The Square Kilometre Array (SKA), even in its first phase (SKA Phase 1, or SKA1) will be the largest ground-based astronomical facility ever built, with unprecedented sensitivity in the frequency ranges for local to highly redshifted HI, and future expansion up to 25 GHz. The range of science cases that the SKA telescopes will cater for will also be the largest of any research facility, from the Epoch of Reionization (EoR) and the Cosmic Down (CD), to tests of Einstein’s General Relativity, to finding all detectable pulsars in the Milky Way, and helping with the Cradle of Life case for Astrobiology. In this talk we will go through the different science cases, with emphasis in those with the most cosmological significance, such as EoR, CD, and probing General Relativity. (Talk presented at CosmoAndes 2018.)

1. The Square Kilometre Array
Science Cases
Juande Santander-Vela
SKA SW Systems Engineer
SQUARE KILOMETRE ARRAY
Exploring the Universewith the worlds’ largest radio telescope

2. Disclaimer!
• I’m half engineer, half astronomer
• When I play the astronomer card, I’m mostly an observational
astronomer working on the nature vs nurture debate, using
isolated galaxies, not necessarily in voids!
• The other part is very much an electronics, DSP, software and
systems engineer
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Not a cosmologist,
sorry!

3. SKA Observatory Vision
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3 sites
2 telescopes
1 observatory
Design Phase:
~ €200M; 600 scientists+engineers,
80% complete
SKA Phase 1 (SKA1)
Construction: 2019 – 2025
Construction cost cap: €674.1M
(2016 inflation-adjusted)
Operations cost: (estimate) €89M/yr
MeerKAT integrated
Observatory Development Programme
(€20M/year planned)
SKA Regional centres out of scope of
centrally-funded SKAO.
SKA Phase 2: start mid-2020s
~2000 dishes across 3500km of
Southern Africa
Major expansion of SKA1-Low
across Western Australia
>50 years lifetime!
Drives need for reliability,
and adaptability

4. SKA Organisation
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! Australia (DoI&S)
" Canada (NRC-HIA)
# China (MOST)
$ India (DAE)
% Italy (INAF)
& Netherlands (NWO)
' New Zealand (MED)
( South Africa (DST)
) Sweden (Chalmers)
* UK (BEIS/STFC)
In discussion with:
+ Germany
, France
- Portugal
. Spain
/ Switzerland
0 Japan
1 South Korea
In the process of
becoming an Inter-
Governmental
Organisation

5. SKA1 Design Consortia
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6. SKA1-Low locations
1600 km
N
➤
➤
N
Data SIO, NOAA, U.S. Navy, NGA, GEBCO
Data SIO, NOAA, U.S. Navy, NGA, GEBCO
Image Landsat / Copernicus
Image Landsat / Copernicus
SKA1-Mid locations
500 km
N
➤
➤
N
Image Landsat / Copernicus
Image Landsat / Copernicus
Data SIO, NOAA, U.S. Navy, NGA, GEBCO
Data SIO, NOAA, U.S. Navy, NGA, GEBCO
SKA1 Sites
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7. SKA Sites: RFI
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SMOS L-band (1-2 GHz)

8. SKA1 Telescopes
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SKA1-LOW: 50 – 350 MHz
Phase 1: ~130,000 antennas
across 65km
SKA1-Mid: 350 MHz – 24 GHz
Phase 1: 200 15-m dishes
across 150 km
More information to
be provided by
SKA Design’s talk

9. What science does the
SKA cater for?
Exploring the Universewith the worlds’ largest radio telescope

10. 1991ASPC...19..428W
SKA: The Hydrogen Array
Early concept stated in in 1990 by
P.N. Wilkinson
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https://ui.adsabs.harvard.edu/#abs/1991ASPC...19..428W/abstract

11. 1991ASPC...19..428W
SKA: The Hydrogen Array
Early concept stated in in 1990
Core science already established:
• Neutral Hydrogen from z=1 to 10
• Continuum at 0.1 µJy 1σ noise level
• Pulsar searches and timing across the
galaxy
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https://ui.adsabs.harvard.edu/#abs/1991ASPC...19..428W/abstract

12. Two volumes,
135 Chapters,
2000 pages
The Current SKA Science Book
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8.8 kg!

