HI across cosmic time

Transcription

1 HI across cosmic time Hubble-ITC Fellow CfA Avi Loeb (CfA) Steve Furlanetto (UCLA) Stuart Wyithe (Melbourne) Mario Santos (Portugal) Hy Trac (CMU) Alex Amblard (Ames) Renyue Cen (Princeton) Asanthe Cooray (UCI)

2 The first billion years CMB Dark ages Story of hydrogen 21 cm mean signal Cosmic Dawn Reionization 21 cm fluctuations Intensity mapping DLA

3 The first billion years CMB Dark ages Cosmic Dawn Reionization Post-overlap

4 The first billion years CMB Recombination: hydrogen becomes neutral Dark ages Cosmic Dawn Reionization Post-overlap

5 The first billion years CMB Recombination: hydrogen becomes neutral Dark ages Thermal decoupling: hydrogen cools Cosmic Dawn Reionization Post-overlap

6 The first billion years CMB Recombination: hydrogen becomes neutral Dark ages Thermal decoupling: hydrogen cools Cosmic Dawn Structures form: hydrogen heated Reionization Post-overlap

7 The first billion years CMB Recombination: hydrogen becomes neutral Dark ages Thermal decoupling: hydrogen cools Cosmic Dawn Structures form: hydrogen heated Reionization Reionization: hydrogen ionized Post-overlap

8 The first billion years CMB Recombination: hydrogen becomes neutral Dark ages Thermal decoupling: hydrogen cools Cosmic Dawn Structures form: hydrogen heated Reionization Reionization: hydrogen ionized Post-overlap only neutral hydrogen in dense clumps

9 Known unknowns Gas temperature [K] CMB Gas Ionized fraction

10 Known unknowns Gas temperature [K] CMB Gas CMB Hydrogen was warm and neutral at z=1100 Ionized fraction

11 Known unknowns Gas temperature [K] QSO CMB Gas CMB Hydrogen was warm and neutral at z=1100 Ionized fraction Flux [10-18 erg cm -2 s -1 A -1 ] Hydrogen is hot and ionized at z<6 Dashed: LBQS composite Dotted: Telfer continuum SDSS J z= Wavelength

12 Known unknowns Gas temperature [K] QSO 21 cm discovery region CMB Gas CMB Hydrogen was warm and neutral at z=1100 Ionized fraction Flux [10-18 erg cm -2 s -1 A -1 ] Hydrogen is hot and ionized at z<6 Dashed: LBQS composite Dotted: Telfer continuum SDSS J z= Wavelength

13 Known unknowns Gas temperature [K] QSO 21 cm discovery region SKA CMB Gas CMB Hydrogen was warm and neutral at z=1100 Ionized fraction Flux [10-18 erg cm -2 s -1 A -1 ] Hydrogen is hot and ionized at z<6 Dashed: LBQS composite Dotted: Telfer continuum SDSS J z= Wavelength

14 What do we know about reionization? CMB optical depth => midpoint of reionization z~10 Gunn-Peterson trough => universe mostly ionized at z<6 Lyman alpha forest => ionizing background at z<6 High redshift galaxies => ionizing background + star formation Reionization complete by z~6.5 Midpoint of reionization z~9-11 Reionization extended, may begin z>15

15 21 cm mean signal

16 21 cm basics Precisely measured transition from water masers ν 21cm =1, 420, 405, ± Hz Hyperfine transition of neutral hydrogen Useful numbers: 11S1/2 10S1/2 n1 n0 λ = 21 cm 200 MHz z =6 100 MHz z = MHz z 20 t Age (z = 6) 1 Gyr t Age (z = 10) 500 Myr t Age (z = 20) 150 Myr Spin temperature describes relative occupation of levels n 1 /n 0 = 3 exp( hν 21cm /kt s ) t Gal (z = 8) 100 Myr

17 21 cm line in cosmology T γ T S T b T k CMB acts as back light z = 13 ν =1.4GHz Neutral gas imprints signal z =0 ν = 100 MHz Redshifted signal detected brightness temperature T b = 27x HI (1 + δ b ) TS T γ T S 1 + z 10 1/2 r v 1 r mk (1 + z)h(z) spin temperature T 1 S = T γ 1 + x α Tα 1 + x c T 1 K 1+x α + x c Coupling mechanisms: Radiative transitions (CMB) Collisions Wouthysen-Field effect

18 Hyperfine structure of HI Wouthysen-Field Effect Resonant Lyman α scattering couples ground state hyperfine levels Coupling Lyα flux 22P1/2 21P1/2 spin colour gas T S T α T K 21P1/2 20P1/2 W-F recoils 11S1/2 10S1/2 λ = 21 cm Wouthysen 1959 Field 1959

