MASSIVE STAR FORMATION IN A GRAVITATIONALLY LENSED H Ⅱ GALAXY AT z = 3.357

摘要

The Lynx arc, with a redshift of 3.357, was discovered during spectroscopic follow-up of the z = 0.570 cluster RX J0848+4456 from the ROSAT Deep Cluster Survey. The arc is characterized by a very red R-K color and strong, narrow emission lines. Analysis of HST WFPC2 imaging and Keck optical and infrared spectroscopy shows that the arc is an H Ⅱ galaxy magnified by a factor of ～10 by a complex cluster environment. The high intrinsic luminosity, the emission-line spectrum, the absorption components seen in Lyα and C Ⅳ, and the rest-frame ultraviolet continuum are all consistent with a simple H Ⅱ region model containing ～10~6 hot O stars. The best-fit parameters for this model imply a very hot ionizing continuum (T_(BB) approx= 80,000 K), a high ionization parameter (log U approx= -1), and a low nebular metallicity (Z/Z_☉ approx= 0.05). The narrowness of the emission lines requires a low mass-to-light ratio for the ionizing stars, suggestive of an extremely low metallicity stellar cluster. The apparent overabundance of silicon in the nebula could indicate enrichment by past pair-instability supernovae, requiring stars more massive than ～140 solar mass.