Collaboration Workshop on Cosmology and Galaxy Formation
3rd floor meeting room
SJTU & Suzhou Bay
This is a largely invitation-based domestic workshop combining science talks with plenty of interactions to share progresses and foster collaborations.
Registration is free of charge. The participant will pay for his/her own accommodation.
New: Click here to download the workshop announcement: 会议通知下载
Please follow the menus on the left or below to register and submit abstracts. The number of participants is limited to ~100.
| Evening, 18th/Sunday | Reception at 白金汉爵酒店 |
| Day 1 & 2: | Talks at SJTU, Room 300 |
| Afternoon, Day 2: | Transfer to Suzhou Bay by shuttle |
| Day 3-5: | Talks at 恒力酒店, 5-8 Meeting room, 3rd floor |
| 2p.m., Day 5 (19/June): | Departure/Transfer to SJTU |
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Opening Remarks 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU-
1
Opening RemarksSpeaker: Xiaohu Yang (上海交通大学)
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1
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Survey 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: Xiaohu Yang (上海交通大学)-
2
Galaxy simulation for the High Latitude Spectroscopic Survey on the Nancy Grace Roman Space Telescope 3rd floor meeting room
3rd floor meeting room
SJTU
Nancy Grace Roman space telescope will conduct a High Latitude Spectroscopic Survey (HLSS) over 2000 square degrees at high redshift. I will introduce the flowdown of the Roman science objectives of galaxy and cosmology based on numerical simulations. With this reference model, we forecast the performance of the survey, including the galaxy type, number density, clustering property and measurement of the expansion history and structure growth history. It also enables an exploration of variation from the fiducial survey design, such as survey area, depth, completeness and purity for large scale structure analysis.
Speaker: Zhongxu Zhai (Shanghai Jiao Tong University) -
3
面向下一代大尺度巡天的超级数值模拟 3rd floor meeting room
3rd floor meeting room
SJTU
介绍面向下一代大尺度巡天建立的4万亿粒子的数值模拟，以及在此基础上建立的数值模拟星表
Speaker: Qiao Wang (NAOC) -
4
DESI Legacy Imaging Surveys Data Release 9: Cosmological Constraints from Galaxy Clustering and Weak Lensing using the Minimal Bias Model
We constrain cosmological parameters Ωm and σ8 from a joint analysis of galaxy clustering and galaxy-galaxy lensing from DESI Legacy Imaging Surveys Data Release 9 (DR9), covering approximately 10000 square degrees and spanning the redshift range of 0.1 to 0.9. In order to study the cosmological parameters dependence on redshift, we divide the galaxies into seven volume-limited lens samples, each with an equal width in photometric redshift. To retrieve the intrinsic projected correlation function wp(rp), we employ a novel method to account for redshift uncertainties. Additionally, we measure the galaxy-galaxy weak lensing signal ∆Σ(rp) for each lens sample, using source galaxies selected from the shear catalog by applying our Fourier Quad pipeline to DR9 images. We model these observables within the flat ΛCDM framework, employing the minimal bias model. To ensure the reliability of the minimal bias model, we apply conservative scale cuts: rp > 8 and 12 h−1Mpc, for wp(rp) and ∆Σ(rp), respectively. With an abundance of lens and source galaxies, our constraints on the derived parameter S 8 ≡ σ8√Ωm/0.3 at low redshift achieve a comparable level of tightness as those obtained from Planck CMB or 3×2pt analysis. Our findings suggest a mild tendency that S8 increases with lens redshift, although this trend is only marginally significant. When we combine non-overlapping samples, the value of S 8 is determined to be 0.85 ± 0.02, consistent with the results from Planck but higher than the 3×2pt analysis at approximately a 2σ level. Although several improvements in measurements and modeling could enhance the accuracy of our final constraints, the general agreement with canonical values demonstrates the potential of our work for future precise and accurate cosmology.
Speaker: 浩杰 许 (上海天文台) -
5
The role of environment in the formation of optically red spiral galaxies 3rd floor meeting room
3rd floor meeting room
SJTU
To understand the formation of massive red spirals, we select optically red spirals with $M_{*}> 10^{10.5} M_{☉}$ based on the u-r color-stellar mass diagram from SDSS DR7 and compared the environment of these spirals with different NUV-r colors. All optically red galaxies have similar properties in the center, i.e., no star formation activity, similar bulge size, central velocity dispersion and star formation history. While most NUV-r blue spirals have odd morphologies, i.e., ring, shell or tidal disruption, and have more NUV flux at 1-2 R$_e$ than NUV-r red spirals. Meanwhile, NUV-r blue spirals have larger disks and higher HI fraction. These suggest star-forming activity due to the disruption of gas in the outer parts of NUV-r blue spirals. The gas disruption may originate from the environment. About half of the NUV-r red spirals are satellites, while ~85% NUV-r blue galaxies are central or isolated galaxies. This implies that NUV-r red spirals may be more susceptible to the environment to lose their gas and quenched. While NUV-r blue galaxies would possess more gas and be triggered star formation in the outskirts due to disruption or interaction.
Speaker: Rui Guo
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2
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10:30 AM
Coffee Break 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU -
Cosmology 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: Pengjie Zhang (Shanghai Jiao Tong University)-
6
Measurement of the BAO with projected three-dimensional correlation function on DES Y3 data
We develop a new statistic, the projected three-dimensional correlation function, for the clustering analysis of the imaging galaxy survey data. This method can retain some of the radial information that is lost in conventional tomographic angular correlation analysis. As it is not strongly correlated with the angular correlation results, it can also provide important crosscheck. We have applied our methodology to the Dark Energy Survey first-three years data to measure the Baryonic Acoustic Oscillations. The sample consists of about 7 million galaxies in the redshift range 0.6 < z_p < 1.1 over a footprint of 4108 deg^2. Using the full sample, D_M / r_s is constrained to be 19.15 +- 0.58 at z_eff = 0.835. This constraint is consistent with the angular correlation function result.
