One - Line Redshifts and Searches for High - Redshift Ly α Emission

We report the serendipitous discovery of two objects close in projection with fairly strong emission lines at long wavelength (λ ∼ 9190 Å). One (A) seems not to be hosted by any galaxy brighter than V555 = 27.5, or I814 = 26.7 (Vega-based 3σ limits in 1. 0 diameter apertures), while the other line is associated with a faint (I814 ≃ 24.4) red galaxy (B) offset by 2. 7 and 7 Å spectrally. Both lines are broad (FWHM ≈ 700 km s−1), extended spatially, and have high equivalent widths (W obs λ (A) > 1225 Å, 95% confidence limit; W obs λ (B) ≈ 150 Å). No secondary spectral features are detected for galaxy A. Blue continuum and the marginal detection of a second weak line in the spectrum of galaxy B is consistent with [O II] (the strong line) and Mg II (the weak line) at z = 1.466. By association, galaxy A is likely at z = 1.464, implying a rest-frame equivalent width of the [O II] emission line in excess of 600 Å and a projected separation of 30 h 50 kpc for the galaxy pair. Conventional wisdom states that isolated emission lines with rest-frame equivalent widths larger than ∼ 200 Å are almost exclusively Lyα. This moderateredshift discovery therefore compromises recent claims of high-redshift Lyα emitters Based on observations at the W.M. Keck Observatory, which is operated as a scientific partnership among the University of California, the California Institute of Technology, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Current address: Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 169-327, Pasadena, CA 91109; [email protected] Current address: Institute of Astronomy, Madingley Road, Cambridge, CB3 OHA, England Hubble Fellow