The DESI Survey Validation: Results from Visual Inspection of Bright Galaxies, Luminous Red Galaxies, and Emission-line Galaxies

Abstract

The Dark Energy Spectroscopic Instrument (DESI) Survey has obtained a set of spectroscopic measurements of galaxies to validate the final survey design and target selections. To assist in these tasks, we visually inspect DESI spectra of approximately 2500 bright galaxies, 3500 luminous red galaxies (LRGs), and 10,000 emission-line galaxies (ELGs) to obtain robust redshift identifications. We then utilize the visually inspected redshift information to characterize the performance of the DESI operation. Based on the visual inspection (VI) catalogs, our results show that the final survey design yields samples of bright galaxies, LRGs, and ELGs with purity greater than 99%. Moreover, we demonstrate that the precision of the redshift measurements is approximately 10 km s−1 for bright galaxies and ELGs and approximately 40 km s−1 for LRGs. The average redshift accuracy is within 10 km s−1 for the three types of galaxies. The VI process also helps improve the quality of the DESI data by identifying spurious spectral features introduced by the pipeline. Finally, we show examples of unexpected real astronomical objects, such as Lyα emitters and strong lensing candidates, identified by VI. These results demonstrate the importance and utility of visually inspecting data from incoming and upcoming surveys, especially during their early operation phases.

The DESI Survey Validation: Results from Visual Inspection of the Quasar Survey Spectra

“…Our basic approach and analyses follow those adopted for the galaxy surveys (Lan et al 2023) with the key difference that we only focus on the spectroscopically identified QSOs rather than using all targets. We primarily take this approach due to the excellent reliability with which our spectroscopic pipelines identify high-quality QSOs; see Table 6.…”

“…However, due to the large variety of optical spectral types identified within the QSO survey (see Section 3.1), a significant fraction of the VI effort within the QSO survey was also devoted to the spectroscopic classification of the selected targets. Consequently, this paper focuses more on the optical spectroscopic classifications of the targets than the galaxy VI paper (see Lan et al 2023) and, ultimately, calculates the performance of the QSO survey using only the spectrally classified QSOs rather than all targets.…”

“…50 Each target spectrum is evaluated using the Prospect visualization tool. 51 A more extended description of Prospect is provided in Lan et al (2023); however, the salient details relevant for an understanding of the QSO survey VI are given here. Prospect displays the unsmoothed optical spectrum and associated noise/error spectrum for each target spectrum; see Figure 1 for example spectra.…”

“…VI quality class 4: the secure identification of two or more spectral features (i.e., emission or absorption lines) indicating a confident spectroscopic redshift. Thanks to the high spectral resolution of the DESI data, the [O II]λ3727,3729 doublet can often be spectrally resolved, yielding a confident spectroscopic redshift even in the absence of no other identified features (see Figure 3 of Lan et al 2023 for an example).…”

Target Selection and Validation of DESI Quasars

“…Myers et al (2022) presents all the documentation describing the target selection pipeline. The Lan et al (2023) and Alexander et al (2022) papers describe the construction of spectroscopic truth tables based on visual inspection for the galaxies and the QSO targets, respectively.…”