Galaxy formation with BECDM  I. Turbulence and relaxation of idealized haloes
Abstract
We present a theoretical analysis of some unexplored aspects of relaxed BoseEinstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same largescale predictions as CDM and potentially overcomes CDM's smallscale problems via a galaxyscale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the SchrödingerPoisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic r^{3} NFWlike profile. We find a fundamental relation of the coretohalo mass with the dimensionless invariant Ξ ≡ E/M^{3}/(Gm/ℏ)^{2} or M_{c}/M ≃ 2.6Ξ^{1/3}, linking the soliton to global halo properties. For r ≥ 3.5 r_{c} core radii, we find equipartition between potential, classical kinetic and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behaviour driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a k^{1.1} power law. This suggests that the vorticity in BECDM haloes is homogeneous, similar to thermallydriven counterflow BEC systems from condensed matter physics, in contrast to a k^{5/3} Kolmogorov power law seen in mechanicallydriven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying that the solitonsized granules carry most of the turbulent energy in BECDM haloes.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 November 2017
 DOI:
 10.1093/mnras/stx1887
 arXiv:
 arXiv:1705.05845
 Bibcode:
 2017MNRAS.471.4559M
 Keywords:

 methods: numerical;
 galaxies: haloes;
 dark matter;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 14 pages, 7 figures, MNRAS accepted