Modelling dark matter halo spin using observations and simulations: application to UGC 5288

Abstract

Dark matter (DM) halo properties are extensively studied in cosmological simulations but are very challenging to estimate from observations. The DM halo density profile of observed galaxies is modelled using multiple probes that trace the DM potential. However, the angular momentum distribution of DM halos is still a subject of debate. In this study, we investigate a method for estimating the halo spin and halo concentration of low surface brightness (LSB), gas-rich dwarf barred galaxy UGC 5288, by forward modelling disc properties derived from observations – stellar and gas surface densities, disc scalelength, H I rotation curve, bar length, and bar ellipticity. We combine semi-analytical techniques, N-body/SPH, and cosmological simulations to model the DM halo of UGC 5288 with both a cuspy Hernquist profile and a flat-core pseudo-isothermal profile. We find that the best match with observations is a pseudo-isothermal halo model with a core radius of rc = 0.23 kpc and halo spin of λ = 0.08 at the virial radius. Although our findings are consistent with previous core radius estimates of the halo density profile of UGC 5288, as well as with the halo spin profiles of similar mass analogues of UGC 5288 in the high-resolution cosmological-magnetohydrodynamical simulation TNG50, there still remain some uncertainties as we are limited in our knowledge of the formation history of the galaxy. Additionally, we find that the inner halo spin (r < 10 kpc) in barred galaxies is different from the unbarred ones, and the halo spin shows weak correlations with bar properties.