Virtually any investigation involving dark matter halos relies on a definition of their radius, mass, and of whether they are a subhalo. The halo boundary is most commonly defined to include a spherical overdensity contrast (such as R200c, Rvir, and R200m), but different thresholds lead to significant differences in radius and mass. The splashback radius has recently been suggested as a more physically motivated (and generally larger) halo boundary, adding to the range of definitions. It is often difficult to assess the impact of a particular choice because most halo catalogs contain only one or a few definitions and generally only one set of host-subhalo relations. To alleviate this issue, we present halo catalogs and merger trees for 14 N-body simulations of LambdaCDM and self-similar universes. Based on ROCKSTAR catalogs, we compute additional halo properties using the SPARTA code and recombine them with the original catalogs. The new catalogs contain numerous variants of spherical overdensity and splashback radii and masses and, most critically, host-subhalo relations for each definition. We also present a new merger tree format where the data is stored as a compressed, two-dimensional matrix. We perform basic tests of the relation between different definitions and present an updated model for the splashback-spherical overdensity connection. The SPARTA code, as well as our catalogs and merger trees, are publicly available.
The classification of dark matter halos as isolated hosts or subhalos is critical for our understanding of structure formation and the galaxy-halo connection. Most commonly, subhalos are defined to reside inside a spherical overdensity boundary such as the virial radius. The resulting host-subhalo relations depend sensitively on the somewhat arbitrary overdensity threshold, but the impact of this dependence is rarely quantified. The recently proposed splashback radius tends to be larger and to include more subhalos than even the largest spherical overdensity boundaries. We systematically inves…
Motivated by the recent proposal of the splashback radius as a physical boundary of dark matter halos, we present a parallel computer code for Subhalo and PARticle Trajectory Analysis (SPARTA). The code analyzes the orbits of all simulation particles in all host halos, billions of orbits in the case of typical cosmological N-body simulations. Within this general framework, we develop an algorithm that accurately extracts the location of the first apocenter of particles after infall into a halo, or splashback. We define the splashback radius of a halo as the smoothed average of the apocenter ra…
The splashback radius ($R_{\rm sp}$) of dark matter halos has recently been detected using weak gravitational lensing and cross-correlations with galaxies. However, different methods have been used to measure $R_{\rm sp}$ and to assess the significance of its detection. In this paper, we use simulations to study the precision and accuracy to which we can detect the splashback radius with 3D density, 3D subhalo, and weak lensing profiles. We study how well various methods and tracers recover $R_{\rm sp}$ by comparing it with the value measured directly from particle dynamics. We show that estim…
Non-gravitational interactions between dark matter particles with strong scattering, but relatively small annihilation and dissipation, has been proposed to match various observables on cluster and group scales. In this paper, we present the results from large cosmological simulations which include the effects of different self-interaction scenarios. In particular we explore a model with the differential cross section that can depend on both the relative velocity of the interacting particles and the angle of scattering. We focus on how quantities, such as the stacked density profiles, subhalo …
We explore how the splashback radius ($R_{\rm sp}$) of galaxy clusters, measured using the number density of the subhalo population, changes based on various selection criteria using the IllustrisTNG cosmological galaxy formation simulation. We identify $R_{\rm sp}$ by extracting the steepest radial gradient in a stacked set of clusters in 0.5 dex wide mass bins, with our clusters having halo masses $10^{13} \leq M_{\rm 200, mean} / {\rm M}_\odot \leq 10^{15}$. We apply cuts in subhalo mass, galaxy stellar mass, $i$-band absolute magnitude and specific star formation rate. We find that, genera…
Recent constraints on the splashback radius around optically selected galaxy clusters from the redMaPPer cluster-finding algorithm in the literature have shown that the observed splashback radius is $\sim 20\%$ smaller than that predicted by N-body simulations. We present analyses on the splashback features around $\sim 3000$ optically selected galaxy clusters detected by the independent cluster-finding algorithm CAMIRA over a wide redshift range of $0.1<z_{\rm cl}<1.0$ from the second public data release of the Hyper Suprime-Cam (HSC) Subaru Strategic Program covering $\sim 427~{\rm deg}^2$ f…
