291 research outputs found
High Rydberg State Carbon Recombination Lines from Interstellar Clouds
We report observations of carbon recombination lines near 34.5 MHz (qunatum
number n=578) and 325 MHz (n=272) made towards Cas A, the Galactic centre and
about ten other directions in the galactic plane. Constraints on the physical
conditions in the line forming regions are derived from these and other
existing observations. The CII regions that produce the low-frequency lines are
most likely associated with the neutral HI component of the ISM.Comment: 4 pages, 3 figures; Presented at the workshop on "New Perspects on
the Interstellare Medium", Penticton, Canada, Aug 199
Carbon Recombination Lines toward the Riegel-Crutcher Cloud and other Cold HI Regions in the inner Galaxy
We report here, for the first time, the association of low frequency CRRL
with \HI\ self-absorbing clouds in the inner Galaxy and that the CRRLs from the
innermost of the Galaxy arise in the Riegel-Crutcher (R-C)
cloud. The R-C cloud is amongst the most well known of \HI\ self-absorbing
(HISA) regions located at a distance of about 125 pc in the Galactic centre
direction. Taking the R-C cloud as an example, we demonstrate that the physical
properties of the HISA can be constrained by combining multi-frequency CRRL and
\HI\ observations. The derived physical properties of the HISA cloud are used
to determine the cooling and heating rates. The dominant cooling process is
emission of the \CII\ 158 \mum line whereas dominant heating process in the
cloud interior is photoelectric emission. Constraints on the FUV flux (G0
4 to 7) falling on the R-C cloud are obtained by assuming thermal
balance between the dominant heating and cooling processes. The H formation
rate per unit volume in the cloud interior is 10 -- 10
s \cmthree, which far exceeds the H dissociation rate per unit
volume. We conclude that the self-absorbing cold \HI\ gas in the R-C cloud may
be in the process of converting to the molecular form. The cold \HI\ gas
observed as HISA features are ubiquitous in the inner Galaxy and form an
important part of the ISM. Our analysis shows that combining CRRL and \HI\ data
can give important insight into the nature of these cold gas. We also estimate
the integration times required to image the CRRL forming region with the
upcoming SKA pathfinders. Imaging with the MWA telescope is feasible with
reasonable observing times.Comment: 11 pages, 4 figures, 5 tables, accepted by MNRA
Low radio frequency signatures of ram pressure stripping in Virgo spiral NGC 4254
We report the detection of extended low radio frequency continuum emission
beyond the optical disk of the spiral galaxy NGC 4254 using the Giant Metrewave
Radio Telescope. NGC 4254, which has an almost face-on orientation, is located
in the outskirts of the Virgo cluster. Since such extended emission is uncommon
in low inclination galaxies, we believe it is a signature of magnetised plasma
pushed out of the disk by ram pressure of the intracluster medium as NGC 4254
falls into the Virgo cluster. The detailed spectral index distribution across
NGC 4254 shows that the steepest spectrum alpha < -1 (S propto nu^{alpha})
arises in the gas beyond the optical disk. This lends support to the ram
pressure scenario by indicating that the extended emission is not from the disk
gas but from matter which has been stripped by ram pressure. The steeper
spectrum of the extended emission is reminiscent of haloes in edge-on galaxies.
The sharp fall in intensity and enhanced polarization in the south of the
galaxy, in addition to enhanced star formation reported by others provide
evidence towards the efficacy of ram pressure on this galaxy. HI 21cm
observations show that the gas in the north lags in rotation and hence is
likely the atomic gas which is carried along with the wind. NGC 4254 is a
particularly strong radio emitter with a power of 7x10^{22} Watts/Hz at 240
MHz. We find that the integrated spectrum of the galaxy flattens at lower
frequencies and is well explained by an injection spectrum with
alpha_0=-0.45+-0.12. We end by comparing published simulation results with our
data and conclude that ram pressure stripping is likely to be a significant
contributor to evolution of galaxies residing in X-ray poor groups and cluster
outskirts.Comment: 10 pages, 7 figures (figures 1,2 and 4 are in jpg format) and 2
tables; Accepted for publication in MNRA
Interpretation of power phenomena in three phase systems with neutral using instantaneous reactive power p-q theory
The Instantaneous Reactive power (IRP) p-q theory considered as a major power theory as well as a primary fundamental for switching compensator control in three-phase systems, is analyzed in order to verify its ability to describe and identify the power properties or power phenomena in a 3pN system with asymmetrical and non-sinusoidal voltages along with unbalanced loads. This analysis is an outcome of the misinterpretations of power phenomena in three-wire circuits shown by IRP p-q theory under non-sinusoidal conditions. Different load and supply conditions such as balanced, unbalanced and Harmonic generating loads along with asymmetrical and non-sinusoidal voltages are assumed for the analysis. The analysis takes in to account illustrations demonstrating various combinations of unfavorable supply and load features in order to realize an actual 3pN system mathematically. Depending on the supply and load conditions used, first the supply voltages and currents are calculated in Clarke coordinates. Then instantaneous active, reactive and zero sequence power defined by the IRP p-q theory in terms of these voltages and currents are calculated. These calculated powers are then analyzed for errors from fundamental electrical engineering perspective
Associated HI absorption in the z=3.4 radio galaxy B2 0902+343 observed with the GMRT
We have made observations of the associated HI absorption of a high redshift
radio galaxy 0902+34 at z=3.395 with the Giant Meterwave Radio Telescope in the
MHz band. We find a narrow absorption line with a flux density of
11.5 mJy at a redshift of 3.397 consistent with that observed by Uson et al.
(1991), Briggs et al. (1993) and de Bruyn (1996).A weak broad absorption
feature reported by de Bruyn (1996) has not been detected in our observations.
We also place an upper limit of 4 mJy (2 ) on emission line strength at
the position where Uson et al. (1991) claimed to have found a narrow emission
line.Comment: To appear in Journal of Astronomy and Astrophysic
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