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Register a new userThe redshift dependence of Alcock-Paczynski effect: cosmological constraints from the current and next generation observations
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The tomographic Alcock-Paczynski (AP) test is a robust large-scale structure (LSS) measurement that receives little contamination from the redshift space distortion (RSD). It has placed tight cosmological constraints by using small and intermediate clustering scales of the LSS data. However, previous works have neglected the cross-correlation among different redshift bins, which could cause the statistical uncertainty being underestimated by $sim$20%. In this work, we further improve this method by including this multi-redshifts full correlation. We apply it to the SDSS DR12 galaxies sample and find out that, for $Lambda$CDM, the combination of AP with the Planck+BAO dataset slightly reduces (within 1-$sigma$) $Omega_m$ to $0.304pm0.007$ (68.3% CL). This then leads to a larger $H_0$ and also mildly affects $Omega_b h^2$, $n_s$ and the derived parameters $z_*$, $r_*$, $z_{re}$ but not $tau$, $A_s$ and $sigma_8$. For the flat $w$CDM model, our measurement gives $Omega_m=0.301pm 0.010$ and $w=-1.090pm 0.047$, where the additional AP measurement reduces the error budget by $sim 25%$. When including more parameters into the analysis, the AP method also improves the constraints on $Omega_k$, $sum m_mu$, $N_{rm eff}$ by $20-30%$. Early universe parameters such as $dn_s/d{rm ln}k$ and $r$, however, are unaffected. Assuming the dark energy equation of state $w=w_0+w_a frac{z}{1+z}$, the Planck+BAO+SNIa+$H_0$+AP datasets prefer a dynamical dark energy at $approx1.5 sigma$ CL. Finally, we forecast the cosmological constraints expected from the DESI galaxy survey and find that combining AP with CMB+BAO method would improve the $w_0$-$w_a$ constraint by a factor of $sim 10$.
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We perform an anisotropic clustering analysis of 1,133,326 galaxies from the Sloan Digital Sky Survey (SDSS-III) Baryon Oscillation Spectroscopic Survey (BOSS) Data Release (DR) 12 covering the redshift range $0.15<z<0.69$. The geometrical distortions of the galaxy positions, caused by incorrect cosmological model assumptions, are captured in the anisotropic two-point correlation function on scales 6 -- 40 $h^{-1}rm Mpc$. The redshift evolution of this anisotropic clustering is used to place constraints on the cosmological parameters. We improve the methodology of Li et al. 2016, to enable efficient exploration of high dimensional cosmological parameter spaces, and apply it to the Chevallier-Polarski-Linder parametrization of dark energy, $w=w_0+w_a{z}/({1+z})$. In combination with the CMB, BAO, SNIa and $H_0$ from Cepheid data, we obtain $Omega_m = 0.301 pm 0.008, w_0 = -1.042 pm 0.067, $ and $w_a = -0.07 pm 0.29$ (68.3% CL). Adding our new AP measurements to the aforementioned results reduces the error bars by $sim$30 -- 40% and improves the dark energy figure of merit by a factor of $sim$2. We check the robustness of the results using realistic mock galaxy catalogues.
The tomographic AP method is so far the best method in separating the Alcock-Paczynski (AP) signal from the redshift space distortion (RSD) effects and deriving powerful constraints on cosmological parameters using the $lesssim40h^{-1} rm Mpc$ clustering region. To guarantee that the method can be easily applied to the future large scale structure (LSS) surveys, we study the possibility of estimating the systematics of the method using fast simulation method. The major contribution of the systematics comes from the non-zero redshift evolution of the RSD effects, which is quantified by $hatxi_{Delta s}(mu,z)$ in our analysis, and estimated using the BigMultidark exact N-body simulation and approximate COLA simulation samples. We find about 5%/10% evolution when comparing the $hatxi_{Delta s}(mu,z)$ measured as $z=0.5$/$z=1$ to the measurements at $z=0$. We checked the inaccuracy in the 2pCFs computed using COLA, and find it 5-10 times smaller than the intrinsic systematics of the tomographic AP method, indicating that using COLA to estimate the systematics is good enough. Finally, we test the effect of halo bias, and find $lesssim$1.5% change in $hatxi_{Delta s}$ when varying the halo mass within the range of $2times 10^{12}$ to $10^{14}$ $M_{odot}$. We will perform more studies to achieve an accurate and efficient estimation of the systematics in redshift range of $z=0-1.5$.
