69 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
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
A powerful (and likely young) radio-loud quasar at z=5.3
We present the discovery of PSO J191.0569686.43172 (hereafter PSO
J19186), a new powerful radio-loud quasar (QSO) in the early Universe (z =
5.32). We discovered it by cross-matching the NRAO VLA Sky Survey (NVSS) radio
catalog at 1.4 GHz with the first data release of the Panoramic Survey
Telescope and Rapid Response System (Pan-STARRS PS1) in the optical. With a
NVSS flux density of 74.2 mJy, PSO J19186 is one of the brightest radio QSO
discovered at z5. The intensity of its radio emission is also confirmed
by the very high value of radio loudness (R>300). The observed radio spectrum
of PSO J19186 shows a possible turnover around 1 GHz (i.e., 6
GHz in the rest frame), making it a Gigahertz-Peaked Spectrum (GPS) source.
However, variability could affect the real shape of the radio spectrum, since
the data in hand have been taken 25 years apart. By assuming a peak of
the observed radio spectrum between 1 and 2 GHz (i.e. 6 and 13 GHz in
the rest-frame) we found a linear size of the source of 10-30 pc and a
corresponding kinetic age of 150-460 yr. This would make PSO J19186 a newly
born radio source. However, the large X-ray luminosity (5.310
erg s), the flat X-ray photon index (=1.32) and the
optical-X-ray spectral index (=1.329) are typical of
blazars. This could indicate that the non-thermal emission of PSO J19186 is
Doppler boosted. Further radio observations (both on arcsec and parsec scales)
are necessary to better investigate the nature of this powerful radio QSO.Comment: 10 pages, 9 figures, 5 tables, Accepted for publication in A&
The first blazar observed at z>6
We present the discovery of PSO J030947.49+271757.31, the radio brightest (23.7 mJy at 1.4 GHz) active galactic nucleus (AGN) at z>6.0. It was selected by cross-matching the NRAO VLA Sky Survey and the Panoramic Survey Telescope and Rapid Response System PS1 databases and its high-z nature was confirmed by a dedicated spectroscopic observation at the Large Binocular Telescope. A pointed Neil Gehrels S wi f t Observatory XRT observation allowed us to measure a flux of 3c3.4
710 1214 erg s 121 cm 122 in the [0.5-10] keV energy band, which also makes this object the X-ray brightest AGN ever observed at z>6.0. Its flat radio spectrum (\u3b1\u3bdr<0.5), very high radio loudness (R>103), and strong X-ray emission, compared to the optical, support the hypothesis of the blazar nature of this source. Assuming that this is the only blazar at this redshift in the surveyed area of sky, we derive a space density of blazars at z 3c6 and with M1450\uc5 < -21.5 of 5.5+11.2 124.6
710 123 Gpc 123. From this number, and assuming a reasonable value of the bulk velocity of the jet (\u393=10), we can also infer a space density of the entire radio-loud AGN population at z 3c6 with the same optical/UV absolute magnitude of 1.10+2.53 120.91 Gpc 123. Larger samples of blazars will be necessary to better constrain these estimates
No strong radio absorption detected in the low-frequency spectra of radio-loud quasars at z > 5.6
© 2023 The Author(s). Published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We present the low-frequency radio spectra of 9 high-redshift quasars at using the Giant Metre Radio Telescope band-3, -4, and -5 observations (300-1200 MHz), archival Low Frequency Array (LOFAR; 144 MHz), and Very Large Array (VLA; 1.4 and 3 GHz) data. Five of the quasars in our sample have been discovered recently, representing some of the highest redshift radio bright quasars known at low-frequencies. We model their radio spectra to study their radio emission mechanism and age of the radio jets by constraining the spectral turnover caused by synchrotron self-absorption (SSA) or free-free absorption (FFA). Besides J0309+2717, a blazar at , our quasars show no sign of a spectral flattening between 144 MHz and a few GHz, indicating there is no strong SSA or FFA absorption in the observed frequency range. However, we find a wide range of spectral indices between and , including the discovery of 3 potential ultra-steep spectrum quasars. Using further archival VLBA data, we confirm that the radio SED of the blazar J0309+2717 likely turns over at a rest-frame frequency of 0.6-2.3 GHz (90-330 MHz observed frame), with a high-frequency break indicative of radiative ageing of the electron population in the radio lobes. Ultra-low frequency data below 50 MHz are necessary to constrain the absorption mechanism for J0309+2717 and the turnover frequencies for the other high- quasars in our sample. A relation between linear radio jet size and turnover frequency has been established at low redshifts. If this relation were to hold at high redshifts, the limits on the turnover frequency of our sample suggest the radio jet sizes must be more extended than the typical sizes observed in other radio-bright quasars at similar redshift. To confirm this deep radio follow-up observations with high spatial resolution are required.Peer reviewe
The rocky road to quiescence: compaction and quenching of quasar host galaxies at z ∼ 2
We resolve the host galaxies of seven gravitationally lensed quasars at
redshift 1.5 to 2.8 using observations with the Atacama Large (sub-)Millimetre
Array. Using a visibility-plane lens modelling technique, we create pixellated
reconstructions of the dust morphology, and CO line morphology and kinematics.
