The Epoch of Reionization: Observational & Theoretical Topics

Transcription

1 The Epoch of Reionization: Observational & Theoretical Topics Lecture 1 Lecture 2 Lecture 3 Lecture 4 Current constraints on Reionization Physics of the 21cm probe EoR radio experiments Expected Scientific outcome i. CMB Polarization. ii. Lyman-a forest data. iii. Opacity of ionizing photons (`Bolton et al). iv. Temperature evolution (Theuns etal, Haiman&Hui) v. Soft Xray BG (Dijkstra..) vi.ir BG (HESS results) vii.hst WPC3 results i. Basic Formulae i. Current & future (Field 1958) experiments. ii. Excitation ii. Key parameters in mechanisms (Lyexperiments. a, collisions,..) iii. Observational issues: uv iii. Global evolution coverage, of the spin temp. foregrounds, iv. Patchy evolution ionosphere, v. Simulation results instrument, noise. iv. Extraction issues. v. Calibration. vi.polarization. i. Cosmology: Density field, ionization frac. Redshift distort, power spect. ii. First sources iii. Ionization history iv. Dark ages and history of spin temperature. v. The future.

2 The Epoch of Reionization: Observational & Theoretical Topics Saleem Zaroubi Kapteyn Astronomical Institute University of Groningen

3 Lecture 1: Observational probes of reionization i. CMB Polarization. ii. Lyman-a forest data. iii. Opacity of ionizing photons. iv. Temperature evolution. v. HST WPC3 results vi. Soft Xray BG vii.ir BG (HESS results)

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5 Key Probes of Reionization CMB (integral constraint) Redshifted 21 cm emission (absorption) 21 cm forest at high z Gamma ray bursts: How many we should have to constrain reionization? Luminosity function of first objects, e.g., Galaxies: Recent results from the new WFC3 aboard HST. Background detections: IR, soft x-ray. Lyman-a absorption system: ionization, metallicity, thermal history, UV background, proximity effect. Lyman alpha emitters Metals at high redshift. Using the local volume to study reionization.

6 CMB and Reionization Infuence of reionization on CMB Temperature fuctuations Infuence of reionization on CMB polarization. References: 1. Scott, White & Silk 1994 (review). 2. Hu & White Aghanim,Subhabrata & Silk 2008 (review) 4. WMAP papers.

7 CMB photons Thomson scatter off free electrons Reionization Scattering zr zrec Free streaming Photon-baryon tight coupling & last scattering

8 The dominant contribution to temperature anisotropies generated during reionization are Doppler shifts of the scatterers redshifted (blueshifted) CMB velocity Free electron Gravitational potential CMB photon,

9 The CMB and Reionization: Temperature Imprint on CMB anisotropies governed by the visibility or probability that a photon scatters out of the line of sight: t is the optical depth given by with xenh the number density of free electrons

10 Reionization & CMB Temperature The infuence of reionization on the CMB temperature angular power spectrum. (from Sugiyama 1995)

11 Reionization Scattering zr Simple visibility Two 'd-functions' zrec zr=10 zrec=1100 Free streaming Photon-baryon tight coupling & last scattering Assuming that the visibility is given by two delta Functions, the CMB is given by the following expression: For the astrophysical reionization scenarios (low optical depth) second term negligible

12 From A. Lewis

13 CMB and Reionization: Polarization U Q Polarization: Stokes parameters Q Q -Q, U U, U amplitude -U under 90 degree rotation -Q under 45 degree rotation angle

14 Thomson scattering Q and U are generated by Thomson scattering of unpolarized light. Notice no V (circular polarization) is generated.

15 E and B polarization modes E-mode has (-1)l parity whereas B-mode (-1)l+1

16 Horizon scale at reionization Observer Horizon scale at recombination Given the geometry of linear polarization the amplitude of the signal at any scale depends on the local quadrupole that scatters the photons. However, at scales larger than horizon scales (either at recombination or during reionization) there is no coherence and the signal decays.

17 The influence of reionization is shown on the large scale amplitude and shape of the E-mode polarization power spectrum. From A. Lewis

18 The WMAP cosntraint t~ The WMAP polarization measurement tells us only about the optical depth not about exact ionization redshift. For that one needs a reionization history model. However, reasonable reionization models suggest that ionization has happened at about z~10.

19 Sudden reionization...

20 The Lyman-a optical depth from Quasar spectra Absorption features due to Lyman-a in the IGM. ta is the optical depth.x is the comoving radial distance. sa is the cross section & nhi is the neutral hydrogen number density

21 Three main classifications Lyman-a forest 1012 N(HI) 1016 cm-2 Ly limit systems 1018 N(HI) 1020 cm-2 Damped Lya N(HI) 1020 cm-2

22 The Lyman-a optical depth from Quasar spectra The cross section peaks at the observed frequency: Then substitution in the optical depth (written in terms Redshift) yields: Which gives the simple result:

23 The Lyman-a optical depth from Quasar spectra The Lyman-a Forest Along Distant n=4 n=3 n= Å Lyman-series transitions Quasar Spectra (tuniverse~1 Billion yr) QSO , zem=3.62, S/N~150 n=1 At z ~ 4 the IGM is 10-4 neutral

24 The Lyman-a forest optical depth at z about 6 Fan et al. 2003, 2006

25 The end of the reionization process The Lyman-alpha forest: At z<6 he Universe is completely ionized The Universe has completed its ionization by redshift 6: SSDS quasars (however, some, e.g., Mesinger 2009, still claim it is still about 10% neutral)

26 The IGM Temperature Evolution Most of the absorption is caused by quasilinear densities that follow a simple equation of state: Since cooling time is long these absorption lines retain information about the thermal history of the IGM

27 Efstathiou et al 1999

28 Measurement of IGM Temperature: Wavelet estimate of width of lines Theuns & Zaroubi 2001

29 The IGM temperature at low z Theuns et al Haiman & Hui 2003 Bolton et al. 2010

30 Measuring the ionizing emissivity Galaxy surveys: Lyman-a forest opacity:

31 Galaxies at z~7-9 HST WPC3 data Oesch et al 2010 Bouwens et a. 2010

32 Galaxies Galaxies appear to become bluer and show more Lyα with decreasing luminosity and increasing redshift. Bouwens et al. 2010

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35 Opacity of the IGM: Photon starved reionization Bolton & Haehnelt 2007

36 Are we missing photons? Courtesy of M. Haehnelt

37 Lyman-a emitters

38 Other probe Soft x-ray background: constrains ionization by (mini-)qsos (weak) IR background: constrains star light from reionization (unclear results) HESS Blazars constrain IR background, gives too little BG (model dependent)...

39 Summary CMB and Lyman-a forest data give the strongest constraints but give no detailed evolution. Current observations indicate too few photons per baryon and even those could not be accounted for by high z galaxies. But this is still the beginning. Many probes of the EoR but most are indirect and/or model dependent.

40 We need data from the redshifted 21cm line, which is the most direct probes of reionization. See lecture tomorrow!