[Paper Review] Dissipative dark matter explains rotation curves

R. Foot|arXiv (Cornell University)|Feb 27, 2015

Dark Matter and Cosmic Phenomena18 references3 citations

TL;DR

This paper proposes that dissipative dark matter—where dark matter particles interact via a massless dark photon—can explain galactic rotation curves by balancing cooling from dark bremsstrahlung with heating from supernovae via kinetic mixing with ordinary photons. The model predicts cored dark matter profiles and successfully reproduces observed rotation curves, including subtle wiggles correlated with gas distributions in dwarf galaxies.

ABSTRACT

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 $U(1)'$ gauge symmetry, leading to a dark photon. Previous work has shown that such models can not only explain the LSS and CMB, 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.

Motivation & Objective

• To explain the discrepancy between cuspy dark matter profiles in cold dark matter simulations and the cored profiles inferred from galactic rotation curves.
• To investigate whether dissipative dark matter, with self-interactions via a massless dark photon, can naturally produce cored halos in disk galaxies.
• To test if supernova-driven heating via photon-dark photon kinetic mixing can balance halo cooling, leading to steady-state, observable rotation curves.
• To develop a model-independent formalism for dissipative dark matter dynamics applicable to generic disk galaxies.
• To compare predictions with observed rotation curves of specific galaxies, including NGC 1560 and dwarfs from the LITTLE THINGS survey.

Proposed method

• Model the dark matter halo as a fluid governed by Euler’s equations, with cooling via dark bremsstrahlung proportional to the square of the dark matter number density.
• Include heating from supernovae via kinetic mixing, where ordinary supernovae produce dark photons that deposit energy into the halo.
• Derive a steady-state condition balancing cooling and heating rates, leading to a simple relation: n(r) ∝ F_γD(r)σ_DP / Λ.
• Assume a Freeman disk profile for supernova distribution and apply a Kennicutt-Schmidt-type power law for star formation to model baryonic sources.
• Use the derived dark matter density profile to compute rotation curves and compare with observational data from NGC 1560 and LITTLE THINGS dwarf galaxies.
• Incorporate spatially varying gas and stellar distributions to test whether wiggles in rotation curves correlate with features in the baryonic disk.

Experimental results

Research questions

• RQ1 Can a dissipative dark matter model with self-interactions via a massless dark photon reproduce the observed cored dark matter profiles in disk galaxies?
• RQ2 Does supernova-driven heating via photon-dark photon kinetic mixing provide a sufficient and physically plausible energy source to balance halo cooling and stabilize the halo?
• RQ3 Can the model explain the observed linear rise in rotation velocity at small radii in dwarf galaxies?
• RQ4 Do the predicted rotation curves reproduce subtle wiggles that correlate with features in the baryonic gas distribution?
• RQ5 Is the model-independent formalism based on heating-cooling balance sufficient to predict rotation curves across diverse galaxies with minimal free parameters?

Key findings

• The model successfully reproduces the observed rotation curves of NGC 1560 and multiple dwarf galaxies from the LITTLE THINGS survey, including their overall shape and cored profiles.
• The predicted rotation curves show a linear rise at small radii, consistent with observations of low-surface-brightness dwarf galaxies.
• Subtle wiggles in the rotation curves are correlated with corresponding features in the baryonic gas distribution, suggesting a physical origin in localized heating from supernovae.
• The steady-state assumption—balancing cooling via dark bremsstrahlung and heating via dark photon flux—leads to a simple relation between dark matter density and local energy flux.
• The model’s predictions are robust across different assumptions for the star formation law, including varying Kennicutt-Schmidt exponents from N=1.0 to N=3.0.
• The framework demonstrates that a single effective parameter can encapsulate model dependence (e.g., kinetic mixing, cross-sections), enabling predictive power across diverse galaxies.