Hydrogen 21cm

Tzu-Ching Chang (ASIAA, Taiwan)

Ue-Li Pen, Kiyo Masui, Jonathan Sievers, Richard Shaw, Rajat Thomas (CITA) Jeff Peterson, Kevin Bandura, Tabitha Voytek, Aravind Natarajan (CMU) Eric Switzer (KICP), Xuelei Chen (NAOC), Victor Liao (ASIAA)

Greg Paciga, Jonathan Sievers, Rajat Thomas (CITA) Jayanta Roy, Yashwant Gupta, Rajaram Nityananda, Nissim Kanekar (NCRA) Steve Myers (NRAO), Chris Hirata (Caltech), Kris Sigurdson (UBC) 21cm Large-Scale Structure Large-scale HI temperature fluctuation intensity mapping; CMB-like,Tracing in 3D large-scale structure The cosmic web at z~0.5, as traced by 10 1 luminous red galaxies Z

M. White LSS;SDSS BAO BOSS EOR A slice 500h-1 Mpc across and 10 h-1 Mpc thick (a) Input box (b) Recovered box 0.5 is astrophysics400 comoving Mpc across at z 9andcontains1283 ∼ ∼ scale => pixels. From [411]. ground lines, terrestrial interference, and ionospheric distortion.

9.4.1 Radio Recombination Lines

Unlike free-free and synchrotron emission, foreground radio recombination lines (RRLs) can introduce significant structure in frequency space. These lines, which are generated by recombination cascades through high-n elec- tronic levels in HII regions, could therefore be serious contaminants. Little is known about the RRL background at the low radio frequencies accessed by redshifted 21 cm instruments; indeed, these experiments could turn out to be a major source of new information about both galactic and extragalactic RRLs. Here we briefly summarize our existing knowledge of the RRL background (for acomprehensivereview,see[419];seealsothediscussionsin [272, 274, 420]).

The most likely source of contamination is our Galaxy. The frequency of a hydrogen RRL between levels n and n ∆n is − n −3 ν 153∆n MHz. (163) ≈ !350"

Observationally, the lines tend to occur every 1–2 MHz over the frequency

156 Observing 21cmTracing large-scaleLarge-Scale structure Structure The1 cosmic web at z~0.5, as traced by 10 luminous red galaxies Z

BAO EOR

M. White SDSS BOSS A slice 500h-1 Mpc across and 10 h-1 Mpc thick z ~1 (a) Input box~10 (b) Recovered box

Fig. 34. A simulation of foreground removal for the SKA, when telescope noise is low Science goal BAO and 21 cm tomography mightEoR be possible. The main features of the box, especially the largest ionized bubbles (shown in black), are robustly recovered. This simulation utilizes a fifth-order Chebyshev polynomial basis for foreground removal, as well as Signal (mK) 0.1 the additional step described10 in the text of zeroing the largebubblestocalibrate the foregrounds. The box is 400 comoving Mpc across at z 9andcontains1283 ∼ ∼ Tsys (K) 30 pixels. From [411]. 300 ground lines, terrestrial interference, and ionospheric distortion. Foreground spatial 0.1 10 fluctuation (K) 9.4.1 Radio Recombination Lines Angular scale ~10’ ~10’ Unlike free-free and synchrotron emission, foreground radio recombination (non-linear scale)lines (RRLs) can introduce (bubble significant scale) structure in frequency space. These lines, which are generated by recombination cascades through high-n elec- First proposed 2007 tronic levels in HII regions,1970’s? could therefore be serious contaminants. Little is First detected 2010 known about the RRL>2011 background at the low radio frequencies accessed by redshifted 21 cm instruments; indeed, these experiments could turn out to be a major source of new information about both galactic and extragalactic RRLs. Strategy single dish Here we briefly summarizeInterferometers our existing knowledge of the RRL background (for acomprehensivereview,see[419];seealsothediscussionsin [272, 274, 420]).

The most likely source of contamination is our Galaxy. The frequency of a hydrogen RRL between levels n and n ∆n is − n −3 ν 153∆n MHz. (163) ≈ !350"

Observationally, the lines tend to occur every 1–2 MHz over the frequency

156 Probing Large-Scale Structure

Measuring Baryon Acoustic Oscillation with HI power spectrum at z~1 Green Bank Telescope HI Intensity Mapping at z=0.8 Cross-correlating GBT HI & DEEP2 optical galaxies at z ~ 0.7-1.1

Measure HI & optical cross-correlation on 9 Mpc (spatial) x 2 Mpc (redshift) comoving scales

HI brightness temperature on these scales at z=0.8:

T = 157 ± 42 μK

-4 ΩHI r b = (5.5 ± 1.5) x 10

Highest-redshift detection of HI in emission at 4- sigma statistical significance. Chang, Pen, Bandura, Peterson, in Nature 2010 GBT: Current limit on HI auto-correlation at z~1 300 hours, 50 deg2 survey at the GBT Measuring the WiggleZ fields at 800 MHz band, 0.5 < z < 1.1 Foreground subtraction using SVD, correcting for frequency dependent beam Observations underway; preliminary!!

Continuum dynamic range ~10 Spectral dynamic range ~1000 100x rescaled Same requirement as EoR GBT: preliminary HI auto-correlation at z~1

Foregrounds Foreground-subtracted “HI” Masui+ Probing Cosmic

Measuring HI power spectrum from Epoch of Reionization (EoR) at z~8.5 GMRT - Giant Meterwave Radio Telescope

U.-L. Pen, T. Chang, G. Paciga, J. Peterson, J. Roy, Y. Gupta, J. Odegova, C. Hirata, K. Sidgurdson, J. Sievers, S. Meyers

GMRT-EoR forecast GMRT: 30 antennae, D=45m diameter, 14 elements within 1km core; 3.3 deg FOV at 150 MHz

20000 m2 collecting area (for EoR), 140-156 MHz, 8

Traditional dish arrays, large collecting area, small field-of- view.

