Analyzing the Gamma-ray Sky with Wavelets

Abstract

We analyze the gamma-ray sky at energies of 0.5 to 50 GeV using the undecimated wavelet transform on the sphere. Focusing on the inner $60^{\circ }\times 60^{\circ }$ of the sky, we identify and characterize four separate residuals beyond the expected Milky Way diffuse emission. We detect the \textit{Fermi} Bubbles, finding compelling evidence that they are diffuse in nature and contain very little small-scale structure. We detect the "cocoon" inside the Southern Bubble, and we also identify its northern counterpart above 2 GeV. The Northern Cocoon lies along the same axis but is $\sim 30\%$ dimmer than the southern one. We characterize the Galactic center excess, which we find extends up to $20^{\circ }$ in $|b|$. At latitudes $|b|\le 5^{\circ }$ we find evidence for power in small angular scales that could be the result of point-source contributions, but for $|b|\ge 5^{\circ }$ the Galactic center excess is dominantly diffuse in its nature. Our findings show that either the Galactic center excess and {\it Fermi} Bubbles connect smoothly or that the Bubbles brighten significantly below $15^{\circ }$ in latitude. We find that the Galactic center excess appears off-center by a few degrees towards negative $\ell$. Additionally, we find and characterize two emissions along the Galactic disk centered at $\ell \simeq +25^{\circ }$ and $-20^{\circ }$. These emissions are significantly more elongated along the Galactic disk than the Galactic center excess.

arXiv comment23 pages, 25 figures, 4 tables, 3 appendices

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