Computer Science
Scientific paper
Feb 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009noao.prop..253d&link_type=abstract
NOAO Proposal ID #2009A-0253
Computer Science
Scientific paper
Strong Lyα and He II 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 Lyα+He II emitters have been found either in Lyα-emitting galaxy searches at high redshift (z>4) or in Lyα emitter surveys at lower redshifts. We have discovered a large ( 45 kpc) Lyα nebula (a `blob') at z 1.67 which exhibits strong, spatially-extended He II emission and very weak or absent C III and C IV emission. The current constraints from the detected emission lines suggests that the nebula contains very low metallicity gas (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 Lyα+He II `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 first known example of a Lyα+He II 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.
Dey Arjun
Jannuzi Buell
Prescott Moire
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