Dissipative dark matter explains rotation curves

Dissipative dark matter, where dark matter particles interact with a massless (or very light) boson, is studied. Such dark matter can arise in simple hidden sector gauge models, including those featuring an unbroken $U(1{)}^{\prime }$ gauge symmetry, leading to a dark photon. Previous work has shown that such models can not only explain the large scale structure and cosmic microwave background, but potentially also dark matter phenomena on small scales, such as the inferred cored structure of dark matter halos. In this picture, dark matter halos of disk galaxies not only cool via dissipative interactions but are also heated via ordinary supernovae (facilitated by an assumed photon–dark photon kinetic mixing interaction). This interaction between the dark matter halo and ordinary baryons, a very special feature of these types of models, plays a critical role in governing the physical properties of the dark matter halo. Here, we further study the implications of this type of dissipative dark matter for disk galaxies. Building on earlier work, we develop a simple formalism which aims to describe the effects of dissipative dark matter in a fairly model independent way. This formalism is then applied to generic disk galaxies. We also consider specific examples, including NGC 1560 and a sample of dwarf galaxies from the LITTLE THINGS survey. We find that dissipative dark matter, as developed here, does a fairly good job accounting for the rotation curves of the galaxies considered. Not only does dissipative dark matter explain the linear rise of the rotational velocity of dwarf galaxies at small radii, but it can also explain the observed wiggles in rotation curves which are known to be correlated with corresponding features in the disk gas distribution.

Figure 1

Dark matter density, $\rho (r,\theta )$ derived from dissipative dynamics [Eqs. (8) and (13)] for various $\theta$ values. Curves from bottom to top are for: $\theta =0$ (direction normal to the disk), $\theta =\pi /6$, $\theta =\pi /4$, $\theta =\pi /3$ and $\theta =2\pi /5$. The reference values $m_D={10}^{11}{m}_{\odot }$, $r_D=4.3\mathrm{kpc}$ are assumed.

Figure 2

Generic rotation curves predicted from this dynamics, Eqs. (8), (9), and (13). The four curves are for parameters: (a) $m_D={10}^8{m}_{\odot }$, $r_D=1.0\mathrm{kpc}$, (b) $m_D={10}^9{m}_{\odot }$, $r_D=1.4\mathrm{kpc}$, (c) $m_D={10}^{10}{m}_{\odot }$, $r_D=2.1\mathrm{kpc}$, and (d) $m_D={10}^{11}{m}_{\odot }$, $r_D=4.3\mathrm{kpc}$. The curves represent only the dark matter contribution to the rotational velocity.

Figure 3

(Top) Predicted rotation curve (dark matter only contribution) for two galaxies with the same baryonic mass $m_D={10}^{10}{m}_{\odot }$ but with two different disk scale lengths: (a) $r_D=2\mathrm{kpc}$ and (b) $r_D=7\mathrm{kpc}$. (Bottom) The same two curves plotted in terms of the dimensionless variable $r/r_D$. The curves coincide as $r_D$ is the only length scale in the problem.

Figure 4

Comparison between the rotation curves from dissipative dynamics for the examples in Fig. 2 (sold lines) with that using the quasi-isothermal profile [Eq. (14)] (dashed lines).

Figure 5

(Top) Baryonic gas density as found in [54]. The blue circles (black squares) represent an average over the northern (southern) half of the galaxy. (Bottom) Predicted rotation curve for NGC 1560 (solid line). Also shown are the separate contributions from the assumed dissipative dynamics, Eq. (17) (dash-dotted line), the baryonic stellar (dashed line) and baryonic gas contributions (dotted line). The data is from [54].

Figure 6

Predicted rotation curve for DDO87 (solid line). Also shown are the separate contributions from the assumed dissipative dynamics, Eq. (17) (dash-dotted line), the baryonic stellar (dashed line) and baryonic gas contributions (dotted line). The data is from [52].

Figure 7

Predicted rotation curve for DDO126 (solid line). Notation as in Fig. 6, data from [52].

Figure 8

Predicted rotation curve for DDO133 (solid line). Notation as in Fig. 6, data from [52].

Figure 9

Predicted rotation curve for DDO52 (solid line). Notation as in Fig. 6, data from [52].

Figure 10

Predicted rotation curve for DDO47 (solid line). Notation as in Fig. 6, data from [52].

Figure 11

Predicted rotation curve for DDO70 (solid line). Notation as in Fig. 6, data from [52].

Figure 12

Predicted rotation curve for NGC 3738 (solid line). Notation as in Fig. 6, data from [52].

Figure 13

Predicted rotation curve for NGC 2366 (solid line). Notation as in Fig. 6, data from [52].

Figure 14

Predicted rotation curve for DDO154 (solid line). Notation as in Fig. 6, data from [52].

Figure 15

Predicted rotation curve ($\text{dark}\text{matter}+\text{baryons}$) for DDO154, with Kennicutt-Schmidt exponent, $N$, varying. Curves from (left) bottom to top are for $N=1.0$, $N=1.5$, $N=2.0$, $N=2.5$, $N=3.0$.