New Astronomy Reviews 43 (1999) 639–642 www.elsevier.nl / locate / newar The environment of Hercules A a ,b ,1 b Nectaria A.B. Gizani , J.P. Leahy a Department of Physics, Section of Astro-Geophysics, University of Ioannina, 45110 Ioannina, Greece b University of Manchester, NRAL, Jodrell Bank, Macclesfield, Cheshire SK11 9DL, UK Abstract We have made VLA radio total intensity and polarisation observations in the A, B and C configurations at 1665, 1435, 1365 and 1295 MHz and in the B, C and D configurations at 8465 and 8415 MHz to study the environment of the powerful radio galaxy Hercules A. We have also made ROSAT PSPC and HRI X-ray observations to study the intracluster gas in the 21 Hercules A cluster. We have mapped the Faraday rotation field with high resolution (1.994 | 2.5 h kpc for q 50), and 100 0 combined this with the X-ray data on the gas distribution in order to map the magnetic field of the cluster. We have found that Hercules A exhibits a strong Laing-Garrington effect: the western side of the radio emission is more depolarised than the eastern side. The X-ray observations have revealed an extended X-ray emission elongated along the radio galaxy axis and a weak nuclear component. The Hercules A cluster is a cooling flow cluster, which appears isothermal at large radii. Comparing the Faraday dispersion profile with the X-ray estimated density profile, we found that the magnetic field is decreasing with radius and we have estimated a central value of 3 & B ( mG) & 9. The estimated core electron density of 0 3 23 n . 6.6 3 10 m reveals a dense environment in which Hercules A is situated.  1999 Elsevier Science B.V. All rights 0 reserved. PACS: 95.85.Bh; 98.54.Cm; 98.54.Gr; 98.65.Cw Keywords: Radio continuum: galaxies; Galaxies: individual (3C 348, Hercules A); Galaxies: active; Galaxies: clusters; Galaxies: magnetic fields; X-rays: galaxies 1. Introduction aligned near the radio axis with a slight offset from the galaxy nucleus (Baum et al., 1996). 3C 348 or Hercules A is an extended source at a The 5 GHz power of Hercules A is P 5 2.4 3 5 GHz 25 21 21 21 low redshift of z 5 0.154. It is identified with a very 10 WHz , with H 5100 km s Mpc and 0 35 elongated 16 mag cD galaxy (Owen & Laing, 1989) q 50. Its total radio luminosity is | 1.5 3 10 W. 0 with a double nucleus and a tail (Sadun & Hayes, Although it is a high luminosity source, its structure 1993), at the centre of a poor, faint cluster, although resembles that of low-luminosity Fanaroff-Riley measurements of the cluster richness may be uncer- class I objects, with some important differences. tain (Owen & Laing, 1989; Yates et al., 1989; Dreher & Feigelson (1984) classify it as intermediate Barthel & Arnaud, 1996). Recent optical HST ob- between the two FR classes. With a linear size of 334 servations discovered kpc scale rings of obscuration, kpc and a width of . 157 kpc, it possesses an unusual jet-dominated morphology, almost symmetrically extended lobes and no compact hot- 1 spots. The western jet shows partial or full ring-like N.G. acknowledges travel support from the European Commis- features that form a linear sequence heading from the sion’s TMR ‘‘Access to Large-Scale Facilities’’ programme, under contract ERBFMGECT950012. core to the lobes and follow an inner jet. The eastern 1387-6473 / 99 / $ – see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S1387-6473(99)00069-X