CUSP is a powerful formalism that recovers, from first principles and with no free parameter, all the macroscopic properties of dark matter haloes found in cosmological N-body simulations and unveils the origin of their characteristic features. Since it is not restricted by the limitations of simulations, it covers the whole mass and redshift ranges. In the present Paper we use CUSP to calculate the mass-scale relations holding for halo density profiles fitted to the usual NFW and Einasto functions in the most relevant cosmologies and for the most usual mass definitions. We clarify the origin of these relations and provide accurate analytic expressions holding for all masses and redshifts. The performance of those expressions is compared to that of previous models and to the mass-concentration relation spanning more than 20 orders of magnitude in mass at $z=0$ obtained in recent simulations of a 100 GeV WIMP universe.
We present results of a study of the virial state of high redshift dark matter haloes in an N-body simulation. We find that the majority of collapsed, bound haloes are not virialized at any redshift slice in our study ($z=15-6$) and have excess kinetic energy. At these redshifts, merging is still rampant and the haloes cannot strictly be treated as isolated systems. To assess if this excess kinetic energy arises from the environment, we include the surface pressure term in the virial equation explicitly and relax the assumption that the density at the halo boundary is zero. Upon inclusion of t…
In this paper, we examine in detail the key structural properties of high redshift dark matter haloes as a function of their spin parameter. We perform and analyze high resolution cosmological simulations of the formation of structure in a LCDM Universe. We study the mass function, ellipticities, shapes, density profiles, rotation curves and virialization for a large sample of dark matter haloes from z = 15 - 6. We also present detailed convergence tests for individual haloes. We find that high spin haloes have stronger clustering strengths (up to 25%) at all mass and redshift ranges at these …
Galaxy clusters are luminous tracers of the most massive dark matter haloes in the Universe. To use them as a cosmological probe, a detailed description of the properties of dark matter haloes is required. We characterize how the dynamical state of haloes impacts the halo mass function at the high-mass end. We used the dark matter-only MultiDark suite of simulations and the high-mass objects M > 2.7e13 M/h therein. We measured mean relations of concentration, offset, and spin as a function of halo mass and redshift. We investigated the distributions around the mean relations. We measured the h…
We present a detailed investigation of the changing relationship between galaxies and the dark matter haloes they inhabit from z~1.2 to the present day. We do this by comparing precise galaxy clustering measurements over 133 deg2 of the "Wide" component of the CFHT Legacy Survey (CFHTLS) with predictions of an analytic HOD model where the number of galaxies in each halo depends only on the halo mass. Starting from a parent catalogue of ~ 3x10^6 galaxies at i'_AB < 22.5 we use accurate photometric redshifts calibrated using ~ 10^4 spectroscopic redshifts to create a series of type-selected volu…
Intermittent type of primordial non-Gaussian fluctuations from modulated preheating can produce an overabundance of $\sim 10^8M_\odot$ mini-haloes at high redshift $z\gtrsim 20$. This may have a significant impact on the formation of high-redshift supermassive black holes.
We study the population statistics of the surviving subhaloes of LCDM dark matter haloes using a set of very high resolution N-body simulations. These include both simulations of representative regions of the Universe and ultra-high resolution resimulations of individual dark matter haloes. We find that more massive haloes tend to have a larger mass fraction in subhaloes. For example, cluster size haloes typically have 7.5 percent of their mass within R200 in substructures of fractional mass larger than 1e-5, which is 25 percent higher than galactic haloes. There is, however, a large variance …
We use the Horizon Run 4 cosmological N -body simulation to study the effects of distant and close interactions on the alignments of the shapes, spins, and orbits of targets haloes with their neighbours, and their dependence on the local density environment and neighbour separation. Interacting targets have a significantly lower spin and higher sphericity and oblateness than all targets. Interacting pairs initially have anti-parallel spins, but the spins develop parallel alignment as time goes on. Neighbours tend to evolve in the plane of rotation of the target, and in the direction of the maj…
