We present results from a parsec-scale jet kinematics study of 409 bright radio-loud active galactic nuclei (AGNs) based on 15 GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 ...and 2016 December 26 as part of the 2 cm VLBA survey and Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) programs. We tracked 1744 individual bright features in 382 jets over at least 5 epochs. A majority (59%) of the best-sampled jet features showed evidence of accelerated motion at the >3 level. Although most features within a jet typically have speeds within ∼40% of a characteristic median value, we identified 55 features in 42 jets that had unusually slow pattern speeds, nearly all of which lie within 4 pc (100 pc deprojected) of the core feature. Our results, combined with other speeds from the literature, indicate a strong correlation between apparent jet speed and synchrotron peak frequency, with the highest jet speeds being found only in low-peaked AGNs. Using Monte Carlo simulations, we find best-fit parent population parameters for a complete sample of 174 quasars above 1.5 Jy at 15 GHz. Acceptable fits are found with a jet population that has a simple unbeamed power-law luminosity function incorporating pure luminosity evolution and a power-law Lorentz factor distribution ranging from 1.25 to 50 with slope −1.4 0.2. The parent jets of the brightest radio quasars have a space density of 261 19 Gpc−3 and unbeamed 15 GHz luminosities above ∼1024.5 W Hz−1, consistent with FR II class radio galaxies.
Radio-faint AGN: a tale of two populations Padovani, P; Bonzini, M; Kellermann, K. I ...
Monthly notices of the Royal Astronomical Society,
09/2015, Letnik:
452, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We study the Extended Chandra
Deep Field-South Very Large Array sample, which reaches a flux density limit at 1.4 GHz of 32.5 μJy at the field centre and redshift ∼4, and covers ∼0.3 deg2. Number ...counts are presented for the whole sample while the evolutionary properties and luminosity functions are derived for active galactic nuclei (AGN). The faint radio sky contains two totally distinct AGN populations, characterized by very different evolutions, luminosity functions, and Eddington ratios: radio-quiet (RQ)/radiative-mode and radio-loud (RL)/jet-mode AGN. The radio power of RQ AGN evolves
$\mathrel {{\rlap{{\lower4pt{\sim }}}{\propto }}}(1+z)^{2.5}$
, similarly to star-forming galaxies, while the number density of RL ones has a peak at z ∼ 0.5 and then declines at higher redshifts. The number density of radio-selected RQ AGN is consistent with that of X-ray selected AGN, which shows that we are sampling the same population. The unbiased fraction of radiative-mode RL AGN, derived from our own and previously published data, is a strong function of radio power, decreasing from ∼0.5 at P
1.4 GHz ∼ 1024 W Hz−1 to ∼0.04 at P
1.4 GHz ∼ 1022 W Hz−1. Thanks to our enlarged sample, which now includes ∼700 radio sources, we also confirm and strengthen our previous results on the source population of the faint radio sky: star-forming galaxies start to dominate the radio sky only below ∼0.1 mJy, which is also where RQ AGN overtake RL ones.
We used the Karl G. Jansky Very Large Array to image one primary beam area at 3 GHz with 8" FWHM resolution and 1.0 mu Jy beam super(-1) rms noise near the pointing center. The P(D) distribution from ...the central 10 arcmin of this confusion-limited image constrains the count of discrete sources in the 1 < S( mu Jy) < 10 range. At this level, the brightness-weighted differential count S super(2)n(S) is converging rapidly, as predicted by evolutionary models in which the faintest radio sources are star-forming galaxies; and asymptotically =96% of the background originating in galaxies has been resolved into discrete sources. About 63% of the radio background is produced by active galactic nuclei (AGNs), and the remaining 37% comes from star-forming galaxies that obey the far-infrared (FIR)/radio correlation and account for most of the FIR background at lambda asymptotically = 160 mu m. Our new data confirm that radio sources powered by AGNs and star formation evolve at about the same rate, a result consistent with AGN feedback and the rough correlation of black hole and stellar masses. The confusion at centimeter wavelengths is low enough that neither the planned Square Kilometre Array nor its pathfinder ASKAP EMU survey should be confusion limited, and the ultimate source detection limit imposed by "natural" confusion is < or =, slant0.01 mu Jy at nu = 1.4 GHz. If discrete sources dominate the bright extragalactic background reported by ARCADE 2 at 3.3 GHz, they cannot be located in or near galaxies and most are < or =, slant0.03 mu Jy at 1.4 GHz.
