DESpec: Key Science Goals

Ofer Lahav University College London

- DES and needs for spectroscopy per probe- The landscape of spectroscopic surveys- Improving DE FoM with DESpec+DES- DE vs. Modified Gravity with DESpec+DES- Neutrino Mass with DESpec+DES- Required calculations and challenges ahead

What will be the next paradigm shift?

• Vacuum energy (cosmological constant)?• Dynamical scalar field?

– w=p/– for cosmological constant: w = -1

• Modified Gravity?• Inhomogeneous Universe?

• What if cosmological constant after all?• Multiverse?• The Anthropic Principle?

The Landscape of Surveys2011-2020

Photometric surveys: DES*, VISTA, Pan-STARRS, HSC, Skymapper, PAU*, LSST*, …

Spetroscopic surveys: WiggleZ, BOSS, e-BOSS, BigBOSS*, DESpec*,HETDEX*, Subaru/Sumire*, VISTA/spec*, SKA, …

Space Missions: Euclid vs. WFIRST

(*) Talks at this meeting

The Dark Energy http://www.darkenergysurvey.org

The Dark Energy Survey • 4 complementary techniques:

Cluster Counts Weak Lensing Large Scale Structure Supernovae Ia

• 8-band survey 5000 deg2 grizY + JHK from VHS 300 million photometric redshifts Survey 2012-2017 (525 nights)

Blanco 4-meter at CTIO

First Light: October 2011 !

DES Science Committee

• SC chair: O. Lahav

• Large Scale Structure: E. Gaztanaga & W. Percival

• Weak Lensing: S. Bridle & B. Jain

• Clusters: T. McKay & J. Mohr

• SN Ia: J. Marriner & B. Nichol

• Photo-z: F. Castander & H. Lin

• Simulations: G. Evrard & A. Kravtsov

• Galaxy Evolution: D. Thomas & R. Wechsler

• QSO: P. Martini & R. McMahon

• Strong Lensing: L. Buckley-Geer & M. Makler

• Milky Way: B. Santiago & B. Yanny

• Theory & Combined Probes: W. Hu & J. Weller

The SC reports to the MC, chaired by DES Director J. Frieman

Photo-z – Spec-z -Dark Energy cross talk

• Approximately, for a photo-z slice:

(w/ w) = 5 (z/ z) = 5 (z/z) Ns-1/2

=> the target accuracy in w

and photo-z scatter z dictate the number of required spectroscopic redshifts

Ns =105-106

Excess power on Gpc scale: systematics or new physics?

Thomas, Abdalla & Lahav (2011)Using MegaZ-LRG (ANNz Photo-z)

Standard rulers

Redshift Distortion as a test of Modified Gravity

Guzzo et al. 2008

Credit: Chris Blake

DESpec: Spectroscopic follow up of DES

• Proposed Dark Energy Spectrometer (DESpec) • 4000–fibre $40M instrument for the 4m Blanco telescope

in Chile (same as DES) – Tom Diehl’s talk• 10 million galaxy spectra, target list from DES, starting

2017• Spectral range approx 550 to 1080nm, R=1500• DES+DESpec can improve DE FoM by several• DES+DESpec can distinguish DE from ModGrav• In the UK we submitted SoI to STFC, alongside 4 other

SoI’s on spectroscopic surveys

Possible DESpec survey strategies

• (A) 100% spectroscopic completeness of the DES galaxies to r=21 mag, with redshift precision of 50 km/sec

• (B) The above plus 50% completeness to r=22.5 mag evenly distributed over all redshifts bins (using photo-z information to distribute the target selection in redshift)

• (C) Redshift precision of ~300km/s with 100% completeness to r=22 mag

Questions presented to DES WGs

• How significant it is to have the spectroscopic follow up for your probe?

• How would the DE FoM be improved for your probe?• What other analyses can be done with spectroscopy (eg

redshift distortion, removing of intrinsic alignments for WL, galaxy properties, etc.)

• What magnitude and colour cuts, survey area and spectral resolution would be ideal for your science?

• Any other clever ideas for utilizing specroscopy?

