Observed and Simulated Foregrounds for Reionization Studies with the Murchison Widefield Array Nithyanandan Thyagarajan, Daniel Jacobs, Judd Bowman + MWA EoR Collaboration (To be submitted to ApJ)

Why study the Epoch of Reionization? Recombination epoch constrained with CMB Information available on nearby universe No direct probes of ``dark ages’’ where matter collapses around density perturbations Formation of large scale structures and evolution of astrophysical objects need to be probed Neutral Hydrogen is a direct probe of the Reionization epoch Current instruments have enough sensitivity for statistical detection of HI from the EoR

Why is radio interferometry suited? HI, the most abundant EoR material emits in radio Measurements in radio interferometry directly measure spatial scale information Antenna voltage correlations (visibilities) measured between antennas are Fourier representation of sky brightness distribution The spectrum of visibilities for a cosmological spectral line represents line of sight distance Frequency Velocity Distance

Thyagarajan et al.(2013) Morales & Hewitt (2004)

Radio Interferometry in one slide EoR HI

Limiting Factor… Loads and loads of foregrounds Power spectrum detection possible if foregrounds removed down to theoretical confusion limit Precise understanding of foreground and its removal required

MWA Sensitivity Predictions Thyagarajan et al. (2013)

Foregrounds in Fourier Space True Foreground Power Baseline or uv--coverage Instrumental Transfer Function in Fourier Space Foreground levels or source confusion in image Synthesized Beam (PSF) Antenna Power Pattern Instrumental Bandpass Response Shift to geometric delay Foreground power through instrument Thyagarajan et al. (2013)

Fourier Space Coordinates

MWA Data Example

Simulation Ingredients Antenna Power Pattern Foreground Emission – Diffuse Emission – Compact Emission Bandpass shapes de Oliveira-Costa et al.(2008)NVSS + SUMSS Catalogs

Data vs. Simulations

Foreground Signatures Diffuse Emission in Fourier Space Compact Emission in Fourier Space ``Pitchfork’’ Effect Bright Galactic Center off- zenith in western horizon Diffuse emission even on wide antenna spacings ``Edge-heavy’’ features Compact emission more centrally concentrated Compact emission in secondary lobes of power pattern visible Compact emissions dominate wedge center Diffuse emission significant even on wide antenna spacings Emission in secondary lobes of power pattern visible

Foreground Mitigation Technique Galactic center is the dominant source of foreground contamination Least contamination with Northward baselines Worst contamination with Eastward baselines Removing susceptible baselines reduces overall contamination by an order of magnitude Foreground mitigation technique can be fine-tuned for optimal response

Summary Very important to understand foreground signatures before their removal in EoR studies Detailed all-sky foreground simulation Bright Galactic Center near the horizon is a significant contaminant Diffuse emission is present even on wide baselines Compact emission dominates central wedge regions Net effect is a ``pitchfork’’ signature in Fourier Space Selective flagging of baselines based on `a priori’ knowledge of foregrounds can mitigate contamination by an order of magnitude