743 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
The impact of a young radio galaxy : Clues from the cosmic ray electron population
In the framework of hierarchical structure formation, active galactic nuclei (AGN) feedback shapes the galaxy luminosity function. Low luminosity, galaxy-scale double radio sources are ideal targets to investigate the interplay between AGN feedback and star formation. We use Very Large Array and BIMA millimetre-wave array observations to study the radio continuum emission of NGC 3801 between 1.4 and 112.4 GHz. We find a prominent spectral break at 10 GHz, where the spectrum steepens as expected from cosmic ray electron (CRe) ageing. Using the equipartition magnetic field and fitting JP models locally, we create a spatially resolved map of the spectral age of the CRe population. The spectral age of Ïint =2.0±0.2Myr agrees within a factor of 2 with the dynamical age of the expanding X-ray emitting shells. The spectral age varies only little across the lobes, requiring an effective mixing process of the CRe such as a convective backflow of magnetized plasma. The jet termination points have a slightly younger CRe spectral age, hinting at in situ CRe re-acceleration. Our findings support the scenario where the supersonically expanding radio lobes heat the interstellar medium (ISM) of NGC 3801 via shock waves, and, as their energy is comparable to the energy of the ISM, are clearly able to influence the galaxy's further evolution.Peer reviewe
Radio bubbles in the composite AGN-starburst galaxy NGC6764
We present multi-frequency radio continuum as well as HI observations of the composite galaxy NGC6764, which has a young, circumnuclear starburst and also harbours an active galactic nucleus (AGN). These observations have been made at a number of frequencies ranging from ~600 MHz to 15 GHz using both the GMRT and the VLA. They reveal the structure of the bipolar bubbles of non-thermal, radio emission which are along the minor axis of the galaxy and extend up to ~1.1 and 1.5 kpc on the northern and southern sides respectively. Features in the radio bubbles appear to overlap with filaments of H_alpha emission. The high-resolution observations reveal a compact source, likely to be associated with the nucleus of the galaxy, and a possible radio jet towards the south-west. We have compiled a representative sample of galaxies with bubbles of non-thermal radio emission and find that these are found in galaxies with an AGN. The HI observations with the GMRT show two peaks of emission on both ends of the stellar-bar and depletion of HI in the central region of the galaxy. We also detect HI in absorption against the central radio peak at the systemic velocity of the galaxy. The HI-absorption spectrum also suggests a possible weak absorption feature blue-shifted by ~120 km/s, which requires confirmation. A similar feature has also been reported from observations of CO in emission, suggesting that the circumnuclear starburst and nuclear activity affect the kinematics of the atomic and molecular gas components, in addition to the ionised gas seen in H_alpha and [N II]
Reliability at the Lower Limits of HIV-1 RNA Quantification in Clinical Samples: A Comparison of RT-PCR versus bDNA Assays
INTRODUCTION:To explore whether an assay change was responsible for an increasing proportion of patients with undetectable HIV viral loads at our urban HIV clinic, we selected highly stable patients, examining their viral loads before and after changing assays. We compared the proportion with detectable viremia during RT-PCR vs. bDNA periods. METHODOLOGY/PRINCIPAL FINDINGS:We selected patients with > or =1 viral loads assessed during both RT-PCR and bDNA periods. We included patients with stable CD4 counts, excluding patients with viral loads > or =1,000 copies/ml or any significant changes in therapy. Out of 4500 clinic patients, 419 patients (1588 viral loads) were included. 39% of viral loads were reported as detectable by RT-PCR vs. 5% reported as detectable by bDNA. The mean coefficient of variation was higher before vs. after assay change. We found an odds' ratio of 16.7 for having a viral load >75 copies/ml during the RT-PCR vs. bDNA periods. DISCUSSION:These data support previous reports, suggesting that bDNA may more reliably discriminate between viral suppression and low level viremia in stable patients on therapy. Low-level viremia, noted more with RT-PCR, may promote unneeded testing, while differences in viral load reliability may impact antiretroviral trial and quality assurance endpoints. Commonly used plasma separator tubes may differentially affect RT-PCR and bDNA results
Probing the subshell closure: factor of the Mg(2) state
The first-excited state ~factor of Mg has been measured relative to
the factor of the Mg() state using the high-velocity
transient-field technique, giving . This new measurement is in
strong disagreement with the currently adopted value, but in agreement with the
-shell model using the USDB interaction. The newly measured factor,
along with and systematics, signal the closure of the subshell at . The possibility that precise -factor
measurements may indicate the onset of neutron admixtures in first-excited
state even-even magnesium isotopes below Mg is discussed and the
importance of precise excited-state -factor measurements on ~shell
nuclei with to test shell-model wavefunctions is noted.Comment: 8 pages, 5 figure
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Mode of accretion in episodic radio galaxies and the dynamics of their outer relic lobes
We present X-ray observations with the X-ray Multi-Mirror Mission Newton (XMM-Newton) telescope of three Double-Double Radio Galaxies (DDRGs). We have detected the core, lobes and the environment of our sample DDRGs in X-rays. We examine the relationships between the radio and X-ray emission and attribute the X-ray emission from the lobes to the inverse-Compton scattering of cosmic microwave background (CMB) photons against the leptons of the radio lobes. The magnetic field strength of the lobes is close to the equipartition value. The X-ray spectrum of the cores of the DDRGs consists of an unabsorbed soft power-law component and no sign of hard power law components. The soft unabsorbed component is likely to be related to the radio jets. In optical wavebands, there is no strong [O III] lines observed and the host galaxies are not detected in all four bands (namely 2.4, 4.6, 12, 22 ”m) of Wide-Field Infrared Survey Explorer (WISE) survey. This shows that they are low excitation radio galaxies. These DDRGs have poor group scale ambient media. We discuss the implications of this observation for models of the episodic activity in DDRGs
A radio study of the superwind galaxy NGC1482
We present multifrequency radio continuum as well as HI observations of the
superwind galaxy NGC1482, with both the GMRT and the VLA. This galaxy has a
remarkable hourglass-shaped optical emission line outflow as well as bi-polar
soft X-ray bubbles on opposite sides of the galactic disk. The low-frequency,
lower-resolution radio observations show a smooth structure. From the
non-thermal emission, we estimate the available energy in supernovae, and
examine whether this would be adequate to drive the observed superwind outflow.
The high-frequency, high-resolution radio images of the central starburst
region located at the base of the superwind bi-cone shows one prominent peak
and more extended emission with substructure. This image has been compared with
the infrared, optical red-continuum, H_alpha, and, soft and hard X-ray images
from Chandra. The peak of infrared emission is the only feature which is
coincident with the prominent radio peak, and possibly defines the centre of
the galaxy. The HI observations with the GMRT show two blobs of emission on
opposite sides of the central region. These are rotating about the centre of
the galaxy and are located at ~2.4 kpc from it. In addition, these observations
also reveal a multicomponent HI-absorption profile against the central region
of the radio source, with a total width of ~250 km/s. The extreme blue- and
red-shifted absorption components are at 1688 and 1942 km/s respectively, while
the peak absorption is at 1836 km/s. This is consistent with the heliocentric
systemic velocity of 1850+/-20 km/s, estimated from a variety of observations.
We discuss possible implications of these results.Comment: 11 pages, 10 figures, 4 tables, accepted for publication in MNRA
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