Low Frequency VLA Observations of Abell 754: Evidence for a Cluster Radio Halo and Possible Radio Relics

We present 74 MHz and 330 MHz VLA observations of Abell 754. Diffuse, halo-like emission is detected from the center of the cluster at both frequencies. At 330 MHz the resolution of 90 distinguishes this extended emission from previously known point sources. In addition to the halo and at a much lower level, outlying steep-spectrum emission regions straddle the cluster center and are seen only at 74 MHz. The location, morphology and spectrum of this emission are all highly suggestive of at least one, and possibly two cluster radio relics. Easily obtained higher resolution, higher sensitivity VLA observations at both frequencies are required to confirm the extended nature of the halo-like emission and the 74 MHz relic detections. However, since there is prior evidence that this cluster is or has recently been in the process of a major merger event, the possible discovery of relics in this system is of great interest in light of recent observational and theoretical evidence in favor of a merger-relic connection. We discuss the possible role the merger shock waves, which are seen in the X-ray emission, may have played in the formation of the halo and radio relics in A754. Subject headings: galaxies: clusters: individual (A754) — galaxies: halos — radiation mechanisms: non-thermal — radio continuum: galaxies — shock waves Naval Research Laboratory, Code 7213, Washington, DC, 20375 USA, [email protected], [email protected] National Radio Astronomy Observatory, 1003 Lopezville Dr., Socorro, NM, 87801, USA, [email protected] Jansky Postdoctoral Fellow Max-Planck-Institut für Astrophysik, Karl-Schwarzschildstr. 1, D-85741 Garching, Germany, [email protected] National Research Council Postdoctoral Fellow CEA/Saclay, Service d’Astrophysique, Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France, [email protected]