Astron. Astrophys. 326, 130-138 (1997)

Clues on the nature of Compact Steep Spectrum radio sources from optical spectroscopy

R. Morganti ^{1, 2}, C.N. Tadhunter ³, R. Dickson ³ and M. Shaw <sup>3

1</sup> Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia
² Istituto di Radioastronomia, CNR, via Gobetti 101, I-40129 Bologna, Italy
³ Department of Physics, University of Sheffield, Sheffield S3, UK

Received 28 January 1997 / Accepted 9 April 1997

Abstract

New long-slit spectra are presented for a group of Compact-Steep-Spectrum (CSS) sources (i.e. powerful radio sources with sub-galactic size and steep spectral index at high radio frequencies) selected from the southern () 2-Jy sample of radio sources with redshift limit of . Their spectra are strong in emission lines (e.g. [O III ] and [O II ] ), as expected for such powerful radio sources. The line luminosities and ratios obtained for these compact sources are compared with those for the other sources of the southern 2-Jy sample. We find that the optical spectra for the CSS sources show characteristics very similar to the extended sources of similar radio power and redshift. In particular, we find that the CSS sources follow the correlation between the radio power and [O III ] and [O II ] luminosities found for the extended sources, although there is tentative evidence that they have lower [O III ] luminosities. Also, the optical continuum spectral energy distribution (SED) and polarization properties of the CSS sources show the same variety of characteristics observed among the extended sources. The first-order similarity that we find between the spectra of CSS sources and the extended sources of similar radio power is consistent with the idea that the CSS sources are young radio sources in which the radio jets have yet to emerge from the central regions of the host galaxies.

Key words: galaxies: active galaxies: nuclei radio continuum: galaxies

Send offprint requests to: R. Morganti

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Contents

• 1. Introduction
• 2. The sample
• 3. The new optical data
• 4. Results
  • 4.1. Reddening
  • 4.2. Temperature and density
  • 4.3. The optical continua and polarisation
• 5. Comparison between CSS sources and the rest of the 2-Jy sample
  • 5.1. The [OIII], [OII] emission lines
  • 5.2. The diagnostic diagrams
• 6. Discussion
• 7. Conclusions
• References

© European Southern Observatory (ESO) 1997

Online publication: April 20, 1998
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