2019/12/16 Observational Cosmology Workshop@Tohoku U.

SKA Cosmology
Daisuke Yamauchi
Kanagawa University

SQUARE KILOMETRE ARRAY➢ Collecting area ： 1 km2➢ Frequency range： 50MHz-30GHz (cm-m; radio frequency)➢ Instrument：・LOW → 1,000,000 dipole antennas
・MID → 2,500 15m diameter dishes➢ Baseline: 200km(LOW), 3,500km(MID)➢ Place： South Africa(MID), Australia(LOW)SKA-LOW(ν<350MHz)

SKA-MID2(ν>350MHz)

Movies from presentation by R. Brown (Science Director, SKAO)SKA Phase 1(2019 – 2028)
Phase 1:130,000 antennas(512stations*256antennas)
across 80km of Australia

Phase 1:200 dishes across 150km
of Southern Africa

Phase 2:
1,000,000 antennas across
200km of Australia(2028 – )Phase 2:2,500 dishes across
3500km of Southern Africa(2028 – )

Scientific goals of SKA
The SKA aims to solve some of the biggest questions.
◆ Fundamental physics : Gravity, Dark Energy,
Cosmic Magnetism◆ Astrophysics : Cosmic Dawn, First galaxies,galaxy assembly and evolution, +…

？

◆ The unknowns : transients + ...

Dark Energy

Cosmic Dawn

MagnetismGalaxy &Transients

Gravity

SKA schedule2022

2019

2027

2030

NOW

Early science (KSP)
Science run[ Cost~50M€/yr ]Phase-1

Construction[ Cost~650M€ ]Precursors

Phase-2

MeerKAT(South Africa)
ASKAP(Australia)
MWA(Australia)
LOFAR(Europe)

2025

Construction[ Cost~1500M€ ]SKA Science Book/Red Book
◆ SKA Science Book [2015]

https://www.skatelescope.org/books/

135 Chapters, 1200 Contributors, 2000 Pages!
◆ Red Book
[Bacon+DY+(2018)]

Contributions fromJapanese community➢ SKA-Japan Consortium◆ SKA-Japan SKA Science Book
[2015, 2020(in prep!)]◆ Review (in English) [DY+(2016)]

http://ska-jp.org/ws2015/SKA-JP/talks/SKAJP_Science_Book_2015.pdf

Plan
1. Introduction

2. SKA Cosmological Surveys
3. SKA Cosmology
3.1 Dark Energy
3.2 Inflation

Why “radio” frequency?
◆Hyperfine transition radiation of neutral hydrogen：21cm line
wavelength λ = 21 cm( ν=1.4GHz : radio freq )

pe

1S

p

5.9×10-6eV

Hyperfine structuree

Why “radio” frequency?
21cm line
observations

Spatial distribution of
IGM/galaxies indark age/structure formation= Information of growth!

Dark AgeHI mainly lives
in IGM.

Formation epoch
HI mainly lives
in galaxies.

➢ HI [21-cm] line survey◆ The redshifting of HI-line provides the redshift information.

✓ HI galaxy redshift survey• The 3D matter distributions can be reconstructed.

✓ Mid-freq HI intensity mapping [after CD/EoR]• The detection of individual galaxies is not required.
• The integrated HI intensity of several galaxies in one pixel is measured.

✓ Low-freq HI intensity mapping [before CD/EoR]• Measure the large-scale distributions of the HI inside the IGM via
the brightness temperature.

➢ Radio continuum survey• Measures galaxy synchrotron radiation radio emissions, which isadvantageous in detecting high-z galaxies.
• Provides a featureless spectrum → The redshift info is not available.

SKA
PhaseredshiftSky
coverage

GalaxynumberPhase-1z<0.8

1/8~ 107(gal)Phase-2z<2

3/4~ 109

HI[21cm line]

HI intensity
mapping survey(MID-IM)

Phase-1z<3z<3.7

3/4
3/4

---

HI
[21cm line]

HI intensity
mapping survey(LOW-IM)

Phase-1

3<z<273<z<27

1/40
3/4

---

Synchrotron
radiation

Continuumsurvey(conti)Phase-1z<6z<63/4
3/4~ 108~ 109

Opticale.g. Euclidz<2

3/8

~ 108

ObservableHI[21cm line]

SurveyHI galaxy
surveyPhase-2

Phase-2

Phase-2

S = 70(SKA1gal), 5(SKA2gal), 1(SKA1cont), 0.1(SKA2cont) [μJy]Δθ = 1(SKA1), 0.1(SKA2) [arcsec], tint = 104 [hr]SKASkyredshiftcoverage
Even phase-1 IM and Phase
RC surveys will coverObservable

Surveygalaxy large
Phase-1
the HI
extremely
survey volumez<0.8HI
surveyfull sky Phase-2
out to very high-z)!
[21cm line] (availablez<2(gal)HI[21cm line]

HI intensity
mapping survey(MID-IM)

Phase-1

HI[21cm line]

HI intensity
mapping survey(LOW-IM)

