Self-Interacting Dark Matter Can Explain Diverse Galactic Rotation Curves

Abstract

The rotation curves of spiral galaxies exhibit a diversity that has been difficult to understand in the cold dark matter (CDM) paradigm. We show that the self-interacting dark matter (SIDM) model provides excellent fits to the rotation curves of a sample of galaxies with asymptotic velocities in the 25 to 300 km/s range that exemplify the full range of diversity. We only assume the halo concentration-mass relation predicted by the CDM model and a fixed value of the self-interaction cross section. In dark matter dominated galaxies, thermalization due to self-interactions creates large cores and reduces dark matter densities. In contrast, thermalization leads to denser and smaller cores in more luminous galaxies, and naturally explains the flat rotation curves of the highly luminous galaxies. Our results demonstrate that the impact of the baryons on the SIDM halo profile and the scatter from the assembly history of halos as encoded in the concentration-mass relation can explain the diverse rotation curves of spiral galaxies.I. Introduction. The ΛCDM model, with a cosmological constant (Λ) and cold dark matter (CDM), explains the observed large-scale structure of the Universe [1] and many aspects of galaxy formation [2,3], but the diverse observed rotation curves do not have a satisfactory explanation. Observations of a number of dwarf and low surface brightness galaxies indicate that the inner halo is often badly fit by the cusped halos predicted by ΛCDM simulations [4][5][6][7][8][9][10][11][12][13]. The core densities exhibit almost an order of magnitude spread for similar total halo masses [14], and galaxies with densities at the upper end of the range are consistent with ΛCDM [15]. There is no clear explanation for the diversity in the inner rotation velocity profiles of different galaxies within similar mass halos [15].In this Letter, we demonstrate how this diversity problem [15] can be solved in the self-interacting dark matter (SIDM) framework [16], where dark matter particles exchange energy by colliding with one another in halos. Dark matter self-interactions only change the inner halo properties in accord with observations, leaving all the successes of CDM intact on large scales, e.g., [17][18][19][20]. While the original SIDM model [16] posited a cross section that is independent of velocity, constraints from galaxy clusters demand an interaction cross section that diminishes with increasing velocity [19,[21][22][23][24]. SIDM models based on a Yukawa potential [25][26][27][28][29][30][31][32] or atomic scattering [33] can naturally accommodate the required velocity dependence. Concrete particle physics realizations of such models can provide a universal solution to small-scale issues from dwarf galaxies to galaxy clusters [23,34].The diversity in the observed rotation curves is solved by a combination of interconnected features in the ΛSIDM model. In the outer parts of galaxies, the ΛSIDM model is the same as the ΛCDM model, inheriting all its successes. In the inner regions, the SIDM density profile ...

Constraining Dark Matter-Dark Radiation interactions with CMB, BAO, and Lyman-α

“…The inclusion of baryonic feedback is crucial for providing a realistic picture of the aforementioned problems and it shows that baryons can indeed partially solve the CDM crisis [7][8][9]. However, in the absence of a compelling solution within the ΛCDM model, alternative scenarios of self-interacting dark matter [10,11] emerged as a possible way to explain the small scale observations [12][13][14][15][16][17][18][19][20][21][22], although the non-trivial interplay between self-interacting dark matter and baryons has to be considered [23].…”

Dark Matter 2017

“…A similar situation is found in the study of the rotation curves of spiral galaxies [11] that shows a substantial flattening for distances ∼ 10 kpc from the center. The pure Newtonian dynamics of the rotation of the luminous matter indicates that gravity field is produced by a sphere of uniform density, and not by a self gravitating ensemble of non-collision particles [12]. A possible explanation of this fact could be the existence of a large mass of dark baryon in the inner part of the spiral galaxies [13], but alternatively it could be also the indication of self-interaction of the DM particles [14].…”

Velocity-dependent self-interacting dark matter from thermal freeze-out and tests in direct detections

“…[28][29][30][31] for more). These small-scale problems may indicate some characters about the main component of DM, and possible strong self-interactions between DM particles could provide a solution to the core-cusp and too-big-to-fail problems [31][32][33][34][35][36][37][38][39]. 1 In this paper, the main component of DM is considered to be self-interacting dark matter (SIDM).…”