The Inner Jet of the Radio Galaxy M87 Kovalev, Y. Y; Lister, M. L; Homan, D. C ...
The Astrophysical journal,
10/2007, Letnik:
668, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report new 2 cm VLBA images of the inner radio jet of M87 showing a limb-brightened structure and unambiguous evidence for a faint 3 mas long counterfeature which also appears limb brightened. ...Multiepoch observations of seven separate jet features show typical speeds of less than a few percent of the speed of light, despite the highly asymmetric jet structure and the implications of the canonical relativistic beaming scenario. The observed morphology is consistent with a two-stream spine-sheath velocity gradient across the jet, as might be expected from the recently discovered strong and variable TeV emission as well as from numerical modeling of relativistic jets. Considering the large jet-to-counterjet flux density ratio and lack of observed fast motion in the jet, we conclude that either the inner part of the M87 jet is intrinsically asymmetric or that the bulk plasma flow speed is much greater than any propagation of shocks or other pattern motions.
RADIO-LOUD AND RADIO-QUIET QSOs Kellermann, K. I.; Condon, J. J.; Kimball, A. E. ...
The Astrophysical journal,
11/2016, Letnik:
831, Številka:
2
Journal Article
Recenzirano
Odprti dostop
ABSTRACT We discuss 6 GHz JVLA observations covering a volume-limited sample of 178 low-redshift ( ) optically selected quasi-stellar objects (QSOs). Our 176 radio detections fall into two clear ...categories: (1) about 20% are radio-loud QSOs (RLQs) with spectral luminosities of that are primarily generated in the active galactic nucleus (AGN) responsible for the excess optical luminosity that defines a bona fide QSO; and (2) the remaining 80% that are radio-quiet QSOs (RQQs) that have and radio sizes , and we suggest that the bulk of their radio emission is powered by star formation in their host galaxies. "Radio-silent" QSOs ( ) are rare, so most RQQ host galaxies form stars faster than the Milky Way; they are not "red and dead" ellipticals. Earlier radio observations did not have the luminosity sensitivity of that is needed to distinguish between such RLQs and RQQs. Strong, generally double-sided radio emission spanning was found to be associated with 13 of the 18 RLQ cores with peak flux densities of ( ). The radio luminosity function of optically selected QSOs and the extended radio emission associated with RLQs are both inconsistent with simple "unified" models that invoke relativistic beaming from randomly oriented QSOs to explain the difference between RLQs and RQQs. Some intrinsic property of the AGNs or their host galaxies must also determine whether or not a QSO appears radio-loud.
ABSTRACT We present 1625 new 15 GHz (2 cm) VLBA images of 295 jets associated with active galactic nuclei (AGNs) from the MOJAVE and 2 cm VLBA surveys, spanning observations between 1994 August 31 ...and 2013 August 20. For 274 AGNs with at least 5 VLBA epochs, we have analyzed the kinematics of 961 individual bright features in their parsec-scale jets. A total of 122 of these jets have not been previously analyzed by the MOJAVE program. In the case of 451 jet features that had at least 10 epochs, we also examined their kinematics for possible accelerations. At least half of the well-sampled features have non-radial and/or accelerating trajectories, indicating that non-ballistic motion is common in AGN jets. Since it is impossible to extrapolate any accelerations that occurred before our monitoring period, we could only determine reliable ejection dates for of those features that had significant proper motions. The distribution of maximum apparent jet speeds in all 295 AGNs measured by our program to date is peaked below , with very few jets with apparent speeds above . The fastest speed in our survey is , measured in the jet of the quasar PKS 0805−07, and is indicative of a maximum jet Lorentz factor of ∼50 in the parent population. An envelope in the maximum jet speed versus redshift distribution of our sample provides additional evidence of this upper limit to the speeds of radio-emitting regions in parsec-scale AGN jets. The Fermi-LAT-detected gamma-ray AGNs in our sample have, on average, higher jet speeds than non-LAT-detected AGNs, indicating a strong correlation between parsec-scale jet speed and the gamma-ray Doppler boosting factor. We have identified 11 moderate-redshift ( ) AGNs with fast apparent speeds ( ) that are strong candidates for future TeV gamma-ray detection. Of the five gamma-ray loud narrow-lined Seyfert I AGNs in our sample, three show highly superluminal jet motions, while the others have sub-luminal speeds. This indicates that some narrow-lined Seyfert I AGNs possess powerful jets with Lorentz factors in excess of 10, and viewing angles less than , consistent with those of typical BL Lac objects and flat-spectrum radio quasars.
