An infrared emission-line galaxy at Z=2.43

An object discovered during an infrared survey of the held near the quasar B2 0149 + 33 has an emission line at 2.25 mu m that we interpret as H alpha at a redshift of 2.43. The K-band image shows two compact components 10 kpc apart, surrounded by more extended emission over similar to 20 kpc. The H alpha emission appears to be extended over similar to 15 kpc (2 ") in a coarsely sampled (0." 8 pixel(-1)) image. The star formation rate may be as high as 250-1000 M. yr(-1), depending on the extinction. Alternatively, the line may be powered by an active nucleus, although the probability of serendipitously discovering an AGN in the survey volume is only similar to 0.02. The increasing number of similar objects reported in the literature indicate that they may be an important, unstudied population in the high-redshift universe.