16,879 research outputs found
Distant star forming galaxies, next generation radio telescopes and the radio universe before re-ionisation
I present the various capabilities of upgraded and next generation radio
telescopes, in particular their ability to detect and image distant star
forming galaxies. I demonstrate that e-MERLIN, EVLA and LOFAR can detect
systems similar to Arp 220 out to cosmological distances. The SKA can detect
such systems out to any reasonable redshift that they might be expected to
exist. Employing very long integration times on the multiple-beam SKA will
require the array to be extended beyond the current specification - simply to
avoid confusion noise limitations at 1.4 GHz. Other arguements for extending
the SKA baseline length are also presented. As well as going ``deeper'' all
these instruments (especially LOFAR and the SKA) will also go ``wider'' -
detecting many tens of thousands of galaxies in a single day's observing. I
briefly comment on the prospects of detecting radio emission at much earlier
epochs, just before the epoch of re-ionisation.Comment: Proceedings of the 6th European VLBI Network Symposium, Ros, E.,
Porcas, R.W., Lobanov, A.P., & Zensus, J.A. (eds.), MPIfR, Bonn, Germany
(2002). 4 pages, 5 figure
Radio Astronomy Transformed: Aperture Arrays - Past, Present & Future
I review the early development of Aperture Arrays and their role in radio
astronomy. The demise of this technology at the end of the 1960's, and the
reasons for the rise of parabolic dishes is also considered. The parallels with
the Antikythera mechanism (see these proceedings) as a lost technology are
briefly presented. Aperture Arrays re-entered the world of radio astronomy as
the idea to build a huge radio telescope with a collecting area of one square
kilometre (the Square Kilometre Array, SKA) arose. Huge ICT technology advances
had transformed Aperture Arrays in terms of their capability, flexibility and
reliability. In the mid-1990s, ASTRON started to develop and experiment with
the first high frequency aperture array tiles for radio astronomy - AAD, OSMA,
THEA & EMBRACE. In the slipstream of these efforts, Phased Array Feeds (PAFs)
for radio astronomy were invented and LOFAR itself emerged as a next generation
telescope and a major pathfinder for the SKA. Meanwhile, the same advantages
that aperture arrays offered to radio astronomy had already made dishes
obsolete in many different civilian and military applications. The first
commissioning results from LOFAR and other Aperture Arrays (MWA, LWA and PAPER)
currently demonstrate that this kind of technology can transform radio
astronomy over 2 decades of the radio spectrum, and at frequencies up to at
least 1.5 GHz. This "reinvention of radio astronomy" has important implications
for the design and form of the full SKA. Building a SKA that is simply the "VLA
on steroids" is simply not good enough. Like the Antikythera mechanism itself,
we must amaze future generations of astronomers - they and the current
generation deserve nothing less.Comment: 9 pages, Paper presented at "From Antikythera to the Square Kilometre
Array: Lessons from the Ancients, Kerastari, Greece 12-15 June 2012" eds.
A.K. Tzioumis et al; Proceedings of Science, 2012,
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=17
Deep Fields: The Faint sub-mJy and microJy Radio Sky - A VLBI Perspective
Until recently, VLBI targets have been drawn almost exclusively from the
brightest and most compact radio sources in the sky, with typical flux
densities well in excess of a few tens of mJy. These sources are predominantly
identified with Active Galactic Nuclei (AGN), located at cosmological
distances. In this lecture I will attempt to summarise what is currently known
about the general properties of the faint sub-mJy and microJy radio source
population, as determined from deep multi-wavelength studies of the HDF-N. In
particular, I will try to provide a VLBI perspective, describing the first
deep, wide-field, VLBI pilot observations of the HDF, together with a summary
of the main results. The role VLBI can play in future high resolution studies
of faint radio sources is also addressed.Comment: 11 pages, 8 figures. To appear in "The Role of VLBI in Astrophysics,
Astrometry and Geodesy", NATO ASI VLBI 2001 School, editor: F. Mantovan
Clifford Geometrodynamics
Classical anti-commuting spinor fields and their dynamics are derived from
the geometry of the Clifford bundle over spacetime via the BRST formulation. In
conjunction with Kaluza-Klein theory, this results in a geometric description
of all the fields and dynamics of the standard model coupled to gravity and
provides the starting point for a new approach to quantum gravity.Comment: 4 pages, no figures. Corrected and included |e| suggested by a reade
Hanny's Voorwerp and the Antikythera Mechanism - similarities, differences and insights
I present some insights into Hanny's Voorwerp and the Antikythera mechanism -
contrasting their similarities and differences. They are both excellent
examples of serendipitous discoveries in which human curiosity and perseverance
have played an important role. Both objects have captured the imagination of
the general public, and their discovery was only made possible via the
introduction of new technologies. One major difference is that there is only
one Antikythera device but there are now many Voorwerpen or "voorwerpjes", as
they are more commonly known. The study of a collection of objects, as is
common in astronomy, greatly aids our understanding of cosmic phenomena. In the
case of the voorwepjes, we now know that such systems are to be identified with
obscured galaxies or Active Galactic Nuclei (AGN) that appear to have recently
and indeed rapidly turned off. Clearly, the discovery of more examples of
devices similar to the Antikythera mechanism would have a significant affect in
advancing our understanding of this object and the people that constructed it.
Thus far, surveys of the site of the Antikythera wreck are incomplete and
non-systematic. Like radio astronomy and other progressive fields,
technological advances proceed exponentially in terms of capacity and
capability. Recent advances in diving technology are no exception to this rule.
