2009/12/18 by A. A. Abdo, LAT collaboration, M. Ackermann +98 · 6 citations
Physics and Astronomy · #Astronomy #Astrophysics #Astrophysics and Cosmic Phenomena #Astrophysics and Star Formation Studies #Cosmic microwave background #Cosmic ray #Dark Matter and Cosmic Phenomena #Fermi Gamma-ray Space Telescope #Galactic Center #Galaxy #Interstellar medium #Molecular cloud #Physics #Stars #Telescope #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/710/1/133
published as Astrophys.J.710:133-149,2010 · 26 pages, 13 figures; accepted for publication by The Astrophysical Journal
arxiv created 2009/12/18 · openalex publication_date 2010/01/15 · arxiv updated 2014/11/20 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We present the analysis of the interstellar γ-ray emission measured by the Fermi Large Area Telescope toward a region in the second Galactic quadrant at 100° ⩽ l ⩽ 145° and −15° ⩽ b ⩽ +30°. This region encompasses the prominent Gould Belt clouds of Cassiopeia, Cepheus, and the Polaris flare, as well as atomic and molecular complexes at larger distances, like that associated with NGC 7538 in the Perseus arm. The good kinematic separation in velocity between the local, Perseus, and outer arms, and the presence of massive complexes in each of them, make this region well suited to probe cosmic rays (CRs) and the interstellar medium beyond the solar circle. The γ-ray emissivity spectrum of the gas in the Gould Belt is consistent with expectations based on the locally measured CR spectra. The γ-ray emissivity decreases from the Gould Belt to the Perseus arm, but the measured gradient is flatter than expectations for CR sources peaking in the inner Galaxy as suggested by pulsars. The X CO = N (H 2 )/ W CO conversion factor is found to increase from (0.87 ± 0.05) × 10 20 cm −2 (K km s −1 ) −1 in the Gould Belt to (1.9 ± 0.2) × 10 20 cm −2 (K km s −1 ) −1 in the Perseus arm. We derive masses for the molecular clouds under study. Dark gas, not properly traced by radio and microwave surveys, is detected in the Gould Belt through a correlated excess of dust and γ-ray emission: its mass amounts to ∼50% of the CO-traced mass.