Speaker: Kwan Chuen Chan (Sun-Yat Sen University) -
7
The optimal BAO reconstruction for DESI Y1-KP4
Dark Energy Spectroscopic Instrument (DESI) is the first on-going Stage IV spectroscopic redshift survey, covering a wide sky area and redshift range. As one of the key goals, DESI will measure the Baryon Acoustic Oscillations (BAO) from different tracers, including BGS, LRG, ELG and QSO at different redshifts. The density field reconstruction is significantly important to reduce the systematics and to improve the precision for the BAO scale measurement. To support the DESI key project on BAO, we study the optimal reconstruction schemes for different DESI tracers. We utilize the first generation of DESI mocks which are based on the AbacusSummit simulation and calibrated from the SV3 DESI data. Based on the realistic mocks, we perform the standard BAO reconstruction using two reconstruction algorithms, i.e. MultiGrid and IterativeFFT, which are implemented in the DESI package pyrecon. For each algorithm, we study the case which removes or contains the redshift space distortion in the reconstructed field, respectively. Varying the density smoothing parameter, we study the systematic influence in detail on the propagator, the reconstructed power spectrum and correlation function, as well as the BAO scale parameters. Our work contributes significantly to the DESI pipeline for the BAO measurement. In my talk, I will mainly show the reconstruction for LRG.
Speaker: Zhejie Ding (Shanghai Jiao Tong University) -
8
Map Reconstruction of radio observations with Conditional Invertible Neural Networks
In radio astronomy, reconstructing a sky map from time ordered data (TOD) is an inverse problem. Map-making techniques and gridding algorithms are commonly used, but they have limitations such as computational inefficiency, numerical instability, and an inability to remove beam effects. To address these issues, this study proposes a novel solution using the conditional invertible neural network (cINN) for efficient sky map reconstruction. By training the neural network with forward modeling, it can accurately reconstruct sky maps from simulated TODs. Using FAST as an example, cINN achieves remarkable performance. The reconstruction errors for each pixel can also be accurately quantified by sampling in the latent space of cINN.
Speaker: Le Zhang (中山大学) -
9
Removal of point source leakage from time-order data filtering
Time-ordered data (TOD) from ground-based CMB experiments is usually filtered before map-making to reduce the contamination from ground and atmospheric emissions. However, when the observation region contains strong point sources, the filtering process will cause a considerable leakage around the point sources, which should be eliminated to provide a clean CMB polarization map for scientific purposes. The method we introduce in this work, which we refer to as “template fitting”, is capable of removing these leakage signals in the pixel domain, meeting the requirement of measuring the primordial gravitational waves from CMB-B modes for at least r < 0.005, while also avoiding time-consuming operations on the TOD.
Speaker: Ms Zhaoxuan Zhang (Sun Yat-sen University)
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6
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12:05 PM
Lunch No 4 Canteen (SJTU)
No 4 Canteen
SJTU
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Dark Matter: structure 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: Houjun Mo (U. Mass.)-
10
Iterative mean-field approach to the spherical collapse of dark matter haloes
Gravitational collapse of dark matter overdensities leads to the formation of dark matter haloes which embed galaxies and galaxy clusters. An intriguing feature of dark matter haloes is that their density profiles closely follow a universal form irrespective of the initial condition or the corresponding growth history. This represents a class of dynamical systems with emergent universalities. 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.
Speaker: Xun Shi -
11
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) -
12
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. 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 on 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 with percent level accuracy for halo virial masses in the range of $10^{11.5}h^{-1}{\rm M}_{\odot}
Speaker: 义丰 周 (上海交通大学) -
13
On the formation process of dark matter deficient galaxies
Recent observations revealed that the dark matter mass contained in two ultra diffuse galaxies in the vicinity of an elliptical galaxy, NGC 1052, is several hundred times lower than the predictions by the theoretical models of galaxy formation and evolution. The dynamics of the galaxies is described by only the gravity of stars. As such dark matter deficient galaxies can be a challenge for the current understanding of galaxy formation and evolution, they have attracted attention from astrophysicists and have been investigated intensively. In this talk, we first consider a formation scenario that dark matter deficient galaxies might be a remnant of violent galaxy interactions. As dark matter is less tightly bound than stars, the gravity of NGC1052 preferentially strips the dark matter mass from a satellite galaxy, transforming a normal satellite galaxy into a dark matter deficient galaxy. Numerical simulations of the interaction between NGC1052 and a possible progenitor of dark matter deficient galaxies reproduce well key observations, such as the mass profile, the effective radius, and the distribution of globular clusters. Therefore, dark matter deficient galaxies can be a remnant of a violent mass-loss event and be explained within the standard framework of cosmic structure formation. We will also consider another scenario that dark matter deficient galaxies might have been originated from a collision of two gas-rich dwarf galaxies, and find that it has difficulties in explaining the extended distribution and number of globular clusters in the galaxies.
Speaker: Prof. Go Ogiya (Zhejiang University)
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10
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3:20 PM
Coffee Break 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU -
Dark Matter: nature 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: Xi Kang (zhejiang university)-
14
Modeling the formation of dark-matter deficient galaxies
Recent observations reported a puzzling dearth of dark matter (DM) in a fraction of massive high-z galaxies and dwarf galaxies, challenging current simulation predictions within the standard LCDM scenario. This discrepancy underscores our limited understanding of the driving forces behind the halo structural evolution, including feedback outflows, mergers, and tidal interaction. Here we introduce "CuspCore2", a novel analytic model providing the first unified and precise framework to trace the violent relaxation of a halo undergoing these processes. Using this model, we developed a scenario for DM-deficient cores in high-z massive galaxies via dynamical heating by infalling satellites followed by DM expansion in response to AGN-driven outflows. The same framework can generate DM-deficient dwarf galaxies through supernova feedback and tidal stripping. Given the universality of the violent relaxation process, our model promises extensive applications for general galactic dynamic problems.
Speaker: Zhaozhou Li -
15
Imprints of cosmic reionization as a probe of dark matter nature in the post-reionization era 3rd floor meeting room
3rd floor meeting room
SJTU
We propose a novel mechanism for constraining warm dark matter (WDM) models via the so-called “memory of reionization” effect, which is that gas in the intergalactic medium (IGM) after cosmic reionization can be affected significantly by inhomogeneous reionization of hydrogen. The suppression of small-scale structure due to WDM affects the evolution of post-reionization IGM, while thermal relics can couple to ionized bubbles at the scales of tens of Mpc. As such, the small-scale effect due to WDM can leave an imprint on the gas at large scales, which can be observed by Ly$\alpha$ forest. We forecast the accuracy of constraints on WDM using Ly$\alpha$ forest 3D power spectrum with DESI-like surveys, and demonstrate that this approach can provide an unprecedentedly tight constraint on WDM mass.
