Fanaroff-Riley I galaxies as the parent population of BL Lacertae objects. II - Optical constraints

Journal Article · Fri Feb 01 04:00:00 EST 1991 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/169701· OSTI ID:5867924

Padovani, P; Urry, C M ^[1]

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1. Space Telescope Science Institute, Baltimore, MD (USA)

The hypothesis is investigated that BL Lacertae objects are a subset of Fanaroff-Riley (FR) I galaxies dominated by beamed emission from a relativistic jet aligned with the line of sight. It is found that FR I galaxies, although of low radio luminosity, are bright optical galaxies. If the beaming hypothesis is correct, the optical luminosity function of BL Lac objects, including the effect of the host galaxy, can be approximated by a double power law with a given differential index. New estimates of the number counts of BL Lac objects are made which constrain their local number density for L(B) greater than about 6 x 10 to the 43rd ergs/s to be in the range 110-720/cu Gpc. The corresponding ratio between the total number densities of BL Lac objects and FR I galaxies is 0.003 to 0.02. This limits the Lorentz factor of the optical emission to the range 8-20, larger than that of the X-ray emitting plasma and roughly of the same order as the radio Lorentz factor. 34 refs.

• OSTI ID: 5867924
• Journal Information: Astrophysical Journal; (USA), Journal Name: Astrophysical Journal; (USA) Vol. 368; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BL LACERTAE OBJECTS
CATALOGS
COSMIC RADIO SOURCES
DOCUMENT TYPES
ELECTROMAGNETIC RADIATION
GALAXIES
GALAXY NUCLEI
IONIZING RADIATIONS
LUMINOSITY
MATHEMATICAL MODELS
MORPHOLOGY
OPTICAL PROPERTIES
ORIGIN
PHYSICAL PROPERTIES
RADIATIONS
RADIO GALAXIES
VISIBLE RADIATION
X RADIATION