTOS.pdf

9:50 AM Extending the unified subhalo model to warm dark matter

Using a set of high-resolution N-body simulations, we extend the unified distribution model of cold dark matter (CDM) subhaloes to the warm dark matter(WDM) case. The same model framework combining the unevolved mass function, unevolved radial distribution, and tidal stripping can predict the mass function and spatial distribution of subhaloes in both CDM and WDM simulations. The dependence of the model on the DM particle property is universally parameterized through the half-mode mass of the initial power spectrum. Compared with the CDM model, the WDM model differs most notably in two aspects. 1) In contrast to the power-law form in CDM, the unevolved subhalo mass function for WDM is scale-dependent at the low mass end due to the cut-off in the initial power spectrum. 2) WDM subhaloes are more vulnerable to tidal stripping and disruption due to their lower concentrations at accretion time. Their survival rate is also found to depend on the infall mass. Accounting for these differences, the model predicts a final WDM subhalo mass function that is also proportional to the unevolved subhalo mass function. The radial distribution of WDM subhaloes is predicted to be mass-dependent. For low mass subhaloes, the radial distribution is flatter in the inner halo and steeper in the outer halo compared to the CDM counterpart, due to the scale-dependent unevolved mass function and the enhanced tidal stripping.

Speaker: Feihong He (SJTU)

S1-3-HE Feihong.pdf

10:05 AM → 10:35 AM coffee break

10:35 AM → 11:55 AM Galaxy: halo occupation

Convener: Hong Guo (Shanghai Astronomical Observatory)

10:35 AM CSST large scale structure analysis pipeline: constructing ideal mock galaxy redshift surveys

We set out to construct a set of ideal mock galaxy redshift surveys (MGRSs) for the future Chinese Space-station Survey Telescope (CSST) observation, where subsequent survey selection effects can be added and evaluated.

Speaker: Xiaohu Yang (SJTU)

S2-1-YANG Xiaohu.pdf

11:00 AM The Conditional Colour-Magnitude Distribution

The Conditional Colour-Magnitude Distribution (CCMD) is a comprehensive model of the colour-magnitude-halo mass distribution of present day galaxies. It reproduces well the observed galaxy abundance and clustering of galaxies defined by arbitrary luminosity and colour cuts. We present a comprehensive comparison of the galaxy colour--magnitude--halo mass relation from the CCMD galaxy mocks and from the galaxy group catalogues of the Sloan Digital Sky Survey DR7. When the same galaxy group finder is applied to both the mocks and data, the same systematic errors in group-finding and mass assignment are inherited to both the resulting CCMD groups and SDSS groups. We adopt two group finders to eliminate any potential dependence of comparison on the group finder. Regardless of which group finder is used, we find nice agreement in the conditional luminosity function, the conditional colour function, and the conditional colour-magnitude distribution inferred from the CCMD and SDSS group catalogues, suggesting that the CCMD mocks are accurate representations of the reality in terms of galaxy colour and luminosity.Within two external central galaxy catalogues whose host halo mass has been calibrated by galaxy lensing measurements, we find their colour-magnitude distribution showing two distinct and orthogonal components, in line with the prediction of the CCMD model. The CCMD galaxy mocks provide the ideal control samples for accessing the statistical significance of any inference from group catalogues.The halo and CCMD mock catalogues are available to the public.

Speaker: Haojie Xu (SHAO)

S2-2-Xu Haojie.pdf

11:20 AM Galaxy-(sub)halo relation in the eye of machine learning

Machine learning techniques are widely implemented to predict galaxy properties based on halo or subhalo properties in semi-analytic models (SAM) and hydrodynamic simulations. The multivariate relation between galaxies and their (sub)halos can be efficiently captured and reproduced. I will present our results on predicting galaxy properties based on different galaxy formation models. Additionally, I will also discuss the impact of baryonic processes on galaxy properties. These studies can provide helpful insights into galaxy formation and evolution. However, the galaxy-(sub)halo relation in galaxy formation models may deviate from those in the real Universe. With the ELUCID simulation which is constructed to reproduce the density field of the SDSS and the SDSS-ELUCID matched catalog which links SDSS galaxies to ELUCID subhalos, we repeat the ML to predict SDSS galaxy properties based on ELUCID subhalo properties. I will show the differences in ML results compared to those based on the galaxy formation models. This comparison is helpful for understanding the galaxy-halo connection in observation.

Speaker: Xiaoju Xu (SJTU)

S2-3-XU Xiaoju.pdf

11:40 AM A Galaxy Group Finder Based on Machine Learning

Galaxy groups and clusters represent systems of galaxies residing within the same dark matter halos. This inherent connection to dark matter halos positions galaxy groups as a direct avenue for addressing pivotal questions in astrophysics, such as the role of the environment in galaxy formation and evolution, as well as the cosmic density field. Various group-finding methodologies have been proposed and implemented across different redshift surveys, including the Friends-of-Friends (FoF) algorithm, halo-based group finders, and the C4 algorithm.

