High Resolution Imaging of the
Cosmic Microwave Background and
the angular power spectrum
Rafael Rebolo
Instituto de Astrofísica de Canarias
Consejo Superior de Investigaciones Científicas
and
VSA Consortium
Cavendish Lab. Cambridge
Jodrell Bank Obs.
IAC
Granada, 17 de Septiembre de 2004
JENAM
Outline
• CMB anisotropies: introduction
• VSA
• CMB mapping. Peaks in the angular power
spectrum: cosmological implications
• Methodology and Constraints on
cosmological parameters
• Conclusions
WMAP
CMB power
spectrum
High l multipoles
bring information on :
•Initial spectrum of
fluctuations
•Inflationary scenarios
• Neutrino contribution to the
matter content of the Universe
•....
Very Small Array (VSA)
•
•
•
•
•
Array of 14 conical horn
antennas located at Tenerife
HEMT based receivers
working in the range 26 - 36
GHz
Single-channel analogue
phase-switched correlator
1.5 GHz bandwidth.
Horn reflectors mounted on
a tip table. Close packing
Compact configuration
FoV 4.5 degrees. Resolution
element : 15 arcmin.
The VSA consortium
Cambridge Astrophysics Group
Mike Hobson (PI)
Mike Jones
Klaus Maisinger
Nutan Rajguru
Roger Boysen
Tony Brown
Keith Grainge( PM)
Richard Saunders
Anze Slosar
Anna Scaife
Mike Crofts
Jerry Czeres
Paul Scott
Angela Taylor
Richard Savage
Dave Titterington
Liz Waldram
Ian Northrop
Anthony Lasenby
Rüdiger Kneissl
Katy Lancaster
Guy Pooley
Roger Dace
Clive Shaw
Jodrell Bank Observatory
Richard Davis
Bob Watson
Colin Baines
Althea Wilkinson
Rod Davies
Kieran Cleary
Jason Marshall
J. P. Leahy
Clive Dickinson
Richard Battye
Eddie Blackhurst
Yasser Hafez
Instituto de Astrofísica de Canarias
Rafa Rebolo
Jose Alberto
Rubiño
Carlos
Gutierrez
Ricardo
Genova
Jose Luis
Salazar
Carmen
Padilla
The Very Small Array
Extended configuration
The Antennas
• Efficient, unblocked with a clean aperture
• Compact for close packing (small aperture)
• Low cross-coupling
• Can track independently (fringe rate tracking)
These conditions are met by conical horn
reflector antennas (CHRA).
The 90º reflector gives the antennas a
periscope-like property so they can be close
packed like organ pipes.
This can be rotated to give one dimension
of independent tracking.
Side blinders are required to block cross
Coupling
Primary beam 2 degrees FWHM ,
Synthetized beam approx. 11 arcmin
The Receivers
The amplifiers are based on the 26-36 GHz Pospieszalski
NRAO design were built and modified by Eddie Blackhurst
at the Jodrell Bank Observatory, and use unpassivated
InP HEMTs from Hughes and Fujitsu.
The bias supplies are fed from a battery pack to give
a low noise protected voltage free from switch transients
which can cause damage to the HEMTs.
Each antenna has a 4-stage (Hughes) and a 2-stage
(Fijitsu) amps. Bias conditions can be set individually
for each transistor to optimize sensitivity.
Noise temperatures of 25 K (including horn) are achieved
across the band which is flat to 1dB.
VSA
VSAExtended
Extended
Configuration
Configuration
Window function
Selection of Fields
The 7 VSA Regions
VSA1: 7 fields
α 00h19m22s δ +29º16’39”
VSA2: 7 fields
09 40 53
+31 46 21
VSA3: 7 fields
15 35 13
+42 45 05
VSA5: 3 fields
03 05 45
+27 16 35
VSA6: 3 fields
07 24 48
+55 05 00
VSA7: 3 fields
12 28 14
+53 48 25
100 µm
Fields chosen to limit Galactic and extragalactic emission by avoiding:
• Bright radio sources (>500 mJy) via NVSS and GB6
• Bright galaxy clusters via Ebeling et al. and Abell catalogues
• Diffuse galactic emission: Synchrotron (408 MHz Halslam et al 1981),
Free-free
(Hα WHAM Haffner et al 2003),
Dust
(100 µm Schlegel et al 1998)
VSA8: 7 fields
17 34 58
+40 53 07
Dickinson et al. 2004 (MNRAS in press)
Typical rms values of 5-25 microK beam-1
Comparison with WMAP
WMAP noise is 100 – 200 µK per 12.6’ pixel as compared to ~20 µK per 11’ beam in the mosaic
Before
after
subtraction of radiosources
VSA
source subtractor
Tenerife.
Before
after
subtraction of radiosources
VSA CMB angular power spectrum
(compact + extended configuration)
(two alternate binnings)
Methodology
Adiabatic models
Initial fluctuation spectrum
Running index
For slow-roll inflation to be well defined:
See e.g. (Leach & Liddle 2003)
Standard 6-parameter flat ΛCDM model
Flat
ΛCDM
model
+
Running
index
Constraints
on Running
index
Omega
matter
Broken
Power-law
models
n(k)=n1 for k<kc and n2 for k>kc
Fraction of
dark matter in
the form of
neutrinos
External priors:
• 2dF (Percival et al. 2001, 2002)
• 2df + fgas (gas fraction in dynamically relaxed
clusters of galaxies Allen et al. 2002)
• 2df+fgas+XLF (observed local X-ray luminosity
function of clusters of galaxies, Allen et al. 2003)
• 2dF+HST (Key project Freedman et al. 2001)
• 2dF+ Cosmic Shear (Hoekstra et al. 2002)
Flat Lambda CDM models
All CMB
WMAP+VSA ----WMAP
.........
Marginalized
distribution for
cosmological parameters
Non-flat Lambda CDM
External priors: 2dF + SNIa
Continuation...
General Lambda
CDM analysis
Cosmological
parameters (68
%C.L.) .
For neutrinos and R
(95% C.L.)
Rebolo et al. 2004
(MNRAS in press)
General Lambda CDM analysis
Conclusions
• In flat Lambda CDM models, VSA modifies the
limits on the cosmological parameters as compared
with those derived by WMAP, while still remaining
compatible.
•The evidence for a negative value of the running
index found with these models is much weaker
when the most general analysis (non-flat, 12
parameters) is performed.
• Upper limit on Neutrino fraction < 0.087 (95%C.L.)
Æ mν < 0.32 eV
(if the three neutrino types have equal mass)
Fig. 9
The future - Enhanced VSA
3x19-field mosaics (shallow)
1x3-field mosaic (deep)
The next step is to increase the ℓ-range further up to 2500 by using bigger carbon fibre reflectors
(55 cm diameter) and scattering the antennas to the edges of the table.
With a shallow survey with big mosaics the 4 and 5 the peaks can be investigated.
A limited deep survey can probe for the CBI excess of sources at ℓ>2000.