Transcript
21cm cosmology Ue-‐Li Pen
K. Masui, E. Switzer, R. Shaw, L. Cailin, G. Paciga, K. Bandura, J. Peterson, T.
Chang, Y. Liao, X. Chen, Y. Li, T. Voytek, A. Natarajan, M. Dobbs, M. Halpern,
J.R. Bond, G. Hinshaw, J. Roy, Y. Gupta, R. Nityananda, and many more
Overview
21cm physics Theory: dark energy, gravity waves, neutrinos, enhanced 21cm pre-‐reionizaTon structures.
ObservaTons: first detecTons and upper bounds (GBT, GMRT)
Future: dedicated surveys (CRT, CHIME, etc )
21cm: HI hyperfine transiTon
• Hyperfine transiTon when electron and proton spins flip: change in magneTc moment
• h ν =α4 me c2 (me/mp) • ν=1420.40575 MHz • Highly forbidden, lifeTme t~107 years • Astronomical Tme scales T>>t
ApplicaTons
Hydrogen Maser Clock Milky way mapping Nearby redshif surveys (HIPASS, ALFALFA) Cosmological redshif surveys (GBT, CHIME/CRT/Tianlai)
High redshif universe (GMRT/LOFAR/MWA/PAPER)
Kalberla et al 2005, from WMAP LAMBDA
21cm sky at z=0
Image courtesy of NRAO/AUI and Chung et al., Columbia University
Atomic physics
-‐-‐ energy splihng=0.068K<<TCMB. -‐-‐ Emission/absorpTon depends on spin temperature TS -‐-‐ Typically collisionally/uv excited. -‐-‐ for TS >> TCMB, emissivity independent of TS: measure hydrogen (HI) mass robustly.
21cm: emission
δ Tb=τ TS = const
Spin evoluTon
Furlanetto Oh & Briggs, 2006
21cm: observaTons
• Hydrogen is the most abundant element in the universe
• 21cm line opTcally thin from the ground over most lines of sight to very high z (~100)
21cm: observaTonal challenges • Inverse square law: required collecTng area proporTonal to distance2.
• Highest redshif direct galaxy detecTons at z~0.2 using 2000 hours of WSRT (5000m2)
• For cosmological interests (1<z<100) and wide sky maps needs km2 array: SKA
Technical challenges
• SensiTvity: bigger telescopes? • Foreground contaminaTon: design/analysis? • Target: Galaxies, Intensity Mapping/BAO, EoR?
The 21 cm universe • Cosmological LSS
treasure trove (UP04, Loeb&Zaldarriaga 04, Lewis&Challinor 07, etc)
• Up to 1018 modes: (Jeans/Hubble)3
• Physics: Lensing, gravity waves, primordial NG, BAO, AP
• GW to r ~ 10-‐8
• fNL~ 10-‐4
• Astrophysics: EoR, galaxy evoluTon
• Experiments NOW Tegmark & Zaldarriaga 08
EoR: GMRT/ LOFAR MWA Paper
CHIME/GBT
SDSS
Fundamental Physics
• 0<z<2: dark energy, BAO, w-‐w' • z>2: Large angle lensing: modified gravity (Lu & UP 2009, Masui et al 2010)
• z>10: gravitaTonal waves
Intensity Mapping • Stars get fainter with distance: hard to see individually at cosmological distance. Galaxies sTll visible.
• Galaxies get fainter with distance: hard to see in HI. Large scale structure sTll visible?
• Large scale structure is LARGE: degree scale. High resoluTon not needed.
• Modest size, monolithic radio telescopes needed. (CPPM 2008, Wyithe&Loeb 2008)
From: talk by O. Lahav
Foreground: GalacTc Synchrotron
Haslam 408 MHz Much brighter than signal, but no spectral structure
Robert C Byrd Telescope: 100m
HI content at z=0.8 Cross-‐correlaTng GBT HI & DEEP2 opTcal galaxies at
z ~ 0.7-‐1.1 (Chang et al, Nature 2010) GBT radio continuum
sources + HI
GBT HI
DEEP2 density
Chang, Pen, Bandura, Peterson, Nature, 2010
• Measure HI & optical cross-correlation on 9 Mpc (spatial) x 2 Mpc (redshift) comoving scales
• HI brightness temperature on these scales at z=0.8:
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• Highest-redshift detection of HI in emission at 4-sigma statistical significance.
GBT 15h auto power
IniTal Intensity Mapping
• Detected collecTve large scale structure with 100h of GBT Tme: first demonstraTon of distant IM. No individual galaxies detected, many galaxies per resoluTon element
• Proposal submited for z=1 BAO survey on 4 pixel array at GBT
Baryon AcousTc OscillaTons – Dark Energy Probe
• CMB acousTc oscillaTons: imprinted standard ruler, 100 Mpc.
• Present in current mater distribuTon
• KinemaTc metric of universe
WMAP5 and other, Nolta et al (2008)
Present LSS BAO DetecTons
• Percival et al 2007
Percival et al 2007
Eisenstein et al 2005
Blake et al 2011: WiggleZ, z~0.6 Masui et al: GBT-BAO proposal 2012, z~1
Dedicated Survey Experiment
• Low frequency technology cheap, modest size: (100 m)2 to z<2
• Large field of view: receiver arrays • High surface brightness sensiTvity: compact arrays
• Stable, reliable: no moving parts • Technologies: aperture arrays (Wyithe, Loeb, Geil 2008), cylinders (Peterson et al)
Molonglo
Molonglo
AUSTRALIA Brisbane
Darwin
Perth Canberra
Hobart
Adelaide Melbourne
Sydney
+ Northern
Cross
Cambridge
Pushchino
Ooty
CMU cylinder in operaTon: J. Peterson, U. Pen, U. Seljak, K. Bandura, K. Sigurdson
CHIME, Tianlai, CRT, etc
Fast Fourier Transform Telescope
New Cylinder Radio Telescopes
Canada, US, China, France, Morocco Map the Hubble volume to 0.8<z<2.5 Most sensiTve BAO, RSD, lensing survey Ancillary science: 21cm absorbers, radio transients, pulsar search/monitoring, magneTc fields
Scalable to z~20: tens of square kilometers
Gravity Waves
• Masui & Pen 2010 (PRL 105, 161302) • Analogous to lensing: shearing of cosmic structure. • Fossil memory effect: h~10-‐6 (inflaTon) • Measure r,nT at z~15 • Requires 1/h2 modes • Separates from lensing: transverse traceless • Structures available to k~10-‐3-‐103:horizon to Jeans scale, ~1018 modes, peaks at z~15
Linear gravity wave memory • GW in iniTal condiTon, then redshifs away
Detectability
Conclusions • 21cm cosmology: probes of dark energy (BAO), modified gravity (lensing), InflaTon (tensor modes), etc. Beyond intrinsic power spectrum. PotenTal measure of gravity waves.
• Intensity Mapping: 21cm unresolved galaxies, accessible in redshif desert z=1-‐3, iniTal HI detecTon and surveys with GBT at z~1. Upper bounds at z=9.
• Prototypes and observaTons under way. Cylinder telescopes a promising technology for fast, large, economic surveys. OpTmal calibraTon and dynamic range.
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