In this study, we introduce a novel group-finding approach that leverages machine learning techniques. Our group finder comprises two distinct machine learning models: a classification model designed to identify central galaxies from their neighboring counterparts and a regression model for estimating the mass of groups formed by galaxies sharing the same central galaxy. These two models are integrated into an iterative process, ultimately producing the final galaxy catalog.

To validate our method, we conducted extensive training and testing using the Millennium Simulation. Our results demonstrate remarkable accuracy, even under extensibility testing scenarios such as raising the apparent magnitude limitation of mock catalogs, utilizing high-redshift galaxy samples, and applying our method to a different simulation (TNG300). Furthermore, we applied our approach to real observational data from the NASA-Sloan Atlas Catalog, based on the Sloan Digital Sky Survey (SDSS). The group catalog will be made available in the near future.

Speaker: JUNTAO MA (NAOC)

S2-4-MA Juntao.pdf

1:00 PM → 5:00 PM free afternoon

6:00 PM → 8:00 PM Banquet

Thursday, November 2

9:00 AM → 10:25 AM Galaxy: gas

Convener: Cheng Li (Tsinghua University)

9:00 AM Deep HI survey in M31 halo region with FAST

Speaker: Jie Wang

9:25 AM On the origin of red but HI-rich galaxies in the local universe

Generally, most of the red galaxies in the local universe are observed to be quenched and have little cold gas, suggesting that the depletion/removal of cold gas is a necessary condition for galaxy quenching. However, current HI surveys are too shallow to detect the HI gas of red galaxies. In this work, we construct a new HI estimator based on the scaling relations of HI gas mass with a variety of optical properties of galaxies, and we apply it to the SDSS galaxy sample to study the HI properties of general galaxy populations like HI mass function (HIMF), conditional HIMF (CHIMF), and HI-halo mass relation. Based on the predicted HI masses by our model, we select a sample of red but HI-rich (RR) galaxies and compare their statistical properties with a control sample of red but HI-normal galaxies (RN). We find RR galaxies are similar to RN galaxies in all the optical properties considered once the two samples are closely matched in stellar mass. On average the HI disk size of the RR galaxies as inferred from the HI size-mass relation is larger than the optical size by a factor of ~3, while the HI and optical sizes are comparable for RN galaxies. This result indicates that the large cold gas reservoir of the RR galaxies is due to the substantially low surface density of the extended HI disk, although the formation process of the HI disk still remains unclear.

Speaker: Xiao Li (Tsinghua University)

S1-2-LI Xiao.pdf

9:40 AM FAST-MeerKAT synergy: evolution of HI gas in galaxies, IGM and CGM

The neutral hydrogen (HI) in galaxies, intergalactic (IGM) and circumgalactic (CGM) mediums can trace the matter flow from large-scale structures to galaxies, and plays important roles in the process of galaxy formation and evolution. In this talk, I will present our efforts to detect the IGM and CGM using HI emission line with the world's largest single-dish radio telescope-FAST combined with the SKA precursor-MeerKAT. To achieve this, we took 13-hours FAST observation in L-band in the COSMOS field, overlapping with one of the MeerKAT MIGHTEE fields. The initial analysis demonstrates that we have reached the N_HI < 10^18 cm^-2 regime, where the diffuse HI gas is considered to be ubiquitous in the cosmic web.

Speaker: Hengxing Pan (University of Oxford)

9:55 AM HI content of massive red spiral galaxies observed by FAST

A sample of 279 massive red spirals was selected optically by Guo et al., among which 166 galaxies have been observed by the ALFALFA survey. In this work, we observe HI content of the rest 113 massive red spiral galaxies using the Five-hundred- meter Aperture Spherical radio Telescope (FAST). 75 of the 113 galaxies have HI detection with a signal-to-noise ratio (S/N) greater than 4.7. Compared with the red spirals in the same sample that have been observed by the ALFALFA survey, galaxies observed by FAST have on average a higher S/N, and reach to a lower HI mass. To investigate why many red spirals contain a significant amount of HI mass, we check colour profiles of the massive red spirals using images observed by the DESI Legacy Imaging Surveys. We find that galaxies with HI detection have bluer outer discs than the galaxies without HI detection, for both ALFALFA and FAST samples. For galaxies with HI detection, there exists a clear correlation between galaxy HI mass and g-r colour at outer radius: galaxies with higher HI masses have bluer outer discs. The results indicate that optically selected massive red spirals are not fully quenched, and the HI gas observed in many of the galaxies may exist in their outer blue discs.

