Discovery of a z=2.76 Dusty Radio Galaxy?

Abstract

We report the discovery of a z=2.76 radio galaxy, MG1019+0535, with an unusual spectrum. Ly$α$, which usually dominates the spectra of high redshift radio galaxies, is very weak and the strongest lines in the spectrum are CIV$λ$1549 and HeII$λ$1640. We speculate that dust is responsible for attenuating the Ly$α$ line. This object provides more evidence for dust formation at early epochs. The optical counterpart of the compact radio source has a double morphology which is orthogonal to the radio source axis and most likely due to the superposition of two distinct objects which may or may not be physically related. There is only one detected line from the brighter component (B) which is close in observed wavelength to the redshifted HeII$λ$1640 line from the z=2.76 galaxy (A). We discuss whether B is at the same redshift as A or whether it is a foreground galaxy at z=0.66. We also report the serendipitous discovery of a very red ($R-K>7$) field object.