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Statistics Of Magnification Perturbations By Substructure In The Cold Dark Matter Cosmological Model
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Book Synopsis Statistics of Magnification Perturbations by Substructure in the Cold Dark Matter Cosmological Model by :
Download or read book Statistics of Magnification Perturbations by Substructure in the Cold Dark Matter Cosmological Model written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the statistical properties of magnification perturbations by substructures in strong lensed systems using linear perturbation theory and an analytical substructure model including tidal truncation and a continuous substructure mass spectrum. We demonstrate that magnification perturbations are dominated by perturbers found within a tidal radius of an image, and that sizable magnification perturbations may arise from small, coherent contributions from several substructures within the lens halo. We find that the root-mean-square (rms) fluctuation of the magnification perturbation is (almost equal to)10% to (almost equal to)20% and both the average and rms perturbations are sensitive to the mass spectrum and density profile of the perturbers. Interestingly, we find that relative to a smooth model of the same mass, the average magnification in clumpy models is lower (higher) than that in smooth models for positive (negative) parity images. This is opposite from what is observed if one assumes that the image magnification predicted by the best-fit smooth model of a lens is a good proxy for what the observed magnification would have been if substructures were absent. While it is possible for this discrepancy to be resolved via nonlinear perturbers, we argue that a more likely explanation is that the assumption that the best-fit lens model is a good proxy for the magnification in the absence of substructure is not correct. We conclude that a better theoretical understanding of the predicted statistical properties of magnification perturbations by CDM substructure is needed in order to affirm that CDM substructures have been unambiguously detected.
Book Synopsis Illuminating Dark Matter by : Rouven Essig
Download or read book Illuminating Dark Matter written by Rouven Essig and published by Springer Nature. This book was released on 2019-11-22 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: Based on a Simons Symposium held in 2018, the proceedings in this volume focus on the theoretical, numerical, and observational quest for dark matter in the universe. Present ground-based and satellite searches have so far severely constrained the long-proposed theoretical models for dark matter. Nevertheless, there is continuously growing astrophysical and cosmological evidence for its existence. To address present and future developments in the field, novel ideas, theories, and approaches are called for. The symposium gathered together a new generation of experts pursuing innovative, more complex theories of dark matter than previously considered.This is being done hand in hand with experts in numerical astrophysical simulations and observational techniques—all paramount for deciphering the nature of dark matter. The proceedings volume provides coverage of the most advanced stage of understanding dark matter in various new frameworks. The collection will be useful for graduate students, postdocs, and investigators interested in cutting-edge research on one of the biggest mysteries of our universe.
Book Synopsis Investigating Inhomogeneous Szekeres Models and Their Applications to Precision Cosmology by : Austin Chandler Peel
Download or read book Investigating Inhomogeneous Szekeres Models and Their Applications to Precision Cosmology written by Austin Chandler Peel and published by . This book was released on 2015 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Exact solutions of Einstein's field equations that can describe the evolution of complex structures in the universe provide complementary frameworks to standard perturbation theory in which to analyze cosmological and astrophysical phenomena. The flexibility and generality of the inhomogeneous and anisotropic Szekeres metric make it the best known exact solution to explore nonlinearities in the universe. We study applications of Szekeres models to precision cosmology, focusing on the influence of inhomogeneities in two primary contexts--the growth rate of cosmic structures and biases in distance determinations to remote sources. We first define and derive evolution equations for a Szekeres density contrast, which quantifies exact deviations from a smooth background cosmology. Solving these equations and comparing to the usual perturbative approach, we find that for models with the same matter content, the Szekeres growth rate is larger through the matter-dominated cosmic era. Including a cosmological constant, we consider exact global perturbations, as well as the evolution of a single extended structure surrounded by an almost homogeneous background. For the former, we use growth data to obtain a best fit Szekeres model and find that it can fit the data as well as the standard Lambda-Cold Dark Matter (LCDM) cosmological model but with different cosmological parameters. Next, to study effects of inhomogeneities on distance measures, we build an exact relativistic Swiss-cheese model of the universe, where a large number of non-symmetric and randomly placed Szekeres structures are embedded within a LCDM background. Solving the full relativistic propagation equations, light beams are traced through the model, where they traverse the inhomogeneous structures in a way that mimics the paths of real light beams in the universe. For beams crossing a single structure, their magnification or demagnification reflects primarily the net density encountered along the path. Despite nontrivial evolution and density distributions of the structures, the effect of tidal shearing on the beams remains small. Finally, we study source magnification probability distributions for various redshifts, finding a limitation of the models in that the distributions do not consistently resemble those of gravitational lensing analyses in cosmological simulations.
