H I absorption in high-frequency peaker galaxies

¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: orienti@ira.inaf.it
² Istituto di Radioastronomia – INAF, via Gobetti 101, 40129 Bologna, Italy
³ Netherlands Foundations for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands

Received: 5 January 2006
Accepted: 4 July 2006

Abstract

WSRT observations have been used to investigate the presence of neutral hydrogen in extremely young radio galaxies. These objects were selected from a sample of High-Frequency Peakers (HFPs). We detect 2 of the 6 observed galaxies confirming previous detection of in these objects. In the case of OQ 208 – for which discrepant results were available – we confirm the presence of a broad (~1800 km s^-1), blue-shifted and shallow absorption. No significant changes in the profile have been found between the two epochs of the observations. The intriguing result is that the derived column densities and upper limits obtained for the most compact sources, do not follow the inverse correlation between the column density and the linear size found for CSS/GPS sources. This can be explained – assuming the gas is already in a torus/disk structure – by a combination of the orientation and the extreme compactness of the sources. In this scenario, our line of sight to the source would intersect the torus in its inner region with low optical depth due to high spin and kinetic temperatures. There is no evidence, with the exception of OQ 208, of unsettled, high column density gas still enshrouding the young radio sources. This can be due to the low filling factor of such a medium.