arXiv subjects

Alexandre Refregier

Publications and source records attributed to Alexandre Refregier.

At least 91 records · Page 5Linked to original sources

arXiv2017

Integrated Cosmological Probes: Extended Analysis

Recent progress in cosmology has relied on combining different cosmological probes. In earlier work, we implemented an integrated approach to cosmology where the probes are combined into a common framework at the map level. This has the advantage of taking full account of the correlations between the different probes, to provide a stringent test of systematics and of the validity of the cosmological model. We extend this analysis to include not only CMB temperature, galaxy clustering, weak lensing from SDSS but also CMB lensing, weak lensing from the DES SV survey, Type Ia SNe and $H_{0}$ measurements. This yields 12 auto- and cross-power spectra as well as background probes. Furthermore, we extend the treatment of systematic uncertainties. For $Λ$CDM, we find results that are consistent with our earlier work. Given our enlarged data set and systematics treatment, this confirms the robustness of our analysis and results. Furthermore, we find that our best-fit cosmological model gives a good fit to the data we consider with no signs of tensions within our analysis. We also find our constraints to be consistent with those found by WMAP9, SPT and ACT and the KiDS weak lensing survey. Comparing with the Planck Collaboration results, we see a broad agreement, but there are indications of a tension from the marginalized constraints in most pairs of cosmological parameters. Since our analysis includes CMB temperature Planck data at $10 < \ell < 610$, the tension appears to arise between the Planck high$-\ell$ and the other measurements. Furthermore, we find the constraints on the probe calibration parameters to be in agreement with expectations, showing that the data sets are mutually consistent. In particular, this yields a confirmation of the amplitude calibration of the weak lensing measurements from SDSS, DES SV and Planck CMB lensing from our integrated analysis. [abridged]

astro-ph.CO↗

arXiv2017

Constraining the X-ray AGN halo occupation distribution: implications for eROSITA

The X-ray emission from active galactic nucleus (AGN) is a major component of extragalactic X-ray sky. In this paper, we use the X-ray luminosity function (XLF) and halo occupation distribution (HOD) formalism to construct a halo model for the X-ray emission from AGNs. Verifying that the two inputs (XLF and HOD) are in agreement with each other, we compute the auto-correlation power spectrum in the soft X-ray band (0.5-2 keV) due to the AGNs potentially resolved by eROSITA (extended ROentgen Survey with an Imaging Telescope Array) mission and explore the redshift and mass dependence of the power spectrum. Studying the relative contribution of the Poisson and the clustering terms to the total power, we find that at multipoles $l\lesssim 1000$ (i.e. large scales), the clustering term is larger than the Poisson term. We also forecast the potential of X-ray auto-correlation power spectrum and X-ray-lensing cross-correlation power spectrum using eROSITA and eROSITA-LSST (Large Synoptic Survey Telescope) surveys, respectively, to constrain the HOD parameters and their redshift evolution. In addition, we compute the power spectrum of the AGNs lying below the flux resolution limit of eROSITA, which is essential to understand in order to extract the X-ray signal from the hot diffuse gas present in galaxies and clusters.

astro-ph.HE↗

arXiv2017

Radio frequency interference mitigation using deep convolutional neural networks

We propose a novel approach for mitigating radio frequency interference (RFI) signals in radio data using the latest advances in deep learning. We employ a special type of Convolutional Neural Network, the U-Net, that enables the classification of clean signal and RFI signatures in 2D time-ordered data acquired from a radio telescope. We train and assess the performance of this network using the HIDE & SEEK radio data simulation and processing packages, as well as early Science Verification data acquired with the 7m single-dish telescope at the Bleien Observatory. We find that our U-Net implementation is showing competitive accuracy to classical RFI mitigation algorithms such as SEEK's SumThreshold implementation. We publish our U-Net software package on GitHub under GPLv3 license.