Baryon acoustic oscillations (BAO), known as one of the largest cosmological objects, is now recognized as standard cosmological tool to measure geometric distances via the Alcock-Paczynski effect, by which the observed BAO exhibits characteristic anisotropies in addition to the redshift distortions. This implies that once we know the correct distances to the observed BAO, the tip points of baryon acoustic peaks in the anisotropic correlation function of galaxies, $xi(sigma,pi)$, can form a great circle (hereafter 2D BAO circle) in the $sigma$ and $pi$ plane, where $sigma$ and $pi$ are the separation of galaxy pair parallel and perpendicular to the line-of-sight, respectively. This 2D BAO circle remains unchanged under the variations of the unknown galaxy bias and/or coherent motion, while it varies transversely and radially with respect to the variations of $D_A$ and $H^{-1}$, respectively. Hereby the ratio between transverse distance $D_A$ and the radial distance $H^{-1}$ reproduces the intrinsic shape of 2D BAO circle, which is {it a priori} given by the known broadband shape of spectra. All BAO peaks of $xi(sigma,pi)$ are precisely calculated with the improved theoretical model of redshift distortion. We test this broadband Alcock--Paczynski method using BOSS--like mock catalogues. The transverse and radial distances are probed in precision of several percentage fractional errors, and the coherent motion is observed to match with the fiducial values accurately.
Euclid will survey galaxies in a cosmological volume of unprecedented size, providing observations of more than a billion objects distributed over a third of the full sky. Approximately 20 million of these galaxies will have spectroscopy available, allowing us to map the three-dimensional large-scale structure of the Universe in great detail. This paper investigates prospects for the detection of cosmic voids therein, and the unique benefit they provide for cosmology. In particular, we study the imprints of dynamic and geometric distortions of average void shapes and their constraining power on the growth of structure and cosmological distance ratios. To this end, we make use of the Flagship mock catalog, a state-of-the-art simulation of the data expected to be observed with Euclid. We arrange the data into four adjacent redshift bins, each of which contains about 11000 voids, and estimate the void-galaxy cross-correlation function in every bin. Fitting a linear-theory model to the data, we obtain constraints on $f/b$ and $D_M H$, where $f$ is the linear growth rate of density fluctuations, $b$ the galaxy bias, $D_M$ the comoving angular diameter distance, and $H$ the Hubble rate. In addition, we marginalize over two nuisance parameters included in our model to account for unknown systematic effects in the analysis. With this approach Euclid will be able to reach a relative precision of about 4% on measurements of $f/b$ and 0.5% on $D_M H$ in each redshift bin. Better modeling or calibration of the nuisance parameters may further increase this precision to 1% and 0.4%, respectively. Our results show that the exploitation of cosmic voids in Euclid will provide competitive constraints on cosmology even as a stand-alone probe. For example, the equation-of-state parameter $w$ for dark energy will be measured with a precision of about 10%, consistent with earlier more approximate forecasts.
We develop an improved Alcock-Paczynski (AP) test method that uses the redshift-space two-point correlation function (2pCF) of galaxies. Cosmological constraints can be obtained by examining the redshift dependence of the normalized 2pCF, which should not change apart from the expected small non-linear evolution. An incorrect choice of cosmology used to convert redshift to comoving distance will manifest itself as redshift-dependent 2pCF. Our method decomposes the redshift difference of the two-dimensional correlation function into the Legendre polynomials whose amplitudes are modeled by radial fitting functions. Our likelihood analysis with this 2-D fitting scheme tightens the constraints on $Omega_m$ and ${w}$ by $sim 40%$ compared to the method of Li et al. (2016, 2017, 2018) that uses one dimensional angular dependence only. We also find that the correction for the non-linear evolution in the 2pCF has a non-negligible cosmology dependence, which has been neglected in previous similar studies by Li et al.. With an accurate accounting for the non-linear systematics and use of full two-dimensional shape information of the 2pCF down to scales as small as $5~h^{-1}{rm Mpc}$ it is expected that the AP test with redshift-space galaxy clustering anisotropy can be a powerful method to constrain the expansion history of the universe.
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