Atomic hydrogen in the one-sided “compact double” radio galaxy 2050+364

¹ Netherl. Foundation for Research in Astronomy (ASTRON), PO Box 2, 7990 AA Dwingeloo, The Netherlands e-mail: rvermeulen@astron.nl
² Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands e-mail: labiano@astro.rug.nl
³ Space Telescope Science Institute, Baltimore, MD 21218, USA
⁴ Center for Imaging Science, Rochester Inst. of Techn., 54 Lomb Memorial Drive, Rochester, NY, 14623, USA
⁵ Lawrence Livermore National Laboratories, USA
⁶ Department of Physics, Rochester Institute of Technology, Rochester, NY, 14623, USA

Received: 19 July 2005
Accepted: 14 October 2005

Abstract

Context. Aims.Localise and study the redshifted 21 cm absorption and the radio morphology of 2050+364. Methods.European VLBI Network UHF band (1049 MHz) spectral imaging, and examination of VLBI continuum images at multiple frequencies. Results.2050+364 may well be a one-sided core-jet source, which appears as a double (the well-known East-West component pair E, W) over a limited frequency range. W would then be the innermost visible portion of the jet, and could be at or adjacent to the canonical radio core. E is probably related to shocks at a sudden bend of the jet, towards an additional Northern extended steep-spectrum area (N), visible in our 1049 MHz image. Our observations have resolved the absorbing region. A remarkably deep and narrow line component is present over the entire projected extent of 2050+364. It coincides in velocity with the [] optical doublet lines to within 10 km s^-1. This absorption could arise in the atomic cores of NLR clouds, and the motion in the NLR is then remarkably coherent both along the line-of-sight and across a projected distance of >300 pc on the plane of the sky. Broader, shallower absorption at lower velocities covers only the plausible core area W. This absorption could be due to gas which is either being entrained by the inner jet or is flowing out from the accretion region; it could be related to the BLR. Conclusions.