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
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
21cm sky at z=0 Kalberla et al 2005, from WMAP LAMBDA
Image courtesy ofNRAO/AUI andChung et al.,ColumbiaUniversity
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: 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
The 21 cm universe • Cosmological LSS treasure trove (UP04, Loeb&Zaldarriaga 04, Lewis&Challinor 07, EoR: etc) GMRT/• Up to 1018 modes: LOFAR (Jeans/Hubble)3 CHIME/ GBT MWA• Physics: Lensing, gravity waves, Paper primordial NG, BAO, SDSS AP • GW to r ~ 10-‐8 • fNL~ 10-‐4 • Astrophysics: EoR, galaxy evoluTon • Experiments NOW Tegmark &
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)
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
• 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: • • Highest-redshift detection of HI in emission at 4-Chang, Pen, Bandura, Peterson, Nature, sigma statistical 2010 signiﬁcance.
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 WMAP5 and other, Nolta et al of universe (2008)
Present LSS BAO DetecTons 2007 Percival et al 2005 Eisenstein et al • Percival et al 2007
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)
Darwin AUSTRALIA Brisbane Perth Sydney Melbourne + Adelaide Canberra Molonglo Hobart Northern Cross Molonglo Ooty Cambridge Pushchino
CMU cylinder in operaTon: J. Peterson, U. Pen, U. Seljak, K. Bandura, K. Sigurdson
Fast Fourier Transform TelescopeCHIME, Tianlai, CRT, etc
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
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.