1. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Study of Foregrounds and Limitations to EoR Detection Nithyanandan Thyagarajan N. Udaya Shankar Ravi Subrahmanyan (Raman Research Institute) Nithyanandan Thyagarajan, RRI, India 1

2. Indo – SA Joint Astronomy Workshop, August 2012 / 22 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 2Nithyanandan Thyagarajan, RRI, India

3. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Challenges due to Contamination Foreground Galactic emission Foreground extragalactic radio continuum sources Residual Errors after Modeling Thermal Noise Expected sources of contamination 3Nithyanandan Thyagarajan, RRI, India

4. Indo – SA Joint Astronomy Workshop, August 2012 / 22 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 Separation of contamination using symmetries in Fourier space Morales & Hewitt (2004) 4Nithyanandan Thyagarajan, RRI, India

5. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Contamination after Foreground Removal 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) Our focus on Classical Source Confusion, mode- mixing contamination & Thermal Noise 5Nithyanandan Thyagarajan, RRI, India

6. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Framework of our Study Radio Source Distribution 128-tile MWA Layout Relations Hopkins et al. (2003) 6Nithyanandan Thyagarajan, RRI, India

7. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Classical Confusion in k-space Consider zenith pixel Smooth variation along frequency of residuals Delta function at k || = 0 Array configuration determines variation along Bandpass spillover into EoR window 7Nithyanandan Thyagarajan, RRI, India k

8. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Bandpass Windows Rectangular Blackman-Nutall Blackman-Nutall window reduces sidelobes by more than 3 orders of magnitude 8 Nithyanandan Thyagarajan, RRI, India

9. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Classical Confusion in k -space Delta function at k || = 0 spills over due to bandpass 9Nithyanandan Thyagarajan, RRI, India Rectangular Window Blackman-Nutall Window

10. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Sidelobe Confusion Classical confusion is the source of sidelobes Sidelobes have frequency structure (results in mode-mixing) 10Nithyanandan Thyagarajan, RRI, India

11. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Mode-mixing Principle Bowman et al. (2009) Vedantham et al. (2011) Transverse structure of contamination translates to a line-of-sight structure due to mode-mixing l-f invariance η cont = u max l / f 11Nithyanandan Thyagarajan, RRI, India

12. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Sidelobe Confusion in k -space k || k u v l m FT IFT 12Nithyanandan Thyagarajan, RRI, India

13. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Sidelobe Confusion in k -space Horizon (l 2 +m 2 =1) First null of Primary Beam Edge Brightening 13Nithyanandan Thyagarajan, RRI, India

14. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Sidelobe Confusion in k -space 14 Nithyanandan Thyagarajan, RRI, India Rectangular Window Blackman-Nutall Window

15. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Observed Sensitivity in k-space 15Nithyanandan Thyagarajan, RRI, India

16. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Thermal Noise V rms (u,v,f)= 2k B T sys /A e (Δf τ) 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 16Nithyanandan Thyagarajan, RRI, India

17. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Thermal Noise in k-space 17Nithyanandan Thyagarajan, RRI, India Snapshot Drift Target

18. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Combined Uncertainty Add in quadrature Thermal noise dominates in snapshot mode 18Nithyanandan Thyagarajan, RRI, India

19. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Modeled EoR Power Spectrum P(k) from Lidz et al.(2008) for z=7.32, ionization fraction=0.54 Peculiar Velocity corrections applied 19Nithyanandan Thyagarajan, RRI, India

20. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Refined EoR window 20 Nithyanandan Thyagarajan, RRI, India Rectangular Window Blackman-Nutall Window

21. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Bandpass windows, Refined EoR windows & EoR Sensitivity Nithyanandan Thyagarajan, RRI, India21

22. Indo – SA Joint Astronomy Workshop, August 2012 / 22 Conclusions Radio source statistics and 128T MWA layout Comprehensive estimate in k-space of 1.Sidelobe confusion due to mode-mixing 2.Classical Source Confusion 3.Thermal Noise Array configuration has different effects on each Thermal Noise overwhelms in snapshot mode but signal detectable with longer integration times Optimal choice of bandpass & EoR windows 22Nithyanandan Thyagarajan, RRI, India