Speaker: Ms Yao Zhang (Tsinghua University) -
16
Model for Warm Dark Matter Subhalo Distribution 3rd floor meeting room
3rd floor meeting room
SJTU
The unified distribution model of cold dark matter (CDM) subhaloes is extended to the warm dark matter (WDM) case using a series of high-resolution N-body simulations with different WDM particle masses. 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 models. 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 suppressed at the low mass end due to the cut-off in the power spectrum. 2) WDM subhaloes are more vulnerable to tidal stripping and disruption due to their lower concentrations at accretion time. These differences result in a mass-dependent spatial distribution of WDM subhaloes which also depends on the WDM particle mass, while both dependences are well reproduced by our model.
Speaker: 飞鸿 何 (上海交通大学物理与天文学院天文系) -
17
A ~300 pc-sized core of Milky Way dark matter halo constrained from the OGLE micro-lensing sky map 3rd floor meeting room
3rd floor meeting room
SJTU
We report the detection of a 282 $^{+34}_{-31}$ pc-sized dark matter core structure in the center of Milky Way at $68\%$ confidence level by using the micro-lensing event rate sky map data from the Optical Gravitational Lensing Experiment (OGLE) survey. For the first time, we apply the spacial information of the micro-lensing sky map and model it with the detailed Milky Way Dark Matter halo structure, the Mini Dark Matter Structure (MDMS) fraction ($f_{\rm MDMS}=\Omega_{\rm MDMS}/\Omega_{\rm DM}$) and the core size.
We find that this sky map can constrain both $f_{\rm MDMS}$ and the core size simultaneously without strong degeneracy while fully considering mass function of stellar components.
This discovery provides not only guidance for dark matter particle models, such as self-interacting dark matter (SIDM), but also the baryonic physics of Milky Way.Speaker: Dr Wentao Luo (DSEL/USTC)
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14
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Galaxy: evolution 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: Yingjie Peng (KIAA, Peking University)-
18
探索研究未发育完全的L*星系
观测以及Lambda冷暗物质模型框架下的标准星系演化模型都表明星系的恒星质量与其暗物质晕质量之间密切相关：红移0处，在Lstar星系（即质量约为5x10^11太阳质量）的暗物质晕中，恒星-暗物质晕质量比达到最高（~1%-5%）。然而，最近对星系团中超弥散星系UDG的研究表明近邻宇宙中可能存在一类维里质量与Lstar星系相当，但恒星-暗物质质量比极低的星系族群，这类特殊星系又被称为未发育完全的Lstar星系（FLG）。我们通过HI动力学的方法，首次寻找到了一批高置信度的FLG星系候选体，其有着极低的恒星质量（10^7-10^9太阳质量）、巨大的暗物质晕（>5x10^11太阳质量）、以及极低的恒星-暗物质质量比（<0.1%）。FLG星系的发现否定了修正牛顿动力学（MOND）理论。此外我们还发现50%的FLG候选者位于由星系团或星系群引力主导的区域，其热气体可能在早期宇宙中受到潮汐或冲压的作用而剥离，导致随后的恒星形成停滞。然而，50%候选者栖息在低密度环境中，不受冲压或潮汐的影响，这些孤立FLG在当今的大型宇宙学流体模拟中并不存在。这表明孤立FLG的存在对标准星系形成模型尤其是AGN反馈方面构成了严峻的挑战，这一结果可能表明在早期宇宙中星系内部可能存在比现有理论更强的反馈机制来阻止这些孤立系统中后续的恒星形成。我们后续对FLG的研究将可能揭示目前尚未全面理解的早期宇宙中星系演化、AGN反馈方面的新规律，这对我们更加完备地理解星系宇宙学有重要的意义，同时也是JWST等新一代望远镜的重要研究方向。
Speaker: Prof. 昱 容 (中国科学技术大学物理学院天文学系) -
19
Observational connections between galaxies and structures at cosmic noon
We carried out a program to identify extremely overdense structures at z~2-3 and investigate connections between galaxy and structure formation. The two very massive structures at z=2.24 are mapped with Ha emission-line galaxies, SMGs and LAEs, and exhibit astonishing features unseen before. In this talk we introduce these finding about different galaxy populations in connections with the structure formation.
Speaker: xianzhong zheng (Purple Mountain Observatory) -
20
Structure evolution in protoclusters at z=2-3
Characterizing the structural properties of galaxies in high-redshift protoclusters is key to our understanding of the environmental effects on galaxy evolution in the early stages of galaxy and structure formation. We assess the structural properties of H$\alpha$ emission-line candidates (HAEs) in the densest regions of massive protoclusters at z=2-3, using HST $H$-band imaging data. Our results show the pair fraction of protocluster galaxies yields to higher merger rate for massive HAEs with $\log (M_\ast/{\rm M}_\odot) \ge 10.3$, compared with field galaxies at the same epoch. Meanwhile, we note that the half-light radii and Sersic indices for protocluster HAEs cover a broader range than field star-forming galaxies, suggesting that the high galaxy density and cold dynamical state (i.e., velocity dispersion) are key factors that drive galaxy mergers and promote structural evolution in protoclusters. Our findings also indicate that both the local environment (on group scales) and the global environment play essential roles in shaping galaxy morphologies in protoclusters. This is evident in the systematic differences observed in the structural properties of galaxies among different protoclusters.
