Abstract Details
| Name: Samir Choudhuri Affiliation: NCRA-TIFR Conference ID: ASI2018_1535 Title : Visibility-based Power Spectrum Estimation for Low-Frequency Radio Interferometric Observations Authors and Co-Authors : Supervisors: Prof. Somnath Bharadwaj (IIT Kharagpur) and Dr. Sk. Saiyad Ali (Jadavpur University) Abstract Type : Thesis Abstract Category : Thesis Abstract : The observations of the redshifted 21-cm signal contain a wealth of cosmological and astrophysical information. The study of this signal from high redshift Universe provides an opportunity to learn about the properties of the first galaxies and stars. But, the problem is particularly challenging due to the presence of foregrounds and system noise. In this thesis we present a visibility based estimator namely, the Tapered Gridded Estimator (TGE) to quantify the fluctuations of sky signal statistically. The TGE has three novel features. First, the estimator uses gridded visibilities to estimate the power spectrum which is computationally much faster than individually correlating the visibilities. Second, a positive noise bias is removed by subtracting the auto-correlation of the visibilities which is responsible for the noise bias. Third, the estimator allows us to taper the field of view so as to suppress the contribution from the sources in the outer regions and the sidelobes of the telescope's primary beam. We validate the estimator and its statistical error using realistic simulations of Giant Meterwave Radio Telescope (GMRT) 150 MHz observations. We also show that the TGE successfully suppresses contributions from the outer region of the primary beam. Finally, we have used the TGE to estimate angular power spectrum for two of the fields observed by TIFR GMRT Sky Survey (TGSS). We find that the sky signal, after subtracting the point sources, is dominated by the diffuse Galactic synchrotron radiation across the angular multipole range 200 to 500. |