The Epoch of Experimentation Theory and Instrumentation Targeting Cosmological Reionization

Transcription

1 The Epoch of Experimentation Theory and Instrumentation Targeting Cosmological Reionization The EOR is the next CMB (Loeb) only better Radio interferometers will (may) enable Direct imaging of the dominant baryonic component: HI 3-D representation of structure (cf. surface of last scattering) Study structure when the first stars/quasars formed HI datasets promise to be enormously richer - more bits Other probes are crude (Lyα, CO lines, IR/mm color) Signatures to keep in mind Global step in the background temperature Power spectra of HI fluctuations Structures (ionized regions around quasars, filaments ) 06 Dec 2005 LFRA/Reber Conference -Greenhill

2 ionized Neutral HI Brief History of the IGM z~6.2 ionized Epoch of Reionization (EOR) culmination of structure formation the first luminous struct ures Uncertainty motivates Epoch of study Experimentation(EoE)

3 EOR Key Science Reionization history of the universe Neutral fraction, f(hi) vs z History of reheating in the IGM and origins Were stars or quasars chiefly responsible? Fragmentation and collapse of Dark Matter / Halos How quickly did baryonic LSS, stars, and quasars form? How is the EOR studied today? Optical Gunn-Petersen trough quasars limited to line-of-sight measures; relatively insensitive in z substantially model dependent How might the EOR be studied tomorrow? HI emission (λ o =21cm) plane-of-sky measures resolved in z space

4 What do we know? Reionization at z>6.2 Deep Lyα spectra f(hi)>10-3 at z~6.3 Gunn-Petersen trough Can we do better? λ opt.

5 The Epoch of Experimentation Recent Progress in Theory and Instrumentation Targeting Cosmological Reionization The EOR is the next CMB (Loeb) only better Radio interferometers will enable (ultimately) Direct imaging of the dominant baryonic component: HI Study structure when the first stars/quasars formed 3-D representation of structure (cf. surface of last scattering) HI datasets promise to be enormously richer. Other EOR probes are crude (Lyα, CO lines, colors) Signatures to keep in mind Global step in the background temperature Power spectra of HI fluctuations Structures (HII regions around quasars, filaments )

6 HI Temperature History Origin of the global step T CMBR Spin HI in absorpt n Lyα heating HI in emiss n Hard to see DnR 1: z 6.2

7 Cosmic Web Power Spectra / Wide-field Imaging (1-2 ) Dark Matter distribution, z~6 Baryonic matter follows the DM COBE/WMAPstyle analysis Springel et al. ( Bowman et al.

8 Warm HI shells Around Quasars Narrow-field imaging ~few-10 Mpc

9 EOR Instruments Worldwide Project Site Style BW (MHz) ATNF AU Expt WSRT NL Facility FoV( ) M N ø A EOR ( m 2 ) 10-3 B (km) 1 14 N/A 2 3 VLA NM Facility GMRT IN Facility core PAPER MWA LFD US/AU AU Expt Expt (?) « PAST CN Expt LOFAR NL Facility hi-band 10 2 % <1km? core 20-4 %<1km? %<1 km? analog digital

10 ATNF PAPER VLA. PaST ~10 10 LOFAR (core) MWA/LFD

11 LF radio astronomy is all-sky imaging 55º 50º 45º 40º de Bruyn ; LFFE (Wb) 3C MHz No matter the config., foreground removal will be the greatest challenge. Line Galactic RRL Continuum - Compact (xgal) - Diffuse (gal) - Polarized 6 h 30 m 6 h 00 m 5 h 30 m 5 h 00 m

12 Diffuse Foregrounds (after de Bruyn) Why is it a potentially serious problem? dipole arrays have high (off-axis) instrumental polarization Faraday rotation makes these frequency dependent calibration residuals could easily be 1% What are Galactic polarization properties? T b (pol) ~ 3-4 K (350 MHz) over 1-10, K (140 MHz) How to deal with this? Beam, depth-depolarization, RM synthesis may lower the levels Observe polarization-ref areas (where are they?) Do a superb job in full Stokes calibration

13 Stokes I Stokes Q+U ~6 Haverkorn MHz ν -2.5

14 Cosmological Reionization Exp t. [ATNF - see poster and later talk] also [T-REX] Unique single aperture concept Measure mk spectral features in radio background Frequency independent log-spiral antenna Drift scan; 1 sr beam; 2 polz. Total and cross power Challenge Calibration is critical (e.g., bandpass) DnR ~ required Learn as you go Science goals Detect IGM reheating Absorption signature of HI on background Up to z~11.5 to start ( MHz) Luxor Sydney

15 PAPER Precision Array to Probe the Epoch of Reionization [Berkeley, NRAO-CV, U. Virginia] Dipole array Phased design and construction Open ended concept Greenbank prototype ; WA c Application of new correlator design FPGA-based Werthimer concept Polyphase filterbank 8 bit, modular, broadly programmable Long range science goals 3 Mpc scale z~8 (6 or 0.2 MHz) HI around HII bubbles Power spectrum over a wide range of k and ν

16 Past (GB) 4 dipoles in min. redundancy config MHz, 1 polz correlation Prototype FPGA-based correlator 100 MHz BW; 1 polz MHz balun Near future (GB) 8(32) dipoles along an ellipse Full implementation of correlator 24 khz channels; full Stokes 10s dump Future (WA) Proven concept deployed to Mileura Challenges Foregrounds Correlator generalization to N»32 Assembly of greater collecting area CasA: 7.5 h 100:1 250m E-W config

