Volume 404, Number 3, June IV 2003
|Page(s)||871 - 881|
|Published online||06 June 2003|
The presence and distribution of H I absorbing gas in sub-galactic sized radio sources
National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
2 Onsala Space Observatory, 439 92 Onsala, Sweden
3 Netherlands Foundation for Research in Astronomy, Postbus 2, 7990 AA Dwingeloo, The Netherlands
Corresponding author: Y. M. Pihlström, firstname.lastname@example.org
Accepted: 20 March 2003
We consider the incidence of Hiabsorption in intrinsically small sub-galactic sized extragalactic sources selected from sources classified as Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources. We find that the smaller sources (<0.5 kpc) have larger Hicolumn densities than the larger sources (>0.5 kpc). Both a spherical and an axi-symmetric gas distribution, with a radial power law density profile, can be used to explain this anti-correlation between projected linear size and Hi column density. Since most detections occur in objects classified as galaxies, we argue that if the unified schemes apply to GPS/CSSs a disk distribution for the Hiis more likely. The most favoured explanation for the compact sizes of the GPS/CSSs is that they are young sources evolving in a power law density medium. For the GPSs with measured expansion velocities, our derived densities are within an order of magnitude of those estimated from ram-pressure confinement of the lobes assuming equipartition. Our results therefore support the youth model.
Key words: galaxies: active / galaxies: evolution / galaxies: ISM / radio lines: galaxies
© ESO, 2003
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