Abstract
We compare proposed solutions to the core vs cusp issue of spiral galaxies, which has also been framed as a diversity problem, and demonstrate that the cuspiness of dark matter halos is correlated with the stellar surface brightness. We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM) . The SIDM model predicts a strong correlation between the core size and the stellar surface density, and it provides the best global fit to the data. The CDM simulations without strong baryonic feedback effects fail to explain the large dark matter cores seen in low surface brightness galaxies. On the other hand, with strong feedback, CDM simulations do not produce galaxy analogs with high stellar and dark matter densities, and therefore they have trouble in explaining the rotation curves of high surface brightness galaxies. This implies that current feedback implementations need to be modified. We also explicitly show how the concentration-mass and stellar-to-halo mass relations together lead to a radial acceleration relation (RAR) in an averaged sense, and reiterate the point that the RAR does not capture the diversity of galaxy rotation curves in the inner regions. These results make a strong case for SIDM as the explanation for the cores and cusps of field galaxies.
Highlights
The cold dark matter (CDM) model is extremely successful in explaining the matter distribution of the Universe on large scales [1] and many important aspects of galaxy formation [2, 3]
We compare the rotation curve fits to the SPARC sample from a self-interacting dark matter (SIDM) model, which self-consistently includes the impact of baryons on the halo profile, and hydrodynamical N-body simulations with cold dark matter (CDM)
We have compared SIDM and CDM explanations to the core vs cusp problem based on fits to the rotation curves of the SPARC samples, obtained from the literature
Summary
The cold dark matter (CDM) model is extremely successful in explaining the matter distribution of the Universe on large scales [1] and many important aspects of galaxy formation [2, 3]. We further propose an one-parameter SIDM model that has only one variable, i.e., the mass-to-light ratio, in fitting the data, as in the case of the RAR We use it to highlight the importance of diverse dark matter distributions in explaining stellar kinematics of spiral galaxies. The overall fits of the galaxy sample are not sensitive to a specific value of the cross section as long as σ/m ∼ O(1) cm2/g [37], so it is hard to use the rotation curve data to pin down σ/m For this range of the cross section, the SIDM model predicts both cored and cuspy profiles, depending on baryon concentration.
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