Speaker: Lan Wang (NAOC)

S1-4-WANG Lan.pdf

10:10 AM Baryonic Tully-Fisher relation at low mass end

The baryonic Tully-Fisher relation (BTFR), which connects the baryonic mass of galaxies with their circular velocities, has been validated across a wide range of galaxies, from dwarf galaxies to massive galaxies. In conflict with observations, modern simulations predict a break-point at 10^9M_sun, below which BTFR bends down toward low masses. This discrepancy is one of the small scale challenges of LCDM. Recent studies have found that several ultra-diffuse galaxies (UDGs) deviate significantly from the BTFR, indicating a galaxy population with abnormal dynamical properties. However, such studies were still confined within a small sample size. In this study, we used the 100% complete Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) to investigate the BTFR of 88 Hi-rich UDGs (HUDGs), which is the largest UDG sample with dynamical information. We found that the HUDGs form a continuous distribution in the BTFR diagram, with high-velocity galaxies consistent with normal dwarf galaxies at 1 σ level, and low-velocity galaxies deviating from the BTFR, in line with that reported in the literature. We point out that the observed deviation may be subject to various selection effects or systemic biases. Nevertheless, we found that the significance of the deviation of HUDGs from the BTFR and TFR are different, i.e., they either deviate from the BTFR or from the TFR. Our result indicates that a high-gas fraction may play an important role in explaining the deviation of HUDGs from BTFR.

Speaker: Huijie Hu (NAOC)

S1-5-HU Huijie.pdf

10:25 AM → 10:55 AM coffee break

10:55 AM → 12:05 PM Galaxy: emissions

Convener: Fulai Guo (Shanghai Astronomical Observatory)

10:55 AM The gas content and dwarf galaxy population in low-z dark matter halos

Galaxies are evolving ecosystems of multiple components which interplay with each other and are distributed over a wide range of spatial scale, from sub-galactic scales up to scales of dark matter halos. Our understanding of the galaxy ecosystems has largely been limited to relatively bright galaxies, however. Other components such as gas of different phases as well as dwarf galaxies with stellar mass below about 10^9 solar mass are still poorly understood. I will talk about our recent studies of the abundance, formation and quenching of low-z dwarf galaxies with stellar mass down to ~10^7 solar mass. I will also talk about our measurements of the cool gas and atomic gas content in low-z dark matter halos.

Speaker: Cheng Li (Tsinghua University)

11:20 AM The hot gas distribution, baryon budget, and mock observations in the semi-analytic model of galaxy formation

We adopt a new kind of one-dimensional model instead of the isothermal sphere to describe the radial distribution of hot gas in the L-Galaxies semi-analytic model. The hot gas halo can be divided into two parts according to the ratio of the local thermal instability time-scale and the free-fall time-scale: a cool core with tTI/tff = 10 and a stable outer halo with tTI/tff > 10. We update the prescriptions of cooling, feedback, and stripping based on the new hot gas profiles, and then reproduce several X-ray observational results like the radial profiles of hot gas density, and the scaling relations of X-ray luminosity and temperature. We find: (1) Consistent with observations, flatter density profiles in halo centers produce lower X-ray emission than an isothermal sphere; (2) Cool core regions prone to precipitation have higher gas temperature than the virial temperature, and a larger TX/T200 ratio in smaller haloes leads to a steeper slope in the LX-TX relation; (3) The ionized gas in the unbounded reservoir and low-temperature intergalactic gas in low-mass haloes could be the main components of the halo 'missing baryons'.

Based on the model outputs of hot gas profiles. We make the mock observations for hot gas components, we generate the mock X-ray spectra with SOXS package and derive the mock images in soft X-ray band. We also make some predictions for the future survey of hot baryons by X-ray facilities (e.g.for HUBS), which should help the target selection for future observations.

Speaker: Jian Fu (SHAO)

S2-2-FU Jian.pdf

11:35 AM AGN luminosities in simulated universe

The study of the spectral energy distribution (SED) of active galactic nuclei (AGN) plays a very important role in several aspects of AGN, such as the physics of black hole (BH) accretion, AGN feedback, and AGN luminosity function (LF). In this work, we explain the observed AGN LF with the SED more physically considered. Specifically, we strictly study the accretion model for a wide range of the dimensionless accretion rate $\dot{m}(\equiv \dot{M}/\dot{M}_\mathrm{Edd})$, then calculate the structure of the accretion flow and the corresponding SED by specifying black hole mass $m(\equiv M_\mathrm{BH}/M_\odot)$ and accretion rate $\dot{m}$. Further, combing with the semi-analytical model of galaxy formation L-Galaxies and Millennium style dark matter simulation for the distribution of ($m, \dot{m}$) at different redshift, we calculate the bolometric, soft X-ray, hard X-ray, and optical/UV LF theoretically. Finally, by comparing with observations, we found a satisfactory agreement between our predictions and observational determined LFs for redshift $z<1$. For $z>1$, our model's prediction deviates from observed LFs. We argue that such deviation may arises from the inherent AGN feedback prescription of the cosmological simulation, and can be alleviated to some extent by exploring the effects of the microphysics (such as viscosity and chaotic magnetic field) of the accretion flow on the SED and therefore on the LF.

