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Nagai D.,Yale University | Lau E.T.,Key Laboratory for Research in Galaxies and Cosmology
Astrophysical Journal Letters | Year: 2011

Recent Suzaku X-ray observations revealed that the observed entropy profile of the intracluster medium (ICM) deviates significantly from the prediction of hydrodynamical simulations of galaxy clusters. In this work, we show that gas clumping introduces significant biases in X-ray measurements of the ICM profiles in the outskirts of galaxy clusters. Using hydrodynamical simulations of galaxy cluster formation in a concordance ΛCDM model, we demonstrate that gas clumping leads to an overestimate of the observed gas density and causes flattening of the entropy profile. Our results suggest that gas clumping must be taken into account when interpreting X-ray measurements of cluster outskirts. © 2011. The American Astronomical Society. All rights reserved. Source

Kozlov M.G.,Yale University | Kozlov M.G.,RAS Petersburg Nuclear Physics Institute | Levshakov S.A.,Key Laboratory for Research in Galaxies and Cosmology
Astrophysical Journal | Year: 2011

Quantum-mechanical tunneling inversion transition in ammonia (NH3) is actively used as a sensitive tool to study possible variations of the electron-to-proton mass ratio, μ = me/mp. The molecule H3O+ has the inversion barrier significantly lower than that ofNH3. Consequently, its tunneling transition occurs in the far-infrared (FIR) region and mixes with rotational transitions. Several such FIR and submillimeter transitions are observed from the interstellar medium in the Milky Way and in nearby galaxies. We show that the rest-frame frequencies of these transitions are very sensitive to the variation of μ, and that their sensitivity coefficients have different signs. Thus, H3O+ can be used as an independent target to test hypothetical changes in μ measured at different ambient conditions of high (terrestrial) and low (interstellar medium) matter densities. The environmental dependence of μ and coupling constants is suggested in a class of chameleon-type scalar field models-candidates to dark energy carrier. © 2011 The American Astronomical Society. All rights reserved. Source

Van den bosch F.C.,Yale University | More S.,University of Chicago | Cacciato M.,Hebrew University of Jerusalem | Mo H.,University of Massachusetts Amherst | Yang X.,Key Laboratory for Research in Galaxies and Cosmology
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present a new method that simultaneously solves for cosmology and galaxy bias on non-linear scales. The method uses the halo model to analytically describe the (non-linear) matter distribution, and the conditional luminosity function (CLF) to specify the halo occupation statistics. For a given choice of cosmological parameters, this model can be used to predict the galaxy luminosity function, as well as the two-point correlation functions of galaxies, and the galaxy-galaxy lensing signal, both as a function of scale and luminosity. These observables have been reliably measured from the Sloan Digital Sky Survey. In this paper, the first in a series, we present the detailed, analytical model, which we test against mock galaxy redshift surveys constructed from high-resolution numerical N-body simulations. We demonstrate that our model, which includes scale dependence of the halo bias and a proper treatment of halo exclusion, reproduces the three-dimensional galaxy-galaxy correlation and the galaxy-matter cross-correlation (which can be projected to predict the observables) with an accuracy better than 10 (in most cases 5) per cent. Ignoring either of these effects, as is often done, results in systematic errors that easily exceed 40 per cent on scales of ~ 1 h-1 Mpc, where the data are typically most accurate. Finally, since the projected correlation functions of galaxies are never obtained by integrating the redshift-space correlation function along the line of sight out to infinity, simply because the data only cover a finite volume, they are still affected by residual redshift-space distortions (RRSDs). Ignoring these, as done in numerous studies in the past, results in systematic errors that easily exceed 20 per cent on large scales (rp ≳ 10 h- 1 Mpc). We show that it is fairly straightforward to correct for these RRSDs, to an accuracy better than ~2 per cent, using a mildly modified version of the linear Kaiser formalism. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Zhang P.,Key Laboratory for Research in Galaxies and Cosmology
Astrophysical Journal | Year: 2010

The galaxy intrinsic alignment is a severe challenge to precision cosmic shear measurement. We propose selfcalibrating the induced gravitational shear-galaxy intrinsic ellipticity correlation (the GI correlation) in weak lensing surveys with photometric redshift measurements. (1) We propose a method to extract the intrinsic ellipticity-galaxy density cross-correlation (I-g) from the galaxy ellipticity-density measurement in the same redshift bin. (2) We also find a generic scaling relation to convert the extracted I-g correlation to the necessary GI correlation. We perform a concept study under simplified conditions and demonstrate its capability to significantly reduce GI contamination. We discuss the impact of various complexities on the two key ingredients of the self-calibration technique, namely the method for extracting the I-g correlation and the scaling relation between the I-g and the GI correlation. We expect that none of them will likely be able to completely invalidate the proposed self-calibration technique. © 2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A. Source

Zhang P.,Key Laboratory for Research in Galaxies and Cosmology | Stebbins A.,Fermilab Theoretical Astrophysics
Physical Review Letters | Year: 2011

The Copernican principle, a cornerstone of modern cosmology, remains largely unproven at the Gpc radial scale and above. Here will show that violations of this type will inevitably cause a first order anisotropic kinetic Sunyaev-Zel'dovich effect. If large scale radial inhomogeneities have an amplitude large enough to explain the "dark energy" phenomena, the induced kinetic Sunyaev-Zel'dovich power spectrum will be much larger than the Atacama Cosmology Telescope and/or South Pole Telescope upper limit. This single test confirms the Copernican principle and rules out the adiabatic void model as a viable alternative to dark energy. © 2011 American Physical Society. Source

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