13. Two volumes,
135 Chapters,
2000 pages
The Current SKA Science Book
Exploring the Universewith the worlds’ largest radio telescope
https://www.skatelescope.org/
books/
https://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=215

14. SKA1 SKA2
The Cradle of Life &
Astrobiology
Proto-planetary disks; imaging inside the snow/ice line
(@ < 100pc), Searches for amino acids.
Proto-planetary disks; sub-AU imaging (@ < 150 pc), Studies
of amino acids.
Targeted SETI: airport radar 10^4 nearby stars. Ultra-sensitive SETI: airport radar 10^5 nearby star, TV ~10
stars.
Strong-field Tests of
Gravity with Pulsars
and Black Holes
1st detection of nHz-stochastic gravitational wave
background.
Gravitational wave astronomy of discrete sources: constraining
galaxy evolution, cosmological GWs and cosmic strings.
Discover and use NS-NS and PSR-BH binaries to provide
the best tests of gravity theories and General Relativity.
Find all ~40,000 visible pulsars in the Galaxy, use the most relativistic
systems to test cosmic censorship and the no-hair theorem.
The Origin and
Evolution of Cosmic
Magnetism
The role of magnetism from sub-galactic to Cosmic Web
scales, the RM-grid @ 300/deg2.
The origin and amplification of cosmic magnetic fields, the RM-
grid @ 5000/deg2.
Faraday tomography of extended sources, 100pc
resolution at 14Mpc, 1 kpc @ z ≈ 0.04.
Faraday tomography of extended sources, 100pc resolution
at 50Mpc, 1 kpc @ z ≈ 0.13.
Galaxy Evolution
probed by Neutral
Hydrogen
Gas properties of 10^7 galaxies, z ≈ 0.3, evolution to z ≈ 1,
BAO complement to Euclid.
Gas properties of 10^9 galaxies, z ≈ 1, evolution to z ≈ 5,
world-class precision cosmology.
Detailed interstellar medium of nearby galaxies (3 Mpc) at
50pc resolution, diffuse IGM down to N_H < 10^17 at 1 kpc.
Detailed interstellar medium of nearby galaxies (10 Mpc) at
50pc resolution, diffuse IGM down to N_H < 10^17 at 1 kpc.
Headline SKA Science (1/2)
Exploring the Universewith the worlds’ largest radio telescope

15. SKA1 SKA2
The Cradle of Life &
Astrobiology
Proto-planetary disks; imaging inside the snow/ice line
(@ < 100pc), Searches for amino acids.
Proto-planetary disks; sub-AU imaging (@ < 150 pc), Studies
of amino acids.
Targeted SETI: airport radar 10^4 nearby stars. Ultra-sensitive SETI: airport radar 10^5 nearby star, TV ~10
stars.
Strong-field Tests of
Gravity with Pulsars
and Black Holes
1st detection of nHz-stochastic gravitational wave
background.
Gravitational wave astronomy of discrete sources: constraining
galaxy evolution, cosmological GWs and cosmic strings.
Discover and use NS-NS and PSR-BH binaries to provide
the best tests of gravity theories and General Relativity.
Find all ~40,000 visible pulsars in the Galaxy, use the most relativistic
systems to test cosmic censorship and the no-hair theorem.
The Origin and
Evolution of Cosmic
Magnetism
The role of magnetism from sub-galactic to Cosmic Web
scales, the RM-grid @ 300/deg2.
The origin and amplification of cosmic magnetic fields, the RM-
grid @ 5000/deg2.
Faraday tomography of extended sources, 100pc
resolution at 14Mpc, 1 kpc @ z ≈ 0.04.
Faraday tomography of extended sources, 100pc resolution
at 50Mpc, 1 kpc @ z ≈ 0.13.
Galaxy Evolution
probed by Neutral
Hydrogen
Gas properties of 10^7 galaxies, z ≈ 0.3, evolution to z ≈ 1,
BAO complement to Euclid.
Gas properties of 10^9 galaxies, z ≈ 1, evolution to z ≈ 5,
world-class precision cosmology.
Detailed interstellar medium of nearby galaxies (3 Mpc) at
50pc resolution, diffuse IGM down to N_H < 10^17 at 1 kpc.
Detailed interstellar medium of nearby galaxies (10 Mpc) at
50pc resolution, diffuse IGM down to N_H < 10^17 at 1 kpc.
Headline SKA Science (1/2)
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16. SKA1 SKA2
The Transient
Radio Sky
Use fast radio bursts to uncover the missing "normal"
matter in the universe.
Fast radio bursts as unique probes of fundamental
cosmological parameters and intergalactic magnetic fields.
Study feedback from the most energetic cosmic explosions
and the disruption of stars by super-massive black holes.
Exploring the unknown: new exotic astrophysical phenomena
in discovery phase space.
Galaxy Evolution
probed in the Radio
Continuum
Star formation rates (10 M_Sun/yr to z ~ 4). Star formation rates (10 M_Sun/yr to z ~ 10).
Resolved star formation astrophysics (sub-kpc active
regions at z ~ 1).
Resolved star formation astrophysics (sub-kpc active regions
at z ~ 6).
Cosmology & Dark
Energy
Constraints on DE, modified gravity, the distribution & evolution
of matter on super-horizon scales: competitive to Euclid.
Constraints on DE, modified gravity, the distribution &
evolution of matter on super-horizon scales: redefines state-
of-art.
Primordial non-Gaussianity and the matter dipole: 2x
Euclid.
Primordial non-Gaussianity and the matter dipole: 10x
Euclid.
Cosmic Dawn and the
Epoch of Reionization
Direct imaging of EoR structures (z = 6-12). Direct imaging of Cosmic Dawn structures (z = 12-30).
Power spectra of Cosmic Dawn down to arcmin scales,
possible imaging at 10 arcmin.
First glimpse of the Dark Ages (z > 30).
Headline SKA Science (2/2)
Exploring the Universewith the worlds’ largest radio telescope

