A cross-correlation study of the Fermi-LAT $\gamma$-ray diffuse extragalactic signal

Understand

In this work, starting from 21 months of data from the Fermi-Large Area Telescope, we derive maps of the residual isotropic gamma-ray emission, a relevant fraction of which is expected to be contributed by the extragalactic diffuse gamma-ray background.

• We compute the angular two-point auto-correlation function of the residual Fermi-LAT maps at energies E>1GeV, E>3GeV and E>30GeV well above the Galactic plane and find no significant correlation signal.
• This is, indeed, what is expected if the EGB were contributed by BL Lacertae, Flat Spectrum Radio Quasars or star-forming galaxies, since, in this case, the predicted signal is very weak.
• Then, we search for the Integrated Sachs-Wolfe signature by cross-correlating the Fermi-LAT maps with the WMAP7-Cosmic Microwave Background map.