THE IMPORTANCE OF WIDE-FIELD FOREGROUND REMOVAL FOR 21 cm COSMOLOGY: A DEMONSTRATION WITH EARLY MWA EPOCH OF REIONIZATION OBSERVATIONS

In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cylindrically averaged power spectra measurements used by 21 cm experiments, with a focus on the effects of the instrument beam response and the associated sidelobes. We then demonstrate this mapping by analyzing power spectra with both simulated and observed data from the Murchison Widefield Array. We find that removing a foreground model which includes sources in both the main field-of-view and the first sidelobes reduces the contamination in high k_parallel modes by several percent relative to a model which only includes sources in the main field-of-view, with the completeness of the foreground model setting the principal limitation on the amount of power removed. While small, a percent-level amount of foreground power is in itself more than enough to prevent recovery of any EoR signal from these modes. This result demonstrates that foreground subtraction for redshifted 21 cm experiments is truly a wide-field problem, and algorithms and simulations must extend beyond the main instrument field-of-view to potentially recover the full 21 cm power spectrum.

A. R. Whitney | S. J. Tingay | T. Prabu | G. Bernardi | D. A. Mitchell | S. M. Ord | L. J. Greenhill | B. Pindor | R. B. Wayth | M. Johnston-Hollitt | N. Udaya Shankar | N. Hurley-Walker | J. C. Pober | M. Tegmark | C. M. Trott | Nithyanandan Thyagarajan | M. E. Bell | N. D. R. Bhat | A. E. E. Rogers | P. Carroll | E. Lenc | K. S. Srivani | L. Hindson | A. R. Offringa | P. Procopio | J. C. Kasper | B. J. Hazelton | M. F. Morales | A. P. Beardsley | J. D. Bowman | F. Briggs | D. Emrich | J. N. Hewitt | D. C. Jacobs | P. Kittiwisit | J. Line | E. Morgan | A. Roshi | R. L. Webster | B. McKinley | N. Kudryavtseva | D. L. Kaplan | J. S. B. Wyithe | Max Tegmark | E. Lenc | D. Kaplan | J. Hewitt | B. Pindor | R. Webster | N. Bhat | S. Tingay | M. Morales | C. Trott | E. Morgan | A. D. Oliveira-Costa | A. Loeb | D. Oberoi | P. Carroll | A. Rogers | B. Corey | R. Cappallo | A. Whitney | I. Sullivan | R. Wayth | P. Procopio | J. Kasper | A. Offringa | J. Pober | A. Beardsley | G. Bernardi | J. Bowman | J. Dillon | A. Ewall-Wice | B. Hazelton | D. Jacobs | P. Kittiwisit | Z. Martinot | A. Neben | N. Thyagarajan | J. Wyithe | R. Goeke | R. Subrahmanyan | M. Johnston-Hollitt | F. Briggs | D. Mitchell | L. Greenhill | S. Ord | C. Lonsdale | S. McWhirter | A. Deshpande | M. Lynch | M. Waterson | M. Bell | L. Hindson | A. Williams | S. Sethi | D. Emrich | N. Hurley-Walker | N. Shankar | K. Srivani | B. McKinley | E. Kratzenberg | A. Roshi | C. Williams | L. Feng | N. Kudryavtseva | T. Prabu | J. Riding | J. Line | N. Barry | A. Williams | R. J. Cappallo | B. E. Corey | A. de Oliveira-Costa | A. A. Deshpande | L. Feng | R. Goeke | E. Kratzenberg | A. Loeb | C. J. Lonsdale | M. J. Lynch | S. R. McWhirter | A. R. Neben | D. Oberoi | J. Riding | R. Subrahmanyan | I. S. Sullivan | M. Waterson | C. L. Williams | Shiv K. Sethi | N. A. Barry | Z. E. Martinot | Joshua. S. Dillon | A. M. Ewall-Wice | Han-Seek Kim | Sourabh Paul | H. Kim | S. Paul

[1]  Meng Su,et al.  MITEoR: a scalable interferometer for precision 21 cm cosmology , 2014, 1405.5527.

