New perspectives on the BOSS small-scale lensing discrepancy for the Planck ΛCDM cosmology

Abstract

We investigate the abundance, small-scale clustering and galaxy-galaxy lensing signal of galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS). To this end, we present new measurements of the redshift and stellar mass dependence of the lensing properties of the galaxy sample. We analyse to what extent models assuming the Planck18 cosmology fit to the number density and clustering can accurately predict the small-scale lensing signal. In qualitative agreement with previous BOSS studies at redshift z ∼ 0.5 and with results from the Sloan Digital Sky Survey, we find that the expected signal at small scales (0.1 < r p < 3 h −1 Mpc) is higher by ∼ 25% than what is measured. Here, we show that this result is persistent over the redshift range 0.1 < z < 0.7 and for galaxies of different stellar masses. If interpreted as evidence for cosmological parameters different from the Planck CMB findings, our results imply S 8 = σ 8 Ω m /0.3 = 0.744 ± 0.015, whereas S 8 = 0.832 ± 0.013 for Planck18. However, in addition to being in tension with CMB results, such a change in cosmology alone does not accurately predict the lensing amplitude at larger scales. Instead, other often neglected systematics like baryonic feedback or assembly bias are likely contributing to the small-scale lensing discrepancy. We show that either effect alone, though, is unlikely to completely resolve the tension. Ultimately, a combination of the two effects in combination with a moderate change in cosmological parameters might be needed.

Atacama Cosmology Telescope: Modeling the gas thermodynamics in BOSS CMASS galaxies from kinematic and thermal Sunyaev-Zel’dovich measurements

“…The impact of baryons is one of many effects considered in [26], the others being measurement systematics, sample selection, assembly bias, and extensions to our concordance cosmological model. It is likely that a combination of these effects is responsible for the low lensing signal (e.g., [98]), since baryonic effects cannot explain the entire difference. FIG.…”

Atacama Cosmology Telescope: Combined kinematic and thermal Sunyaev-Zel’dovich measurements from BOSS CMASS and LOWZ halos

“…Galaxy-galaxy lensing can be calibrated directly by measuring the kSZ signal around the lens sample. In [36], we show that the current measurement is precise enough to pin down the baryon contribution to CMASS galaxy-galaxy lensing measurements and inform the "lensing is low" tension on halo scales [39][40][41], by directly measuring the baryon profiles on the relevant scales. For cosmic shear, some modeling and extrapolation may be required to encompass all of the halos that contribute to the power spectrum on mildly nonlinear scales.…”

“…In the absence of kSZ measurements, this approach would be limited by the modeling of the gas temperature (for tSZ) and clumping (x rays) [37,38]. This joint tSZ and kSZ measurement also informs the "lensing is low" tension, where the galaxygalaxy lensing signal of BOSS galaxies is found to be anomalously low, compared to the expected signal based on their clustering [39][40][41]. This paper and companion paper [36] are a first step in constraining the gas thermodynamics in galaxy groups and directly measuring the baryonic effects in weak lensing.…”

Lensing without borders – I. A blind comparison of the amplitude of galaxy–galaxy lensing between independent imaging surveys

“…Another such difference is the "lensing is low" effect. This is the observation that the lensing amplitude around luminous red galaxies is lower than predicted by their clustering in a Planck cosmology (Cacciato et al 2013;Leauthaud et al 2017;Lange et al 2019;Singh et al 2020). Measurements of the EG statistic (e.g.…”