Book Synopsis Simulations of Scale-Free Cosmologies for the Small-Scale Cold Dark Matter Universe by :
Download or read book Simulations of Scale-Free Cosmologies for the Small-Scale Cold Dark Matter Universe written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Cosmological simulations show that dark matter halos contain a wealth of substructure. These subhalos are assumed have a mass distribution that extends down to the smallest mass in the Cold Dark Matter (CDM) hierarchy, which lies below the current resolution limit of simulations. Substructure has important ramifications for indirect dark matter detection experiments as the signal depends sensitively on the small-scale density distribution of dark matter in the Galactic halo. A clumpy halo produces a stronger signal than halos where the density is a smooth function of radius. However, the small-scale Universe presents a daunting challenge for models of structure formation. In the CDM paradigm, structures form in a hierarchical fashion, with small-scale perturbations collapsing first to form halos that then grow via mergers. However, near the bottom of the hierarchy, dark matter structures form nearly simultaneously across a wide range of scales. To explore these small scales, I use a series of simulations of scale-free cosmological models, where the initial density power spectrum is a power-law. I can effectively examine various scales in the Universe by using the index in these artificial cosmologies as a proxy for scale. This approach is not new, but my simulations are larger than previous such simulations by a factor of 3 or more. My results call into question the often made assumption that the subhalo population is scale-free. The subhalo population does depend on the mass of the host. By combining my study with others, I construct a phenomenological model for the subhalo mass function. This model shows that the full subhalo hierarchy does not greatly boost the dark matter annihilation flux of a host halo. Thus, the enhancement of the Galactic halo signature due to substructure can not alone account the observed flux of cosmic rays produced by annihilating dark matter. Finally, I examine the nonlinear power spectrum, which is used to determine cosmological parame.
Book Synopsis From Supermassive Black Holes to Supersymmetric Dark Matter by : Savvas Michael Koushiappas
Download or read book From Supermassive Black Holes to Supersymmetric Dark Matter written by Savvas Michael Koushiappas and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: It is without doubt that in recent years cosmology has entered an era where cosmological parameters are now measured precisely enough to derive conclusions about the underlying characteristics of the Universe. I present an overview of the methods used to estimate the parameters that lead to the standard cosmological model. After a brief detour on the current understanding of the mechanisms that lead to galaxy formation, I present a model in which the seeds of supermassive black holes observed in galactic spheroids form out of the lowest angular momentum gas in proto-galaxies at high redshift. I assume that the gas in early-forming, rare-peak halos has a distribution of specific angular momentum similar to that derived for the dark matter. In halos more massive than a critical threshold, proto-galactic disks are gravitationally unstable and experience an efficient viscosity that transfers angular momentum outward allowing mass inflow. This process continues until the first massive stars disrupt the disk. The seed black holes created in this manner have a characteristic mass scale, roughly independent of the redshift of formation. By the redshift of reionization, the comoving mass density is comparable to that inferred from observations, with room for appropriate additional luminous growth during a later quasar accretion phase. The hierarchical merger process naturally leads to a linear correlation between black-hole mass and stellar spheroid mass. Quite orthogonal to this study, I estimate the probability of detecting gamma-rays from the annihilation of neutralino dark matter in the Milky Way substructure. I characterize substructure statistically based on Monte Carlo realizations of the formation of a Milky Way-like halo. I find that it may be possible for upcoming experiments to detect gamma-rays from dark matter substructure if the neutralino is relatively light, while for a heavy neutralino such a detection would be unlikely. I find that the probability of detection is sensitive to poorly-constrained input parameters, particularly those that characterize the primordial power spectrum. I conclude that the lack of a detected gamma-ray signal gives very little information about the supersymmetric parameter space due to uncertainties associated with both the properties of substructure and cosmological parameters.
