VLBA Continuum Observations of NGC 4258: Constraints onan Advection-dominated Accretion Flow

Herrnstein, J. R.; Greenhill, L. J.; Moran, J. M.; Diamond, P. J.; Inoue, Makoto; Nakai, Naomasa; Miyoshi, Makoto

doi:10.1086/311284

Cited by 77 publications

(92 citation statements)

References 25 publications

(23 reference statements)

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“…We see that it fits the results of Turner & Ho (1994) and Herrnstein et al (1998) very well 8 . Moreover, in our result, the 22 GHz emission mainly comes from the location ∼0.4 mas from the nucleus, satisfying the observed (time variable) 0.35−0.46 mas offset (Herrnstein et al 1998). We explain the variation of the offset with time as due to the variation of the shock location z 0 .…”

Section: Infrared To X-ray Spectral Fitting Resultssupporting

confidence: 88%

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NGC 4258: A jet-dominated low-luminosity AGN?

Yuan

Markoff

Falcke

et al. 2002

A&A

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Abstract. Low-luminosity AGNs (LLAGNs) are a very important class of sources since they occupy a significant fraction of local galaxies. Their spectra differ significantly from the canonical luminous AGNs, most notably by the absence of the "big blue bump". In the present paper, taking a typical LLAGN-NGC 4258-as an example, we investigate the origin of their spectral emission. The observational data of NGC 4258 is extremely abundant, including water maser emission, putting very strict constraints to its theoretical models. The infrared (IR) spectrum is well described by a steep power-law form f ν ∝ ν −1.4 , and may extend to the optical/UV band. Up until now there is no model which can explain such a steep spectrum, and we here propose a coupled jet plus accretion disk model for NGC 4258. The accretion disk is composed of an inner ADAF (or radiatively inefficient accretion flow) and an outer standard thin disk. A shock occurs when the accretion flow is ejected out of the ADAF to form the jet near the black hole, accelerating the electrons into a power-law energy distribution. The synchrotron and self-Comptonized emission from these electrons greatly dominates over the underlying accretion disk and can well explain the spectrum ranging from IR to X-ray bands. The further propagation of the shocked gas in the jet can explain the flat radio spectrum of NGC 4258. Several predictions of our model are presented for testing against future observations, and we briefly discuss the application of the model to other LLAGNs.

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Section: Infrared To X-ray Spectral Fitting Resultssupporting

confidence: 88%

“…c : The two values correspond to two scattering models (1) Turner & Ho (1994); (2) Herrnstein et al (1998); (3) Chary et al (2000); (4) Rieke & Lebofsky (1978); (5) W95.…”

Section: Infraredmentioning

confidence: 99%

NGC 4258: A jet-dominated low-luminosity AGN?

Yuan

Markoff

Falcke

et al. 2002

A&A

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“…Two more northern galaxies, NGC 4258 and NGC 1068, have been well studied in the past (e.g., Herrnstein et al 1998;Gallimore et al 2001) and were therefore also not included in our sample.…”

