Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment Richard Shaw
Dark Energy 45 HST Discovered Ground Discovered µ 40 35 30 (m-m) (mag) 0.5 0.0-0.5 Binned Gold data Ω M =1.0, Ω Λ =0.0 Empty (Ω=0) Ω M =0.29, Ω Λ =0.71 high-z gray dust Evolution ~ z pure acceleration: q(z)=-0.5 w=-1.2, dw/dz=-0.5 w=-0.8, dw/dz=+0.5 ~ pure deceleration: q(z)=0.5 0.0 0.5 1.0 1.5 2.0 z 0.5 1.0 1.5 2.0 z Acceleration explained by dark energy. Negative pressure Key quantity is equation of state Controls the expansion rate: H(z) 2 m (1 + z) 3 + DE exp w(z) =p/ < 1/3 applez z 0 (1 + w(z)) dz 1+z
Standard Candles d L (z) 2 = L/4 F Distance Modulus 45 40 35 30 HST Discovered Ground Discovered (m-m) (mag) 0.5 0.0-0.5 Binned Gold data Ω M =1.0, Ω Λ =0.0 Empty (Ω=0) Ω M =0.29, Ω Λ =0.71 high-z gray dust Evolution ~ z pure acceleration: q(z)=-0.5 w=-1.2, dw/dz=-0.5 w=-0.8, dw/dz=+0.5 ~ pure deceleration: q(z)=0.5 0.0 0.5 1.0 1.5 2.0 z 0.5 1.0 1.5 2.0 z
Baryon Acoustic Oscillations Eisenstein
Baryon Acoustic Oscillations Sounds waves propagating in the early Universe. Leave acoustic peaks in the CMB Weaker imprint left in the matter distribution Gives a standard (statistical) ruler Temperature Fluctuations [µk 2 ] 10 6000 5000 4000 3000 2000 1000 0 r s = Multipole moment l 100 500 1000 90 2 0.5 0.2 Z 0 Angular Size c s d 100 h 1 Mpc
Galaxy redshift surveys 15 h 14 h 13 h 12 h 11 h 10 h 0.00 0.05 0.10 Redshift z SDSS DR7, http://www.sdss.org/ Sanchez et al. 2012
2D correlation function 140 120 Radial Separation / h 1 Mpc 100 80 60 40 20 0 0 20 40 60 80 100 120 140 Transverse Separation / h 1 Mpc Correlation function: (r k,r? )=h (x) (x + r)i
140 120 Radial Separation / h 1 Mpc 100 80 60 40 20 r s 0 0 20 40 60 80 100 120 140 Transverse Separation / h 1 Mpc
0 Radial separation r s = c z H(z) 0 0 0 0 0 0 r s 0 0 20 40 60 80 100 120 140 Transverse separation r s = d A (z)
Baryon Acoustic Oscillations 15 h 14 h 13 h Sounds waves propagating in the early Universe. 12 h 11 h Leave a weak imprint in the matter distribution 0.00 0.05 0.10 Redshift z 10 h Gives a standard (statistical) ruler Exact peak position tells you angular diameter distance and Hubble parameter at the redshift Sanchez et al. 2012
Baryon Acoustic Oscillations Shape of this curve given by expansion history/ contents of the Universe. Tells us about Dark Energy Like to be able to measure this at higher redshifts z~1-2. Optically this is difficult - the redshift desert Potentially 21cm could extend this to higher redshifts Anderson et al. 2012, http://arxiv.org/pdf/1105.2862
21cm Intensity Mapping
Hydrogen in the Universe Dark ages Reionisation HI in galaxies
Cosmological 21cm 21cm line is the transition between parallel and antiparallel spins of neutral Hydrogen The ratio between the two occupancies determines the spin temperature T S n 1 /n 0 =(g 1 /g 0 )exp( T /T S ) We can observe the contrast relative to the CMB T = 23.8 1+z 10 1/2 [1 x(1 + x )] (1 + b )(1 v) apple TS T S T mk
Galaxy Redshift Survey 15 h 14 h 13 h Detect all galaxies with high significance. 12 h Take spectra to determine redshift 11 h Only interested in large scales 10 h 0.00 0.05 0.10 Redshift z
Intensity Mapping 15 h 14 h 13 h Observe galaxies with a line transition 12 h Automatically gives redshift 11 h Don t need to resolve individual 10 h galaxies 0.00 0.05 0.10 Redshift z Chang et al, 2008; Wyithe and Loeb 2008
21cm Intensity Mapping In 21cm the frequency gives the redshift. Observe the diffuse emission from many unresolved galaxies Changes the game in telescope design: Previously: large field of view, large collecting area, large angular resolution (SKA?) Now: large field of view, large collecting area, modest angular resolution (compact arrays, single dishes). Chang, Pen, Peterson and McDonald, 2008, http://arxiv.org/pdf/0709.3672
Foreground Challenges Cosmological 21cm Signal ~ 1mK
Foreground Challenges Galaxy: up to 700K
A way out?
