分类： 天文学 >> 天文学 提交时间： 2023-02-19
David M. Alexander
Tamara M. Davis
E. Chaussidon
V. A. Fawcett
Alma X. Gonzalez-Morales
Ting-Wen Lan
Christophe Yeche
S. Ahlen
J. N. Aguilar
E. Armengaud
S. Bailey
D. Brooks
Z. Cai
R. Canning
A. Carr
S. Chabanier
Marie-Claude Cousinou
K. Dawson
A. de la Macorra
A. Dey
摘要： A key component of the Dark Energy Spectroscopic Instrument (DESI) survey validation (SV) is a detailed visual inspection (VI) of the optical spectroscopic data to quantify key survey metrics. In this paper we present results from VI of the quasar survey using deep coadded SV spectra. We show that the majority (~70%) of the main-survey targets are spectroscopically confirmed as quasars, with ~16% galaxies, ~6% stars, and ~8% low-quality spectra lacking reliable features. A non-negligible fraction of the quasars are misidentified by the standard spectroscopic pipeline but we show that the majority can be recovered using post-pipeline "afterburner" quasar-identification approaches. We combine these "afterburners" with our standard pipeline to create a modified pipeline to improve the overall quasar yield. At the depth of the main DESI survey both pipelines achieve a good-redshift purity (reliable redshifts measured within 3000 km/s) of ~99%; however, the modified pipeline recovers ~94% of the visually inspected quasars, as compared to ~86% from the standard pipeline. We demonstrate that both pipelines achieve an median redshift precision and accuracy of ~100 km/s and ~70 km/s, respectively. We constructed composite spectra to investigate why some quasars are missed by the standard spectroscopic pipeline and find that they are more host-galaxy dominated (i.e., distant analogs of "Seyfert galaxies") and/or dust reddened than the standard-pipeline quasars. We also show example spectra to demonstrate the overall diversity of the DESI quasar sample and provide strong-lensing candidates where two targets contribute to a single spectrum.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Adam D. Myers
John Moustakas
Stephen Bailey
Benjamin A. Weaver
Andrew P. Cooper
Jaime E. Forero-Romero
Bela Abolfathi
David M. Alexander
David Brooks
Edmond Chaussidon
Chia-Hsun Chuang
Kyle Dawson
Arjun Dey
Biprateep Dey
Govinda Dhungana
Peter Doel
Kevin Fanning
Enrique Gaztañaga
Satya Gontcho A Gontcho
Alma X. Gonzalez-Morales
摘要： In 2021 May, the Dark Energy Spectroscopic Instrument (DESI) began a 5 yr survey of approximately 50 million total extragalactic and Galactic targets. The primary DESI dark-time targets are emission line galaxies (ELGs), luminous red galaxies (LRGs) and quasars (QSOs). In bright time, DESI will focus on two surveys known as the Bright Galaxy Survey (BGS) and the Milky Way Survey (MWS). DESI also observes a selection of "secondary" targets for bespoke science goals. This paper gives an overview of the publicly available pipeline (desitarget) used to process targets for DESI observations. Highlights include details of the different DESI survey targeting phases, the targeting ID (TARGETID) used to define unique targets, the bitmasks used to indicate a particular type of target, the data model and structure of DESI targeting files, and examples of how to access and use the desitarget code base. This paper will also describe "supporting" DESI target classes, such as standard stars, sky locations, and random catalogs that mimic the angular selection function of DESI targets. The DESI target selection pipeline is complex and sizable; this paper attempts to summarize the most salient information required to understand and work with DESI targeting data.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Samantha Youles
Julian E. Bautista
Andreu Font-Ribera
David Bacon
James Rich
David Brooks
Tamara M. Davis
Kyle Dawson
Govinda Dhungana
Peter Doel
Kevin Fanning
Enrique Gaztañaga
Satya Gontcho A Gontcho
Alma X. Gonzalez-Morales
Julien Guy
Klaus Honscheid
Vid Iršič
Robert Kehoe
David Kirkby
Theodore Kisner
摘要： Using synthetic Lyman-$\alpha$ forests from the Dark Energy Spectroscopic Instrument (DESI) survey, we present a study of the impact of errors in the estimation of quasar redshift on the Lyman-$\alpha$ correlation functions. Estimates of quasar redshift have large uncertainties of a few hundred $\text{km s}^{-1}\,$ due to the broadness of the emission lines and the intrinsic shifts from other emission lines. We inject Gaussian random redshift errors into the mock quasar catalogues, and measure the auto-correlation and the Lyman-$\alpha$-quasar cross-correlation functions. We find a smearing of the BAO feature in the radial direction, but changes in the peak position are negligible. However, we see a significant unphysical correlation for small separations transverse to the line of sight which increases with the amplitude of the redshift errors. We interpret this contamination as a result of the broadening of emission lines in the measured mean continuum, caused by quasar redshift errors, combined with the unrealistically strong clustering of the simulated quasars on small scales.
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