Speaker: Shuang Liu (Purple Mountain Observatory, CAS) -
21
Dynamical hotness, star formation quenching and growth of supermassive black holes
A stellar system is dynamically hot when its kinetic energy is dominated by random motion represented by the velocity dispersion $\sigma_{hot}$. We use MaNGA data to obtain inner and outer dispersion of a galaxy, $\sigma_{in}$ and $\sigma_{out}$, to characterize its dynamical status and study its connection with star-formation quenching and the growth of supermassive black hole(SMBH). We divide galaxies into fully quenched (FQGs), partially quenched (PQGs) and fully star-forming (FSGs) populations, and identify quenched central cores (QCCs) in PQGs. The galaxy distribution in $\sigma_{in}/\sigma_{hot}$-$\sigma_{out}/\sigma_{hot}$ diagram is L-shaped, consisting of a horizontal sequence ($\sigma_{out}/\sigma_{hot}\sim0$) and a vertical sequence ($\sigma_{in}/\sigma_{hot}\sim1$). FQGs and QCCs are located at the top of the vertical sequence, $\sigma_{out}/\sigma_{hot}\sim1$, and are thus dynamically hot over their entire bodies. PQGs reside along the vertical sequence, so they have hot center but cold outskirt. FSGs are diverse and can be found in both sequences. Galaxy structural properties, star formation and AGN activities make a transition along the horizontal sequence at $\sigma_{in}/\sigma_{hot}\sim 0.5$, and along the vertical sequence at $\sigma_{out}/\sigma_{hot}\sim 0.5$. The fractions of optical AGNs and barred galaxies increase rapidly in the first transition and decline rapidly in the second; radio galaxies are located at the top of the vertical sequence. Our results demonstrate that star formation quenching and SMBH growth are effective only in dynamically hot systems. A simple model along this line can reproduce the observed SMBH scaling relations. We discuss how secular processes and strong interactions can make a system dynamically hot, and lead to the SMBH growth and
star-formation quenching.Speaker: Ms 慧 洪 (中国科学技术大学)
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18
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10:20 AM
Coffee Break 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU -
Galaxy: structure 3rd floor meeting room (SJTU)
3rd floor meeting room
SJTU
Convener: xianzhong zheng (Purple Mountain Observatory)-
22
Dissecting the Baryon Cycle and ISM Properties with JWST NIRISS and NIRSpec Spectroscopy
Using state-of-the-art analysis methods, we reduce the new NIRISS wide-field grism data and NIRSpec multi-object spectroscopic (MOS) data. The cross calibration of two complementary spectroscopic modes opens up new key window on unbiased investigation of star formation, feedback, and ISM properties in and beyond the cosmic noon epoch. We bring forth the first spatially resolved analysis of high-redshift galaxies with JWST grism instruments and measure the first gas-phase metallicity radial gradient with sub-kpc resolution at z≥3. Using the NIRSpec MOS data in high-resolution gratings, we compile a large sample of galaxies at z~0-7 whose [S ii] λ6732/[S ii]λ6718 and [O ii]λ3726/[O ii]λ3729 line doublets are well resolved to shed light upon their ISM electron density and ionization properties. The exquisite sensitivity and wavelength coverage of the NIRSpec spectroscopy in prism mode gives us an excellent chance to identify unique spectral features in galaxies in the epoch of reionization. We discover the highest redshift galaxy, spectroscopically confirmed at z=8.1623, with PopIII-like stellar populations. This galaxy candidate hosting the first generation stars opens up new key frontiers on galaxy evolution and stellar physics in the early Universe.
Speaker: 鑫 王 -
23
Semi-Analytic Catalog For CSST With Emission Lines
In anticipation of the upcoming deployment of the Chinese Space Station Telescope (CSST), 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.
Speaker: 文祥 裴 (国家天文台) -
24
The Chocolate Chip Cookie Model: Dust Geometry of Disk Galaxies
We present a new two-component dust geometry model of disk galaxies, the Chocolate Chip Cookie (CCC) model, where the clumpy nebular regions are embedded in a diffuse stellar/interstellar medium disk, like chocolate chips in a cookie. Our model solves the dust attenuation process for both the emission lines and stellar continua via analytical approaches, which successfully fits the inclination dependence of both the effective dust reddening of the stellar components and that of the emission lines characterized by the Balmer decrement. In CCC model, the dust attenuation curve of the stellar population naturally depends on the inclination, and its median case is consistent with the classical Calzetti law. Not only that, our model shows that the dust-to-gas ratio (DGR) of clumpy HII regions increases monotonically with the stellar mass of galaxies. At a given stellar mass, DGR shows a linear correlation with the gas-phase metallicity, which implies a constant dust-to-metal ratio of galaxies at a given stellar mass. Our CCC model provides a sophisticated framework of the galactic dust attenuation of disk galaxies, which can be applied in numerical simulations or semi-analytical models of galaxy formation and evolution.
Speaker: Mr 世银 沈 (上海天文台) -
25
The formation of exponential star-forming disk and the corresponding metal enrichment in the modified accretion disk framework
I will talk about the formation of exponential star-forming disk and the corresponding metal enrichment in the modified accretion disk (MAD) framework. The MAD is suggested by the recent simulations that coplanar gas inflow mainly provides the fuel of star formation. We treat the galactic gas disk as a simple gas-regulator system that the SFR is instantaneously determined by the gas content, which is regulated by the interplay between inflow, outflow and star formation. Based on this simple model, we can obtain the analytic solution of radial profile of the gas-phase metallicity, which well characterises the overall features of the observed ones. The negative gradient of gas-phase metallicity is a natural consequence of the radial inflow of cold gas which is continuously enriched by in-situ star formation. We also show that magnetic stresses from magneto-rotational instability are the most plausible source of the required viscosity that sustains the exponential star-forming disk.
