FIGURE: Keck image of the field around a luminous galaxy at redshift 5.74 in the Constellation of Aquarius. Deep exposures at far red and infrared wavelengths were combined to make this picture. An image taken in a narrowband filter which captures light from the redshifted 1216 Å Hydrogen Lyman alpha line excited by star formation is responsible for the green halo around the faint, distant galaxy at the center, and shows that substantial star formation is taking place.
High redshift galaxies showing strong Hydrogen Lyman alpha emission from may be extremely faint, or undetected, in deep optical or IR continuum images - even in deep exposures made with the 10 m Keck Telescope or with the Hubble Space Telescope. These objects may provide us with a view of galaxies in the earliest stages of the formation process, when there is massive star formation that can excite the Lyman alpha emission line, but which has not yet produced substantial amounts of dust that can suppress this line. Important consequences for our understanding of the early universe are:
The 10 m Keck II telescope Narrow Band Searches for high z Lyman alpha emitting galaxies are described in more detail in this companion paper. Most of the objects found by this method are star forming galaxies. A few of the emission line objects are AGN. A custom filter, shown here, matched to the optics of Keck's LRIS spectrograph and imager, was used to image distant galaxies in Lyman alpha emission light.
See our selected bibliography for additional papers on emission-line searches and deep galaxy surveys. A separate set of catalogs for the Hubble Deep Field is also available.
Spectral Searches for these extremely faint emission lines rely on being able to accurately subtract the night sky background to extremely high precision as is described here.
GIF images of the redshift 5.74 galaxy in individual color bands from the paper