A direct measure of free electron gas via the Kinematic Sunyaev-Zel'dovich effect in Fourier-space analysis [CEA]


We present the measurement of the kinematic Sunyaev-Zel’dovich (kSZ) effect in Fourier space, rather than in real space. We measure the density-weighted pairwise kSZ power spectrum, the first use of this promising approach, by cross-correlating a cleaned Cosmic Microwave Background (CMB) temperature map, which jointly uses both Planck Release 2 and Wilkinson Microwave Anisotropy Probe nine-year data, with the two galaxy samples, CMASS and LOWZ, derived fr om the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 12. With the current data, we constrain the average optical depth $\tau$ multiplied by the ratio of the Hubble parameter at redshift $z$ and the present day, $E=H/H_0$; we find $\tau E = (3.95\pm1.62)\times10^{-5}$ for LOWZ and $\tau E = ( 1.25\pm 1.06)\times10^{-5}$ for CMASS, with the optimal angular radius of an aperture photometry filter to estimate the CMB temperature distortion associ ated with each galaxy. By repeating the pairwise kSZ power analysis for various aperture radii, we measure the optical depth as a function of aperture ra dii. While this analysis results in the kSZ signals with only evidence for a detection, ${\rm S/N}=2.54$ for LOWZ and $1.24$ for CMASS, the combination of future CMB and spectroscopic galaxy surveys should enable precision measurements. We estimate that the combination of CMB-S4 and data from DESI shoul d yield detections of the kSZ signal with ${\rm S/N}=70-100$, depending on the resolution of CMB-S4.

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N. Sugiyama, T. Okumura and D. Spergel
Tue, 23 May 17

Comments: 23 pages, 15 figures

Is it time to go beyond $Λ$CDM universe? [CEA]


Concordance $\Lambda$CDM universe is the simplest model that is consistent with a large variety of cosmological observations till date. But few recent observations indicate inconsistencies in $\Lambda$CDM model. In this paper, we consider the combination of recent SnIa+Bao+Cmb+Growth+$H(z)$+$H_{0}$ measurements to revisit the constraints on the dark energy evolution using the widely studied CPL parametrisation for the dark energy equation of state. Although the reconstructed behaviour for the dark energy equation of state confirms the inconsistency of $\Lambda$CDM at $95\%$ confidence level, the reconstructed $Om$ diagnostic which is a {\it null test} for $\Lambda$CDM, still allows the concordance $\Lambda$CDM behaviour with a lower range of $\Omega_{m0}$ than that obtained by Planck-2015. {\it This confirms that $\Lambda$CDM is still the best choice for the dark energy model}. We also measure the parameter $S = \sigma_{8}\sqrt{\Omega_{m0}/0.3} = 0.728 \pm 0.023$ which is consistent with its recent measurement by KiDS survey. The confidence contour in the $\Omega_{m0}-\sigma_{8}$ parameter plane is also fully consistent with KiDS survey measurement.

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A. Lonappan, Ruchika. and A. Sen
Tue, 23 May 17

Comments: 13 pages, LateX style, 1 table, 6 eps figures. Comments are welcome

Model-independent characterisation of perturbers to strong gravitational lenses with almost point-like caustics [CEA]


In galaxy-galaxy strong gravitational lensing, Einstein rings are generated when the lensing galaxy has an axisymmetric lensing potential and the source galaxy is aligned with its symmetry centre along the line of sight. Using a Taylor expansion around the Einstein radius and eliminating the unknown source, I derive a set of analytic equations that determines differences of the deflection angle of the perturber weighted by the convergence of the axisymmetric lens and ratios of the convergences at the positions of the arcs from measurable radii of the arcs. In the same manner, asymmetries in the brightness distributions along an arc determine differences of the deflection angle of the perturber. These equations are the only model-independent information retrievable from observations to leading order in the Taylor expansion. General constraints on the derivatives of the perturbing lens are derived such that the perturbation does not change the number of critical curves. To infer physical properties like the mass of the perturber or its position, models need to be inserted. The same conclusions about the scale of detectable masses (on the order of $10^8 M_\odot$) and model-dependent degeneracies as in other approaches are then found and supported by analysing B1938+666 as an example. Yet, the model-indenpedent equations show that, apart from the radii and brightness distributions of the arcs, independent information on the axisymmetric lens or the perturber has to be employed in order to break a so-far unnoted degeneracy that entangles the axisymmetric lens with the perturber. This degeneracy can be broken by inserting the position of a luminous perturber into the equations, or measuring the velocity dispersion.