[2]  M. I. Large,et al.  The Molonglo Reference Catalogue of radio sources. , 1981 .

[3]  J. Starck,et al.  The scale of the problem: Recovering images of reionization with Generalized Morphological Component Analysis , 2012, 1209.4769.

[4]  Abraham Loeb,et al.  21 cm cosmology in the 21st century , 2011, Reports on progress in physics. Physical Society.

[5]  S. J. Tingay,et al.  The Low-Frequency Environment of the Murchison Widefield Array: Radio-Frequency Interference Analysis and Mitigation , 2015, Publications of the Astronomical Society of Australia.

[6]  Cathryn M. Trott,et al.  Epoch of reionization window. I. Mathematical formalism , 2014, 1404.2596.

[7]  J. M. Martin,et al.  21 cm observation of large-scale structures at z ~ 1 - Instrument sensitivity and foreground subtraction , 2011, 1108.1474.

[8]  Tao An,et al.  EXPLORING THE COSMIC REIONIZATION EPOCH IN FREQUENCY SPACE: AN IMPROVED APPROACH TO REMOVE THE FOREGROUND IN 21 cm TOMOGRAPHY , 2013 .

[9]  M. Morales,et al.  Reionization and Cosmology with 21-cm Fluctuations , 2009, 0910.3010.

[10]  Bryna Hazelton,et al.  FOUR FUNDAMENTAL FOREGROUND POWER SPECTRUM SHAPES FOR 21 cm COSMOLOGY OBSERVATIONS , 2012, 1202.3830.

[11]  Christopher L. Williams,et al.  LOW-FREQUENCY IMAGING OF FIELDS AT HIGH GALACTIC LATITUDE WITH THE MURCHISON WIDEFIELD ARRAY 32 ELEMENT PROTOTYPE , 2012, 1203.5790.

[12]  Max Tegmark,et al.  A method for 21 cm power spectrum estimation in the presence of foregrounds , 2011, Physical Review D.

[13]  Steven Furlanetto,et al.  Cosmology at low frequencies: The 21 cm transition and the high-redshift Universe , 2006 .

[14]  S. J. Tingay,et al.  Measuring phased‐array antenna beampatterns with high dynamic range for the Murchison Widefield Array using 137 MHz ORBCOMM satellites , 2015, 1505.07114.

[15]  David R. DeBoer,et al.  WHAT NEXT-GENERATION 21 cm POWER SPECTRUM MEASUREMENTS CAN TEACH US ABOUT THE EPOCH OF REIONIZATION , 2013, 1310.7031.

[16]  David R. DeBoer,et al.  MULTIREDSHIFT LIMITS ON THE 21 cm POWER SPECTRUM FROM PAPER , 2014, 1408.3389.

[17]  Max Tegmark,et al.  Mapmaking for precision 21 cm cosmology , 2014, Physical Review D.

[18]  Christopher Hirata,et al.  A simulation-calibrated limit on the H i power spectrum from the GMRT Epoch of Reionization experiment , 2013, 1301.5906.

[19]  A. A. Deshpande,et al.  FAST HOLOGRAPHIC DECONVOLUTION: A NEW TECHNIQUE FOR PRECISION RADIO INTERFEROMETRY , 2012, 1209.1653.

[20]  A. Stebbins,et al.  ALL-SKY INTERFEROMETRY WITH SPHERICAL HARMONIC TRANSIT TELESCOPES , 2013, 1302.0327.

[21]  A. R. Whitney,et al.  The Murchison Widefield Array: The Square Kilometre Array Precursor at Low Radio Frequencies , 2012, Publications of the Astronomical Society of Australia.

[22]  David F. Moore,et al.  NEW 145 MHz SOURCE MEASUREMENTS BY PAPER IN THE SOUTHERN SKY , 2011, 1105.1367.

[23]  Max Tegmark,et al.  FOREGROUNDS IN WIDE-FIELD REDSHIFTED 21 cm POWER SPECTRA , 2015, 1502.07596.

[24]  Matias Zaldarriaga,et al.  An improved method for 21‐cm foreground removal , 2009, 0903.4890.

