One-Line Redshifts and Searches for High-Redshift Lyman-Alpha Emission
  We report the serendipitous discovery of two objects close in projection with fairly strong emission lines at long wavelength (~9190 A). 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 arcsec diameter apertures), while the other line is associated with a faint (I(814)~24.4) red galaxy (B) offset by 2.7 arcsec and 7 A spectrally. Both lines are broad (FWHM 700 km/s), extended spatially, and have high equivalent widths (W(A,obs)>1225 A, 95% confidence limit; W(B,obs)~150 A). 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 [OII] (the strong line) and MgII (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 [OII] emission line in excess of 600 A and a projected separation of 30 kpc for the galaxy pair. Conventional wisdom states that isolated emission lines with rest-frame equivalent widths larger than ~200 A are almost exclusively Lyman-alpha. This moderate-redshift discovery therefore compromises recent claims of high-redshift Lyman-alpha emitters for which other criteria (i.e., line profile, associated continuum decrements) are not reported. We discuss observational tests to distinguish Lyman-alpha emitters at high redshift from foreground systems. 
Daniel Stern (1 and 2), Andrew J. Bunker (1 and 3), Hyron Spinrad (1)   and Arjun Dey (4) ((1) UC-Berkeley, (2) JPL/Caltech,...