Detailed study of the ELAIS N1 field with the uGMRT - I. Characterizing the 325 MHz foreground for redshifted 21 cm observations

Abstract

In this first paper of the series, we present initial results of newly upgraded Giant Meterwave Radio Telescope (uGMRT) observation of European Large-Area ISO Survey-North 1 (ELAIS-N1) at 325 MHz with 32 MHz bandwidth. Precise measurement of fluctuations in Galactic and extragalactic foreground emission as a function of frequency as well as angular scale is necessary for detecting redshifted 21-cm signal of neutral hydrogen from Cosmic Dawn, Epoch of Reionization (EoR) and post-reionization epoch. Here, for the first time we have statistically quantified the Galactic and extragalactic foreground sources in the ELAIS-N1 field in the form of angular power spectrum using the newly developed Tapered Gridded Estimator (TGE). We have calibrated the data with and without direction-dependent calibration techniques. We have demonstrated the effectiveness of TGE against the direction dependent effects by using higher tapering of field of view (FoV). We have found that diffuse Galactic synchrotron emission (DGSE) dominates the sky, after point source subtraction, across the angular multipole range 1115 5083 and 1565 4754 for direction-dependent and -independent calibrated visibilities respectively. The statistical fluctuations in DGSE has been quantified as a power law of the form C = A −β . The best fitted values of (A, β) are (62 ± 6 mK 2 , 2.55 ± 0.3) and (48 ± 4 mK 2 , 2.28 ± 0.4 ) for the two different calibration approaches. For both the cases, the power law index is consistent with the previous measurements of DGSE in other parts of sky.

A study of Kepler supernova remnant: angular power spectrum estimation from radio frequency data

“…A detailed study (Choudhuri et al 2016a) has demonstrated, using simulations, that the TGE is able to suppress the contribution from extraneous sources (foregrounds) in the outer regions of the telescope's field of view (FoV) while faithfully estimating C ℓ from the visibility data. The same has been recently demonstrated using 325 MHz uGMRT observations (Chakraborty et al 2019) of the diffuse Galactic synchrotron emission (DGSE).…”

Stringent constraint on the radio signal from dark matter annihilation in dwarf spheroidal galaxies using the TGSS

“…We choose this 𝑈 range because 𝑈 < 5deg −1 the power spectrum is convolved with the Fourier transform of the window function, and 𝑘 > 30deg −1 the image is convolved with the synthesized beam. These measured slopes of the angular power spectrum are consistent with earlier power spectra measurements of the diffuse Galactic synchrotron emission (Bernardi et al 2009;Ghosh et al 2012;Iacobelli et al 2013;Choudhuri et al 2017;Chakraborty et al 2019). Apart from an overall consistency check, this result clearly indicates that the TGSS data are suitable to probe diffuse emission at large angular scale, similar to the expected radio signal associated with the DM halo of the dSph galaxies, present in the field.…”

Calibration requirements for Epoch of Reionization 21-cm signal observations -- II. Analytical estimation of the bias and variance with time-correlated residual gains

“…This method and its variants (Datta et al (2007); Choudhuri et al (2014Choudhuri et al ( , 2016Choudhuri et al ( , 2019; Bharadwaj et al (2019) etc.) have been used to estimate the angular power spectrum of the diffused galactic foreground (Ghosh et al 2012;Choudhuri et al 2017b;Chakraborty et al 2019a;Choudhuri et al 2020) as well as the power spectrum of H i distribution in nearby galaxies (Dutta et al 2009;Dutta & Bharadwaj 2013;Nandakumar & Dutta 2020). These works propagate the uncertainties in each visibility estimate and combine that with the sample variance error in measuring the power spectrum to quote uncertainties in the power spectrum estimates.…”