1. SKA - The next steps...
An update on planning for the Square Kilometre Array:
Jan 2002: ‘Level 1 science drivers’ (unique, high-priority science) for SKA identified by ISAC working groups
July 2002: Release of seven engineering concept studies
August 2002: Aim to identify critical issues related to science/engineering/budget trade-offs (input welcome). Where are more calculations/simulations needed?
Aug/Sep 2002: ARC CoE proposal

2. The Square Kilometre Array (SKA) The next generation radio telescope
Main goals:
Large collecting area for high sensitivity (1 km2), 100x sensitivity of current VLA.
Array elements (stations) distributed over a wide area for high resolution (needed to avoid confusion at very faint flux levels).
For good uv plane coverage (especially for HI observations), stations can’t be too sparse.

3. Proposed Specifications for the SKA (SKA Technical Workshop, 1997)

4. SKA timeline
2000 ISSC formed (Europe; US; Australia, Canada, China, India)
2001 EMT, ISAC formed
2002 Concept studies, 7 designs
Agreement on technical implementation and site
2008 SKA scientific and technical proposal completed
2010 SKA construction begins
2015 SKA completed
A critical date is around the middle of this decade when a decision about the technical implementation (e.g. which antenna concept) is taken. The completion date may be mildy optimistic but who knows?

5. SKA Science Goals
“The driving ambition for this new facility… is no less than to chart a complete history of time” (Taylor & Braun 1999)
Structure and kinematics of the universe before galaxy formation
Formation and evolution of galaxies
Understanding key astrophysical processes in star formation and planetary formation
Tests of general relativity, etc.

6. HI and the Cosmic Web Where from? - diffuse galaxy halos ? SKA
Spectra of QSOs show many deep Ly-a absorption lines due to low col. density hydrogen (1016 –1017 cm-2 )
Where from?
- diffuse galaxy halos ?
- undetected low SB galaxies ?
- dwarf galaxies ?
- the “cosmic web” ?
Predicted by CDM simulations  filaments and sheets with “galaxies” in the over-dense regions
See the discussion on Large Scale Structure and Galaxy Evolution in the SKA Science Case section The specific dicussion of the Ly-alpha forest and HI is in section The present slide and further discussion below is derived from the Cote et al. poster at Berkeley 2001
Spectra of distant QSOs have revealed a large number of Lyman a absorption lines, due to absorption by foreground condensations of gas in their line-of-sight. Numerical simulations suggest that this Lyman a ‘ forest ’ emerges from the complicated structures of gaseous filaments and sheets connecting overdense regions populated by galaxies formed in the underlying dark matter potential. The background of this poster shows such a N-body simulation, from the GIF Consorium (Springel et al 2001), for a LCDM universe at z=0.84.
The absorbing material may be related to enormous diffuse HI haloes, or primordial clouds, or haloes of undetected low-surface-brightness galaxies, or dwarf galaxies. The SKA all-sky survey will reveal in emission HI gas with column density below 1017 cm-2 while a Deep Field survey will image to a column density limit of less than 1016 cm-2 . This is well within the range of HI column densities of many measured Ly a lines. For example the HST spectrum of PKS (Shull et al 1998), where several strong absorbers have NHI = (2-5)x1016 cm-2. A deep VLA image around this object detects galaxies at > 400 kpc from the line-of-sight, which, if responsible for the Lya lines, would have huge haloes. The Lya lines could also arise from intragroup gas, undetected galaxies below the mass limit, or from the putative cosmic web. The limit on HI from a 40hr VLA integration is ~1019 cm-2 . With the SKA’s 100x better sensitivity , the structure of the gas giving rise to these Ly a lines, and its connection to galaxies, will be revealed for the first time.
SKA will detect the web via HI in emission!
All-sky survey  <1017 cm-2
Deep field survey  <1016 cm-2
SKA

