Dr Harry Desmond

Abstract:

We present a new empirical relation between galaxy dark matter halo mass (Mhalo) and the velocity along the flat portion of the rotation curve (Vflat), derived from 120 late-type galaxies from the SPARC data base. The orthogonal scatter in this relation is comparable to the observed scatter in the baryonic Tully–Fisher relation (BTFR), indicating a tight coupling between total halo mass and galaxy kinematics at r ≪ Rvir. The small vertical scatter in the relation makes it an extremely competitive estimator of total halo mass. We demonstrate that this conclusion holds true for different priors on M*/L[3.6μ] that give a tight BTFR, but requires that the halo density profile follow DC14 rather than NFW. We provide additional relations between Mhalo and other velocity definitions at smaller galactic radii (i.e. V2.2, Veff, and Vmax) which can be useful for estimating halo masses from kinematic surveys, providing an alternative to abundance matching. Furthermore, we constrain the dark matter analogue of the radial acceleration relation and also find its scatter to be small, demonstrating the fine balance between baryons and dark matter in their contribution to galaxy kinematics.

Abstract:

In a ΛCDM cosmology, galaxy formation is a globally inefficient process: it is often the case that far fewer baryons are observed in galaxy discs than expected from the cosmic baryon fraction. The location of these ‘missing baryons’ is unclear. By fitting halo profiles to the rotation curves of galaxies in the SPARC data set, we measure the ‘missing baryon’ mass for individual late-type systems. Assuming that haloes initially accrete the cosmological baryon fraction, we show that the maximum energy available from supernovae is typically not enough to completely eject these ‘missing baryons’ from a halo, but it is often sufficient to heat them to the virial temperature. The energy available from supernovae has the same scaling with galaxy mass as the energy needed to heat or eject the ‘missing baryons’, indicating that the coupling efficiency of the feedback to the ISM may be constant with galaxy virial mass. We further find that the energy available from supernova feedback is always enough to convert a primordial cusp into a core and has magnitude consistent with what is required to heat the ‘missing baryons’ to the virial temperature. Taking a census of the baryon content of galaxies with 109 < Mvir/M⊙ < 1012 reveals that ∼86 per cent of baryons are likely to be in a hot phase surrounding the galaxies and possibly observable in the X-ray, ∼7 per cent are in the form of cold gas, and ∼7 per cent are in stars.

Abstract:

In recentwork, Lelli et al. argue that the tightness of the baryonic Tully–Fisher relation (BTFR) of the SPARC galaxy sample, and the weakness of the correlation of its residuals with effective radius, pose challenges to Λ cold dark matter cosmology. In this Letter, we calculate the statistical significance of these results in the framework of halo abundance matching, which imposes a canonical galaxy–halo connection. Taking full account of sample variance among SPARC-like realizations of the parent halo population, we find the scatter in the predicted BTFR to be 3.6σ too high, but the correlation of its residuals with galaxy size to be naturally weak. Further, we find abundance matching to generate BTFR curvature in 3.0σ disagreement with the data, and a fraction of galaxies with non-flat rotation curves somewhat larger than observed.