The Very Large Array

Thompson, Alexander; Clark, B. G.; Wade, C. M.; Napier, P. J.

doi:10.1086/190688

Cited by 255 publications

(155 citation statements)

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“…All observations were taken over 22.5 hours on 9 October 2004, when the VLA was in A configuration (Thompson et al 1980). During the observations only two antennas were excluded from the array, and the weather conditions were good.…”

Section: Observations and Data Analysismentioning

confidence: 99%

The Radio Quiescence of Active Galaxies with High Accretion Rates

Greene

Ulvestad

2006

ApJ

106

110

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We present 6 cm Very Large Array observations of the Greene & Ho (2004) sample of 19 low-mass active galaxies with high accretion rates. This is one of the only studies of a uniform sample of narrow-line Seyfert 1 (NLS1) galaxies with such high sensitivity and resolution. Although we detect only one source, the entire sample is very radio-quiet down to strong limits. GH10 was found to have a radio power of 8.5 ×10 21 W Hz −1 , and a ratio R ≡ f 6cm / f 4400 of 2.8. The 3 σ upper limits for the remaining nondetections correspond to radio powers from 3 × 10 20 to 8 × 10 21 W Hz −1 and 0.47 < R < 9.9. Stacking all nondetections yields an even stronger upper limit of R ≤ 0.27. An assessment of existing observations in the literature confirms our finding that NLS1s are consistently radio-quiet, with a radio-loud fraction of 0%-6%, which is significantly lower than the 10%-20% observed in the general quasar population. By analogy with stellar-mass black holes, we argue that AGNs undergo a state transition at L bol /L Edd ≈ 0.01. Below this value a radiatively inefficient accretion flow effectively drives an outflow, which disappears when the flow turns into an optically thick, geometrically thin disk, or a radiation pressure-dominated slim disk at still higher L bol /L Edd .

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Section: Observations and Data Analysismentioning

confidence: 99%

The Radio Quiescence of Active Galaxies with High Accretion Rates

Greene

Ulvestad

2006

ApJ

106

110

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“…Because of the constraints of limited observing time, we selected a distance-limited sample of 41 of these galaxies lying within 30 Mpc. In this sample, 15 objects had 6 cm data at d1 00 resolution in the VLA archive, from observations made in the high-resolution A and B configurations, or the hybrid BnA configuration with a long north arm (see Thompson et al 1980). Data for these objects were extracted from the archive.…”

Section: Sample Selection and Observationsmentioning

confidence: 99%

A Search for Active Galactic Nuclei in Sc Galaxies with HiiSpectra

Ulvestad¹,

Ho²

2002

ApJ

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We have searched for nuclear radio emission from a statistically complete sample of 40 Sc galaxies within 30 Mpc that are optically classified as star-forming objects, in order to determine whether weak active galactic nuclei might be present. Only three nuclear radio sources were detected, in NGC 864, NGC 4123, and NGC 4535. These galaxies have peak 6 cm radio powers of $10 20 W Hz À1 at arcsecond resolution, while upper limits of the nondetected galaxies typically range from 10 18:4 to 10 20 W Hz À1 . The three nuclear radio sources are all resolved and appear to have diffuse morphologies, with linear sizes of $300 pc. This strongly indicates that circumnuclear star formation has been detected in these three H ii galaxies. Comparisons with previous 20 cm Very Large Array (VLA) results for the detected galaxies show that the extended nuclear radio emission has a flat spectrum in two objects and is almost certainly generated by thermal emission from gas ionized by young stars in the centers of those galaxies. The 6 cm radio powers are comparable to predictions for thermal emission that are based on the nuclear H luminosities and imply nuclear star formation rates of 0.08-0.8 M yr À1 , while the low-resolution NRAO VLA Sky Survey implies galaxy-wide star formation rates of 0.3-1.0 M yr À1 in stars above 5 M . In a few of the undetected galaxies, the upper limits to the radio power are lower than predicted from the H luminosity, possibly because of overresolution of central star-forming regions. Although the presence of active nuclei powered by massive black holes cannot be definitively ruled out, the present results suggest that they are likely to be rare in these late-type galaxies with H ii spectra.

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“…Radio data were obtained from the NRAO 2 Very Large Array (VLA; Thompson et al 1980) archive and the MER-LIN 3 archive (see Table 1 for a summary). The VLA data (5 and 15 GHz) were calibrated in AIPS (Greisen 1988) utilizing standard procedures and self-calibrated in the Caltech DIFMAP package (Shepherd, Pearson, & Taylor 1994).…”

Section: Description Of Archival Observationsmentioning

confidence: 99%

Detection of Optical Synchrotron Emission from the Radio Jet of 3C 279

Cheung

2002

The Astrophysical Journal

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We report the detection of optical and ultraviolet emission from the kiloparsec-scale jet of the well-known quasar 3C 279. A bright knot, discovered in archival V-and U-band Hubble Space Telescope Faint Object Camera images, is coincident with a peak in the radio jet ∼0Љ .6 from the nucleus. The detection was also confirmed in Wide Field Planetary Camera 2 images. Archival Very Large Array and MERLIN radio data are also analyzed, and these data help to show that the high-energy optical/UV continuum and the spectrum are consistent with a synchrotron origin from the same population of relativistic electrons responsible for the radio emission.

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The Very Large Array

Cited by 255 publications

References 0 publications

The Radio Quiescence of Active Galaxies with High Accretion Rates

The Radio Quiescence of Active Galaxies with High Accretion Rates

A Search for Active Galactic Nuclei in Sc Galaxies with HiiSpectra

Detection of Optical Synchrotron Emission from the Radio Jet of 3C 279

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