In Quest of Devising Tools of Probing Cosmology and Gravity using Galaxy Clusters

Galaxy clusters are the biggest gravitationally bound objects in the Universe with various properties which allow us to test gravitational and cosmological models. One such way of testing theoretical models is by directly measuring density profiles of different matter components (i.e. weak lensing and X-ray provide information about baryon and dark matter mass distributions). A recent version of Emergent Gravity (EG) predicts a specific connection between baryonic and dark matter which can be directly tested using galaxy clusters. By using a sample of 23 galaxy clusters, we find that the EG predictions (based on no dark matter) are acceptable fits only near the virial radius. In the cores and in the outskirts, the mass profile shape differences allow us to rule out EG at >5 sigma level. However, when we account for systematic uncertainties in the observed weak-lensing and X-ray profiles, we conclude that we cannot formally rule our EG as an alternative to dark matter on the cluster scale and that we require better constraints on the weak-lensing and gas mass profile shapes in the region 0.310^14 Solar masses) systems over the range 0.4< r/r200< 1. We show that the numerically modeled suppression is independent of velocity anisotropy over the range (-2.5,0.5). Finally, we show that suppression is mass and cosmology independent and can be successfully modeled by inverse power-law (Zv=1+(N0/N)^L) with best-fit parameters N0=14.205, L=0.467. We conclude that the 3D cluster escape velocity profile can be inferred from projected phase-space data without knowledge of cosmology or the use of simulations. We applied this suppression function to test cosmology and our preliminary results produced a tight constraints on cosmological parameters. By statistically analyzing the set of 38 galaxy clusters, we were able to constraint matter energy-density Omega_m=0.325 (+0.014(stat)+0.003(sys), -0.021(stat)-0.001(sys)) and the Hubble constant h=0.733 (+0.007(stat)+0.035(sys), -0.006(stat)-0.029(sys)) in the framework of flat universe and fixed equation of state of dark energy (w=-1). The systematic error budget includes 5% uncertainties on the weak lensing mass calibration and 5% uncertainties in the density model differences between the NFW and the Einasto functions. This result is in a good agreement with other probes, while in general favor CMB observations of Omega_m by Planck Collaboration and h by using Cepheids.PHDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/153453/1/vithal_1.pd

Emergent gravity fails to explain color-dependent galaxy-galaxy lensing signals from SDSS Dr7

We test the Emergent Gravity(EG) theory using the galaxy-galaxy lensing technique based on SDSS DR7 data. In the EG scenario, we do not expect color dependence of the galaxy sample in the 'apparent dark matter' predicted by EG, which is exerted only by the baryonic mass. If the baryonic mass is similar, then the predicted lensing profiles from the baryonic mass should be similar according to the EG, regardless of the color of the galaxy sample. We use the stellar mass of the galaxy as a proxy of its baryonic mass. We divide our galaxy sample into 5 stellar mass bins, and further classify them as red and blue subsamples in each stellar mass bin. If we set halo mass and concentration as free parameters, $\Lambda$CDM is favored by our data in terms of the reduced $\chi^2$ while EG fails to explain the color dependence of ESDs from the galaxy-galaxy lensing measurement.Comment: 7 pages, 3 figures. Accepted by Ap

Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter

Data collected by the Pierre Auger Observatory through 31 August 2007 showed evidence for anisotropy in the arrival directions of cosmic rays above the Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{$6\times 10^{19}$eV}. The anisotropy was measured by the fraction of arrival directions that are less than $3.1^\circ$ from the position of an active galactic nucleus within 75 Mpc (using the V\'eron-Cetty and V\'eron $12^{\rm th}$ catalog). An updated measurement of this fraction is reported here using the arrival directions of cosmic rays recorded above the same energy threshold through 31 December 2009. The number of arrival directions has increased from 27 to 69, allowing a more precise measurement. The correlating fraction is $(38^{+7}_{-6})$, compared with $21$ expected for isotropic cosmic rays. This is down from the early estimate of $(69^{+11}_{-13})$. The enlarged set of arrival directions is examined also in relation to other populations of nearby extragalactic objects: galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in hard X-rays by the Swift Burst Alert Telescope. A celestial region around the position of the radiogalaxy Cen A has the largest excess of arrival directions relative to isotropic expectations. The 2-point autocorrelation function is shown for the enlarged set of arrival directions and compared to the isotropic expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201

The Fluorescence Detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics Research Section

Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory

The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies $E>E_{th}=5.5\times 10^{19}$ eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at $E>E_{th}$ are heavy nuclei with charge $Z$, the proton component of the sources should lead to excesses in the same regions at energies $E/Z$. We here report the lack of anisotropies in these directions at energies above $E_{th}/Z$ (for illustrative values of $Z=6,\ 13,\ 26$). If the anisotropies above $E_{th}$ are due to nuclei with charge $Z$, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies

Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluoresence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to author list and references in v

Search for First Harmonic Modulation in the Right Ascension Distribution of Cosmic Rays Detected at the Pierre Auger Observatory

We present the results of searches for dipolar-type anisotropies in different energy ranges above $2.5\times 10^{17}$ eV with the surface detector array of the Pierre Auger Observatory, reporting on both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution. Upper limits on the amplitudes are obtained, which provide the most stringent bounds at present, being below 2% at 99% $C.L.$ for EeV energies. We also compare our results to those of previous experiments as well as with some theoretical expectations.Comment: 28 pages, 11 figure