Cosmological bulk flow in the QCDM model: (in)consistency with ΛCDM

Abstract

ABSTRACT We study the bulk flow of the local universe with Type Ia supernova data (a compilation of Union2 and Pantheon data) in the spatially flat homogeneous and isotropic space–time. In particular, we take the so-called QCDM models, which consist of cold dark matter (CDM) and a Q-component described by a scalar field with its self-interactions determined by an exponential potential. We use different cumulative redshift slices of the Union2 and Pantheon catalogues. A maximum-likelihood analysis of peculiar velocities confirms that, at low redshifts 0.015 < z < 0.1, the bulk flow is moving in the $l=272^{+17}_{-17}, b=33^{+12}_{-12}$, and $302^{+20}_{-20},3^{+10}_{-10}$ directions with $v _\mathrm{bulk} = 225^{+38}_{-35}$ and $246^{+64}_{-46}$ km s−1 for the Pantheon and Union2 data respectively, in good agreement with the direction of the cosmic microwave background dipole and with a number of previous studies at 1σ. However, for high redshifts 0.1 < z < 0.2, we get $v _\mathrm{bulk} = 708^{+110}_{-110}$ and $v_\mathrm{bulk}=1014^{+86}_{-114}\,\text{km\,s}^{-1}$ towards l = 318 ± 10°, b = −15 ± 9° and $l=254^{+16}_{-14},\ b=6^{+7}_{-10}$ for the Pantheon and Union2 data respectively. This indicates that for low redshifts our results are approximately consistent with the ΛCDM model; however, for high redshifts they disagree with ΛCDM and support the results of those studies that report a large bulk flow for the universe.