A Pair of Compact Red Galaxies at Redshift 2.38, Immersed in a 100 Kiloparsec Scale Lyα Nebula

We present Hubble Space Telescope and ground-based observations of a pair of galaxies at a redshift of 2.38, which are collectively known as 2142-4420 B1. Both galaxies are luminous extremely red objects (EROs) and are separated by 0.8". They are embedded within a 100 kpc scale diffuse Lyα nebula (or blob) of luminosity ~10⁴⁴ ergs s^-1. The radial profiles and colors of both red objects are most naturally explained if they are young elliptical galaxies, the most distant galaxies of this type found to date. It is not possible, however, to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of ~10¹¹ M_solar and ages of ~7×10⁸ yr. Both galaxies have color gradients: their centers are significantly bluer than their outer regions. The surface brightness of both galaxies is roughly 1 order of magnitude greater than would be predicted by the Kormendy relation. A chain of diffuse star formation extending 1" from the galaxies may be evidence that they are interacting or merging. The Lyα nebula surrounding the galaxies shows apparent velocity substructure of amplitude ~700 km s^-1. We propose that the Lyα emission from this nebula may be produced by fast shocks that are powered either by a galactic superwind or by the release of gravitational potential energy. Based upon observations with the Anglo-Australian Telescope, the Cerro Tololo Blanco Telescope, the ESO New Technology Telescope (NTT) at the La Silla Observatory under program 63.0-0291A, and the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.