astro-ph.IM↗

arXiv2017

HIDE & SEEK: End-to-End Packages to Simulate and Process Radio Survey Data

As several large single-dish radio surveys begin operation within the coming decade, a wealth of radio data will become available and provide a new window to the Universe. In order to fully exploit the potential of these data sets, it is important to understand the systematic effects associated with the instrument and the analysis pipeline. A common approach to tackle this is to forward-model the entire system - from the hardware to the analysis of the data products. For this purpose, we introduce two newly developed, open-source Python packages: the HI Data Emulator (HIDE) and the Signal Extraction and Emission Kartographer (SEEK) for simulating and processing single-dish radio survey data. HIDE forward-models the process of collecting astronomical radio signals in a single-dish radio telescope instrument and outputs pixel-level time-ordered-data. SEEK processes the time-ordered-data, removes artifacts from Radio Frequency Interference (RFI), automatically applies flux calibration, and aims to recover the astronomical radio signal. The two packages can be used separately or together depending on the application. Their modular and flexible nature allows easy adaptation to other instruments and data sets. We describe the basic architecture of the two packages and examine in detail the noise and RFI modeling in HIDE, as well as the implementation of gain calibration and RFI mitigation in SEEK. We then apply HIDE & SEEK to forward-model a Galactic survey in the frequency range 990 - 1260 MHz based on data taken at the Bleien Observatory. For this survey, we expect to cover 70% of the full sky and achieve a median signal-to-noise ratio of approximately 5 - 6 in the cleanest channels including systematic uncertainties. However, we also point out the potential challenges of high RFI contamination and baseline removal when examining the early data from the Bleien Observatory.

astro-ph.IM↗

arXiv2016

Update on the BINGO 21cm intensity mapping experiment

21cm intensity mapping is a novel approach aimed at measuring the power spectrum of density fluctuations and deducing cosmological information, notably from the Baryonic Acoustic Oscillations (BAO). We give an update on the progress of BAO from Integrated Neutral Gas Observations (BINGO) which is a single dish intensity mapping project. First we explain the basic ideas behind intensity mapping concept before updating the instrument design for BINGO. We also outline the survey we plan to make and its projected science output including estimates of cosmological parameters.

astro-ph.CO↗

arXiv2016

Constraining a halo model for cosmological neutral hydrogen

We describe a combined halo model to constrain the distribution of neutral hydrogen (HI) in the post-reionization universe. We combine constraints from the various probes of HI at different redshifts: the low-redshift 21-cm emission line surveys, intensity mapping experiments at intermediate redshifts, and the Damped Lyman-Alpha (DLA) observations at higher redshifts. We use a Markov Chain Monte Carlo (MCMC) approach to combine the observations and place constraints on the free parameters in the model. Our best-fit model involves a relation between neutral hydrogen mass $M_{\rm HI}$ and halo mass $M$ with a non-unit slope, and an upper and a lower cutoff. We find that the model fits all the observables but leads to an underprediction of the bias parameter of DLAs at $z \sim 2.3$. We also find indications of a possible tension between the HI column density distribution and the mass function of HI-selected galaxies at $z\sim 0$. We provide the central values of the parameters of the best-fit model so derived. We also provide a fitting form for the derived evolution of the concentration parameter of HI in dark matter haloes, and discuss the implications for the redshift evolution of the HI-halo mass relation.

astro-ph.CO↗

arXiv2016

Integrated approach to cosmology: Combining CMB, large-scale structure and weak lensing

Recent observational progress has led to the establishment of the standard $Λ$CDM model for cosmology. This development is based on different cosmological probes that are usually combined through their likelihoods at the latest stage in the analysis. We implement here an integrated scheme for cosmological probes, which are combined in a common framework starting at the map level. This treatment is necessary as the probes are generally derived from overlapping maps and are thus not independent. It also allows for a thorough test of the cosmological model and of systematics through the consistency of different physical tracers. As a first application, we combine current measurements of the Cosmic Microwave Background (CMB) from the Planck satellite, and galaxy clustering and weak lensing from SDSS. We consider the spherical harmonic power spectra of these probes including all six auto- and cross-correlations along with the associated full Gaussian covariance matrix. This provides an integrated treatment of different analyses usually performed separately including CMB anisotropies, cosmic shear, galaxy clustering, galaxy-galaxy lensing and the Integrated Sachs-Wolfe (ISW) effect with galaxy and shear tracers. We derive constraints on $Λ$CDM parameters that are compatible with existing constraints and highlight tensions between data sets, which become apparent in this integrated treatment. We discuss how this approach provides a complete and powerful integrated framework for probe combination and how it can be extended to include other tracers in the context of current and future wide field cosmological surveys.

