Samir Choudhuri

Visiting Fellow
Email: samir [at]
Phone: +91 - 20 - 25719240
Extn: 9240
Office: G124
National Centre for Radio Astrophysics
Tata Institute of Fundamental Research
Savitribai Phule Pune University Campus,
Pune 411 007
Maharashtra, INDIA

Main Research Areas: Epoch of Reionization; 21-cm Cosmology; Low Frequency Radio Interferometry; Diffuse Synchrotron Emission


Samir Choudhuri obtained a B.Sc. in Physics from Suri Vidyasagar College in 2009 and an M.Sc in Physics from Jadavpur University, Kolkata, in 2011. He then joined the Indian Institute of Technology, Kharagpur for his Ph.D. under the guidance of Prof. Somnath Bharadwaj (IIT-Kharagpur) and Dr. Sk. Saiyad Ali (Jadavpur University, Kolkata), completing his Ph.D. in 2016. He is currently a post-doctoral fellow at NCRA-TIFR.

Research description:

The Universe changed its phase from a cold and neutral state to a mostly warm and ionized state due to ionizing radiation from the first sources at high redshifts, z ~ 6-20. This epoch is known as the Epoch of Reionization (EoR). The study of reionization provides an opportunity to learn about the properties of the first galaxies and stars. The timing, duration and characteristics of the subsequent events, which led to the reionization of the Universe, contain an enormous amount of information about the first cosmic structures. Observations of the redshifted HI 21cm transition can be used to probe this epoch. This HI 21cm signal, is, however, buried in the emission from other astrophysical sources which are collectively referred to as ``foregrounds''. Understanding and characterizing the foreground properties are necessary in order to study the cosmological signal, and the study of foregrounds is interesting also in its own right. The fluctuations of synchrotron radiation detected in total intensity radio maps directly reflect the spectrum of density and magnetic field fluctuations. It is currently perceived that a statistical analysis of these fluctuations in terms of the power spectrum holds a great potential for characterizing the HI 21cm signal and also the foregrounds.
Visibility based Power Spectrum Estimator:
We have developed a new estimator (the ``Tapered Gridded Estimator'') to estimate the angular power spectrum of the sky signal. The Tapered Gridded Estimator (TGE) estimates the angular power spectrum directly from the interferometric visibility data, removes the noise bias self-consistently and also tapers the sky signal while gridding the visibilities to remove the effect of unsubtracted foreground components at the outer regions of the field of view. We have further generalized the angular power spectrum estimator (TGE) into a 3-D power spectrum estimator to measure the amplitude of the different Fourier modes in a space that is the Fourier conjugate of the comoving distance.

Selected publications:

1. The visibility based Tapered Gridded Estimator (TGE) for the redshifted 21-cm power spectrum (S. Choudhuri, S. Bharadwaj, S. Chatterjee, S. S. Ali, N. Roy & A. Ghosh, 2016, MNRAS, 463, 4093)

2. Imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA (R. Ghara, T. Roy Choudhury, K. K. Datta & S Choudhuri, 2017, MNRAS, 464, 2234)

3. Tapering the sky response for angular power spectrum estimation from low-frequency radio-interferometric data (S. Choudhuri, S. Bharadwaj, N. Roy, A. Ghosh & S. S. Ali, 2016, MNRAS, 459, 151)

4. Visibility based angular power spectrum estimation in low frequency radio interferometric observations (S. Choudhuri, S. Bharadwaj, A. Ghosh & S. S. Ali, 2014, MNRAS, 445, 4351)