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Issue A&A
Volume 404, Number 3, June IV 2003
Page(s) 871 - 881
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20030469



A&A 404, 871-881 (2003)
DOI: 10.1051/0004-6361:20030469

The presence and distribution of H $\!$ I absorbing gas in sub-galactic sized radio sources

Y. M. Pihlström1, 2, J. E. Conway2 and R. C. Vermeulen3

1  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

(Received 14 February 2003 / Accepted 20 March 2003)

Abstract
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

Offprint request: Y. M. Pihlström, ypihlstr@aoc.nrao.edu

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© ESO 2003


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