We review models for giant radio halos in clusters of galaxies, with a focus on numerical and theoretical work. After summarising the most important observations of these objects, we present an introduction to the theoretical aspects of hadronic models. We compare these models with observations using simulations and find severe problems for hadronic models. We give a short introduction to reacceleration models and show results from the first simulation of CRe reaccel- eration in cluster mergers. We find that in-line with previous theoretical work, reacceleration models are able to elegantly explain main observables of giant radio halos.
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…
Non-linear halo bias for accurate modelling of cosmic infrared background anisotropies
Université de Strasbourg（斯特拉斯堡大学）；Foundation for Research and Technology Hellas (FORTH)（希腊研究与技术基金会）；Aix Marseille Univ（艾克斯-马赛大学）；Université Savoie Mont-Blanc（萨瓦蒙布朗大学）
Giant Radio Sources as a probe of the cosmological evolution of the IGM, II. The observational constraint for the model of the radio-jets propagation through the X-ray halo--IGM interface
Source REconstruction of Arcs behind Cluster Halos (SourceREACH): A New Source Reconstruction Algorithm Optimized for Giant Arcs and Galaxy Cluster Lenses
Small- and intermediate-scale galaxy clustering can be used to establish the galaxy-halo connection to study galaxy formation and evolution and to tighten constraints on cosmological parameters. With the increasing precision of galaxy clustering measurements from ongoing and forthcoming large galaxy surveys, accurate models are required to interpret the data and extract relevant information. We introduce a method based on high-resolution N-body simulations to accurately and efficiently model the galaxy two-point correlation functions (2PCFs) in projected and redshift spaces. The basic idea is …
We present a fast numerical screened halo model algorithm (CHAM) for modeling non-linear power spectrum for the alternative models to LCDM. This method has three obvious advantages. First of all, it is not being restricted to a specific dark energy/modified gravity model. In principle, all of the screened scalar-tensor theories can be applied. Second, the least assumptions are made in the calculation. Hence, the physical picture is very easily understandable. Third, it is very predictable and does not rely on the calibration from N-body simulation. As an example, we show the case of Hu-Sawicki…
Halo model is a physically intuitive method for modelling the non-linear power spectrum, especially for the alternatives to the standard $Λ$CDM models. In this paper, we exam the Sheth-Tormen barrier formula adopted in the previous \texttt{CHAM} method \citep{2018MNRAS.476L..65H}. As an example, we model the ellipsoidal collapse of top-hat dark matter haloes in $f(R)$ gravity. A good agreement between Sheth-Tormen formula and our result is achieved. The relative difference in the ellipsoidal collapse barrier is less than or equal to $1.6\%$. Furthermore, we verify that, for F4 and F5 cases of …
Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and dark matter halos. Unfortunately, the modelling is typically not sufficiently accurate for ruling out models statistically. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. In this paper, we attempt to push halo modelling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. With our forward-modell…
The unusually large "dwarf" galaxy Crater II, with its small velocity dispersion, $\simeq 3$ km/s, defies expectations that low mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius $\simeq 0.71^{+0.09}_{-0.08}$ kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by "Wave Dark Matter" as a Bose-Einstein condensate, $ψ$DM, where the ground state soliton core is surrounded …
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…
We investigate how a property of a galaxy correlates most tightly with a property of its host dark matter halo, using state-of-the-art hydrodynamical simulations of galaxy formation EAGLE, Illustris, and IllustrisTNG. Unlike most of the previous work, our analyses focus on all types of galaxies, including both central and satellite galaxies. We find that the stellar mass of a galaxy at the epoch of the peak circular velocity with an evolution correction gives the tightest such correlation to the peak circular velocity $V_{\rm peak}$ of the galaxy's underling dark matter halo. The evolution of …
We study the matter bispectrum of large structure by comparing theoretical models (perturbation theories and halo models) to numerical simulations using shape and amplitude correlators. We show that among the perturbation theories at one loop the effective field theory of large scale structure extends the furthest into the non-linear regime. We analyse the one and two-loop bispectra in the renormalised perturbation theory and we show that there is a significant extension in the range where results are accurate when going to two loops. In the case of the halo model, we show that there are defic…
Halo models provide a simple and computationally inexpensive way to investigate the connection between galaxies and their dark matter haloes. However, these models rely on the assumption that the role of baryons can be easily parametrized in the modelling procedure. We aim to examine the ability of halo occupation distribution (HOD) modelling to reproduce the galaxy clustering found in two different hydrodynamic simulations, Illustris and EAGLE. For each simulation, we measure several galaxy clustering statistics on two different luminosity threshold samples. We then apply a simple five parame…
