theory and instrumentation targeting cosmological reionization · • dipole array – phased...

The Epoch of ExperimentationTheory 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/ReberConference -Greenhill

Brief History of the IGM

•culmination ofstructure formation

•the first luminous structuresUncertaintymotivates study

Epoch of Reionization (EOR)

ionized

Neutral HI

ionized

Epoch of Experimentation(EoE)

z~6.2

• 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 (λo=21cm)

• plane-of-sky measures• resolved in z space

EOR Key Science

What do we know? Reionization at z>6.2

f(HI)>10-3

at z~6.3

Can we do better?

Not @ λopt.

Gunn-Petersentrough

Deep Lyαspectra

The Epoch of ExperimentationRecent 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…)

HI Temperature HistoryOrigin of the global step

CMBR

TSpin

6.2103 102 101

HI in absorpt’n

“Lyαheating”HI in emiss’n

z

Hard to seeDnR 1:5×104

Cosmic WebPower Spectra / Wide-field Imaging

Springel et al. (http://www.mpa-garching.mpg.de/galform/millennium/) Bowman et al.

Dark Matter distribution, z~6Baryonic matter follows the DM

COBE/WMAP-style analysis

(1-2°)

Warm HI shells Around Quasars“Narrow-field” imaging

~few-10 Mpc

Project Site Style BW (MHz)

FoV(°) M×Nø AEOR( m2)×10-3

B (km)

ATNF AU ExptFacility

Facility

Facility

ExptExpt

Expt

114-228 60

Facility

N/AWSRT NL 117-163 5-8

114

27

GMRT IN 150-165 4 core 14

7 1

PAPER US/AU 100-200 60(?) 8⇒32 « 1 0.4500×16

PAST CN 70-200 5 80×125 % <1km?

20-4 %<1km?

6×12 %<1 km?

2 3

MWALFD

AU 80-200+ 20-30 10-5 1.5

32×100 ×16core

LOFAR NL 110-200 hi-band

10 ×2°

80-30 1.7×2.2

VLA NM 190-200 4-5 4+ 1

EOR Instruments Worldwideanalog

di gita l

××××

××

× ××××

×

PAPERVLA

... …

PaST

MWA/LFDLOFAR (core)

~10×10 ××××

ATNF

50º

55º

45º

40º

6h30m 6h00m 5h30m 5h00m

“LF radio astronomy is all-sky imaging”

de Bruyn ; LFFE (Wb) 3C147 163 MHzNo matter the config., foreground removal will be the greatest challenge.

• LineGalactic RRL

• Continuum- Compact (xgal)- Diffuse (gal)

- Polarized

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 ?– Tb(pol) ~ 3 - 4 K (350 MHz) over 1-10´, 30-40 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

Stokes I Stokes Q+U

~6°

350 MHz ∝ν-2.5

Haverkorn

2003

Cosmological ReionizationExp’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 ~ 5×104 required• Learn as you go

• Science goals– Detect IGM reheating

• Absorption signature of HI on background• Up to z~11.5 to start (114-228 MHz) Luxor⇔Sydney

PAPERPrecision Array to Probe the Epoch of

Reionization[Berkeley, NRAO-CV, U. Virginia]

• Dipole array– Phased design and construction– Open ended concept– Greenbank prototype - 2006.5; WA c. 2006.8

• Application of new correlator design – FPGA-based “Werthimer” concept

• Polyphase filterbank• 8 bit, modular, broadly programmable

• Long range science goals– 3 Mpc scale structure @ z~8 (6´ or 0.2 MHz)

• HI around HII bubbles– Power spectrum over a wide range of k and ν

• Past (GB)– 4 dipoles in min. redundancy config.

• 100-150 MHz, 1 polz correlation• Prototype FPGA-based correlator

– 100 MHz BW; 1 polz• 20-350 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: 7.5h 100:1250m E-W config

PaSTPrimeval 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

• 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

MWA/LFDMileura 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

• 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 aTIFF (Uncompressed) decompressor

are needed to see this picture.

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

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 structure @ z~6.3 (15´ or ~2

MHz)• HI around HII bubbles ionized by SDSS

quasars; 3 prospects• Data acquisition in T1 2007

– Build experience with foreground removal [and RFI]

– Legacy science at z~7.5 feasible after T1 2007.

Components: http://astrosun2.astro.cornell.edu/academics/courses//astro201 & courtesy of NRAO/AUI

Greenhill, Blundell, Carilli, Perley, SAO receiver lab, Loeb, Zaldarriaga, Furlanetto, Morales, Mitchell, Bowman, students, NRAO operations

First 195 MHz VLA Images

3C295 (85 Jy)

SBS1410+530

3 antennas0.78 MHz (TV10)2.9h

S/N~300

RMS∝t-0.5 over 8h

Noise 10x thermal due to 3 element u,v coverage and source density on sky.

No RFI impact - but it can only get worse…

- Mating of dipole feed & mechanical antenna. - Similar to Wb/LFFE- In contrast to MWA, LOFAR, & PaST(purpose-built

facilities)

Traditional VLA receiversλ20 cm-λ7mm

RX

Feed

Passive L/C balunDipole Hub

Gen-{N-1}Receiver

(ex Q-hybridand notches)

Gen-{N} Feed

• 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

RFI: TV/translators

TV stn.

Translator

See talk by Perley

××××

× ×× ××××

×

... …

××××

The Epoch of Experimentation

Evangelical SummaryThe 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.

Diversity in approach!

R.F.I. VLA RFI environment• analog TV/translators

- ch 8-11• digital TV

- ch 9, 10 (soon 8)• internal signals• military transmissions

Mitigation involves• coordination

- ch 9, 10, military• filtration

- 184-198 MHz BPF- ch 11

• subtraction

Internal / External RFI

See also talk by Perley

But RFI is not always that bad

A

B

||

C

Internal RFI that does not correlate

VLA Prototype PerformanceMeasured Goal

Primary Beam 4.3° √Beam sidelobes A few % √

Line RMS/450h 3.6 mK@15′

Tsys / ε600-800 K†

(prototype receiver)

400-500 K

Receiver X-polz 10-40% 10%(NB gal. foreground)

Impact: λ20cmImpact: λ92cm

1±1%< 0% √

† Prior to RFI subtraction. Corresponds to ε~ 30%; Tsys~200 K (195 MHz). Wb obtains ε~ 30%; Tsys~400 K (150± MHz)

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 receiversλ20 cm-λ7mm

Long-term Goal: HIIR

7.5′ 15′

250h - D-array / Tsys=180 / ηe=0.4 / 0.8 MHz / warm IGM / f(HI)=1

3′30′

See also e.g., Zaldarriaga, Furlanetto, & Hernquist ‘04

Long-term Goal: Fluctuations

Zaldarriaga & Carilli

Progression of EOR Theory

• Physics of Population III stars (M»102 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)