Speaker: Tong Su (National Astronomical Observatories, Chinese Academy of Sciences)

S2-3-SU Tong.pdf

11:50 AM The UV luminosity function at 0.6 < z < 1 from UVCANDELS

UVCANDELS is a HST Cycle-26 Treasury Program awarded 164 orbits of primary ultraviolet (UV) F275W imaging and coordinated parallel optical F435W imaging in four CANDELS fields: GOODS-N, GOODS-S, EGS, and COSMOS, covering a total area of $\sim430$ arcmin$^2$. This is $\sim2.5$ times larger than the area covered by previous UV data combined, reaching a depth of 27 ABmag. We present a robust analysis of the rest-frame UV luminosity function (LF), relying on our UV-optimized aperture photometry method yielding a factor of $1.5\times$ increase in the signal-to-noise ratios in our F275W imaging. Using well tested photometric redshift measurements and signal-to-noise ratio cut, we identify in total $5,810$ galaxy candidates at redshift range of $0.6 < z < 1$, down to $M_{UV} = -14.3 $. We restrict our analysis to sources with above $30\%$ completeness, in order to minimize the effect of uncertainties in estimating the completeness function especially at the faint-end. An unbiased maximum likelihood estimate is then performed on the unbinned data to derive the best-fit Schechter parameters of UV LF. We report a best-fit faint-end slope of $\alpha = -1.285^{+0.043}_{-0.042}$ at $z \sim 0.8$. By splitting our total sample to sub-samples at $z\sim0.7$ and $z\sim0.9$, respectively, we give a hint to the evolution behavior of $\alpha$ with redshift. The unobscured UV luminosity density at $M_\text{UV}<-10$ is derived as $\rho_\text{UV}=1.24^{+0.25}_{-0.25}\ (\times10^{26} \text{ergs/s/Hz/Mpc}^3)$ using our best-fit LF parameters.

Speaker: Lei Sun (UCAS)

S2-4-SUN Lei.pdf

2:00 PM → 3:35 PM Cosmology: probes

Convener: Yi Zheng (SYSU)

2:00 PM Constructing observables on the sky

I shall first present a novel approach to the flat-sky angular power spectrum approximation, highlighting its comparison to the full-sky formalism and presenting fast and efficient computational methods paramount for the data analysis of upcoming galaxy surveys. I will then construct the 3D galaxy observables like the power spectrum, systematically exploring the projection effects and relations of these observables to the theoretically computed quantities. These are becoming increasingly important in times of large-volume surveys that have an opportunity to detect GR effects related to the Hubble scale.

Speaker: Zvonimir Vlah

2:25 PM On model selection, validation and reconstruction in the context of physical cosmology

I revisit the old subject of comparing Bayesian and frequentist approaches in model selection and validation in the context of physical cosmology. I discuss caveats of both approaches dealing with unknowns and how using reliable non-parametric methods of reconstruction can help validating models without comparing them with each other. I discus the importance of this subject in the era of Big precision data and how inaccuracies due to systematics or wrong assumptions can result to unreal discoveries.

Speaker: Arman Shafieloo (Korea Astronomy and Space Science Institute)

S3-1-Shafieloo Arman.pdf

2:50 PM A new marked correlation function scheme for testing gravity

We apply the marked correlation function test proposed by Armijo et al. 2023 to samples of luminous red galaxies (LRGs) from the final data release of the Sloan Digital Sky Survey (SDSS) III. The test assigns a density dependent mark to galaxies in the estimation of the projected marked correlation function. Two gravity models are compared: general relativity (GR) and $f(R)$ gravity. We build mock catalogues which, by construction, reproduce the measured galaxy number density and two point correlation function of the LRG samples, using the halo occupation distribution model (HOD). A range of HOD models give acceptable fits to the observational constraints and this uncertainty is fed through to the error on the predicted marked correlation functions. The uncertainty from the HOD modelling is comparable to the sample variance for the SDSS-III LRG samples. Our analysis shows that current galaxy catalogues are too small for the test to distinguish a popular $f(R)$ model from GR. However, upcoming surveys with a better measured galaxy number density and smaller errors on the two point correlation function, or a better understanding of galaxy formation, may allow our method to distinguish between viable gravity models.

Speaker: Joaquin Armijo (Kavli IPMU)

S3-3-ARMIJO.pdf

3:05 PM Suppressing the sample variance of DESI-like galaxy clustering via fast simulations

The current and forthcoming Stage-IV galaxy surveys are going to map the Unvierse in a large sky area and redshift range. The statistical error will be dramatically reduced, hence, controlling the modelling systematics below the statistical error becomes crucial in the era of precision cosmology. Usually, N-body simulations are adopted to study theoretical systematics of models. In order to mitigate the sample variance of simulations, it is typical to conduct a significant number of simulations. However, it is too expensive in terms of computational time and disk usage to run simulations with a large volume. In our study, we apply the CARPool method to suppress the sample variance of AbacusSummit galaxy clustering with the assistance of FastPM simulations. For the paired FastPM with the same initial conditions from AbacusSummit, we apply the halo occupation distribution model to obtain the galaxy number density and two-point clustering well matched to those of AbacusSummit. For both luminous red galaxies and emission line galaxies of AbacusSummit, we obtain a significant reduction factor on the sample variance. Therefore, our study can be substantial for a tighter constraint on the systematics of BAO and RSD models for the DESI survey.