We critically examine the methodology behind the claimed observational detection of halo assembly bias using optically selected galaxy clusters by Miyatake et al. (2016) and More et al. (2016). We mimic the optical cluster detection algorithm and apply it to two different mock catalogs generated from the Millennium simulation galaxy catalog, one in which halo assembly bias signal is present, while the other in which the assembly bias signal has been expressly erased. We split each of these cluster samples into two using the average cluster-centric distance of the member galaxies to measure the…
The density field in the outskirts of dark matter halos is discontinuous due to a caustic formed by matter at its first apocenter after infall. In this paper, we present an algorithm to identify the "splashback shell" formed by these apocenters in individual simulated halos using only a single snapshot of the density field. We implement this algorithm in the code SHELLFISH (SHELL Finding In Spheroidal Halos) and demonstrate that the code identifies splashback shells correctly and measures their properties with an accuracy of $<5\%$ for halos with more than 50,000 particles and mass accretion r…
This paper introduces SMACC -- Subhalo Mass-loss Analysis using Core Catalogs. SMACC adds a mass model to substructure merger trees based on halo "core tracking." Our approach avoids the need for running expensive subhalo finding algorithms and instead uses subhalo mass-loss modeling to assign masses to halo cores. We present details of the SMACC methodology and demonstrate its excellent performance in describing halo substructure and its evolution. Validation of the approach is carried out using cosmological simulations at significantly different resolutions. We apply SMACC to the 1.24 trilli…
We develop empirical methods for modeling the galaxy population and populating cosmological N-body simulations with mock galaxies according to the observed properties of galaxies in survey data. We use these techniques to produce a new set of mock catalogs for the DEEP2 Galaxy Redshift Survey based on the output of the high-resolution Bolshoi simulation, as well as two other simulations with different cosmological parameters, all of which we release for public use. The mock-catalog creation technique uses subhalo abundance matching to assign galaxy luminosities to simulated dark-matter halos. …
We develop a novel abundance matching method to construct a mock catalog of luminous red galaxies (LRGs) in SDSS, using catalogs of halos and subhalos in N-body simulations for a LCDM model. Motivated by observations suggesting that LRGs are passively-evolving, massive early-type galaxies with a typical age >5Gyr, we assume that simulated halos at z=2 (z2-halo) are progenitors for LRG-host subhalos observed today, and we label the most tightly bound particles in each progenitor z2-halo as LRG ``stars''. We then identify the subhalos containing these stars to z=0.3 (SDSS redshift) in descending…
The Milky Way's dark matter halo is thought to contain large numbers of smaller subhalos. These objects can contain very high densities of dark matter, and produce potentially observable fluxes of gamma rays. In this article, we study the gamma ray sources in the Fermi Gamma Ray Space Telescope's recently published First Source Catalog, and attempt to determine whether this catalog might contain a population of dark matter subhalos. We find that, while approximately 20-60 of the catalog's unidentified sources could plausibly be dark matter subhalos, such a population cannot be clearly identifi…
We utilize the Millennium-II simulation databases to study the spin bias of dark subhalos in the Local Group-like systems which have two prominent satellites with comparable masses. Selecting the group-size halos with total mass similar to that of the Local Group (LG) from the friends-of-friends halo catalog and locating their subhalos from the substructure catalog, we determine the most massive (main) and second to the most massive (submain) ones among the subhalos hosted by each selected halo. When the dimensionless spin parameter (lambda) of each subhalo is derived from its specific angular…
The dark matter halo of the Milky Way is expected to contain an abundance of smaller subhalos. These subhalos can be dense and produce potentially observable fluxes of gamma rays. In this paper, we search for dark matter subhalo candidates among the sources in the Fermi-LAT Second Source Catalog which are not currently identified or associated with counterparts at other wavelengths. Of the nine high-significance, high-latitude (|b|>60 degrees), non-variable, unidentified sources contained in this catalog, only one or two are compatible with the spectrum of a dark matter particle heavier than a…
