Somak Raychaudhury
Research Interests
Superclusters of galaxies
Even though the Universe is supposed to be homogeneous and isotropic on large
scales, very large structures spanning ten of megaparsecs seem to be pretty
common.
Numerical simulations
show that in the currently favoured cosmologies, the largest structures expected
to exist today are supercluster-sized filaments.
I started
work on the observational evidence of such large structures as early as the
late-1980s. In a Nature paper in 1989, I announced the discovery of the largest
nearby supercluster (z<0.1), named it the Shapley Supercluster [1],
and discussed its importance in the motion of our own galaxy, following up with detailed X-ray and optical studies [2-5,7]. Since then,
numerical simulations have revealed how clusters and groups of galaxies trace a
network of such filaments.
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Star formation in galaxies in supercluster
filaments: My PhD student Scott Porter and I are working on various aspects
of the variation of star formation properties of galaxies in supercluster
filaments. The first paper, relating to galaxies in the Pisces-Cetus
Supercluster [8] shows various levels of enhanced star formation in rich and
poor groups belonging on the supercluster, as opposed to suppressed star
formation in rich clusters. Investigation of a number of filaments in SDSS and
2dFGRS is under way.
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A catalogue of local superclusters and
the motion of the Local Group: With the application of
a novel topological technique (minimal spanning tree), I have produced a
catalogue of nearby superclusters of galaxies, with Prof. S. Bhavsar (Kentucky)
and Prof. J. Huchra (Harvard). Some of these remarkable structures, like the
Shapley Supercluster [1-6,8] and the Pisces-Cetus Supercluster [9], are being
studying in detail, to characterise the mass density of the largest structures
around us, in order to assess their importance in being able to distinguish
between dark matter models of structure formation.
-
Radio-selected super-filaments at higher redshift:
One such large-scale filament, discovered by us in a radio survey
[8] and emerging in the Sloan redshift survey, might be up to 100 Mpc long, and
has been awarded substantial
XMM and
Chandra time,
to be observed over the next year. The project will involve analysing these
observations, in conjunction with
Sloan Survey
observations in its vicinity, and to look for similar filaments in various
surveys.
Here are some references on the web to this work:
The Shapley Supercluster in
An Atlas of the Universe and the
Encyclopedia of Astronomy and Astrophysics
My Publications in this field
-
The distribution of galaxies in the direction of the
`Great
Attractor'
Raychaudhury, Somak, 1989, Nature, 342, 251-255
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X-Ray and Optical Observations of the Shapley Supercluster in
Hydra-Centaurus
Raychaudhury, Somak, Fabian, A. C., Edge, A. C.,
Jones, C. & Forman, W., 1991, MNRAS, 248, 101-111.
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GINGA Observations of the Shapley Supercluster
Day, C. S. R., Fabian, A. C., Edge, A. C. & Raychaudhury, Somak,
1991, MNRAS, 252, 394-402
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Einstein X-ray observations of the core of the
Shapley Supercluster in northern Centaurus
Breen, J., Raychaudhury, Somak,
Forman, W., & Jones, C., 1994, ApJ, 424, 59-67
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Spectroscopic Observations in the Cluster A3558
(Shapley 8) and in the core region of the Shapley
Supercluster
Quintana, H., Ramírez, A., Melnick, J.,
Raychaudhury, Somak & Slezak, E., 1995, AJ, 110, 463
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The Shapley Concentration
Raychaudhury, Somak, 2001,
Encyclopedia of Astronomy and Astrophysics (eaa.iop.org), ed. P. Murdin,
Nature and IoP publishing (Invited and refereed review article)
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Shock Acceleration and Intergalactic
Magnetic Fields in a Large-Scale Filament of Galaxies ZwCl 2341.1+0000
Bagchi, Joydeep, Ensslin, Torsten A., Miniati, Francesco,
Stalin C.S., Singh, M., Raychaudhury, Somak and Humeshkar, N. B.,
2002, New Astronomy, 7, 249-277
(astro-ph/0204389)
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FLASH redshift survey---I. Observations and Catalogue
Kaldare Raven, Colless Matthew,
Raychaudhury Somak, and Peterson B.A., 2003,
MNRAS, 339, 652-662
(astro-ph/0109415)
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The Pisces-Cetus
Supercluster: a remarkable filament of galaxies in the
2dF Galaxy Redshift Survey and Sloan Digital Sky surveys
Porter,
Scott C. and Raychaudhury Somak, 2005, MNRAS, 364, 1387
(astro-ph/0511050)
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Star formation properties in supercluster filaments
Raychaudhury Somak and Porter,
Scott C.
2005,
BAAS, 207, 177.15
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List of publications