The background image


The picture shows a 1800 s R-band exposure of the object RGB 1745+398 obtained at the 2.6m Nordic Optical Telescope. The field size is 207" x 209". The bright reddish object to the lower left of the center is a BL Lac object at the center of a cluster of galaxies. The blue, arclike structure about 8" southeast of the BL Lac is interpreted as a gravitationally enhanced image of a background galaxy.

RGB 1745+398 was identified as a BL Lac object by Laurent-Muehleisen et al. (1998) in optical follow up observations of a correlation between the ROSAT All Sky Survey and the Green Bank 5 GHz radio survey (Brinkmann et al. 1995). The discovery of the arclike structure was presented by Nilsson et al. (1999).

The location of this nearby BL Lac object (z = 0.267) in the center of a cluster suggests that some portion of the X-ray emission is coming from the intra-cluster gas. This object nicely illustrates the commonly found close relationship between Active Galactic Nuclei and Clusters of Galaxies.

Back to Extragalactic homepage

[red line]