[25]  C. Dickinson,et al.  H i intensity mapping: a single dish approach , 2012, 1209.0343.

[26]  Stephanie Thalberg,et al.  Interferometry And Synthesis In Radio Astronomy , 2016 .

[27]  Donald C. Backer,et al.  CALIBRATION OF LOW-FREQUENCY, WIDE-FIELD RADIO INTERFEROMETERS USING DELAY/DELAY-RATE FILTERING , 2009, 0901.2575.

[28]  Jingying Wang,et al.  A METHOD TO EXTRACT THE ANGULAR POWER SPECTRUM OF THE EPOCH OF REIONIZATION FROM LOW-FREQUENCY RADIO INTERFEROMETERS , 2012, 1209.2750.

[29]  K. Gorski,et al.  HEALPix: A Framework for High-Resolution Discretization and Fast Analysis of Data Distributed on the Sphere , 2004, astro-ph/0409513.

[30]  Saleem Zaroubi,et al.  The Scale of the Problem : Recovering Images of Reionization with GMCA , 2012, 1209.4769.

[31]  Roger Cappallo,et al.  The Murchison Widefield Array Commissioning Survey: A Low-Frequency Catalogue of 14 110 Compact Radio Sources over 6 100 Square Degrees , 2014, Publications of the Astronomical Society of Australia.

[32]  Judd D. Bowman,et al.  FOREGROUND CONTAMINATION IN INTERFEROMETRIC MEASUREMENTS OF THE REDSHIFTED 21 cm POWER SPECTRUM , 2008, 0807.3956.

[33]  Cathryn M. Trott,et al.  THE IMPACT OF POINT-SOURCE SUBTRACTION RESIDUALS ON 21 cm EPOCH OF REIONIZATION ESTIMATION , 2012, 1208.0646.

[34]  E. Lenc,et al.  GLEAM: The GaLactic and Extragalactic All-Sky MWA Survey , 2015, Publications of the Astronomical Society of Australia.

[35]  E. R. Switzer,et al.  MEASUREMENT OF 21 cm BRIGHTNESS FLUCTUATIONS AT z ∼ 0.8 IN CROSS-CORRELATION , 2012, 1208.0331.

[36]  Alan E. E. Rogers,et al.  Science with the Murchison Widefield Array , 2012, Publications of the Astronomical Society of Australia.

[37]  J. Roerdink,et al.  A morphological algorithm for improving radio-frequency interference detection , 2012, 1201.3364.

[38]  A. R. Whitney,et al.  A 189 MHz, 2400 deg2 POLARIZATION SURVEY WITH THE MURCHISON WIDEFIELD ARRAY 32-ELEMENT PROTOTYPE , 2013, 1305.6047.

[39]  Max Tegmark,et al.  CONFIRMATION OF WIDE-FIELD SIGNATURES IN REDSHIFTED 21 cm POWER SPECTRA , 2015, 1506.06150.

[40]  Hannes Jensen,et al.  Reionization and the Cosmic Dawn with the Square Kilometre Array , 2012, 1210.0197.

[41]  Rachel L. Webster,et al.  Overcoming real-world obstacles in 21 cm power spectrum estimation: A method demonstration and results from early Murchison Widefield Array data , 2013, 1304.4229.

[42]  Cathryn M. Trott,et al.  Epoch of reionization window. II. Statistical methods for foreground wedge reduction , 2014, 1404.4372.

[43]  Roger J. Cappallo,et al.  Real-Time Calibration of the Murchison Widefield Array , 2008, IEEE Journal of Selected Topics in Signal Processing.

[44]  E. R. Switzer,et al.  Determination of z ∼ 0.8 neutral hydrogen fluctuations using the 21 cm intensity mapping autocorrelation , 2013, 1304.3712.

[45]  Max Tegmark,et al.  A fast method for power spectrum and foreground analysis for 21 cm cosmology , 2013 .

[46]  Judd D. Bowman,et al.  IMPROVING FOREGROUND SUBTRACTION IN STATISTICAL OBSERVATIONS OF 21 cm EMISSION FROM THE EPOCH OF REIONIZATION , 2006 .

