Morphology of the Galactic dark matter synchrotron emission with self-consistent cosmic-ray diffusion models

Abstract

A generic prediction in the paradigm of weakly interacting dark matter is the production of relativistic particles from dark matter pair-annihilation in regions of high dark matter density. Ultrarelativistic electrons and positrons produced in the center of the Galaxy by dark matter annihilation should produce a diffuse synchrotron emission. While the spectral shape of the synchrotron dark matter haze depends on the particle model (and secondarily on the galactic magnetic fields), the morphology of the haze depends primarily on (1) the dark matter density distribution, (2) the galactic magnetic field morphology, and (3) the diffusion model for high-energy cosmic-ray leptons.Interestingly, an unidentified excess of microwave radiation with characteristics similar to those predicted by dark matter models has been claimed to exist near the galactic center region in the data reported by the WMAP satellite, and dubbed the "WMAP haze". In this study, we carry out a self-consistent treatment of the variables enumerated above, enforcing constraints from the available data on cosmic rays, radio surveys and diffuse gamma rays. We outline and make predictions for the general morphology and spectral features of a "dark matter haze" and we compare them to the WMAP haze data. We also characterize and study the spectrum and spatial distribution of the inverse Compton emission resulting from the same population of energetic electrons and positrons.We point out that the spectrum and morphology of the radio emission at different frequencies is a powerful diagnostics to test whether a galactic synchrotron haze indeed originates from dark matter annihilation. *

Cosmic ray feedback in the FIRE simulations: constraining cosmic ray propagation with GeV γ-ray emission

“…For example, Trotta et al (2011) constrained the isotropically-averaged diffusivity κ to be ∼ 6 × 10 28 cm 2 /s to within a factor of a few, at ∼GeV energy with GALPROP, using the measured energy spectra and abundances of nuclei species in CRs, and adopting a flat halo diffusion model (Ginzburg & Ptuskin 1976; see Introduction for a brief description). Implicitly, these abundances depend on the residence time of CRs in the Galaxy, so there is a degeneracy between κ and the CR halo height z h (typically 1-10 kpc), out of which CRs can freely propagate (see Figure 3 in Trotta et al 2011 or Figure 10 in Linden et al 2010; this issue was also discussed in Ginzburg & Ptuskin 1976). Even in this model, it is possible to match the observational data with a significantly larger κ (up to factors of several) if a larger halo size is adopted.…”

“…12 For example,Fig. 10inLinden et al (2010) shows isotropically-averaged κ ∼ 3 × 10 28 cm 2 /s with z h ∼ 3 kpc but κ ∼ 10 29 cm 2 /s with a larger z h ∼ 5 kpc).…”

Heavy dark matter particle annihilation in dwarf spheroidal galaxies: Radio signals at the SKA telescope

“…The spectrum as well as the dynamics of the particle physics scenario, along with the DM profile in a dSph, is responsible for DM annihilation as well as the subsequent cascades leading to electron-positron pairs. The electron(positron) energy distribution at the initial level is also the determined by the above factors [39][40][41]. However, they subsequently pass through the interstellar medium (ISM) of the galaxy, facing several additional effects.…”

Reconciling cosmic-ray transport theory with phenomenological models motivated by Milky-Way data

“…This degeneracy is lifted once 𝑧 𝐻 𝑟 ∼ 10kpc, i.e. of order the CR injection length scale in the disk (see, e.g., Figure 10 in Linden et al 2010). The physical reason is that for 𝑧 𝑟, CRs start propagating spherically away from the galaxy and have a smaller chance of making it back to the disk.…”