To quantify how rare the bullet-cluster-like high-velocity merging systems are in the standard LCDM cosmology, we use a large-volume 27 (Gpc/h)^3 MICE simulation to calculate the distribution of infall velocities of subclusters around massive main clusters. The infall-velocity distribution is given at (1-3)R_{200} of the main cluster (where R_{200} is similar to the virial radius), and thus it gives the distribution of realistic initial velocities of subclusters just before collision. These velocities can be compared with the initial velocities used by the non-cosmological hydrodynamical simulations of 1E0657-56 in the literature. The latest parameter search carried out recently by Mastropietro and Burkert showed that the initial velocity of 3000 km/s at about 2R_{200} is required to explain the observed shock velocity, X-ray brightness ratio of the main and subcluster, and displacement of the X-ray peaks from the mass peaks. We show that such a high infall velocity at 2R_{200} is incompatible with the prediction of a LCDM model: the probability of finding 3000 km/s in (2-3)R_{200} is between 3.3X10^{-11} and 3.6X10^{-9}. It is concluded that the existence of 1E0657-56 is incompatible with the prediction of a LCDM model, unless a lower infall velocity solution for 1E0657-56 with < 1800 km/s at 2R_{200} is found.
We study the distribution of intragroup dark matter in small groups of dark matter halos of galaxy-like size in a LCDM cosmology. These groups are identified using a physical criterion and may be an appropriate representation of small galaxy groups. We quantify the amount of intragroup dark matter and characterize its distribution. We find that compact associations of halos, as well as those intermediate and loose groups, have rather flat intragroup dark matter profiles with logarithmic slopes of gamma ~0 and ~-0.2$, respectively. Hence, the intragroup dark matter of these halo systems does no…
We present a method to measure the growth of structure and the background geometry of the Universe -- with no a priori assumption about the underlying cosmological model. Using Canada-France-Hawaii Lensing Survey (CFHTLenS) shear data we simultaneously reconstruct the lensing amplitude, the linear intrinsic alignment amplitude, the redshift evolving matter power spectrum, P(k,z), and the co-moving distance, r(z). We find that lensing predominately constrains a single global power spectrum amplitude and several co-moving distance bins. Our approach can localise precise scales and redshifts wher…
$Λ$CDM-model predicts an excess of dark halos compared to the observations. The excess is seen from the estimates of the virialized mass inside the Local Supercluster and its surroundings. It is shown that account for cosmological velocity fluctuations in the process of formation of the population of dark halos it is possible to eliminate this contradiction remaining within the framework of the $Λ$CDM cosmology. Based on the formalism of Press and Schechter, we suggest a model of formation of dark halo population which takes into account the kinematic effects in the dark matter. The model allo…
The Challenge of the Largest Structures in the Universe to Cosmology
大星系红移巡天长期以来一直被用来限制宇宙学模型和结构形成的假设。特别是，观测发现的最大结构被认为携带了关于大尺度密度波动或宇宙均匀性的重要信息，并且经常挑战标准宇宙学框架。最近在斯隆数字巡天（SDSS）地区发现的斯隆长城（SGW）对具有宇宙学常数的和谐宇宙学模型（即平直LCDM模型）提出了质疑。在这里，我们证明了SGW的存在与LCDM模型完全一致，这一结果只有我们的超大型宇宙学N体模拟（Horizon Run 2，HR 2）才能提供。此外，我们报告发现的SDSS中的空隙复合物比SGW大得多，并表明，这种最大的空隙的大小也预测在LCDM范例。我们的结果表明，一个初始均匀的各向同性宇宙与原始高斯随机相位密度波动增长按照广义相对论，可以解释的丰富性和规模的观测到的大尺度结构的SDSS。使用HR2模拟，我们预测，未来的星系红移调查约4倍深或3级暗极限比SDSS应该揭示一个最大的结构的明亮星系的两倍大的SGW。
The generalized Chaplygin gas cosmology provides a prime example for the class of unified dark matter models, which substitute the two dark components of the standard cosmological LCDM concordance model by a single dark component. The equation of state of the generalized Chaplygin gas is characterised by a parameter alpha such that the standard LCDM model is recovered in the case alpha=0 with respect to the background dynamics and the cosmic microwave background (CMB) statistics. This allows to investigate the concordance of different cosmological data sets with respect to alpha. We compare th…
The Bullet Cluster (1E0657-56) is well-known as providing visual evidence of dark matter but it is potentially incompatible with the standard $Λ$CDM cosmology due to the high relative velocity of the two colliding clusters. Previous studies have focussed on the probability of such a high relative velocity amongst selected candidate systems. This notion of `probability' is however difficult to interpret and can lead to paradoxical results. Instead, we consider the expected number of Bullet-like systems on the sky up to a specified redshift, which allows for direct comparison with observations. …
The goodness-of-fit (GoF) of the Cosmicflows-2 (CF2) database of peculiar velocities with the LCDM standard model of cosmology is presented. Standard application of the Chi^2 statistics of the full database, of its 4,838 data points, is hampered by the small scale nonlinear dynamics which is not accounted for by the (linear regime) velocity power spectrum. The bulk velocity constitutes a highly compressed representation of the data which filters out the small scales non-linear modes. Hence the statistics of the bulk flow provides an efficient tool for assessing the GoF of the data given a mode…
In this paper we review the main theoretical and experimental achievements in the field of Dark Matter from the Cosmological and Astrophysical point of view. We revisit it from the very first surveys of local astrophysical matter, up to the stringent constraints on matter properties, coming from the last release of data on cosmological scales. To bring closer and justify the idea of dark matter, we will go across methods and tools for measuring dark matter characteristics, and in some cases a combination of methods that provide one of the greatest direct proofs for dark matter, such as Bullet …