If dark matter consists of weakly interacting massive particles (WIMPs), dark matter subhalos in the Milky Way could be detectable as gamma-ray point sources due to WIMP annihilation. In this work, we perform an updated study of the detectability of dark matter subhalos as gamma-ray sources with the Fermi Large Area Telescope (Fermi LAT). We use the results of the Via Lactea II simulation, scaled to the Planck 2015 cosmological parameters, to predict the local dark matter subhalo distribution. Under optimistic assumptions for the WIMP parameters --- a 40 GeV particle annihilating to $b\bar{b}$…
Splashback refers to the process of matter that is accreting onto a dark matter halo reaching its first orbital apocenter and turning around in its orbit. The cluster-centric radius at which this process occurs, r_sp, defines a halo boundary that is connected to the dynamics of the cluster. A rapid decline in the halo profile is expected near r_sp. We measure the galaxy number density and weak lensing mass profiles around redMaPPer galaxy clusters in the first year Dark Energy Survey (DES) data. For a cluster sample with mean M_200m mass ~2.5 x 10^14 M_sun, we find strong evidence of a splashb…
We select satellite galaxies from the galaxy group catalog constructed with the SDSS spectroscopic galaxies and measure the tangential shear around these galaxies with source catalog extracted from CFHT/MegaCam Stripe-82 Survey to constrain the mass of subhalos associated with them. The lensing signal is measured around satellites in groups with masses in the range [10^{13}, 5x10^{14}]h^{-1}M_{sun}, and is found to agree well with theoretical expectation. Fitting the data with a truncated NFW profile, we obtain an average subhalo mass of log M_{sub}= 11.68 \pm 0.67 for satellites whose project…
Symfind: Addressing the Fragility of Subhalo Finders and Revealing the Durability of Subhalos
SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；Department of Physics, Stanford University（斯坦福大学物理系）；Carnegie Observatories（卡内基观测站）；Department of Astronomy, University of Maryland, College Park（马里兰大学帕克分校天文学系）
The Large Area Telescope (LAT) aboard the Fermi satellite allows us to study the high-energy gamma-ray sky with unprecedented sensitivity. However, the origin of 31% of the detected gamma-ray sources remains unknown. This population of unassociated gamma-ray sources may contain new object classes, among them sources of photons from self-annihilating or decaying non-baryonic dark matter. Fermi-LAT might be capable to detect up to a few of these dark matter subhalos as faint and moderately extended gamma-ray sources with a temporally steady high-energy emission. After applying corresponding sele…
Mock Catalogs of Strongly Lensed Gravitational Waves via A Halo Model Approach with Ground-based Detectors
School of Physics and Technology, Wuhan University（武汉大学物理科学与技术学院）；National Centre for Nuclear Research（波兰国家核研究中心）；School of Physics and Optoelectronic, Yangtze University（长江大学物理与光电工程学院）
Constructing a Mock Galaxy Catalog for the All-sky SPECtroscopic Survey of Nearby Galaxies (A-SPEC) Using the Machine-assisted Semi-Simulation Model
Seoul National University（首尔大学）；Institute for Data Innovation in Science, Seoul National University（首尔大学数据创新科学研究所）；NSF-Simons AI Institute for the Sky (SkAI)（美国国家科学基金会-西蒙斯天空人工智能研究所）；SNU Astronomy Research Center, Seoul National University（首尔大学天体物理学研究中心）；Korea Astronomy and Space Science Institute（韩国天文与空间科学研究院）；Center for Theoretical Physics, Department of Physics and Astronomy, Seoul National University（首尔大学物理与天文学系理论物理中心）；Korea Institute for Advanced Study（韩国高等科学研究院）
Dark matter annihilations taking place in nearby subhalos could appear as gamma-ray sources without detectable counterparts at other wavelengths. In this study, we consider the collection of unassociated gamma-ray sources reported by the Fermi Collaboration in an effort to identify the most promising dark matter subhalo candidates. While we identify 24 bright, high-latitude, non-variable sources with spectra that are consistent with being generated by the annihilations of ~20-70 GeV dark matter particles (assuming annihilations to $b\bar{b}$), it is not possible at this time to distinguish the…
We investigate machine learning (ML) techniques for predicting the number of galaxies (N_gal) that occupy a halo, given the halo's properties. These types of mappings are crucial for constructing the mock galaxy catalogs necessary for analyses of large-scale structure. The ML techniques proposed here distinguish themselves from traditional halo occupation distribution (HOD) modeling as they do not assume a prescribed relationship between halo properties and N_gal. In addition, our ML approaches are only dependent on parent halo properties (like HOD methods), which are advantageous over subhalo…