We test the history of structure formation from redshift 1 to today by matching galaxies from VIPERS and SDSS with dark matter haloes in the MultiDark SMDPL N-body simulation. We first show that the standard subhalo abundance matching (SHAM) recipe implemented with MultiDark characterizes the clustering of galaxies well both at redshift 0 for SDSS and at redshift 1 for VIPERS. This is an important validation of the SHAM model at high redshift. We then remap the simulation timesteps to test alternative growth histories and infer the growth index $γ=0.6\pm0.3$. This analysis demonstrates the pow…
We present a new statistical method to determine the relationship between the stellar masses of galaxies and the masses of their host dark matter haloes over the entire cosmic history from z~4 to the present. This multi-epoch abundance matching (MEAM) model self-consistently takes into account that satellite galaxies first become satellites at times earlier than they are observed. We employ a redshift-dependent parameterization of the stellar-to-halo mass relation to populate haloes and subhaloes in the Millennium simulations with galaxies, requiring that the observed stellar mass functions at…
We construct merger trees of dark matter haloes and quantify their merger rates and mass growth rates using the joint dataset from the Millennium and Millennium-II simulations. The finer resolution of the Millennium-II Simulation has allowed us to extend our earlier analysis of halo merger statistics to an unprecedentedly wide range of descendant halo mass (10^10 < M0 < 10^15 Msun), progenitor mass ratio (10^-5 < xi < 1), and redshift (0 < z < 15). We update our earlier fitting form for the mean merger rate per halo as a function of M_0, xi, and z. The overall behavior of this quantity is unch…
Understanding the formation of the first objects in the universe critically depends on knowing whether the properties of small dark matter structures at high-redshift (z > 15) are different from their more massive lower-redshift counterparts. To clarify this point, we performed a high-resolution N-body simulation of a cosmological volume 1 Mpc/h comoving on a side, reaching the highest mass resolution to date in this regime. We make precision measurements of various physical properties that characterize dark matter haloes (such as the virial ratio, spin parameter, shape, and formation times, e…
Quasars represent the brightest Active Galactic Nuclei (AGN) in the Universe and are thought to indicate the location of prodigiously growing Black Holes (BHs), with luminosities as high as 10^48 erg/sec. It is often expected though that such an extremely energetic process will take place in the most massive bound structures in the dark matter (DM) distribution. We show that in contrast to this expectation, in a galaxy formation model which includes AGN feedback, quasars are predicted to live in average DM halo environments with typical masses of a few times 10^12 Msun. This fundamental predic…
We investigate the accuracy of Eulerian perturbation theory for describing the matter and galaxy power spectra in real and redshift space in light of future observational probes for precision cosmology. Comparing the analytical results with a large suite of N-body simulations (160 independent boxes of 13.8 (Gpc/h)^3 volume each, which are publicly available), we find that re-summing terms in the standard perturbative approach predicts the real-space matter power spectrum with an accuracy of < 2% for k < 0.20 h/Mpc at redshifts z < 1.5. This is obtained following the widespread technique of wri…
We introduce the Ultramarine simulation, an extremely large $N$-body simulation of the structure formation and evolution to redshift 5.5 at which cosmic reionization was just completed. The simulation evolves 2.1 trillion particles within a $512~h^{-1}$Mpc cube and has an unprecedented mass and force resolution for large volume simulations of this kind, $5.6\times 10^6 h^{-1}$M$_\odot$ and $1.2~h^{-1}$kpc, respectively. We present some basic statistical results of the simulation, including the halo mass function, halo bias parameter as well as halo mass-concentration relation at high redshifts…
We use N-body simulations to investigate the evolution of the orientation and magnitude of dark matter halo angular momentum within the large scale structure since z=3. We look at the evolution of the alignment of halo spins with filaments and with each other, as well as the spin parameter, which is a measure of the magnitude of angular momentum. It was found that the angular momentum vectors of dark matter haloes at high redshift have a weak tendency to be orthogonal to filaments and high mass haloes have a stronger orthogonal alignment than low mass haloes. Since z=1, the spins of low mass h…
We present the evolution of the structure of relaxed cold dark matter haloes in the cosmology from the Planck satellite. Our simulations cover 5 decades in halo mass, from dwarf galaxies to galaxy clusters. Due to the increased matter density and power spectrum normalization the concentration mass relation in the Planck cosmology has a 20 percent higher normalization at redshift z=0 compared to WMAP cosmology. We confirm that CDM haloes are better described by the Einasto profile; for example, at scales near galaxy half-light radii CDM haloes have significantly steeper density profiles than im…