astro-ph.CO↗

arXiv2016

Searching for Cosmic Strings in CMB Anisotropy Maps using Wavelets and Curvelets

We use wavelet and curvelet transforms to extract signals of cosmic strings from cosmic microwave background (CMB) temperature anisotropy maps, and to study the limits on the cosmic string tension which various ongoing CMB temperature anisotropy experiments will be able to achieve. We construct sky maps with size and angular resolution corresponding to various experiments. These maps contain the signals of a scaling solution of long string segments with a given string tension $G μ$, the contribution of the dominant Gaussian primordial cosmological fluctuations, and pixel by pixel white noise with an amplitude corresponding to the instrumental noise of the various experiments. In the case that we include white noise, we find that the curvelets are more powerful than wavelets. For maps with Planck specification, we obtain bounds on the string tension comparable to what was obtained by the Planck collaboration. Experiments with better angular resolution such as the South Pole Telescope third generation (SPT-3G) survey will be able to yield stronger limits. For maps with a specification of SPT-3G we find that string signals will be visible down to a string tension of $G μ= 1.4 \times 10^{-7}$.

astro-ph.CO↗

arXiv2016

The mass-sheet degeneracy and time-delay cosmography: Analysis of the strong lens RXJ1131-1231

We present extended modeling of the strong lens system RXJ1131-1231 with archival data in two HST bands in combination with existing line-of-sight contribution and velocity dispersion estimates. Our focus is on source size and its influence on time-delay cosmography. We therefore examine the impact of mass-sheet degeneracy and especially the degeneracy pointed out by Schneider & Sluse (2013) using the source reconstruction scale. We also extend on previous work by further exploring the effects of priors on the kinematics of the lens and the external convergence in the environment of the lensing system. Our results coming from RXJ1131-1231 are given in a simple analytic form so that they can be easily combined with constraints coming from other cosmological probes. We find that the choice of priors on lens model parameters and source size are subdominant for the statistical errors for $H_0$ measurements of this systems. The choice of prior for the source is sub-dominant at present (2% uncertainty on $H_0$) but may be relevant for future studies. More importantly, we find that the priors on the kinematic anisotropy of the lens galaxy have a significant impact on our cosmological inference. When incorporating all the above modeling uncertainties, we find $H_0 = 86.6^{+6.8}_{-6.9}$ km s$^{-1}$Mpc$^{-1}$, when using kinematic priors similar to other studies. When we use a different kinematic prior motivated by Barnabè et al. (2012) but covering the same anisotropic range, we find $H_0 = 74.5^{+8.0}_{-7.8}$ km s$^{-1}$Mpc$^{-1}$. This means that the choice of kinematic modeling and priors have a significant impact on cosmographic inferences. The way forward is either to get better velocity dispersion measures which would down weight the impact of the priors or to construct physically motivated priors for the velocity dispersion model.

astro-ph.CO↗

arXiv2016

An Integrated System at the Bleien Observatory for Mapping the Galaxy

We describe the design and performance of the hardware system at the Bleien Observatory. The system is designed to deliver a map of the Galaxy for studying the foreground contamination of low-redshift (z=0.13--0.43) H$_{\rm I}$ intensity mapping experiments as well as other astronomical Galactic studies. This hardware system is composed of a 7m parabolic dish, a dual-polarization corrugated horn feed, a pseudo correlation receiver, a Fast Fourier Transform spectrometer, and an integrated control system that controls and monitors the progress of the data collection. The main innovative designs in the hardware are (1) the pseudo correlation receiver and the cold reference source within (2) the high dynamic range, high frequency resolution spectrometer and (3) the phase-switch implementation of the system. This is the first time these technologies are used together for a L-band radio telescope to achieve an electronically stable system, which is an essential first step for wide-field cosmological measurements. This work demonstrates the prospects and challenges for future H$_{\rm I}$ intensity mapping experiments.

astro-ph.IM↗

arXiv2016

A new method to measure galaxy bias by combining the density and weak lensing fields

