• C. H. Ishwara-Chandra

      Articles written in Journal of Astrophysics and Astronomy

    • GMRT detection of HI 21 cm associated absorption towards thez = 1.2 red quasar 3C 190

      C. H. Ishwara-Chandra K. S. Dwarakanath K. R. Anantharamaiah

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      We report the GMRT detection of associated HI 21 cm-line absorption in thez = 1.1946 red quasar 3C 190. Most of the absorption is blue-shifted with respect to the systemic redshift. The absorption, at ∼ 647.7 MHz, is broad and complex, spanning a velocity width of ∼ 600 kms−1. Since the core is self-absorbed at this frequency, the absorption is most likely towards the hotspots. Comparison of the radio and deep optical images reveal linear filaments in the optical which overlap with the brighter radio jet towards the south-west. We therefore suggest that most of the HI 21 cm-line absorption could be occurring in the atomic gas shocked by the south-west jet.

    • The Double–Double Radio Galaxy 3C293

      S. A. Joshi S. Nandi D. J. Saikia C. H. Ishwara-Chandra C. Konar

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      We present the results of radio continuum observations at frequencies ranging from ∼ 150–5000 MHz of the misaligned double–double radio galaxy (DDRG) 3C293 (J1352+3126) using the GMRT and the VLA, and estimate the time-scale of interruption of jet activity to be less than ∼ 0.1 Myr.

    • High-Redshift Radio Galaxies from Deep Fields

      C. H. Ishwara-Chandra S. K. Sirothia Y. Wadadekar S. Pal

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      Most of the radio galaxies with 𝑧 > 3 have been found using the red-shift spectral index correlation.We have started a programme with the Giant Metrewave Radio Telescope (GMRT) to exploit this correlation at flux density levels about 100 times deeper than the known high-redshift radio galaxies, with an aim to detect candidate high-redshift radio galaxies. Here we present results from the deep 150 MHz observations of LBDS-Lynx field, which has been imaged at 327, 610 and 1412 MHz with the Westerbork Synthesis Radio Telescope (WSRT) and at 1400 and 4860 MHz with the Very Large Array (VLA). We find about 150 radio sources with spectra steeper than 1. About two-thirds of these are not detected in Sloan Digital Sky Survey (SDSS), hence are strong candidate high-redshift radio galaxies, which need to be further explored with deep infra-red imaging and spectroscopy to estimate the red-shift.

    • Deep GMRT 150 MHz Observations of the DEEP2 Fields: Searching for High Red-Shift Radio Galaxies Revisited

      Susanta K. Bisoi C. H. Ishwara-Chandra S. K. Sirothia P. Janardhan

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      High red-shift radio galaxies are best searched at low radio frequencies, due to its steep radio spectra. Here we present preliminary results from our programme to search for high red-shift radio galaxies to ∼ 10 to 100 times fainter than the known population till date. We have extracted ultra-steep spectrum (USS) samples from deep 150 MHz Giant Meter-wave Radio Telescope (GMRT) observations from one of the three well-studied DEEP2 fields to this effect. From correlating these radio sources with respect to the high-frequency catalogues such as VLA, FIRST and NVSS at 1.4 GHz, we find ∼ 100 steep spectrum (spectral index, 𝛼 > 1) radio sources, which are good candidates for high red-shift radio galaxies.

    • Synergy Between Radio and Optical Telescopes: Optical Followup of Extragalactic Radio Sources

      C. H. Ishwara-Chandra

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      Distance measurement is a must to characterize any source in the sky. In the radio band, it is rarely possible to get distance or redshift measurements. The optical band is the most used band to get distance estimate of sources, even for those originally discovered in other bands of the electromagnetic spectrum. However, the spectroscopic redshift measurements even for fairly bright radio sample is grossly incomplete, implying un-explored discovery space. Here we discuss the scope of optical follow up of radio sources, in particular the radio loud AGNs, from the present generation radio telescopes.

  • 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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