Author :Colloquium on the Age of the Universe St Publisher :National Academies Press ISBN 13 :9780309060264 Total Pages :100 pages Book Rating :4.0/5 (62 download)
Book Synopsis Colloquium on the Age of the Universe, Dark Matter, and Structure Formation by : Colloquium on the Age of the Universe St
Download or read book Colloquium on the Age of the Universe, Dark Matter, and Structure Formation written by Colloquium on the Age of the Universe St and published by National Academies Press. This book was released on 1998-01-01 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Structure and Substructure of Cold Dark Matter Halos by :
Download or read book The Structure and Substructure of Cold Dark Matter Halos written by and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the structure and substructure of Lambda-CDM halos using a suite of high-resolution cosmological N-body simulations. Our analysis of the substructure population of dark matter halos focuses on their mass and peak circular velocity functions, as well as their spatial distribution and dynamics. In our analysis, we consider the whole population of subhalos physically associated with the main halo, defined as those that have, at some time, crossed within the virial radius of the main progenitor. We find that this population extends beyond 3 times the virial radius and includes objects on unorthodox orbits, several of which travel at velocities approaching the nominal escape speed from the system. We trace the origin of these unorthodox orbits to the tidal dissociation of bound groups, which results in the ejection of some systems along tidal streams. This process primarily influences low-mass systems leading to clear mass-dependent biases in their spatial distribution and kinematics: the lower the subhalo mass at accretion time the more concentrated and kinematically hotter their descendant population. When quantified in terms of present day subhalo mass these trends disappear, presumably due to the increased effect of dynamical friction and tidal stripping on massive systems. We confirm several of these results using the ultra-high resolution Aquarius simulations, which extend the dynamic range of the subhalo mass function by nearly 3 orders of magnitude. Using these simulations we confirm that the substructure mass function follows a power-law, $dN/dM\propto M^{-1.9}$, and exhibits very little halo-to-halo scatter. This implies that the total mass in substructure within a given halo is bounded to a small fraction of the total halo mass, with the smooth component dominating the halo inner regions. Using the Aquarius simulations we study the structure of galaxy-sized Lambda-CDM halos. We find that the spherically averaged density profiles become increasingly sh.
Book Synopsis Cold Dark Matter Substructure and Galactic Disks I by :
Download or read book Cold Dark Matter Substructure and Galactic Disks I written by and published by . This book was released on 2007 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: We conduct a series of high-resolution, fully self-consistent dissipation less N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the [Lambda]CDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. Substructure mass functions, orbital distributions, internal structures, and accretion times are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. We demonstrate that accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z ≈ 1 should be common occurrences. In contrast, extremely few satellites in present-day CDM halos are likely to have a significant impact on the disk structure. This is due to the fact that massive subhalos with small orbital pericenters that are most capable of strongly perturbing the disk become either tidally disrupted or suffer substantial mass loss prior to z = 0. One host halo merger history is subsequently used to seed controlled N-body experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. These simulations track the effects of six dark matter substructures, with initial masses in the range ≈ (0.7-2) x 101° M{sub {circle_dot}} (≈ 20-60% of the disk mass), crossing the disk in the past ≈ 8 Gyr. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a long-lived, low-surface brightness, ring-like feature in the outskirts; a significant flare; a central bar; and faint filamentary structures that (spuriously) resemble tidal streams in configuration space. The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard 'thin-thick' disk decomposition, where the 'thick' disk component has emerged primarily as a result of the interaction with the most massive subhalo. We conclude that satellite-disk encounters of the kind expected in [Lambda]CDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and in other nearby and distant disk galaxies. These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm.
Download or read book Dark Matter written by Jean Audouze and published by Frontières. This book was released on 1988 with total page 520 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Cold dark matter substructure problem and gravitational lensing by : Dandan Xu
Download or read book Cold dark matter substructure problem and gravitational lensing written by Dandan Xu and published by . This book was released on 2010 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Cold Dark Matter Density Perturbation by : Andrew R. Liddle
Download or read book The Cold Dark Matter Density Perturbation written by Andrew R. Liddle and published by . This book was released on 1993 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Probes of Dark Matter from the Universe's Past and Present by : Chih-Liang Wu (Scientist in physics)
Download or read book Probes of Dark Matter from the Universe's Past and Present written by Chih-Liang Wu (Scientist in physics) and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: There are compelling evidences of gravitational effects from dark matter in cosmology and astronomy. By studying other imprints besides gravity, we might be able to infer its properties and interactions with Standard Model particles. This thesis explores how different dark matter models generate interesting observables and what can be learned by looking into various datasets. I demonstrate that novel techniques and datasets from indirect searches can be combined to set stringent constraints on the model parameters. In particular, this thesis details the calculations of constraints from two directions: on the one hand I will show how to constrain the rate of scattering, decay, and annihilation by taking advantage of cosmological observables including the Cosmic Microwave Background and the 21-cm neutral hydrogen line; on the other hand I will exploit astronomical datasets to infer properties of dark matter substructures and halo structures. The sources of the observables span a wide of range of cosmological time from cosmological recombination to the late-time universe, and they can be applied to probe complementary parameter space. With the upcoming precision measurements of astronomy, these novel ideas and calculations of indirect detections will lead insight into the nature of dark matter.
