FERMI OBSERVATIONS OF CASSIOPEIA AND CEPHEUS: DIFFUSE GAMMA-RAY EMISSION IN THE OUTER GALAXY

Abdo, A A; Ackermann, M; Ajello, M; Bechtol, K; Berenji, B; Bloom, E D; Borgland, A W; Baldini, L; Bellazzini, R; Bregeon, J; Brez, A; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bonamente, E; Brigida, M; Bruel, P; Burnett, T H; Buson, S

doi:10.1088/0004-637X/710/1/133

FERMI OBSERVATIONS OF CASSIOPEIA AND CEPHEUS: DIFFUSE GAMMA-RAY EMISSION IN THE OUTER GALAXY

Journal Article · Wed Feb 10 04:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/710/1/133· OSTI ID:21394523

Abdo, A A ^[1]; Ackermann, M; Ajello, M; Bechtol, K; Berenji, B; Bloom, E D; Borgland, A W ^[2]; Baldini, L; Bellazzini, R; Bregeon, J; Brez, A ^[3]; Ballet, J ^[4]; Barbiellini, G ^[5]; Bastieri, D ^[6]; Baughman, B M ^[7]; Bonamente, E ^[8]; Brigida, M ^[9]; Bruel, P ^[10]; Burnett, T H ^[11]; Buson, S ^[12]

Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette (France)
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States)
Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
Dipartimento di Fisica 'M. Merlin' dell'Universita e del Politecnico di Bari, I-70126 Bari (Italy)
Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS/IN2P3, Palaiseau (France)
Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States)
Dipartimento di Fisica 'G. Galilei', Universita di Padova, I-35131 Padova (Italy)

We present the analysis of the interstellar gamma-ray emission measured by the Fermi Large Area Telescope toward a region in the second Galactic quadrant at 100{sup 0} <= l <= 145{sup 0} and -15{sup 0} <= b <= +30{sup 0}. 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 gamma-ray emissivity spectrum of the gas in the Gould Belt is consistent with expectations based on the locally measured CR spectra. The gamma-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{sub CO} = N(H{sub 2})/W{sub CO} conversion factor is found to increase from (0.87 +- 0.05) x 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -1} in the Gould Belt to (1.9 +- 0.2) x 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -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 gamma-ray emission: its mass amounts to {approx}50% of the CO-traced mass.

OSTI ID:: 21394523

Journal Information:: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 710; ISSN ASJOAB; ISSN 0004-637X

Country of Publication:: United States

Language:: English

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FERMI OBSERVATIONS OF CASSIOPEIA AND CEPHEUS: DIFFUSE GAMMA-RAY EMISSION IN THE OUTER GALAXY

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