Constraints on Bose-Einstein-condensed axion dark matter from the Hi nearby galaxy survey data

Abstract

One of the leading candidates for dark matter is the axion or axionlike particle in the form of a Bose-Einstein condensate (BEC). In this paper, we present an analysis of 17 high-resolution galactic rotation curves from the Hi nearby galaxy survey (THINGS) data [F. Walter et al., Astron. J. 136, 2563 (2008)] in the context of the axionic Bose-Einstein condensed dark matter model. Assuming a repulsive two-body interaction, we solve the nonrelativistic Gross-Pitaevskii equation for $N$ gravitationally trapped bosons in the Thomas-Fermi approximation. We obtain the maximum possible radius $R$ and the mass profile $M(r)$ of a dilute axionic Bose-Einstein condensed gas cloud. A standard least-${\ensuremath{\chi}}^{2}$ method is employed to find the best-fit values of the total mass $M$ of the axion BEC and its radius $R$. The local mass density of BEC axion dark matter is ${\ensuremath{\rho}}_{a}\ensuremath{\simeq}0.02\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$, which agrees with that presented by Beck [C. Beck, Phys. Rev. Lett. 111, 231801 (2013)]. The axion mass ${m}_{a}$ we obtain depends not only on the best-fit value of $R$, but also on the $s$-wave scattering length $a$ (${m}_{a}\ensuremath{\propto}{a}^{1/3}$). The transition temperature ${T}_{a}$ of an axion BEC on galactic scales is also estimated. Comparing the calculated ${T}_{a}$ with the ambient temperature of galaxies and galaxy clusters implies that $a\ensuremath{\sim}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{fm}$. The corresponding axion mass is ${m}_{a}\ensuremath{\simeq}0.58\text{ }\text{ }\mathrm{meV}$. We compare our results with others.