Key Laboratory for Research in Galaxies and Cosmology

Shanghai, China

Key Laboratory for Research in Galaxies and Cosmology

Shanghai, China
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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.

Borisov A.,University of Pennsylvania | Jain B.,University of Pennsylvania | Zhang P.,Key Laboratory for Research in Galaxies and Cosmology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

We use one-dimensional numerical simulations to study spherical collapse in the f(R) gravity models. We include the nonlinear self-coupling of the scalar field in the theory and use a relaxation scheme to follow the collapse. We find an unusual enhancement in density near the virial radius which may provide observable tests of gravity. We also use the estimated collapse time to calculate the critical overdensity δ c used in calculating the mass function and bias of halos. We find that analytical approximations previously used in the literature do not capture the complexity of nonlinear spherical collapse. © 2012 American Physical Society.

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.

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.

Zhang P.,Key Laboratory for Research in Galaxies and Cosmology | Pan J.,CAS National Astronomical Observatories | Zheng Y.,Key Laboratory for Research in Galaxies and Cosmology
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2013

Massive spectroscopic surveys will measure the redshift space distortion (RSD) induced by galaxy peculiar velocity to unprecedented accuracy and open a new era of precision RSD cosmology. We develop a new method to improve the RSD modeling and to carry out robust reconstruction of the 3D large scale peculiar velocity through galaxy redshift surveys, in light of RSD. (1) We propose a mathematically unique and physically motivated decomposition of peculiar velocity into three eigencomponents: an irrotational component completely correlated with the underlying density field (vδ), an irrotational component uncorrelated with the density field (vS), and a rotational (curl) component (vB). The three components have different origins, different scale dependences, and different impacts on RSD. (2) This decomposition has the potential to simplify and improve the RSD modeling. (i) vB damps the redshift space clustering. (ii) v S causes both damping and enhancement to the redshift space power spectrum Ps(k,u). Nevertheless, the leading order contribution to the enhancement has a u4 directional dependence, distinctively different from the Kaiser formula. Here, u≡kz/k, k is the amplitude of the wave vector, and kz is the component along the line of sight. (iii) v δ is of the greatest importance for the RSD cosmology. We find that the induced redshift clustering shows a number of important deviations from the usual Kaiser formula. Even in the limit of vS→0 and v B→0, the leading order contribution â̂(1+fWË œ(k)u2)2. It differs from the Kaiser formula by a window function WËœ(k). Nonlinear evolution generically drives WËœ(k) ≤1. We hence identify a significant systematical error causing underestimation of the structure growth parameter f by as much as O(10%) even at a relatively large scale k=0.1h/Mpc. (iv) The velocity decomposition reveals the three origins of the "finger-of-God" (FOG) effect and suggests how to simplify and improve the modeling of FOG by treating the three components separately. (v) We derive a new formula for the redshift space power spectrum. Under the velocity decomposition scheme, all high order Gaussian corrections and non-Gaussian corrections of order δ3 can be taken into account without introducing extra model uncertainties. Here δ is the nonlinear overdensity. (3) The velocity decomposition clarifies issues in peculiar velocity reconstruction through 3D galaxy distribution. We discuss two possible ways to carry out the 3D vδ reconstruction. Both use the otherwise troublesome RSD in velocity reconstruction as a valuable source of information. Both have the advantage of rendering the reconstruction of a stochastic 3D field into the reconstruction of a deterministic window function Ws(k,u) of limited degrees of freedom. Both can automatically and significantly alleviate the galaxy bias problem and, in the limit of a deterministic galaxy bias, completely overcome it. Part 1 of this series of works lays out the methodology. Companion papers Y. Zheng (in preparation). will extensively evaluate its performance against N-body simulations. © 2013 American Physical Society.

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.

Yang X.,Key Laboratory for Research in Galaxies and Cosmology | Mo H.J.,University of Massachusetts Amherst | Van Den Bosch F.C.,Yale University | Zhang Y.,Key Laboratory for Research in Galaxies and Cosmology | Han J.,Key Laboratory for Research in Galaxies and Cosmology
Astrophysical Journal | Year: 2012

