SPECTRAL POLARIZATION OF THE REDSHIFTED 21 cm ABSORPTION LINE TOWARD 3C 286
- Department of Physics, and Center for Astrophysics and Space Sciences, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0424 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 OHA (United Kingdom)
- Sydney Institute for Astronomy, University of Sydney, NSW 2006 (Australia)
- Department of Astronomy, University of California, Berkeley, CA 95064 (United States)
A reanalysis of the Stokes-parameter spectra obtained of the z = 0.692 21 cm absorption line toward 3C 286 shows that our original claimed detection of Zeeman splitting by a line-of-sight magnetic field, B{sub los} = 87 {mu}G, is incorrect. Because of an insidious software error, what we reported as Stokes V is actually Stokes U: the revised Stokes V spectrum indicates a 3{sigma} upper limit of B{sub los}< 17 {mu}G. The correct analysis reveals an absorption feature in fractional polarization that is offset in velocity from the Stokes I spectrum by -1.9 km s{sup -1}. The polarization position-angle spectrum shows a dip that is also significantly offset from the Stokes I feature, but at a velocity that differs slightly from the absorption feature in fractional polarization. We model the absorption feature with three velocity components against the core-jet structure of 3C 286. Our {chi}{sup 2} minimization fitting results in components with differing (1) ratios of H I column density to spin temperature, (2) velocity centroids, and (3) velocity dispersions. The change in polarization position angle with frequency implies incomplete coverage of the background jet source by the absorber. It also implies a spatial variation of the polarization position angle across the jet source, which is observed at frequencies higher than the 839.4 MHz absorption frequency. The multi-component structure of the gas is best understood in terms of components with spatial scales of {approx}100 pc comprised of hundreds of low-temperature (T {<=} 200 K) clouds with linear dimensions of <<100 pc. We conclude that previous attempts to model the foreground gas with a single uniform cloud are incorrect.
- OSTI ID:
- 21576805
- Journal Information:
- Astrophysical Journal, Vol. 733, Issue 1; Other Information: DOI: 10.1088/0004-637X/733/1/24; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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