17. SKA1 SKA2
The Transient
Radio Sky
Use fast radio bursts to uncover the missing "normal"
matter in the universe.
Fast radio bursts as unique probes of fundamental
cosmological parameters and intergalactic magnetic fields.
Study feedback from the most energetic cosmic explosions
and the disruption of stars by super-massive black holes.
Exploring the unknown: new exotic astrophysical phenomena
in discovery phase space.
Galaxy Evolution
probed in the Radio
Continuum
Star formation rates (10 M_Sun/yr to z ~ 4). Star formation rates (10 M_Sun/yr to z ~ 10).
Resolved star formation astrophysics (sub-kpc active
regions at z ~ 1).
Resolved star formation astrophysics (sub-kpc active regions
at z ~ 6).
Cosmology & Dark
Energy
Constraints on DE, modified gravity, the distribution & evolution
of matter on super-horizon scales: competitive to Euclid.
Constraints on DE, modified gravity, the distribution &
evolution of matter on super-horizon scales: redefines state-
of-art.
Primordial non-Gaussianity and the matter dipole: 2x
Euclid.
Primordial non-Gaussianity and the matter dipole: 10x
Euclid.
Cosmic Dawn and the
Epoch of Reionization
Direct imaging of EoR structures (z = 6-12). Direct imaging of Cosmic Dawn structures (z = 12-30).
Power spectra of Cosmic Dawn down to arcmin scales,
possible imaging at 10 arcmin.
First glimpse of the Dark Ages (z > 30).
Headline SKA Science (2/2)
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18. Sensitivity comparison
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19. Survey-speed comparison
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20. Resolution comparison
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21. Simulated SKA1-Low continuum transit snap-shot dirty image at 140 MHz.
Simulated LOFAR continuum transit snap-shot dirty image at 140 MHz.
SKA1-Low vs LOFAR
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Simulated SKA1-Low continuum transit snap-shot dirty image at 140 MHz.
SKA1-Low (simulated @140 MHz) LOFAR (simulated @140 MHz)
Single SKA1-Low snap-shot compared to LOFAR-INTL snap-shot

22. SKA1-Mid vs VLA
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SKA1-Mid (simulated) VLA (A+B+C+D; simulated)
Single SKA1-Mid snap-shot compared to combination of snap-shots in each of VLA A+B+C+D

