Time variations in the high-redshift 21 centimeter absorption spectrum of the BL Lacertae object AO 0235+164

Journal Article · Sun Aug 15 04:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160187· OSTI ID:6698353

Wolfe, A M; Davis, M M; Briggs, F H

We present evidence for time variations of the redshifted (z = 0.524) 21 cm absorption spectrum of the BL Lac object AO 0235+164. A 4 year monitoring program with the 305 m telescope at Arecibo shows that the line depths of the four deepest features (A..-->..D) vary in time. The strongest changes occur in feature D, which was observed to double its line depth in 0.5 yr. Weaker variations (between 15 and 35%) with durations between 0.25 and 0.5 yr are observed in all four features, and there is tentative evidence for a monthly flickering with amplitudes of approx.10%. Whereas each of the features evolves independently during some epochs, they appear to vary synchronously during others. We have also monitored the velocity centroids and velocity widths of the features and find that neither varies by more than approx. 1 km s/sup -1/. We have placed a 3 sigma upper limit of 0.75 km s/sup -1/ for centroid variations of feature D. But there is tentative evidence for systematic and correlated variations of approx.0.2 km s/sup -1/ in the velocity centroids of features A, B, and C. Throughout the monitoring program the continuum flux density at the observed frequency (932 MHz) of the 21 cm line has remained nearly constant.

• Research Organization: Department of Physics and Astronomy, University of Pittsburgh
• OSTI ID: 6698353
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 259:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABSORPTION SPECTRA
BL LACERTAE OBJECTS
COSMIC GASES
COSMIC RADIO SOURCES
DATA ANALYSIS
ELECTROMAGNETIC RADIATION
FLUIDS
FLUX DENSITY
GASES
H1 REGIONS
MATHEMATICAL MODELS
MONTE CARLO METHOD
RADIATION FLUX
RADIATIONS
RADIOWAVE RADIATION
SPECTRA
SPECTRAL SHIFT
VARIATIONS