Astronomy and Astrophysics, volume 289, 54-60 (1994/9-1)
TX 0211-122: a starburst radio galaxy at z=2.34?
VAN OJIK R., ROETTGERING H.J.A., MILEY G.K., BREMER M.N., MACCHETTO F. and CHAMBERS K.C.
Abstract (from CDS):
We report the discovery of a distant galaxy at a redshift z=2.34 with a peculiar emission line spectrum. It is an ultra steep spectrum radio source and identified with an object of R-magnitude 22.7. The optical spectrum is highly anomalous with a flux ratio of Lyα to NVλ1240 of 1.1, a factor of ∼30 smaller than that for a typical high-redshift radio galaxy. Lyα is weak and NVλ1240 is strong when compared with CIVλ1549, HeIIλ1640 and CIII]λ1909. The spectrum resembles that of the z=2.29 IRAS galaxy F10214+4724. Possible mechanisms for simultaneously depressing Lyα and enhancing NV are considered. The relatively large NV/CIV ratio indicates that the line-emitting gas is overabundant in nitrogen. We conclude that TX0211-122 is likely to be undergoing a massive starburst in the central region, possibly as the result of the passage of the radio jet. The vigorous starburst would produce (i) the dust responsible for attenuating the central Lyα emission and (ii) a relative overabundance of nitrogen. The NVλ1240 emission can be produced either by shocks or by photoionization. Shocks could be due to supernovae from the starburst or from the passage of the radio jet and photoionization could be due to the youngest stars and the AGN. The peculiar spectrum of TX0211-122 is further evidence that radio jets may trigger vigorous star formation in high-redshift galaxies.