Speaker: Enci Wang (USTC)
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22
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12:00 PM
Lunch & transport to Suzhou No 4 Canteen (SJTU)
No 4 Canteen
SJTU
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(sat)Galaxy-(sub)halo Conference room (Hengli Hotel)
Conference room
Hengli Hotel
Suzhou BayConvener: 慧元 王 (中国科学技术大学)-
26
Constructing the connection between dark matter halos and emission line galaxies (ELGs)
In ongoing and future cosmological surveys, such as DESI, PFS, Euclid, CSST, and WFIRST, ELGs are a critically major tracer to explore the acceleration of the cosmic expansion and to test modified gravity theories. To achieve the high-precision observations aimed by the surveys on the Hubble parameter, cosmic growth rate and neutrino mass etc, one needs to have an accurate understanding of the connection between ELGs and dark matter halos. Because of the complicated target selections both in color and in magnitude, the population of ELGs is expected to change significantly with redshift, which makes the parameters of HOD always changing with redshift. We propose a novel method (Gao et al; Paper I) to construct the relation. In this method, after the relation is established for galaxies in the whole population (i.e. normal galaxies), the ELGs can be obtained by a random selection based on the observed number density once the probability Psat of a satellite galaxy becoming an ELG is reasonably reduced. We have applied the method to DESI SV3 (or 1 Percent Sample) survey, and found it very successful. With only 7-parameters, we can accurately describe the clustering of ELGs both in real and redshift spaces at all redshift range (0.8<z<1.5; Gao et al. Paper II). We also demonstrate that galaxy conformity is necessary and easy to be implemented in the framework to accurately describe the small-scale clustering of ELGs in DESI SV3 (Gao et al, Paper III). Compared with HOD models in literature, our method has only a minimal set of parameters (8 when galaxy conformity is included), has clear physical meaning (Psat is reduced; galaxy conformity), is universal for all redshift range, and is accurate for describing clustering from 0.010 Mpc/h up to large scales.
Speaker: Yipeng Jing -
27
Photometric Objects Around Cosmic Webs (PAC) Delineated in a Spectroscopic Survey. VI. High Satellite Fraction of Quasars Around Galaxies at Redshift 0.8 - 1.0
The Photometric objects Around Cosmic webs (PAC) approach developed in \cite{2022ApJ...925...31X} has the advantage of making full use of the spectroscopic and deeper photometric surveys. With the merits of PAC, we can accurately measure quasars-galaxy cross-correlations at small scale down to $0.1\,h^{-1}{\rm{Mpc}}$ and at different stellar mass bins. We calculate the excess surface density $\bar{n}_2w_{{\rm{p}}}$ of photometric objects around quasars down to stellar mass $10^{10.80}\,M_{\odot}$ at redshift $0.8
Speaker: shanquan gui (Shanghai JiaoTong University) -
28
The measurements of galaxy abundance and clustering at 0<z<2
This work consists of two parts. The first is the study of the galaxy population in the SDSS galaxy groups with DESI imaging data. The second is the study on how to measure galaxy abundance and clustering at high redshift from incomplete spectroscopic data.
In the first part, we use the most recent data release (DR9) of the DESI legacy imaging survey and SDSS galaxy groups to measure the conditional luminosity function (CLF) for groups with halo mass $M_{\rm h}> 10^{12}M_{\odot}$ and $0.01< z< 0.08$, down to $M_{\rm r}=-10\sim-12$. For a given halo mass we measure the CLF for the total satellite population, as well as separately for the red and blue populations classified using the $(g-z)$ color. We find a clear faint-end upturn in the CLF of red satellites, with a slope $\alpha\approx-1.8$ which is almost independent of halo mass. Our stellar population synthesis modeling shows that the $(g-z)$ color provides a clean red/blue division, and that group galaxies in the red population defined by $(g-z)$ are all dominated by old stellar populations. The fraction of old galaxies as a function of galaxy luminosity shows a minimum at a luminosity $M_{\rm r}\sim-18$, corresponding to a stellar mass $M_\ast\sim10^{9.5}M_\odot$. This mass scale is independent of halo mass and is comparable to the characteristic luminosity at which galaxies show a dichotomy in surface brightness and size, suggesting that the dichotomy in the old fraction and in galaxy structure may have a common origin.
In the second part, we use the mock samples to study the influence of the selection effects in high redshift spectroscopic surveys on the measurements of galaxy abundance and clustering. We show that target selection and redshift incompleteness can lead to significantly biased results, especially due to the flux limit selection criteria, using realistic mock catalogs. We develop a new method to correct the flux limit effect, using information provided by the parent photometric data from which the spectroscopic sample is constructed. Our tests using realistic mock samples show that our methods are able to reproduce the true stellar mass function and correlation function reliably. Mock catalogs are constructed for the existing surveys zCOSMOS and VIPERS, as well as the forthcoming PFS galaxy evolution survey. The same set of mock samples are used to quantify the total variance expected for different sample sizes. We find that the total variance decreases very slowly when the survey area reach 4 deg$^2$ for abundance and 8 deg$^2$ for clustering, indicating that cosmic variance is no longer the dominant source of error for PFS-like surveys. The relative error in the PFS-like galaxy survey will be significantly smaller than the current zCOSMOS and VIPERS survey.
Speaker: 佳程 孟 (清华大学天文系)
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26
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10:05 AM
Coffee Break Hengli Hotel
Hengli Hotel
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(sat)Galaxy-(sub)halo Hengli Hotel
Hengli Hotel
Convener: Zhongxu Zhai (Shanghai Jiao Tong University)-
29
The spatial distribution of satellite galaxies
In the framework of the standard cosmological model, dark matter halos grow by hierarchical clumping. The spatial distribution of satellite galaxies is closely related to the nature of the halo and its accretion history. Firstly, using SDSS and Millennium simulations we study the spatial distribution of satellites in galaxy clusters. We find that the distribution of satellite galaxies is anisotropic, which is related to the host halo, large-scale structure and the anisotropic accretion history of satellites. Then, in SDSS, we find that the satellite galaxy pairs distributed on the opposite side of the primary galaxy, are more likely to have the same sign direction of motion, which means counter-rotating. We find Millennium and IllustrisTNG show discrepancies with the observations at 4.3𝜎 and 4.0𝜎, respectively. Finally, using the MaNGA integral field spectroscopic data and the SDSS galaxy group catalogue, we investigate the alignment between the angular momentum of the central galaxy and the orbital angular momentum of the satellite galaxy. We find a weak signal of alignment for the overall sample; an enhanced signal of alignment for red satellite galaxies in the intermediate-mass galaxy groups.
