1. Deep Radio continuum surveys
With acknowledgements to the  Wajarri Yamatji people, the traditional owners of ASKAP land
Ray Norris
Auckland SKANZ meeting, 16 Feb 2012

2. Overview Background: Radio continuum surveys
Square Kilometre Array (SKA)
The South African SKA Pathfinder (Meerkat)
The Australian SKA Pathfinder (ASKAP)
Mapping the Evolution of the Universe (EMU/MIGHTEE)
The SKA PAthfinders Continuum Survey WG (SPACS)

3. Astronomy often works in an “explorer” mode as well as a “Popperian” mode:

4. Using redshift to see back in time
Photons get stretched (redshift)
ATLAS
2dFGRS

5. Using deep surveys to understand galaxy evolution
Find a patch of dark sky free from bright stars, dust clouds, etc
Make deep images at several different wavelengths
Make a census of all galaxies within it
Sequence in age (= redshift)
Identify
different evolutionary tracks
rare but important transitional stages

6. The Hubble Deep Field South

7. Can we do this at radio wavelengths?
Because of the increasing sensitivity of radio telescopes, current radio surveys:
Can trace cosmic SFR to z>1, and AGNs to z>6
Are unaffected by dust
Are most powerful when combined with IR and optical data
Can trace the origin and evolution of galaxies over cosmic time
Explian how radio astronomy used to be a niche – now mainstream
but we really need to cross that line

8. ATLAS=Australia Telescope Large Area Survey
Slide courtesy Minnie Mao

9. SKA Pathfinders Pioneer potential SKA technology
Are powerful science-driven observatories
Examples:
ASKAP (Australia)
MeerKAT (South Africa)
LOFAR (Netherlands)
Apertif (Netherlands)
MWA (Australia)
EVLA (USA)
eMERLIN (UK)
eEVN (Europe)
stress the role of the pathfinders – bothe technology and science
will guide the science drivers (and hence design) for SKA

10. Current major 20cm surveys
SKA pathfinders
Limit of conventional radio-telescopes
note complementary – not competing

11. Current major 20cm surveys
NVSS
75% of sky
rms=450μJy
EMU
rms=10μJy
EMU+WODAN
100% of sky
Increasing area
Increasing sensitivity

12. Deep radio image of 75% of the sky (to declination +30°)
Frequency range: MHz
40 x deeper than NVSS
10 μJy rms across the sky
5 x better resolution than NVSS (10 arcsec)
Better sensitivity to extended structures than NVSS
Will detect and image ~70 million galaxies at 20cm
All data to be processed in pipeline
Images, catalogues, cross-IDs, to be placed in public domain
Survey starts 2013(?)
Total integration time: ~1.5 years ?

13. Complementary radio surveys
Westerbork-WODAN
using Apertif PAF on Westerbork telescope
will achieve similar sensitivity to EMU
will observe northern quarter of sky (δ>+30°)
well-matched to EMU
LOFAR continuum surveys
lower frequency
covering Northern half(?) of sky
valuable because yields spectral index
Meerkat-MIGHTEE
Potentially deeper over smaller area, but will be limited by confusion until Meerkat Phase II (2016?)

14. ATLAS =Australia Telescope Large Area Survey
covers 7 sq deg centred on CDFS and ELAIS-S1
has the same rms sensitivity (10μJy) as EMU
has the same resolution (10 arcsec) as EMU
expect to catalogue galaxies
Final data release early 2012 using EMU prototype tools
Slide courtesy of Minnie Mao

15. Redshift distribution of EMU sources
<z>=1.1 for SF/SB
<z>=1.9 for AGN
Based on SKADS (Wilman et al; 2006, 2008)

16. Cross-identification with other wavelengths
ATLAS 20cm
Spitzer 3.6μm

17. Cross-Identification for EMU (WG chair: Loretta Dunne, Canterbury Uni)
We plan to develop a pipeline to automate cross-IDS
using intelligent criteria
not simple nearest-neighbour
working closely with other survey groups
use all available information (probably Bayesian algorithm)
Expect to be able to cross-ID 70% of the 70 million objects
20% won’t have optical/IR ID’s
What about the remaining 10% (7 million galaxies)?

