Dark matter implications of the WMAP-Planck Haze

Abstract

Gamma rays and microwave observations of the Galactic Center and surrounding areas indicate the presence of anomalous emission, whose origin remains ambiguous. The possibility of dark matter annihilation explaining both signals through prompt emission at gamma rays and secondary emission at microwave frequencies from interactions of highenergy electrons produced in annihilation with the Galactic magnetic fields has attracted much interest in recent years. We investigate the dark matter interpretation of the Galactic Center gamma-ray excess by searching for the associated synchrotron emission in the WMAP and Planck microwave data. Considering various magnetic field and cosmic-ray propagation models, we predict the synchrotron emission due to dark matter annihilation in our Galaxy, and compare it with the WMAP and Planck data at 23-70 GHz. In addition to standard microwave foregrounds, we separately model the microwave counterpart to the Fermi Bubbles and the signal due to dark matter annihilation, and use component separation techniques to extract the signal associated with each template from the total emission. We confirm the presence of the Haze at the level of ≈7% of the total sky intensity at 23 GHz in our chosen region of interest, with a harder spectrum (I ∼ ν −0.8 ) than the synchrotron from regular cosmic-ray electrons. The data do not show a strong preference towards fitting the Haze by either the Bubbles or dark matter emission only. Inclusion of both components provides a better fit with a dark matter contribution to the Haze emission of ≈20% at 23 GHz, however, due to significant uncertainties in foreground modeling, we do not consider this a clear detection of a dark matter signal. We set robust upper limits on the annihilation cross section by ignoring foregrounds, and also report best-fit dark matter annihilation parameters obtained from a complete template analysis. We conclude that the WMAP and Planck data are consistent with a dark matter interpretation of the gamma-ray excess.

WIMP dark matter candidates and searches—current status and future prospects

“…The hard edge-like structures observed for Fermi bubbles disfavor its DM-induced origin. However, it is still possible that some part of the WMAP/Planck haze are not due to the Fermi bubbles and can be better fitted with DM annihilations associated with subsequent microwave synchrotron emission (see, e.g., [346]).…”

A review of indirect searches for particle dark matter

“…Secondary emission plays an important role in the interpretation of excess emission in this energy range due to the many processes that can contribute. Bounds on a dark matter origin have been derived using multi-wavelength observations [137,138] and cosmic-ray data [137,139].…”

“…With the improved data set, morphological features in the Planck Haze have been detected which strongly point to a common origin with the Fermi Bubbles, in particular a sharp edge in the microwave Haze aligned with the edge observed in the Fermi Bubbles. However, it is still possible that some fraction of the Haze does have a dark matter origin, which could be the microwave counterpart of the GeV excess in the Inner Galaxy [138]. 6.3.…”

Light weakly interacting massive particles

“…[104] and [105] and references therein). In any event, a component of synchrotron radiation from e − and e + produced in DM annihilation (accelerated in magnetic fields) could contribute to the "Haze" and present upper limits on this component do not contradict the DM parameter regions needed to fit the GC γ-ray excess [101].…”