EoR prediction: 20-sigma measurement on the HI power Ilive et al. 2008 spectrum at k~0.1 !"#$%&'()*+',-./',,$+0$#

67(%'0','.(). %'8)*-#*9%.$#

@*+*#A/$%$B 1)0+', C A/'#$-8$,'<# 23-45 C D'%'8'<-%*('()*+

F+(/%*A*0$+). @+($%>$%$+.$ :','.().-$4)##)*+ ;#<+./%*(%*+-= >%$$->%$$? !"##$%&'%"##%()* Galactic intensity foreground fluctuations: ~1K at 150 MHz E$($.(*% Polarized foregrounds fluctuations: ~50K at 150 MHz?

Courtesy of Chris Hirata Software Correlator at GMRT

15 nodes taking data (30x2 inputs); 16 nodes perform real-time correlation (data rate ~1.6 TByte/hour), allowing high time & freq resolutions; collected more than 300 hrs of data Removing Broadband RFI Sky fringe-rotates but RFI’s don’t Arrange data in a time-lag matrix Use SVD-based technique to filter out largest few eigen modes Successful RFI removal (reduced >1 orders of magnitude in temperature)

LAG

TIME Phase calibration

Use pulsar as phase calibrator Take gated data: 16 gates per pulsar period; (pulsar-on - pulsar- off) = clean, pulsar-only sky; solve for antenna gains Use parallatic angle rotation to separate sky polarization and leakage RFI mitigation: near-field imaging

❖Due to small emissivity, HI in emission is difficult to detect. Currently, HI direct detection at z~0.2 (Verheijen et al 2007), stacking at z~0.3 (Lah et al. 2007); both on galaxy scales. ❖ Brightness temperature fluctuations on the sky: just like CMB temperature field, but in 3D ❖ Low angular resolution redshift survey: economical Solving for hyperbolic functions (constant delays) RFI: near-field imaging

17

Radio Frequency Interference Foregrounds

150K - 200 K; 300 hrs observation

Haslam 408 MHz Foregrounds: much brighter than signal, but no spectral structure Upper limits on the Polarized Foregrounds from GMRT

Polarized foregrounds were thought to fluctuate at >10 K level at low freq, could leak to 21cm map We find no polarized point sources (except for pulsar) in our 3 deg field Upper limit on the polarized foregrounds is ~ 1 K Good news for EoR, but P to I leakage correction is still important

Pen et al. 2009 GMRT current upper limits:

Straight forward foreground subtraction: subtract mean of (8, 2, 0.5) MHz, 60 < |U| < 200

NO SUBTRACTION 2 MHZ CONSTANT R BUBBLES 8 MHZ

TS = TG 2 MHZ TS = TG 0.5MHZ

0.5MHZ TS >> TCMB TS >> TCMB

JELIC 08 MODELS ILIEV 08 MODELS T~70 mK, for the 0.5 MHz case Cross-day HI auto power spectrum Paciga et al., 2011 GMRT work in progress: EoRgridr expand the CBIgridr (Myers et al. 2003) for 2D CMB to 3D EoR purpose added w-projection effect in the gridder ˜ v˜ = As˜ +˜n 1 ∆˜ = R˜− d˜ d˜= R˜s˜ +˜nd EoRGridr ˜ ˜T ˜ ˜ ∆ν ∆ν = S + F R˜ = H˜ A˜W,˜ n˜d = H˜ n˜ T 1 1 T 1 T ￿ ￿ ∆˜ =(R˜ N − R˜)− R˜ N − d˜,N =< n˜dn˜d >

Phase Amplitude GMRT work in progress: EoRgridr SVD foreground-subtracted estimated (normalized) signal T covariance < Δν Δν > ~ S After subtraction - no coherent phase structure Very preliminary!

Phase Amplitude !"#$%&'()*+',-./',,$+0$#

67(%'0','.(). %'8)*-#*9%.$# Pulsar phase No polarized point Upper limit at referencing sources found ~100 mK @*+*#A/$%$B successful 1)0+', C A/'#$-8$,'<# 23-45 C D'%'8'<-%*('()*+ “EoRgrider” Foreground F+(/%*A*0$+). subtraction @+($%>$%$+.$ underway :','.().-$4)##)*+ ;#<+./%*(%*+-= >%$$->%$$? RFI mitigation !"##$%&'%"##%()* successful; Galactic intensity foreground fluctuations: ~1K at 150 MHz physical elimination in E$($.(*% Upper limits on polarized progress diffuse foregrounds ~ 1K Installed software correlator; collected a few x 100 hours of data Courtesy of Chris Hirata Outlook On-going data analysis: EoRgridr Extend to 3D for foreground/power spectra analysis More GMRT observations: drift scan, near-transit observations, mosaicking RFI mitigation this summer: team of summer students Current state-of-art spectral foreground subtraction limits on 10’ scales : GBT (single dish): 1000:1 -- foreground spectrally smooth! GMRT (interferometric): 100:1 important metric for EoR measurements GMRT currently leads EoR power spectrum limit (70 mK) c.f. Bebbington+ 1986 (~5K), Ali+ 2008 (~4K), Parsons+ 2010 (5K) LOFAR, MWA, PAPER in operation - more results soon!