HST WFPC2 Image of z=4.19 Emitter WFPC2 image in the F814W (`wide I') filter band of the 36 × 30 arcmin2 field surrounding the z=4.19 Lyman alpha emitter (circled position).  The object is undetected even in this 2.6 hr-long observation made with the Hubble Space Telescope.  The strength of the Lyman alpha emission line makes it feasible to search for such objects with narrowband filter imaging

When the contrast between the object seen in the narrowband image as compared with a broadband, continuum image is very high, the emission line sampled by the narrowband filter can be identified as the Lyman alpha line with a high degree of confidence.  In a few cases, the selection has turned up active galaxies or quasars.

An important feature of both our spectroscopic and narrowband surveys is the use of target fields which also have deep Hubble Space Telescope images.  This allows us to identify both high-redshift galaxies and very faint, low-redshift emission line galaxies, and to separate them by their spectroscopic properties.  The faint spiral to the southeast of the z=4.19 emitter's position is at z=0.56.  Even such faint galaxies have other emission lines and continuua which allow them to easily be distinguished from the Lyman alpha emitters.   LRIS covers a wide field, and in some cases new emission-line objects are found which lie outside the HST images.  In these cases we use complementary deep images from groundbased observations.

ESO r Image of z=5.64 EmitterA very deep r band image taken with the SUSI camera on the ESO 3.5m NTT (D'Odorico, Fontana, Giallongo, and Cristiani) showing the position of the z=5.64 emission-line object. The multi-color data for this quasar field is described in a paper (Giallongo et al.) [astro-ph/9802340] giving combined optical and infrared data. No detectable object is seen in stellar continuum light at these levels.


CFHT QUIRC K Image of z=5.64 Emitter The position of the z=5.64 emission-line object in a very deep infrared (K) image taken with the University of Hawaii QUIRC camera. These infrared bands may sample wavelength regions that are better able to pick out faint continuum starlight for very distant galaxies.There is possibly a faint object near the position sampled by the Keck LRIS slit, but again, no convincing detection in continuum light.


Esther M. Hu

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Last Revision: March 5th 1998