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21.
Chandreyee Sengupta † Ramesh Balasubramanyam K. S. Dwarakanath 《Monthly notices of the Royal Astronomical Society》2007,378(1):137-147
Environment plays an important role in the evolution of the gas contents of galaxies. Gas deficiency of cluster spirals and the role of the hot intracluster medium in stripping gas from these galaxies is a well-studied subject. Loose groups with diffuse X-ray emission from the intragroup medium (IGM) offer an intermediate environment between clusters and groups without a hot IGM. These X-ray bright groups have smaller velocity dispersion and lower temperature than clusters, but higher IGM density than loose groups without diffuse X-ray emission. A single-dish comparative study of loose groups with and without diffuse X-ray emission from the IGM, showed that the galaxies in X-ray bright groups have lost more gas on average than the galaxies in non X-ray bright groups. In this paper we present GMRT H i observations of 13 galaxies from four X-ray bright groups: NGC 5044, 720, 1550 and IC1459. The aim of this work is to study the morphology of H i in these galaxies and to see if the hot IGM has in any way affected their H i content or distribution. In addition to disturbed H i morphology, we find that most galaxies have shrunken H i discs compared to the field spirals. This indicates that IGM-assisted stripping processes like ram pressure may have stripped gas from the outer edges of the galaxies. 相似文献
22.
R. A. Angiras † C. J. Jog † A. Omar † K. S. Dwarakanath † 《Monthly notices of the Royal Astronomical Society》2006,369(4):1849-1857
The H i surface density maps for a sample of 18 galaxies in the Eridanus group are Fourier analysed. This analysis gives the radial variation of the lopsidedness in the H i spatial distribution. The lopsidedness is quantified by the Fourier amplitude A 1 of the m = 1 component normalized to the average value. It is also shown that in the radial region where the stellar disc and H i overlap, their A 1 coefficients are comparable. All the galaxies studied show significant lopsidedness in H i . The mean value of A 1 in the inner regions of the galaxies (1.5–2.5 scalelengths) is ≥ 0.2. This value of A 1 is twice the average value seen in the field galaxies. Also, the lopsidedness is found to be smaller for late-type galaxies; this is opposite to the trend seen in the field galaxies. These two results indicate a different physical origin for disc lopsidedness in galaxies in a group environment compared to the field galaxies. Further, a large fraction (∼30 per cent) shows a higher degree of lopsidedness ( A 1 ≥ 0.3). It is also seen that the disc lopsidedness increases with the radius as demonstrated in earlier studies, but over a radial range that is two times larger than done in the previous studies. The average lopsidedness of the halo potential is estimated to be ∼10 per cent, assuming that the lopsidedness in H i disc is due to its response to the halo asymmetry. 相似文献
23.
Jayadev Rajagopal G. Srinivasan K. S. Dwarakanath 《Journal of Astrophysics and Astronomy》1998,19(3-4):117-131
In the preceding paper (Paper I), we presented HI absorption spectra towards radio sources very close to the lines of sight
towards twenty five bright stars against which optical absorption spectra had been obtained earlier, In this paper we analyse
the results and draw some conclusions.
To summarize briefly, in most cases we found HI absorption at velocities corresponding to the optical absorption features
provided one restricted oneself to velocities ≲10 kms-1. At higher velocities we did not detect any HI absorption down to
an optical depth limit of 0.1 (except in four cases which we attribute to gas in systematic motion rather than clouds in random
motion). After discussing various scenarios, we suggest that this trend should perhaps be understood in terms of the high
velocity interstellar clouds being accelerated, heated and ablated by expanding supernova remnants. 相似文献
24.
Jayadev Rajagopal G. Srinivasan K. S. Dwarakanath 《Journal of Astrophysics and Astronomy》1998,19(3-4):97-116
This investigation is aimed at clarifying the nature of the interstellar gas seen in absorption against bright O and B stars.
