1,075 research outputs found
An HI study of three long-tailed irregular galaxies in the cluster Abell1367
We present the results on the distribution and kinematics of H\sc{i} gas
with higher sensitivity and in one case of higher spectral resolution as well
than reported earlier, of three irregular galaxies CGCG 097073, 097079 and
097087 (UGC 06697) in the cluster Abell 1367. These galaxies are known to
exhibit long (5075 kpc) tails of radio continuum and optical emission lines
(H) pointing away from the cluster centre and arcs of starformation on
the opposite sides of the tails. These features as well as the H{\sc i}
properties, with two of the galaxies (CGCG 097073 and 097079) exhibiting
sharper gradients in H{\sc i} intensity on the side of the tails, are
consistent with the H{\sc i} gas being affected by the ram pressure of the
intracluster medium. However the H{\sc i} emission in all the three galaxies
extends to much smaller distances than the radio-continuum and H tails,
and are possibly still bound to the parent galaxies. Approximately 2030 per
cent of the H{\sc i} mass is seen to accumulate on the downstream side due to
the effects of ram pressure.Comment: 19 pages, 19 figures, 3 tables, accepted for publication in the
Bulletin of the Astronomical Society of Indi
HI gas in rejuvenated radio galaxies: GMRT observations of the DDRG J1247+6723
We report the detection of HI absorption towards the inner double of the
double-double radio galaxy (DDRG) J1247+6723 with the Giant Metrewave Radio
Telescope (GMRT). The inner double is a Giga-hertz peaked spectrum (GPS) source
with a linear size of 14 pc while the overall size defined by the outer double
is 1195 kpc, making it a giant radio source. The absorption profile is well
resolved and consists of a number of components on either side of the optical
systemic velocity. The neutral hydrogen column density is estimated to be
N(HI)=6.73*10^{20}(T_s/100)(f_c/1.0) cm^{-2}, where T_s and f_c are the spin
temperature and covering factor of the background source respectively. We
explore any correlation between the occurrence of HI absorption and
rejuvenation of radio activity and suggest that there could be a strong
relationship between them.Comment: 5 pages, 2 figures, accepted for publication in MNRAS Letter
Giant Radio Sources
We present multi-frequency VLA observations of two giant quasars, 0437-244
and 1025-229, from the Molonglo Complete Sample. These sources have
well-defined FRII radio structure, possible one-sided jets, no significant
depolarization between 1365 and 4935 MHz and low rotation measure (). The giant sources are defined to be those whose overall
projected size is 1 Mpc. We have compiled a sample of about 50 known
giant radio sources from the literature, and have compared some of their
properties with a complete sample of 3CR radio sources of smaller sizes to
investigate the evolution of giant sources, and test their consistency with the
unified scheme for radio galaxies and quasars. We find an inverse correlation
between the degree of core prominence and total radio luminosity, and show that
the giant radio sources have similar core strengths to the smaller sources of
similar total luminosity. Hence their large sizes are unlikely to be due to
stronger nuclear activity. The degree of collinearity of the giant sources is
also similar to the sample of smaller sources. The luminosity-size diagram
shows that the giant sources are less luminous than our sample of smaller-sized
3CR sources, consistent with evolutionary scenarios where the giants have
evolved from the smaller sources losing energy as they expand to these large
dimensions. For the smaller sources, radiative losses due to synchrotron
radiation is more significant while for the giant sources the equipartition
magnetic fields are smaller and inverse Compton losses with the microwave
background radiation is the dominant process. The radio properties of the giant
radio galaxies and quasars are consistent with the unified scheme.Comment: 14 pages with 12 figures, MNRAS LaTex. Accepted for publication in
MNRAS. Minor changes in the text and couple of references adde
J0041+3224: a new double-double radio galaxy
We report the discovery of a double-double radio galaxy (DDRG), J0041+3224,
with the Giant Metrewave Radio Telescope (GMRT) and subsequent high-frequency
observations with the Very Large Array (VLA). The inner and outer doubles are
aligned within about 4 deg and are reasonably collinear with the parent optical
galaxy. The outer double has a steeper radio spectrum compared with the inner
one. Using an estimated redshift of 0.45, the projected linear sizes of the
outer and inner doubles are 969 and 171 kpc respectively. The time scale of
interruption of jet activity has been estimated to be about 20 Myr, similar to
other known DDRGs. We have compiled a sample of known DDRGs, and have
re-examined the inverse correlation between the ratio of the luminosities of
the outer to the inner double and the size of the inner double, l_{in}. Unlike
the other DDRGs with l_{in} larger than about 50 kpc, the inner double of
J0041+3224 is marginally more luminous than the outer one. The two DDRGs with
l_{in} less than about a few kpc have a more luminous inner double than the
outer one, possibly due to a higher efficiency of conversion of beam energy as
the jets propagate through the dense interstellar medium. We have examined the
symmetry parameters and find that the inner doubles appear to be more
asymmetric in both its armlength and flux density ratios compared with the
outer doubles, although they appear marginally more collinear with the core
than the outer double. We discuss briefly possible implications of these
trends.Comment: Accepted for publication in MNRAS, 9 pages, 10 figure
Collimation of extragalactic radio jets in compact steep spectrum and larger sources
We study the collimation of radio jets in the high-luminosity Fanaroff-Riley
class II sources by examining the dependence of the sizes of hotspots and knots
in the radio jets on the overall size of the objects for a sample of compact
steep-spectrum or CSS and larger-sized objects. The objects span a wide range
in overall size from about 50 pc to nearly 1 Mpc. The mean size of the hotspots
increases with the source size during the CSS phase, which is typically taken
to be about 20 kpc, and the relationship flattens for the larger sources. The
sizes of the knots in the compact as well as the larger sources are consistent
with this trend. We discuss possible implications of these trends. We find that
the hotspot closer to the nucleus or core component tends to be more compact
for the most asymmetric objects where the ratio of separations of the hotspots
from the nucleus, r_d > 2. These highly asymmetric sources are invariably CSS
objects, and their location in the hotspot size ratio - separation ratio
diagram is possibly due to their evolution in an asymmetric environment. We
also suggest that some soures, especially of lower luminosity, exhibit an
asymmetry in the collimation of the oppositely-directed radio jets.Comment: MNRAS in press, 9 pages and 3 figures, MNRAS LaTe
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