We present a new algorithm for identifying the substructure within simulated dark matter haloes. The method is an extension of that proposed by Tormen et al. (2004) and Giocoli et al. (2008a), which identifies a subhalo as a group of self-bound particles that prior to being accreted by the main progenitor of the host halo belonged to one and the same progenitor halo (hereafter satellite). However, this definition does not account for the fact that these satellite haloes themselves may also have substructure, which thus gives rise to sub-subhaloes, etc. Our new algorithm identifies substructure…
Many distant objects can only be detected, or become more scientifically valuable, if they have been highly magnified by strong gravitational lensing. We use EAGLE and BAHAMAS, two recent cosmological hydrodynamical simulations, to predict the probability distribution for both the lens mass and lens redshift when point sources are highly magnified by gravitational lensing. For sources at a redshift of two, we find the distribution of lens redshifts to be broad, peaking at z=0.6. The contribution of different lens masses is also fairly broad, with most high-magnification lensing due to lenses w…
It has been shown by Shchekinov & Vasiliev2006 (SV06) that HD molecules can be an important cooling agent in high redshift z >10 haloes if they undergo mergers under specific conditions so suitable shocks are created. Here we build upon Prieto et al. (2012) who studied in detail the merger-generated shocks, and show that the conditions for HD cooling can be studied by combining these results with a suite of dark-matter only simulations. We have performed a number of dark matter only simulations from cosmological initial conditions inside boxes with sizes from 1 to 4 Mpc. We look for haloes wit…
We introduce a new method for the identification of galaxy systems in redshift surveys based on the halo model. This method is a modified version of the K-means identification algorithm developed by Yang et al (2005). We have calibrated and tested our algorithms using mock catalogs generated using the Millennium simulations (Springel et al. 2005) and applied them to the NYU-DR7 galaxy catalog (based on the SDSS datasets). Using this local sample of groups and clusters of galaxies we have measured the effect of gravitational redshift produced by their host dark matter haloes. Our results shows …
In this paper we investigate how the halo mass function evolves with redshift, based on a suite of very large (with N_p = 3072^3 - 6000^3 particles) cosmological N-body simulations. Our halo catalogue data spans a redshift range of z = 0-30, allowing us to probe the mass function from the dark ages to the present. We utilise both the Friends-of-Friends (FOF) and Spherical Overdensity (SO) halofinding methods to directly compare the mass function derived using these commonly used halo definitions. The mass function from SO haloes exhibits a clear evolution with redshift, especially during the r…
Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. Using the Horizon Run 4 cosmological N-body simulation, we studied the frequency and type of halo interactions, and their redshift evolution as a function of the environment defined by the large-scale density, pair separation, mass ratio, and target halo mass. Most interactions happen at large-scale density contrast $δ\approx 20$, regardless of the redshift, corresponding to groups and relatively dense part of filaments. However, the fraction of interacting target is maximum at $δ\approx 1000$. We pro…
We used high resolution dark matter only cosmological simulations to investigate the structural properties of Lambda Cold Dark Matter ($Λ$CDM) haloes over cosmic time. The haloes in our study range in mass from $\sim 10^{10}$ to $\sim 10^{12} \mathrm{M}_\odot$, and are resolved with $10^5$ to $10^7$ particles. We fit the spherically averaged density profiles of DM haloes with the three parameter Einasto function. For our sample of haloes, the Einasto shape parameter, $α$, is uncorrelated with the concentration, $c$, at fixed halo mass, and at all redshifts. Previous reports of an anti-correlat…
The formation of supermassive stars has generally been studied under the assumption of rapid accretion of pristine metal-free gas. Recently it was found, however, that gas enriched to metallicities up to $Z \sim 10^{-3}$ Z$_{\odot}$ can also facilitate supermassive star formation, as long as the total mass infall rate onto the protostar remains sufficiently high. We extend the analysis further by examining how the abundance of supermassive star candidate haloes would be affected if all haloes with super-critical infall rates, regardless of metallicity were included. We investigate this scenari…
