A comprehensive radio study of the Z = 0.524 absorption system in AO 0235 + 164

Abstract

view Abstract Citations (55) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A comprehensive radio study of the z = 0.524 absorption system in AO 0235+164. Wolfe, A. M. ; Broderick, J. J. ; Condon, J. J. ; Johnston, K. J. Abstract We present pencil-beam and VLB observations of the 932 MHz absorption line and continuum of the BL Lacertae object AO 0235+164, and pencil-beam observations of its 318 and 430 MHz continuum. We find that this redshifted (z = 0.524) 21 em line consists of many narrow components with r > 0.002 that are spread over a velocity range of 105 km i A comparison with the z = 0.524 optical absorption spectrum suggests that both types of lines arise in the same material rather than in two distinct regions as suggested by previous radio spectra. This leads to a determination of element abundances relative to hydrogen and a reevaluation of limits on the variation of certain physical constants over cosmic time scales. The VLB continuum fringe visibility implies a source angular diameter O < 0'.'006. The VLB phase and amplitude spectrum shows lines of the same optical depth as the pencil-beam profile and the lack of any phase shift between line and continuum. If the absorption arises in a galaxy like our own, the VLB line data indicate O < 0'.'0027. The resulting limit on the 932 MHz brightness temperature is Tb(932)> 1012 K, which may violate the Compton limit. The low4requency continuum data show that the 300-400 MHz flux has changed by a factor of 2 in 3 years, making AO 0235+164 the most active known low-frequency variable. If AO 0235+164 is cosmologically distant, this source must either expand relativistically or emit coherently. All the data available indicate that the z = 0.524 absorption system is extremely difficult to understand in terms of ejection from AO 0235+164. Our data are consistent with absorption by an intervening galaxy with a cosmological red shift of z = 0.524, but do not exclude the possible association of the BL Lacertae object with the z = 0.524 absorber. Subject headings: BL Lacertae objects - cosmology - radio sources: 21 em radiation - radio sources: variable Publication: The Astrophysical Journal Pub Date: June 1978 DOI: 10.1086/156195 Bibcode: 1978ApJ...222..752W Keywords: Absorption Spectra; Cosmology; Radio Sources (Astronomy); Ultrahigh Frequencies; Hydrogen Clouds; Infrared Absorption; Molecular Absorption; Radiant Flux Density; Red Shift; Astrophysics; BL Lacertae Objects:Radio Radiation; BL Lacertae Objects:Redshifts full text sources ADS | data products SIMBAD (3) NED (1)