• N. G. Kantharia

      Articles written in Journal of Astrophysics and Astronomy

    • Carbon recombination lines from the Galactic plane at 34.5 & 328 MHz

      N. G. Kantharia K. R. Anantharamaiah

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      We present the results of a search for carbon recombination lines in the Galaxy at 34.5 MHz (C575α) made using the dipole array at Gauribidanur near Bangalore. Observations made towards 32 directions resulted in detections of lines, in absorption at nine positions. Followup observations at 328 MHz (C272α) using the Ooty Radio Telescope detected these lines in emission. A VLA D-array observation of one of the positions at 330 MHz yielded no detection implying a lower limit of 10′ for the angular size of the line forming region.

      The longitude-velocity distribution of the observed carbon lines indicate that the line forming regions are located mainly between 4 kpc and 7 kpc from the Galactic centre. Combining our results with published carbon recombination line data near 76 MHz (Erickson, McConnell & Anantharamaiah 1995), we obtain constraintson the physical parameters of the line forming regions. We find thatif the angular size of the line forming regions is ≥ 4°, then the range of parameters that fit the data are:Te=20–40 K,ne ∼ 0.1–0.3 cm−3 and pathlengths ∼ 0.07–0.9 pc which may correspond to thin photodissociated regions around molecular clouds. On the other hand, if the line forming regions are ∼ 2° in extent, then warmer gas (Te ∼ 60–300 K) with lower electron densities (ne ∼ 0.03–0.05 cm−3) extending over several tens of parsecs along the line of sight and possibly associated with atomic HI gas can fit the data. Based on the range of derived parameters, we suggest that the carbon line regions are most likely associated with photo-dissociation regions.

    • GMRT and VLA Observations at 49 cm and 20 cm of the HII Region near 𝑙 = 24.8°, 𝑏 = 0.1°

      N. G. Kantharia W. M. Goss D. Anish Roshi Niruj R. Mohan Francois Viallefond

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      We report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near 𝑙 = 24.8°, 𝑏 = 0.1° using the Giant Metrewave Radio Telescope(GMRT) at 1.28 GHz (𝑛 = 172), 0.61 GHz (𝑛 = 220) and the Very Large Array (VLA) at 1.42 GHz (𝑛 = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at 𝑙 = 24.8° and 𝑏 = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ∼ 550 M with a linear size of 7 pc and an rms electron density of ∼ 110 cm-3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5.

      We also report detection of hydrogen recombination lines from the HII region at 𝑙 = 24.8° and 𝑏 = 0.1° at all observed frequencies near 𝑉𝑙𝑠𝑟 = 100 km s-1. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model has an electron density comparable to that derived from the continuum.We also report detection of hydrogen recombination lines from two other HII regions in the field.

    • GMRT Detection of a New Wide-Angle Tail (WAT) Radio Source Associated with the Galaxy PGC 1519010

      N. G. Kantharia M. Das Gopal-Krishna

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      We report the serendipitous detection of a Wide-Angle Tail (WAT) radio galaxy at 240 and 610 MHz, using the Giant Metrewave Radio Telescope (GMRT). This WAT is hosted by a cD galaxy PGC 1519010 whose photometric redshift given in the SDSS DR6 catalogue is close to the spectroscopic redshifts (0.105, 0.106 and 0.107) of three galaxies found within $4'$ of the cD. Using the SDSS DR6, we have identified a total of 37 galaxies within $15'$ of the cD, whose photometric redshifts are between 0.08 and 0.14. This strongly suggests that the cD is associated with a group of galaxies whose conspicuous feature is a north–south chain of galaxies (filament) extending to at least 2.6 Mpc. The ROSAT all-sky survey shows a faint, diffuse X-ray source in this direction, which probably marks the hot intracluster gas in the potential well of this group.

      We combine the radio structural information for this WAT with the galaxy clustering in that region to check its overall consistency with the models of WAT formation. The bending of the jet before and after its disruption forming the radio plume, are found to be correlated in this WAT, as seen from the contrasting morphological patterns on the two sides of the core. Probable constraints imposed by this on the models ofWAT formation are pointed out. We also briefly report on the other interesting radio sources found in the proximity of the WAT. These include a highly asymmetric double radio source and an ultra-steep spectrum radio source for which no optical counterpart is detected in the SDSS.

    • GMRT Low Radio Frequency Study of the Wolf Rayet Galaxy NGC 4214 and Detection of a Distant Galaxy

      Shweta Srivastava N. G. Kantharia D. C. Srivastava

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      In this paper, we present the first low frequency (< 1.4 GHz) radio continuum study of a Wolf Rayet galaxy NGC 4214 using the Giant Meterwave Radio Telescope (GMRT). We detect diffuse extended emission from the galaxy disk at 325 MHz and find that the radio emission closely follows the ultraviolet emission mapped by GALEX. The galaxy is undergoing continuous star formation which can explain the diffuse emission. We suggest that the diffuse radio continuum emission and X-ray emission detected in the northern part of NGC 4214 is associated with a background galaxy, 2MASX J12153795+3622218.

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    • 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.

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      Posted on July 25, 2019

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