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Study of Foregrounds and Limitations to EoR Detection

Study of Foregrounds and Limitations to EoR Detection. Nithyanandan Thyagarajan N. Udaya Shankar Ravi Subrahmanyan (Raman Research Institute). 1. HI Power Spectrum. Statistical detections seem feasible Forms a key science of SKA precursors & pathfinders MWA LOFAR GMRT LWA PAPER.

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Study of Foregrounds and Limitations to EoR Detection

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  1. Study of Foregrounds and Limitations to EoR Detection Nithyanandan Thyagarajan N. Udaya Shankar Ravi Subrahmanyan (Raman Research Institute) Nithyanandan Thyagarajan, RRI, India 1

  2. HI Power Spectrum • Statistical detections seem feasible • Forms a key science of SKA precursors & pathfinders • MWA • LOFAR • GMRT • LWA • PAPER Lidz et al. (2008) HI EoR Power Spectrum detection seem feasible Nithyanandan Thyagarajan, RRI, India

  3. Challenges due to Contamination Expected sources of contamination Nithyanandan Thyagarajan, RRI, India Foreground Galactic emission Foreground extragalactic radio continuum sources Residual Errors after Modeling Thermal Noise

  4. Foreground Removal • Knowledge of spectral information • Galactic modeling • Extragalactic source spectral index • Knowledge of power spectrum symmetry • HI power spectrum isotropic • Foregrounds not isotropic and contain structure in Fourier space Morales & Hewitt (2004) Separation of contamination using symmetries in Fourier space Nithyanandan Thyagarajan, RRI, India

  5. Contamination after Foreground Removal Our focus on Classical Source Confusion, mode-mixing contamination & Thermal Noise Nithyanandan Thyagarajan, RRI, India Confusion from unresolved unsubtracted/mis-subtracted sources due to poor angular resolution & limited flux sensitivity (Classical Source Confusion) Confusion from sidelobes of frequency dependent beams due to mode-mixing Thermal Noise Contamination from imaging algorithms (Vedantham et al. 2011)

  6. Framework of our Study Hopkins et al. (2003) Nithyanandan Thyagarajan, RRI, India Radio Source Distribution 128-tile MWA Layout Relations

  7. Classical Confusion in k-space k Nithyanandan Thyagarajan, RRI, India Consider zenith pixel Smooth variation along frequency of residuals Delta function at k|| = 0 Array configuration determines variation along Bandpass spillover into EoR window

  8. Bandpass Windows Rectangular Blackman-Nutall Blackman-Nutall window reduces sidelobes by more than 3 orders of magnitude NithyanandanThyagarajan, RRI, India

  9. Classical Confusion in k-space Blackman-Nutall Window Rectangular Window Delta function at k|| = 0 spills over due to bandpass Nithyanandan Thyagarajan, RRI, India

  10. Sidelobe Confusion Nithyanandan Thyagarajan, RRI, India Classical confusion is the source of sidelobes Sidelobes have frequency structure (results in mode-mixing)

  11. Mode-mixing Principle Bowman et al. (2009) ηcont = umax l / f Vedantham et al. (2011) Transverse structure of contamination translates to a line-of-sight structure due to mode-mixing l-f invariance Nithyanandan Thyagarajan, RRI, India

  12. Sidelobe Confusion in k-space k|| m v IFT k l u FT Nithyanandan Thyagarajan, RRI, India

  13. Sidelobe Confusion in k-space Horizon (l2+m2=1) First null of Primary Beam Edge Brightening NithyanandanThyagarajan, RRI, India

  14. Sidelobe Confusion in k-space Blackman-Nutall Window Rectangular Window NithyanandanThyagarajan, RRI, India

  15. Observed Sensitivity in k-space Nithyanandan Thyagarajan, RRI, India

  16. Thermal Noise Nithyanandan Thyagarajan, RRI, India Vrms(u,v,f)= 2kBTsys/Ae (Δfτ)1/2 Thermal noise uniform along k|| Distribution along k-perp determined by Baseline distribution Snapshot mode: 8 sec integration time Drift Scan mode: 2 hours Target mode: 1000 hours

  17. Thermal Noise in k-space Snapshot Drift Target Nithyanandan Thyagarajan, RRI, India

  18. Combined Uncertainty • Add in quadrature • Thermal noise dominates in snapshot mode Nithyanandan Thyagarajan, RRI, India

  19. Modeled EoR Power Spectrum • P(k) from Lidz et al.(2008) for z=7.32, ionization fraction=0.54 • Peculiar Velocity corrections applied Nithyanandan Thyagarajan, RRI, India

  20. Refined EoR window Blackman-Nutall Window Rectangular Window NithyanandanThyagarajan, RRI, India

  21. Bandpass windows, Refined EoR windows & EoR Sensitivity Nithyanandan Thyagarajan, RRI, India

  22. Conclusions Nithyanandan Thyagarajan, RRI, India • Radio source statistics and 128T MWA layout • Comprehensive estimate in k-space of • Sidelobe confusion due to mode-mixing • Classical Source Confusion • Thermal Noise • Array configuration has different effects on each • Thermal Noise overwhelms in snapshot modebut signal detectable with longer integration times • Optimal choice of bandpass & EoR windows

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