The velocity function derived from large scale surveys can be compared with the predictions of LCDM cosmology, by matching the measured rotation velocities Vrot of galaxies to the maximum circular velocity of dark matter (DM) halos Vmax. For Vrot<50km/s, a major discrepancy arises between the observed and LCDM velocity functions. However, the manner in which different observational measures of Vrot are associated with Vmax is not straight forward in dwarf galaxies. We instead relate galaxies to DM halos using the empirical baryon- mass to halo-mass relation, and show that different observation…
Unlike other observational signatures in cosmology, the angular-diameter distance d_A(z) uniquely reaches a maximum (at z_max) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, we estimate and use z_max inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing d_A(z) using Gaussian processes, and (3) comparing the predictions of seven different…
We present LCDM cosmological parameter constraints obtained from delensed microwave background power spectra. Lensing maps from a subset of DR4 data from the Atacama Cosmology Telescope (ACT) are used to undo the lensing effect in ACT spectra observed at 150 and 98 GHz. At 150 GHz, we remove the lensing distortion with an effective efficiency of 30% (TT), 30% (EE), 26% (TE) and 20% (BB); this results in detections of the delensing effect at 8.7 sigma (TT), 5.1 sigma (EE), 2.6 sigma (TE), and 2.4 sigma (BB) significance. The combination of 150 and 98 GHz TT, EE, and TE delensed spectra is well …
We use a recently proposed luminosity distance measure for relatively nearby active galactic nuclei (AGNs) to test the predicted expansion of the Universe in the R_h=ct and LCDM cosmologies. This comparative study is particularly relevant to the question of whether or not the Universe underwent a transition from decelerated to accelerated expansion, which is believed to have occurred---on the basis of Type Ia SN studies---within the redshift range (0 < z < 1.3) that will eventually be sampled by these objects. We find that the AGN Hubble Diagram constructed from currently available sources doe…
A previous analysis of starburst-dominated HII Galaxies and HII regions has demonstrated a statistically significant preference for the Friedmann-Robertson-Walker cosmology with zero active mass, known as the R_h=ct universe, over LCDM and its related dark-matter parametrizations. In this paper, we employ a 2-point diagnostic with these data to present a complementary statistical comparison of R_h=ct with Planck LCDM. Our 2-point diagnostic compares---in a pairwise fashion---the difference between the distance modulus measured at two redshifts with that predicted by each cosmology. Our results…
The ratio of baryonic to dark matter densities is assumed to have remained constant throughout the formation of structure. With this, simulations show that the fraction f_gas(z) of baryonic mass to total mass in galaxy clusters should be nearly constant with redshift z. However, the measurement of these quantities depends on the angular distance to the source, which evolves with z according to the assumed background cosmology. An accurate determination of f_gas(z) for a large sample of hot (kT_e > 5 keV), dynamically relaxed clusters could therefore be used as a probe of the cosmological expan…
We present the discovery of ringlike diffuse radio emission structures in the peripheral regions of the Bullet cluster 1E 0657$-$55.8. Ring formations are spanning between 1--3 Mpc away from the center of the cluster, significantly further away from the two already reported relics. Integrated fluxes of four of the sub-regions in the inner `ring' from 4.5 to 10 GHz have also been reported. To understand the possible origin of these structures, here we present a maiden attempt of numerical modelling of a 3D and realistic `bullet' like event in a full cosmological ($Λ$CDM) environment with N-body…
The relevance of the cosmic microwave background for cosmology
Helmholtz Institute for Radiation and Nuclear Physics, University of Bonn（波恩大学赫尔霍兹辐射与核物理研究所）；Astronomical Institute, Charles University（查理大学天文研究所）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）；Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University), Ministry of Education（教育部现代天体物理学与天文学重点实验室（南京大学））；Department of Physics, University of Ottawa（渥太华大学物理系）
SPT-3G D1: CMB temperature and polarization power spectra and cosmology from 2019 and 2020 observations of the SPT-3G Main field
Sorbonne Université（索邦大学）；CNRS（法国国家科学研究中心）；Institut d’Astrophysique de Paris（巴黎天体物理研究所）；Argonne National Laboratory（阿贡国家实验室）；University of Chicago（芝加哥大学）；Kavli Institute for Cosmological Physics（卡弗里宇宙学物理研究所）；Kavli Institute for Particle Astrophysics and Cosmology（卡弗里粒子天体物理与宇宙学研究所）；Stanford University（斯坦福大学）；University of California, Berkeley（加州大学伯克利分校）
If the Universe is dominated by cold dark matter and dark energy as in the currently popular LCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M > ~10^14 Msun appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few x 10^13 Msun at redshifts between z=0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited s…
We map the neutral atomic gas content of M33 using high resolution VLA and GBT observations and fit a tilted ring model to determine the orientation of the extended gaseous disk and its rotation curve. The disk of M33 warps from 8 kpc outwards without substantial change of its inclination with respect to the line of sight. Rotational velocities rise steeply with radius in the inner disk, reaching 100 km/s in 4 kpc, then the rotation curve becomes more perturbed and flatter with velocities as high as 120-130 km/s out to 23 kpc. We derive the stellar mass surface density map of M33's optical dis…
