The DESI Milky Way Survey (MWS) will observe $\ge$8 million stars between $16 < r < 19$ mag, supplemented by observations of brighter targets under poor observing conditions. The survey will permit an accurate determination of stellar kinematics and population gradients; characterize diffuse substructure in the thick disk and stellar halo; enable the discovery of extremely metal-poor stars and other rare stellar types; and improve constraints on the Galaxy's 3D dark matter distribution from halo star kinematics. MWS will also enable a detailed characterization of the stellar populations within 100 pc of the Sun, including a complete census of white dwarfs. The target catalog from the preliminary selection described here is public

Aguado, DS

Blum, R

Brooks, D

Cooper, AP

Dey, A

Duan, Y

Eftekharzadeh, S

Eisenstein, DJ

Gaztañaga, E

Gänsicke, BT

Kehoe, R

Koposov, SE

Landriau, M

Lee, C-H

Levi, ME

Li, T

Manser, C

Meisner, AM

Myers, AD

Najita, J

Nidever, DL

Olsen, K

Palanque-Delabrouille, N

Poppett, C

Prada, F

Prieto, CA

Rockosi, C

Schlegel, DJ

Schubnell, M

Tarlé, G

Valluri, M

Wang, M-Y

Wechsler, RH

Yèche, C

English

UCL Discovery

Lawrence Berkeley National LaboratoryRecent WorkTitlePreliminary Target Selection for the DESI Milky Way Survey (MWS)Permalinkhttps://escholarship.org/uc/item/3np7x2zxJournalResearch Notes of the AAS, 4(10)ISSN2515-5172AuthorsPrieto, Carlos AllendeCooper, Andrew PDey, Arjunet al.Publication Date2020-10-01DOI10.3847/2515-5172/abc1dc Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaDraft version October 23, 2020Typeset using LATEX RNAAS style in AASTeX63Preliminary Target Selection for the DESI Milky Way Survey (MWS)Carlos Allende Prieto,1, 2 Andrew P. Cooper,3 Arjun Dey,4 Boris T. Gänsicke,5 Sergey E. Koposov,6, 7, 8 Ting Li,9, 10, ∗Christopher Manser,5 David L. Nidever,4, 11 Constance Rockosi,12, 13 Mei-Yu Wang,7, 14 David S. Aguado,8 Robert Blum,15David Brooks,16 Daniel J. Eisenstein,17 Yutong Duan,18 Sarah Eftekharzadeh,19 Enrique Gaztañaga,20, 21 Robert Kehoe,22Martin Landriau,23 Chien-Hsiu Lee,4 Michael E. Levi,23 Aaron M. Meisner,4 Adam D. Myers,24 Joan Najita,4 Knut Olsen,25Nathalie Palanque-Delabrouille,26 Claire Poppett,23, 27 Francisco Prada,28 David J. Schlegel,23 Michael Schubnell,29Gregory Tarlé,29 Monica Valluri,30 Risa H. Wechsler,31, 32 and Christophe Yèche261Instituto de Astrof́ısica de Canarias, Vı́a Láctea S/N, 38205 La Laguna, Tenerife, Spain2Universidad de La Laguna, Departamento de Astrof́ısica, 38206 La Laguna, Tenerife, Spain3Institute of Astronomy and Department of Physics, National Tsing Hua University, 101 Kuang-Fu Rd. Sec. 2, Hsinchu 30013, Taiwan4NSF’s NOIRLab, 950 N. Cherry Ave., Tucson, AZ 85719, USA5Department of Physics, University of Warwick, Coventry, CV4 7AL, UK6Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK7McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Ave, PA, 15213, USA8Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK9Observatories of the Carnegie Institution for Science, 813 Santa Barbara St., Pasadena, CA 91101, USA10Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA11Department of Physics, Montana State University, P.O. Box 173840, Bozeman, MT 59717-384012Department of Astronomy and Astrophysics, University of California Santa Cruz, 1156 High Street, Santa Cruz, CA, 95064, USA13University of California Observatories14Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15312, USA15Vera C. Rubin Observatory/NSF’s NOIRLab, 950 N. Cherry Ave., Tucson, AZ, 85719, USA16Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK17Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA18Physics Department, Boston University, 590 Commonwealth Avenue, Boston, MA 02215, USA19Department of Physics and Astronomy, The University of Utah, 115 South 1400 East, Salt Lake City, UT 84112, USA20Institute of Space Sciences (ICE, CSIC), 08193 Barcelona, Spain21Institut d´ Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain22Department of Physics, Southern Methodist University, 3215 Daniel Avenue, Dallas, TX 75275, USA23Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA24University of Wyoming, 1000 E. University Ave., Laramie, WY 82071, USA25Community Science and Data Center/NSF’s NOIRLab, 950 N. Cherry Ave., Tucson, AZ, 85719, USA26IRFU, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette, France27Space Sciences Laboratory, University of California, Berkeley, 7 Gauss Way, Berkeley, CA 94720, USA28Instituto de Astrofisica de Andalućıa, Glorieta de la Astronomı́a, s/n, E-18008 Granada, Spain29Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA30Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA31Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Stanford, CA 