AAS 202nd Meeting, May 2003
Session 11 Galaxies, Cosmology and Higher Redshift Objects
Poster, Monday, May 26, 2003, 9:20am-6:30pm, West Exhibit Hall

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[11.10] Discovery of a z~6 Galaxy in the Chandra Deep Field South

A.J. Bunker, E.R. Stanway (Institute of Astronomy, Cambridge), R.S. Ellis (Caltech Astronomy), R.G. McMahon (Institute of Astronomy, Cambridge), P.J. McCarthy (OCIW)

We report the discovery of a luminous z=5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an ``i-drop'' from the GOODS public survey imaging with {\em HST}/ACS (object 3 in Stanway, Bunker & McMahon 2003, astro-ph/0302212). The large colour of (i'-z')\rm AB=1.6 indicated a spectral break consistent with the Lyman-\alpha forest absorption short-ward of Lyman-\alpha at z\approx 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08\,arcsec, so r\rm hl<0.5\,h-170\,kpc). We have obtained a deep (5.5-hour) spectrum of this z'\rm AB=24.7 galaxy with the DEIMOS optical spectrograph on Keck, and here we report the discovery of a single emission line centered on (8245±1)\,Å\ detected at 20\,\sigma with a flux of f\approx 2\times 10-17\,{\rm ergs\,cm}-2\,{\rm s}-1. The line is clearly resolved with detectable structure at our resolution of better than 55\,km\,s-1, and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman-\alpha emission from a z=5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using {\em HST} data. The velocity width (\Delta v\rm FWHM=260\,{\rm km\,s}-1) and rest-frame equivalent width (W\rm rest\rm Ly\alpha=20\,Å) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N{\scriptsize~V}\,\lambda\,1240\,Å\ emission line, and the absence of this source from the deep {\em Chandra} X-ray images. The star formation rate inferred from the rest-frame UV continuum is 33.8\,h70-2\,M\odot\,{\rm yr}-1 (\OmegaM=0.3, \Omega\Lambda=0.7). This is the most luminous starburst known at z>5. Our spectroscopic redshift for this object confirms the validity of the i'-drop selection technique of Stanway, Bunker & McMahon (2003) to select star-forming galaxies at z\approx 6.

If you would like more information about this abstract, please follow the link to http://www.ast.cam.ac.uk/~bunker/internal/CambridgeGOODS/index.html. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.

The author(s) of this abstract have provided an email address for comments about the abstract: bunker@ast.cam.ac.uk

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.