We compare the substructure evolution in pure dark matter (DM) halos with those in the presence of baryons (PDM and BDM). The prime halos have been analyzed by Romano-Diaz et al (2009). Models have been evolved from identical initial conditions using Constrained Realizations, including star formation and feedback. A comprehensive catalog of subhalos has been compiled and properties of subhalos analyzed in the mass range of 10^8 Mo - 10^11 Mo. We find that subhalo mass functions are consistent with a single power law, M_sbh^{alpha}, but detect a nonnegligible shift between these functions, alph…
We develop a new code, the Hierarchical Bound-Tracing (HBT for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of this code to a recent benchmark test of finding subhaloes demonstrates that HBT stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding algorithm with an adaptive source subhalo management. We keep a full record of the…
CWTHF: Subhalo Identification with Continuous Wavelet Transform
Center for Theoretical Physics, College of Physics, Jilin University（吉林大学物理学院理论物理中心）；Key Laboratory of Material Simulation Methods & Software of Ministry of Education, College of Physics, Jilin University（吉林大学物理学院教育部材料模拟方法与软件重点实验室）；Center for High Energy Physics, Peking University（北京大学高能物理研究中心）
A machine learning-based method for populating dark matter halos in N-body simulations with substructure
Center for Cosmology and Particle Physics, Department of Physics, New York University（纽约大学物理系宇宙学与粒子物理中心）；Department of Physics, Sharif University of Technology（谢里夫理工大学物理系）
In hierarchical structure formation, dark matter halos that merge with larger halos can persist as subhalos. These subhalos are likely hosts of visible galaxies. While the dense halo environment rapidly strips subhalos of their dark mass, the compact luminous material can remain intact for some time, making the correspondence of galaxies with severely stripped subhalos unclear. Many galaxy evolution models assume that satellite galaxies eventually merge with their central galaxy, but this ignores the possibility of satellite tidal disruption. We use a high-resolution $N$-body simulation of cos…
Based on galaxies from the Sloan Digital Sky Survey (SDSS) and subhalos in the corresponding reconstructed region from the constrained simulation of ELUCID, we study the alignment of central galaxies relative to their host groups in the group catalog, as well as the alignment relative to the corresponding subhalos in the ELUCID simulation. Galaxies in observation are matched to dark matter subhalos in the ELUCID simulation using a novel neighborhood abundance matching method. In observation, the major axes of galaxies are found to be preferentially aligned to the major axes of their host group…
We use weak lensing observations to make the first measurement of the characteristic depletion radius, one of the three radii that characterize the region where matter is being depleted by growing haloes. The lenses are taken from the halo catalog produced by the extended halo-based group/cluster finder applied to DESI Legacy Imaging Surveys DR9, while the sources are extracted from the DECaLS DR8 imaging data with the Fourier_Quad pipeline. We study halo masses $12 < \log ( M_{\rm grp} ~[{\rm M_{\odot}}/h] ) \leq 15.3$ within redshifts $0.2 \leq z \leq 0.3$. The virial and splashback radii ar…
We investigate the use of the halo mass-gap statistic --- defined as the logarithmic difference in mass between the host halo and its most massive satellite subhalo --- as a probe of halo age and concentration. A cosmological N-body simulation is used to study N ~25, 000 group/cluster sized halos in the mass range 10^12.5 < M_halo/M_sol < 10^14.5. In agreement with previous work, we find that halo mass-gap is related to halo formation time and concentration. On average, older and more highly concentrated halos have larger halo mass-gaps, and this trend is stronger than the mass-concentration r…
We present multi-wavelength studies of optically-defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers, which is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple-peaks and single clusters with single-peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of…
One of the predictions of the $Λ$CDM cosmological framework is the hierarchical formation of structure, giving rise to dark matter (DM) halos and subhalos. When the latter are massive enough they retain gas (i.e., baryons) and become visible. This is the case of the dwarf satellite galaxies in the Milky Way (MW). Below a certain mass, halos may not accumulate significant amounts of baryons and remain completely dark. However, if DM particles are Weakly Interacting Massive Particles (WIMPs), we expect them to annihilate in subhalos, producing gamma rays which can be detected with the Fermi sate…
