Elizabeth R. Stanway — Page 3

arXiv2004

Three Lyman-alpha Emitters at z approx 6: Early GMOS/Gemini Data from the GLARE Project

We report spectroscopic detection of three z~6 Lyman-alpha emitting galaxies, in the vicinity of the Hubble Ultra Deep Field, from the early data of the Gemini Lyman-$α$ at Reionisation Era (GLARE) project. Two objects, GLARE#3001 (z =5.79) and GLARE#3011 (z =5.94), are new detections and are fainter in $z'$ (z'_{AB} =26.37 and 27.15) than any Lyman break galaxy previously detected in Lyman-alpha. A third object, GLARE#1042 (z =5.83) has previously been detected in line emission from the ground; we report here a new spectroscopic continuum detection. Gemini/GMOS-S spectra of these objects, obtained using nod & shuffle, are presented together with a discussion of their photometric properties. All three objects were selected for spectroscopy via the i-drop Lyman Break technique, the two new detections from the GOODS v1.0 imaging data. The red i'-z' colors and high equivalent widths of these objects suggest a high-confidence z>5 Lyman-alpha identification of the emission lines. This brings the total number of known z>5 galaxies within 9 arcmin of the Hubble Ultra Deep Field to four, of which three are at the same redshift (z=5.8 within 2000 km/s suggesting the existence of a large-scale structure at this redshift.

astro-ph↗

arXiv2003

A star-forming galaxy at z=5.78 in the Chandra Deep Field South

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 HST/ACS (object 3 in Stanway, Bunker & McMahon 2003, astro-ph/0302212). The large colour of (i'-z')_AB=1.6 indicated a spectral break consistent with the Lyman-alpha forest absorption short-ward of Lyman-alpha at z~6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08arcsec, so r_hl<0.5kpc/h_70). We have obtained a deep (5.5-hour) spectrum of this z'(AB)=24.7 galaxy with the DEIMOS optical spectrograph on Keck, and here we report the discovery of a single emission line centred on 8245Ang detected at 20sigma with a flux of f~2E-17 ergs/s/cm^2. The line is clearly resolved with detectable structure at our resolution of better than 55km/s, 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 HST data. The velocity width Delta(v)_FWHM=260km/s and rest-frame equivalent width (W=20Ang) 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 NV1240Ang emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34M_sun/yr/h^2_70 (Omega_M=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 technique of Stanway, Bunker & McMahon (2003) to select star-forming galaxies at z~6.

astro-ph↗