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Register a new userProbing gravity with the DES-CMASS sample and BOSS spectroscopy
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The DES-CMASS sample (DMASS) is designed to optimally combine the weak lensing measurements from the Dark Energy Survey (DES) and redshift-space distortions (RSD) probed by the CMASS galaxy sample from the Baryonic Oscillation Spectroscopic Survey (BOSS). In this paper, we demonstrate the feasibility of adopting DMASS as the equivalent of BOSS CMASS for a joint analysis of DES and BOSS in the framework of modified gravity. We utilize the angular clustering of the DMASS galaxies, cosmic shear of the DES METACALIBRATION sources, and cross-correlation of the two as data vectors. By jointly fitting the combination of the data with the RSD measurements from the BOSS CMASS sample and Planck data, we obtain the constraints on modified gravity parameters $mu_0 = -0.37^{+0.47}_{-0.45}$ and $Sigma_0 = 0.078^{+0.078}_{-0.082}$. We do not detect any significant deviation from General Relativity. Our constraints of modified gravity measured with DMASS are tighter than those with the DES Year 1 redMaGiC galaxy sample with the same external data sets by $29%$ for $mu_0$ and $21%$ for $Sigma_0$, and comparable to the published results of the DES Year 1 modified gravity analysis despite this work using fewer external data sets. This improvement is mainly because the galaxy bias parameter is shared and more tightly constrained by both CMASS and DMASS, effectively breaking the degeneracy between the galaxy bias and other cosmological parameters. Such an approach to optimally combine photometric and spectroscopic surveys using a photometric sample equivalent to a spectroscopic sample can be applied to combining future surveys having a limited overlap such as DESI and LSST.
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The combination of Galaxy-Galaxy Lensing (GGL) and Redshift Space Distortion of galaxy clustering (RSD) is a privileged technique to test General Relativity predictions, and break degeneracies between the growth rate of structure parameter $f$ and the amplitude of the linear power-spectrum $sigma_8$. We perform a joint GGL and RSD analysis on 250 sq. degrees using shape catalogues from CFHTLenS and CFHT-Stripe 82, and spectroscopic redshifts from the BOSS CMASS sample. We adjust a model that includes non-linear biasing, RSD and Alcock-Paczynski effects. We find $f(z=0.57) =0.95pm0.23$, $sigma_8(z=0.57)=0.55pm0.07$ and $Omega_{rm m} = 0.31pm0.08$, in agreement with Planck cosmological results 2018. We also estimate the probe of gravity $E_{rm G} = 0.43pm0.10$ in agreement with $Lambda$CDM-GR predictions of $E_{rm G} = 0.40$. This analysis reveals that RSD efficiently decreases the GGL uncertainty on $Omega_{rm m}$ by a factor of 4, and by 30% on $sigma_8$. We use an N-body simulation supplemented by an abundance matching prescription for CMASS to build a set of overlapping lensing and clustering mocks. Together with additional spectroscopic data, this helps us to quantify and correct several systematic errors, such as photometric redshifts. We make our mock catalogues available on the Skies and Universe database.
We present an $8.1sigma$ detection of the non-Gaussian 4-Point Correlation Function (4PCF) using a sample of $N_{rm g} approx 8times 10^5$ galaxies from the BOSS CMASS dataset. Our measurement uses the $mathcal{O}(N_{rm g}^2)$ NPCF estimator of Philcox et al. (2021), including a new modification to subtract the disconnected 4PCF contribution (arising from the product of two 2PCFs) at the estimator level. This approach is unlike previous work and ensures that our signal is a robust detection of gravitationally-induced non-Gaussianity. The estimator is validated with a suite of lognormal simulations, and the analytic form of the disconnected contribution is discussed. Due to the high dimensionality of the 4PCF, data compression is required; we use a signal-to-noise-based scheme calibrated from theoretical covariance matrices to restrict to $sim$ $100$ basis vectors. The compression has minimal impact on the detection significance and facilitates traditional $chi^2$-like analyses using a suite of mock catalogs. The significance is stable with respect to different treatments of noise in the sample covariance (arising from the limited number of mocks), but decreases to $4.7sigma$ when a minimum galaxy separation of $14 h^{-1}mathrm{Mpc}$ is enforced on the 4PCF tetrahedra (such that the statistic can be modelled more easily). The detectability of the 4PCF in the quasi-linear regime implies that it will become a useful tool in constraining cosmological and galaxy formation parameters from upcoming spectroscopic surveys.