Canadian Hydrogen Intensity Mapping Experiment
CHIME Collaboration Kevin Bandura J-F Cliche Matt Dobbs Adam Gilbert David Hanna Juan Mena Parra Graeme Smecher Amy Tang Tom Landecker Philippe Berger Dick Bond Liam Connor Nolan Denman Peter Klages Laura Newburgh Ue-Li Pen Andre Recnick Richard Shaw Keith Vanderlinde Kendrick Smith (Perimeter) Jeff Peterson (CMU) Graeme Addison Mandana Amiri Meiling Deng Mateus Fandino Kenneth Gibbs Carolin Hofer Mark Halpern Adam Hincks Gary Hinshaw Kiyoshi Masui Kris Sigurdson Mike Sitwell Rick Smegal Don Wiebe
CHIME Overview 100m N 80m Located at DRAO in BC Transit radio interferometer Observe between 400-800 MHz 0.4 MHz spectral resolution 1280 dual pol antennas (T recv = 50K) 120 x 2 degree FoV Beam: ~120 x 2 deg N
Interlude: Transit Interferometers Traditionally interferometers emphasised high resolution observations of small fields We can turn them into high speed survey instruments. We need maximal sensitivity to large scales. Means measuring smallest fourier modes (hence many short baselines)
Interferometers Complex correlation of two feeds Z R = d 2ˆn A 2 (ˆn) e 2 iˆn u I(ˆn) For small parts of sky this is 2d Fourier mode Z R = dl dm A 2 (l, m) e 2 i(ul+vm) I(l, m)
2x2 Interferometer 30 50m
2x2 Interferometer
2x2 Interferometer Measure fourier modes in redbox (primary beam)
2x2 Interferometer Measure fourier modes in redbox (primary beam)
2x2 Interferometer Linear combinations give independent beams
2x2 Interferometer Each beam has noise T 4x faster, with same noise and resolution
5x5 Interferometer 25x faster
Lessons FoV (primary beam) given by size of individual elements Resolution fixed by total size of array
CHIME Overview 100m N 80m Located at DRAO in BC Transit radio interferometer Observe between 400-800 MHz 0.4 MHz spectral resolution 1024 dual pol antennas (T recv = 50K) 120 x 2 degree FoV 4x256 beams = 15 arcmin resolution Beam: ~120 x 2 deg N
CHIME Overview 100m N 80m Science Goals Intensity mapping for BAOs Pulsar observations Radio transients Fully funded! Beam: ~120 x 2 deg N
CHIME
CHIME
Full CHIME site Pathfinder
Survey Volume WiggleZ: 1.2 (h -1 Gpc) 3 BOSS LRG: 5.3 (h -1 Gpc) 3 Lyα: 37 (h -1 Gpc) 3 CHIME: 203 (h -1 Gpc) 3 DESI ELG: 50 (h -1 Gpc) 3 Scaled such that: area of patch=volume of survey
BAO Forecasts Powerspectrum constraints Distance constraints
BAO Forecasts DVrs,fid/rs (Mpc h 1 ) 3000 2000 1000 500 full CHIME BOSS WiggleZ SDSS-II 6dFGS CHIME pathfinder BOSS Ly-a 1.05 1.00 0.95 (DV/rs)/(DV/rs)fid1.10 0.90 6dFGS BOSS SDSS-II WiggleZ Distance constraints Full CHIME BOSS Ly-a CHIME pathfinder 0.0 0.5 1.0 1.5 2.0 2.5 z
CHIME Pathfinder
CHIME Pathfinder