23. A selection of cases
• The Cradle of Life & Astrobiology
• Strong-field Tests of Gravity with
Pulsars and Black Holes
• The Origin and Evolution of
Cosmic Magnetism
• Galaxy Evolution probed by
Neutral Hydrogen
• The Transient Radio Sky
• Galaxy Evolution probed in the
Radio Continuum
• Cosmology & Dark Energy
• Cosmic Dawn and the Epoch of
Reionization
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24. Cradle of Life & AB
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25. Cradle of Life & AB
Proto-planetary disk
processes and
characteristic
wavelengths for different
instruments
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26. From Testi et al. “Protoplanetary disks and the dawn of planets with SKA” (2015)
SKA1-Mid Band 5

27. Cradle of Life AB
Line sensitivity simulations
The SKA1-Mid can be ~10 times
more sensitive to molecular lines
from glycine in cold pre-stellar
core (such as L1544)
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From Testi et al. “Protoplanetary disks and the dawn of planets with SKA” (2015)
SKA1-Mid Band 5

28. Pulsar science with SKA
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29. !

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38. Pulsar science with SKA
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Cumulative distribution of pulsar discoveries; the ramp on the right panel assumes a SKA first light of 2022
From Kramer and Stappers “Pulsar Science with the SKA” (2015)

39. SKA and International Pulsar
Timing Arrays (IPTA) will be
sensitive to the nanoHertz
background of gravitational
waves from supermassive
black hole binaries
(SMBHBs)
Pulsar science: GWs and PTA
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From Jansen et al. “Gravitational wave
astronomy with the SKA” (2015)

40. 0 2 4 6 8 10
Total observing time span/yr
0.0
0.2
0.4
0.6
0.8
1.0
Fraction
of
simulations
IPTA
Background
Single source
Any detection
0 2 4 6 8 10
Total observing time span/yr
0.0
0.2
0.4
0.6
0.8
1.0
Fraction
of
simulations
SKA1 − 50%
Background
Single source
Any detection
0 2 4 6 8 10
Total observing time span/yr
0.0
0.2
0.4
0.6
0.8
1.0
Fraction
of
simulations
SKA1 (BD)
Background
Single source
Any detection
0 2 4 6 8 10
Total observing time span/yr
0.0
0.2
0.4
0.6
0.8
1.0
Fraction
of
simulations
SKA2
Background
Single source
Any detection
0 2 4 6 8 10
Total observing time span/yr
0
2
4
6
8
10
S/N
SKA1 (BD)
Background
Single source
0 2 4 6 8 10
Total observing time span/yr
0
10
20
30
40
50
S/N
SKA2
Background
Single source
With 50% of SKA1-Mid, only after 10
years there will be signs of detection
with 50% chance; full SKA1 reaches
50% for any event in ~4 years, and
full SKA2 in less than two years.
GW detection probability
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From Jansen et al. “Gravitational wave astronomy with
the SKA” (2015)

41. Cosmology Dark Energy
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42. Cosmology Dark Energy
• SKA2 is the end game: the mythical billion galaxy survey
• Santos et al. “Cosmology from a SKA HI intensity mapping survey” (2015):
«All-sky neutral hydrogen (HI) intensity mapping surveys that do not detect
individual galax- ies but only the integrated HI emission of galaxies in each
pixel, together with very accurate redshifts at each tomographic
slice.» → large-scale structure tomography
• Jarvis et al. “Cosmology with SKA Radio Continuum Surveys” (2015): «All-
sky radio continuum surveys that detect radio galaxies through their total
emission out to very high redshift.» → probe of large-scale structure
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Make SKA1 competitive

43. Camera, Harrison, Bonaldi, Brown
Weak Lensing
• Extensive simulations by the Manchester group
• SKA1 continuum weak lensing is competitive with
DES (auto/cross-corr)
• Radio x optical weak lensing cross-correlation is a
powerful way of removing important systematics
(hard to trust DES/LSST weak lensing results
without SKA1!)
• Bayesian approach allows to extract a large number
of redshifts using the HI line in combination with
continuum information (Harrison et al.)
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44. Cosmic Dawn EoR
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45. Cosmic Dawn EoR
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From Koopmans et al. “The Cosmic Dawn and Epoch of Reionization with the Square Kilometre Array” (2015)
“When was the last time your
baryons did something
interesting?”
Sangeeta Malhotra

