Volume 426, Number 2, November I 2004
|Page(s)||L29 - L32|
|Published online||11 October 2004|
Letter to the Editor
Dust in 3CR radio galaxies: On the FR 1 – FR 2 difference *
Astronomisches Institut, Ruhr-Universität Bochum (AIRUB), Universitätsstr. 150 / NA7, 44780 Bochum, Germany e-mail: email@example.com
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
Accepted: 6 September 2004
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
© ESO, 2004
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