Cosmological implications of the anisotropy of ten galaxy cluster scaling relations

Abstract

The hypothesis that the late Universe is isotropic and homogeneous is adopted by most cosmological studies, including studies of galaxy clusters. The cosmic expansion rate H0 is thought to be spatially constant, while bulk flows are often presumed to be negligible compared to the Hubble expansion, even at local scales. The effects of bulk flows on the redshift–distance conversion are hence usually ignored. Any deviation from this consensus can strongly bias the results of such studies, and thus the importance of testing these assumptions cannot be understated. Scaling relations of galaxy clusters can be effectively used for this testing. In previous works, we observed strong anisotropies in cluster scaling relations, whose origins remain ambiguous. By measuring many different cluster properties, several scaling relations with different sensitivities can be built. Nearly independent tests of cosmic isotropy and large bulk flows are then feasible. In this work, we make use of up to 570 clusters with measured properties at X-ray, microwave, and infrared wavelengths to construct ten different cluster scaling relations and test the isotropy of the local Universe; to our knowedge, we present five of these scaling relations for the first time. Through rigorous and robust tests, we ensure that our analysis is not prone to generally known systematic biases and X-ray absorption issues. By combining all available information, we detect an apparent 9% spatial variation in the local H0 between (l, b)∼(280°−35°+35°, −15°−20°+20°) and the rest of the sky. The observed anisotropy has a nearly dipole form. Using isotropic Monte Carlo simulations, we assess the statistical significance of the anisotropy to be > 5σ. This result could also be attributed to a ∼900 km s−1 bulk flow, which seems to extend out to at least ∼500 Mpc. These two effects will be indistinguishable until more high-z clusters are observed by future all-sky surveys such as eROSITA.

Bianchi IX gravitational collapse of matter inhomogeneities

“…In the past years there has been a growing interest in tests of the cosmological principle through astrophysical and cosmological observations, see for example Refs. [19][20][21][22][23][24][25][26][27] for an incomplete list, with no general consensus on the results. In particular, X-ray measurements of the scaling relations of galaxy clusters seems to point towards the existence of anisotropies in our local Universe, see Refs.…”

Superhorizon Perturbations: A Possible Explanation of the Hubble–Lemaître Tension and the Large-scale Anisotropy of the Universe

“…A recent study claims a dipole signal in quasar source counts at infrared frequencies which shows a deviation from the expected CMB dipole at the 4.9σ level (Secrest et al 2021). Several claims of anisotropy in the Hubble constant also exist (Biermann 1976;Wiltshire et al 2013;Luongo et al 2021;Migkas et al 2021). These observations suggest a potential departure from isotropy on the largest distance scales.…”

Lorentzian Vacuum Transitions for Anisotropic Universes

“…We could try another factorization of the Hamiltonian or equivalently another ordering factor but we fail to obtain a particular factorization that could lead us to both a solvable system for a zero potential and an expression for the integral in (111) that is computable. In order to visualize what is the consequence of having an anisotropic universe for the transition probability, we plot the probability (16) for this metric using (118) with different values of α which measures the degree of anisotropy of the system, having in the limit α → 0 the isotropy limit which is the flat FLRW case with result (57). Let us choose the minus sign both in the left and in the right of (118) so we have a well behaved probability and the plot given in units such that 2Vol(X) = 1 in both cases.…”

“…Other groups have studied the anisotropy using based-space X-ray observations and have found some results compatible with a non-vanishing degree of large scale anisotropy [15]. More recently some implications of the anisotropy in galaxy clusters is analysed in [16]. Then the debate about the possible existence of a certain degree of anisotropy is still not conclusive when all observations are taken into account.…”