We describe and demonstrate a technique for correcting direction dependent artifacts due to asymmetries in antenna patterns and differences among antennas used in radio interoferometric imaging. The ...technique can correct images in all Stokes parameters I, Q, U and V and is shown with simulated data to reduce the level of artifacts to near the level of those from the basic imaging technique. The demonstrations use simulations of a mixed array of 13.5 and 15 m antennas with asymmetric patterns. The flux densities and spectral indices of the sources in a high dynamic range realistic simulated sky model are well recovered. Source polarization properties are also recovered in tests using unpolarized and partly polarized sources. The additional computational run time for Stokes I correction is about 50% in a realistic test described.
Abstract
Brightness-weighted differential source counts
S
2
n
(
S
) spanning the eight decades of flux density between 0.25
μ
Jy and 25 Jy at 1.4 GHz were measured from (1) the confusion brightness ...distribution in the MeerKAT DEEP2 image below 10
μ
Jy, (2) counts of DEEP2 sources between 10
μ
Jy and 2.5 mJy, and (3) counts of NVSS sources stronger than 2.5 mJy. We present our DEEP2 catalog of 1.7 × 10
4
discrete sources complete above
S
= 10
μ
Jy over Ω = 1.04 deg
2
. The brightness-weighted counts converge as
S
2
n
(
S
) ∝
S
1/2
below
S
= 10
μ
Jy, so >99% of the Δ
T
b
∼ 0.06 K sky brightness produced by active galactic nuclei and ≈96% of the Δ
T
b
∼ 0.04 K added by star-forming galaxies has been resolved into sources with
S
≥ 0.25
μ
Jy. The Δ
T
b
≈ 0.4 K excess brightness measured by ARCADE 2 cannot be produced by faint sources smaller than ≈50 kpc if they cluster like galaxies.
Abstract
We matched the 1.4 GHz local luminosity functions of star-forming galaxies (SFGs) and active galactic nuclei to the 1.4 GHz differential source counts from 0.25
μ
Jy to 25 Jy using ...combinations of luminosity and density evolution. We present the most robust and complete local far-infrared (FIR)/radio luminosity correlation to date in a volume-limited sample of ≈4.3 × 10
3
nearby SFGs, finding that it is very tight but distinctly sublinear:
L
FIR
∝
L
1.4
GHz
0.85
. If the local FIR/radio correlation does not evolve, the evolving 1.4 GHz luminosity function of SFGs yields the evolving star formation rate density (SFRD)
ψ
(
M
⊙
yr
−1
Mpc
−3
) as a function of time since the Big Bang. The SFRD measured at 1.4 GHz grows rapidly at early times, peaks at “cosmic noon” when
t
≈ 3 Gyr and
z
≈ 2, and subsequently decays with an
e
-folding timescale
τ
= 3.2 Gyr. This evolution is similar to, but somewhat stronger than, SFRD evolution estimated from UV and FIR data.
We have developed a semi-empirical simulation of the extragalactic radio continuum sky suitable for aiding the design of next generation radio interferometers such as the Square Kilometre Array ...(SKA). The emphasis is on modelling the large-scale cosmological distribution of radio sources rather than the internal structure of individual galaxies. Here we provide a description of the simulation to accompany the online release of a catalogue of ≃320 million simulated radio sources. The simulation covers a sky area of 20 × 20 deg2- a plausible upper limit to the instantaneous field of view attainable with future (e.g. SKA) aperture array technologies - out to a cosmological redshift of z= 20, and down to flux density limits of 10 nJy at 151, 610 MHz, 1.4, 4.86 and 18 GHz. Five distinct source types are included: radio-quiet active galactic nuclei (AGN), radio-loud AGN of the Fanaroff-Riley type I (FR I) and FR II structural classes, and star-forming galaxies, the latter split into populations of quiescent and starbursting galaxies.
In our semi-empirical approach, the simulated sources are drawn from observed (or extrapolated) luminosity functions and grafted on to an underlying dark matter density field with biases which reflect their measured large-scale clustering. A numerical Press-Schechter style filtering of the density field is used to identify and populate clusters of galaxies. For economy of output, radio source structures are constructed from point source and elliptical subcomponents, and for FR I and FR II sources an orientation-based unification and beaming model is used to partition flux between the core and extended lobes and hotspots. The extensive simulation output gives users the flexibility to post-process the catalogues to achieve more complete agreement with observational data in the years ahead. The ultimate aim is for the 'idealized skies' generated by this simulation and associated post-processing to be fed to telescope simulators to optimize the design of the SKA itself.
ABSTRACT
We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length l ≈ 1.57 Mpc) X-shaped radio source PKS 2014−55 with an ...unprecedented combination of brightness sensitivity and angular resolution. They show the clear ‘double boomerang’ morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC 064440. The magnetic field orientation in PKS 2014−55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint ($T_\mathrm{b} \approx 0.5 \mathrm{\, K}$) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intragroup medium. The position angle of the much smaller (l ∼ 25 kpc) restarted central source is within 5° of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.