Section: Samplementioning

confidence: 99%

Radio continuum of galaxies with H₂O megamaser disks: 33 GHz VLA data

Kamali

Henkel

Brunthaler

et al. 2017

A&A

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Context. Galaxies with H 2 O megamaser disks are active galaxies in whose edge-on accretion disks 22 GHz H 2 O maser emission has been detected. Because their geometry is known, they provide a unique view into the properties of active galactic nuclei. Aims. The goal of this work is to investigate the nuclear environment of galaxies with H 2 O maser disks and to relate the maser and host galaxy properties to those of the radio continuum emission of the galaxy. Methods. The 33 GHz (9 mm) radio continuum properties of 24 galaxies with reported 22 GHz H 2 O maser emission from their disks are studied in the context of the multiwavelength view of these sources. The 29-37 GHz Ka-band observations are made with the Jansky Very Large Array in B, CnB, or BnA configurations, achieving a resolution of ∼ 0.2 -0.5 arcseconds. Hard X-ray data from the Swift/BAT survey and 22 µm infrared data from WISE, 22 GHz H 2 O maser data and 1.4 GHz data from NVSS and FIRST surveys are also included in the analysis. Results. Eighty-seven percent (21 out of 24) galaxies in our sample show 33 GHz radio continuum emission at levels of 4.5 -240 σ. Five sources show extended emission (deconvolved source size larger than 2.5 times the major axis of the beam), including one source with two main components and one with three main components. The remaining detected 16 sources (and also some of the above-mentioned targets) exhibit compact cores within the sensitivity limits. Little evidence is found for extended jets (>300 pc) in most sources. Either they do not exist, or our chosen frequency of 33 GHz is too high for a detection of these supposedly steep spectrum features. In only one source among those with known maser disk orientation, NGC 4388, did we find an extended jet-like feature that appears to be oriented perpendicular to the H 2 O megamaser disk. NGC 2273 is another candidate whose radio continuum source might be elongated perpendicular to the maser disk. Smaller 100-300 pc sized jets might also be present, as is suggested by the beam-deconvolved morphology of our sources. Whenever possible, central positions with accuracies of 20-280 mas are provided. A correlation analysis shows that the 33 GHz luminosity weakly correlates with the infrared luminosity. The 33 GHz luminosity is anticorrelated with the circular velocity of the galaxy. The black hole masses show stronger correlations with H 2 O maser luminosity than with 1.4 GHz, 33 GHz, or hard X-ray luminosities. Furthermore, the inner radii of the disks show stronger correlations with 1.4 GHz, 33 GHz, and hard X-ray luminosities than their outer radii, suggesting that the outer radii may be affected by disk warping, star formation, or peculiar density distributions.

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“…In order for this jet model to be valid, the 0.54 mas upper limit to the size requires i 40 . The second model uses the parameters FB99 derived for NGC 4258, where a jet is seen by the VLBA (e.g., Herrnstein et al 1998), with e ¼ 630 (dotted lines). For most inclination angles, È jet is much larger in the e ¼ 630 model compared to the e ¼ 300 model, and the 0.54 mas upper limit in size further (25) is shown as a function of frequency for three LLAGNs in this sample.…”

Section: Model Comparisonmentioning

confidence: 99%

Low‐Luminosity Active Galactic Nuclei at the Highest Resolution: Jets or Accretion Flows?

Anderson

Ulvestad

2004

ApJ

106

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Six low-luminosity active galactic nuclei (AGNs) have been imaged at multiple frequencies from 1.7 to 43 GHz (2.3-15 GHz for three of the galaxies) using the Very Long Baseline Array. In spite of dynamic ranges of about 100 in several frequency bands, all six galaxies remain unresolved, with size limits at 8.4 GHz of 10 3 -10 4 times the Schwarzschild radii of the black holes inferred at their galactic centers. The galaxy spectra are roughly flat from 1.7 to 43 GHz, rather than steepening to classical optically thin synchrotron spectra at high frequencies. Although the spectral slopes somewhat resemble predictions for advection-dominated accretion flows, the luminosities are too high for the black hole masses of the galaxies, and the slight spectral steepening at high frequencies cannot be explained by standard simple models of such accretion flows. In contrast, compact jets can accommodate the average spectral index, the relatively high radio luminosity, and the unresolved appearance, but only if the jets in all six galaxies are fairly close to our line of sight. This constraint is in agreement with inclination angle predictions for five of the six AGNs based on the dusty torus unification model.

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VLBA Continuum Observations of NGC 4258: Constraints onan Advection-dominated Accretion Flow

Cited by 77 publications

References 25 publications

NGC 4258: A jet-dominated low-luminosity AGN?

NGC 4258: A jet-dominated low-luminosity AGN?

Radio continuum of galaxies with H₂O megamaser disks: 33 GHz VLA data

Low‐Luminosity Active Galactic Nuclei at the Highest Resolution: Jets or Accretion Flows?

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VLBA Continuum Observations of NGC 4258: Constraints onan Advection-dominated Accretion Flow

Cited by 77 publications

References 25 publications

NGC 4258: A jet-dominated low-luminosity AGN?

NGC 4258: A jet-dominated low-luminosity AGN?

Radio continuum of galaxies with H2O megamaser disks: 33 GHz VLA data

Low‐Luminosity Active Galactic Nuclei at the Highest Resolution: Jets or Accretion Flows?

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Radio continuum of galaxies with H₂O megamaser disks: 33 GHz VLA data