Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...21010704b&link_type=abstract
American Astronomical Society Meeting 210, #107.04; Bulletin of the American Astronomical Society, Vol. 39, p.327
Astronomy and Astrophysics
Astronomy
Scientific paper
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.
Abraham Robert G.
Bunker Andrew J.
Chiu Kuenley
Colless Matthew
Crampton David
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