Spreading out and staying sharp – creating diverse rotation curves via baryonic and self-interaction effects

Abstract

Galactic rotation curves are a fundamental constraint for any cosmological model. We use controlled N-body simulations of galaxies to study the gravitational effect of baryons in a scenario with collisionless cold dark matter (CDM) versus one with a self-interacting dark matter (SIDM) component. In particular, we examine the inner profiles of the rotation curves in the velocity range V max = [30 − 250] km s −1 , whose diversity has been found to be greater than predicted by the ΛCDM scenario. We find that the scatter in the observed rotation curves exceeds that predicted by dark matter only mass-concentration relations in either the CDM nor SIDM models. Allowing for realistic baryonic content and spatial distributions, however, helps create a large variety of rotation curve shapes; which is in better agreement with observations in the case of self-interactions due to the characteristic cored profiles being more accommodating to the slowly rising rotation curves than CDM. We find individual fits to model two of the most remarkable outliers of similar V max , UGC 5721 and IC 2574, the former a cusp-like rotation curve and the latter a seemingly 8 kpc cored profile. This diversity in SIDM arises as permutations of overly concentrated halos with compact baryonic distributions versus underdense halos with extended baryonic disks. The SIDM solution is promising and its feasibility ultimately depends on the sampling of the halo mass-concentration relation and its interplay with the baryonic profiles, emphasising the need for a better understanding of the frequency of extreme outliers present in current observational samples.

Self-Interacting Dark Matter Subhalos in the Milky Way’s Tides

“…In principle, one should also include the selfscattering effect for the main halo. However, for a MW-like galaxy, where the baryons dominate the central regions, an SIDM halo profile can be similar to an NFW one, because SIDM thermalization with the baryonic potential increases the central dark matter density [10,19,21,23,43]. We have checked that the NFW halo we take here is a good approximation to the SIDM MW halo constructed in [23].…”

“…We explicitly show the mechanism and critical conditions leading to core collapse in the tidal field and study mass loss for both SIDM and CDM subhalos. We further demonstrate that Draco and Fornax, two extremes in the dark matter content among the bright MW dSphs, can be explained in the SIDM model with σ/m = 3 cm 2 /g, the value used to fit the diverse rotation curves of spiral galaxies in the field [9][10][11]. Simulation setup.…”

6-quark Dark Matter: viable + explains many observations

“…But cases like UGC7399 and other examples not shown such as UGC8490, where structure in the gas is not reflected in the rotation curves, invalidate that interpretation because in MOND there should be no exceptions to the correlation. The last panel shows an example from different authors [36] which manifests the same phenomenon, namely that the fit would be better if the DM contribution reflected the shape of the gas contribution.…”

“…[36]. Gas densities are shown as dashed lines [34] and green squares [36]. UGC7524 (left) and IC2574 (right) are examples of rotation curves with a distinctive non-smooth structure suggestive of a scaled-up version of the gas density distribution, while UGC7388 (center) has a smooth rotation curve in spite of the bumps in the gas density profile.…”

Unification of the standard model and dark matter sectors in [SU(5) × U(1)]4

“…[13] for a review of SIDM). For example, SIDM can explain the diversity of galactic rotation curves [14][15][16], while it is not easy for collisionless DM [17] (see, e.g., Ref. [18] for a review of the smallscale crisis).…”