The DMASS sample is a photometric sample from the DES Year 1 data set designed to replicate the properties of the CMASS sample from BOSS, in support of a joint analysis of DES and BOSS beyond the small overlapping area. In this paper, we present the measurement of galaxy-galaxy lensing using the DMASS sample as gravitational lenses in the DES Y1 imaging data. We test a number of potential systematics that can bias the galaxy-galaxy lensing signal, including those from shear estimation, photometric redshifts, and observing conditions. After careful systematic tests, we obtain a highly significant detection of the galaxy-galaxy lensing signal, with total $S/N=25.7$. With the measured signal, we assess the feasibility of using DMASS as gravitational lenses equivalent to CMASS, by estimating the galaxy-matter cross-correlation coefficient $r_{rm cc}$. By jointly fitting the galaxy-galaxy lensing measurement with the galaxy clustering measurement from CMASS, we obtain $r_{rm cc}=1.09^{+0.12}_{-0.11}$ for the scale cut of $4~h^{-1}{rm Mpc}$ and $r_{rm cc}=1.06^{+0.13}_{-0.12}$ for $12~h^{-1}{rm Mpc}$ in fixed cosmology. By adding the angular galaxy clustering of DMASS, we obtain $r_{rm cc}=1.06pm 0.10$ for the scale cut of $4~h^{-1}{rm Mpc}$ and $r_{rm cc}=1.03pm 0.11$ for $12~h^{-1}{rm Mpc}$. The resulting values of $r_{rm cc}$ indicate that the lensing signal of DMASS is equivalent to the one that would have been measured if CMASS had populated the DES region within the given statistical uncertainty. The measurement of galaxy-galaxy lensing presented in this paper will serve as part of the data vector for the forthcoming cosmology analysis in preparation.
In this study, we probe the transition to cosmic homogeneity in the Large Scale Structure (LSS) of the Universe using the CMASS galaxy sample of BOSS spectroscopic survey which covers the largest effective volume to date, $3 h^{-3} mathrm{Gpc}^3$ at $0.43 leq z leq 0.7$. We study the scaled counts-in-spheres, $mathcal{N}(<r)$, and the fractal correlation dimension, $mathcal{D}_2(r)$, to assess the homogeneity scale of the universe using a $Landy & Szalay$ inspired estimator. Defining the scale of transition to homogeneity as the scale at which $mathcal{D}_2(r)$ reaches 3 within $1%$, i.e. $mathcal{D}_2(r)>2.97$ for $r>mathcal{R}_H$, we find $mathcal{R}_H = (63.3pm0.7) h^{-1} mathrm{Mpc}$, in agreement at the percentage level with the predictions of the $Lambda$CDM model $mathcal{R}_H=62.0 h^{-1} mathrm{Mpc}$. Thanks to the large cosmic depth of the survey, we investigate the redshift evolution of the transition to homogeneity scale and find agreement with the $Lambda$CDM prediction. Finally, we find that $mathcal{D}_2$ is compatible with $3$ at scales larger than $300 h^{-1} $Mpc in all redshift bins. These results consolidate the Cosmological Principle and represent a precise consistency test of the $Lambda CDM$ model.
General relativistic effects have long been predicted to subtly influence the observed large-scale structure of the universe. The current generation of galaxy redshift surveys have reached a size where detection of such effects is becoming feasible. In this paper, we report the first detection of the redshift asymmetry from the cross-correlation function of two galaxy populations which is consistent with relativistic effects. The dataset is taken from the Sloan Digital Sky Survey DR12 CMASS galaxy sample, and we detect the asymmetry at the $2.7sigma$ level by applying a shell-averaged estimator to the cross-correlation function. Our measurement dominates at scales around $10$ h$^{-1}$Mpc, larger than those over which the gravitational redshift profile has been recently measured in galaxy clusters, but smaller than scales for which linear perturbation theory is likely to be accurate. The detection significance varies by 0.5$sigma$ with the details of our measurement and tests for systematic effects. We have also devised two null tests to check for various survey systematics and show that both results are consistent with the null hypothesis. We measure the dipole moment of the cross-correlation function, and from this the asymmetry is also detected, at the $2.8 sigma$ level. The amplitude and scale-dependence of the clustering asymmetries are approximately consistent with the expectations of General Relativity and a biased galaxy population, within large uncertainties. We explore theoretical predictions using numerical simulations in a companion paper.
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