The standard cosmological paradigm currently lacks a detailed account of physics in the dark sector, the dark matter and energy that dominate cosmic evolution. In this paper, we consider the distinguishing factors between three alternative models - warm dark matter, quintessence and coupled dark matter-energy - and \lcdm{} through numerical simulations of cosmological structure formation. Key halo statistics - halo spin/velocity alignment between large-scale structure and neighboring haloes, halo formation time and migration - were compared across cosmologies within the redshift range 0$\leq$$…
The structural and dynamic properties of the dark matter halos, though an important ingredient in understanding large-scale structure formation, require more conservative particle resolution than those required by halo mass alone in a simulation. This reduces the parameter space of the simulations, more severely for high-redshift and large-volume mocks which are required by the next-generation large sky surveys. Here, we incorporate redshift and cosmology dependence into an algorithm that assigns accurate halo properties such as concentration, spin, velocity, and spatial distribution to the su…
We study the amount and distribution of dark matter substructures within dark matter haloes, using a large set of high-resolution simulations ranging from group size to cluster size haloes, and carried our within a cosmological model consistent with WMAP 7-year data. In particular, we study how the measured properties of subhaloes vary as a function of the parent halo mass, the physical properties of the parent halo, and redshift. The fraction of halo mass in substructures increases with increasing mass. There is, however, a very large halo-to-halo scatter that can be explained only in part by…
We study the halo mass function and inner halo structure at high redshifts ($z\geq5$) for a suite of simulations within the structure formation ETHOS framework. Scenarios such as cold dark matter (CDM), thermal warm dark matter (WDM), and dark acoustic oscillations (DAO) of various strengths are contained in ETHOS with just two parameters $h_{\rm peak}$ and $k_{\rm peak}$, the amplitude and scale of the first DAO peak. The Extended Press-Schechter (EPS) formalism with a smooth-$k$ filter is able to predict the cut-off in the halo mass function created by the suppression of small scale power in…
We reconsider the ellipsoidal-collapse model and extend it in two ways: We modify the treatment of the external gravitational shear field, introducing a hybrid model in between linear and non-linear evolution, and we introduce a virialisation criterion derived from the tensor virial theorem to replace the ad-hoc criterion employed so far. We compute the collapse parameters delta_c and Delta_v and find that they increase with ellipticity e and decrease with prolaticity p. We marginalise them over the appropriate distribution of e and p and show the marginalised results as functions of halo mass…
We use the extensive catalog of dark matter haloes from the Millennium simulation to investigate the statistics of the mass accretion histories (MAHs) and accretion rates of ~500,000 haloes from redshift z=0 to 6. We find only about 25% of the haloes to have MAHs that are well described by a 1-parameter exponential form. For the rest of the haloes, between 20% (Milky-Way mass) to 50% (cluster mass) experience late-time growth that is steeper than an exponential, whereas the remaining haloes show plateau-ed late-time growth that is shallower than an exponential. The haloes with slower late-time…
We make use of publicly available results from N-body Millennium Simulation to create mock samples of lensed supernovae type Ia and core-collapse. Simulating galaxy-galaxy lensing we derive the rates of lensed supernovae and find than at redshifts higher that 0.5 about 0.06 per cent of supernovae will be lensed by a factor two or more. Future wide field surveys like Gaia or LSST should be able to detect lensed supernovae in their unbiased sky monitoring. Gaia (from 2013) will detect at least 2 cases whereas LSST (from 2018) will see more than 500 a year. Large number of future lensed supernova…
We use numerical simulations to investigate how the statistical properties of dark matter (DM) haloes are affected by the baryonic processes associated with galaxy formation. We focus on how these processes influence the spin and shape of a large number of DM haloes covering a wide range of mass scales, from galaxies to clusters at redshifts zero and one, extending to dwarf galaxies at redshift two. The haloes are extracted from the OverWhelmingly Large Simulations, a suite of state-of-the-art high-resolution cosmological simulations run with a range of feedback prescriptions. We find that the…
The concentrations of dark matter haloes provide crucial information about their internal structure and how it depends on mass and redshift -- the so-called concentration-mass-redshift relation, denoted $c(M,z)$. We present here an extensive study of the cosmology-dependence of $c(M,z)$ that is based on a suite of 72 gravity-only, full N-body simulations in which the following cosmological parameters were varied: $σ_{8}$, $Ω_{\mathrm{M}}$, $Ω_{\mathrm{b}}$, $n_{\mathrm{s}}$, $h$, $M_ν$, $w_{0}$ and $w_{\mathrm{a}}$. We characterize the impact of these parameters on concentrations for different…
