Searching for a Cosmological Preferred Direction with 147 Rotationally Supported Galaxies

Abstract

Abstract It is well known that the Milgrom’s modified Newtonian dynamics (MOND) explains well the mass discrepancy problem in galaxy rotation curves. The MOND predicts a universal acceleration scale below which the Newtonian dynamics is still invalid. We get the universal acceleration scale of 1.02 × 10−10 m s−2 by using the Spitzer Photometry and Accurate Rotation Curves (SPARC) data set. Milgrom suggested that the acceleration scale may be a fingerprint of cosmology on local dynamics and related to the Hubble constant g † ∼ cH 0. In this paper, we use the hemisphere comparison method with the SPARC data set to investigate possible spatial anisotropy on the acceleration scale. It is found that the hemisphere of the maximum acceleration scale is in the direction , with g †,max = 1.10 × 10−10 m s−2, while the hemisphere of the minimum acceleration scale is in the opposite direction , with g †,min = 0.76 × 10−10 m s−2. The level of anisotropy reaches up to 0.37 ± 0.04. Robust tests show that such an anisotropy cannot be reproduced by a statistically isotropic data set. We also show that the spatial anisotropy on the acceleration scale is less correlated with the non-uniform distribution of the SPARC data points in the sky. In addition, we confirm that the anisotropy of the acceleration scale does not depend significantly on other physical parameters of the SPARC galaxies. It is interesting to note that the maximum anisotropy direction found in this paper is close with other cosmological preferred directions, particularly the direction of the “Australia dipole” for the fine structure constant.