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M. Stiavelli (STScI), C. Scarlata (STScI and Padova), S. Lilly (Victoria), N. Panagia (STScI and ESA), T. Treu (Caltech), G. Bertin (Milano and SNS, Pisa), F. Bertola (Padova)
We have carried out a search of Lyman \alpha candidates over a field of 1200 \sq ' using the CFH12K camera at the CFHT and a custom medium band filter. The search has unconvered 155 candidates, corresponding to a density of ~0.13 \sq ' -1. We find that our sources have very red colors which imply either that a large fraction of the light is reddened and we are detecting Lyman \alpha through special lines of sight or that the objects contain an underlying older stellar population. While for each individual objects we cannot discriminate between these models, we expect that most of the objects will actually contain an older components since the star formation rate inferred from the model with reddening would exceed by a large factor the peak star formation rate as measured by Madau et al. and Steidel et al. Thus it appears that typical Lyman \alpha emitters at z=2.4 experienced their major episode of star formation at higher redshift.