Speaker: Zhejie Ding (Shanghai Jiao Tong University)

S3-4-Ding Zhejie.pdf

3:20 PM Accurate Kappa Reconstruction Algorithm for masked shear catalog (AKRA) Algorithm

Weak gravitational lensing is an invaluable tool for understanding fundamental cosmological physics.
In this study, we introduce the Accurate Kappa Reconstruction Algorithm for masked shear catalog (AKRA), a novel approach that overcomes the limitations in traditional methods and significantly improves the accuracy of the reconstructions. Using simulated experiments, we demonstrate that the AKRA method outperforms traditional methods across a range of masks, achieving high-quality reconstructions in both well-sampled and partially masked regions. Moreover, our results show that the AKRA method substantially reduces errors in power spectrum estimation and cross correlation coefficient compared to the widely-used Kaiser Squire (KS) method.
We also investigate the impact of mask shape and pixel ratio on reconstruction quality and find that increasing the masked pixel ratio does not compromise the reconstruction quality when the ratio is below 50%.
This study emphasizes the importance of accurate and reliable weak gravitational lensing convergence map reconstruction techniques and provides valuable insights for upcoming surveys.

Speaker: Yuan Shi (SJTU)

S3-5-SHI Yuan.pdf

3:35 PM → 4:05 PM coffee break

4:05 PM → 5:05 PM Cosmology: probes

Convener: Yu Yu (SJTU)

4:05 PM Statistics of thermal gas pressure as a probe of cosmology and galaxy formation

The statistics of thermal gas pressure are a new and promising probe of cosmology and astrophysics. The large-scale cross-correlation between galaxies and the thermal Sunyaev-Zeldovich effect gives the bias-weighted mean electron pressure, $\langle b_\mathrm{h}P_e\rangle$. In this paper, we show that $\langle b_\mathrm{h}P_e\rangle$ is sensitive to the amplitude of fluctuations in matter density, for example $\langle b_\mathrm{h}P_e\rangle\propto \left(\sigma_8\Omega_\mathrm{m}^{0.81}h^{0.67}\right)^{3.15}$ at redshift $z=0$.
We find that at $z<0.5$ the observed $\langle b_\mathrm{h}P_e\rangle$ is smaller than that predicted by the state-of-the-art hydrodynamical simulations of galaxy formation, MillenniumTNG, by a factor of $0.93$.
%We find that state-of-the-art hydrodynamical simulations of galaxy formation, \emph{Magneticum} and MillenniumTNG, predict a larger $\langle b_\mathrm{h}P_e\rangle$ than that observed at $z<0.5$ by a factor of $1.05$.
This can be explained by a lower value of $\sigma_8$ and $\Omega_\mathrm{m}$, similar to the so-called ``$S_8$ tension'' seen in the gravitational lensing effect. The difference between \emph{Magneticum} and MillenniumTNG at $z<2$ is small, indicating that the difference in the galaxy formation models used by these simulations has little impact on $\langle b_\mathrm{h}P_e\rangle$ at this redshift range. At higher $z$, we find that both simulations are in a modest tension with the existing upper bounds on $\langle b_\mathrm{h}P_e\rangle$. We also find a significant difference between these simulations, which we attribute to the difference in the galaxy formation models. Therefore, more precise measurements of $\langle b_\mathrm{h}P_e\rangle$ at $z>2$ will provide a new test of our understanding of galaxy formation, and those at $z<2$ will be a powerful probe of cosmology.

Speaker: Ziyang Chen (SJTU)

S4-1-CHEN Ziyang.pdf

4:20 PM synergy of RSD and kSZ effects

I will talk about the synergy between the RSD and kSZ effects on detecting the cosmic growth history and gas contents within dark matter halos, for the next generation of LSS and CMB surveys.

Speaker: Yi Zheng (SYSU)

S4-2-ZHENG Yi.pdf

4:35 PM Estimation of line-of-sight velocities of individual galaxies using neural networks I. Modelling redshift space distortion at large scales

Line-of-sight velocity disturbs the observed spatial positions of galaxies, thereby introducing anisotropies in their observed distribution, which is known as redshift space distortions (RSD). This complication inevitably affects the accurate extraction of important feature of the density field, such as baryonic acoustic oscillations (BAO). In this work, we propose a new scheme based on artificial neural networks (ANN), to directly estimate the line-of-sight velocities of individual galaxies from an observed redshift space galaxy distribution. By training the network with environmental characteristics surrounding each galaxy in redshift space, our ANN model can recover the line-of-sight velocity of each individual galaxy accurately. When using this velocity to eliminate the RSD effect, the two-point correlation function (TPCF) in real space can be recovered with better than 1% accuracy at $s$ > 8 $h^{-1}\mathrm{Mpc}$, with only 4% deviation over all scales compared to the ground truth. The real-space power spectrum can be recovered with better than 3% deviation on $k$< 0.5 $\mathrm{Mpc}^{-1}h$, and less than 5% for all $k$-modes. The quadrupole moment of the TPCF or power spectrum is almost zero down to $s$ = 10 $h^{-1}\mathrm{Mpc}$ or all $k$-modes, in excellent agreement with the expected results in the real space, which demonstrates an efficient correction of the spatial anisotropy introduced by the RSD effect. Although our ANN is trained using simulation data with one cosmological model, tests with other cosmological models indicate a weak cosmology dependency. Our scheme offers a novel avenue to predict the peculiar velocity of galaxies, to eliminate the RSD effect directly in future large galaxy surveys, and to reconstruct the 3-D cosmic velocity field accurately.

