The Radio Properties of Seyfert Nuclei (original) (raw)
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Parsec‐Scale Radio Structures in the Nuclei of Four Seyfert Galaxies
The Astrophysical Journal, 1999
We present 18-cm radio maps of four Seyfert nuclei, Mrk 1, Mrk 3, Mrk 231 and Mrk 463E, made with the European VLBI Network (EVN). Linear radio structures are present in three out of four sources on scales of ∼100 pc to ∼1 kpc, and the 20-mas beam of the EVN enables us to resolve details within the radio structures on scales of < 10 pc. Mrk 3 was also imaged using MERLIN and the data combined with the EVN data to improve the sensitivity to extended emission. We find an unresolved flat-spectrum core in Mrk 3, which we identify with the hidden Seyfert 1 nucleus in this object, and we also see marked differences between the two highly-collimated radio jets emanating from the core. The western jet terminates in a bright hotspot and resembles an FRII radio structure, whilst the eastern jet has more in common with an FRI source. In Mrk 463E, we use the radio and optical structure of the source to argue that the true nucleus lies approximately 1 arcsec south of the position of the radio and optical brightness peaks, which probably represent a hotspot at the working surface of a radio jet. The EVN data also provide new evidence for a 100-pc radio jet powering the radio source in the Type 1 nucleus of Mrk 231. However, the Seyfert 2 galaxy Mrk 1 shows no evidence for radio jets down to the limits of resolution (∼ 10 pc). We discuss the range of radio source size and morphology which can occur in the nuclei of Seyfert galaxies and the implications for Seyfert unification schemes and for radio surveys of large samples of objects.
2016
A radio study of a carefully selected sample of 20 Seyfert galaxies that are matched in orientationindependent parameters, which are measures of intrinsic active galactic nuclei (AGN) power and host galaxy properties is presented to test the predictions of the unified scheme hypothesis. Our sample sources have core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the feasibility requirements. These simultaneous pc-scale and kpc-scale radio observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal tendency to show compact radio structures on mas-scales, (ii) the distributions of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert galaxies, (iv) similar distributions of source spectral indices in spite of the fact that Seyferts show nuclear radio flux density variations, and (v) the distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are not significantly different as would be expected in the unified scheme. The latter could be mainly due to a relatively large spread in the intrinsic sizes. We also find that a starburst alone cannot power these radio sources. Finally, an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample shows results consistent with the predictions of the unified scheme.
Seyfert Galaxies: Nuclear Radio Structure and Unification
The Astrophysical Journal, 2011
A radio study of a carefully selected sample of 20 Seyfert galaxies that are matched in orientationindependent parameters, which are measures of intrinsic active galactic nuclei (AGN) power and host galaxy properties is presented to test the predictions of the unified scheme hypothesis. Our sample sources have core flux densities greater than 8 mJy at 5 GHz on arcsec-scales due to the feasibility requirements. These simultaneous pc-scale and kpc-scale radio observations reveal (i) that Seyfert 1 and Seyfert 2 galaxies have equal tendency to show compact radio structures on mas-scales, (ii) the distributions of pc-scale and kpc-scale radio luminosities are similar for both Seyfert 1 and Seyfert 2 galaxies, (iii) no evidence for relativistic beaming in Seyfert galaxies, (iv) similar distributions of source spectral indices in spite of the fact that Seyferts show nuclear radio flux density variations, and (v) the distributions of projected linear size for Seyfert 1 and Seyfert 2 galaxies are not significantly different as would be expected in the unified scheme. The latter could be mainly due to a relatively large spread in the intrinsic sizes. We also find that a starburst alone cannot power these radio sources. Finally, an analysis of the kpc-scale radio properties of the CfA Seyfert galaxy sample shows results consistent with the predictions of the unified scheme.
2000
We present 8.4 GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of . These 0.25 arcsec resolution observations allow elongated radio structures tens of parsecs in size to be resolved and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering ninety percent of the sample have been collected and these represent the largest sub-arcsecond-resolution radio imaging survey of a homogeneously-selected sample of Seyfert galaxies to date.
2000
We present 8.4 GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of Rush et al (1993). These 0.25 arcsec resolution observations allow elongated radio structures tens of parsecs in size to be resolved and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering ninety percent of the sample have been collected and these represent the largest sub-arcsecond-resolution radio imaging survey of a homogeneously-selected sample of Seyfert galaxies to date. We use our observations to identify 5 radio-loud AGN in the sample. The nature of the radio emission from Seyfert nuclei will be discussed in subsequent papers.
AIP Conference Proceedings, 1997
Observations with Compton Gamma Ray Observatory have provided key insights to the high energy emission mechanisms in Active Galactic Nuclei (AGN) and clearly separate them into a class of Blazars, with apparent non-thermal jet emissions often peaking in the EGRET energy band, and into the Seyfert class with emissions more closely related to the accretion disk presumably energizing the nuclear black hole. OSSE measurements indicate that the high energy emission from Seyfert AGN has a high energy cuto below 100 ? 200 keV and no Seyferts have been detected by COMPTEL or EGRET. Here, we review the X-ray and -ray observations of Seyferts and Radio Galaxies and the broad band emission models that describe the observed spectral characteristics. A comparision of Seyfert 1, Seyfert 2, and radio galaxies can be made in the context of the AGN uni cation models.