18. What about the difficult cross-IDs?

19. How did galaxies form and evolve?
Science Goals

20. Science Goals Evolution of SF from z=2 to the present day,
using a wavelength unbiased by dust or molecular emission.
Evolution of massive black holes
how come they arrived so early? How do binary MBH merge?
what is their relationship to star-formation?
Explore the large-scale structure and cosmological parameters of the Universe.
E.g, Independent tests of dark energy models
Explore an uncharted region of observational parameter space
almost certainly finding new classes of object.
Explore Diffuse low-surface-brightness radio objects
see the Melanie session yesterday
Generate an Atlas of the Galactic Plane – see Tom Franzen talk
Create a legacy for surveys at all wavelengths (Herschel, JWST, ALMA, etc)

21. Science Goal 1: measure SFR, unbiased by dust
To trace the evolution of the dominant star-forming galaxies from z=5 to the present day, using a wavelength unbiased by dust or molecular emission.
Will detect about 45 million SF galaxies to z~2
Can stack much higher
Can measure SFR unbiased by extinction

22. SFR measurable (5σ) by EMU
HyperLIRG
z=4
Arp220
z=2
Measured radio SFR does not need any extinction correction
M82
z=0.4
Milky Way
z=0.1
With 45 million SF galaxies, can stack to measure SFR to much higher z

23. Science goal 2: Trace the evolution of AGN
EMU will detect 25 million AGN, including rare objects, such as
high-z AGN
composite AGN/SF galaxies
galaxies in brief transition phases
Norris et al. 2008, arXiv:
S20cm= 9mJy
z = 0.932
L20cm= 4 x 1025 WHz-1
Other questions:
How much early activity is obscured from optical views?
Can we use trace the evolution of MBH with z?
When did the first MBH form?
How do binary MBH merge?

24. F00183-7111 (ULIRG with L=9.1012 Lo) P=6.1025 W/Hz z=0.327
1 kpc
20kpc
z=0.327
P= W/Hz
Merger of two cool spirals:
SB just turned on - AGN just turned on
radio jets already at full luminosity, boring out through the dust/gas
Almost no sign of this at optica/IR wavelengths
see Norris et al. arXiv:

25. Science Goal 3: Cosmology and Fundamental Physics
EMU
EMU (70 million galaxies) has fewer objects than DES (300 million) but samples a larger volume
=> complementary tests

26. Integrated Sachs-Wolfe Effect
From
~10°

27. Dark Energy Current error ellipse Current best value Standard ΛCDM
EMU error ellipse
See Raccanelli et al. ArXiv
“Current error ellipse” is based on Amanullah et al., 2010, ApJ, 716, 712, plus Planck data

28. Modified Gravity Current error ellipse Current best value Standard GR
EMU error ellipse
See Raccanelli et al. ArXiv

29. The future - SKA Carilli & Rawlings science book written 8 years ago
Much has changed (e.g. much of the stuff in this talk wasn’t there to be discussed 10 years ago!)
How much of this talk will still be relevant in 10 years time when SKA starts?
Current SKA Pathfinders are pathfinding science as well as technology
The questions change, but we find we need the SKA even more!

30. Challenge: difficult to get redshifts, or even optical/IR photometry

31. Solution: “statistical redshifts”
Photometric redshifts are poor-mans spectroscopic redshifts
Statistical redshifts are poor-mans photometric redshifts.
Useful if you want to know the statistical properties of a sample.
E.g. median z of EMU is 1.1
select polarised sources=> median z = 1.9
select steep-spectrum polarised source => median z =2+(?)
Radio/MIR ratio also correlates with z, so even a K-band non-detection is valauble

32. How to find out more? Join the EMU meeting on Friday:
WF 710 (on the 7th floor of the WF building. )
See the EMU description: Norris et al. PASA, 28, 215 (arXiv )
Join the EMU collaboration
Attend the next meeting of SPARCS (SKA PAthfinders Radio Continuum Survey WG) in Sydney on 30 May - 1 June (see spacs.pbworks.com)

33. SPACS: SKA PAthfinders Continuum Survey WG
Coordinating design studies and survey goals for continuum surveys on SKA pathfinders
Meerkat, ASKAP, Apertif, LOFAR, EVLA, etc.
In process of starting up

34. SPACS membership Ray Norris (ASKAP, Australia ) (chair)
Kurt van Heyden (Meerkat, South Africa)
Huub Rottgering (LOFAR, The Netherlands)
Tom Oosterloo (APERTIF, The Netherlands)
Joe Lazio (SKA, USA)
Jim Condon (EVLA, USA)
Geoff Bower (ATA, USA)
Rob Beswick (eMERLIN, UK)
+ many others
(i.e. this is an open group)

35. Coordinate development of techniques
SPACS Goals
Coordinate development of techniques
avoid duplication of effort
ensure that each project has access to best practice.
Hold cross-project discussions of science goals
cross-fertilise ideas
optimise survey strategies.
Coordinate the surveys to maximise
area
depth
location on the sky
commensality
etc

36. SPACS working groups (TBD)
Source extraction
Cross identification
Separating AGN from SF Galaxies
Cosmology
Low-surface brightness
First face-to-face meeting planned for Feb 2011
in Leiden, NL

37. Conclusion We can get transformational science from SKA Pathfinders
We can maximise the science by collaborating, not competing
Ultimately this will mean better science from the SKA itself (wherever it is built!)

38. EMU Survey Design Paper (Norris et al. , PASA, in press, http://arxiv

39. Western Australia