The MICE Grand Challenge Lightcone Simulation III: Galaxy lensing mocks from all-sky lensing maps

TL;DR

This work builds the MICE Grand Challenge framework into all-sky lensing maps via the onion-universe approach, enabling accurate convergence, deflection, and shear modeling from linear to nonlinear scales for a realistic galaxy mock (MICECAT v1.0) up to redshift z≈1.4. By validating 2-point lensing statistics in harmonic and configuration space against non-linear theory and exploring mass-resolution effects, the authors demonstrate that their mocks faithfully reproduce lensing observables down to ≈arcminute scales. They also introduce and validate magnification effects—both in background magnitudes and positions—that induce measurable cross-correlations between foreground and background samples, including novel magnification-magnitude cross-correlations. The results support the use of these all-sky lensing mocks for near-future surveys and include a public data release to facilitate broader community analyses.

Abstract

In paper I of this series (Fosalba et al. 2013), we presented a new N-body lightcone simulation from the MICE collaboration, the MICE Grand Challenge (MICE-GC), containing about 70 billion dark-matter particles in a (3 Gpc)^3 comoving volume, from which we built halo and galaxy catalogues using a Halo Occupation Distribution and Halo Abundance Matching technique, as presented in the companion Paper II (Crocce et al. 2013). Given its large volume and fine mass resolution, the MICE-GC simulation also allows an accurate modeling of the lensing observables from upcoming wide and deep galaxy surveys. In the last paper of this series (Paper III), we describe the construction of all-sky lensing maps, following the "Onion Universe" approach (Fosalba et al. 2008), and discuss their properties in the lightcone up to z=1.4 with sub-arcmin spatial resolution. By comparing the convergence power spectrum in the MICE-GC to lower mass-resolution (i.e., particle mass ~ 10^11 Msun) simulations, we find that resolution effects are at the 5 % level for multipoles l ~ 10^3 and 20 % for l ~ 10^4. Resolution effects have a much lower impact on our simulation, as shown by comparing the MICE-GC to recent numerical fits by Takahashi et al 2012. We use the all-sky lensing maps to model galaxy lensing properties, such as the convergence, shear, and lensed magnitudes and positions, and validate them thoroughly using galaxy shear auto and cross-correlations in harmonic and configuration space. Our results show that the galaxy lensing mocks here presented can be used to accurately model lensing observables down to arcminute scales.

Figures (14)

• Figure 1: All-sky map of the convergence field, $\kappa$, for the MICE-GC simulation, for sources at $z_s=1$, with a pixel resolution of $0.85$ arcmin. The sphere is gridded in $\sim 50$ sq.deg patches. The color scale shown spans over the range $-\sigma < \kappa< 3\, \sigma$, where $\sigma$ is the rms fluctuation of the all-sky convergence map, illustrating the richness in the lensing structures resolved.
• Figure 2: Angular power spectrum of the Convergence map for sources at $z_s=1$. Dashed, solid and long-dashed lines show linear theory, the Halofit (Smith et al 2003) and revised Halofit (Takahashi et al 2012) non-linear theory predictions, respectively. Lower panel shows relative deviations with respect to theory predictions. Filled symbols show simulations measurements including shot-noise, open symbols display measurements without shot-noise (shown only for the MICE-GC, where its is a subdominant effect). We show Gaussian error bars to guide the eye (see text for details). Mass resolution effects estimated as the difference between the MICE-IR and the MICE-GC simulations, are at the 5$\%$ level for $\ell\sim 10^3$ and 20 $\%$ for $\ell\sim 10^4$. In turn that MICE-GC displays a comparable lack of power with respect to the revised Halofit prediction.
• Figure 3: Angular power spectrum of the deflection angle for sources at $z_s=1.4$ measured in the MICE-GC simulation (wiggly blue line), compared to the non-linear Halofit prediction (smooth black line).
• Figure 4: Comparison between simulation measurements (wiggly thick solid lines) and non-linear theory expectations (Halofit, smooth thin lines) for the convergence (black) and shear amplitudes (blue), for sources at $z_s=1$. Shot-noise (magenta line) is taken into account and subtracted from the power measured in the simulation.
• Figure 5: Top panels: (Left) 7x7 sq.deg patch showing the fluctuations in the convergence field (the bar at the bottom of each panel shows the gray scale/color code used to depict the field value, which is dimensionless) and shear vectors (scale for vector length displayed is shown at the bottom left; field is dimensionless) from dark-matter "onion shells" of the MICE-GC simulation, for sources at $z=1$. Rectangular grid has cells of $1$ sq.deg, corresponding to comoving transverse lengths of $21$ Mpc/h. Shear amplitude is given by length of the vectors, with scale as given in the bottom left of the plot. (Right) Zoom-in: central 1 sq.deg grid cell of patch shown in left panel. It shows shear vectors are tangential to matter over-densities, as expected. Bottom Panels: Same as Top panels but for the "Intermediate" resolution simulation MICE-IR, which has a factor of $8$ lower mass resolution. Mass resolution effects are reflected in the lack of small-mass halos (or substructure in the convergence/shear maps). This is more clearly seen in the zoom-in picture (right panels).