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J. Wagner
Tue, 23 May 17

Comments: 8 pages, 3 figures, 1 table, submitted to Astronomy & Astrophysics, comments welcome

Imprints of Reionization in Galaxy Clustering [CEA]


Reionization, the only phase transition in the Universe since recombination, is a key event in the cosmic history of baryonic matter. We derive, in the context of the large-scale bias expansion, the imprints of the epoch of reionization in the large-scale distribution of galaxies, and identify two contributions of particular importance. First, the Compton scattering of CMB photons off the free electrons lead to a drag force on the baryon fluid. This drag induces a relative velocity between baryons and CDM which is of the same order of magnitude as the primordially-induced relative velocity, and enters in the evolution of the relative velocity as calculated by Boltzmann codes. This leads to a unique contribution to galaxy bias involving the matter velocity squared. The second important effect is a modulation of the galaxy density by the ionizing radiation field through radiative transfer effects, which is captured in the bias expansion by so-called higher-derivative terms. We constrain both of these imprints using the power spectrum of the BOSS DR12 galaxy sample. While they do not lead to a shift in the baryon acoustic oscillation scale, including these terms is important for unbiased cosmology constraints from the shape of the galaxy power spectrum.

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F. Schmidt and F. Beutler
Tue, 23 May 17

Comments: 17 pages, 5 figures; comments welcome

Consistency Relations in Effective Field Theory [CEA]


The consistency relations in large scale structure relate the lower-order correlation functions with their higher-order counterparts. They are direct outcome of the underlying symmetries of a dynamical system and can be tested using data from future surveys such as Euclid. Using techniques from standard perturbation theory (SPT), previous studies of consistency relation have concentrated on continuity-momentum (Euler)-Poisson system of an ideal fluid. We investigate the consistency relations in effective field theory (EFT) which adjusts the SPT predictions to account for the departure from the ideal fluid description on small scales. We provide detailed results for the 3D density contrast $\delta$ as well as the {\em scaled} divergence of velocity $\bar\theta$. Assuming a $\Lambda$CDM background cosmology, we find the correction to SPT results becomes important at $k \gtrsim 0.05 \rm h/Mpc$ and that the suppression from EFT to SPT results that scales as square of the wave number $k$, can reach $40\%$ of the total at $k \approx 0.25\rm h/Mpc$ at $z=0$. We have also investigated whether effective field theory corrections to models of primordial non-Gaussianity can alter the squeezed limit behaviour, finding the results to be rather insensitive to these counterterms. In addition, we present the EFT corrections to the squeezed limit of the bispectrum in redshift space which may be of interest for tests of theories of modified gravity.

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D. Munshi and D. Regan
Tue, 23 May 17

Comments: 23 pages + bibliography, 6 figures

Viscosity, pressure, and support of the gas in simulations of merging cool-core clusters [CEA]


Major mergers are considered to be a significant source of turbulence in clusters. We performed a numerical simulation of a major merger event using nested-grid initial conditions, adaptive mesh refinement, radiative cooling of primordial gas, and a homogeneous ultraviolet background. By calculating the microscopic viscosity on the basis of various theoretical assumptions and estimating the Kolmogorov length from the turbulent dissipation rate computed with a subgrid-scale model, we are able to demonstrate that most of the warm-hot intergalactic medium can sustain a fully turbulent state only if the magnetic suppression of the viscosity is considerable. Accepting this as premise, it turns out that ratios of turbulent and thermal quantities change only little in the course of the merger. This confirms the tight correlations between the mean thermal and non-thermal energy content for large samples of clusters in earlier studies, which can be interpreted as second self-similarity on top of the self-similarity for different halo masses. Another long-standing question is how and to which extent turbulence contributes to the support of the gas against gravity. From a global perspective, the ratio of turbulent and thermal pressures is significant for the clusters in our simulation. On the other hand, a local measure is provided by the compression rate, i.e. the growth rate of the divergence of the flow. Particularly for the intracluster medium, we find that the dominant contribution against gravity comes from thermal pressure, while compressible turbulence effectively counteracts the support. For this reason it appears to be too simplistic to consider turbulence merely as an effective enhancement of thermal energy.

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W. Schmidt, C. Byrohl, J. Engels, et. al.
Mon, 22 May 17

Comments: 16 pages, 16 figures, accepted for publication by MNRAS

The first-year shear catalog of the Subaru Hyper Suprime-Cam SSP Survey [CEA]


We present and characterize the catalog of galaxy shape measurements that will be used for cosmological weak lensing measurements in the Wide layer of the first year of the Hyper Suprime-Cam (HSC) survey. The catalog covers an area of 136.9 deg$^2$ split into six fields, with a mean $i$-band seeing of 0.58 arcsec and $5\sigma$ point-source depth of $i\sim 26$. Given conservative galaxy selection criteria for first year science, the depth and excellent image quality results in unweighted and weighted source number densities of 24.6 and 21.8 arcmin$^{-2}$, respectively. Point-spread function (PSF) modeling is carried out on individual exposures, while galaxy shapes are measured on a linear coaddition. We define the requirements for cosmological weak lensing science with this catalog, characterize potential systematics in the catalog using a series of internal null tests for problems with PSF modeling, shear estimation, and other aspects of the image processing, and describe systematics tests using two different sets of image simulations. Finally, we discuss the dominant systematics and the planned algorithmic changes to reduce them in future data reductions.

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R. Mandelbaum, H. Miyatake, T. Hamana, et. al.
Mon, 22 May 17

Comments: 23 figures, 4 tables, submitted to PASJ