Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCosmological constraints from the redshift dependence of the Alcock-Paczynski effect: Possibility of estimateing the non-linear systematics using fast simulations
66
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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 $z=0-1.5$.
rate research
Read More
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 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 $sim 10$.
We perform an Alcock-Paczynski test using stacked cosmic voids identified in the SDSS Data Release 7 main sample and Data Release 10 LOWZ and CMASS samples. We find ~1,500 voids out to redshift $0.6$ using a heavily modified and extended version of the watershed algorithm ZOBOV, which we call VIDE (Void IDentification and Examination). To assess the impact of peculiar velocities we use the mock void catalogs presented in Sutter et al. (2013). We find a constant uniform flattening of 14% along the line of sight when peculiar velocities are included. This flattening appears universal for all void sizes at all redshifts and for all tracer densities. We also use these mocks to identify an optimal stacking strategy. After correcting for systematic effects we find that our Alcock-Paczynski measurement leads to a preference of our best-fit value of $Omega_{rm M}sim 0.15$ over $Omega_{rm M} = 1.0$ by a likelihood ratio of 10. Likewise, we find a factor of $4.5$ preference of the likelihood ratio for a $Lambda$CDM $Omega_{rm M} = 0.3$ model and a null measurement. Taken together, we find substantial evidence for the Alcock-Paczynski signal in our sample of cosmic voids. Our assessment using realistic mocks suggests that measurements with future SDSS releases and other surveys will provide tighter cosmological parameter constraints. The void-finding algorithm and catalogs used in this work will be made publicly available at http://www.cosmicvoids.net.
The tomographic Alcock-Paczynski (AP) method can result in tight cosmological constraints by using small and intermediate clustering scales of the large scale structure (LSS) of the galaxy distribution. By focusing on the redshift dependence, the AP distortion can be distinguished from the distortions produced by the redshift space distortions (RSD). In this work, we combine the tomographic AP method with other recent observational datasets of SNIa+BAO+CMB+$H_0$ to reconstruct the dark energy equation-of-state $w$ in a non-parametric form. The result favors a dynamical DE at $zlesssim1$, and shows a mild deviation ($lesssim2sigma$) from $w=-1$ at $z=0.5-0.7$. We find the addition of the AP method improves the low redshift ($zlesssim0.7$) constraint by $sim50%$.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
