Emission Line Measurements in the Magnified z = 3.357 HII Region Behind a Cluster at z = 0.54

Abstract.

Emission line spectroscopy of stellar-photoionized nebulae (HII regions/galaxies) at high redshift is crucial for tracking the chemical evolution of galaxies at early epochs. The recognition of ‘primordial’ HII regions will be based on both the gas-phase element abundances and on the effective temperature of the ionizing stellar radiation field which is dependent on the upper stellar mass function. The desire to find and analyse the emission lines from such objects is one of the primary scientific drivers for NGST NIR spectroscopy [1] which will allow measurements to be made of the restframe optical spectrum. In addition to their obvious importance for element abundance studies, such objects offer the intriguing possibility of studying the size and mass of objects seeing perhaps their first burst of star formation. While the calibration of the relationship between HII region/galaxy emission line velocity dispersions and H$\beta$ luminosity has been carried out in the local Universe ([2] hereafter MTT, and references therein), the extension of this technique to high redshifts (and hence, presumably, low metallicities) can be of real value as a cosmological tool. This poster reports measurements of restframe UV emission line strengths and widths in an HII region at z = 3.357, lensed by a cluster at z = 0.543.