46. Cosmic Dawn EoR
• Cosming Dawn and EoR go from z ~ 6 to z ~ 30 (350 MHz to 50 MHz)
→ SKA1‑Low range
• Observing strategies:
• Direct imaging (a.k.a. tomography) of neutral hydrogen down to the 1σ ≈ 1mK
brightness temperature level on 5-arcmin scales at z ≈ 6, rising to degree scales at
z=28.
• Statistical (including power-spectrum) methods to variance levels 1σ ≈ 0.01 − 1
mK2 over the redshift regime z=6-28, respectively, at k0.1 Mpc−1 and to k1 Mpc−1
at z 15.
• 21-cm absorption line observations against high-z radio sources, if present, with
1- 5 kHz spectral resolution (2-10 km/s at z=10) with S/N5 on 1 mJy.
Exploring the Universewith the worlds’ largest radio telescope
All of them require control of
thermal noise only possible
with SKA1-Low

47. Cosmic Dawn EoR
• Deep survey
• 1000hr integrations on 5 separate 20-square degree windows
→ 100 square-degrees
• 50-200MHz frequency range with 0.1 MHz spectral resolution
(150 MHz bandwidth, ~1500 channels)
• SKA1-Low multi-beaming can allow this to be done in 2500h with 2
beams (up to 300 MHz bandwidth; makes the two beams identical)
Exploring the Universewith the worlds’ largest radio telescope

48. Cosmic Dawn EoR
• Medium+Shallow Survey
• Medium survey: 50 times 100-hr integrations covering 1,000 square
degrees
• Shallow survey: 500 times 10-hour integrations covering 10,000 square
degrees; precedes the medium survey to select targets
• 50-200MHz frequency range with 0.1 MHz spectral resolution
(150 MHz bandwidth, ~1500 channels)
• SKA1-Low multi-beaming can allow this to be done in 2500h with 2
beams (up to 300 MHz bandwidth; makes the two beams identical)
Exploring the Universewith the worlds’ largest radio telescope

49. Cosmic Dawn EoR
• 21-cm absorption survey
• 21-cm absorption line spectra from (rare) radio sources at z 6 — probes very
small scales (i.e. k ∼ 1000 Mpc−1) or virialized structures (mini-haloes)
• state, thermal history and chemistry of the IGM, study the first stars, black
holes and galaxies and constrain cosmology, the physics of dark matter and
gravity.
• Deep 1000-hrs integrations on selected sources with a flux of 1 mJy
(selected from Deep Survey fields)
• 1-5 kHz resolution (requires more than 64k channels) over the 50-200 MHz
frequency range (z ∼ 6 − 28).
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50. How will science data
get to scientists?
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51. SKA Regional Centres
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52. SKA
Observatory
SRC 1
SRC 2
SRC n
SRC 3
SKA Regional Centre Alliance
Users
SRC
Science
Gateway
Exploring the Universewith the worlds’ largest radio telescope
SKA Regional Centres
• Collaborative alliance
• Transparent and location agnostic
interface to SRCs for users
• SKA users should not care where
their data products are
• All SKA users should be able to
access their data products,
irrespective of whether their country
or region hosts a regional centre

53. SKA
Observatory
SRC 1
SRC 2
SRC n
SRC 3
SKA Regional Centre Alliance
Users
SRC
Science
Gateway
Exploring the Universewith the worlds’ largest radio telescope
SKA Regional Centres
• SKA Regional Centres (SRCs) will
host the SKA science archive
• Provide access and distribute data
products to users
• Provide access to compute and
storage resources
• Provide analysis capabilities
user support
• Multiple regional SRCs, locally
resourced and staffed

54. Conclusion
SKA1 telescopes will provide
transformational science
• Even after re-baselining and cost-
control project, SKA1 telescopes
will provide unprecedented
sensitivity, resolution, and survey
speed (with low thermal noise)
• Will provide both PI and KSP
science
• SKA time will be allocated mostly
to KSPs, and PIs of member
countries
• Many KSPs fall in cosmology field
• SKA time will be allocated to
those who contribute to both
construction and operations
• An amount of time will be
devoted to open-skies!
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55. Thanks!
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SQUARE KILOMETRE ARRAY
j.santander-vela@skatelescope.org