A NARROW-BAND IMAGING SURVEY FOR PRIMEVAL GALAXIES

We present the results of a narrowband imaging survey for Ly alpha emission from young and forming ellipticals or spheroids at high redshifts. A total of 11 independent datacubes, each consisting of 6-11 images at slightly different central wavelengths, were obtained using a Fabry-Perot imaging interferometer on fields of similar to 5 arcmin square. Each datacube spans Delta z-0.2 while the total survey spans a redshift range of 2.78-4.89 for Ly alpha line emission. We reach a 1 sigma limiting Line flux (in an aperture of twice the seeing FWHM) of similar to 1.5 X 10(-17) ergs cm(-2) s(-1) over 0.05 deg(2), with a total of 0.63 deg(2) surveyed to a limiting line flux of similar to 8.5X10(-17) ergs cm(-2) s(-1). The survey reaches a 1 sigma average limiting restframe Ly alpha emission line luminosity of similar to 1.5X10(42) ergs s(-1) over a volume of 3000 comoving Mpc(3), with a total volume of 110 000 comoving Mpc(3) surveyed to an emission line luminosity of similar to 2.0X10(43) ergs s(-1) (for H-0 = 75 km s(-1) Mpc(-1) and Ohm(0)=0.2). No obvious population of Ly alpha luminous primeval galaxies has been detected so far, although a number of candidates remain which need to be checked by follow-up spectroscopy. Possible explanations for the lack of detection of a population of primeval galaxies at optical wavelengths in this and similar surveys include the possibility that they were obscured by dust or that the bulk of galaxy formation occurred at redshifts z(gf)greater than or equal to 5. The instrument used for this survey is also briefly described. (C) 1995 American Astronomical Society.