Giant radio galaxy DA 240 group: content and environment

Abstract

Context. There is a group of about twenty galaxies around the giant radio galaxy (GRG) DA 240 which we are studying to investigate the environment of the radio source. We have noted that 11 members are aligned with the radio emission (Peng et al. 2004, A&A, 415, 487). The alignment occurs within a small angle similar to the width of the GRG radio lobes, and there may be some physical causal relationship. After finishing observations of the four candidates not included in Paper I, we have completed our study of the brighter members of the sample of galaxies around DA 240.

Aims. We aim to see if more galaxies have similar redshifts to the host galaxy of DA 240, to confirm the galaxy grouping and further study their distribution.

Methods. Spectra of the four candidate galaxies were obtained with the 2.16 m spectroscopic telescope at XingLong observing station of the NAOC, and the galaxies’ positions were established with respect to the radio emission. We have discovered two more members associated with the group of galaxies around DA 240. In addition, the work of other researchers provides one other new member.

Results. The number of confirmed galaxies associated with the DA 240 group has increased by almost a quarter to 20. There are now 14 galaxies (including the host) lying along the major axis of the radio source. We further consider the relationship of the group to adjacent galaxy associations, noting that it may form a binary pair with the slightly closer UGC 3957 group. They both lie on the periphery of the much more substantial cluster, Abell 576.