Galaxies and gamma-ray astronomy

Journal Article · Sat Sep 15 04:00:00 EDT 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157323· OSTI ID:5637071

Bignami, G F; Fichtel, C E; Hartman, R C; Thompson, D J

Comparisons between the recently measured X-ray spectra of active galaxies, the intensity upper limits to the ..gamma..-ray emission above 35 MeV from the same objects obtained from data from SAS 2, and other ..gamma..-ray data are used to address the nature of the high-energy spectra of several types of active galaxies, their contribution to the measured diffuse ..gamma..-ray emission between 1 and 150 MeV, and constraints which may be placed on cosmological evolutionary factors. It is found that a substantial increase in slope of the photon energy spectrum must occur in the low-energy ..gamma..-ray region for Seyfert galaxies, BL Lac objects, and emission line galaxies. A spectral steepening is also seen for 3C 273 and Cen A, the only quasar and radio galaxy for which accurate X-ray spectra are presently available above 20 keV. A cosmological integration shows that Seyfert galaxies, BL Lac objects, and quasars may account for most of the 1--150 MeV diffuse background, even without significant evolution. Sharp emission line galaxies and radio galaxies made a much smaller contribution under the same assumptions. The observed isotropic ..gamma..-radiation limits the ..gamma..-ray evolution possible for Seyfert galaxies, BL Lac objects, and quasars. The high-latitude galactic radiation limits the ..gamma..-ray evolution of normal field galaxies. The integrated emission of normal field galaxies with evolution back to z=4 cannot exceed about 10 times the integrated emission assuming no evolution.

• Research Organization: NASA Goddard Space Flight Center
• OSTI ID: 5637071
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 232:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ASTRONOMY
COSMIC RADIO SOURCES
COSMOLOGY
ELECTROMAGNETIC RADIATION
GALAXIES
GAMMA ASTRONOMY
GAMMA RADIATION
IONIZING RADIATIONS
QUASARS
RADIATIONS
RADIO GALAXIES
SEYFERT GALAXIES
SPECTRA
X RADIATION
X-RAY SPECTRA