Radio Continuum Emission at 21 cm near Stephan's Quintet

Abstract

AN area about one degree square centred at α = 22 h 33.80 m, δ = 33° 41.0′ (1950) near Stephan's Quintet of galaxies has been observed with the Westerbork Synthesis Radio Telescope at 21.2 cm. The measurements consist of 12 h registrations at 40 interferometer spacings from 36 to 1,440 m in intervals of 36 m. The observations were Fourier-transformed to produce a map of the radio brightness of the region with a synthesized beam 25 arc s wide at the half-power points. The results in the immediate neighbourhood of Stephan's Quintet are shown in Fig. 1. The radio contours are drawn over a photograph of the Quintet which has been taken from ref. 1. The radio features detected consist of an unresolved source (indicated by the white cross on the photograph) located very near the nucleus of the spiral galaxy NGC 7319, and an unusual, approximately semicircular arc of emission which appears to partially envelope this galaxy. Any radio emission from the nucleus of NGC 7320 is less than 2.5×10⁻²⁹ W m⁻² Hz⁻¹; a similar limit also applies to NGC 7317.