Measuring the Hubble Constant through the Galaxy Pairwise Peculiar Velocity

Abstract The Hubble constant H 0 , the current expansion rate of the Universe, is one of the most important parameters in cosmology. The cosmic expansion regulates the mutually approaching motion of a pair of celestial objects due to their gravity. Therefore, the mean pairwise peculiar velocity of celestial objects, which quantifies their relative motion, is sensitive to both H 0 and the dimensionless total matter density Ω m . Based on this, using the Cosmicflows-4 data, we measured H 0 for the first time via the galaxy pairwise velocity in the nonlinear and quasi-linear range. Our results yield H 0 = 75.5 ± 1.4 km s −1 Mpc −1 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mo mathvariant="normal">Ω</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.31</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.028</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.029</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> . The uncertainties of H 0 and Ω m can be improved to around 0.6% and 2%, respectively, if the statistical errors become negligible in the future.