DESpec: benefits per probe• Photo-z/spec TF: better photo-z calibration (Abdalla)• LSS: RSD and radial BAO (Percival), FoM improved by several (3-6) • Clusters: better redshifts and velocity dispersions (Gerke), FoM up

by several• WL: little improvement for FoM (as projected mass, but may help

with IA)• WL+LSS: a lot for both DE and for ModGrav (Gaztanaga, Kirk,

Bacon)• SN Ia: Spectra of host galaxies and for photo-z training, improving

FoM by 2 (Sako)• Galaxy Evolution: galaxy properties and star-formation history

(Thomas)• Strong Lensing: improved cluster mass models

•

LSS improvement with DESpec

Percival & Samushia

FoM (DESpec+DES4+II+Planck) / FoM(DES4+II+Planck) = 3 - 6

Assume for 10 million spectra over 0.2<z<1.7 (sample 1)

DES(WL) + DESpec(LSS)

10 million spectrawith uniform density over0.2 < z < 1.7

Kirk, Lahav & Bridle, in prep

Note these are sensitive to assumed priors

Deviations from standard GR?

Lensing is sensitive to the sum of potentials,while velocities respond to the temporal potential

Reyes et al. (Nature, 2010) Claimed GR is confirmed from lensing and galaxy velocities

Dark Energy vs Modifed GravityDES-like (WL, clusters, SN, BAO)

Assumed DE Assumed Mod Grav

Shapiro et al. (2010)

Combining imaging & spectroscopyto constrain modified gravity

Guzik, Jain & Takada 2009

Neutrinos decoupled when they were still relativistic, hence they wiped out structure on small scalesk > knr = 0.026 (m/1 eV)1/2 m

1/2 h/Mpc

CDM+ 1.9 eV neutrinos

CDM

hheVeV

Agarwal & Feldman 2010

Neutrino mass from MegaZ-LRG700,000 galaxies within 3.3 (Gpc/h)^3

Thomas, Abdalla & Lahav, PRL(2010)

0.05 < Total mass < 0.28 eV (95% CL)

Total Neutrino Mass DES+Planck vs. KATRIN

M< 0.1 eV M < 0.6 eV

t

Lahav, Kiakotou, Abdalla and Blake (2010) 0910.4714

Very interesting if DESpec+DES+Planck can reach 0.05eV

Calculations needed for DESpec+DES

• Standard DE FoM with careful attention to k-range, systematics and to priors, including Planck

• Modified Gravity vs. DE (new metrics needed) and neutrino mass

• Impact of spectral range and resolution on the probes• Optimal survey strategy• Quantify the benefits of same sky (phase correlations) for

DES and DESpec

* Impact of DESpec on future surveys (e.g. LSST and Euclid)

THE END

DES Synergy with VISTA(8 filters together)

500 sq deg of the DES footprint (Stripe 82 and SPT region) already observed

in J, H, K (median depth 21.0, 20.8, 20.4)

850 sq deg by March 2011

M. Banerji and R. McMahon

DES Area and Depth: Synergy with South Pole DES Area and Depth: Synergy with South Pole TelescopeTelescope

• South Pole Telescope (10m, bolometer array, 150, 250, 270 GHz):

• 2500 sq. deg. Survey (to end of 2011)

• to detect ~1,000 clusters through Sunyaev-Zel’dovich effect• Dark Energy Survey: measure photometric redshifts for these clusters to z ~ 1-1.3

Galactic Dust Map

Dark Energy Science ProgramFour Probes of Dark Energy• Galaxy Clusters

• clusters to z>1• SZ measurements from SPT• Sensitive to growth of structure and geometry

• Weak Lensing• Shape measurements of 300 million galaxies • Sensitive to growth of structure and geometry

• Large-scale Structure• 300 million galaxies to z = 1 and beyond• Sensitive to geometry

• Supernovae• 15 sq deg time-domain survey• ~3000 well-sampled SNe Ia to z ~1• Sensitive to geometry

Plus QSOs, Strong Lensing, Milky Way, Galaxy Evolution

Neutrino mass from DES:LSS & Planck

Lahav, Kiakotou, Abdalla & Blake 2010(0910.4714)

Input: M =0.24 eV

Output: M =0.24 +- 0.12 eV (95% CL)