19 Hyperfine structure of HI Wouthysen-Field Effect Resonant Lyman α scattering couples ground state hyperfine levels Coupling Lyα flux 22P1/2 21P1/2 spin colour gas T S T α T K 21P1/2 20P1/2 W-F recoils 11S1/2 10S1/2 λ = 21 cm Wouthysen 1959 Field 1959

20 Hyperfine structure of HI Wouthysen-Field Effect Resonant Lyman α scattering couples ground state hyperfine levels Coupling Lyα flux 22P1/2 21P1/2 spin colour gas T S T α T K 21P1/2 20P1/2 W-F recoils 11S1/2 10S1/2 λ = 21 cm Wouthysen 1959 Field 1959

21 Hyperfine structure of HI Wouthysen-Field Effect Resonant Lyman α scattering couples ground state hyperfine levels Coupling Lyα flux 22P1/2 21P1/2 spin colour gas T S T α T K 21P1/2 20P1/2 W-F recoils 11S1/2 10S1/2 λ = 21 cm Wouthysen 1959 Field 1959

22 What did the first galaxies look like? Lyman alpha photons originate from stars Population II or III? (cooling by metals or hydrogen) Star formation rate? (feedback from radiation or heating) Clustering properties? (host halo mass)

23 Thermal history X-rays likely dominant heating source in the early universe - (Lya heating inefficient, uncertain shock contribution) Long X-ray mean free path allows heating far from source X-ray HI e - HII photoionization e - collisional ionization HI Ly! excitation 1eV=10,000 K heating Shull & van Steenberg 1985 Furlanetto & Johnson 2010

24 What were the first X-ray sources? X-ray binary SNR mini-quasar Only weak constraints from diffuse soft X-ray background Dijkstra, Haiman, Loeb 2004 Fiducial model extrapolates local X-ray-FIR correlation to connect X-ray emission to star formation rate ~1 kev per baryon in stars Glover & Brand 2003 Might track growth of black holes instead of star formation Zaroubi+ 2007

25 21 cm mean signal TK TS Main processes: 1) Collisional coupling 2) Lya coupling 3) X-ray heating 4) Photo-ionization TCMB adiabatic cooling X-ray heating collisional Lya coupling Furlanetto 2006 Pritchard & Loeb 2010

26 Time after Big Bang (years) Brightness (mk) 10 million 100 million EoR signal 250 million 500 million Redshift >100 MHz >70 MHz >50 MHz 1 billion 50 First galaxies form 0 Reionization begins Reionization ends 50 Dark ages Cosmic time 100 Heating begins Pritchard & Loeb 2010 Frequency (MHz) (mk)

27 Uncertain high redshift sources Properties of first galaxies are very uncertain X-ray emissivity Frequencies below 100 MHz probe period of X-ray heating & Lya coupling Possibility of heating from shocks or exotic physics too Lyα emissivity Pritchard & Loeb 2010

28 Global 21 cm experiments EDGES Global signal can be probed by single dipole experiments e.g. EDGES - Bowman & Rogers 2008 CoRE - Ekers+ Bowman & Rogers 2010 today s Nature Switch between sky and calibrated noise source

29 Frequency subtraction Foreground Look for sharp 21 cm signal against smooth foregrounds Shaver log T fit = N poly i=0 a i log(ν/ν 0 ) i. Signal ll generally recast TS>>TCMB no spin temperature dependence log Extended reionization histories closer to foregrounds T b (z) = T z 10 1/2 z zr tanh z +1

30 Latest results from EDGES 1500 redshift, z Bowman & Rogers 2010 today s Nature T A [K] 1000 Three months integration at low duty cycle at MWA site Thermal noise ~ 6mK ! MHz Role off at edges of band due to instrumental response

31 Reionization constraints z reionization durations consistent with data Bowman & Rogers 2010 today s Nature 0.1 marginalising over 12th order polynomial fit to foregrounds and instrument response! z Some channels lost to RFI reionization durations inconsistent with data Δz<0.06 excluded at 95% level " MHz

32 21 cm fluctuations

33 Brightness Fluctuations brightness temperature density neutral fraction gas temperature Lyman alpha flux peculiar velocities b cosmology reionization X-ray heating Lya sources } Neutral } spin cosmology hydrogen temperature

34 Brightness Fluctuations brightness temperature density neutral fraction gas temperature Lyman alpha flux peculiar velocities b cosmology reionization X-ray heating Lya sources cosmology Dark Ages Cosmic Dawn Twilight EoR DLA

35 Numerical simulation Santos+ 2008

36 Numerical simulations Basics of reionization simulation well understood - dynamic range is hard Fast approximate schemes being developed: - Santos Fast21CM - Mesinger cmFast - Thomas BEARS Santos /h Mpc ~ 1 Detailed numerical simulation including spin temperature limited but underway: - Baek+ 2008, 2010