We describe the parsec-scale kinematics of 200 active galactic nucleus (AGN) jets based on 15 GHz Very Long Baseline Array (VLBA) data obtained between 1994 August 31 and 2011 May 1. We present new ...VLBA 15 GHz images of these and 59 additional AGNs from the MOJAVE and 2 cm Survey programs. Nearly all of the 60 most heavily observed jets show significant changes in their innermost position angle over a 12-16 yr interval, ranging from 10degrees to 150degrees on the sky, corresponding to intrinsic variations of ~0degrees.5 to ~2degrees. We have derived vector proper motions for 887 moving features in 200 jets having at least five VLBA epochs. For 557 well-sampled features, there are sufficient data to additionally study possible accelerations. We find that the moving features are generally non-ballistic, with 70% of the well-sampled features showing either significant accelerations or non-radial motions.
The sub-mJy radio population is a mixture of active systems, that is star-forming galaxies (SFGs) and active galactic nuclei (AGNs). We study a sample of 883 radio sources detected at 1.4 GHz in a ...deep Very Large Array survey of the Extended Chandra Deep Field-South that reaches a best rms sensitivity of 6 μJy. We have used a simple scheme to disentangle SFGs, radio-quiet (RQ), and radio-loud (RL) AGNs based on the combination of radio data with Chandra X-ray data and mid-infrared observations from Spitzer. We find that at flux densities between about 30 and 100 μJy, the radio population is dominated by SFGs (~60 per cent) and that RQ AGNs become increasingly important over RL ones below 100 μJy. We also compare the host galaxy properties of the three classes in terms of morphology, optical colours and stellar masses. Our results show that both SFG and RQ AGN host galaxies have blue colours and late-type morphology while RL AGNs tend to be hosted by massive red galaxies with early-type morphology. This supports the hypothesis that radio emission in SFGs and RQ AGNs mainly comes from the same physical process: star formation in the host galaxy. PUBLICATION ABSTRACT
Abstract
We present multiepoch, parsec-scale core brightness temperature observations of 447 active galactic nucleus (AGN) jets from the MOJAVE and 2 cm Survey programs at 15 GHz from 1994 to 2019. ...The brightness temperature of each jet over time is characterized by its median value and variability. We find that the range of median brightness temperatures for AGN jets in our sample is much larger than the variations within individual jets, consistent with Doppler boosting being the primary difference between the brightness temperatures of jets in their median state. We combine the observed median brightness temperatures with apparent jet speed measurements to find the typical intrinsic Gaussian brightness temperature of 4.1( ± 0.6) × 10
10
K, suggesting that jet cores are at or below equipartition between particle and magnetic field energy in their median state. We use this value to derive estimates for the Doppler factor for every source in our sample. For the 309 jets with both apparent speed and brightness temperature data, we estimate their Lorentz factors and viewing angles to the line of sight. Within the BL Lac optical class, we find that high-synchrotron-peaked BL Lacs have smaller Doppler factors, lower Lorentz factors, and larger angles to the line of sight than intermediate and low-synchrotron-peaked BL Lacs. We confirm that AGN jets with larger Doppler factors measured in their parsec-scale radio cores are more likely to be detected in
γ
rays, and we find a strong correlation between
γ
-ray luminosity and Doppler factor for the detected sources.
PDF