It is almost 40 years ago that Jacques Cousteau led the last adhoc survey of
the Antikythera wreck - the time has surely come to revisit the site and
conduct a proper scientific and systematic survey. The deepest areas of the
site are so far completely unexplored while it is known that some artefacts did
fall into this area during the original excavation. During this workshop, I
called for a return to the site using the most modern diving technologies.Comment: 8 pages, 5 figures. Paper presented at "From Antikythera to the
Square Kilometre Array: Lessons from the Ancients, Kerastari, Greece 12-15
June 2012" eds. A.K. Tzioumis et al; Proceedings of Science, 2012,
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=17
SETI surveys of the nearby and distant universe employing wide-field radio interferometry techniques
Long baseline radio interferometers can provide some interesting
opportunities for future SETI searches. Known advantages (compared to single
dishes or beam-formed arrays), include the large reduction in false-positives
due to the interferometer's natural suppression of RFI. This paper presents
other advantages - the presence of multiple interferometer baselines in an
array provide an important level of redundancy and additional confidence
(verification) in the detection of faint and potentially transient signals. The
SETI requirement for high time and frequency resolution is well matched to
wide-field VLBI techniques that permits the simultaneous analysis of thousands
of potential SETI targets within the field-of-view. Searching for a SETI signal
in the image plane has the important advantage that the signal location on the
sky is likely to be invariant on short timescales - this is a useful constraint
when potentially almost everything else could be changing (eg frequency drift
due to Doppler accelerations). Using archive data, we demonstrate how VLBI can
be used to conduct SETI searches. We target two targets within the field of
view - a galactic star and a galaxy at a redshift of 0.14. We place coarse
upper limits on any SETI signals from the two SETI targets, and note that while
the EIRP associated with the galaxy is comparable to the energy resources of a
Kardashev Type 2 civilisation, a distributed array of coherent transmitters
with excellent forward gain, could reduce this to more modest levels. We
therefore argue that targeted observations of extragalactic sources may also be
merited by interferometer surveys. Using VLBI to study the precise location and
motion of confirmed SETI signals is also discussed.Comment: 5 pages, 5 figures. Presentation presented at IAC 2018 Session SETI 1
and EVN Symposium 201
e-VLBI... a Wide-field Imaging Instrument with milliarcsecond Resolution & microJy Sensitivity
The European VLBI Network (EVN) is in the process of establishing an e-VLBI
array in which the radio telescopes and the EVN correlator at JIVE are
connected in real-time, via high-speed national fibre optic networks and the
pan-European research network, GEANT. This paper reports on recent test
results, including the production of the first real-time e-VLBI astronomical
image. In a parallel and related development, the field-of-view of VLBI is also
expanding by many orders of magnitude, and the first results of deep,
wide-field surveys capable of detecting many sources simultaneously are
summarised. The detection of sources as faint as 10 microJy should soon be
possible in the era of ``Mk5'' and e-VLBI.Comment: 4 pages, 3 figures. Paper presented in a conference held in Berlin
"Exploring the Cosmic Frontier: Astrophysical Instruments for the 21st
Century", May 2004 proceedings to be published in the Springer-Verlag series
"ESO Astrophysics Symposia
The FIR/Radio correlation of high redshift glaxies in the region of the HDF-N
The correlation between the far-infrared (FIR) and radio emission is well
established for nearby star forming galaxies. Many applications, in particular
the radio-to-submm spectral index redshift indicator, tacitly assume that the
relation holds well beyond our local neighbourhood, to systems located at
cosmological distances. In order to test this assumption I have constructed a
sample of 22 HDF-N galaxies, all with measured spectroscopic redshifts, and all
detected by both ISO and the WSRT at 15 micron and 1.4 GHz respectively. The
galaxies span a wide range of redshift with a median value of z ~ 0.7. The ISO
15 micron data were k-corrected and extrapolated to the FIR (60 and 100 micron)
by assuming a starburst (M82) spectral energy distribution (SED) for the entire
sample. An initial analysis of the data suggests that the correlation between
the FIR and the radio emission continues to apply at high redshift with no
obvious indication that it fails to apply beyond z ~ 1.3. The sample is
``contaminated'' by at least 1 distant (z=4.4), radio-loud AGN, VLA
J123642+621331. This source has recently been detected by the first deep field
VLBI observations of the HDF-N and is clearly identified as an ``outlier'' in
the FIR/radio correlation. I briefly comment on the impact upgraded and next
generation radio instruments (such as e-MERLIN and the Square Km Array) can
have in studies of star formation in the early Universe.Comment: 6 pages, 4 figures (better figures at
http://www.jive.nl/~mag/fir-radio.html) To appear in "The central kpc of
starbursts and AGN: the La Palma connection", Eds. J.H. Knapen, J.E. Beckman,
I. Shlosman and T.J. Mahoney, ASP conf. series, in press (2001
A New Strategy for the Routine Detection & Imaging of Faint Radio Sources with VLBI
In this paper I outline a new strategy for the routine detection and imaging
of faint (sub-mJy and microJy) radio sources with VLBI and SVLBI. The strategy
relies on a combination of in-beam phase-referencing, wide-field VLBI imaging
and simultaneous correlation of multiple field centres. A combination of these
techniques, together with the steeply rising radio source counts observed at cm
wavelengths, permit routine high resolution observations of radio sources
previously considered too faint for conventional VLBI.Comment: 4 pages, 1 figure. VSOP Symposium (ISAS, Tokyo 2000) proceedings will
be published as "Astrophysical Phenomena Revealed by Space VLBI" eds. H.
Hirabayashi, P.G. Edwards and D.W. Murphy. See
http://www.jive.nl/~mag/deep.html for more details and better figur
Lie Group Cosmology
Our universe is a deforming Lie group.Comment: 42 pages, 1 figure; v2: minor correction
- …