We present a new method to measure the redshift-dependent galaxy bias by combining information from the galaxy density field and the weak lensing field. This method is based on Amara et al. (2012), where they use the galaxy density field to construct a bias-weighted convergence field kg. The main difference between Amara et al. (2012) and our new implementation is that here we present another way to measure galaxy bias using tomography instead of bias parameterizations. The correlation between kg and the true lensing field k allows us to measure galaxy bias using different zero-lag correlations, such as / or / . Our method measures the linear bias factor on linear scales under the assumption of no stochasticity between galaxies and matter. We use the MICE simulation to measure the linear galaxy bias for a flux-limited sample (i < 22.5) in tomographic redshift bins using this method. This paper is the first that studies the accuracy and systematic uncertainties associated with the implementation of the method, and the regime where it is consistent with the linear galaxy bias defined by projected 2-point correlation functions (2PCF). We find that our method is consistent with linear bias at the percent level for scales larger than 30 arcmin, while nonlinearities appear at smaller scales. This measurement is a good complement to other measurements of bias, since it does not depend strongly on sigma8 as the 2PCF measurements. We apply this method to the Dark Energy Survey Science Verification data in a follow-up paper.

astro-ph.CO↗

arXiv2016

Quantifying Concordance in Cosmology

Quantifying the concordance between different cosmological experiments is important for testing the validity of theoretical models and systematics in the observations. In earlier work, we thus proposed the Surprise, a concordance measure derived from the relative entropy between posterior distributions. We revisit the properties of the Surprise and describe how it provides a general, versatile, and robust measure for the agreement between datasets. We also compare it to other measures of concordance that have been proposed for cosmology. As an application, we extend our earlier analysis and use the Surprise to quantify the agreement between WMAP 9, Planck 13 and Planck 15 constraints on the $Λ$CDM model. Using a principle component analysis in parameter space, we find that the large Surprise between WMAP 9 and Planck 13 (S = 17.6 bits, implying a deviation from consistency at 99.8% confidence) is due to a shift along a direction that is dominated by the amplitude of the power spectrum. The Planck 15 constraints deviate from the Planck 13 results (S = 56.3 bits), primarily due to a shift in the same direction. The Surprise between WMAP and Planck consequently disappears when moving to Planck 15 (S = -5.1 bits). This means that, unlike Planck 13, Planck 15 is not in tension with WMAP 9. These results illustrate the advantages of the relative entropy and the Surprise for quantifying the disagreement between cosmological experiments and more generally as an information metric for cosmology.

astro-ph.CO↗

arXiv2016

Cosmology in doubly coupled massive gravity: constraints from SNIa, BAO and CMB

Massive gravity in the presence of doubly coupled matter field via en effective composite metric yields an accelerated expansion of the universe. It has been recently shown that the model admits stable de Sitter attractor solutions and could be used as a dark energy model. In this work, we perform a first analysis of the constraints imposed by the SNIa, BAO and CMB data on the massive gravity model with the effective composite metric and show that all the background observations are mutually compatible at the one sigma level with the model.

astro-ph.CO↗

arXiv2016

Cosmology in massive gravity with effective composite metric

This paper is dedicated to scrutinizing the cosmology in massive gravity. A matter field of the dark sector is coupled to an effective composite metric while a standard matter field couples to the dynamical metric in the usual way. For this purpose, we study the dynamical system of cosmological solutions by using phase analysis, which provides an overview of the class of cosmological solutions in this setup. This also permits us to study the critical points of the cosmological equations together with their stability. We show the presence of stable attractor de Sitter critical points relevant to the late-time cosmic acceleration. Furthermore, we study the tensor, vector and scalar perturbations in the presence of standard matter fields and obtain the conditions for the absence of ghost and gradient instabilities. Hence, massive gravity in the presence of the effective composite metric can accommodate interesting dark energy phenomenology, that can be observationally distinguished from the standard model according to the expansion history and cosmic growth.

gr-qc↗

arXiv2016

Simulating the Large-Scale Structure of HI Intensity Maps

Intensity mapping of neutral hydrogen (HI) is a promising observational probe of cosmology and large-scale structure. We present wide field simulations of HI intensity maps based on N-body simulations of a $2.6\, {\rm Gpc / h}$ box with $2048^3$ particles (particle mass $1.6 \times 10^{11}\, {\rm M_\odot / h}$). Using a conditional mass function to populate the simulated dark matter density field with halos below the mass resolution of the simulation ($10^{8}\, {\rm M_\odot / h} < M_{\rm halo} < 10^{13}\, {\rm M_\odot / h}$), we assign HI to those halos according to a phenomenological halo to HI mass relation. The simulations span a redshift range of 0.35 < z < 0.9 in redshift bins of width $Δz \approx 0.05$ and cover a quarter of the sky at an angular resolution of about 7'. We use the simulated intensity maps to study the impact of non-linear effects and redshift space distortions on the angular clustering of HI. Focusing on the autocorrelations of the maps, we apply and compare several estimators for the angular power spectrum and its covariance. We verify that these estimators agree with analytic predictions on large scales and study the validity of approximations based on Gaussian random fields, particularly in the context of the covariance. We discuss how our results and the simulated maps can be useful for planning and interpreting future HI intensity mapping surveys.