7. SKA sensitivities for HI
ΔV = 30 km s-1; Θ = 1” hour integration
Sensitivity: (each polarization)
s = 3.8 μJy/beam = 2.39 K
Mass Sensitivity: (5 s)
~ 1 x 106 M @ 100 Mpc
~ 4 x 108 M @ z = 1 (resolution ~ 10 kpc)
Sub-dwarf galaxies
ΔV = 300 km s-1 Θ = 1” hour integration
Sensitivity: (each polarization)
s = 1.2 μJy/beam = 0.76 K
The top box (higher velocity resolution) is most relevant to low redshift studies; the bottom box (much lower velocity resolution) to high redshift studies Note that the integration time assumed is only 8 hours. An SKA Key Programme will obtain a much longer integration time---see the discussion in the SKA Science Case section for the resulting sensitivities in a Deep SKA HI Pencil Beam Survey based on an integration time 360 hours (resulting in detection levels ~7 times fainter than those listed above).
HI Mass Sensitivity: (5 s)
~3 x 106 M @ 100 Mpc
~1.2 x 109 M @ z = 1 (resolution ~ 10 kpc)
~3 x 1010 M @ z = 4
M101-like galaxies at z=4

8. SKA’s 10 field-of-view for surveys and transient events in 106 galaxies !
SKA 20 cm
SKA 6cm
HST
15 Mpc at z = 2
ALMA
The surface density of optically detected galaxies inferred from the HDF and other deep surveys is ~1 million galaxies per square degree. With dust obscuration probably playing a major role at high redshift there may be many more still to be found.

9. Large area survey of galaxies in HI
Redshifts and HI content of distant galaxies will be
obtained for many galaxies
HI mass-based census of universe in the
simplest atomic
species…
“Shallow” survey to z~1 is complementary to the Deep HI SKA field discussed in previous slides. See the discussion in SKA Science case section Based on the Zwaan et al (1997) HI mass function expect to detect 107 galaxies in volume of ~107 Mpc3. This is orders of magnitude more than in the optical surveys e.g. 2dF and SDSS. The properties of the SKA wide field survey
Are compared to that of the optical surveys in this slide. The large number of galaxies detected makes it possible to trace the evolution of large scale structure out to z~1.3  pwerful test of
Various cosmoligical models. Note especially the ability to count clusters *****
Also use the Tully-Fisher method to derive distances independent of redshift and to probe the
Peculiar velocity field to detrmine the mass density field in the universe.
SKA will be superior to SDSS
SKA

10. Studying normal galaxies at high z
Unlike O/NIR radio is not affected by dust obscuration
In continuum, HI, OH and
H20 masers
SKA sensitivity radio
image of any object seen
in other wavebands
Continuum
Natural resolution
advantage cf. ALMA,
NGST, HST
Underpinning a main SKA science thrust in the introductory section this slide is based on a recent estimate of the star formation rate as a function of cosmic epoch – the Madau Curve – it is now believed that this underestimates the rate at high redshifts due to dust obscuration biassing our view in the optical waveband.
Neutral Hydrogen
OH megamasers
H2O masers
SKA can study the earliest galaxies in detail

11. Star formation rates in the Universe
M82 optical
Starburst galaxies e.g. M82
Radio VLBI reveals expanding supernovae through dust
Infer star birth rate from death rate rather directly
SKA: Image “M82s” to ~100Mpc : Detect “M82s” at high z
Calibrate integrated radio continuum  SFR at high z
Madau curve underestimates SFR at z>1.5
M82 VLA+ MERLIN+VLBI
M82 comprises a whole laboratory of SNR at same distance – much work to be done SNR in M82 suspected for 20 yrs, resolved 6 yrs ago, and now studied in detail. Some salient papers in the series are: Macdonald et al. MNRAS, 322,100 (2001); Pedlar et al MNRAS, 307, 761 (1999)
Muxlow et al, MNRAS, 266,455 (1994)
Countng supernova remants and measuring their sizes and expansion rates (via VLBI) – as has been done for the remants in the nearest starburst M82, allows the age of the remnants and hence their rate of formation to be determined. This is the stellar death rate for massive stars which can then be related to the stellar birth rate for all stars via a mass function (Salpeter). This is a more direct means than those based on integrated fluxes (radio, sub-mm, ir, optical) to determine the star formation rate. Current instruments (e.g. VLA,MERLIN VLBI) are not able to perform this test on very many galaxies – and hence to calibrate the integrated flux methods which can be applied at high redshift. A discussion of the derivation of the global starformation rate from the 1.4 GHz luminosity function is given by Cram, ApJ, 506, L85, (1998). Cram finds that the local SFR is
estimated to be twice that inferred from Ha studies.
SKA will be able to study many local starburst systems with the same quality of data as M82. See also the discussion in the SKA Science Case section 2.7

