12,228 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
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
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
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
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
When you wish upon a star: Future developments in astronomical VLBI
In this paper, I present the likely technological development of VLBI, and
its impact on the astronomical community over the next 1-5 years. VLBI is
currently poised to take advantage of the rapid development in commercial
off-the-shelf (COTS) PC-based products. The imminent deployment of disk-based
recording systems will enable Gbps data rates to be achieved routinely by both
cm and mm-VLBI networks. This, together with anticipated improvements in
collecting area, receiver systems and coherence time is set to transform the
performance of VLBI in terms of both baseline and image noise sensitivity. At
the same time the feasibility of using fibre based communication networks as
the basis for production, real-time VLBI networks will begin. Fantastic new
correlator output data rates, and the ability to deal with these via powerful
PC clusters promises to expand the typical VLBI field-of-view to scales
previously reserved for connected, short baseline interferometers. By
simultaneously sampling the summed response of all compact radio sources within
(and indeed beyond) the half-power point of the VLBI telescope primary beam,
simple self-calibration of the target field will ALWAYS be possible at
frequencies below a few GHz. Unbiased, broad-band continuum surveys will be
conducted over huge areas of sky, and (redshifted) spectral-features will be
detected too. By the end of the decade the microJy radio sky will be accessible
to VLBI: dozens of sources will be simultaneosuly observed, correlated,
detected and fully analysed all within the same day.Comment: 17 pages, 9 figures, To appear in ASP Conf. series - "New
Technologies for VLBI", ed. Y.C. Minh (Korean VLBI Network
Discovering the microJy Radio VLBI Sky via "Full-beam" Self-calibration
We demonstrate that at 1.4 GHz the combined response of sources detected
serendipitously in deep, wide-field VLBI images is sufficient to permit
self-calibration techniques to be employed. This technique of "full-beam" VLBI
self-calibration permits coherent VLBI observations to be successfully
conducted in any random direction on the sky, thereby enabling very faint radio
sources to be detected. Via full-beam self-calibration, Global VLBI
observations can equal and indeed surpass the level of sensitivity achieved by
connected arrays. This technique will enable large-scale VLBI surveys of the
faint radio source population to be conducted, in addition to targeted
observations of faint sources of special interest (e.g. GRBs, SNe, SNR and
low-luminosity AGN).Comment: 4 pages. 5 figures. Proceedings of the 7th European VLBI Network
Symposium held in Toledo, Spain on October 12-15, 2004. Editors: R.
Bachiller, F. Colomer, J.-F. Desmurs, P. de Vicente (Observatorio Astronomico
Nacional), p. 35-38. Needs evn2004.cl
The Deepest and Widest VLBI Survey yet: VLBA+GBT 1.4 GHz observations in Bootes
We present preliminary results from the deepest VLBI observations yet
conducted. VLBA+GBT 1.4 GHz observations of a region within NOAO-N, reach an
r.m.s. noise level of 9 microJy per beam. Three sources are clearly detected (>
7 sigma) within the inner 2 arcmins of the GBT primary beam, including two
sub-mJy sources and the ``in-beam'' calibrator. In addition, by tapering the
data, we map out a much larger area of sky, reaching well beyond the half-power
point of the GBT primary beam. An additional 6 sources are detected in the
extended field. We comment briefly on the scientific motivation for even deeper
and wider VLBI surveys, and note that the summed response of sources in the
field will permit self-calibration techniques to be employed in any region of
the radio sky, including so-called ``blank'' fields.Comment: 6 pages, 2 figures. To appear in the proceedings of the conference
"Radio Galaxies: Past, present and future", Leiden, 11-15 Nov 2002, eds. M.
Jarvis et al. Paper with improved figures at
http://www.jive.nl/~mag/leiden.ps.g
21st Century VLBI: Deep Wide-Field Surveys
A 20-hour VLBI observation with the NRAO VLBA and GBT in the NOAO Bootes
field reaches an rms noise of 9 microJy per beam at 1.4 GHz. Three sources were
detected at 10-milliarcsecond resolution within the GBT primary beam of FWHM
8.6', including the 20-milliJy calibrator and two sub-milliJy sources. By
tapering the visibility data, portions of the VLBA primary beam of FWHM 29'
were imaged at poorer sensitivity and resolution to yield five further
detections. New developments at JIVE will permit deeper and wider VLBI surveys
at full sensitivity and resolution, enabling new types of survey science.Comment: 5 pages, 1 figure. Presented at the meeting on "Future Directions in
High Resolution Astronomy: A Celebration of the 10th Anniversary of the
VLBA", held June 8-12, 2003, in Socorro, New Mexico, US
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