CHIME Pathfinder 2x20m cylinder, 40m long First light was late 2013 Pathfinder commissioning almost finished Figure 2: The CHIME telescope consists of five parabolic, cylindrical reflectors and associa receivers and correlators. The structure is 100m 100m. Note the people in the figure, The telescope has no moving parts, and maps half of the sky every day. Observing frequency 800 to 400 MHz Observing wavelength 37 to 75 cm Redshift z 0.8 to2.5 System noise temperature 50K Beam size 0.26 to 0.52 Field of view, N-S 180 Field of view, E-W 1.3 to 2.5 Number of cylinders 5 Cylinder size 100 m 20 m Collecting area 10,000 m 2 Dual-polarization antenna spacing 31 cm Number of antennas per cylinder 256 Bandwidth of channeled outputs 1 MHz
Data Analysis Analysis is challenging: Wide field at given instant (~ 120 x 2 degrees) Effectively an all sky survey (3π sr) Data volume (>~ 1 TB/day for pathfinder) Polarisation leakage Foreground removal (> 10 6 times brighter)
m-mode transform Developed m-mode formalism Transit telescopes only (stationary noise) Naturally full sky, wide-field, and exact (no UV plane) Breaks problem into statistically independent modes (efficient) Published in arxiv:1302.0327; arxiv:1401.2095 Enables an efficient cleaning of foregrounds: Use covariance of data to find a statistical separation (KL Transform/SN eigenmodes) Fully treats mode mixing effects
Unpolarised Foreground 480 460 440 420 400 270 280 290 300 500 Frequency / MHz 500 Polarised Foreground (Q) Frequency / MHz Frequency / MHz Simulated Sky d Foreground Cleaning 480 460 440 420 400 330 340 f / degrees 0K 350 360 21cm Signal 500 480 460 440 420 400 270 280 f / degrees 750 K 2K 290 300 f / degrees 2K 140 µk Foregrounds 106 times larger than signal 140 µk
420 400 270 280 290 300 440 420 400 330 340 f / degrees 750 K 2K 480 460 440 420 420 400 270 280 290 300 500 480 460 440 420 400 330 340 350 140 µk 0.5 µk 2K 300 360 140 µk 21cm Signal 500 480 460 440 420 400 270 280 f / degrees 30 750µK K 290 f / degrees 2K f / degrees 30 0 KµK 440 Polarised Foreground (Q) Frequency / MHz 500 280 360 460 f / degrees Unpolarised Foreground 400 270 350 Frequency / MHz 0K Frequency Frequency Frequency 440 460 Foreground Cleaning Frequency / MHz S Foreground SimulatedFiltered Sky d 460 290 300 f / degrees 0.5 µk 2K 120 140 µk Foreground residuals significantly smaller than signal 120 140 µk
Summary BAOs are an alternative probe of dark energy 21cm Intensity Mapping is a promising technique for mapping the Universe and measuring BAOs - foregrounds are challenging CHIME Pathfinder is operating, full instrument starting construction early 2015 Analysis is fun! Polarised radio sky simulation and 21cm data analysis code all available at: http://github.com/radiocosmology/