VLBI, MERLIN and HST observations of the giant radio galaxy 3C 236

Abstract

Abstract. We present VLBI and MERLIN data at 1.66 and 4.99 GHz on the central component coincident with the nucleus of the giant radio galaxy, 3C 236. The nuclear radio structure is composed of two complexes of emission which are resolved on scales from 1 milli-arcsec (mas) to 1 arcsec. Oscillations with an amplitude of ∼5• can be seen in the compact radio structure. Spectral index distributions are plotted at angular resolutions of 10 and 25 mas and allow us to identify the core component in the south-east emission complex. Re-examination of the HST WFPC-2 image of 3C 236 by de Koff et al. (2000), shows that the normal to the dust disk in the nucleus is ∼30• from the plane of the sky and within 12• of parallel to the overall orientation of the radio source. We suggest that the radio axis is also at an angle of ∼30• to the plane of the sky and that the north-west jet is on the approaching side. This orientation implies an overall size of 4.5 Mpc (H0 = 75 km s −1 Mpc −1 , q0 = 0.5) for 3C 236. The coincidence of a dust feature and the south-east compact jet, within the astrometric errors, leads us to suggest that the dust may be in the form of a cloud encountered by the jet in the first ∼400 pc of its journey out from the nucleus. One-sided emission at 5 GHz on 1 mas scales would suggest that the jets are ejected initially at ≤ 35• to the line of sight, but this is difficult to reconcile with the obvious orientation stability of the jet system as a whole. Free-free absorption of the counter-jet may be an alternative explanation for the one-sideness. At the resolution of WSRT data at 327 MHz, the jet to the south-east is apparently continuous over a distance of 2.5 Mpc, making this the largest jet known in the universe. It is likely, however, that activity in the nucleus of 3C 236 is episodic but with a shorter duty cycle than in the double-double sources studied by Schoenmakers et al. (2000) and Kaiser et al. (2000).

Host Galaxies, Obscuration, and Nuclear Structure of Three Nearby Compact Symmetric Objects

“…Similar statements have been made for 3C 236 (OÏDea et al 2001 ;Schilizzi et al 2001), a CSS with both compact, 2 kpcÈsize inner radio lobes and a megaparsecscale radio halo. The size of the variations in isophotal P.A.…”

An HST Proper-Motion Study of the Large-Scale Jet of 3c273

“…We therefore adopt the 7°.2 as the maximum angle for the kiloparsec-scale jet as well. A further global limit on the angle to the line of sight can be calculated by assuming that the 24″ jet does not exceed 1 Mpc in total (deprojected) length, as very few radio galaxies exceed this length (e.g., 3C 236, Schilizzi et al (2001); this gives a lower limit θ = 3°. 8.…”

The circumnuclear cold gas environments of the powerful radio galaxies 3C 236 and 4C 31.04

“…The outer 4.5 Mpc scale lobes make 3C 236 one of the largest single objects in the universe. The inner 2 kpc sized radio source structure is highly asymmetric with respect to the identified VLBI core (Barthel et al 1985;Schilizzi et al 2001) and is misaligned with respect to the outer mega-parsec scale structure by about 7…”

“…It has been speculated that a gas cloud encountered by the jet in the inner 400 pc of its journey out from the nucleus may have caused the bending of the inner jet structure (Schilizzi et al 2001). On the one to few kpc scale, Hubble Space Telescope (HST) observations show a dust lane which wraps around the core, almost perpendicular to the jet axis (Martel et al 1999;de Koff et al 2000).…”