University of California, San Diego（加州大学圣地亚哥分校）；University of California, Berkeley（加州大学伯克利分校）；The Observatories of the Carnegie Institution for Science（卡内基科学研究所天文台）
Strong gravitational lensing has been identified as a promising astrophysical probe to study the particle nature of dark matter. In this paper we present a detailed study of the power spectrum of the projected mass density (convergence) field of substructure in a Milky Way-sized halo. This power spectrum has been suggested as a key observable that can be extracted from strongly lensed images and yield important clues about the matter distribution within the lens galaxy. We use two different $N$-body simulations from the ETHOS framework: one with cold dark matter and another with self-interacti…
Several occupational distributions for satellite galaxies more massive than ms~4E7 Msun around MW-sized hosts are presented and used to predict their internal dynamics. For this, a galaxy group mock catalog is constructed on the basis of (sub)halo-to-stellar mass relations constrained with the observed Galaxy Stellar Mass Function decomposed into centrals and satellites, and the 2-point correlation functions. For the MW-sized hosts we find that: 6.6% have 2 satellites in the SMC-LMC mass range; their probabilities to have 1, 2 or 3 satellites equal or larger than the LMC, the SMC or Sgr, respe…
Merger trees follow the growth and merger of dark-matter haloes over cosmic history. As well as giving important insights into the growth of cosmic structure in their own right, they provide an essential backbone to semi-analytic models of galaxy formation. This paper is the first in a series to arise from the SUSSING MERGER TREES Workshop in which ten different tree-building algorithms were applied to the same set of halo catalogues and their results compared. Although many of these codes were similar in nature, all algorithms produced distinct results. Our main conclusions are that a useful …
Merger tree codes are routinely used to follow the growth and merger of dark matter haloes in simulations of cosmic structure formation. Whereas in Srisawat et. al. we compared the trees built using a wide variety of such codes here we study the influence of the underlying halo catalogue upon the resulting trees. We observe that the specifics of halo finding itself greatly influences the constructed merger trees. We find that the choices made to define the halo mass are of prime importance. For instance, amongst many potential options different finders select self-bound objects or spherical re…
Merger trees are routinely used to follow the growth and merging history of dark matter haloes and subhaloes in simulations of cosmic structure formation. Srisawat et al. (2013) compared a wide range of merger-tree-building codes. Here we test the influence of output strategies and mass resolution on tree-building. We find that, somewhat surprisingly, building the tree from more snapshots does not generally produce more complete trees; instead, it tends to short- en them. Significant improvements are seen for patching schemes which attempt to bridge over occasional dropouts in the underlying h…
As the second paper of a series on studying galaxy-galaxy lensing signals using the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we present our measurement and modelling of the lensing signals around groups of galaxies. We divide the groups into four halo mass bins, and measure the signals around four different halo-center tracers: brightest central galaxy (BCG), luminosity-weighted center, number-weighted center and X-ray peak position. For X-ray and SDSS DR7 cross identified groups, we further split the groups into low and high X-ray emission subsamples, both of which are assigned wit…
We use the kinematics of satellite galaxies that orbit around the central galaxy in a dark matter halo to infer the scaling relations between halo mass and central galaxy properties. Using galaxies from the Sloan Digital Sky Survey, we investigate the halo mass-luminosity relation (MLR) and the halo mass-stellar mass relation (MSR) of central galaxies. In particular, we focus on the dependence of these scaling relations on the colour of the central galaxy. We find that red central galaxies on average occupy more massive haloes than blue central galaxies of the same luminosity. However, at fixe…
We introduce the Uchuu suite of large high-resolution cosmological $N$-body simulations. The largest simulation, named Uchuu, consists of 2.1 trillion ($12800^3$) dark matter particles in a box of side-length 2.0 Gpc/h, with particle mass $3.27 \times 10^{8}$ Msun/h. The highest resolution simulation, Shin-Uchuu, consists of 262 billion ($6400^3$) particles in a box of side-length 140 Mpc/h, with particle mass $8.97 \times 10^{5}$ Msun/h. Combining these simulations we can follow the evolution of dark matter halos and subhalos spanning those hosting dwarf galaxies to massive galaxy clusters ac…
