BRIGHT SOURCE SUBTRACTION REQUIREMENTS FOR REDSHIFTED 21 cm MEASUREMENTS

Abstract

The HI 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ( 1 Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well as frequency independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the HI power spectrum. For calibration errors, 0.05 % accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, k ⊥ 0.05 Mpc −1 , in the two-dimensional power spectrum.

THE FUNDAMENTAL MULTI-BASELINE MODE-MIXING FOREGROUND IN 21 cm EPOCH OF REIONIZATION OBSERVATIONS

“…The power spectrum is reduced to the two dimensions shown here by doing a variance weighted average along annuli in the k x and k y directions. This power spectrum is similar to those shown in Datta et al (2010), with a clear wedge shape and a less contaminated EoR window (above the dashed line). The lowest k mode shown is the flat-spectrum (k = 0) mode, which would contain all the foreground power if there were no mode mixing.…”

“…While these single-baseline effects are very important, the mode-mixed power in the Datta et al (2010) simulations is dominated by a multi-baseline effect that we identify in this paper. Multi-baseline mode mixing occurs when measurements from non-identical baselines are combined together to increase the power spectrum sensitivity, as they are for nearly all proposed observations.…”

“…We use this approach because it can be shown to be information lossless (Tegmark 1997a(Tegmark , 1997b, but the results are general to any analysis that combines measurements from non-identical baselines. Following Datta et al (2010), we used the array layout from the originally proposed MWA instrument ) with 512 square antennas (Tingay et al 2013). The normalized antenna response (B) for the central frequency used in the simulation is shown in Figure 1.…”

“…Precision mode-mixing simulations by Datta et al (2010) first identified a distinctive wedge shape in k space, with the mode mixing predominantly below a k ∝ k ⊥ line. Investigations of the response of single baselines to flat-spectrum foregrounds by several groups Trott et al 2012;Vedantham et al 2012;Parsons et al 2012) showed that the wedge shape is characteristic of smooth spectrum astrophysical sources interacting with the chromatic response of the baselines.…”

PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM ATz= 8.4

“…This relationship, known colloquially as "the wedge," was derived analytically (P12b; Vedantham et al 2012;Thyagarajan et al 2013;Liu et al 2014aLiu et al , 2014b, and has been confirmed in simulations (Datta et al 2010;Hazelton et al 2013) and observationally Dillon et al 2014). As described in P12b, the wedge is the result of the delay between when a wavefront originating from foreground emission arrives at the two antennas in a baseline.…”