DESIThe Dark Energy Spectroscopic Instrument

Ofer Lahav (UCL)on behalf of DESI:UCL & DESI:UK

1600 scientists from 82 institutions; led by LBL

New 6-lens wide-field Corrector

on Hexapod

DESI Overview

Fibre View Camera

Focal Plane Assembly

w/5000 fiber positioners

Ten thermally-controlled 3-channel Spectrographs 360-980 nm

w Fibre-fed multi-object spectrograph using Baryon Acoustic Oscillation (BAO) & Redshift Distortion to measure the expansion history of the Universe, neutrino mass, etc.

w Spectra of 35M galaxies and quasars and 10M stars over 14,000 deg2 in five years.

w 5000 robotically positioned optical fibres.

w 8 sq.deg. FOV.w Ten 3-channel spectrographs.

49 meter, 10-cable fibre run

Mayall Telescope

All-new upper ring, spider, cage

• ~35 million redshifts over 14,000 sq. degrees (baseline survey)• After commissioning in Sep 2019, Survey validation and then 5 years of

observations.

DESI Survey Strategy(‘10 times BOSS’)

2.4 million QSOs

17 million ELGs

6 million LRGs

10 million brightest galaxies

DESI Survey Area & Imaging

North: BASS g, r + MzLS— Mayall zSouth:DECALS — DECam g, r, z9000 sq. deg.

DR6: 6th public release is out, Final release DR9 expected June 2019

• 14,000 sq. degree footprint defined by low Galactic and atmospheric extinction, with three public surveys

• DESI collaboration is leading imaging surveys for DESI target selection ~1000 nights of telescope time.

DESI Science

w Bright Galaxy Survey (r < 19.5)w Clustering, Clusters, and Cross-

Correlationsw Galaxy & Quasarsw Ly-alpha forestw Milky Wayw Time Domain

UCL’s involvement Via the STFC £2.4M grant to DESI:UK8 UCL staff are Participants, each can bring 2 post-docs and unlimited number of students

w Optical corrector leads (Peter Doel and David Brooks)w Member of the DESI Executive Committee and Meetings

and Press Committees, Co-chair of the DESI Publications Policy Committee and chair of DESI:UK (Ofer Lahav)

w Co-convenor of the Lyman- alpha WG(Andreu Font Ribera);DESI motivated work on emulators of the Ly-alphaforest (Andreu Font Ribera, Hiranya Peiris, Andrew Pontzen),

w Cosmic Web statistics and data compression (Ofer Lahav) w Milky Way Science (Jay Farihi)w …

Extra slides

DESI Bright Galaxy Survey

w ~10 million galaxiesw 14K sq. deg.w r < 19.5 (median redshift z ~ 0.2)w BAO only: increases FOM by about 30%w RSD, cluster & group counts, cross-correlation with imaging surveys, modified gravity tests

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BAO

Dark Energy Survey (DES) & Dark Energy Spectroscopic Instrument (DESI)

w Modern instruments installed on old twin 4m telescopes: DES/DECam (imaging) on Blanco (Chile) and DESI(spectroscopy) on the Mayall (Kitt Peak)

w DESI emerged as a merger of the BigBOSS & DESpec proposals

w DESI follows DES funding model (£2.4M/£1.7M from STFC; most from DOE + other countries)

w DES completed 6 seasons (2019) w DESI is expected on the sky in 2019 (commissioning in Sep)w 500 sq deg overlap of DES & DESI footprintsw DECALS: DES camera (DECam) used as imaging for DESI

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Combining imaging and spectroscopy

w0

wa

−2 −1.5 −1 −0.5 0−5

−4

−3

−2

−1

0

1

2

3

4

5ee FoM = 1.6nn FoM = 0.9ee + nn FoM = 7.2ee + ne + nn FoM = 27.8

Q0Q

0(1+R

0)/2

−4 −2 0 2 4 60

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2ee MGFoM = 0.3nn MGFoM = 0.6ee + nn MGFoM = 50.1ee + ne + nn MGFoM = 112.7

• DES-like WGL + DESI-like LSS (incl. RSDs)• Assumes 5000 sq deg for each survey, • 300 million DES galaxies• 10 million DESI galaxies

Kirk, OL et al., arXiv:1307.8062

Dark Energy (W0, Wa) Mod Grav (Q, R)

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Two-parameter model:1. A Modification of Poisson's equation:2. An inequality in Newton's potentials:

In Standard GR: Q=R=1 Q,R may be z-dependent.

Example of Modified Gravity Formalism

Cosmic shear is sensitive to sum of potentials

Peculiar velocities are sensitive to the temporal

potential

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Current and plannedLarge Surveys

RPP 2017