TOMOGRAPHY OF THE FERMI-LAT γ-RAY DIFFUSE EXTRAGALACTIC SIGNAL VIA CROSS CORRELATIONS WITH GALAXY CATALOGS

Journal Article · Tue Mar 24 00:00:00 EDT 2015 · The Astrophysical Journal. Supplement Series (Online)

DOI:https://doi.org/10.1088/0067-0049/217/1/15· OSTI ID:1355175

Xia, Jun-Qing  ^[1]; Cuoco, Alessandro ^[2]; Branchini, Enzo  ^[3]; Viel, Matteo ^[4]

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1. Chinese Academy of Sciences, Beijing (China). Key Laboratory of Particle Astrophysics, Institute of High Energy Physics; Collaborative Innovation Center of Modern Astronomy and Space Exploration (China)
2. Univ. of Torino (Italy). Department of Physics; Istituto Nazionale di Fisica Nucleare, Torino (Italy); Stockholm Univ. (Sweden). AlbaNova University Center
3. Roma Tre University (Italy). Department of Mathematics and Physics; INFN, Sezione di Roma Tre (Italy); INAF, Osservatorio Astronomico di Roma (Italy)
4. INAF Osservatorio Astronomico di Trieste (Italy); INFN, Sezione di Trieste (Italy)

Building on our previous cross-correlation analysis (Xia et al. 2011) between the isotropic γ-ray background (IGRB) and different tracers of the large-scale structure of the universe, we update our results using 60 months of data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope (Fermi). For this study, we perform a cross-correlation analysis both in configuration and spherical harmonics space between the IGRB and objects that may trace the astrophysical sources of the IGRB: QSOs in the Sloan Digital Sky Survey (SDSS) DR6, the SDSS DR8 Main Galaxy Sample, luminous red galaxies (LRGs) in the SDSS catalog, infrared-selected galaxies in the Two Micron All Sky Survey (2MASS), and radio galaxies in the NRAO VLA Sky Survey (NVSS). The benefit of correlating the Fermi-LAT signal with catalogs of objects at various redshifts is to provide tomographic information on the IGRB, which is crucial in separating the various contributions and clarifying its origin. The main result is that, unlike in our previous analysis, we now observe a significant (>3.5σ) cross-correlation signal on angular scales smaller than 1° in the NVSS, 2MASS, and QSO cases and, at lower statistical significance (~3.0σ), with SDSS galaxies. The signal is stronger in two energy bands, E > 0.5 GeV and E > 1 GeV, but it is also seen at E > 10 GeV. No cross-correlation signal is detected between Fermi data and the LRGs. These results are robust against the choice of the statistical estimator, estimate of errors, map cleaning procedure, and instrumental effects. Finally, we test the hypothesis that the IGRB observed by Fermi-LAT originates from the summed contributions of three types of unresolved extragalactic sources: BL Lacertae objects (BL Lacs), flat spectrum radio quasars (FSRQs), and star-forming galaxies (SFGs). Finally, we find that a model in which the IGRB is mainly produced by SFGs ($$72_{-37}^{+23}$$% with 2σ errors), with BL Lacs and FSRQs giving a minor contribution, provides a good fit to the data. We also consider a possible contribution from misaligned active galactic nuclei, and we find that, depending on the details of the model and its uncertainty, they can also provide a substantial contribution, partly degenerate with the SFG one.

• Research Organization: SLAC National Accelerator Lab., Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC02-76SF00515
• OSTI ID: 1355175
• Journal Information: The Astrophysical Journal. Supplement Series (Online), Vol. 217, Issue 1; ISSN 1538-4365
• Publisher: American Astronomical Society/IOP
• Country of Publication: United States
• Language: English

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