Motivated by previous findings that the magnitude gap between certain satellite galaxy 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 modelling of the host halo mass using a machine learning approach. We employ data from the hydrodynamical simulation IllustrisTNG and train a Random Forest (RF) algorithm to predict a halo mass from the stellar masses of its member galaxies. Exhaustive feature selection is adopted to disentangle the importances of different galaxy members. W…
Many dynamical models of the Milky Way halo require assumptions that the distribution function of a tracer population should be independent of time (i.e., a steady state distribution function) and that the underlying potential is spherical. We study the limitations of such modelling by applying a general dynamical model with minimal assumptions to a large sample of galactic haloes from cosmological $N$-body and hydrodynamical simulations. Using dark matter particles as dynamical tracers, we find that the systematic uncertainties in the measured mass and concentration parameters typically have …
We present the study of the dynamical status of the galaxy cluster CL1821+643, a rare and intriguing cool-core cluster hosting a giant radio halo. We base our analysis on new spectroscopic data for 129 galaxies acquired at the Italian Telescopio Nazionale Galileo. We also use spectroscopic data available from the literature and photometric data from the Sloan Digital Sky Survey. We select 120 cluster member galaxies and compute the cluster redshift <z> ~ 0.296 and the global line-of-sight velocity dispersion $σ_{\rm V}$ ~ 1100 km/s. The results of our analysis are consistent with CL1821+643 be…
We report on a spectral study at radio frequencies of the giant radio halo in A2142 (z=0.0909), which we performed to explore its nature and origin. A2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. We performed deep radio observations with the GMRT at 608 MHz, 322 MHz, and 234 MHz and with the VLA in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A2142. We studied the spectral index in two regions: t…
We present the results of new Suzaku observations of the Coma Cluster, the X-ray brightest, nearby, merging system hosting a well studied, typical giant radio halo. It has been previously shown that, on the western side of the cluster, the radio brightness shows a much steeper gradient compared to other azimuths. XMM-Newton and Planck revealed a shock front along the southern half of the region associated with this steep radio gradient, suggesting that the radio emission is enhanced by particle acceleration associated with the shock passage. Suzaku demonstrates for the first time that this sho…
Mapping the Dynamics of a Giant Ly-alpha Halo at z=4.1 with MUSE: The Energetics of a Large Scale AGN-Driven Outflow around a Massive, High-Redshift Galaxy
Understanding the galaxy-halo connection is fundamental for contemporary models of galaxy clustering. The extent to which the haloes' assembly history and environment impact galaxy clustering (a.k.a. galaxy assembly bias; GAB), remains a complex and challenging problem. Using a semi-analytic galaxy formation model, we study the individual contributions of different secondary halo properties to the GAB signal. These are obtained by comparing the clustering of stellar-mass selected samples to that of shuffled samples where the galaxies are randomly reassigned to haloes of fixed mass and a specif…
Lyman-alpha Blobs Like Company : The Discovery of A Candidate 100 kpc Lyman-alpha Blob Near to A Radio Galaxy with A Giant Lyman-alpha halo, B3 J2330+3927 at z=3.1
We construct halo occupation distribution (HOD) models of high redshift ($z \gtrsim 7.5$) galaxies with $M_{*}>10^8~M_{\odot}/h$ using the BlueTides hydrodynamic simulation suite, with a particular emphasis on modelling the small scale / 1-halo clustering ($0.01\lesssim r \lesssim 1~ h^{-1}\rm{Mpc}$). Similar to low redshift studies, we find that the central and satellite mean HODs ($\left<N_{\mathrm{cen}}\right>$ and $\left<N_{\mathrm{sat}}\right>$) can be modeled by a smoothed step function and a power law respectively. The number density of satellite galaxies is however significantly suppre…
Using hydrodynamical simulations, we study how well the underlying gravitational potential of a galaxy cluster can be modelled dynamically with different types of tracers. In order to segregate different systematics and the effects of varying estimator performances, we first focus on applying a generic minimal assumption method (oPDF) to model the simulated haloes using the full 6-D phasespace information. We show that the halo mass and concentration can be recovered in an ensemble unbiased way, with a stochastic bias that varies from halo to halo, mostly reflecting deviations from steady stat…
A Salpeter IMF and an NFW halo: Disentangling the dark and stellar mass of an elliptical galaxy through precise lens modelling of a double-source-plane system
University of Portsmouth（朴茨茅斯大学）；The University of Sydney（悉尼大学）
We estimate the 3D density profile of the Galactic dark matter (DM) halo within $r \lesssim 30$ kpc from the Galactic centre by using the astrometric data for halo RR Lyrae stars from Gaia DR2. We model both the stellar halo distribution function and the Galactic potential, fully taking into account the survey selection function, the observational errors, and the missing line-of-sight velocity data for RR Lyrae stars. With a Bayesian MCMC method, we infer the model parameters, including the density flattening of the DM halo $q$, which is assumed to be constant as a function of radius. We find …
