21 cm Reionization Forecast and Search at GMRT
Ue-Li Pen 彭威礼Tzu-Ching Chang 張慈錦
Julia Odegova
Jeff Peterson, CMU
Chris Hirata, Kris Sigurdson, Yashwant Gupta, Jayanta Roy
Radiative Xfer simulation by Iliev, Mellema, Shapiro, Pen, et al
τ=0.09+/-0.03, zr=11
WMAP 3yr
Universe at recombination
Universe at reionization
Reionization
• First objects: • 21cm @ z=6-15• 90-200 Mhz• ΔT ~ 20 mK, • ~μJy- mJy (up to 1016
Mּס of HI)• Angular scale
5’<Θ<30’, freq res 500 khz
• Challenging theory
Iliev, Mellema, Pen, Shapiro 2006. 100/h Mpc, 1o FOV
Cosmic Reionization
(Iliev, Mellema, Pen, Shapiro 2006)
Largest radiative transfer cosmological reionization simulations: 1 degree FOV.
Detection in 21cm hyperfine transition with radio telescopes. Structure on large scales (>20’).
See also Furlanetto, Oh, Zaldarriaga, Zahn, Morales, Mesinger, Croft, Ciardi, etc
log10 T (mK)
Iliev et al, astro-ph/0702099
Iliev et al, Astro-ph/0702099
Foreground: Galactic Synchrotron
Haslam 408 MHz Much brighter than signal, but no spectral structure
Indian Giant Meterwave Radio Telescope
30 dishes @45m ea.
Operates in 2m band
Collaborators: Y. Gupta (chief scientist), Rajaram Nityananda (director), J. Roy, J. Peterson (CMU), C. Hirata (IAS), T. Chang (CITA), J. Odegova (Toronto), K. Sigurdson (UBC)
GMRT EoR Search• Operating telescope, 50,000m2 (geometric), up to
32 MHz BW, fully polarized, lowest band 100-200 MHz, sky limited. Currently biggest collecting area in this band.
• Half in central 1km core (relevant for EoR), rest in 20 km Y (useful for calibration).
• Previously reached RFI limit at 150 MHz after a few minutes of integration: power lines, TV stations, HAM amateurs, faulty home electronics.
• Software correlator: success of new RFI mitigation schemes, nearfield clean.
• Current effort invests 100 hours observing time per semester.
Step 1: new software correlator:imaging the full sky+horizon
Power Line Noise
Time-lag: Folded 70ms data on short baseline
Step 2: Phase calibration
Real time pulsar gated imaging calibration
Pen et al 2007, GMRT internal report
Antenna based phase solutions
Fourier (u-v) map (Im)
Current Status
• Sensitivity forecasts for GMRT promising• RFI mitigation successful, physical
elimination under investigation.• Pulsar phase referencing successful.• Polarization calibration and imaging
achieved – no non-pulsar sources found.• Foreground subtraction under way.
Frequency dependent primary beam: holographic pulsar beam mapping.
Outlook
• Existing constraints: optical depth from WMAP (Pol’n), SDSS QSO’s.
• Theoretical progress: direct simulations indicate power on larger scales (>20’), making detections more tractable.
• current: large data sets from GMRT, data analysis in progress. RFI problems solved: separate imaging of sky and RFI. Foreground subtraction main challenge.
• Bright outlook: several experiments underway to tap the next cosmic horizon: GMRT, LOFAR, MWA, Past/21CMA, Paper …
• Exciting new window on universe for precision cosmology. Open field for theory and experiment.