Astron. Astrophys. 358, 499-513 (2000)

ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum radio galaxies

C. Fanti ^1,2, F. Pozzi ^3,2, R. Fanti ^1,2, S.A. Baum ⁴, C.P. O'Dea ⁴, M. Bremer ⁵, D. Dallacasa ^3,2, H. Falcke ⁶, T. de Graauw ⁷, A. Marecki ⁸, G. Miley ⁹, H. Rottgering ⁹, R.T. Schilizzi ¹⁰, I. Snellen ¹¹, R.E Spencer ¹² and C. Stanghellini <sup>13

1</sup> Università di Bologna, Dipartimento di Fisica, Via Irnerio 46, 40126 Bologna,Italy
² Istituto di Radioastronomia del CNR, Via Gobetti 101, 40129 Bologna, Italy
³ Università di Bologna, Dipartimento di Astronomia, Via Ranzani 1, 40127 Bologna, Italy
⁴ STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ Bristol University, Department of Physics, H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol, BS8 1TL, UK
⁶ Max-Planck-Institut f. Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁷ Laboratorium voor Ruimteonderzoek, SRON, Postbus 800, 9700 AV Groningen, The Netherlands
⁸ Toru Centre for Astronomy, N. Copernicus University, ul. Gagarina 11, 87-100 Torun, Poland
⁹ Sterrewacht, Oort Gebouw, P.O. Box 9513, 2300 RA Leiden, The Netherlands
¹⁰ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
¹¹ Institute of Astronomy, Madingley Road, Cambridge CB3 0HA, UK
¹² University of Manchester, Jodrell Bank Observatory, Macclesfield, Cheshire SK 11 9L, UK
¹³ Istituto di Radioastronomia del CNR, C.P. 141, 96017 Noto (SR), Italy

Received 21 December 1999 / Accepted 10 April 2000

Abstract

We present results from observations obtained with ISOPHOT, on board the ISO satellite ¹, of a representative sample of seventeen CSS/GPS radio galaxies and of a control sample of sixteen extended radio galaxies spanning similar ranges in redshift () and radio luminosity ( W/Hz). The observations have been performed at = 60, 90, 174 and 200 µm. The original purpose of these observations was to check whether CSS/GPS sources are associated with very gas rich galaxies, as required by the scenario in which the growth of the radio source is inhibited by the dense medium of the host galaxy.

Unfortunately the resulting performance of ISOPHOT was worse than expected. As a consequence, the detection limit at 60µm is similar to that obtained previously with IRAS but better than that at 90µm.

Seven of the CSS/GPS sources have detections at one or more wavelengths, one of which is detected at . For the comparison sample five objects have detections one of which is at .

By co-adding the data we have obtained average flux densities at the four wavelengths.

We found no evidence that the FIR luminosities of the CSS/GPS sources are significantly different from those of the extended objects and therefore there is not any support for CSS/GPS sources being objects "frustrated" by an abnormally dense ambient medium.

The two samples were then combined, providing FIR information on a new sample of radio galaxies at intermediate redshifts. We compare this information with what previously known from IRAS and discuss the average properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission cannot be accounted for by extrapolation of the synchrotron radio spectrum and we attribute it to thermal dust emission. The average FIR luminosity is . Over the observed frequency range the infrared spectrum can be described by a power law with spectral index . Assuming the emission to be due to dust, a range of temperatures is required, from K to K. The dust masses required to explain the FIR emission range from for the hotter component up to for the colder one.

We present also observations on four nearby () GPS radio galaxies, two of which are detected at all four wavelengths.

Key words: galaxies: active galaxies: ISM infrared: galaxies infrared: ISM: continuum radio continuum: galaxies

Send offprint requests to: F. Pozzi

Correspondence to: cfanti@astbo1.bo.cnr.it

SIMBAD Objects

Contents

• 1. Introduction
• 2. The sample
• 3. Observations
• 4. Data reduction
  • 4.1. Calibration
  • 4.2. Vignetting corrections
  • 4.3. Flux density determination
  • 4.4. Estimate of statistical flux density errors
• 5. Results
  • 5.1. Individual detections
  • 5.2. Comparison with IRAS data
  • 5.3. Comments on some individual sources
    • 1345+125.
    • 3C 318
    • 1622+663
    • 1718-649
    • 1819+39
    • 1934-638
    • 1946+70
    • 3C459
  • 5.4. Average detections
• 6. Discussion
  • 6.1. FIR tail of synchrotron emission
  • 6.2. FIR luminosities of the combined CSS/GPS and comparison sample
  • 6.3. Temperature and dust masses
  • 6.4. What heats the dust?
  • 6.5. Implications for the circumnuclear torus
  • 6.6. Back to the frustration scenario for CSS/GPS sources
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: June 8, 2000
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