We investigate the nature of the extragalactic unresolved Î³-ray background (UGRB) by cross-correlating several galaxy catalogs with sky maps of the UGRB built from 78 months of Pass 8 Fermi-Large Area Telescope data. This study updates and improves similar previous analyses in several aspects. First, the use of a larger Î³-ray data set allows us to investigate the energy dependence of the cross-correlation in more detail, using up to eight energy bins over a wide energy range of [0.25,500] GeV. Second, we consider larger and deeper catalogs (2MASS Photometric Redshift catalog, 2MPZ; WISE Ã SuperCOSMOS, WIÃSC; and SDSS DR12 photometric redshift data set) in addition to the ones employed in the previous studies (NVSS and SDSS QSOs). Third, we exploit the redshift information available for the above catalogs to divide them into redshift bins and perform the cross-correlation separately in each of them. Our results confirm, with higher statistical significance, the detection of cross-correlation signals between the UGRB maps and all the catalogs considered, on angular scales smaller than 1Â°. Significances range from 16.3Ï for NVSS 7Ï, for SDSS DR12 and WIÃSC, to 5Ï for 2MPZ and for 4Ï SDSS QSOs. Furthermore, including redshift tomography, the significance of the SDSS DR12 signal strikingly rises up to â¼12Ï and that of WIÃSC to â¼10.6Ï. We offer a simple interpretation of the signal in the framework of the halo model. The precise redshift and energy information allows us to clearly detect a change over redshift in the spectral and clustering behavior of the Î³-ray sources contributing to the UGRB.
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|Titolo:||Tomographic Imaging of the Fermi-LAT Î³-Ray Sky through Cross-correlations: A Wider and Deeper Look|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||01.01 - Articolo su rivista|