37 Power spectrum bias source properties density Lya Lya fluctuations add power on large scales Largest scales give information on source bias Intermediate scales on source spectrum Barkana & Loeb 2004 Chuzhoy, Alverez & Shapiro 2006 Pritchard & Furlanetto 2006 T fluctuations give information on thermal history T K <T! clustering/growth of mini-quasars could be very different Pritchard & Furlanetto 2007 T K >T! X-rays

38 Amplitude and Tilt Lidz Slope Amplitude Power spectrum flattens and drops as reionization proceeds MWA/LOFAR probably limited to amplitude and slope -> neutral fraction measurement at 10% level at several redshifts Ionized fraction

39 More massive sources dominate HII region morphology L m 1/3 L m L m 5/3 S2 S1 S3 S4 m > m Minihaloes less important M3 M2 M1 z = 7.3 z = 7.7 z = 8.7 McQuinn x i = 0.55 x i = 0.8 HII region morphology determined primarily by: 1. neutral fraction 2. Sources 3. Sinks 4. Thermal feedback Precise power spectrum measurements can distinguish these different scenarios

40 Evolution of power spectrum DLA reionization First gal. Dark ages Evolution of signal means that detecting signal at z=20 not necessarily more difficult than at z=10 Distinguish different contributions via shape and redshift evolution z=30-50 range much harder! Pritchard & Loeb 2008

41 Evolution of power spectrum DLA reionization First gal. Dark ages Evolution of signal means that detecting signal at z=20 not necessarily more difficult than at z=10 Distinguish different contributions via shape and redshift evolution z=30-50 range much harder! Pritchard & Loeb 2008

42 Evolution of the power spectrum Mesinger More from Santos next...

43 Intensity mapping in outline Can also target neutral hydrogen after reionization out to z~3 with instruments at frequencies > 350 MHz Measure power spectrum of galaxies by integrating 21 cm flux => big picture of distribution of galaxies without spending time on resolving details

44 Intensity mapping in outline Can also target neutral hydrogen after reionization out to z~3 with instruments at frequencies > 350 MHz Figure 1 Cosmic surveys and pointillism. Traditionally, astronomers map out the large-scale structure constan The ies at la science tre Arr measu HI 21-c is one o Chang nique t Measure power spectrum of galaxies by integrating 21 cm flux => big picture of distribution of galaxies without spending time on resolving details Carilli 2010

45 Intensity mapping and dark energy Figure 1. Sensitivity to Dark Energy Models. The plot shows projected error ellipses in the parameter space laid out by the Dark Energy Task Force. w 0 = p/! is the dark energy equation of state, and w a is the first derivative of w. Plotted in black are 1-" and 2-" contours Cylinder for HI Intensity Radio Mapping assuming Telescope a Cylinder ~ Radio 10,000 Telescope mof area 2 10,000 sq meters. Also plotted are contours for the optical BAO experiments SDSS-III after combining the Large Red Galaxy and Lyman-alpha surveys (red) and WFMOS (blue). ' ' BAO first peak ~130 h -1 Mpc BAO third peak ~ 35 h -1 Mpc corresponds to ~20 arcmin Chang, Pen, Bandura & Peterson 2010 Covering large volumes allows strong constraints on dark energy and geometry Also learn about ΩHI

46 Intensity mapping results Spatial distance (h 1 Mpc) a ,800 2,000 2,200 2,400 2,600 b ,800 2,000 2,200 2,400 2,600 c ,800 2,000 2,200 2,400 2,600 Redshift distance (h 1 Mpc) Chang, Pen, Bandura & Peterson 2010 Correlation (10 4 K) Lag (h 1 Mpc) Figure 2 The cross-correlation between the DEEP2 density field and GBT H I brightness temperature. Crosses, measured cross-correlation temperature. Error bars, 1s bootstrap errors generated using randomized optical data. Diamonds, mean null-test values over 1,000 randomizations as described in Supplementary Information. The same bootstrap procedure performed on randomized radio data returns very similar null-test values and error bars. Solid line, a DEEP2 galaxy correlation model, which assumes a power law correlation and includes the GBT telescope beam pattern as well as velocity distortions, and uses the best-fit value of the cross-correlation amplitude. Observations at 0.5<z<1 showing cross-correlation between radio and galaxy signal

47 Conclusions Currently know very little observationally about reionization history Need to understand both sources and IGM => 21 cm observations with SKA-low key 21 cm global experiments capable of constraining broad-brush properties of signal 21 cm fluctuations complement the global signal and contain wealth of information - Lyman alpha fluctuations => star formation rate - Temperature fluctuations => X-ray sources - Neutral fraction fluctuations => topology of reionization For specified assumptions can begin to calculate 21 cm signal including all relevant physics - still large uncertainties in what assumptions about first galaxies are reasonable Spatial and redshift information are critical to separating the different contributions to the 21 cm signal SKA1 and SKA2 potentially sensitive to very first galaxies at lowest frequency range 21 cm intensity mapping provides a powerful alternative to galaxy surveys that should be explored