Constraining a late time transition of Geff using low-z galaxy survey data
Phys. Rev. D 106, 023526
Abstract:
It has recently been pointed out that a gravitational transition taking place at a recent redshift zt, reducing the effective gravitational constant Geff by about 10% for z>zt, has the potential to lead to a resolution of the Hubble tension if zt≲0.01. Since H(z)2∼Geff, such a transition would also lead to sharp change of the slope of the Hubble diagram at z=zt and a sharp decrease in the number of galaxies per redshift bin at zt. Here we attempt to impose constraints on such a transition by using two robust low-z redshift survey datasets (z<0.01), taken from the Six-degree Field Galaxy Survey (6dFGS) as well as the 2MASS Redshift Survey (2MRS). In both surveys, we bin the data in redshift bins and focus on the number of galaxies in each bin (ΔN(zi)). We observe a peak in the distribution of galaxies near a distance of approximately 20 Mpc in both datasets. This feature could be attributed to galactic density fluctuations, to coherent peculiar velocities of galaxies or to an ultra late-time gravitational transition in the same era. In the context of the later scenario we show that this feature could have been induced by a sharp change of Geff by ΔGeff/Geff≃0.6 at zt≃0.005. Thus, in a conservative approach, this method can be used to impose constraints on a possible abrupt change of the gravitational constant taking place at very low redshifts.
On cosmological bias due to the magnification of shear and position samples in modern weak lensing analyses
Monthly Notices of the Royal Astronomical Society Oxford University Press 515:1 (2022) 1130-1145
Abstract:
The magnification of galaxies in modern galaxy surveys induces additional correlations in the cosmic shear, galaxy-galaxy lensing and clustering observables used in modern lensing “3x2pt” analyses, due to sample selection. In this paper, we emulate the magnification contribution to all three observables utilising the SLICS simulations suite, and test the sensitivity of the cosmological model, galaxy bias and redshift distribution calibration to un-modelled magnification in a Stage-IV-like survey using Monte-Carlo sampling. We find that magnification cannot be ignored in any single or combined observable, with magnification inducing > 1σ biases in the w0 − σ8 plane, including for cosmic shear and 3x2pt analyses. Significant cosmological biases exist in the 3x2pt and cosmic shear from magnification of the shear sample alone. We show that magnification induces significant biases in the mean of the redshift distribution where a position sample is analysed, which may potentially be used to identify contamination by magnification.Euclid preparation
Astronomy & Astrophysics EDP Sciences 662 (2022) a112
MIGHTEE - H I. The relation between the H I gas in galaxies and the cosmic web
Monthly Notices of the Royal Astronomical Society Oxford University Press 513:2 (2022) 2168-2177