Book Synopsis Reconstructing Cosmological Matter Perturbations Using Standard Candles and Rulers by :
Download or read book Reconstructing Cosmological Matter Perturbations Using Standard Candles and Rulers written by and published by . This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: For a large class of dark energy (DE) models, for which the effective gravitational constant is a constant and there is no direct exchange of energy between DE and dark matter (DM), knowledge of the expansion history suffices to reconstruct the growth factor of linearized density perturbations in the non-relativistic matter component on scales much smaller than the Hubble distance. In this paper, we develop a non-parametric method for extracting information about the perturbative growth factor from data pertaining to the luminosity or angular size distances. A comparison of the reconstructed density contrast with observations of large-scale structure and gravitational lensing can help distinguish DE models such as the cosmological constant and quintessence from models based on modified gravity theories as well as models in which DE and DM are either unified or interact directly. We show that for current supernovae (SNe) data, the linear growth factor at z = 0.3 can be constrained to 5% and the linear growth rate to 6%. With future SNe data, such as expected from the Joint Dark Energy Mission, we may be able to constrain the growth factor to 2%-3% and the growth rate to 3%-4% at z = 0.3 with this unbiased, model-independent reconstruction method. For future baryon acoustic oscillation data which would deliver measurements of both the angular diameter distance and the Hubble parameter, it should be possible to constrain the growth factor at z = 2.5%-9%. These constraints grow tighter with the errors on the data sets. With a large quantity of data expected in the next few years, this method can emerge as a competitive tool for distinguishing between different models of dark energy.
Book Synopsis Probabilistic Inference of Dark Matter Properties in Galaxy Clusters and the Cosmic Web by : Yin-Yee Ng
Download or read book Probabilistic Inference of Dark Matter Properties in Galaxy Clusters and the Cosmic Web written by Yin-Yee Ng and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: "Mass tells spacetime how to curve, spacetime tells mass how to move". This famous quote by physicist John Archibald Wheeler succinctly summarizes General Relativity, the most successful theory that describes our universe at large scale. However, most of the mass that General Relativity describes, namely dark matter (DM), remains a mystery. We have solid evidence of the existence of DM from various observations, but we know little or nothing about the particle nature of DM and how DM particles interact with different particles. Completing this knowledge gap would improve or revolutionize our established cosmological model, the Lambda Cold-Dark Matter (CDM) model, and give directions to theories beyond the standard particle physics model.This work attempts to study DM by examining and extending existing modeling approaches of DM and its visible tracers in a probabilistic way. The single verified form of DM interaction is gravitational. Currently, the only way to infer the properties of DM is through visible tracers. Most of these indirect detections either have low signal-to-noise, sparse coverage, or missing variables. These limitations introduce additional modeling choices and uncertainties. A probabilistic approach allows us to propagate the uncertainties appropriately and marginalize any missing variables. There are two recurring types of visible tracers that my work uses. The first type of tracers are galaxies and observables in the overdense regions of DM. These tracers allow usto infer the macroscopic dynamical properties of DM distribution that we want to study. The second type of tracers, on the hand, are in the background, i.e. further away than the foreground dark matter, from us observers. The gravity of DM can bend spacetime such that the path of light traveling in the vicinity would also curve, leaving distortions in the galaxy images. The gravitational distortion of the images of the background galaxies is also known as gravitational lensing. In the introduction (first chapter) of this thesis, I will layout the technical history, terminology and the reasons behind choosing the various data sets and give an overview of the analysis methods for my thesis work. In chapter two, I will present the study based on the observational data of El Gordo, one of the most massive, most ancient, merging galaxy clusters. Under the extreme collision speeds during a merger of a galaxy cluster, it is more probable for DM particles in the cluster to manifest eects of self-interaction. Thus, if DM particles can interact with one another, some preliminary simulations have shown that large-scale spatial distribution of DM can show discrepancies from its galaxy-counterparts. This discrepancy is also known as the galaxy-DM offset, with a caveat. The long duration (millions of years) of a merger means that we cannot detect the direction of motions of the components directly to confirm the offset as a lag. My work on El Gordo was the first to show a quantitative method of estimating how likely the DM components of El Gordo are to be moving in a certain direction. This study was made possible by utilizing informative observables in various wavelengths, including