Speaker: Hongxiang Chen (NAOC)

S4-3-CHEN Hongxiang.pdf

4:50 PM Photometric BAO reconstruction

The reconstruction technique has been widely used to improve the BAO measurement in spectroscopic survey data. In this work, we explore reconstruction of the BAO signals in photometric data. We generalize the standard Zel’dovich reconstruction technique to study the transverse BAO reconstruction in the presence of photo-z uncertainties. The performance of the BAO reconstruction is checked with N-body simulations. We find that for dense enough sample, the transverse BAO reconstruction can improve the BAO signals in photometric data. The method can be easily adapted for application in survey data.

Speaker: Kwan Chuen Chan (Sun-Yat Sen University)

Friday, November 3

9:00 AM → 10:15 AM Cosmology: simulations

Convener: Yin Li

9:00 AM ELUCID - Exploring the Local Universe with reConstructed Initial Density field

I will introduce our series of works related to the ELUCID project that reconstructs the initial condition of the local Universe and studies large-scale structures and galaxy formation using constrained simulations. I will first briefly review the reconstruction methods developed in the literature. Then, I will introduce our own method in detail. After that, I will introduce several works using constrained simulations and multi-band observational data to investigate galaxy quenching, galaxy clustering, cosmic variance, IGM/ICM, and galaxy formation models.

Speaker: Huiyuan Wang (USTC)

9:25 AM The CAMELS project

I will present and describe the CAMELS project, whose aim is to build bridges between cosmology and galaxy formation by combining numerical simulations and machine learning. Containing a set of more than 10,000 simulations, both N-body and state-of-the-art hydrodynamic simulations, it is currently the largest dataset of cosmological simulations designed to train artificial intelligence algorithms. I will present some of the results the CAMELS collaboration has obtained recently, such as the finding of a universal relation in subhalo properties, how neural networks can extract cosmological information while marginalizing over baryonic effects at the field level, the first constraints on the mass of the Milky Way and Andromeda from AI, and the prospects of doing cosmology with individual galaxies. I will conclude by presenting a potential strategy the scientific community may pursue to extract the maximum amount of information from cosmological surveys, highlighting the multiple challenges associated with it.

Speaker: Francisco Villaescusa-Navarro

S1-2-VILLAESCUSA-NAVARRO.pdf

9:50 AM How cosmology influences baryonic feedback: lessons from FLAMINGO

The large-scale distribution of matter is influenced both by cosmology and by astrophysical processes, such as feedback from active galactic nuclei (AGN), which themselves are not independent of cosmology. This coupling gives rise to non-factorizable corrections to matter power spectrum, which will affect the cosmological interpretation of upcoming weak lensing surveys, such as Euclid and LSST. We will present a model for the non-factorizable corrections, based on a new suite of cosmological hydrodynamical simulations called FLAMINGO. The model explains the dependence of AGN feedback on cosmology in terms of a single parameter that controls the balance between the accumulation of gas by central supermassive black holes and the gravitational binding energy of halos that counteracts large-scale outflows driven by AGN. We find that baryonic feedback is stronger when combined with a mechanism to suppress structure formation, which may help address the present tension between cosmic microwave background and large-scale structure measurements of S_8.

Speaker: Willem Elbers (Durham)

S1-3-ELBERS Willem.pdf

10:15 AM → 10:45 AM coffee break

10:45 AM → 12:10 PM Cosmology: Measurements & Detections

Convener: Jun Zhang (Shanghai Jiao Tong University)

10:45 AM HSC Year 3 Weak Lensing Cosmology Results

The accelerating expansion of the universe is one of the most mysterious phenomena. Cosmic acceleration implies the existence of dark energy or the breakdown of Einstein’s general relativity. Either way, revealing the source of cosmic acceleration can result in a paradigm shift in modern physics. Weak gravitational lensing is a subtle, coherent distortion of distant galaxy images due to gravitational potential, allowing the direct measurement of the spatial distribution of dark matter. Weak lensing is one of the most powerful cosmological probes because of its capability to measure the nature of cosmic acceleration through the evolution of the large-scale structure of the universe. Hyper Suprime-Cam (HSC), a newly developed prime focus camera at Subaru Telescope, started a wide, deep galaxy imaging survey in 2014, covering 1,100 sq. degrees of the sky down to the i-band limiting magnitude of 26. The wide field of view, light-gathering power, and superb image quality of HSC make it possible to measure weak lensing distortions with unprecedented precision. In this talk, I will present cosmology results from the Subaru Hyper Suprime-Cam Survey Year 3 data, mainly about cosmological constraints from cosmic shear and the combination of galaxy-galaxy lensing and clustering.

