Extended Ly-alpha emission associated with 3C 294

Abstract

We report the discovery of a large cloud of ionized gas associated with the radio galaxy 3C 294 at a redshift of 1.786. The radio source is a powerful double with a weak core. We detect Lya emission with a total monochromatic luminosity of L Lya = 7.6 x 10 44 ergs s -1 extended over ~100 x 170 kpc. The emission-line cloud is highly elongated and is well aligned with the inner radio source axis. Long-slit spectra, taken along the major axis, show spatially extended emission lines of N v 21240, C iv 21550, He n 21640, and C m 21909. The extended Lya emission shows a large, smooth velocity gradient (1500 km s -1 ) and large intrinsic line widths (700-2600 km s -1 ). The high-ionization lines, particularly C iv, show large velocity changes that are systematically different from those of Lya.3C 294 appears to be another, even more spectacular member of a class of powerful radio galaxies at high redshift typified by 3C 326.1. We discuss our observations from the point of view of star formation and the interaction of nuclear activity with ambient material. We consider two scenarios for the ionization of the Lya cloud: ionization by a population of extremely massive stars and ionization by a nonthermal continuum from the radio nucleus. Stellar photoionization appears to be insufficient in both the total number of ionizing photons and its ability to produce highly ionized species. We propose that the 150 kpc cloud of gas is photoionized by a central nonstellar source. We detect a very red compact object at 2.2 /mi nearly coincident with the radio core. It is unclear whether the light from this object is primarily stellar or nonstellar. Subject headings: galaxies: evolution -galaxies: individual (3C 294) -galaxies: redshiftsradio sources: galaxies I. INTRODUCTION Early radio observations of 3C 294 with the Cambridge 5 km telescope were reported by Jenkins, Pooley, and Riley (1977). These observations showed it to be a strong (5 178 = 10.3 Jy) source with extended structure. Optically, the source remained unidentified until the present work, in large part because of the presence of a F = 12 mag subgiant K star, only 10" to the west of the radio centroid (Kristian, Sandage, and Katern 1974;Riley, Longair, and Gunn 1980). Current groundbased imaging with any detector is hampered by scattered light from this Galactic star.Given that many of the recently identified 3CR sources are associated with faint galaxies having strong Lya emission (Spinrad et al. 1985), and in some cases very extended Lya emission (McCarthy et al 1987a), it seemed reasonable that 3C 294 might be detectable spectroscopically, without the benefit of an optical identification. After receiving a report of a tenta-1 Based, in part, on observations obtained at Lick Observatory, which is owned and operated by the University of California, and the Multiple Mirror Observatory, a joint facility of the Smithsonian Astrophysical Observatory and the University of Arizona.

Radio Galaxies atz= 1.1 to 3.8: Adaptive Optics Imaging and ArchivalHubble Space TelescopeData

“…A moderate-resolution (0>4 FWHM) VLA map at 5.0 GHz has been obtained by McCarthy et al (1990) and indicates that 3C 294 has a double-lobed morphology along an axis from northeast to southwest. An unresolved core is also detected.…”

“…Attempts to obtain non-AO, ground-based NIR images of the RG have been hampered by the bright (R = 12) star 9 00 to the west (McCarthy et al 1990). This proximity was an asset for AO imaging.…”

Gas Accretion and Giant Lyα Nebulae

“…the classical approach used by McCarthy et al (1990). In this case, integrating the Lyα emissivity given above one would simply obtain:…”

Giant Lyα nebulae in the high redshift (z⩾2) Universe

“…Reuland et al 2003, Villar-Martín et al 2003, McCarthy et al 1990) and sometimes beyond the radio structures (e.g. Maxfield et al 2002, Pentericci et al 2000, Eales et al 1993.…”