170 research outputs found
A novel search for gravitationally lensed radio sources in wide-field VLBI imaging from the mJIVE-20 survey
We present a novel pilot search for gravitational lenses in the mJIVE-20
survey, which observed radio sources selected from FIRST with the
VLBA at an angular resolution of 5 mas. We have taken the visibility data for
an initial sources that were detected by the mJIVE-20 observations and
re-mapped them to make wide-field images, selecting fourteen sources that had
multiple components separated by mas, with a flux-ratio of
: and a surface brightness consistent with gravitational lensing.
Two of these candidates are re-discoveries of gravitational lenses found as
part of CLASS. The remaining twelve candidates were then re-observed at 1.4 GHz
and then simultaneously at 4.1 and 7.1 GHz with the VLBA to measure the
spectral index and surface brightness of the individual components as a
function of frequency. Ten were rejected as core-jet or core-hotspot(s)
systems, with surface brightness distributions and/or spectral indices
inconsistent with gravitational lensing, and one was rejected after lens
modelling demonstrated that the candidate lensed images failed the parity test.
The final lens candidate has an image configuration that is consistent with a
simple lens mass model, although further observations are required to confirm
the lensing nature. Given the two confirmed gravitational lenses in the
mJIVE-20 sample, we find a robust lensing-rate of :() for a
statistical sample of 635 radio sources detected on mas-scales, which is
consistent with that found for CLASS.Comment: 31 pages, 22 figures; accepted for publication in MNRA
Gravitational lensing at milliarcsecond angular resolution
Gravitational lensing is a powerful tool for studying the mass content in distant galaxies, but also for performing a detailed study of high-redshift sources. In this thesis, we use milliarcsecond angular resolution observations of radio-loud gravitationally lensed sources to investigate both the properties of lensing galaxies and background sources. We present high-resolution global Very Long Baseline Interferometric (VLBI) observations of the gravitationally lensed radio source MG J0751+2716 (at z = 3.2), that shows evidence of both compact and extended structure (core-jet morphology) across several gravitational arcs. These data provide a wealth of observational constraints that are used to determine the inner (baryonic and dark matter) mass profile of a group of galaxies and also investigate the smoothness of the dark matter distribution on mas-scales. By complementing spectral line radio observations with optical and near-infrared imaging at high angular resolution, in the second chapter we investigate the cold molecular gas, stars and dust content in two high redshift galaxies (MG J0751+2716 and JVAS B1938+666). Moreover, by comparing two observations at milliarcsecond angular resolution separated by 15 years, we find evidence for proper motions observed for the first time in the gravitational lensing system MG B2016+112. The analysis of these data can constrain the formation model for super-massive black holes. Finally, we present a new pilot gravitational lens search in the VLBI survey mJIVE-20 in perspective of future surveys with the next generation of radio interferometers
Proper motion in lensed radio jets at redshift 3:A possible dual super-massive black hole system in the early Universe
In this paper, we exploit the gravitational lensing effect to detect proper
motion in the highly magnified gravitationally lensed source MG B2016+112. We
find positional shifts up to 6 mas in the lensed images by comparing two Very
Long Baseline Interferometric (VLBI) radio observations at 1.7 GHz that are
separated by 14.359 years, and provide an astrometric accuracy of the order of
tens of as. From lens modelling, we exclude a shift in the lensing galaxy
as the cause of the positional change of the lensed images, and we assign it to
the background source. The source consists of four sub-components separated by
pc, with proper motion of the order of tens as yr for
the two components at highest magnification () and of the order of
a few mas yr for the two components at lower magnification ().
We propose single AGN and dual AGN scenarios to explain the source plane.
Although, the latter interpretation is supported by the archival
multi-wavelength properties of the object. In this case, MG B2016+112 would
represent the highest redshift dual radio-loud AGN system discovered thus far,
and would support the merger interpretation for such systems. Also, given the
low probability () of detecting a dual AGN system that is also
gravitationally lensed, if confirmed, this would suggest that such dual AGN
systems must be more abundant in the early Universe than currently thought.Comment: 11 pages, 4 figures; accepted for publication by Astronomy and
Astrophysic
Parsec-scale properties of the radio brightest jetted AGN at z > 6
We present Director's Discretionary Time multi-frequency observations
obtained with the Jansky Very Large Array (VLA) and the Very Long Baseline
Array (VLBA) of the blazar PSO J030947.49+271757.31 (hereafter PSO J0309+27) at
. The milliarcsecond angular resolution of our VLBA
observations at 1.5, 5 and 8.4 GHz unveils a bright one-sided jet extended for
parsecs in projection. This high-z radio-loud AGN is resolved into
multiple compact sub-components, embedded in a more diffuse and faint radio
emission, which enshrouds them in a continuous jet structure. We derive limits
on some physical parameters directly from the observable quantities, such as
viewing angle, Lorentz and Doppler factors. If PSO J0309+27 is a genuine
blazar, as suggested by its X-ray properties, then we find that its bulk
Lorentz factor must be relatively low (less than 5). Such value would be in
favour of a scenario currently proposed to reconcile the paucity of high-z
blazars with respect to current predictions. Nevertheless, we cannot exclude
that PSO J0309+27 is seen under a larger viewing angle, which would imply that
the X-ray emission must be enhanced, for example, by inverse Compton with the
Cosmic Microwave Background. More stringent constraints on the bulk Lorentz
factor in PSO J0309+27 and the other high-z blazars are necessary to test
whether their properties are intrinsically different with respect to the low-z
blazar population.Comment: 10 pages, 5 figures, accepted for publication in A&A Letter
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