A galaxy cluster in the innermost Zone of Avoidance, close to the radio phoenix VLSSJ2217.5+594

TL;DR

This study identifies a galaxy cluster associated with a steep spectrum radio source in the Zone of Avoidance, using infrared imaging and spectroscopy, confirming its classification as a radio phoenix.

Contribution

First detection of a galaxy cluster in the innermost Zone of Avoidance linked to a radio phoenix source through multi-wavelength analysis.

Findings

Galaxy cluster at z = 0.163 confirmed near the radio source.

Spectroscopic analysis of three galaxies supports cluster membership.

Radio source VLSSJ2217.5+5943 is associated with a massive galaxy cluster.

Abstract

The steep spectrum radio source VLSSJ2217.5+5943 shows a complex, filamentary morphology and a curved spectrum. Therefore, the source has previously been classified as a radio phoenix. However, no galaxy cluster associated with this radio source has been confidently detected so far because the source is located in the direction of the innermost zone of the Galactic Plane at b = +2.4 degr (innermost Zone of Avoidance, ZoA). We analysed archival observations in the near infrared (UKIDSS) and mid infrared (Spitzer) to select the galaxies in the immediate neighbourhood of the radio source. A sample of 23 galaxies was selected as candidate cluster members. Furthermore, we carried out deep integral field spectroscopy covering 6450 to 10500 AA with the red unit of the Hobby-Eberly Telescope second generation low resolution spectrograph (LRS2-R). We also reanalysed archival GMRT observations at 325 and 610 MHz. We selected 23 galaxies within a radius of 2.5 arcmin, centered on RA=22:17.5, DEC=+59:43 (J2000). Spectra were obtained for three of the brightest galaxies. For two galaxies we derived redshifts of z = 0.165 and z = 0.161, based on NaD absorption and TiO band heads. Their spectra correspond to E-type galaxies. Both galaxies are spatially associated with VLSSJ2217.5+5943. The spectrum of the third galaxy, which is slightly more distant from the radio source, indicates a LINER at z = 0.042. It is apparently a foreground galaxy with respect to the cluster we identified. VLSSJ2217.5+5943 is associated with a massive galaxy cluster at redshift z = 0.163 +- .003, supporting its classification as radio phoenix.