Dark Energy Spectroscopic Instrument (DESI)

DESI successfully completes commissioning phase

by

Daniel Eisenstein, Harvard University
April 2, 2020

DESI commissioning has raced forward this winter, and we have now demonstrated the key performance parameters of the instrument! Since installation, refinement of the performance of the 8 square degree corrector, high-precision (10 micron) positioning of the fibers under active feedback, accurate calibration of the spectrographs, and on-sky commissioning of the whole user interface have been demonstrated.

All of this progress culminated in the successful demonstration in March of spectroscopy with the full DESI system of many tens of thousands of survey targets.  We have observed spectra of faint galaxies and quasars with redshift distributions and spectroscopic signal-to-noise that match well to what we expected.

Here is the infrared spectrum of one of our early luminous red galaxy targets, easily revealing the distinctive Balmer-line signature of a post-starburst galaxy at an impressive redshift z= 1.286. This galaxy is magnitude 19.9 (AB) in the z-band, about a factor of 2 brighter than our planned flux limit. DESI observed this target for 45 minutes on March 15. The spectrum has been smoothed for presentation.

Unfortunately, as it is with so many around the world, the COVID-19 outbreak is forcing us to adjust our plans.  We’re taking a break from on-sky observing until it is easier for our collaboration members to travel safely to Arizona.  But we’re fortunate that this winter’s commissioning produced so much data that we can work on it, in the meantime.  DESI will be back, we hope soon, with continued momentum toward our next goal of validating the survey design.

This target was selected from the Data Release 8 of the DESI Legacy Imaging Surveys (Dey et al., AJ, 157, 168, 2019); the object is shown in the center of the small image here, formed from the g, r, and z-band images.