First test of Verlinde's theory of emergent gravity using weak gravitational lensing measurements

Abstract

Verlinde (2016) proposed that the observed excess gravity in galaxies and clusters is the consequence of Emergent Gravity (EG). In this theory the standard gravitational laws are modified on galactic and larger scales due to the displacement of dark energy by baryonic matter. EG gives an estimate of the excess gravity (described as an apparent dark matter density) in terms of the baryonic mass distribution and the Hubble parameter. In this work we present the first test of EG using weak gravitational lensing, within the regime of validity of the current model. Although there is no direct description of lensing and cosmology in EG yet, we can make a reasonable estimate of the expected lensing signal of low redshift galaxies by assuming a background ΛCDM cosmology. We measure the (apparent) average surface mass density profiles of 33, 613 isolated central galaxies, and compare them to those predicted by EG based on the galaxies' baryonic masses. To this end we employ the ∼ 180 deg 2 overlap of the Kilo-Degree Survey (KiDS) with the spectroscopic Galaxy And Mass Assembly (GAMA) survey. We find that the prediction from EG, despite requiring no free parameters, is in good agreement with the observed galaxy-galaxy lensing profiles in four different stellar mass bins. Although this performance is remarkable, this study is only a first step. Further advancements on both the theoretical framework and observational tests of EG are needed before it can be considered a fully developed and solidly tested theory.

Testing emergent gravity on galaxy cluster scales

“…The theory has already been tested with several methods and on a range of scales. In [6] the average surface mass density profiles of isolated central galaxies were used to test Emergent Gravity, finding that the predictions of the theory are in good agreement with measured galaxy-galaxy lensing profiles. More recently the predictions of Emergent Gravity were compared with the predictions from selected modified gravity theories for a single galaxy cluster, showing that Emergent Gravity only approaches the measured acceleration profile data at the outskirt of the cluster [10].…”

“…• There is also no geodesic equation in Emergent Gravity so far, so we will make a crucial assumption that lensing works in EG the same way as in GR. In particular, following the work in [6], we will assume that the extra gravity effects predicted by Emergent Gravity, affect the paths of photons in the same way as dark matter does in GR. Future theoretical and observational work will be required to test the validity of this assumption; however, in this work we assume that it is valid and test the outcomes of such an assumption.…”

“…The cooling function was calculated using XSPEC software(Arnaud 1996) and utilised the APEC model(Smith et al 2001) over a range of 0.5keV to 2keV[26,27] 6. To put it simply, the mentioned covariance matrix, Ci,j quantifies how the change in an ith data point affects the jth data point.…”

The third data release of the Kilo-Degree Survey and associated data products

“…These include photo-z probability distribution functions, machinelearning photo-z's, weak lensing shear catalogues and lensingoptimized image data. The first applications of this new data set have appeared already and include the first cosmological results from KiDS (Joudaki et al 2017;Brouwer et al 2017;Hildebrandt et al 2017).…”

Emergent dark gravity from (non)holographic screens

“…Furthermore, it is shown that one can reproduce many key empirical findings in cosmology, such as Milgrom's fitting formula of MOND and the baryonic Tully-Fisher relation within this formalism [18,19]. There is also strong agreement between this framework and weak-lensing observations [20].…”