a pair of radio shockwaves on the outer skirt of the cluster, enhanced X-ray emissivity and the decrement of the Sunyaev-Zel'Dovich effect for the infra-red observations. This comprehensive set of observables allowed us to formulate probabilistic constraints in our Monte Carlo simulation of El Gordo. Furthermore, the study also brought up several questions about the modeling choices for comparing the DM and the member-galaxy distributions of a cluster. For instance, do the DM maps and the galaxy maps have high enough resolution to show the delicate offset signal produced by the possible self-interaction of DM (SIDM)? To address my concerns from the study of El Gordo, I conducted a second investigation of galaxy clusters in a cosmological simulation, which is described in chapter 3. The dataset I chose was from the Illustris simulation. As this simulation assumes a Cold-Dark-Mattermodel (CDM) without requiring an SIDM model, any offset between DM and the member galaxies in a galaxy cluster provides an estimate of the variability of the galaxy-DM offset. My study shows that the variability in this setting is non-negligible compared to the small observed offsets, it is likely that random variation can account for the galaxy-DM offsets inobservations. The result weakens our belief that SIDM is the cause of the offsets. The fourth chapter of my dissertation builds on top of my previous experience with analyzing the weak lensing data for El Gordo. This time, I performed the weak lensing study for a dataset of a much larger spatial scale, such that, galaxy clusters look like parts of a homogeneous and isotropic DM web. At this scale, it is possible to compare the spatial distribution of DM to simulations to give competitive constraints on cosmological parameters. Using weak lensing signals for estimating cosmological parameters is also known as cosmic shear inference. While I used a parametric technique to estimate the mass of El Gordo in chapter 2, my work in chapter 4 introduces a new non-parametric model using a Gaussian Process. A Gaussian Process is a generalization of the multivariate normal distribution to higher dimensions. We can draw functional models from a Gaussian Process to describe our data. While the realizations are drawn from a multivariate normal distribution, we can specify the parameters and the functional structure of the covariance (kernel) matrix of the underlying distribution. This generative model gives us the ability to put probabilistic estimates of DM density in regions without any background galaxies. As I have built the lensing physics into the very core of the covariance kernel matrix, we can also simultaneously infer the several important lensing observables, such as shear and convergence, given some lensed galaxy shapes. More importantly, this technique relies on fewer assumptions about the photometric redshift than traditional cosmic shear analysis technique. This may reduce the bias towards a ducial cosmology and lead to interesting discoveries. However, this new technique is not without its challenges. Computationally, this technique requires an O(n3) runtime. Despite my best attempts to parallelize the computation, the algorithm takes longer for generating DM mass maps than traditional approaches. My work here marks the beginning of an alternative method for cosmic shear inference. Many promising approximation techniques have emerged to drastically speed up the runtime of doing inference with a Gaussian Process. Incorporating these approximations may make it possible to use this method to give tighter cosmological constraints from future sky surveys such as the Large Synoptic Survey Telescope. I conclude my work in Chapter 5 and discuss the implications of my work. This includes some future directions for analyzing DM by using simulations with different underlying DM models and real data.
Book Synopsis Mapping Dark Matter with Cosmic Magnification by :
Download or read book Mapping Dark Matter with Cosmic Magnification written by and published by . This book was released on 2005 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We develop a new tool to generate statistically precise dark matter maps from the cosmic magnification of galaxies with distance estimates. We show how to overcome the intrinsic clustering problem using the slope of the luminosity function, because magnificability changes strongly over the luminosity function, while intrinsic clustering only changes weakly. This may allow precision cosmology beyond most current systematic limitations. SKA is able to reconstruct projected matter density map at smoothing scale ≈ 10' with S/N ≈> 1, at the rate of 200-4000 deg2 per year, depending on the abundance and evolution of 21cm emitting galaxies. This power of mapping dark matter is comparable to, or even better than that of cosmic shear from deep optical surveys or 21cm surveys.
Book Synopsis Galaxy Formation and Evolution by : Houjun Mo
Download or read book Galaxy Formation and Evolution written by Houjun Mo and published by Cambridge University Press. This book was released on 2010-05-20 with total page 841 pages. Available in PDF, EPUB and Kindle. Book excerpt: A coherent introduction for researchers in astronomy, particle physics, and cosmology on the formation and evolution of galaxies.
Download or read book Physics Briefs written by and published by . This book was released on 1993 with total page 1420 pages. Available in PDF, EPUB and Kindle. Book excerpt:
