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Session 12 - Radio Galaxies, VLBI.
Display session, Monday, January 15
North Banquet Hall, Convention Center

[12.02] Dust in 3CR radio galaxies.

S. de Koff, S. Baum, W. Sparks, J. Biretta, D. Golombek, F. D. Macchetto (STScI), P. J. McCarthy (Carnegie Obs.), G. K. Miley (Leiden Obs.)

We present results on the dust in 38 3CR radio galaxies in the redshift range 0 < z < 0.5. We obtained the images by conducting a snapshot survey of the 3CR catalog with HST, WFPC2, using a broadband red (F702W) filter. The images have \sim 0.1" resolution.

We find dust (lanes, patches, wisps) out to a redshift of 0.48. Roughly 30-50% of the 3CR galaxies from 0 < z < 0.5 show evidence for dust. For the lower redshifts, the distribution of the dust is frequently disk-like, but can be unsettles and filamentary. At the highest resolution the disks appear to seperate into series of parallel strands. Structure in the dust is more difficult to detect at z > 0.1, but the effects of dust obscuration are seen.

We examine the orientation of dust `disks' (measured closest to the nucleus) with respect to the radio source axis for 38 radio galaxies in the redshift range 0 < z < 0.5. We find a strong tendancy for the dust major axis to be perpendicular to the radio source axis. This confirms the earlier result (Kotanyi amp; Ekers, 1979), giving credence to the idea that gas from kpc scales feeds the central engine and affects its collimation axis. There is a suprising dispersion in the result, there are some sources in which the radio jets issue directly into the dust disk.

We have investigated the `clumpiness' of the galaxy images in the redshift range 0.1 < z < 0.5 to study the `alignment' effect. We find a tendancy for the clumpiness of the sources to increase strongly with redshift in the redshift range 0.15 to 0.4. At the same time we find little correlation of radio power and clumpiness, suggesting that clumpiness may be due more to galaxy evolution than to the activity itself. The sources that have their optical continuum aligned with the radio source major axis are preferrentially those with dust. This suggests a connection between the presence of dust and the `alignment effect'.

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