All-sky angular power spectra from cleaned WISE×SuperCOSMOS galaxy number counts

Abstract

Aiming to extract cosmological information from linear scales of the WISE×SuperCOSMOS photometric redshift catalog, we perform a characterization of the systematic effects associated with stellar content, evidencing the presence of contamination and obscuration. We create an integrated model for these effects (which together we call "usurper contamination"), devise a method to remove both of them simultaneously and show its functionality by applying it to a set of mock catalogs. When administered to WISE×SuperCOSMOS data, our method shows to improve the measurements of angular power spectra on scales 15 and the extraction of cosmological parameters therefrom, even though a significant excess of power remains at these scales. When ignoring scales < 15, we still find strong indications of systematics, albeit these can be localized in the southern equatorial hemisphere. An independent analysis of the northern hemisphere at ≥ 15 agrees with the ΛCDM model with parameters from the Planck satellite and gives Ω c = 0.254 ± 0.020 and Ω b < 0.065 at 95% confidence limit when combined with priors on H 0 , A s and n s . lensing of the cosmic microwave background (CMB) -which serves as a consistency check for our cosmological model, besides helping improve constraints on halo bias and on the amplitude of matter perturbationspeaks at large angular scales [25]. This is also the case for the integrated Sachs-Wolfe effect [26], probed by the cross-correlation of CMB temperature maps with galaxy distribution, whose signal comes from the evolution of gravitational potential along the CMB photon path. Another topic that requires almost full-sky galaxy surveys is the measurement of our own peculiar velocity with respect to all other galaxies [27][28][29]. Large galaxy surveys can also help us improve our understanding of galaxy bias, that could be enhanced at the largest scales if we assume that galaxies form at density peaks (see e.g. [30]).This type of studies are among the main aims of the largest forthcoming surveys. The Large Synoptic Survey Telescope 1 (LSST) [31] will cover 18, 000 deg 2 up to redshifts z 3, while the Euclid space telescope 2 will observe 15,000 deg 2 and detect galaxies up to z 2 [32]. The huge volume probed by these surveys will lead to such a high number of observed galaxies and quasars that spectroscopic measurements will be performed only for a small fraction of them, while for most sources we will have to rely on photometric redshifts (photo-zs hereafter) and photometric classification. These techniques are, however, plagued with high contamination levels, large systematic effects and uncertainties, which must be controlled and understood in order to fully mine the relevant datasets.An existing testbed for such surveys is the WISE×SuperCOSMOS catalog [33] (WSC hereafter), a fullsky photometric galaxy dataset reaching z 0.4. Our goal in this paper is to estimate cosmological parameters from this sample under the standard cosmological model ΛCDM. In this process, we characterize the systematic effects ass...

Largest scales from the largest galaxy surveys: the pseudo Karhunen-Loève method

“…It is worth pointing out that this orthogonalization approach only mitigates additive systematics and not multiplicative ones. Strategies for dealing with multiplicative effects are given in [23,24,41].…”

“…2.1, it can be used as a "switch" for each one of the different separable selection functions defined over each sub-domain h: W (r) = h W h (r), where the non-zero regions of W h (r) do not overlap. Another real example is the WISE×SuperCOSMOS catalog, built from observations made with different telescopes that lead to differences between the two equatorial hemispheres [24,50]. These hemispheres can be described as sub-domains of separable selection functions (see the right panel of Fig.…”

“…Galaxy surveys provide a wealth of information about the Universe [1][2][3][4][5][6][7][8][9][10] and different methods for analyzing galaxy clustering have been proposed in the literature [11,12], focusing on: minimizing the variance and bias of 2-point statistics estimators [13,14]; minimizing the mode-coupling effect caused by the finite survey volume or partial sky coverage [15]; dealing with redshift space distortions (RSD) [16][17][18][19], luminosity-dependent bias [20], growth and non-linear structure [21,22], multiplicative errors in the selection function [23,24] and contamination by stars and quasars [25]. One such method is the so-called pseudo Karhunen-Loève (pKL) method [26,27], first introduced in the context of cosmology in [28] and applied to the Two-degree-Field galaxy redshift survey (2dF) [29,30] and to the Sloan Digital Sky Survey (SDSS) [31,32].…”

“…As demonstrated by SDSS [41], even well calibrated surveys might suffer from selection effects that make the radial selection function dependent on the direction of the line of sight; and surveys relying on different instruments for different regions of the sky (e.g. the Euclid ground segment 1 [42]) may also require spatially varying selection functions [24,43]. As a bonus, our treatment permits the combination of multiple surveys, and such combination was shown to significantly improve their constraints on the amplitude of matter perturbations σ 8 and the total mass of neutrinos m ν [42].…”

Cross-correlating dark sirens and galaxies: measurement of $H_0$ from GWTC-3 of LIGO-Virgo-KAGRA

“…WSC is constructed in a similar way, but cross-matching AllWISE and SuperCOSMOS only. For WSC, we further apply a color cut of W1 − W2 > 0.2 to the publicly available sample to reduce stellar contamination and increase uniformity [54]. The galaxy samples are further described and validated in [55], including the impact of changing the selection criteria.…”