We present a new model to describe the galaxy-dark matter connection across cosmic time, which unlike the popular subhalo abundance-matching technique is self-consistent in that it takes account of the facts that (1) subhalos are accreted at different times and (2) the properties of satellite galaxies may evolve after accretion. Using observations of galaxy stellar mass functions (SMFs) out to z 4, the conditional SMF at z 0.1 obtained from Sloan Digital Sky Survey galaxy group catalogs, and the two-point correlation function (2PCF) of galaxies at z 0.1 as a function of stellar mass, we constrain the relation between galaxies and dark matter halos over the entire cosmic history from z 4 to the present. This relation is then used to predict the median assembly histories of different stellar mass components within dark matter halos (central galaxies, satellite galaxies, and halo stars). We also make predictions for the 2PCFs of high-z galaxies as function of stellar mass. Our main findings are the following: (1) Our model reasonably fits all data within the observational uncertainties, indicating that the ΛCDM concordance cosmology is consistent with a wide variety of data regarding the galaxy population across cosmic time. (2) At low-z, the stellar mass of central galaxies increases with halo mass as M 0.3 and M ≳ 4.0 at the massive and low-mass ends, respectively. The ratio M *, c/M reveals a maximum of 0.03 at a halo mass M 1011.8 h -1 M , much lower than the universal baryon fraction (0.17). At higher redshifts the maximum in M *, c/M remains close to 0.03, but shifts to higher halo mass. (3) The inferred timescale for the disruption of satellite galaxies is about the same as the dynamical friction timescale of their subhalos. (4) The stellar mass assembly history of central galaxies is completely decoupled from the assembly history of its host halo; the ratio M *, c/M initially increases rapidly with time until the halo mass reaches 10 12 h -1 M , at which point M *, c/M 0.03. Once M ≳ 1012 h -1 M , there is little growth in M *, c, causing the ratio M *, c/M to decline. In Milky Way (MW)-sized halos more than half of the central stellar mass is assembled at z ≲ 0.5. (5) In low-mass halos, the accretion of satellite galaxies contributes little to the formation of their central galaxies, indicating that most of their stars must have formed in situ. In massive halos more than half of the stellar mass of the central galaxy has to be formed in situ, and the accretion of satellites can only become significant at z ≲ 2. (6) The total mass in halo stars is more than twice that of the central galaxy in massive halos, but less than 10% of M *, c in MW-sized halos. (7) The 2PCFs of galaxies on small scales hold important information regarding the evolution of satellite galaxies, which at high-z is predicted to be much steeper than at low-z, especially for more massive galaxies. We discuss various implications of our findings regarding the formation and evolution of galaxies in a ΛCDM cosmology. © 2012. The American Astronomical Society. All rights reserved..

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.

Zhang P.,Key Laboratory for Research in Galaxies and Cosmology
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

Recently, Kashlinsky et al. reported a discovery of a ~103 kms-1 bulk flow of the Universe out to z ≈ 0.3, through the dark flow induced cosmic microwave background (CMB) dipole in directions of clusters. We point out that, if this dark flow exists, it will also induce observable CMB temperature fluctuations at multipole ℓ ~ 103, through modulation of the inhomogeneous electron distribution on the uniform dark flow. The induced small-scale kinetic Sunyaev-Zel'dovich (SZ) effect will reach ~1 μK2 at multipole 103 ≲ ℓ ≲ 104, only a factor of ~2 smaller than the conventional kinetic SZ effect. Furthermore, it will be correlated with the large-scale structure (LSS) and its correlation with Two-Micron All-Sky Survey (2MASS) galaxy distribution reaches 0.3 μK at ℓ = 103, under a directional dependent optimal weighting scheme. We estimate that, Wilkinson Microwave Anisotropy Probe plus 2MASS should already be able to detect this dark flow induced small-scale kinetic SZ effect with ~6σ confidence. Deeper galaxy surveys such as the Sloan Digital Sky Survey can further improve the measurement. Planck plus existing galaxy surveys can reach ≳14σ detection. Existing CMB-LSS cross-correlation measurements shall be reanalysed to test the existence of the dark flow and, if it exists, shall be used to eliminate possible bias on the integrated Sachs-Wolfe effect measurement through the CMB-LSS cross-correlation. © 2010 The Authors. Journal compilation © 2010 RAS.

Zhang P.,Key Laboratory for Research in Galaxies and Cosmology
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2010

The galaxy intrinsic alignment causes the galaxy ellipticity-ellipticity power spectrum between two photometric redshifts to decrease faster with respect to the redshift separation ΔzP, for fixed mean redshift. This offers a valuable diagnosis on the intrinsic alignment. We show that the distinctive dependences of the GG, II and GI correlations on ΔzP over the range | ΔzP| ≤ 0.2 can be understood robustly without strong assumptions on the intrinsic alignment. This allows us to measure the intrinsic alignment within each conventional photo-z bin of typical size ≥0.2, through lensing tomography of photo-z bin size ~0.01. Both the statistical and systematical errors in the lensing cosmology can be reduced by this self-calibration technique. © 2010 The Author. Journal compilation © 2010 RAS.

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