• Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Dark Energy Spectroscopic Instrument (DESI)

  • / science /
    • science overview
    • cosmology and dark energy
    • redshifts and distance
    • mapping the universe
    • the DESI science mission
    • the DESI survey
    • imaging surveys
  • / instrument /
    • instrument overview
    • telescope
      • tohono o’odham
    • corrector
    • focal plane system
    • fiber system
    • spectrograph
    • instrument control system
    • data systems
    • bringing DESI to life
      • commissioning Instrument
      • protoDESI
  • / collaboration /
    • DESI team
    • DESI builders
    • collaborating institutions
    • sponsors
    • vendors
    • diversity, equity, and inclusion
    • collaboration policies
  • / press /
    • announcements
    • in the news
    • press releases
    • blog
    • tweets by desisurvey
    • acknowledgement statement
  • / galleries /
    • image gallery
    • videos
  • / for scientists /
    • instrument design
    • imaging data
    • target selection and survey validation
    • theory and simulations
    • other DESI science
    • all DESI papers
    • team login
    • request a DESI speaker
    • internal
  • / education & outreach /
    • meet a DESI member
    • blog
    • planetarium show
    • DESI high
    • interactive visualizations
    • swag shop

DESI Target Selection

November 4, 2020 by

Adam Myers, University of Wyoming
November 4, 2020

The Dark Energy Spectroscopic Instrument will conduct spectroscopy of truly vast numbers of cosmological and astrophysical sources. These include Bright Galaxies, Emission Line Galaxies (ELGs), Luminous Red Galaxies (LRGs), Quasars, and objects in our own Milky Way Galaxy. DESI spectra are obtained by aligning optical fibers with locations on the sky, to collect light to be analyzed by dedicated spectrographs. But, how do DESI scientists know where to place those optical fibers in the first place?

Sources for the DESI key projects are targeted using images of the sky from the DESI Legacy Imaging Surveys. The Legacy Surveys include optical photometry from dedicated campaigns with the Mayall and Bok telescopes at Kitt Peak National Observatory, near Tucson, and the Blanco telescope at Cerro Tololo Inter-American Observatory near La Serena in Chile. The Legacy Surveys also incorporate infrared imaging from the WISE and NEOWISE missions, and source detections from the Gaia survey.

When envisioning the process of finding distinct objects in the sky, it is tempting to picture a bright, extended galaxy, such as this one:

Image from the Legacy Survey Viewer, using data from DR8 at right ascension of ~217.6 deg. and declination of ~11.9. See original here. credit: Legacy Surveys / D. Lang (Perimeter Institute)

But, in truth, the vast majority of DESI targets are far less spectacular to the eye, and are selected based on properties such as their color in addition to their shape. Below is the same image from the Legacy Survey Viewer above with the targets identified with circles. You’ll see that there are many more DESI targets in this field than you might have naively expected!

Same image as above from the Legacy Survey Viewer with the targets identified. You can do this yourself by selecting “DESI Targets” in the Legacy Survey Viewer menu. credit: Legacy Surveys / D. Lang (Perimeter Institute)

To determine which of the one-and-a-half-billion or so sources in the Legacy Surveys will be the lucky few tens-of-millions targeted by DESI requires sophisticated computer algorithms to sift through sources and target objects with specific photometric properties. The publicly available software that DESI uses, which is called desitarget, comprises tens-of-thousands of lines of code and has received contributions from dozens of DESI scientists.

The DESI collaboration recently released a series of research notes detailing the currently expected targeting algorithms for the DESI five-year survey:

  • Bright Galaxies (Ruiz-Macias et al.)
  • Luminous Red Galaxies (Zhou et al.)
  • Emission Line Galaxies (Raichoor et al.)
  • Quasars (Yèche et al.)
  • Milky Way Sources (Allende Prieto et al.)

The target catalogs that correspond to these notes, which are drawn from Data Release 8 of the DESI Legacy Imaging Surveys, are publicly available here in a format described here.

Although it is a significant milestone to have the first official DESI target catalogs in-hand, the dedicated effort of the collaboration continues. The next data release of the Legacy Surveys (Data Release 9) will soon be used to optimize, refine and finalize the target catalogs for the DESI five-year survey, during a phase of the project known as Survey Validation.

Filed Under: blog

Primary Sidebar

  • Sneaking around with DESI data
  • Lightning and a lunar eclipse over Kitt Peak
  • Untangling the Cosmic Web
  • Recovery effort update two months after the Contreras Fire
  • First batch of Year 1 Key Project 1 papers
  • Contreras Fire Threatens DESI and Kitt Peak National Observatory
  • One Year and 12.8 Million Galaxy Redshifts
  • DESI on a T-shirt (and stickers of course!)
  • Selecting Targets for the DESI Survey
  • The Old is New Again: Social Distancing While Mapping the Universe
  • Congratulations to Frank Valdes
  • The DESI peculiar velocity survey
  • DESI Breaking Records
  • A DIY Guide for Upgrading Your 100 Million Dollar World Class Astronomical Instrument
  • An Upgraded DESI Returns to the Sky
  • Cosmic Cartography
  • Diversity of DESI SV Quasars
  • The Beginnings of the 3-Dimensional Map
  • What do DESI’s 5000 eyes see?
  • Plugging Away
  • DESI Begins Search for Elusive Dark Energy
  • DESI begins its “1% Survey”
  • DESI Embarks on Survey Validation
  • An Undergrad Perspective on DESI
  • Women in DESI on International Women’s Day
  • Hunting the Oxygen Doublet in Distant Galaxies
  • Congratulations to David Weinberg
  • DESI Imaging Leaves a Legacy at Infrared Wavelengths
  • DESI Target Selection
  • DESI Successfully Completes Commissioning Phase

Footer

TEAM LOGIN

twitter   instagram   facebook

Copyright © 2018 Dark Energy Spectroscopic Instrument [DESI]

Copyright © 2023 · Parallax Pro DESI on Genesis Framework · WordPress · Log in