12. Basic design criteria:
Sensitivity alone is not enough:
hence SKA
Must be sensitive to a wide range of surface brightness
many “stations” in the array
and wide range of baselines
Comparisons made with VLA for simplicity and immediate undertanding for a typical audience. The range and extent of baselines envisaged for SKA is, of course, very much greater than in the VLA.
Must cover factor >10 frequency range
Must have wide field & ideally multiple beams
multi-user; surveying speed
and interference mitigation

13. SKA Configurations
Determining (and agreeing on) the optimum SKA configuration is a significant challenge

14. For high resolution, array stations are distributed across a continent
(M. Wieringa)

15. SKA design concepts July 2002
US ATA
Australia Luneburg Lenses
Dutch phased array
China KARST
Canada Large reflector
Australia cylindrical paraboloid
Point out that KARST and LAR involve large primary mirrors (100s metres) and hence will involve small numbers of these (small N). The US (Allen Telescope Array) has small antennas (6.2m)
and hence will involve large N as will the the Australian Luneberg lenses which will be of order 10m in diameter. The Dutch phased array concept is qualitatively different but is also a large N concept.
+India: GMRT-model dishes

16. ‘Large N, Small D’ Array (USA)
Advantages: Reaches high-freq. (34 GHz)

17. Phased arrays (Europe)
1000km
(Courtesy NFRA)

18. Phased array concept
Replace mechanical pointing, beam forming by electronic means

19. Array station of Luneberg lenses (Australia)

20. Luneburg Lens Spherical lens with variable permittivity
A collimated beam is focussed onto the other side of the sphere
Tests currently underway at ATNF/CSIRO with metre-scale prototypes. With a phased array on the back surface. This concept offers the potential of a multi-beam SKA. Problems to be overcome include dielectric losses at frequencies above a few GHz.
Beam can come from any direction

21. Large [Arecibo-like] Reflectors (China)

22. Aerostat-mounted receiver above Large Adaptive Reflector (Canada)

23. Cylindrical reflector (Australia)
Molonglo
AUSTRALIA
Brisbane
Darwin
Perth
Canberra
Hobart
Adelaide
Melbourne
Sydney +
SKAMP

24. ISAC Working Groups
1. Nearby galaxies (Chair: John Dickey, USA) Transient phenomena (Joe Lazio, USA) Early Universe, Lge-scale structure (Frank Briggs, Aust) 4. Galaxy formation (Thijs van de Hulst, NL) 5. AGN and black holes (Heino Falcke, Ger) 6. Life Cycle of stars (Sean Dougherty, Can) 7. Solar system and planetary science Intergalactic medium (Luigina Ferretti, Italy) 9. Spacecraft tracking (Dayton Jones, USA)
Current Australian ISAC members: Frank Briggs (ANU), Carole Jackson (ANU), Geraint Lewis (AAO), Elaine Sadler (Sydney)

25. ‘Level 1 Science Drivers’
Jan 2002: Each ISAC working group identified the one or two most important science goals which are unique to SKA (level 1). Level 2 drivers are second priority or not unique to SKA.
e.g. WG4 (Galaxy formation) - “Sensitive, wide-field HI 21cm and radio continuum surveys” (CO surveys, currently level 2, may be added)
Next goal for the ISAC is to study the seven concept proposals, determine to what extent they meet the requirements of the Level 1 Science Drivers, and provide feedback to proposers and EMT.

26. Some topics for discussion in Groningen (Aug 2002)
Low and high frequency limits: Only US design goes above 9 GHz. Are frequencies above 5 GHz scientifically compelling?
Multibeaming: Are fast response times (~ 1 sec) likely to be needed? Is 10 sec, or 100 sec just as useful?
Sensitivity: Does the SKA need a 106 m2 equivalent collecting area at all frequencies, or only below 1.4 GHz?
Field of View: What kind of trade-offs between field of view and bandwidth are acceptable (e.g. for HI surveys)?
Input from everyone is welcome...