We present a study on the clustering of a stellar mass selected sample of galaxies with stellar masses M*>10^10Msol at redshifts 0.4<z<2.0, taken from the Palomar Observatory Wide-field Infrared Survey. We examine the clustering properties of these stellar mass selected samples as a function of redshift and stellar mass, and find that galaxies with high stellar masses have a progressively higher clustering strength than galaxies with lower stellar masses. We also find that galaxies within a fixed stellar mass range have a higher clustering strength at higher redshifts. We further estimate the …
We construct merger trees based on the extended Press-Schechter theory (EPS) in order to study the merger rates of dark matter haloes over a range of present day mass ($10^{10}M_{\sun}\leq M_0 \leq10^{15}M_{\sun}$), progenitor mass $(5\times10^{-3}\leq ξ\leq1$) and redshift ($0\leq z\leq 3$). We used the first crossing distribution of a moving barrier of the form $B(S,z)=p(z)+q(z)S^γ$, proposed by Sheth & Tormen, to take into account the ellipsoidal nature of collapse. We find that the mean merger rate per halo $B_m/n$ depends on the halo mass $M$ as $M^{0.2}$ and on the redshift as $(\mathrm{…
We use two cosmological simulations of structure formation in the LambdaCDM scenario to study the evolutionary histories of dark-matter haloes and to characterize the Lagrangian regions from which they form. We focus on haloes identified at redshift z_id=0 and show that the classic ellipsoidal collapse model systematically overestimates their collapse times. If one imposes that halo collapse takes place at z_id, this model requires starting from a significantly lower linear density contrast than what is measured in the simulations at the locations of halo formation. We attempt to explain this …
In the standard model of structure formation galaxies reside in virialized dark matter haloes which extend much beyond the observational radius of the central system. The dark matter halo formation process is hierarchical, small systems collapse at high redshift and then merge together forming larger ones. In this work we study the mass assembly history of host haloes at different observation redshifts and the mass function of accreted satellites (haloes that merge directly on the main halo progenitor). We show that the satellite mass function is universal, both independent on the host halo ma…
We use the large catalogues of haloes available for the Millennium Simulation to test whether recently merged haloes exhibit stronger large-scale clustering than other haloes of the same mass. This effect could help to understand the very strong clustering of quasars at high redshift. However, we find no statistically significant excess bias for recently merged haloes over the redshift range 2 < z < 5, with the most massive haloes showing an excess of at most ~5%. We also consider galaxies extracted from a semianalytic model built on the Millennium Simulation. At fixed stellar mass, we find an…
Dark matter haloes in Lambda CDM simulations grow by mergers with other haloes as well as accretion of "diffuse" non-halo material. We quantify the mass growth rates via these two processes, dM_mer/dt and dM_dif/dt, and their dependence on halo environment using the ~500,000 haloes in the Millennium simulation. Adopting a local mass density parameter as a measure of halo environment, we find the two rates show strong but opposite environmental dependence, with mergers playing an increasingly important role for halo growths in overdense regions and diffuse accretion dominating growth in voids. …
We calculate merger rates of dark matter haloes using the Extended Press-Schechter approximation (EPS) for the Spherical Collapse (SC) and the Ellipsoidal Collapse (EC) models. Merger rates have been calculated for masses in the range $10^{10}M_{\odot}\mathrm{h}^{-1}$ to $10^{14}M_{\odot}\mathrm{h}^{-1}$ and for redshifts $z$ in the range 0 to 3 and they have been compared with merger rates that have been proposed by other authors as fits to the results of N-body simulations. The detailed comparison presented here shows that the agreement between the analytical models and N-body simulations de…
Mass and concentration of clusters of galaxies are related and evolving with redshift. We study the properties of a sample of 31 massive galaxy clusters at high redshift, 0.8 < z < 1.5, using weak and strong lensing observations. Concentration is a steep function of mass, c_{200} ~M_{200}^{-0.83 +-0.39}, with higher-redshift clusters being less concentrated. Mass and concentration from the stacked analysis, M_{200}=(4.1+-0.4)x10^{14}M_Sun/h and c_{200}=2.3+-0.2, are in line with theoretical results extrapolated from the local universe. Clusters with signs of dynamical activity preferentially f…
