Extended Lyα emission associated with 3C 294

Creators: McCarthy, Patrick J.; Spinrad, Hyron; van Breugel, Wil; Liebert, James; Dickinson, Mark; Djorgovski, S.; Eisenhardt, Peter

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 Lyα emission with a total monochromatic luminosity of L_(Lyα) = 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 λ1240, C IV λ1550, He II λ1640, and C III λ1909. The extended Lyα 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 Lyα. 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 Lyα cloud: ionization by a population of extremely massive stars and ionization by a non thermal 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 μm nearly coincident with the radio core. It is unclear whether the light from this object is primarily stellar or nonstellar.

Additional Information

© 1990 The American Astronomical Society. Received 1989 April 20; accepted 1990 June 15. 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. We would like to thank the staffs of the Lick Observatory, the Multiple Mirror Observatory, the Kitt Peak National Observatory, and the National Radio Astronomy Observatory for their expert assistance with the observations. We also thank Robert Laing and Frazer Owen for communicating early radio data, John Huchra for obtaining an observation of 3C 294 with the MMT, and John Stauffer for suggesting the final J-band reduction step. Finally, we thank the referee for helpful comments. This research was supported by grants AST 85-13416 (H. S.) and AST 84-16177 (W. vB.) from the National Science Foundation and by the Carnegie Institution of Washington (P. M.), and the California Institute of Technology and Harvard University (S. D.). The Lick Observatory is operated by the University of California and is supported in part by grant AST 86-14510 for the National Science Foundation.

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