PPT Slide
Cluster members 2: Red Galaxies
Two of the Ly-alpha sources have extremely red continuum colours: they belong to the class of extremely red objects by most definitions. They are very luminous in the observed-frame near-IR (K ~ 19), but faint in the optical (R~26). These red colours could be caused by either dust obscured star formation, or by the 4000 Angstrom break of an old stellar population.
To discriminate between these possibilities, we obtained good JHK photometry. If they were dusty starbursts their flux should steadily decrease over this redshift range, while older stellar populations should show a sharp break between J and H.