We derive an estimate of the rate of formation of dark matter halos per unit volume as a function of the halo mass and redshift of formation. Analytical estimates of the number density of dark matter halos are useful in modeling several cosmological phenomena. We use the excursion set formalism for computing the formation rate of dark matter halos. We use an approach that allows us to differentiate between major and minor mergers, as this is a pertinent issue for semi-analytic models of galaxy formation. We compute the formation rate for the Press-Schechter and the Sheth-Tormen mass function. …
We study the behaviour of multiple radiative cooling algorithms implemented in seven Semi-Analytic Models (SAMs) of galaxy formation, including a new model we propose in this paper. We use versions of the models without feedback and apply them to dark matter haloes growing in a cosmological context, which have final masses that range from 10^{11}Msun to 10^{14}Msun. First, using simplified smoothly-growing halo models, we demonstrate that the different algorithms predict cooling rates and final cold gas masses that differ by a factor of ~5 for massive haloes (>10^{12}Msun). The algorithms are …
The statistics of peaks of the initial, Gaussian density field can be used to interpret the abundance and clustering of massive dark matter haloes. I discuss some recent theoretical results related to their clustering and its redshift evolution. Predictions from the peak model are qualitatively consistent with measurements of the linear bias of high mass haloes, which also show some evidence for a dependence on the halo mass M at fixed peak height. The peak approach also predicts a distinctive scale-dependence in the bias of haloes across the baryon acoustic feature, a measurement of which wou…
Intrinsic alignments of galaxies are a significant astrophysical systematic affecting cosmological constraints from weak gravitational lensing. Obtaining numerical predictions from hydrodynamical simulations of expected survey volumes is expensive, and a cheaper alternative relies on populating large dark matter-only simulations with accurate models of alignments calibrated on smaller hydrodynamical runs. This requires connecting the shapes and orientations of galaxies to those of dark matter haloes and to the large-scale structure. In this paper, we characterise galaxy-halo alignments in the …
The origins of the ~10^9 Msun quasar supermassive black holes (BHs) at redshifts z > 6 remain a theoretical puzzle. One possibility is that they grew from ~10^5 Msun BHs formed in the 'direct collapse' of pristine, atomic-cooling (temperatures T ~ 8000 K; PAC) gas that did not fragment to form ordinary stars due to a lack of molecular hydrogen and metals. We propose that baryonic streaming---the relic relative motion of gas with respect to dark matter from cosmological recombination---provides a natural mechanism for establishing the conditions necessary for direct collapse. This effect delays…
The mass aggregation and merger histories of present-day distinct haloes selected from the cosmological Millennium Simulations I and II are mapped into stellar mass aggregation and galaxy merger histories of central galaxies by using empirical stellar-to-halo and stellar-to-gas mass relations. The growth of bulges driven by the galaxy mergers/interactions is calculated using dynamical prescriptions. The predicted bulge demographics at redshift z~0 is consistent with observations (Zavala+2012). Here we present the evolution of the morphological mix (traced by the bulge-to-total mass ratio, B/T)…
A very large dynamic range with simultaneous capture of both large- and small-scales in the simulations of cosmic structures is required for correct modelling of many cosmological phenomena, particularly at high redshift. This is not always available, or when it is, it makes such simulations very expensive. We present a novel sub-grid method for modelling low-mass ($10^5\,M_\odot\leq M_{\rm halo}\leq 10^9\,M_\odot$) haloes, which are otherwise unresolved in large-volume cosmological simulations limited in numerical resolution. In addition to the deterministic halo bias that captures the averag…
We present a study on the clustering of a stellar mass selected sample of 18,482 galaxies with stellar masses M*>10^10M(sun) at redshifts 0.4<z<2.0, taken from the Palomar Observatory Wide-field Infrared Survey. We examine the clustering properties of these stellar mass selected samples as a function of redshift and stellar mass, and discuss the implications of measured clustering strengths in terms of their likely halo masses. We find that galaxies with high stellar masses have a progressively higher clustering strength, and amplitude, than galaxies with lower stellar masses. We also find tha…
