Evidence of cross-correlation between the CMB lensing and the gamma-ray sky

TL;DR

This study provides the first evidence of a cross-correlation between the CMB lensing potential and the unresolved gamma-ray sky, supporting the extragalactic origin of the isotropic gamma-ray background and aligning with models of AGN and star-forming galaxies.

Contribution

It reports the first measurement of the cross-correlation between CMB lensing and gamma-ray sky maps, confirming the extragalactic origin of the gamma-ray background with statistical significance.

Findings

3.0σ statistical evidence of cross-correlation

Correlation consistent with models of AGN and star-forming galaxies

Supports the extragalactic origin of the isotropic gamma-ray background

Abstract

We report the measurement of the angular power spectrum of cross-correlation between the unresolved component of the Fermi-LAT gamma-ray sky-maps and the CMB lensing potential map reconstructed by the Planck satellite. The matter distribution in the Universe determines the bending of light coming from the last scattering surface. At the same time, the matter density drives the growth history of astrophysical objects, including their capability at generating non-thermal phenomena, which in turn give rise to gamma-ray emissions. The Planck lensing map provides information on the integrated distribution of matter, while the integrated history of gamma-ray emitters is imprinted in the Fermi-LAT sky maps. We report here the first evidence of their correlation. We find that the multipole dependence of the cross-correlation measurement is in agreement with current models of the gamma-ray luminosity function for AGN and star forming galaxies, with a statistical evidence of 3.0$\sigma$. Moreover, its amplitude can in general be matched only assuming that these extra-galactic emitters are also the bulk contribution of the measured isotopic gamma-ray background (IGRB) intensity. This leaves little room for a big contribution from galactic sources to the IGRB measured by Fermi-LAT, pointing toward a direct evidence of the extragalactic origin of the IGRB.