Probing the Redshift Desert Using the Gemini Deep Deep Survey: observing galaxy mass assembly at z>1

Abstract

The aim of the Gemini Deep Deep Survey is to push spectroscopic studies of complete galaxy samples (both red and blue objects) significantly beyond z=1; this is the redshift where the current Hubble sequence of ellipticals and spirals is already extant. In the Universe at z=2 the only currently spectroscopically confirmed galaxies are blue, star-forming and of fragmented morphology. Exploring this transition means filling the `redshift desert&#39; 1<z<2 where there is a dearth of spectroscopic measurements. To do this we need to secure redshifts of the oldest, reddest galaxies (candidate ellipticals) beyond z>1 which has led us to carry out the longest exposure redshift survey ever done: 100 ksec spectroscopic MOS exposures with GMOS on Gemini North. We have developed an implementation of the CCD ``nod & shuffle&#39;&#39; technique to ensure precise sky-subtraction in these ultra-deep exposures. At the halfway mark the GDDS now has ~36 galaxies in the redshift desert 1.2<z<2 extending up to z=1.97 and I<24.5 with secure redshifts based on weak rest-frame UV absorption features complete for both red, old objects and young, blue objects. The peak epoch of galaxy assembly is now being probed by direct spectroscopic investigation for the first time. On behalf of the GDDS team I present our first results on the properties of galaxies in the `redshift desert&#39;.