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.