Speaker: 青 谷 (国家天文台) -
30
Mining the Information Content of Member Galaxies in Halo Mass Modeling
Motivated by previous findings that the magnitude gap between certain satellite galaxies and the central galaxy can be used to improve the estimation of halo mass, we carry out a systematic study of the information content of different member galaxies in the modeling of the host halo mass using a machine-learning approach. We employ data from the hydrodynamical simulation IllustrisTNG and train a random forest algorithm to predict a halo mass from the stellar masses of its member galaxies. Exhaustive feature selection is adopted to disentangle the importance of different galaxy members. We confirm that an additional satellite does improve the halo mass estimation compared to that estimated by the central alone. However, the magnitude of this improvement does not differ significantly using different satellite galaxies. When three galaxies are used in the halo mass prediction, the best combination is always that of the central galaxy with the most massive satellite and the smallest satellite. Furthermore, among the top seven galaxies, the combination of a central galaxy and two or three satellite galaxies gives a near-optimal estimation of halo mass, and further addition of galaxies does not raise the precision of the prediction. We demonstrate that these dependence can be understood from the shape variation of the conditional satellite distribution, with different member galaxies accounting for distinct halo-dependent features in different parts of the cumulative stellar mass function.
Speaker: 艳蕊 周 -
31
Measuring the conditional luminosity and stellar mass functions of galaxies by combining the DESI LS DR9, SV3 and Y1 data
In this investigation, we leverage the combination of DESI legacy imaging surveys DR9, survey vilification (sv3), and year 1 (Y1) spectroscopic redshift data to estimate the conditional luminosity and stellar mass functions (CLFs & CSMFs) of galaxies across various halo mass bins and redshift ranges, with the help of a realistic DESI mock galaxy redshift survey (MGRS) generated from a high-resolution Jiutian simulation, and utilizing the same halo-based group finder utilized in DESI observation. (1) Through a comparison of the $r$ and $z$-band luminosity functions (LFs) and stellar mass functions (SMFs) derived using both photometric and spectroscopic data, we uncover the significant impact of photoz errors on the faint-end slope of the galaxy LFs and SMFs at low redshift. There is a clear upturn in the LFs and SMFs below $10^{9} h^{-2}\rm L_\odot$ (or $h^{-2}\rm M_\odot$), with a slope that is in nice agreement with that of halo mass function at the low mass end. (2) By leveraging both the mock galaxy and mock group samples, and correcting the aforementioned photoz systematics, we obtain a set of CLF & CSMF measurements. We find at low redshift that the faint end slope of CLFs and CSMFs below $10^{9} h^{-2}\rm L_\odot$ (or $h^{-2}\rm M_\odot$) show nice agreement with that of the subhalo mass functions. These measurements have the potential to facilitate further investigations aimed at gaining a deeper understanding of the evolution of galaxies in dark matter halos.
Speaker: Yirong Wang (上海交通大学) -
32
MAHGIC: A model adapter for the halo-galaxy inter-connectionSpeaker: Yangyao Chen
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29
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11:50 AM
Lunch
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Tour to Kunshan Supercomputing Center
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Simulation & inference: constrained simulation Hengli Hotel
Hengli Hotel
Convener: Hong Guo (Shanghai Astronomical Observatory)-
33
Reconstructing and stacking, a promising way to study galaxy formation and evolution
I will present a review on how to use targets provided by galaxies, galaxy groups and reconstructed density field to study the cosmic web, galaxy formation and evolution.
Speaker: Prof. Houjun Mo (U. Mass.) -
34
Connection between SDSS galaxies and ELUCID subhalos 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 galaxy and halo or subhalo can be captured and reproduced efficiently. However, the galaxy formation and evolution in galaxy formation models may deviate from those in the real Universe, as well as the galaxy-halo connections. 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 train random forest (RF) models to predict SDSS galaxy properties based on ELUCID subhalo properties. The RF recovers the absolute magnitude of galaxies reasonably well but exhibits low accuracy in color prediction. To investigate the possible reasons for this, we perform similar RF predictions using galaxies from SAM and hydrodynamic simulation and compare the results with that from the SDSS-ELUCID sample. Uncertainties in the galaxy-subhalo connection of the SDSS-ELUCID sample arising from the limited accuracy of the ELUCID construction are also considered. Our analysis is helpful for a better understanding of the differences in the galaxy-subhalo connection between galaxy formation models and the real Universe.
Speaker: Xiaoju Xu (上海交通大学) -
35
Using Constrained Hydro Simulations to Explore the Gas Properties of the Cosmic Web
Using reconstructed initial conditions in the Sloan Digital Sky Survey (SDSS) survey volume, we carry out constrained hydrodynamic simulations in three regions representing different types of the cosmic web: the Coma cluster of galaxies; the SDSS Great Wall; and a large low-density region at z ∼ 0.05. The simulations successfully predict some discontinuities associated with shock fronts and contact edges, which can be tested using observations of the thermal Sunyaev–Zel’dovich effect and X-rays. The constrained simulations, which follow the formation and heating history of the observed cosmic web, provide an important avenue to interpret observational data. We also find a tight correlation between the gas temperature and the strength of the local tidal field, which may show the connection between gas and dark matter.
Speaker: Renjie Li -
36
Differentiable Cosmological Simulation with Adjoint Method
Rapid advances in deep learning have brought not only myriad powerful neural networks, but also breakthroughs that benefit established scientific research. In particular, automatic differentiation (AD) tools and computational accelerators like GPUs have facilitated forward modeling of the Universe with differentiable simulations. Current differentiable cosmological simulations are limited by memory, thus are subject to a trade-off between time and space/mass resolution. They typically integrate for only tens of time steps, unlike the standard non-differentiable simulations. We present a new approach free of such constraints, using the adjoint method and reverse time integration. It enables larger and more accurate forward modeling, and will improve gradient based optimization and inference. We implement it in a particle-mesh (PM) N-body library pmwd (particle-mesh with derivatives). Based on the powerful AD system JAX, pmwd is fully differentiable, and is highly performant on GPUs.
Speaker: Yin Li
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33
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10:25 AM
Coffee Break 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU -
Simulation & inference: Machine learningConvener: Yin Li
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37
Analyzing the large-scale structure of the Universe with the assistance of machine learning techniques
I will discuss our work on the reconstruction of the cosmic velocity field from the redshift-space distribution of dark matter halos using the state-of-the-art deep learning technique. We were able to accurately recover the magnitude, divergence and vorticity of the velocity field, with the power spectra recovered at 80% accuracy at $k < 1.1\ h$/Mpc. This approach is very promising and presents an alternative method to correct the redshift-space distortions using the measured 3D spatial information of halos. Additionally, I will present our recent work on the estimation of cosmological parameters using deep learning algorithms. Our work shows that machine learning technique has the potential to greatly improve our understanding of the Universe and its evolution.
