One-line redshifts and searches for high-redshift Lyα emission

We report the serendipitous discovery of two objects close in projection with fairly strong emission lines at long wavelength (lambda similar to 9190 Angstrom). One (A) seems not to be hosted by any galaxy brighter than V-555 = 27.5, Or I-814 = 26.7 (Vega-based 3 sigma limits in 1." 0 diameter apertures), while the other line is associated with a faint (I-814 similar or equal to 24.4) red galaxy (B) offset by 2." 7 and 7 Angstrom spectrally. Both lines are broad (FWHM approximate to 700 km s(-1)), are extended spatially, and have high equivalent widths [W-lambda(obs)(A) > 1225 Angstrom, 95% confidence limit; W-lambda(obs)(B) approximate to 150 Angstrom] 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 Angstrom and a projected separation of 30 h(50)(-1) kpc for the galaxy pair. Conventional wisdom states that isolated emission lines with rest-frame equivalent widths larger than similar to 200 Angstrom are almost exclusively Ly alpha. This moderate-redshift discovery therefore compromises recent claims of high-redshift Ly alpha emitters for which other criteria (i.e., line profile, associated continuum decrements) are not reported. We discuss observational tests to distinguish Ly alpha emitters at high redshift from foreground systems.