94305, USA32SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USAABSTRACTThe DESI Milky Way Survey (MWS) will observe ≥8 million stars between 16 < r < 19 mag,supplemented by observations of brighter targets under poor observing conditions. The survey willpermit an accurate determination of stellar kinematics and population gradients; characterize diffusesubstructure in the thick disk and stellar halo; enable the discovery of extremely metal-poor starsand other rare stellar types; and improve constraints on the Galaxy’s 3D dark matter distributionfrom halo star kinematics. MWS will also enable a detailed characterization of the stellar populationswithin 100 pc of the Sun, including a complete census of white dwarfs. The target catalog from thepreliminary selection described here is publica).a) Available at https://data.desi.lbl.gov/public/ets/target/catalogs/ and detailed at https://desidatamodel.readthedocs.ioarXiv:2010.11284v1  [astro-ph.GA]  21 Oct 20202Keywords: Milky Way Galaxy, Radial velocity, Stellar abundances, White dwarf starsAlthough DESI is conceived primarily as a cosmological experiment, in bright time the survey will obtain spectra ofMilky Way stars within the DESI footprint selected from the Gaia DR2 catalog (Gaia Collaboration et al. 2018) andthe DESI Legacy Imaging Surveys (LS; Dey et al. 2019). This Milky Way Survey (MWS) at Galactic latitudes |b| > 22◦will share the DESI focal plane with the Bright Galaxy Survey (BGS; Ruiz-Macias et al. 2020), using approximatelyhalf of the DESI fibers available during bright time. In addition, bright stars across the entire sky (including Galacticplane sources) will be observed in twilight and poor weather conditions.The MWS target selection is designed to be simple, inclusive, and amenable to forward modeling. It will yield anessentially magnitude-limited random sample of stars over a significant fraction of the sky that can be compared totheoretical predictions, a philosophy similar to that of the SDSS main galaxy sample. Comprised of ∼8 million sourceswith Gaia parallaxes and proper motions but fainter than the G = 16 limit of Gaia’s radial velocity spectrograph,MWS will more completely sample stellar kinematics far from the Galactic center.MWS Main SampleThe MWS Main sample will target all stars (i.e., sources of type “PSF” from LS with Gaia DR2 astromet-ric excess noise < 3 mas) in the range 16 < r < 19 mag, where r is the LS apparent r-band magnitude corrected forGalactic extinction. A small number of stars with uncorrected magnitude robs < 20 will be excluded to ensure spectraof sufficient signal-to-noise (the DESI bright-time survey footprint is mostly at high latitude, hence low extinction).Stars will be assigned to one of following three target classes based on their color and Gaia DR2 astrometry (Fig. 1).• MWS Main Blue: all stars with g − r < 0.7 mag.• MWS Main Red: stars with g − r ≥ 0.7 mag; good parallaxes (Gaia astrometric params solved = 31,parallax π < max(3σπ, 1) mas); and very small proper motion (|µ| < 7 mas/yr).• MWS Main Broad: stars with g − r ≥ 0.7 not included in MWS Main Red.For g−r < 0.7, the selection is a magnitude-limited random sampling, valuable for high-resolution kinematic studiesof the thick disc and nearby halo using turn-off stars. For g − r ≥ 0.7, the Main Red astrometric criteria exclude asignificant fraction of nearby dwarfs and hence increase the probability of targeting more distant halo giants, usefulfor studies of kinematic and stellar population gradients to ∼ 100 kpc. The Main Blue and Main Red selections areweighted equally in fiber assignment. The remaining stars are included in the Main Broad sample and assigned fibersat lower priority. The completeness and purity of the Main Red sample will be evaluated during the DESI SurveyValidation (SV) phase (a precursor to the DESI ‘main’ science survey). The magnitude, color, proper motion, andparallax limits will be adjusted, if necessary, before the survey commences. We will prioritize all known Gaia RRLyrae with 14 < G < 19 (Clementini et al. 2019), and evaluate a blue horizontal branch (BHB) star selection basedon Gaia and LS in this range.The Backup SurveyDuring poor weather and twilight conditions, when the MWS Main and BGS observations are not possible, DESIwill observe an “unbiased” bright star sample (10.5 < G < 16 mag) at declination δ ≥ −30◦. This Backup Surveyis expected to yield spectroscopic parameters, abundances, and kinematics for several million stars, creating a richresource for studies of disk stellar populations, stellar evolution, and Galactic structure.Sparse high-value targetsMWS will also include sparse (< 10 deg−2) samples of high-value targets. These will be given higher priority forfiber assignment but will not perturb the main sample selection function significantly.