Gemini/GMOS Spectroscopy of Faint z=6 Ly-alpha Line Emitters in The Hubble Ultra Deep Field
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.- Publication:
-
American Astronomical Society Meeting Abstracts #210
- Pub Date:
- July 2007
- Bibcode:
- 2007AAS...21010704B