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Issue A&A Volume 426, Number 2, November I 2004 Page(s) L29 - L32 Section Letters DOI 10.1051/0004-6361:200400067

A&A 426, L29-L32 (2004)
DOI: 10.1051/0004-6361:200400067

Letter

Dust in 3CR radio galaxies: On the FR 1 - FR 2 difference

S. A. H. Müller¹, M. Haas¹, R. Siebenmorgen², U. Klaas³, K. Meisenheimer³, R. Chini¹ and M. Albrecht<sup>4

1</sup>  Astronomisches Institut, Ruhr-Universität Bochum (AIRUB), Universitätsstr. 150 / NA7, 44780 Bochum, Germany
    e-mail: smueller@astro.rub.de
²  European Southern Observatory (ESO), Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
³  Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
⁴  Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile

(Received 6 August 2004 / Accepted 6 September 2004 )

Abstract
We compare three 3CR samples of 11 FR 1 galaxies, 17 FR 2 galaxies and 18 lobe-dominated quasars contained in the ISO Data Archive. In contrast to the powerful FR 2 galaxies with edge-brightened lobes, the low radio power FR 1 galaxies in our sample do not exhibit any high MIR or FIR dust luminosity, which is typical for a buried, intrinsically more luminous AGN. This consolidates the fact already inferred from optical studies that their AGNs have only a relatively low luminosity. Also the FR 1 galaxies show a high FIR/MIR luminosity ratio, compared to quasars, suggesting that their FIR luminosity is substantially powered by the interstellar radiation field (ISRF) of the giant elliptical hosts. Finally, we discuss the FR 1 - FR 2 morphological dichotomy. FR 1 galaxies do not have more interstellar matter (ISM) than FR 2s as traced - on the large scale - by the cool FIR emitting dust and - in the nuclear region - by the warm MIR emitting dust. Due to the lack of central gas we suggest that the black holes of our FR 1 galaxies are fed at a lower accretion rate than those of the FR 2 galaxies.

Key words: galaxies: fundamental parameters -- galaxies: photometry -- quasars: general -- infrared: galaxies

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© ESO 2004

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