• Nirupam Roy

      Articles written in Journal of Astrophysics and Astronomy

    • Prospects of Measuring the Angular Power Spectrum of the Diffuse Galactic Synchrotron Emission with SKA1 Low

      Sk. Saiyad Ali Somnath Bharadwaj Samir Choudhuri Abhik Ghosh Nirupam Roy

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      The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum $C_\ell$ of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the $C_\ell$ of the DGSE using 150 MHz GMRT data. Earlier measurements of $C_\ell$ are restricted to $\ell \le \ell _{\max } \sim 10^{3}$ for the DGSE, the signal at the larger $\ell$ values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the $C_\ell$ of the DGSE to larger values of $\ell _{\max }$ with SKA1 Low. Our results show that it should be possible to achieve $\ell _{\max }\sim 10^{4}$ and $∼10^5$ with 2 minutes and 10 hours of observations respectively.

    • Editorial

      Tirthankar Roy Choudhury Abhirup Datta Preeti Kharb Nirupam Roy

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    • Probing galaxy evolution through Hi 21-cm emission and absorption: current status and prospects with square kilometre array


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      One of the major science goals of square kilometre array (SKA) is to understand the role played by atomic hydrogen (Hi) gas in the evolution of galaxies throughout cosmic time. The hyperfine transition line of the hydrogen atom at 21-cm is one of the best tools to detect and study the properties of Hi gas associated with galaxies. In this paper, we review our current understanding of Hi gas and its relationship with galaxies through observations of the 21-cm line both in emission and absorption. In addition, we provide an overviewof the Hi science that will be possible with SKA and its precursors and pathfinders, i.e., Hi 21-cm emission and absorption studies of galaxies from nearby to high redshifts that will trace various processes governing galaxy evolution.

  • Journal of Astrophysics and Astronomy | News

    • Continuous Article Publication

      Posted on January 27, 2016

      Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

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