17 PaST Primeval Structure Telescope [CMU, CITA, NAOC] Unique dipole array concept Very low cost Rapid deployment First on line (Ulastai) Simplicity Yagi antennas No-tracking (NCP) eases correlation Science goals Power spectrum (z~6-20) Structure for lower z range Cosmological parameters from GRB prompt emission

18 Near future (c. 02/06) 80 stations of ~100 antennas - configuration Dual polarization stations - not elements 2 channel correlator Challenges Quality of the NCP field Are we lucky? Calibration Foregrounds Polarization FOV (< MWA, LOFAR) Low cost system noise (at high frequencies) ~Today

19 MWA/LFD Mileura Wide-field Array - Low Freq Demonstrator [MIT/Haystack, SAO/Harvard, ANU, Curtin, Melbourne + ] Dipole array Large-N Dense uv-sampling Wide FOV (»20 ) via full correlation, all-sky (N N) No stations. 2 Gvis s -1 output Design emphasizes control over systematics Long range EOR science goals Power spectrum over a wide range of k (6.3<z<10) HI around HII bubbles

20 Challenges Pipeline processing of data flow Foregrounds Maintaining control over systematics Visualization of data products All radio sky pseudo-real time display in θ & z Collaboration with Harvard Initiative in Innovative Computing? Forging links to non-radio projects, e.g., LSST QuickTime and a TIFF (Uncompressed) decompressor are needed to see this picture.

21 LOFAR Greatest raw sensitivity Greatest collecting area Most sophisticated correlation scheme thus far Extensive preparatory work - LFFE Challenges Complexity (time for skakedown) Use of multi-beam mosaics to obtain wide FOV RFI (impact on array core) N+1 hierarchy in layout Management of dynamic station beams

22 VLA EOR Extension [SAO/Harvard, NRAO, Yale] Conventional approach Array of parabolic reflectors Leverage existing infrastructure Crash program Aperture, electronics, correlator Last peer review pending demo. (Jan.) Science goal Tight focus. Easy redshifts. 5 Mpc scale z~6.3 (15 or ~2 MHz) HI around HII bubbles ionized by SDSS quasars; 3 prospects Data acquisition in T Build experience with foreground removal [and RFI] Legacy science at z~7.5 feasible after T Components: & courtesy of NRAO/AUI Greenhill, Blundell, Carilli, Perley, SAO receiver lab, Loeb, Zaldarriaga, Furlanetto, Morales, Mitchell, Bowman, students, NRAO operations

23 First 195 MHz VLA Images SBS C295 (85 Jy) 3 antennas 0.78 MHz (TV10) 2.9 h S/N~300 RMS t -0.5 over 8 h Noise 10x thermal due to 3 element u,v coverage and source density on sky. No RFI impact - but it can only get worse

24 Traditional VLA receivers λ20 cm-λ7mm RX - Mating of dipole feed & mechanical antenna. - Similar to Wb/LFFE - In contrast to MWA, LOFAR, & PaST (purpose-built facilities) Feed

25 Dipole Hub Passive L/C balun Gen-{N} Feed Gen-{N-1} Receiver (ex Q-hybrid and notches)

26 Timeline 3 prototype receivers on the array for 8 months Production test units are being deployed now New feeds: holography (installed 11/11/05) New receivers: SEFD measures (to be installed 12/20/05) NRAO pre-deployment delta-review early in Jan (?) Challenges (just a few) Speed: design, test, deploy receivers in ~ 1 year The VLA correlator RFI excision strategy enforces inefficient bandwidths Calibration Cross-polarization response of feeds in situ Foregrounds RFI - coordination with broadcasters KCHF DTV-10; critical partner No DTV coordination possible after 2007! Gaining adequate obs./test time w/in a nat l obs tory

27 RFI: TV/translators Translator TV stn.

28 The Epoch of Experimentation. Diversity in approach! Evangelical Summary The EOR is a new frontier for astronomy, one along which LF radio astronomy will be in the vanguard. The EoE is an exciting time. But theory is in the lead. The real excitement will come when observation provides challenges.

29 R.F.I. VLA RFI environment analog TV/translators -ch8-11 digital TV - ch 9, 10 (soon 8) internal signals military transmissions Mitigation involves coordination - ch 9, 10, military filtration MHz BPF -ch11 subtraction

30 Internal / External RFI See also talk by Perley

31 But RFI is not always that bad A B Internal RFI that does not correlate C

32 T sys ~200 K (195 MHz). Wb obtains ε~ 30%; Tsys~400 K ± VLA Prototype Performance Measured Goal Primary Beam 4.3 Beam sidelobes A few % T sys / ε K (prototype receiver) Receiver X-polz 10-40% Line RMS/450 h Impact: λ20cm Impact: λ92cm 3.6 mk@15 1±1% < 0% K 10% (NB gal. foreground) Prior to RFI subtraction. Corresponds to ε~ 30%;

33 What does the VLA EOR ext. look like? - Mating of dipole feed & mechanical antenna. - Similar to Westerbork. - Contrast to MWA- LFD, LOFAR, & PAST purpose- built facilities Traditional VLA receivers λ20 cm-λ7mm

34 Long-term Goal: HIIR 250 h - D-array / Tsys=180 / η e =0.4 / 0.8 MHz / warm IGM / f(hi)=

35 Long-term Goal: Fluctuations 30 3 Zaldarriaga & Carilli See also e.g., Zaldarriaga, Furlanetto, & Hernquist 04

36 Progression of EOR Theory Physics of Population III stars (M»10 2 M ) Loeb 2003 HII regions excited by quasars Wyithe & Loeb 2004a,b Wyithe, Loeb, & Barnes 2005 Preliminary evidence: Gunn-Petersen troughs in Lyα spectra Dominance of * s over quasars in reionization Details of power spectra Velocity anisotropies (cite)