Dark matter haloes in which galaxies reside are likely to have a significant impact on their evolution. We investigate the link between dark matter haloes and their constituent galaxies by measuring the angular two-point correlation function of radio sources, using recently released 3 GHz imaging over $\sim 2 \ \mathrm{deg}^2$ of the COSMOS field. We split the radio source population into Star Forming Galaxies (SFGs) and Active Galactic Nuclei (AGN), and further separate the AGN into radiatively efficient and inefficient accreters. Restricting our analysis to $z<1$, we find SFGs have a bias, $…
Recent high-resolution N-body CDM simulations indicate that nonsingular three-parameter models such as the Einasto profile perform better than the singular two-parameter models, e.g. the Navarro, Frenk and White, in fitting a wide range of dark matter haloes. While many of the basic properties of the Einasto profile have been discussed in previous studies, a number of analytical properties are still not investigated. In particular, a general analytical formula for the surface density, an important quantity that defines the lensing properties of a dark matter halo, is still lacking to date. To …
We examine the formation of groups of multiple supermassive black holes (SMBHs) in gas-poor galactic nuclei due to the high merger rate of galaxies at high redshifts. We calculate the relative likelihood of binary, triple, and quadruple SMBH systems, by considering the timescales for relevant processes and combining merger trees with N-body simulations for the dynamics of stars and SMBHs in galactic nuclei. Typical haloes today with mass $M_0\approx 10^{14}$ M$_\odot$ have an average mass $M_{z=6}=5\times 10^{11}$ M$_\odot$ at $z\sim 6$, while rare haloes with current mass $M_0\gtrsim 10^{15}$…
We address the issue of the cosmological bias between matter and galaxy distributions, looking at dark-matter haloes as a first step to characterize galaxy clustering. Starting from the linear density field at high redshift, we follow the centre of mass trajectory of the material that will form each halo at late times (proto-halo). We adopt a fluid-like description for the evolution of perturbations in the proto-halo distribution, which is coupled to the matter density field via gravity. We present analytical solutions for the density and velocity fields, in the context of renormalized perturb…
Dark matter is an important ingredient of galaxies, as was recognised early on by Ken Freeman himself! Evidence for dark matter halos is still indirect, based on analysing motions of tracers such as gas and stars. In a sense the visible galaxy is the mask through which we can study the dark matter. Light rays are also sensitive to gravitational fields, and dark haloes cause observable gravitational lensing effects. There are three regimes: microlensing (which probes the clumpiness of dark matter haloes), strong lensing (sensitive to the inner mass distribution) and weak lensing (which can prob…
The Environmental Dependence of Halo Intrinsic Alignments: Stronger Signals in Underdense Regions
The University of Tokyo（东京大学）；Center for Data-Driven Discovery (CD3), Kavli IPMU (WPI), UTIAS, The University of Tokyo（数据驱动发现中心 (CD3)，Kavli宇宙物理数学研究所 (WPI)，UTIAS，东京大学）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study (UTIAS), The University of Tokyo（Kavli宇宙物理数学研究所 (WPI)，东京大学高级研究学院 (UTIAS)，东京大学）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理学研究所）
We present a detailed study of HI and metals for 110 MgII absorption systems discovered at 1.98 <= z <= 5.33 in the infrared spectra of high redshift QSOs. Using new measurements of rest-frame UV lines from optical spectra of the same targets, we compare the high redshift sample with carefully constructed low redshift control samples from the literature to study evolutionary trends from z=0 --> 5.33 (>12 Gyr). We observe a significant strengthening in the characteristic N(HI) for fixed MgII equivalent width as one moves toward higher redshift. Indeed at our sample's mean zbar=3.402, all MgII s…
We apply the empirical method built for z=0 in the previous work of Wang et al. to a higher redshift, to link galaxy stellar mass directly with its hosting dark matter halo mass at z~0.8. The relation of the galaxy stellar mass and the host halo mass M_infall is constrained by fitting both the stellar mass function and the correlation functions at different stellar mass intervals of the VVDS observation, where M_infall is the mass of the hosting halo at the time when the galaxy was last the central galaxy. We find that for low mass haloes, their residing central galaxies are less massive at hi…
We propose a new framework for testing gravity using cluster observations, which aims to provide an unbiased constraint on modified gravity models from Sunyaev Zel'dovich (SZ) and X-ray cluster counts and the cluster gas fraction, among other possible observables. Focusing on a popular $ f(R) $ model of gravity, we propose a novel procedure to recalibrate mass scaling relations from $ Λ$CDM to $ f(R) $ gravity for SZ and X-ray cluster observables. We find that the complicated modified gravity effects can be simply modelled as a dependence on a combination of the background scalar field and red…