Phase-1

Synchrotron
radiation

Continuumsurvey(conti)Phase-1

Opticale.g. Euclid

Phase-2

Phase-2

Phase-2

Galaxynumber

1/8

~ 107

3/4

~ 109

z<3z<3.7

3/4
3/4

---

3<z<273<z<27

1/40
3/4

---

z<6z<6

3/4
3/4

~ 108
~ 109

z<2

3/8

~ 108

S = 70(SKA1gal), 5(SKA2gal), 1(SKA1cont), 0.1(SKA2cont) [μJy]Δθ = 1(SKA1), 0.1(SKA2) [arcsec], tint = 104 [hr]When the Phase-2 is constructed, the flux threshold will
be drastically improved
the spectropic
SKA (~5μJy), providingSkyGalaxy
Observable
Surveyredshiftsurvey of 1 billion(!) HI galaxies canbe delivered.
Phasecoverage
number7
HI galaxyPhase-1
z<0.8
1/8~
10HI
[21cm line]

survey(gal)

Phase-2z<23/4~ 109HI[21cm line]

HI intensity
mapping survey(MID-IM)

Phase-1z<3z<3.7

3/4
3/4---

HI[21cm line]

HI intensity
mapping survey(LOW-IM)

Phase-1

3<z<273<z<27

1/40
3/4---

Synchrotron
radiation

Continuum
survey(conti)

Phase-1z<6z<63/4
3/4~ 108~ 109

Opticale.g. Euclidz<23/8~ 108

Phase-2

Phase-2

Phase-2

S = 70(SKA1gal), 5(SKA2gal), 1(SKA1cont), 0.1(SKA2cont) [μJy]Δθ = 1(SKA1), 0.1(SKA2) [arcsec], tint = 104 [hr]

[Bull+ 1405.1452,SKA Science Book(BAO) (2015)]

SKA constraining power✓ gal, MID-IM : high-precision
measurement of BAO and RSD✓ LOW-IM : fluc remains linearorder even on small scales
EuclidWave number [1/Mpc]

Pgal(BAO)/Pgal(no BAO)-1✓ conti : No redshift info, but
possible to detect high-z gal

SKA1 (gal)

SKA1 (MID-IM)

SKA2 (gal)

Wave number [1/Mpc]

[SKA Phase 1 Science Priority Outcomes]

A Key Science with SKA➢List of highest priority SKA1 science“Constraints on primordial non-Gaussianity andtests of gravity on super-horizon scales”＝ “Inflation & Dark Energy”

Plan
1. Introduction

2. SKA Cosmological Surveys
3. SKA Cosmology
3.1 Dark Energy
3.2 Inflation

How do we characterize Dark Energy?
◆Expansion historyEquation-of-state◆Growth of large-scale structure : δ=δρ/ρ
Growth index

[SKA Cosmology Red Book(2018), Bull(2016)]

Error on Hubble parameter σH/H

Cosmic expansion rate [BAO]
LOW-IM [LOW]gal [B2]
HETDEX gal
MID-IM [B1]
MID-IM[B2]

Euclid gal(SKA2 gal)

Redshift z

[SKA Cosmology Red Book(2018), Bull(2016)]

Growth rate [RSD]
Error on growth rate σfσ8/fσ8Current obs.

LOW-IM [LOW]gal [B2]
MID-IM [B1]
MID-IM [B2]HETDEX gal

Euclid gal(SKA2 gal)

Redshift zz
赤方偏移[Planck XIV(2013)]

Dark Energy Equation-of-State[Planck XIV(2013)]

Dark Energy Equation-of-State

SKA2(HIgal)
宇宙項SKA1(MID-IM[B1])
SKA1(MID-IM[B2])

The SKA1 MID-IM survey will be able to provide
comparable constraints with e.g. Euclid, and the SKA2 HI
galaxy survey is expected to allow further improvements.

[Bull(2016), SKA Science Book(RSD) (2015)]

Growth index and Dark Energy◆ can trace the (linear) growth history.
◆ can distinguish and hopefully exclude the dark energy models.

Growth index

DGP braneworld
GRMassive gravityf(R) gravity
KGB gravity
Equation-of-state[Bull(2016), SKA Science Book(RSD) (2015)]

Growth index and Dark Energy◆ can trace the (linear) growth history.
◆ can distinguish and hopefully exclude the dark energy models.

Growth index

SKA1(LOW-IM)

SKA1(MID-IM[B1])
SKA2 (gal)SKA1(MID-IM[B2])BOSS

Equation-of-stateDark Energy and Scalar-Tensor Theories
 Scalar-Tensor Theories have been widely studied as analternative to the dark energy.

 GW170817+GRB 170817A gave the stringent constraint on
the speed of GW : |cGW/cEM-1|<10-15, which rules out theories
which predict a variable GW speed.
The most general framework that has been developed so far[Langlois+Saito+DY+Noui (2018)]

[Hirano+Kobayashi+DY+Yokoyama (2019)]

Growth index and Scalar-Tensor Theories“GLPV” parameter αH/(1-Ωm)◆ The precise measurement of growth of structure can provide
the severe constraint on the wide class of modified gravity.
We hunt down modified gravity by
combining this with local constraint!

