All-sky angular power spectrum – I. Estimating brightness temperature fluctuations using the 150-MHz TGSS survey

Monthly Notices of the Royal Astronomical Society, vol. 494, pp. 1936–1945

Abstract

ABSTRACT Measurements of the Galactic synchrotron emission are important for the 21-cm studies of the epoch of reionization. The study of synchrotron emission is also useful for quantifying the fluctuations in the magnetic field and the cosmic-ray electron density of the turbulent interstellar medium (ISM) of our Galaxy. Here, we present the all-sky angular power spectrum (Cℓ) measurements of the diffuse synchrotron emission obtained using the TIFR GMRT Sky Survey (TGSS) at 150 MHz. We estimate Cℓ using visibility data both before and after subtracting the modelled point sources. The amplitude of the measured Cℓ decreases significantly after subtracting the point sources, and it is slightly higher in the Galactic plane for the residual data. The residual Cℓ is most likely to be dominated by the Galactic synchrotron emission. The amplitude of the residual Cℓ decreases significantly away from the Galactic plane. We find that the measurements are quite symmetric in the Northern and Southern hemispheres except in the latitude range 15°−30°, which is the transition region from the disc-dominated to the diffuse halo-dominated region. A comparison between this interferometric measurement and the scaled version of the Haslam rms map at 150 MHz shows that the correlation coefficient (r) is greater than 0.5 for most of the latitude ranges considered here. This indicates that the TGSS is quite sensitive to the diffuse Galactic synchrotron radiation.

Authors 6

1. Samir Choudhuri corresponding

   National Centre for Radio Astrophysics · Queen Mary University of London

   Affiliation as printed

   Astronomy Unit, Queen Mary University of London, Mile End Road, London E1 4NS, UK

   National Centre For Radio Astrophysics, Post Bag 3, Ganeshkhind, Pune 411 007, India

2. Abhik Ghosh

   South African Radio Astronomy Observatory · Banwarilal Bhalotia College · University of the Western Cape

   Affiliation as printed

   Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, Bellville 7535, South Africa

   Department of Physics, Banwarilal Bhalotia College, GT Rd, Ushagram, Asansol, West Bengal, India

   The South African Radio Astronomy Observatory (SARAO), 2 Fir Street, Black River Park, Observatory, Cape Town 7925, South Africa

3. Nirupam Roy

   Indian Institute of Science Bangalore

   Affiliation as printed

   Department of Physics, Indian Institute of Science, Bangalore 560012, India

4. Somnath Bharadwaj

   Indian Institute of Technology Kharagpur

   Affiliation as printed

   Department of Physics and Centre for Theoretical Studies, IIT Kharagpur, Kharagpur 721 302, India

5. Huib T. Intema Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory, Leiden University, Niels Bohrweg 2, NL-2333CA, Leiden, The Netherlands

6. Sk. Saiyad Ali

   Jadavpur University

   Affiliation as printed

   Department of Physics, Jadavpur University, Kolkata 700032, India