Abstract
The IRAS Revised Bright Galaxy Sample (RBGS) comprises galaxies and unresolved mergers stronger than
S
= 5.24 Jy at
λ
= 60
μ
m with Galactic latitudes ∣
b
∣ > 5°. Nearly all are dusty ...star-forming galaxies whose radio continuum and far-infrared luminosities are proportional to their current rates of star formation. We used the MeerKAT array of 64 dishes to make 5 × 3 minutes snapshot observations at
ν
= 1.28 GHz covering all 298 southern (J2000
δ
< 0°) RBGS sources identified with external galaxies. The resulting images have
θ
≈ 7.″5 FWHM resolution and rms fluctuations
σ
≈ 20
μ
Jy beam
−1
≈ 0.26 K low enough to reveal even faint disk emission. The rms position uncertainties are
σ
α
≈
σ
δ
≈ 1″ relative to accurate near-infrared positions, and the image dynamic ranges are DR ≳ 10
4
: 1. Cropped MeerKAT images of all 298 southern RBGS sources are available in FITS format from
10.48479/dnt7-6q05
.
Measurement of the evolution of both active galactic nuclei (AGN) and star-formation in galaxies underpins our understanding of galaxy evolution over cosmic time. Radio continuum observations can ...provide key information on these two processes, in particular via the mechanical feedback produced by radio jets in AGN, and via an unbiased dust-independent measurement of star formation rates. In this paper, we determine radio luminosity functions at 325 MHz for a sample of AGN and star-forming galaxies by matching a 138 deg2 radio survey conducted with the Giant Metrewave Radio Telescope, with optical imaging and redshifts from the Galaxy And Mass Assembly survey. We find that the radio luminosity function at 325 MHz for star-forming galaxies closely follows that measured at 1.4 GHz. By fitting the AGN radio luminosity function out to z = 0.5 as a double power law, and parametrizing the evolution as Φ ∝ (1 + z)
k
, we find evolution parameters of k = 0.92 ± 0.95 assuming pure density evolution and k = 2.13 ± 1.96 assuming pure luminosity evolution. We find that the Low Excitation Radio Galaxies are the dominant population in space density at lower luminosities. Comparing our 325 MHz observations with radio continuum imaging at 1.4 GHz, we determine separate radio luminosity functions for steep- and flat-spectrum AGN, and show that the beamed population of flat-spectrum sources in our sample can be shifted in number density and luminosity to coincide with the unbeamed population of steep-spectrum sources, as is expected in the orientation-based unification of AGN.
This study assesses the user burden, reliability, and longitudinal validity of the AHQ, a novel VH patient-reported outcomes measure (PROM).
We developed and psychometrically validated the AHQ as the ...first VH-specific, stakeholder-informed PROM. Yet, there remains a need to assess the AHQ's clinical applicability and further validate its psychometric properties.
To assess patient burden, pre- and postoperative patients were timed while completing the corresponding AHQ form. To measure test-retest reliability, a subset of patients completed the AHQ within a week of initial completion, and consecutive responses were correlated. Lastly, patients undergoing VH repair were prospectively administered the pre- and postoperative AHQ forms, the Hernia-Related Quality of Life Survey and the Short Form-12 both preoperatively and at postoperative intervals, up to over a year after surgery. Quality-of-Life scores were correlated from the 3 PROMs and effect sizes were compared using analysis of normal variance.
Median response times for the pre- and postoperative AHQ were 1.1 and 2.7 minutes, respectively. The AHQ demonstrates high test-retest reliability coefficients for pre- and postoperative instruments ( r = 0.91, 0.89). The AHQ appropriately and proportionally measures expected changes following surgery and significantly correlates with all times points of theHernia-Related Quality of Life Survey and Short Form-12 MS and 4/5 (80%) SF12-PS.
The AHQ is a patient-informed, psychometrically-validated, clinical instrument for measuring, quantifying, and tracking PROMs in VH patients. The AHQ exhibits low response burden, excellent reliability, and effectively measures hernia-specific changes in quality-of-Life following ventral hernia repair.
We use the Sloan Digital Sky Survey, along with the NRAO VLA Sky Survey and the Westerbork Northern Sky Survey to define a sample of 746 radio-loud quasars and measure their 330 MHz-1.4 GHz spectral ...indexes. Following previous authors we take the radio spectral index as an indicator of the orientation towards the quasars such that more pole-on sources tend to have flatter spectral indexes. We use this proxy for the orientation of quasars to investigate the effect orientation may have on optical spectra.
Quasars with flatter spectral indexes tend to be brighter. However, we find no indication of reddening in steep-spectrum quasi-stellar objects (QSOs) to indicate obscuration of the accretion disc by a torus as a possible explanation. Nor do we find increased reddening in the flat-spectrum sources which could imply a contribution from jet-related synchrotron emission.
We reproduce a previously described anticorrelation between the width of the Mg ii line and radio spectral index that indicates a disc-like geometry for the Mg ii broad-line region (BLR). However, in contrast to previous authors we find no such correlation for the C iv line suggesting a more isotropic high-ionization BLR.
Both the O ii and O iii narrow lines have more flux in steep spectrum sources, while the O iii/O ii flux ratio is lower in these sources. To describe both of these effects we propose a simple geometric model in which the narrow-line region (NLR) exists primarily on the surface of optically thick clouds facing the active nucleus and the NLR is stratified such that higher ionization lines are found preferentially closer to the nucleus.
Quantitatively we find that orientation may effect the observed strength of narrow lines, as well as ratios between lines, by a factor of ∼2. These findings have implications for the use of O iii and O ii emission lines to estimate bolometric luminosities, as well as comparisons between narrow-line luminosity functions for type 1 and 2 objects and the potential of emission-line diagnostic diagrams as an accurate tool with which to distinguish types of active galactic nuclei.
Finally we find no evidence that broad-absorption line (BAL) QSOs have a different spectral index distribution to non-BALs although we only have 25 obvious BALs in our sample.
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