2001
We discuss the properties of compact nuclear radio components in Seyfert galaxies from the extended 12-micron AGN sample of Rush et al.(1993). Our main results can be summarised as follows. Type 1 and type 2 Seyferts produce compact radio components which are indistinguishable in strength and aspect, indicating that their central engines are alike as proposed by the unification model. Infrared IRAS fluxes are more closely correlated with low-resolution radio fluxes than high-resolution radio fluxes, suggesting that they are dominated by kiloparsec-scale, extra-nuclear emission regions; extra-nuclear emission may be stronger in type 2 Seyferts. Early-type Seyfert galaxies tend to have stronger nuclear radio emission than late-type Seyfert galaxies. V-shaped extended emission-line regions, indicative of `ionisation cones', are usually found in sources with large, collimated radio outflows. Hidden broad lines are most likely to be found in sources with powerful nuclear radio sources. Type 1 and type 2 Seyferts selected by their IRAS 12-micron flux densities have well matched properties.
The Radio Properties of Seyfert Galaxies in the 12 Micron and CfA Samples
The Astrophysical Journal, 1996
We report the results of 20, 6, and 2 cm VLA and 1.5 cm OVRO observations of two similar AGN samples: the optically-selected CfA Seyfert galaxies and the bolometricflux-limited 12 µm active galaxy sample. Every object observed was detected at 6 cm. Only ∼ 6 − 8% of the 12 µm-sample Seyferts (3-4 objects) are radio-loud (and none of the CfA sample), as compared to 15-20% for the BQS quasars. These radio-loud objects are compact and have flat spectra, distinguishing them from the more common radio-quiet objects. The 6-20 cm slopes of the Seyfert 1s and 2s are similar, with average values of <α 20 6cm > = −0.66 and-0.71, respectively. Although several Seyfert 1s are significantly flatter than this in their 6-20 and/or 1.5-6 cm slopes, there is no systematic trend for either Seyfert type to display upward or downward spectral curvature. Excluding the radio-loud quasars, the integrated 6 cm radio luminosity is linearly proportional to the 60 µm luminosity over several orders of magnitude, with on average twice the radio power of normal spirals of the same far-infrared power. About half of the objects show extended 6 cm emission, contributing on average 33% of the total flux. Thus the luminosities of these extended components alone are comparable to normal spirals of similar infrared luminosities. The 12 µm sample radio luminosity function is slightly higher than that of the CfA sample. The integrated space density of Seyfert 2s is ∼ 2 times that of Seyfert 1s over their common range in luminosity. In terms of the standard unified model, this ratio in space density corresponds to a typical half-angle of the torus of θ ∼ 48 • .
Monthly Notices of the Royal Astronomical Society, 2001
We present 8.4 GHz VLA A-configuration observations of 87 sources from the mid-infrared-selected AGN sample of . These 0.25 arcsec resolution observations allow elongated radio structures tens of parsecs in size to be resolved and enable radio components smaller than 3.5 arcsec to be isolated from diffuse galactic disc emission. When combined with previous data, matched radio observations covering ninety percent of the sample have been collected and these represent the largest sub-arcsecond-resolution radio imaging survey of a homogeneously-selected sample of Seyfert galaxies to date.
Low-frequency radio observations of Seyfert galaxies: A test of the unification scheme
Astronomy & Astrophysics, 2013
Aims. We present low-frequency radio imaging and spectral properties of a well-defined sample of Seyfert galaxies using GMRT 240/610 MHz dual frequency observations. Radio spectra of Seyfert galaxies over 240 MHz to 5.0 GHz are investigated using 240 MHz, 610 MHz flux densities derived from GMRT, and 1.4 GHz and 5.0 GHz flux densities mainly from published VLA data. We test the predictions of Seyfert unification scheme by comparing the radio properties of Seyfert type 1s and type 2s. Methods. We chose a sample such that the two Seyferts subtypes have matched distributions in parameters that are independent of the orientation of AGN, obscuring torus, and the host galaxy. Our sample selection criteria allowed us to assume that the two Seyfert subtypes are intrinsically similar within the framework of the unification scheme. Results. The new observations at 240/610 MHz, together with archival observations at 1.4 GHz, 5.0 GHz show that types 1s and 2s have statistically similar radio luminosity distributions at 240 MHz, 610 MHz, 1.4 GHz, and 5.0 GHz. The spectral indices at selected frequency intervals (α 610 MHz 240 MHz , α 1.4 GHz 610 MHz , and α 5.0 GHz 1.4 GHz), as well as index measured over 240 MHz to 5.0 GHz (α int) for the two Seyfert subtypes, have similar distributions with median spectral index (α) ∼ −0.7 (S ν ∝ ν α), consistent with the synchrotron emission from optically thin plasma. In our snapshot 240/610 MHz GMRT observations, most of the Seyfert galaxies primarily show an unresolved central radio component, except for a few sources in which faint kpc-scale extended emission is apparent at 610 MHz. Our results on the statistical comparison of the multifrequency radio properties of our sample Seyfert galaxies agree with the predictions of the Seyfert unification scheme.