79 research outputs found
Applications of high-frequency resolution, wide-field VLBI: observations of nearby star-forming galaxies & habitable exoplanetary candidates
In this thesis, I investigate the radio source populations and properties of two nearby star-forming galaxies. In addition, I present an independent method to estimate the supernova and massive star-formation rates of star-forming galaxies. This study makes use of a new technique that allows multiple astronomical objects to be simultaneously observed via very high resolution radio interferometry. Furthermore, using this technique I develop a new method to search for evidence of extraterrestrial intelligence from habitable planetary candidates
From radio-quiet to radio-silent: low luminosity Seyfert radio cores
A strong effort has been devoted to understand the physical origin of radio
emission from low-luminosity AGN (LLAGN), but a comprehensive picture is still
missing. We used high-resolution (1 arcsec), multi-frequency (1.5, 5.5, 9
and 14 GHz) NSF's Karl G. Jansky Very Large Array (VLA) observations to
characterise the state of the nuclear region of ten Seyfert nuclei, which are
the faintest members of a complete, distance-limited sample of 28 sources. With
the sensitivity and resolution guaranteed by the VLA-A configuration, we
measured radio emission for six sources (NGC3185, NGC3941, NGC4477, NGC4639,
NGC4698 and NGC4725), while for the remaining four (NGC0676, NGC1058, NGC2685
and NGC3486) we put upper limits at tens uJy/beam level, below the previous
0.12 mJy/beam level of Ho&Ulvestad (2001), corresponding to luminosities down
to L W/Hz at 1.5 GHz for the highest RMS observation. Two sources,
NGC4639 and NGC4698, exhibit spectral slopes compatible with inverted spectra
(0, ), hint for radio emission
from an optically-thick core, while NGC4477 exhibits a steep (+0.520.09)
slope. The detected sources are mainly compact on scales arcseconds,
predominantly unresolved, except NGC3185 and NGC3941, in which the resolved
radio emission could be associated to star-formation processes. A significant
X-ray - radio luminosities correlation is extended down to very low
luminosities, with slope consistent with inefficient accretion, expected at
such low Eddington ratios. Such sources will be one of the dominant Square
Kilometre Array (SKA) population, allowing a deeper understanding of the
physics underlying such faint AGN.Comment: accepted for publication on MNRAS (19 pages, 26 figures
Is an obscured AGN at the centre of the disk galaxy IC 2497 responsible for Hanny's Voorwerp?
We present the results of VLBI and MERLIN observations of the massive disk
galaxy IC 2497. Optical observations of IC 2497 revealed the existence of a
giant emission nebula "Hanny's Voorwerp" in the proximity of the galaxy.
Earlier short-track 18 cm observations with e-VLBI at 18 cm, detected a compact
radio component (C1) at the centre of IC 2497. The brightness temperature of C1
was measured to be greater than 4E5 K. Deeper, long-track e-VLBI observations
presented here, re-confirm the existence of C1 but also reveal the existence of
a second compact component (C2) located about 230 milliarcseconds to the
North-East of C1. The brightness temperature of C2 is measured to be greater
than 1.4E5 K, suggesting that both components may be related to AGN activity
(e.g. a radio core and jet hotspot). Lower resolution 18cm MERLIN observations
show both components. C1 is shown to be compact with a slight elongation along
the direction of Hanny's Voorwerp, and C2 shows a lot of extended emission in
an almost perpendicular direction to the direction of the Voorwerp. Our results
continue to support the hypothesis that IC 2497 contains an Active Galactic
Nucleus (AGN), and that a jet associated with this AGN clears a path that
permits ionising radiation from the AGN to directly illuminate the emission
nebula.Comment: Presented at The 8th International e-VLBI Workshop: the Science and
Technology of Long Baseline Real-Time Interferometry, EXPReS09, June 22-26
2009 Madrid, Spain. 5 pages, 5 article
Application of rep-PCR as a molecular tool for the genetic diversity assessment of Jatropha curcas
Jatropha curcas L., a non-edible Euphorbiaceae oil-rich crop cultivated in subtropical/tropical countries, has gained global attention as a promising renewable resource for biodiesel production. Rep polymerase chain reaction (PCR) was used to investigate the genetic diversity of 15 populations of J. curcas L. Distinct populations of the plant growing wildly in Mauritius were characterised using three molecular markers random-amplified polymorphic DNA (RAPD), repetitive extragenic palindromic (REP), and BOX. Furthermore, to confirm that the amplicons obtained with rep-PCR were derived from mitochondrial genomes, six randomly chosen bands were cloned and sequenced to demonstrate that the amplified products were mitochondrial genome-specific. The average polymorphism information content (PIC) values were 0.329 and the average percentage of polymorphic loci obtained were 89.28 for BOX primer, followed by RAPD (83.41), and REP (55.81) among the different populations with the percentage polymorphic loci ranging from 13.95 to 100. The homology recorded clearly indicated that the amplified products were mitochondrial genome-specific. Rep-PCR provides a quick and cheap method to study diversity at the mitochondrial level in plants.Keywords: Genetic diversity, Jatropha curcas, rep-polymerase chain reaction (PCR
Measuring the spin of the primary black hole in OJ287
The compact binary system in OJ287 is modelled to contain a spinning primary
black hole with an accretion disk and a non-spinning secondary black hole.
Using Post Newtonian (PN) accurate equations that include 2.5PN accurate
non-spinning contributions, the leading order general relativistic and
classical spin-orbit terms, the orbit of the binary black hole in OJ287 is
calculated and as expected it depends on the spin of the primary black hole.
Using the orbital solution, the specific times when the orbit of the secondary
crosses the accretion disk of the primary are evaluated such that the record of
observed outbursts from 1913 up to 2007 is reproduced. The timings of the
outbursts are quite sensitive to the spin value. In order to reproduce all the
known outbursts, including a newly discovered one in 1957, the Kerr parameter
of the primary has to be . The quadrupole-moment contributions
to the equations of motion allow us to constrain the `no-hair' parameter to be
where 0.3 is the one sigma error. This supports the `black hole
no-hair theorem' within the achievable precision.
It should be possible to test the present estimate in 2015 when the next
outburst is due. The timing of the 2015 outburst is a strong function of the
spin: if the spin is 0.36 of the maximal value allowed in general relativity,
the outburst begins in early November 2015, while the same event starts in the
end of January 2016 if the spin is 0.2Comment: 12 pages, 6 figure
Repetitive element palindromic PCR (rep-PCR) as a genetic tool to study interspecific diversity in Euphorbiaceae family
Background: The classification of diversity in germplasm collections
is important for plant breeding. The repetitive element
palindromic-polymerase chain reaction (rep-PCR) technique was used to
investigate inter-specific diversity within 17 species from the
Euphorbiaceae family using REP and BOX primers. Results: The
agglomerative cluster analysiswas used to evaluate the scoring data.
BOX and REP gave amplification with polymorphism of 98.84% and 100%
respectively. REP marker demarcated between the subgenus peltatae. Both
markers confirmed Jatropha tanjorensis as a natural hybrid between
Jatropha gossypifolia and Jatropha curcas . Five random sequences
from the rep-PCR gels were chosen, cloned and sequenced. The blast
results demonstrated that the amplified products were from the
mitochondrial genomes. Conclusion: The rep-PCR molecular tool can be
used to characterize diversity in plants as they are suitable for
distinguishing eukaryotic genomes effectively
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