∗ NHFP Einstein Fellow30.0 0.5 1.0 1.5 2.0g-r [mag]0.000.250.500.751.001.251.501.752.00log 10|/(1mas/yr)|Main RedMain BlueMain Broad0.0 0.5 1.0 1.5 2.0g-r [mag]15.516.016.517.017.518.018.519.019.520.0r [mag]Main Blue Main Red + BroadFigure 1. Left: Source density as a function of g − r color and proper motion for stars in the magnitude range 16 < r < 19near the North Galactic Pole. Redward of g − r = 0.7, cuts in parallax (π < 3σπ + 1) and proper motion exclude fast-movingnearby dwarfs. Main Red and Main Blue targets are observed at equal priority and constitute the bulk of the MWS main surveysample; Main Broad targets are observed at lower priority. Right: Selection in color–magnitude space, illustrating that MainBlue targets are halo/disk main sequence turn-off (MSTO) and BHB stars, while Red/Broad targets are MW giants/dwarfs.White Dwarfs—White dwarf (WD) stars can constrain the local star formation history, the nature of SN Ia progen-itors, and the composition of exo-planetesimals. Selected following Gentile Fusillo et al. (2019), their priority will bethe highest of all bright-time targets.Stars within 100 pc—Gaia is complete for stars within 100 pc, and DESI will provide a comprehensive stellarpopulation census of the solar neighborhood. This will establish strong constraints on the initial mass function andlocal chemical evolution. Target selection: 16 ≤ G ≤ 20, π+σπ ≥ 10 mas. Stars with G < 16 are in the Backup Survey.MWS may include these additional high-value targets:Distant halo tracers—RR Lyrae, BHB and giant stars are excellent tracers of halo structure because reliable distancescan be determined for them. We will target faint (G > 19) Gaia RR Lyrae and color-selected BHBs, and use DDO51photometry over 10,000 deg2 (Slater et al. 2016) to select a sparse sample of giants.Close white dwarf binaries—Understanding the evolution of WD binaries, which include SN Ia progenitors and low-frequency gravitational wave sources, requires robust observational constraints (Toloza et al. 2019). These targets willbe selected using Gaia/GALEX data as follows: π/σπ > 5, 16 ≤ G ≤ 20, FUV + 5 log 10(π[′′]) + 5 > 1.5 + 1.28 ×(FUV −G).Cluster members—We will use proper motion to select likely members of a few bright dwarf galaxies and globularclusters out to ∼ 10 times their half-light radius. DESI is ideal for surveying the environs of such objects for signs oftidal interactions and extended halos.ACKNOWLEDGMENTSAPC is supported by the Taiwan Ministry of Education Yushan Fellowship and MOST grant 109-2112-M-007-011-MY3. SK was partially supported by NSF grants AST-1813881, AST-1909584. TSL is supported by NASA throughHubble Fellowship grant HST-HF2-51439.001. MYW acknowledges the support of the McWilliams Postdoctoral Fel-lowship. MV is supported by NASA-ATP awards NNX15AK79G and 80NSSC20K0509 and the Michigan Institute forComputational Discovery and Engineering (MICDE).This research is supported by the Director, Office of Science, Office of High Energy Physics of the DOE underContract No. DE–AC02–05CH1123, and by NERSC, a DOE Office of Science User Facility under the same contract;4additional support for DESI is provided by NSF, Division of Astronomical Sciences under Contract No. AST-0950945to the NSF’s NOIRLab; the UK STFC; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; theFrench Alternative Energies and Atomic Energy Commission (CEA); the National Council of Science and Technologyof Mexico; the Ministry of Economy of Spain, and by the DESI Member Institutions. The authors are honored to bepermitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance tothe Tohono O’odham Nation.REFERENCESClementini, G., Ripepi, V., Molinaro, R., et al. 2019, A&A,622, A60, doi: 10.1051/0004-6361/201833374Dey, A., Schlegel, D. J., Lang, D., et al. 2019, AJ, 157, 168,doi: 10.3847/1538-3881/ab089dGaia Collaboration, Brown, A. G. A., Vallenari, A., et al.2018, A&A, 616, A1, doi: 10.1051/0004-6361/201833051Gentile Fusillo, N. P., Tremblay, P.-E., Gänsicke, B. T.,et al. 2019, MNRAS , 482, 4570,doi: 10.1093/mnras/sty3016Slater, C. T., Nidever, D. L., Munn, J. A., Bell, E. F., &Majewski, S. R. 2016, ApJ , 832, 206,doi: 10.3847/0004-637X/832/2/206Toloza, O., Breedt, E., De Martino, D., et al. 2019, BAAS,51, 168. https://arxiv.org/abs/1903.04612

Preliminary Target Selection for the DESI Milky Way Survey (MWS)

https://discovery.ucl.ac.uk/10142292/1/eScholarship%20UC%20item%203np7x2zx.pdf

Preliminary Target Selection for the DESI Milky Way Survey (MWS)

Abstract

Similar works

Full text

Available Versions

UCL Discovery