Compact radio cores in Seyfert galaxies

Roy, A. L.; Norris, R. P.; Kesteven, Michael; Troup, E. R.; Reynolds, J. E.

doi:10.1086/174589

Cited by 69 publications

(74 citation statements)

References 43 publications

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“…Our large number of detections is also unusual for Seyfert galaxies selected in the optical or infrared. Roy et al (1994) observed samples of Seyfert galaxies with similar spatial resolution to our VLBI snapshots and detected compact radio cores in $38%.…”

Section: Morphologg Iessupporting

confidence: 64%

Radio-ExcessIRASGalaxies. III. Radio Properties

et al. 2004

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This is the third in a series of papers discussing the nature of radio-excess IRAS galaxies. This paper investigates in more detail the radio source properties of the radio-excess galaxies that are luminous in the far infrared (FIR). Spectral energy distributions derived from data from the Australia Telescope Compact Array confirm that the radio spectral energy distributions of the FIR-luminous radio-excess galaxies are mostly steep or show a turnover at gigahertz frequencies. VLBI snapshot data indicate that most sources are compact and thus resemble compact steep-spectrum (CSS) or gigahertz-peaked spectrum (GPS) sources. Images of two representative FIRluminous radio-excess galaxies are analyzed. Their morphologies appear disrupted and do not resemble typical CSS/GPS sources with symmetric double lobes. Synchrotron cooling timescales are derived for several sources and are found to be P10 6 yr. The jet energy fluxes inferred are 10 36 -10 37 W, an order of magnitude lower than typical radio-loud CSS/GPS sources. A dynamical model of a jet-fed lobe is used to derive ages $10 4 yr and jet energy fluxes of $10 37 W for the sources observed with VLBI. Expansion velocities less than 0.01c are derived for the lobes using this model. Thus, the ages of the FIR-luminous radio-excess galaxies are similar to young radio-loud sources, but the jet energy fluxes and expansion velocities are significantly lower than CSS/GPS sources. We conclude that the lower jet energy fluxes are responsible for their observed weaker radio powers when compared with CSS/GPS sources. We do not expect that the radio-excess sources will evolve into classical radio galaxies in the manner envisaged for CSS/GPS sources.

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Section: Morphologg Iessupporting

confidence: 64%

Radio-ExcessIRASGalaxies. III. Radio Properties

et al. 2004

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“…dyn (KSR) to ensure a statistical connection between the two scales. Roy et al (1998) found that Seyfert galaxies with bright compact radio cores, independent of the presence of any larger scale outflow, also deviate significantly from the far-infrared-radio correlation. They pointed out that the compact radio source alone does not suffice to explain the radio excess, but that there must be significant radio emission on scales larger than 0B1, the detection limit of the interferometer.…”

Section: Ksrs Originate From Nuclear Jetsmentioning

confidence: 86%

A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei

et al. 2006

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Seyfert galaxies commonly host compact jets spanning 10-100 pc scales, but larger structures are resolved out in long-baseline aperture synthesis surveys. Previous, targeted studies showed that kiloparsec-scale radio structures ( KSRs) may be a common feature of Seyfert and LINER galaxies, and the origin of KSRs may be starbursts or active galactic nuclei (AGNs). We report a new Very Large Array survey of a complete sample of Seyfert and LINER galaxies. Out of all of the surveyed radio-quiet sources, we find that 44% (19 out of 43) show extended radio structures at least 1 kpc in total extent that do not match the morphology of the disk or its associated star-forming regions. The detection rate is a lower limit owing to the combined effects of projection and resolution. The infrared colors of the KSR host galaxies are unremarkable compared to other Seyfert galaxies, and the large-scale outflows orient randomly with respect to the host galaxy axes. The KSR Seyfert galaxies instead stand out by deviating significantly from the far-infrared-radio correlation for star-forming galaxies, with tendency toward radio excess, and they are more likely to have a relatively luminous, compact radio source in the nucleus; these results argue that KSRs are powered by the AGNs rather than starbursts. The high detection rate indicates that Seyfert galaxies generate radio outflows over a significant fraction of their lifetime, which is much longer than the dynamical timescale of an AGNpowered jet but is comparable instead to the buoyancy timescale. The likely explanation is that the KSRs originate from jet plasma that has been decelerated by interaction with the nuclear interstellar medium ( ISM ). Based on a simple ram pressure argument, the kinetic power of the jet on kiloparsec scales is about 3 orders of magnitude weaker than the power of the jet on 10-100 pc scales. This result is consistent with the interaction model, in which case virtually all of the jet power must be lost to the ISM within the inner kiloparsec.

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“…A study by Roy et al (1994) shows that compact cores are more common in Seyfert 2 galaxies (46%) than in Seyfert 1 galaxies (26%). Increasing the free-free absorption optical depths in the Narrow Line Region may account for the different detection rates within a unified AGN model.…”

Section: Evaluation Of the Radio Classificationmentioning

confidence: 99%

Radio properties of FIR-megamaser nuclei

Baan¹,

Klöckner²

2006

A&A

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Aims. Radio data on the nuclear emissions have been used to characterize the dominant nuclear activity in a sample of FIR (ultra-) luminous galaxies and the subgroup of known OH Megamasers. This study complements an earlier study of the optical classification of these Megamaser nuclei. Methods. Classification of the radio activity in the nuclei is based on three critical parameters: the radio brightness temperature, the radio spectral index, and the ratio of FIR and radio fluxes. A first method gives equal weight to the three parameters and a second method uses a weighted function to classify the nuclei.Results. The present sample shows that only 43% of the sample shows some -weak or strong -AGN characteristics. About 66% of the OH-MM sample and 81% of the non-OH-MM sample can be actually classified as Starburst-dominated sources. Radio diagnostic diagrams using these diagnostic parameters show a continuous distribution ranging between AGN-dominated and SBN-dominated sources. The diagnostic diagrams also support the notion that AGNs and starbursts coexist in the nuclei. Conclusions. A comparison of the radio and optical classifications shows a consistency in the extreme cases of clear SBN and AGNs. A significant part of the sources with optical AGN-like activity have an SBN classification in the radio. The discrepant classifications are discussed in order to arrive at a final classification of the dominant power source in the nucleus.

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Compact radio cores in Seyfert galaxies

Cited by 69 publications

References 43 publications

Radio-ExcessIRASGalaxies. III. Radio Properties

Radio-ExcessIRASGalaxies. III. Radio Properties

A Survey of Kiloparsec-Scale Radio Outflows in Radio-Quiet Active Galactic Nuclei

Radio properties of FIR-megamaser nuclei

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