Speaker: Hironao Miyatake (Nagoya University)

S2-1-MIYATAKE Hironao.pdf

11:10 AM Galaxy clustering at small scale and measurement of structure growth

The spatial distribution of galaxies contains a significant amount of information of the underlying cosmology. However, fully extracting this information can be challenging, especially at small scale due to the non-linearity of the dark matter dynamics, as well as the complicated physics of galaxy formation and evolution. I will introduce the emulator approach in the modeling of galaxy large scale structure and focus on non-linear scale using high resolution N-body simulations. I will also introduce the latest result from the application to the data of massive galaxies from BOSS and eBOSS survey. The analysis reports a tight constraint on the linear growth rate with some tension with other experiments. I will show follow-up works and extensions from both observational side and modeling side.

Speaker: Zhongxu Zhai (Shanghai Jiao Tong University)

S2-2-ZHAI Zhongxu.pdf

11:30 AM Tomographic Alcock-Paczyński Test with Redshift-space Correlation Function: Evidence for the Dark Energy Equation-of-state Parameter w > -1

The apparent shape of galaxy clustering depends on the adopted cosmology used to convert observed redshift to comoving distance, the r(z) relation, as it changes the line elements along and across the line of sight differently. The Alcock-Paczyński (AP) test exploits this property to constrain the expansion history of the universe. We present an extensive review of past studies on the AP test. We adopt an extended AP test method introduced by Park et al., which uses the full shape of redshift-space two-point correlation function (CF) as the standard shape, and apply it to the Sloan Digital Sky Survey DR7, BOSS, and eBOSS LRG samples covering the redshift range up to z = 0.8. We calibrate the test against the nonlinear cosmology-dependent systematic evolution of the CF shape using Multiverse simulations. We focus on examining whether or not the flat Lambda cold dark matter (ΛCDM) concordance model is consistent with observation. We constrain the flat wCDM model to have $w=−0.892^{+0.045}_{−0.050}$ and $\Omega_m=0.282^{+0.024}_{−0.023}$ from our AP test alone, which is significantly tighter than the constraints from the BAO or SNe Ia methods by a factor of 3-6. When the AP test result is combined with the recent BAO and SNe Ia results, we obtain $w=−0.903^{+0.023}_{−0.023}$ and $\Omega_m=0.285^{+0.014}_{−0.009}$. This puts a strong tension with the flat ΛCDM model with $w = -1$ at the 4.2$\sigma$ level. Consistency with $w = -1$ is obtained only when the Planck cosmic microwave background (CMB) observation is combined. It remains to be seen whether this tension between observations of galaxy distribution at low redshifts and CMB anisotropy at the decoupling epoch becomes greater in future studies and leads us to a new paradigm of cosmology.

Speaker: Dr Fuyu Dong (SWIFAR/Yunnan University)

S2-3-DONG Fuyu.pdf

11:55 AM Detection of pairwise kSZ effect with DESI galaxy clusters and Planck in Fourier space

We report a $\sim5.8\sigma$ detection of the kinetic Sunyaev–Zel’dovich (kSZ) effect in Fourier space, by combining the DESI galaxy clusters and the Planck data. We use the density-weighted pairwise kSZ power spectrum as the summary statistic, and the detailed procedure of the measurement is presented in this paper. Selected by a varying lower mass threshold $M_{\rm th}$, the galaxy cluster catalogs with different median masses ($\tilde{M}$) are constructed from the DR9 data of the DESI Legacy Imaging Surveys. $\tilde{M}$ spans a wide range of $\sim10^{13}-10^{14}{\rm M}_\odot/h$ and the heaviest $\tilde{M}\sim10^{14} {\rm M}_\odot/h$ is larger than those of most other kSZ detections. When the aperture photometric filter radius $\theta_{\rm AP}$ is set to be $4.2$ arcmin, the $\tilde{M}=1.75\times10^{13}{\rm M}_\odot/h$ cluster sample at the median redshift $\tilde{z}=0.64$ has the highest kSZ detection ${\rm S/N}=5.8$. By fitting $\bar{\tau}$s from various samples against their $\tilde{M}$s, we obtain a linear $\log\bar{\tau}-\log \tilde{M}$ relation: $\log\bar{\tau} = \gamma(\log \tilde{M}-14)+\log\alpha$, in which $\gamma=0.95\pm0.08$. We also vary the aperture photometric filter radius and measure the $\bar{\tau}$ profiles of cluster samples, whose constraints on the baryon distribution within and around dark matter halos will be discussed in a companion paper.

