Exploring the dark matter disk model in dwarf galaxies : Insights from the LITTLE THINGS sample

Abstract

We conducted an analysis of the velocity field of dwarf galaxies in the sample collected by the Local Irregulars That Trace Luminosity Extremes and The H I Nearby Galaxy Survey (LITTLE THINGS) and focused on deriving 2D velocity maps that encompass the transverse and radial velocity fields. Within the range of radial distances in which velocity anisotropies are sufficiently small for the disk to be considered supported by rotation and where the warped geometry of the disk can be neglected, we reconstructed the rotation curve while taking the effect of the asymmetric drift into account. To fit the rotation curves, we employed the standard halo model and the dark matter disk (DMD) model, which assumes that dark matter is primarily confined to the galactic disks and can be traced by the distribution of H I. Interestingly, our analysis revealed that the fits from the DMD model are statistically comparable to those obtained using the standard halo model, but the inferred masses of the galaxies in the DMD model are approximately 10 to 100 times lower than the masses inferred in the standard halo model. In the DMD model, the inner slope of the rotation curve is directly related to a linear combination of the surface density profiles of the stellar and gas components, which generally exhibit a flat core. Consequently, the observation of a linear relation between the rotation curve and the radius in the central disk regions is consistent with the framework of the DMD model.