The Discovery of a Large Lyman-alpha+HeII Nebula at z~1.67: A Candidate Low Metallicity Region?

Abstract

We have discovered a ~45 kpc Lya nebula (or Lya ``blob'') at z~1.67 which exhibits strong, spatially-extended HeII emission and very weak CIV and CIII] emission. This is the first spatially-extended Lya+HeII emitter observed and the lowest redshift Lya blob yet found. Strong Lya and HeII-1640 emission in the absence of metal lines has been proposed as a unique observational signature of primordial galaxy formation (e.g., from gravitational cooling radiation or Population III star formation), but no convincing examples of spatially-extended Lya+HeII emitters have surfaced either in Lya-emitting galaxy surveys at high redshifts (z > 4) or in studies of Lya nebulae at lower redshifts. From comparisons with photoionization models, we find that the observed line ratios in this nebula are consistent with low metallicity gas (Z < 10^-2 - 10^-3 Z_sun), but that this conclusion depends on the unknown ionization parameter of the system. The large HeII equivalent width (~37+/-10A) and the large HeII/Lya ratio (0.12+/-0.04) suggest that the cloud is being illuminated by a hard ionizing continuum, either an AGN or very low metallicity stars, or perhaps powered by gravitational cooling radiation. Thus far there is no obvious sign of a powerful AGN in or near the system, so in order to power the nebula while remaining hidden from view even in the mid-infrared, the AGN would need to be heavily obscured. Despite the strong Lya+HeII emission, it is not yet clear what is the dominant power source for this nebula. The system therefore serves as an instructive example of how the complexities of true astrophysical sources will complicate matters when attempting to use a strong Lya+HeII signature as a unique tracer of primordial galaxy formation.

Accepted for publication in ApJ; emulateapj format, 17 pages, 7 figures, 3 tables; updated coordinates

References in corpus (17)

• Cosmological Simulations of Intergalactic Medium Enrichment from Galactic Outflows
• The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lya Emitters from z=3.1 to 5.7 in the 1 deg^2 Field: Luminosity Functions and AGN
• The Massive Hosts of Radio Galaxies Across Cosmic Time
• Spitzer's Contribution to the AGN Population
• C, N, O Abundances in the Most Metal-Poor Damped Lyman alpha Systems
• A Luminosity Function of Lyman Alpha Emitting Galaxies at Redshift 4.5
• Effects of Dust Geometry in Lyman Alpha Galaxies at z = 4.4
• Deep spectroscopy of the FUV-optical emission lines from a sample of radio galaxies at z~2.5: metallicity and ionization
• Evidence for Cold Accretion onto a Massive Galaxy at High Redshift?
• A photometric survey for Lyalpha-HeII dual emitters: Searching for Population III stars in high-redshift galaxies
• Deep Spectroscopy of Systematically Surveyed Extended Lyman-alpha Sources at z~3-5
• Metal enriched gaseous halos around distant radio galaxies: Clues to feedback in galaxy formation
• High-Resolution Submillimeter Imaging of the Ly-alpha Blob1 in SSA 22
• The Mid-Infrared Properties of X-ray Sources
• Infrared and millimetre-wavelength evidence for cold accretion within a z = 2.83 Lyman-alpha blob
• Continuum Emission by Cooling Clouds
• Physical Properties of Weak MgII Absorbers at z~2

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