Exciting new sky survey with GMRT

The Giant Metrewave Radio Telescope (GMRT), located 80 kilometres north of Pune, at Khodad village near Narayangaon, is capable of viewing nearly 90 percent of the entire sky, due to India's location near the earth's equator. Therefore, radio astronomers at the National Centre for Radio Astrophysics (NCRA, Pune), which is a center of Tata Institute of Fundamental Research (TIFR, Mumbai), have launched an ambitious project to use the GMRT for imaging nearly the entire sky at the radio wavelength of about 2 metres (150 MHz). This radio survey of the sky is called TGSS (TIFR GMRT Sky Survey). It was one of the key scientific goals of the GMRT. The TIFR GMRT Sky Survey achieves a major jump in both sensitivity and angular resolution (image sharpeness) compared to any other sky surveys made so far at metre/decametre wavelengths elsewhere in the world. TGSS is therefore expected to deliver many interesting scientific results and discoveries, e.g. of giant radio galaxies, relic galaxies, reborn radio galaxies and colliding clusters of galaxies, etc., said Professor Swarna Kanti Ghosh, Centre Director, NCRA-TIFR. 

Consisting of 30 fully steerable dish type telescopes parabolic dishes of 45 metre diametre each, installed across 25 kilometre region, GMRT is the world's most powerful radio telescope operating at metre wavelengths. The telescope, conceived and built by NCRA scientists and engineers under the leadership of Prof. Govind Swarup, is now being used extensively by astronomers from 22 countries across the world including those from Cambridge, Oxford and Stanford Universities. The TGSS core team consists of Dr S.K.Sirothia (Principal Investigator), Dr Nimisha Kantharia, Dr Ishwara Chandra and Prof. Gopal Krishna. The other contributing members of the team are Dr Arti Goyal and Raju Baddi. For making the TGSS survey, the data from the GMRT is processed using complex algorithms running on specially designed computer cluster, consisting of nearly 100 powerful computers, set-up at NCRA by the TGSS team. 

Optical images of the sky often show stars and galaxies, but objects exclusively seen in the radio images at metre wavelengths emit strong synchrotron radiation from relativistic electrons in a galaxy, generated by dying-stars, shock-waves from cosmic collisions & explosions and powerful jets ejected from spinning supermassive blackholes at center of galaxies. The TGSS survey has generated world wide excitement among astronomers. Its website has already been hit by 30,000 times for data and information download. Even before the second data release, images around size of 1 Terabyte from the first release amounting to 3% of the sky have been distributed to astronomers world wide. Now that the data release size is doubled, the demand will further increase. Finding new galaxies where blackhole activity is on the decline, if not ceased altogether, and clusters of galaxies in the process of formation in the early Universe, are going to be the prime subjects of research from this GMRT survey. Since jets of relativistic electrons from black holes are believed to control evolution of galaxies and clusters in an episodic but violent manner, this low frequency survey or 'archaeological search of blackhole's past activity' is poised to start a new era of outstanding research using the GMRT. 

The GMRT observations for the entire TGSS survey are expected to be completed by the end of 2011. The TGSS survey is being carried out as a service to the world-wide astronomical community by making the radio images public from time to time. With the second TGSS data release in June, 2011, radio images covering 2100 square degree area in the southern sky have been released for use by astronomers across the world. The website http://tgss.ncra.tifr.res.in has been set up for accessing TGSS data products. When completed, the TGSS will yield images of nearly 2 million cosmic radio sources, distributed across 90% of the sky. These would include clusters of galaxies, quasars, radio galaxies, normal galaxies, pulsars, stellar binaries containing black holes and hopefully, types of cosmic sources not yet found.

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