Speaker: 霄栋 李 (中山大学) -
38
DarkAI: Mapping the large-scale density field of dark matter using AI
We develop a deep learning technique to reconstruct the dark matter density field from the redshift-space distribution of dark matter halos. We implement a UNet-architecture neural network and successfully trained it using the COLA fast simulation, which is an approximation of the N-body simulation with $512^3$ particles in a box size of $500 \mpch$. We evaluate the resulting UNet model not only using the training-like test samples, but also using the typical N-body simulations, including the Jiutian simulation which has $6144^3$ particles in a box size of $1000 \mpch$, and the ELUCID simulation which has a different cosmology. The real-space dark matter density fields in the three simulations can all be recovered consistently with only a small reduction of the cross-correlation power spectrum at 1\% and 10\% levels at $k=0.1$ and $0.3~h\mathrm{Mpc^{-1}}$, respectively. It is evident that the reconstruction helps to correct for the redshift-space distortions and is unaffected by the different cosmologies between the training sample ({\bf Planck2018}) and the test sample ({\bf WMAP5}). In addition, we tested the application of the UNet-reconstructed density field to recover the velocity \& tidal field and found it outperforms the traditional approach based on the linear bias model, showing a 12.2 percent improvement in the correlation slope and a 21.1 percent reduction in the scatter between the predicted and the true velocities. As a result, our method is highly efficient and has an outstanding level of extrapolation reliability beyond the training set. This offers an optimal solution that determines the three-dimensional underlying density field from the abundant galaxy survey data.
Speaker: Feng Shi (Xidian University) -
39
Estimation of photo-z probability density functions via deep learning with statistical basis
Obtaining well-calibrated probability density functions (PDFs) of photometric redshift (photo-z) for galaxies without using spectroscopy remains a challenge for many science goals. Deep learning tools have proven to be powerful for this task and gained growing popularity. These include, in particular, state-of-the-art deep neural networks that are typically fed with multi-band galaxy images or photometry and produce density estimates that mimic PDFs. However, in addition to the absence of interpretability, such density estimates usually lack rigorous statistical basis and suffer from systematic biases. To tackle these problems, we develop a two-stage method that endows statistical basis for estimating photo-z PDFs by incorporating a weighted k-nearest-neighbor (kNN) algorithm into the conventional neural network. In the first stage, we establish a latent space that properly encodes redshift information via a representation learning framework, trained with observed galaxy images and spectroscopic redshift labels. In the second stage, we select k nearest neighbors for each query galaxy in the learnt latent space and construct a photo-z PDF using their labels, with the optimal k determined by diagnostics for the local distribution of probability integral transform (PIT). By fitting and assigning different weights to the neighbors, this approach further allows for recalibrating the PDFs and resolving distribution mismatch between the inference set and the training set. Experiments on the SDSS data and the CFHTLS data have shown that our method produces well-calibrated photo-z PDFs over different redshift ranges. In contrast to benchmark methods, our method exhibits robustness under distribution mismatch in the aspect of restricting photo-z-dependent biases, and is able to do so without compromising the accuracy and thus holds promises for future large-scale surveys. Furthermore, the local PIT diagnostics applied in our method has the power of probing the local structure of data, which increases model interpretability by suggesting possible correlations between redshift and observational or physical variables, and may offer meaningful insights on the properties of different galaxy populations.
Speaker: Qiufan Lin (Pengcheng Lab) -
40
Relating galaxies across different redshift to study galaxy evolutionSpeaker: Kai Wang
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37
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Gas: hot Hengli Hotel
Hengli Hotel
Convener: 鑫 王-
41
Introducing SIRIUS: a new semi-numerical method for simulating cosmic reionization and IGM heating
我们介绍一种新的模拟宇宙再电离和加热过程的半数值方法 SIRIUS (Simulation of IGM Reionization In the Universe with Shell-wise method)。国际流行的半数值模拟软件21cmFAST是基于excursion set model of reionization，在大尺度上有一定局限性。SIRIUS对标21cmFAST，但采用了完全不同的近似方案：利用一维辐射转移近似模拟紫外光子的辐射转移，并利用球壳窗口函数进行数值加速；同时，采用线性微扰再电离模型模拟X射线光子的辐射转移和加热效应。我们的新方法在单光源测试中获得与解析解一致的结果，并在宇宙学物质场的再电离测试中获得有效的结果。
Speaker: 萌 周 (清华大学) -
42
Simulating the observations of hot gas and cold gas in ISM and CGM
The gas components play very important role in the baryon cycles and evolution processes in galaxy formation. In this talk, we present our recent work on simulating the observations of HI gas in ISM and hot ionized gas in CGM and ICM.
For the cold gas, we generate the mock observation of the 21cm interferometer signals by radio arrays for HI gas in galaxies. We developed a software OmniUV, which offer the ability to simulate the visibility data and image reconstructions. We use the HI gas outputs from Illustris-TNG and L-Galaxies to generate the 21cm signals of HI gas by radio arrays and adopt the configurations of SKA1-mid and MeerKAT into OmniUV and generate the visibility data and reconstruct the mock images for HI gas in nearby universe. The work can help to test the observations strategies and data processing for HI sources by future interferometer arrays, like SKA, FASTA etc.
For the ionized hot gas, we use the model outputs of our recent semi-analytic models with the radial distribution of hot gas profiles. 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: Dr 坚 富 (shanghai astronomical observatory) -
43
The hot gas distribution, X-ray luminosity and baryon budget in L-Galaxies semi-analytic model of galaxy formation
Hot ionized gas is important in the baryon cycle of galaxies and may contribute the majority of their “missing baryons”. Up till now, most semi-analytic models of galaxy formation have paid little attention to the hot gaseous haloes and their X-ray emission. In this paper, we adopt the one-dimensional model from Sharma et al. instead of the isothermal sphere in L-Galaxies semi-analytic models to describe the radial distribution of hot gas. The hot gas halo can be divided into two parts according to the ratio of local thermal instability time scale and the free-fall time scale: a cool core with $t_{TI}/t_{ff} = 10$ and a stable region in outer halo with $t_{TI}/t_{ff} > 10$. We update the prescriptions of gas cooling, feedback and gas stripping based on the new hot gas profiles, and then successfully reproduce several X-ray observational results, like the radial profiles of hot gas density, and the scaling relations of $L_X$ and $T_X$. We find: (1) Flatter density profiles in the halo centers produce more accurate X-ray emission than the isothermal sphere; (2) Cool core regions prone to precipitation have higher $T_{gas}$ than $T_{vir}$, and a higher ratio of $T_X/T_{vir}$ in smaller haloes leads to a steeper slope in $L_X − T_X$ relation; (3) The ionized gas in unbounded reservoir and low temperature intergalactic gas in low mass haloes could be the main components for the halo “missing baryons”. Our model outputs can predict the observations of hot gas in nearby universe and mock the surveys of the baryon budgets by future X-ray telescopes.