We find that the quasar hosts in our sample can be distinguished into two
types: 1) galaxies characterised by clumpy, extended dust distributions
( kpc) and mean star formation rate surface densities
comparable to sub-mm-selected dusty star-forming galaxies ( M yr kpc); 2) galaxies that have sizes in
dust emission similar to coeval passive galaxies and compact starbursts
( kpc), with high mean star formation rate surface
densities ( 4004500 M yr kpc)
that may be Eddington-limited or super-Eddington. The small size of some quasar
hosts suggests that we observe them at a stage in their transformation into
compact spheroids, where a high density of dynamically unstable gas leads to
efficient star formation and black hole accretion. For the one system where we
probe the mass of the gas reservoir, we find a gas fraction of just and a depletion timescale of Myr, suggesting it is
transitioning into quiescence. In general, we expect that the extreme level of
star formation in the compact quasar host galaxies will rapidly exhaust their
gas reservoirs and could quench with or without help from active galactic
nuclei feedback.Comment: Accepted by MNRAS; 22 page
A Highly Magnified Gravitationally Lensed Red QSO at z = 2.5 with a Significant Flux Ratio Anomaly
We present the discovery of a gravitationally lensed dust-reddened QSO at z =
2.517, identified in a survey for QSOs by infrared selection. Hubble Space
Telescope imaging reveals a quadruply lensed system in a cusp configuration,
with a maximum image separation of ~1.8\arcsec. We find that compared to the
central image of the cusp, the neighboring brightest image is anomalous by a
factor of ~ 7 - 10, which is the largest flux anomaly measured to date in a
lensed QSO. Incorporating high-resolution Jansky Very Large Array radio imaging
and sub-mm imaging with the Atacama Large (sub-)Millimetre Array, we conclude
that a low-mass perturber is the most likely explanation for the anomaly. The
optical through near-infrared spectrum reveals that the QSO is moderately
reddened with E(B - V) = 0.7 - 0.9. We see an upturn in the ultraviolet
spectrum due to ~ 1% of the intrinsic emission being leaked back into the line
of sight, which suggests that the reddening is intrinsic and not due to the
lens. The QSO may have an Eddington ratio as high as L/L_Edd ~ 0.2. Consistent
with previous red QSO samples, this source exhibits outflows in its spectrum as
well as morphological properties suggestive of it being in a merger-driven
transitional phase. We find a host-galaxy stellar mass of log M_*/M_Sun = 11.4,
which is higher than the local M_BH vs. M_* relation, but consistent with other
high redshift QSOs. When de-magnified, this QSO is at the knee of the
luminosity function, allowing for the detailed study of a more typical
moderate-luminosity infrared-selected QSO at high redshift.Comment: Accepted for publication in ApJ; 29 pages, 18 figures, 8 tables.
arXiv admin note: text overlap with arXiv:1807.0543
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