astro-ph.CO↗

arXiv2016

Modelling the cosmic neutral hydrogen from DLAs and 21 cm observations

We review the analytical prescriptions in the literature to model the 21-cm (emission line surveys/intensity mapping experiments) and Damped Lyman-Alpha (DLA) observations of neutral hydrogen (HI) in the post-reionization universe. While these two sets of prescriptions have typically been applied separately for the two probes, we attempt to connect these approaches to explore the consequences for the distribution and evolution of HI across redshifts. We find that a physically motivated, 21-cm based prescription, extended to account for the DLA observables provides a good fit to the majority of the available data, but cannot accommodate the recent measurement of the clustering of DLAs at $z \sim 2.3$. This highlights a tension between the DLA bias and the 21-cm measurements, unless there is a very significant change in the nature of HI-bearing systems across redshifts 0-3. We discuss the implications of our findings for the characteristic host halo masses of the DLAs and the power spectrum of 21-cm intensity fluctuations.

astro-ph.CO↗

arXiv2015

Probing the circumgalactic baryons through cross-correlations

We study the cross-correlation of distribution of galaxies, the Sunyaev-Zel'dovich (SZ) and X-ray power spectra of galaxies from current and upcoming surveys and show these to be excellent probes of the nature, i.e. extent, evolution and energetics, of the circumgalactic medium (CGM). The SZ-galaxy cross-power spectrum, especially at large multipoles, depends on the steepness of the pressure profile of the CGM. This property of the SZ signal can, thus, be used to constrain the pressure profile of the CGM. The X-ray cross power spectrum also has a similar shape. However, it is much more sensitive to the underlying density profile. We forecast the detectability of the cross-correlated galaxy distribution, SZ and X-ray signals by combining South Pole Telescope-Dark Energy Survey (SPT-DES) and eROSITA-DES/eROSITA-LSST (extended ROentgen Survey with an Imaging Telescope Array-Large Synoptic Survey Telescope) surveys, respectively. We find that, for the SPT-DES survey, the signal-to-noise ratio (SNR) peaks at high mass and redshift with SNR $\sim 9$ around $M_h\sim 10^{13} h^{-1} M_{\odot}$ and $z\sim 1.5\hbox{--} 2$ for flat density and temperature profiles. The SNR peaks at $\sim 6 (12 )$ for the eROSITA-DES (eROSITA-LSST) surveys. We also perform a Fisher matrix analysis to find the constraint on the gas fraction in the CGM in the presence or absence of an unknown redshift evolution of the gas fraction. Finally, we demonstrate that the cross-correlated SZ-galaxy and X-ray-galaxy power spectrum can be used as powerful probes of the CGM energetics and potentially discriminate between different feedback models recently proposed in the literature; for example, one can distinguish a `no active galactic nuclei feedback' scenario from a CGM energized by `fixed-velocity hot winds' at greater than $3σ$.

astro-ph.CO↗

arXiv2015

Beam calibration of radio telescopes with drones

We present a multi-frequency far-field beam map for the 5m dish telescope at the Bleien Observatory measured using a commercially available drone. We describe the hexacopter drone used in this experiment, the design of the flight pattern, and the data analysis scheme. This is the first application of this calibration method to a single dish radio telescope in the far-field. The high signal-to-noise data allows us to characterise the beam pattern with high accuracy out to at least the 4th side-lobe. The resulting 2D beam pattern is compared with that derived from a more traditional calibration approach using an astronomical calibration source. We discuss the advantages of this method compared to other beam calibration methods. Our results show that this drone-based technique is very promising for ongoing and future radio experiments, where the knowledge of the beam pattern is key to obtaining high-accuracy cosmological and astronomical measurements.

astro-ph.IM↗