The LOFAR-EoR project

Ger de Bruyn

for the LOFAR-EoR project team

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Outline

o The LOFAR EoR team and their preparations

o The science goals: what do we already know, signal strength

o EoR relevant LOFAR array specs (frequency, baselines, sensitivity,..)

o Some RFI statistics in the EoR band

o The EoR observing plan/proposal

o Commissioning: plans and some first results

o Our processing, re-processing and inversion cluster

o Conclusions

The EoR project team

PI and co-PI’s (the Management Team)

Ger de Bruyn, Michiel Brentjens, Leon Koopmans, Saleem Zaroubi

Additional core members:

Gianni Bernardi, Benedetta Ciardi, Vibor Jelic, Geraint Harker, Panos Lampropoulos, Garrelt Mellema, Andre Offringa, Vishambhar Pandey, Joop Schaye, Rajat Thomas, Sarod Yatawatta

+ about a dozen ‘associate’ members (scientists and (software) engineers)

+ more students postdoc to join.

Delivered 3 PhD theses:

Rajat Thomas, Mar09; Vibor Jelic, May10, Panos Lampropoulos, Sep10

For more info: http://www.astro.rug.nl/~LofarEoR

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Preparing for EoR experiments and challenges

Our EoR group has been active in many areas for up to 10 years now:

o Conducting WSRT observation in 115-175 MHz range Bernardi et al, ‘09,’10o Analytic reionization models Thomas et al, ’09o Simulating foreground properties Jelic et al, ’08

+ adding polarization Jelic et al, ’10 o Data model and inversion approaches Lampropoulos, thesis Sep10o End-to-end simulations with realistic errors Lampropoulos et al, ‘10

o Fitting approaches to remove Galactic foreground Harker etal, ‘08,’09,’10

o ‘Optimal’ design of LOFAR array (we are to ‘blame’ for 48 2x24 tiles)

o Efficient RFI mitigation algorithms

Main science goals of the LOFAR EoR project

When was the Universe reionized ?

How did it happen ?

Who did it ?

Observational constraints through:

— Statistical detection of global signal

— Evolution in z=7-11 range

— Characterization of ionization bubble-sizes

— Search for a 21cm forest (against high-z RGs)

— Cross correlation with other probes: Ly- , CMB, ..

Vibor Jelic

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SLOAN QSOs Ly-α absorption spectra

Fan et al, ‘03, ‘06

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Gunn-Peterson results on Sloan high-z QSOs

End of reionizationat z ~ 6.5

Gnedin (2002)

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Intensity of 21cm line (emission and/or absorption)

Zaroubi

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One (of many) simulation: Gnedin

Lots and lots of simulations……

Rajat Thomas, 2009, thesis

Which ionizing sources dominated ?

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Evolution of relevant temperatures

Scott and Rees, 1990Loeb and Zaldarriaga, 2004Pritchard and Loeb, 2008Thomas and Zaroubi, 2010Baek et al, 2010

Probably we will onlysee emission betweenz = 6.5-11.5 (LOFAR)

The LOFAR core area near Exloo

+ 4 more stations to be added (June 2010 decision)

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uv-coverages after 4,6,8h using 24x2 Core Stations

4h magenta6h blue8h black

Two 12-bit ADC sampling modes: 200 MHz and 160 MHz clock

Frequency filtering done in two digital (Poly-Phase-Filter) stages:

- at station 512 subbands (either 156 or 195 kHz)

- at CEP (BG/P) 256 channels for each of 248 subbands split

LOFAR has superb frequency resolution

48 MHz total bandwidth 63,488 channels of 0.8 kHz !

RFI & wide-field VLBI

(+ 21cm & rec lines)

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Some results on our RFI flagging (Offringa et al, 2010)

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Air traffic Satellite Amateurs Mobile Pager

RFI statistics in a 6h daytime observations (24 stations)

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24 April 2010

Locating the optimum EoR - ‘windows’

Haslam et al (1981)

408 MHz

All-sky (0.85o PSF)

Location of 4 WSRT learning fields

— ‘FAN’ (polarized !)

— North Celestial Pole

— 3C196

— North Polar Spur

Galactic coordinates

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Field location aspects

nighttime !

uv-coverage ( > 6 h)

track length and elevation

Low Galactic noise contribution

Dec +50o (3C196) Dec +86o (near NCP)

These 2 locations have few secretsleft, and probably these will be ourfirst 2 ‘windows’

Bernardi etal, ‘09

Deep WSRT imaging on low Galactic latitude field

WSRT 6x12h nov ‘07

138-157 MHz

FAN region (3h, +66o)

diffuse Galactic structures and thousands of

discrete sources

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Power spectrum of WSRT ‘Fan’ data (138-157 MHz)

Bernardi et al, ‘09

Confusion noise

Linear polarization

WSRT Stokes Q ,U images at Faraday depth = - 2 rad/m2

Very rich polarization structure at 150 MHz !Will soon be observed as part of the Magnetism KSP

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Non-isoplanaticity & peeling WSRT 145 MHz

Bernardi etal, 2009

3C196

80 Jy peak

~ 0.6 mJy noise

(confusion 3mJy)

DR 100,000:1

2000+ sources

Separately peeled

DD-solutions

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LOFAR-EoR observing proposal

Observations in ~ 5 ‘EoR-windows’ (constrained by the 20-25o tile beam)

For 16-bit data transport: 48 MHz-1beam available

If 4-bit data transport 192 MHz-beams available- per window we correlate 3 station beams- allocate each beam ~60 MHz (115-175 MHz) - plus ~ 12 x 1 MHz flanking ‘calibrator beams’

We aim for an integration per window of~ 600 hours (in 100 nights of ~ 6h)

Start around Dec 2010 (with 1 beam? ) ?

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Foreground fitting and PS extraction

Geraint Harker et al, 2009, 2010

Simulation with:

- EoR signal (blue solid)- Realistic thermal noise (red dash) - Wp fitted (points+errorbars)

- Instrumental response included

- 300 - 1200h on 5 window (1 beam)

- Three redshift bins (8 MHz each):z = 7.4, 8.5, 10.0

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Leon Koopmans, sep10

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Conclusions

o EoR project (great team !) almost ready to start processing and analyzing data

o Commissioning pilot real observations in Oct/Dec 2010

o 2 windows selected (to be ‘commissioned’/approved next 2 months)

o Processing on our own CPU/GPU cluster (80 nodes x 8 cores, 0.3 PByte)

o Detection of an EoR signal 201... Stay tuned !