Constraint fromstellar structure
BOSS:|γ-6/11|<0.1
SKA :|γ-6/11|<0.007“DHOST” parameter β1/(1-Ωm)[Gray(stellar structure):
Kobayashi+DY+(2015),
Saito+DY+(2015),
Sakstein+(2015) ][DY+Yokoyama+Tashiro (2017)]

Quasi-nonlinear Growth and Dark Energy◆ Even if wDE=-1 and γ=γGR, it is NOT necessary that our Universe
is described by ΛCDM with GR.
◆ Non-Gaussianity should be generated from nonlinear growth.

SKA1(gal)

2nd order index

SKA2 (gal)nKGB

EuclidHorndeski(wDE=-1, γ=γGR)

Growth index

2nd order index
can carry new info thatis not included in thelinear-order!

Plan
1. Introduction

2. SKA Cosmological Surveys
3. SKA Cosmology
3.1 Dark Energy
3.2 Inflation

matter overdensity δmGalaxy bias

Luminous sources should betreated as biased tracer of LSS.

δcr
Short-wavelength
perturbation
Long-wavelength
perturbation

position

fNLlocal induces scale-dependence[Dalal+Dore+Huterer+Shirokov(2008) ]◆“Rough” estimation

ΦNG = φG + fNL(φG)2Acting the Laplacian on ΦNG…

2∇ΦNG2=∇ φ2
G + 2fNLφG∇ φG +・・・∝ δNG∝δ∝ δ/k2∝δδNG ≃ (1+ 2fNLφG)δ

fNLlocal induces scale-dependence➢ Local-type PNG induces Δb∝1/k2 dependence
such that the effect dominates at very large scales:[Dalal+(2008), Desjacques+(2009)]

fNL=+100fNL=+500

fNL=-100fNL=-500[Dalal+(2008)]

fNLlocal induces scale-dependence
Pgg = (b1 + bNG(f) fNLlocal/k2)2 Pmm
Heavier galaxy
sampleLighter galaxysample[Ferremacho+(2014)]

Multi-tracer cosmology
Cosmic variance: fundamental limit to large-scale obs.
• Only a finite number of Fourier modes in our Hubble volume• Biased populations probe the same DM field → deterministic• Tracer-dependent quantities are no CV-limited [Seljak(2008)]

Tracer1

Tracer2

δ1 = (b1 + f μ2) δDM
Tracers are stochastic2δ2 = (b2 + f μ ) δDM

δ1/δ2 = (b1 + f μ2)/(b2 + f μ2)
Ratio is deterministic
Noise on MT quantities scales like shot noise→ Need high source density & large bias ratioamplitude

bhbh/blbl
Shape of CV noise is same…

Pgal,h= (bh)2PDM
Pgal,l= (bl)2PDM

PDM
wave number

Constraining fNLlocal with SKA+Euclid[DY+Takahashi+Oguri(2014)]

Constraining local PNG with SKA+Euclid[DY+Takahashi(2015)]

σ(gNL)/103=
21 [SKA1]
7.4 [SKA2]
18 [Euclid](65 [Planck])σ(τNL)=
43 [SKA1]
23 [SKA2]
62 [Euclid](2800 [Planck])[DY+Takahashi(2015)]

Confirming Suyama-Yamaguchi ineq.
Consistency relation τNL ≧((6/5)fNL)2[Suyama+T.Takahashi+S.Yokoyama+(2010), Suyama+Yamaguchi(2008),…]It is possible todetect the region
where the SYinequality is NOTsatisfied.

The region where both fNL and τNL are detected at 1σ

[DY+S.Yokoyama+K.Takahashi (2016)]

Non-local fNL with galaxy bispectrum◆ SKA can provide the galaxy higher-order correlation.
◆ Galaxy bispectrum can constrain non-local PNG.
✓ Equilateral → Sound speed✓ Orthogonal → Vacuum stateSummary➢ The SKA will be able to deliver competitive andtransformational cosmology.
➢ Other topics :Various Synergies

 With CMB observations：Delensing[Namikawa+DY+Sherwin+Nagata (2015)]

 With optical galaxy survey：Multitracer[DY+ (2014), DY+K.Takahashi(2015), DY+Yokoyama+K.Takahashi(2016)]

 With particle physics：Lepton asymmetry, ν,…
[Kohri+Oyama+Sekiguchi+T.Takahashi (2014),…]Thank you!

SKA1 Phase-1 Design Baselineにおける宇宙論サーベイ
サーベイ
MediumDeep Band2Survey

観測
掃天
時間[hr] [deg2]
10,000

5,000

赤方偏移
<0.4

サイエンス
連続線弱重力レンズ
HI銀河赤方偏移[磁場SWGとcommensal]

Wide
Band1
Survey10,000Deep
SKA1-LOW
Survey5,000

20,000 0.35-3

連続線銀河サーベイ
MID-HI強度マッピング[連続線SWGとcommensal]

100

3-6

LOW-HI強度マッピング[LOW SWGとcommensal]