Cosmological simulations of number counts

In this paper we present for the first time the angular power spectra C ℓ(z,z') for number counts from relativistic N-body simulations. We use the relativistic N-body code gevolution with its exact integration of lightlike geodesics which include all relativistic scalar contributions to the number counts. We compare our non-perturbative numerical results with the results from class using the hmcode approximation for the non-linear matter power spectrum. We find that this simple description is excellent for both, the density and the convergence. On the other hand, the current implementation of redshift-space distortions in Boltzmann codes is not accurate. We also find that the largest contribution to the unequal-redshift power spectra is the cross-correlation of the density and the lensing contribution to the number counts, especially for redshift bins that are far apart. Correlating the number counts with the convergence map we find that the signal is dominated by the lensing-lensing term when the convergence field redshift is not higher than the number counts one, while it is dominated by the density-lensing term in the opposite case. In the present study, the issue of galaxy bias is deliberately left aside by considering only unbiased samples of matter particles from the simulations.

Cosmology with the Roman Space Telescope - synergies with the Rubin Observatory Legacy Survey of Space and Time

We explore synergies between the Nancy Grace Roman Space Telescope and the Vera Rubin Observatory’s Legacy Survey of Space and Time (LSST). Specifically, we consider scenarios where the currently envisioned survey strategy for the Roman Space Telescope’s High Latitude Survey (HLS reference), i.e. 2000 deg2 in four narrow photometric bands is altered in favour of a strategy of rapid coverage of the LSST area (to full LSST depth) in one band. We find that in only 5-month a survey in the W-band can cover the full LSST survey area providing high-resolution imaging for >95 per cent of the LSST Year 10 gold galaxy sample. We explore a second, more ambitious scenario where the Roman Space Telescope spends 1.5 years covering the LSST area. For this second scenario we quantify the constraining power on dark energy equation of state parameters from a joint weak lensing and galaxy clustering analysis. Our survey simulations are based on the Roman Space Telescope exposure time calculator and redshift distributions from the CANDELS catalog. Our statistical uncertainties account for higher-order correlations of the density field, and we include a wide range of systematic effects, such as uncertainties in shape and redshift measurements, and modeling uncertainties of astrophysical systematics, such as galaxy bias, intrinsic galaxy alignment, and baryonic physics. We find a significant increase in constraining power for the joint LSST+HLS wide survey compared to LSST Y10 (FoMHLSwide= 2.4 FoMLSST) and compared to LSST+HLS (FoMHLSwide= 5.5 FoMHLSref).

Extended fast action minimization method: application to SDSS-DR12 combined sample

ABSTRACT We present the first application of the extended Fast Action Minimization method (eFAM) to a real data set, the SDSS-DR12 Combined Sample, to reconstruct galaxies orbits back-in-time, their two-point correlation function (2PCF) in real-space, and enhance the baryon acoustic oscillation (BAO) peak. For this purpose, we introduce a new implementation of eFAM that accounts for selection effects, survey footprint, and galaxy bias. We use the reconstructed BAO peak to measure the angular diameter distance, $D_\mathrm{A}(z)r^\mathrm{fid}_\mathrm{s}/r_\mathrm{s}$, and the Hubble parameter, $H(z)r_\mathrm{s}/r^\mathrm{fid}_\mathrm{s}$, normalized to the sound horizon scale for a fiducial cosmology $r^\mathrm{fid}_\mathrm{s}$, at the mean redshift of the sample z = 0.38, obtaining $D_\mathrm{A}(z=0.38)r^\mathrm{fid}_\mathrm{s}/r_\mathrm{s}=1090\pm 29$(Mpc)−1, and $H(z=0.38)r_\mathrm{s}/r^\mathrm{fid}_\mathrm{s}=83\pm 3$(km s−1 Mpc−1), in agreement with previous measurements on the same data set. The validation tests, performed using 400 publicly available SDSS-DR12 mock catalogues, reveal that eFAM performs well in reconstructing the 2PCF down to separations of ∼25h−1Mpc, i.e. well into the non-linear regime. Besides, eFAM successfully removes the anisotropies due to redshift-space distortion (RSD) at all redshifts including that of the survey, allowing us to decrease the number of free parameters in the model and fit the full-shape of the back-in-time reconstructed 2PCF well beyond the BAO peak. Recovering the real-space 2PCF, eFAM improves the precision on the estimates of the fitting parameters. When compared with the no-reconstruction case, eFAM reduces the uncertainty of the Alcock-Paczynski distortion parameters α⊥ and α∥ of about 40 per cent and that on the non-linear damping scale Σ∥ of about 70 per cent. These results show that eFAM can be successfully applied to existing redshift galaxy catalogues and should be considered as a reconstruction tool for next-generation surveys alternative to popular methods based on the Zel’dovich approximation.

Improving estimates of the growth rate using galaxy–velocity correlations: a simulation study

ABSTRACT We present an improved framework for estimating the growth rate of large-scale structure, using measurements of the galaxy–velocity cross-correlation in configuration space. We consider standard estimators of the velocity autocorrelation function, ψ1 and ψ2, the two-point galaxy correlation function, ξgg, and introduce a new estimator of the galaxy–velocity cross-correlation function, ψ3. By including pair counts measured from random catalogues of velocities and positions sampled from distributions characteristic of the true data, we find that the variance in the galaxy–velocity cross-correlation function is significantly reduced. Applying a covariance analysis and χ2 minimization procedure to these statistics, we determine estimates and errors for the normalized growth rate fσ8 and the parameter β = f/b, where b is the galaxy bias factor. We test this framework on mock hemisphere data sets for redshift z < 0.1 with realistic velocity noise constructed from the l-picola simulation code, and find that we are able to recover the fiducial value of fσ8 from the joint combination of ψ1 + ψ2 + ψ3 + ξgg, with 15 per cent accuracy from individual mocks. We also recover the fiducial fσ8 to within 1σ regardless of the combination of correlation statistics used. When we consider all four statistics together we find that the statistical uncertainty in our measurement of the growth rate is reduced by $59{{\ \rm per\ cent}}$ compared to the same analysis only considering ψ2, by $53{{\ \rm per\ cent}}$ compared to the same analysis only considering ψ1, and by $52{{\ \rm per\ cent}}$ compared to the same analysis jointly considering ψ1 and ψ2.