Scalar field dark matter in clusters of galaxies

Abstract

One alternative to the cold dark matter (CDM) paradigm is the scalar field\ndark matter (SFDM) model, which assumes dark matter is a spin-0 ultra-light\nscalar field (SF) with a typical mass $m\\sim10^{-22}\\mathrm{eV}/c^2$ and\npositive self-interactions. Due to the ultra-light boson mass, the SFDM could\nform Bose-Einstein condensates (BEC) in the very early Universe, which are\ninterpreted as the dark matter haloes. Although cosmologically the model\nbehaves as CDM, they differ at small scales: SFDM naturally predicts fewer\nsatellite haloes, cores in dwarf galaxies and the formation of massive galaxies\nat high redshifts. The ground state (or BEC) solution at zero temperature\nsuffices to describe low-mass galaxies but fails for larger systems. A possible\nsolution is adding finite-temperature corrections to the SF potential which\nallows combinations of excited states. In this work, we test the\nfinite-temperature multistate SFDM solution at galaxy cluster scales and\ncompare our results with the Navarro-Frenk-White (NFW) and BEC profiles. We\nachieve this by fitting the mass distribution of 13 \\textit{Chandra} X-ray\nclusters of galaxies, excluding the region of the brightest cluster galaxy. We\nshow that the SFDM model accurately describes the clusters' DM mass\ndistributions offering an equivalent or better agreement than the NFW profile.\nThe complete disagreement of the BEC model with the data is also shown. We\nconclude that the theoretically motivated multistate SFDM profile is an\ninteresting alternative to empirical profiles and ad hoc fitting-functions that\nattempt to couple the asymptotic NFW decline with the inner core in SFDM.\n