Detailed study of the ELAIS N1 field with the uGMRT – I. Characterizing the 325 MHz foreground for redshifted 21 cm observations. Issue 3 (10th June 2019)

• Record Type: Journal Article
• Authors: Chakraborty, Arnab; Datta, Abhirup; Choudhuri, Samir; Roy, Nirupam; Intema, Huib; Choudhury, Madhurima; Datta, Kanan K; Pal, Srijita; Bharadwaj, Somnath; Dutta, Prasun; Choudhury, Tirthankar Roy
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 487:Issue 3(2019)
• Page Start: 4102
• Page End: 4113
• Publication Date: 2019-06-10
• Subjects: methods: data analysis -- diffuse radiation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stz1580
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: In this first paper of the series, we present initial results of newly upgraded Giant Metrewave 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 $1115 \leqslant \mathcal {\ell } \leqslant 5083$ and $1565 \leqslant \mathcal {\ell } \leqslant 4754$ for direction-dependent and -independent calibrated visibilities, respectively. The statistical fluctuations in DGSE has been quantified as a power law of the form $\mathcal {C}_{\mathcal {\ell }}= A \mathcal {\ell }^{-\beta }$ . The best-fitting 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.