[47]  Marc Moniez,et al.  BAORadio: A digital pipeline for radio interferometry and 21 cm mapping of large scale structures , 2012, 1209.3266.

[48]  Mervyn J. Lynch,et al.  THE PRECISION ARRAY FOR PROBING THE EPOCH OF RE-IONIZATION: EIGHT STATION RESULTS , 2009, 0904.2334.

[49]  S. Zaroubi,et al.  Foregrounds for observations of the cosmological 21 cm line - I. First Westerbork measurements of Galactic emission at 150 MHz in a low latitude field , 2009, 0904.0404.

[50]  S. Markoff,et al.  LOFAR - low frequency array , 2006 .

[51]  Alan E. E. Rogers,et al.  The Murchison Widefield Array: Design Overview , 2009, Proceedings of the IEEE.

[52]  Michael Biehl,et al.  Post‐correlation radio frequency interference classification methods , 2010, 1002.1957.

[53]  James Aguirre,et al.  A SENSITIVITY AND ARRAY-CONFIGURATION STUDY FOR MEASURING THE POWER SPECTRUM OF 21 cm EMISSION FROM REIONIZATION , 2011, 1103.2135.

[54]  David F. Moore,et al.  New Limits on 21cm EoR From PAPER-32 Consistent with an X-Ray Heated IGM at z=7.7 , 2013, 1304.4991.

[55]  N. Udaya Shankar,et al.  IMAGING THE EPOCH OF REIONIZATION: LIMITATIONS FROM FOREGROUND CONFUSION AND IMAGING ALGORITHMS , 2011, 1106.1297.

[56]  B. Parker.  The first galaxies. , 1981 .

[57]  David R. DeBoer,et al.  THE BARYON ACOUSTIC OSCILLATION BROADBAND AND BROAD-BEAM ARRAY: DESIGN OVERVIEW AND SENSITIVITY FORECASTS , 2012, 1210.2413.

[58]  L. Knox,et al.  Multifrequency Analysis of 21 Centimeter Fluctuations from the Era of Reionization , 2005 .

[59]  Abhirup Datta,et al.  BRIGHT SOURCE SUBTRACTION REQUIREMENTS FOR REDSHIFTED 21 cm MEASUREMENTS , 2010 .

[60]  Tim J. Cornwell,et al.  The Noncoplanar Baselines Effect in Radio Interferometry: The W-Projection Algorithm , 2008, IEEE Journal of Selected Topics in Signal Processing.

[61]  E. Lenc,et al.  Understanding instrumental Stokes leakage in Murchison Widefield Array polarimetry , 2014, 1412.4466.

[62]  David F. Moore,et al.  A TECHNIQUE FOR PRIMARY BEAM CALIBRATION OF DRIFT-SCANNING, WIDE-FIELD ANTENNA ELEMENTS , 2011, 1111.2882.

[63]  Christopher L. Williams,et al.  A STUDY OF FUNDAMENTAL LIMITATIONS TO STATISTICAL DETECTION OF REDSHIFTED H i FROM THE EPOCH OF REIONIZATION , 2013, 1308.0565.

[64]  David F. Moore,et al.  A PER-BASELINE, DELAY-SPECTRUM TECHNIQUE FOR ACCESSING THE 21 cm COSMIC REIONIZATION SIGNATURE , 2012, 1204.4749.

[65]  H. Rottgering,et al.  Ionospheric calibration of low frequency radio interferometric observations using the peeling scheme I. Method description and first results , 2009, 0904.3975.

[66]  Jason Manley,et al.  OPENING THE 21 cm EPOCH OF REIONIZATION WINDOW: MEASUREMENTS OF FOREGROUND ISOLATION WITH PAPER , 2013, 1301.7099.

[67]  Miguel F. Morales,et al.  Software holography: interferometric data analysis for the challenges of next generation observatories , 2008, 0810.5107.

[68]  David F. Moore,et al.  PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM AT z = 8.4 , 2015, 1502.06016.

[69]  L. Knox,et al.  Multifrequency Analysis of 21 Centimeter Fluctuations from the Era of Reionization , 2004, astro-ph/0408515.