Towards this end we have obtained for the first time HI absorption spectra towards radio sources very close to the lines of
sight towards twenty five bright stars previously studied. In this paper we describe the selection criteria, the details regarding
our observations, and finally present the absorption spectra. In the accompanying paper we analyse the results and draw conclusions. 相似文献
25.
J.H. van Gorkom H. Bravo-Alfaro K.S. Dwarakanath P. Guhathakurta B.M. Poggianti D. Schiminovich M. Valluri M. Verheijen E. Wilcots A. Zabludoff 《Astrophysics and Space Science》2003,285(1):219-224
We outline the project of multifrequency observation of five clusters of galaxies spanning a redshift between 0.05 and 0.2.
The core of the project is an HI survey of clusters accomplished with the VLA in its C configuration, and complemented with
GMRT data. The 21 cm imaging is being combined with optical spectroscopy and deep NIR imaging with the aim to obtain a database
on galaxy evolution in the nearby universe. We choose a sample of clusters with different degrees of dynamical evolution,
some containing an important population of starburst or/and post–starburst galaxies, and a hot intracluster medium with emission
in X–ray.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
DNAPL Removal from a Heterogeneous Alluvial Aquifer by Surfactant-Enhanced Aquifer Remediation 总被引:2,自引:0,他引:2
27.
K. S. Dwarakanath A. A. Deshpande N. Udaya Shankar 《Journal of Astrophysics and Astronomy》1990,11(3):311-322
A simple but effective modification to the conventional CLEAN algorithm is suggested. This modification ensures both stability
and speed when CLEAN is applied to maps containing a mixture of point sources and extended structures. The method has been
successfully applied to the recently-completed sky survey at 34.5 MHz (Dwarakanath & Udaya Shankar 1990). This survey was
made using the Gauribidanur T array (GEETEE)1 in 1-D aperture synthesis mode. Since in this case the ‘dirty beam’ (point spread
function) cannot be directly computed, a method to obtain this is discussed in detail. The results of this deconvolution procedure
have been encouraging in terms of reduced computing time and improved dynamic range in our maps. This algorithm should find
wider application in deconvolving maps which have both extended structures and point sources
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore & the Raman Research Institute, Bangalore. 相似文献
28.
The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is
a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies
in the group is ≈240 km s−1. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp
+ Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from
31 galaxies. The channel rms of ≈ 1 mJy beam−1 was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈
1 × 1020 cm−2 for a velocity-width of ≈ 13.4 km s−1. The 3σ detection limit of HI mass is ≈ 1.2 X 107 Mpd for a line-width of 50 km s−1. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation
curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies.
These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos,
and the kinematical and HI lopsidedness in galaxies. 相似文献
29.
Ch. V. Sastry K. S. Dwarakanath R. K. Shevgaonkar 《Journal of Astrophysics and Astronomy》1981,2(3):339-347
We have observed the large supernova remnant Cygnus Loop at 34.5 MHz with the low frequency radio telescope at Gauribi-danur,
India. A radio map of the region with a resolution of 26 arcmin × 40 arcmin (α × δ) is presented. The integrated flux density
of the Cygnus Loop at this frequency is 1245 ± 195 Jy. The radio fluxes of different parts of the nebula at this frequency
were also measured and used to construct their spectra. It is found that the spectrum of the region associated with the optical
nebulosity NGC 6992/5 is not flat at low frequencies, and also exhibits a break at a frequency around 400 MHz. The spectrum
of the region associated with NGC 6960 also shows a break but around 1000 MHz, while the spectrum of the region associated
with NGC 6974 is straight in the entire frequency range 25 to 5000 MHz. The implication of these results on the basis of existing
theories of the origin of radio emission from supernova remnants is discussed. 相似文献
30.
The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant
HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies
is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight
radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions.
It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions
are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the
hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could
have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that
tidal interaction is likely to be an effective mechanism for transforming spirals to S0s. 相似文献