Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment. Richard Shaw

Transcription

1 Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment Richard Shaw

2 Dark Energy 45 HST Discovered Ground Discovered µ (m-m) (mag) 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)= z 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

3 Standard Candles d L (z) 2 = L/4 F Distance Modulus HST Discovered Ground Discovered (m-m) (mag) 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)= z z

4 Baryon Acoustic Oscillations Eisenstein

5 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 ] r s = Multipole moment l Z 0 Angular Size c s d 100 h 1 Mpc

6 Galaxy redshift surveys 15 h 14 h 13 h 12 h 11 h 10 h Redshift z SDSS DR7, Sanchez et al. 2012

7 2D correlation function Radial Separation / h 1 Mpc Transverse Separation / h 1 Mpc Correlation function: (r k,r? )=h (x) (x + r)i

8 Radial Separation / h 1 Mpc r s Transverse Separation / h 1 Mpc

9 0 Radial separation r s = c z H(z) r s Transverse separation r s = d A (z)

10 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 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

11 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,

12 21cm Intensity Mapping

13 Hydrogen in the Universe Dark ages Reionisation HI in galaxies

14 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 = z 10 1/2 [1 x(1 + x )] (1 + b )(1 v) apple TS T S T mk

15 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 Redshift z

16 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 Redshift z Chang et al, 2008; Wyithe and Loeb 2008

17 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,

18 Foreground Challenges Cosmological 21cm Signal ~ 1mK

19 Foreground Challenges Galaxy: up to 700K

20 A way out?

21 Canadian Hydrogen Intensity Mapping Experiment

22 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

23 CHIME Overview 100m N 80m Located at DRAO in BC Transit radio interferometer Observe between MHz 0.4 MHz spectral resolution 1280 dual pol antennas (T recv = 50K) 120 x 2 degree FoV Beam: ~120 x 2 deg N

24 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)

25 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)

26 2x2 Interferometer 30 50m

27 2x2 Interferometer

28 2x2 Interferometer Measure fourier modes in redbox (primary beam)

29 2x2 Interferometer Measure fourier modes in redbox (primary beam)

30 2x2 Interferometer Linear combinations give independent beams

31 2x2 Interferometer Each beam has noise T 4x faster, with same noise and resolution

32 5x5 Interferometer 25x faster

33 Lessons FoV (primary beam) given by size of individual elements Resolution fixed by total size of array

34 CHIME Overview 100m N 80m Located at DRAO in BC Transit radio interferometer Observe between 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

35 CHIME Overview 100m N 80m Science Goals Intensity mapping for BAOs Pulsar observations Radio transients Fully funded! Beam: ~120 x 2 deg N

36 CHIME

37 CHIME

38 Full CHIME site Pathfinder

39 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

40 BAO Forecasts Powerspectrum constraints Distance constraints

41 BAO Forecasts DVrs,fid/rs (Mpc h 1 ) full CHIME BOSS WiggleZ SDSS-II 6dFGS CHIME pathfinder BOSS Ly-a (DV/rs)/(DV/rs)fid dFGS BOSS SDSS-II WiggleZ Distance constraints Full CHIME BOSS Ly-a CHIME pathfinder z

42 CHIME Pathfinder

43 CHIME Pathfinder

44 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

45 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)

46 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: ; arxiv: Enables an efficient cleaning of foregrounds: Use covariance of data to find a statistical separation (KL Transform/SN eigenmodes) Fully treats mode mixing effects

47 Unpolarised Foreground Frequency / MHz 500 Polarised Foreground (Q) Frequency / MHz Frequency / MHz Simulated Sky d Foreground Cleaning f / degrees 0K cm Signal f / degrees 750 K 2K f / degrees 2K 140 µk Foregrounds 106 times larger than signal 140 µk

48 f / degrees 750 K 2K µk 0.5 µk 2K µk 21cm Signal f / degrees µK K 290 f / degrees 2K f / degrees 30 0 KµK 440 Polarised Foreground (Q) Frequency / MHz f / degrees Unpolarised Foreground Frequency / MHz 0K Frequency Frequency Frequency Foreground Cleaning Frequency / MHz S Foreground SimulatedFiltered Sky d f / degrees 0.5 µk 2K µk Foreground residuals significantly smaller than signal µk

49 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: