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Title:
Gemini/GMOS Spectroscopy of Faint z=6 Ly-alpha Line Emitters in The Hubble Ultra Deep Field
Authors:
Bunker, Andrew J.; Stanway, E. R.; Glazebrook, K.; Abraham, R. G.; Rhoads, J.; Malhotra, S.; Crampton, D.; Colless, M.; Chiu, K.; GLARE project (Gemini Lyman-Alpha at Reionzation Era)
Affiliation:
AA(Univ. of Exeter, United Kingdom), AB(Univ. of Bristol, United Kingdom), AC(Swiburne University, Australia), AD(Univ. of Toronto, Canada), AE(Arizona State University), AF(Arizona State University), AG(Dominion Astrophysical Observatory, Canada), AH(Anglo-Australian Observatory, Australia), AI(Univ. of Exeter, United Kingdom), AJ()
Publication:
American Astronomical Society Meeting 210, #107.04; Bulletin of the American Astronomical Society, Vol. 38, p.327
Publication Date:
07/2007
Origin:
AAS
Bibliographic Code:
2007AAS...21010704B

Abstract

Redshift 6, one billion years after the Big Bang, marks the end of the reionization epoch. A crucial question is whether the UV flux from young starbursts at this redshift is sufficient to achieve this reionzation. We have used the Lyman break technique to identify candidate star-forming galaxies at this redshift in deep HST/ACS images. Using the Hubble Ultra Deep Field, we identified i-band drop-outs as faint as z(AB)=28.5mag, corresponding to unobscured star-formation rates of 1Msun/yr at z 6. Spectroscopic confirmation of this population is crucial, to guard against low-redshift interlopers (Extremely Red Objects at z 1-2 and low-mass Galactic stars) and to study the Lyman-alpha emission line properties of z 6 galaxies. We have undertaken the deepest spectroscopy yet to achieve this. The Gemini Lyman-Alpha at Reionisation Era project (GLARE) has obtained 36 hours of spectroscopy on a single GMOS slitmask from Gemini-South, with a spectral resolution of lambda/Delta(lambda) 1000. This resolving power is sufficient to see the characteristic asymmetric Lyman-alpha profile, and reject the [OII] emission line doublet from lower redshift sources. We have secured spectroscopic redshifts for the some of the faintest continuum-selected objects yet, and place tight constraints on the equivalent width of Lyman-alpha emission for much of our i-drop sample. We find that the fraction of galaxies with little or no emission is similar to that at z 3, but that the z 6 population has a tail of sources with high rest frame equivalent widths. Possible explanations for this effect include a tendency towards stronger line emission in faint sources, which may arise from extreme youth or low metallicity in the Lyman-break population at high redshift, or possibly a top-heavy initial mass

function.

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