Speaker: Shaohong Li (SYSU)

S2-4-LI Shaohong.pdf

2:00 PM → 3:15 PM Cosmology: systematics & tensions

Convener: Zhongxu Zhai (Shanghai Jiao Tong University)

2:00 PM Prior effects and the cosmological tensions

With the newest cosmological observations there was an increase in the precision that we measure cosmological parameters. This new precision also led to the emergence of discrepancies in different measurements of these parameters, the so-called cosmological tensions. These could hint systematic effects or new physics. Also, with this increase in precision comes an inflation in the number of nuisance parameters that enter the statistical analysis leading to possible marginalization or prior volume effects in standard MCMC statistical cosmological analysis that influence the resulting cosmological parameters inferred. In this talk, I will show a few instances where this volume effects are relevant. I will give particular attention to the case of the early dark energy, in the context of the Hubble tension, where we use the marginalization free method, the profile likelihood, to show that these effects are relevant. I finalize by pointing out that this effect needs to be taken into consideration in current and future parameter inference analysis since they are particularly important for the cosmological tensions.

Speaker: Elisa Gouvea Mauricio Ferreira (Kavli Institute for the Physics and Mathematics of the Universe)

S3-1-FERREIRA Elisa.pdf

2:25 PM Cosmological Analysis of the Future CSST Survey Data Using the Tomographic AP Method

As the stage-IV surveys are beginning, we need to make good preparations for data analysis. The "tomographic Alcock-Pacyznski method" is a unique analysis method that can explore smaller clustering scales. When applied to the SDSS survey, it successfully improved the probing precision of dark energy, the Hubble constant, and neutrino masses parameters by 30-100%. In this talk, I will present our ongoing research aimed at improving the analysis strategy: (1) Adopting statistics beyond standard two-point correlation to enhance the statistical power; (2) Employing data dimension reduction algorithms to compress statistics and alleviate the difficulties of covariance estimation; (3) Examining the cosmology dependencies of the RSDs, and studying the systematics induced by the redshift errors in the CSST survey. Our goal is to ensure the successful application of this method in the stage-IV surveys, achieving better scientific outcomes in exploring the nature of dark energy and dark matter, resolving the Hubble constant tension problem, probing neutrino masses, and so on.

Speaker: Xiaodong Li (SYSU)

S3-2-LI Xiaodong.pdf

2:45 PM Is the large-scale structure traced by the BOSS LOWZ galaxies consistent with Planck?

Recently, several studies reported a significant discrepancy between
the clustering and lensing of the Baryon Oscillation Spectroscopic
Survey (BOSS) galaxies in the Planck cosmology. We construct a
simple yet powerful model based on the linear theory to assess whether
this discrepancy points toward deviations from Planck. Focusing
on scales $10{<}R{<}30\,h^{-1}\mathrm{Mpc}$, we model the amplitudes of
clustering and lensing of BOSS LOWZ galaxies using three parameters:
galaxy bias $b_\mathrm{g}$, galaxy-matter cross-correlation coefficient
$r_\mathrm{gm}$, and $A$, defined as the ratio between the true and
Planck values of $\sigma_8$. Using the cross-correlation matrix
as a diagnostic, we detect systematic uncertainties that drive spurious
correlations among the low-mass galaxies. After building a clean LOWZ
sample with $r_\mathrm{gm}{\sim}1$, we derive a joint constraint of
$b_\mathrm{g}$ and $A$ from clustering+lensing, yielding
$b_\mathrm{g}{=}2.47_{-0.30}^{+0.36}$ and $A{=}0.81_{-0.09}^{+0.10}$,
i.e., a $2\sigma$ tension with Planck. However, due to the strong
degeneracy between $b_\mathrm{g}$ and $A$, systematic uncertainties in
$b_\mathrm{g}$ could masquerade as a tension with $A{=}1$. To ascertain
this possibility, we develop a new method to measure $b_\mathrm{g}$
from the cluster-galaxy cross-correlation and cluster weak lensing
using an overlapping cluster sample. By applying the independent bias
measurement ($b_\mathrm{g}{=}1.76{\pm}0.22$) as a prior, we
successfully break the degeneracy and derive stringent constraints of
$b_\mathrm{g}{=}2.02_{-0.15}^{+0.16}$ and $A{=}0.96{\pm}{0.07}$.
Therefore, our result suggests that the large-scale clustering and
lensing of LOWZ galaxies are consistent with Planck, while the
different bias estimates may be related to some observational
systematics that needs to be mitigated in future surveys.

Speaker: Zhiwei Shao (Shanghai Jiao Tong University)

S3-3-SHAO Zhiwei.pdf

3:00 PM Towards precision cosmology ---- systematics removal with Stage III data

Precision cosmology is a very important target for the coming Stage IV weak lensing studies. It is also hard to achieve due to multiple systematical errors. In this talk we present systematics mitigation performed in 2 published papers and some ongoing works. More specifically, we present intrinsic alignment mitigation with KiDS data, and shear bias removal as well as redshift error measurements with DECaLS data and Obiwan image simulation. With the experience on the calibrations with current Stage III data, we forecast the requirements for CSST systematics control, which will guide our calibration process in the future.

Speaker: Ji Yao (Shanghai Astronomical Observatory)

S3-4-YAO Ji.pdf

3:15 PM → 3:35 PM Conference summary