Speaker: Mr 文心 钟 (中国科学院上海天文台) -
44
Transport mechanisms in the intracluster medium
Recently, the high metallicity in the outskirts of galaxy clusters has been puzzling and asks for a deeper investigation of the transport mechanisms in the intracluster medium (ICM). We studied the transport mechanisms in the ICM using tracer particle re-simulation of the Omega500 cosmological hydrosimulation, and focused on the particle transport during major mergers. We used pair dispersion statistics to study the effect of particle transport at various epochs of the cluster assembly history. In a system filled with Kolmogorov turbulence, the squared displacement of particles is described by the ‘super-diffusion’ Richardson scaling $
Speaker: 一纬 张 (云南大学中国西南天文研究所)
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41
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10:20 AM
Coffee Break 3rd floor meeting room
3rd floor meeting room
SJTU & Suzhou Bay
School of Physics and Astronomy, SJTU -
Gas: cold Hengli Hotel
Hengli Hotel
Convener: 坚 富-
45
Gas in semi-analytic model
Gas is the essential component in a galaxy that dominates its evolution. It also provides insight into the large-scale structure and the evolution of the Universe. In this talk, I will introduce an overview of treatments of gas and star formation in our updated semi-analytic model. Our model includes a self-consistent partition of HI and H$_2$ in the cold gas disk, as well as environmental effects on multi-phase gas. It presents one of the best matches with observed gas measurements among the state-of-art models and simulations at z=0. I will discuss the impact of different physical processes on the gas abundances and star formation rates of central and satellite galaxies. I will then introduce our efforts on improving the model predictions at high redshifts.
Speaker: Lizhi Xie (Tianjin Normal University) -
46
Cosmic Evolution of Atomic and Molecular Gas within Dark Matter Halos
Accurately modeling the cold gas content in the universe is challenging for current theoretical models. We propose a new empirical model NeutralUniverseMachine to describe the evolution of HI and H2 gas along with the dark matter halos based on the UniverseMachine catalog. It is able to accurately fit the observed HI and H2 mass functions, molecular-to-atomic ratio, HI-halo mass relation, HI-stellar mass relations for star-forming and quenched galaxies, HI clustering measurements at z~0 and the HI-stellar mass relations at higher redshifts, as well as the evolution of cosmic gas densities in 0<z<6. Such a model framework would be useful for the next generation HI and H2 surveys.
Speaker: Hong Guo (Shanghai Astronomical Observatory) -
47
Empirical Models of the Atomic Hydrogen Content in Dark Matter Halos
Atomic hydrogen (HI) gas, mostly residing in dark matter halos after cosmic reionization, is the fuel for star formation. Its relation with properties of host halo is the key to understand the cosmic HI distribution. In this work, we propose a flexible, empirical model of HI-halo relation. In this model, while the HI mass depends primarily on the mass of host halo, there is also secondary dependence on other halo properties. We apply our model to the observation data of the Arecibo Fast Legacy ALFA Survey (ALFALFA), and find it can successfully fit to the cosmic HI abundance ($\Omega_{\rm HI}$), average HI-halo mass relation $\langle M_{\rm HI}|M_{\rm h}\rangle$, and the HI clustering. The bestfit of the ALFALFA data rejects with high confidence level the model with no secondary halo dependence of HI mass and the model with secondary dependence on halo spin parameter ($\lambda$), and shows strong dependence on halo formation time ($a_{1/2}$) and halo concentration ($c_{\rm vir}$). In attempt to explain these findings from the perspective of hydrodynamical simulations, the IllustrisTNG simulation confirms the dependence of HI mass on secondary halo parameters. However, the IllustrisTNG results show strong dependence on $\lambda$ and weak dependence on $c_{\rm vir}$ and $a_{1/2}$, and also predict a much larger value of HI clustering on large scales than observations. This discrepancy between the simulation and observation calls for improvements in understanding the HI-halo relation from both theoretical and observational sides.
Speaker: Zhixing Li -
48
Conditional HI Mass Functions and the H I-to-halo Mass Relation in the Local Universe
We present a new H I mass estimator that relates log10(MHI/M*) to a linear combination of four galaxy properties: stellar surface mass density, color index u − r, stellar mass, and concentration index, with the scatter of individual galaxies around the mean H I mass modeled with a Gaussian distribution function. We calibrate the estimator using the xGASS sample, including both H I detection and nondetection, and constrain the model parameters through Bayesian inferences. Tests with mock catalogs demonstrate that our estimator provides unbiased H I masses for optical samples like SDSS. We apply our estimator to the SDSS spectroscopic sample to estimate the H I mass function (HIMF) of local galaxies, as well as the conditional H I mass function in galaxy groups and the H I–halo mass relation. Our HIMF agrees with the ALFALFA measurements at MHI > 5 × 10^9 Me, but with higher amplitude and a steeper slope at lower masses. We show that this discrepancy is caused primarily by the cosmic variance, which is corrected for the SDSS sample but not for ALFALFA. The total CHIMFs for all halo masses can be described by a single Schechter function, while those of central galaxies show a double-Gaussian profile. The total H I mass in a group increases monotonically with halo mass, but for central galaxies, the H I mass shows weak dependence on halo mass when Mh > 10^12 M☉. The observed H I–halo mass relation is not reproduced by current hydrodynamic simulations and semianalytic models of galaxy formation.
Speaker: Xiao Li (Tsinghua University)
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45
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