NOAO >   Observing Info >   Approved Programs >   2009A-0253

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Proposal Information for 2009A-0253


PI: Arjun Dey, NOAO, dey@noao.edu
Address: 950 N. Cherry Ave., Tucson, AZ 85719, USA

CoI: Moire Prescott, Steward Observatory/University of Arizona
CoI: Buell Jannuzi, NOAO

Title: The Temperature, Ionization, and Metallicity of a Protogalactic Lyman Alpha `Blob'

Abstract: Strong \lya and \heii emission in the absence of strong metal lines has been proposed in the theoretical literature as a potentially unique observational signature of primordial HII regions, powered by PopIII stars. Thus far, no convincing cases of \lya+\heii emitters have been found either in \lya-emitting galaxy searches at high redshift (z>4) or in \lya emitter surveys at lower redshifts. We have discovered a large (~45 kpc) \lya nebula (a `blob') at z~1.67 which exhibits strong, spatially-extended \heii emission and very weak or absent \ciii and \civ emission. The current constraints from the detected emission lines suggests that the nebula contains very low metallicity gas (\rm log(Z/Z_\sun)<-2 to -3) and is powered by a hard ionizing continuum. Although no obvious AGN is observed in the vicinity, the discovery spectra are insufficient to determine whether the nebula is powered by an obscured AGN, very low metallicity (PopIII?) stars, or gravitational cooling radiation. We propose to map this \lya+\heii `blob' with deep optical and near-IR long-slit spectroscopy (using LRIS and NIRSPEC) in order to measure a host of diagnostic emission lines in the restframe UV and optical and put strong constraints on the temperature, ionization parameter, extinction, and metallicity of the gas. As the \underline\it first known example of a \lya+\heii emitter, this source provides a completely unique opportunity to study low metallicity gas and search for evidence of very low metallicity star formation in what may be a site of ongoing galaxy formation.


National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360



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