Ahumada, J. C., Chevalier, R. M., and Sammartino, R.: Actinomycosis of the Ovary

Greenhill, J.P.

doi:10.1016/s0002-9378(15)31430-7

Cited by 4 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The thin disk might then flare out with increasing distance from the nucleus and gradually transform into a thick disk. Recent high resolution observations of NGC 1068 (Greenhill et al 1996) suggest that some maser emission is associated with the inner edge of the torus.…”

Section: Agn Classmentioning

confidence: 99%

“…The combination of a nuclear hard X-ray source and a thin, warped molecular disk, as seen in NGC 4258, is one possibility. Another is a nuclear hard X-ray source surrounded by a thick torus, with the maser emission originating from the heated inner edge of torus, as may be the case in NGC 1068 (Greenhill et al 1996). We might then expect to find other observable manifestations of these special conditions in the galaxies detected as H 2 O megamasers.…”

Section: Introductionmentioning

confidence: 96%

See 1 more Smart Citation

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

Braatz¹,

Wilson²,

Henkel³

1997

ASTROPHYS J SUPPL S

151

147

View full text Add to dashboard Cite

A survey for megamaser emission from 354 active galaxies has resulted in the detection of 10 H 2 O new sources, making 16 known altogether. The galaxies surveyed include a distance-limited sample (covering Seyferts and LINERs with recession velocities less than 7000 km s~1) and a magnitude-limited sample (covering Seyferts and LINERs withIn order to determine whether the m B ¹ 14.5). H 2 O-detected galaxies are "" typical ÏÏ active galactic nuclei (AGNs) or have special properties that facilitate the production of powerful masers, we have accumulated a database of physical, morphological, and spectroscopic properties of the observed galaxies. The most signiÐcant Ðnding is that megamasers are H 2 O detected only in Seyfert 2 and LINER galaxies, not Seyfert 1Ïs. This lack of detection in Seyfert 1Ïs indicates either that they do not have molecular gas in their nuclei with physical conditions appropriate to produce 1.3 cm masers or that the masers are beamed away from Earth, presumably in the plane H 2 O of the putative molecular torus that hides the Seyfert 1 nucleus in Seyfert 2Ïs. LINERs are detected at a similar rate to Seyfert 2Ïs, which constitutes a strong argument that at least some nuclear LINERs are AGNs rather than starbursts, since starbursts have not been detected as megamasers. We prefer-H 2 O entially detect emission from the nearer galaxies and from those that are apparently brighter at H 2 O mid-and far-infrared and centimeter radio wavelengths. There is also a possible trend for the H 2 Ogalaxies to be more intrinsically luminous in nuclear 6 cm radio emission than the undetected detected ones, though these data are incomplete. We Ðnd evidence that Seyfert 2Ïs with very high (N H [ 1024 cm~2) X-rayÈabsorbing columns of gas are more often detected as maser emitters than Seyfert 2Ïs H 2 O with lower columns. It may be that the probability of detecting maser emission in Seyfert galaxies H 2 O increases with increasing column of cool gas to the nucleus, from Seyfert 1Ïs through narrow-line X-ray galaxies to Seyfert 2Ïs.

show abstract

Section: Agn Classmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

Braatz¹,

Wilson²,

Henkel³

1997

ASTROPHYS J SUPPL S

151

147

View full text Add to dashboard Cite

show abstract

“…The second most compelling case of a rotating structure, delineated by water maser emission, is found in the nucleus of NGC 1068 (Gallimore et al 1996;Greenhill et al 1996). The maser emission extends about ±300 km s −1 from the galactic systemic velocity, tracing sub-Keplerian differential rotation around a central mass of ∼ 10 7 M ⊙ that lies within a radius of about 0.7 pc.…”

Section: Other Circumnuclear Disksmentioning

confidence: 99%

“…The Doppler-shift asymmetry is as striking as in NGC 4258, except that in NGC 1068 the red-shifted, high-velocity maser emission is stronger even than the low-velocity emission complex at the systemic velocity of the galaxy. The VLBI observations by Greenhill et al (1996) currently provide the most precise image of the disk, but only of its receding side. It is delineated by five dominant clumps of maser emission, distributed in a nearly planar configuration on the sky: one at the systemic velocity of the galaxy, and the others at relatively red-shifted velocities.…”

Section: Other Circumnuclear Disksmentioning

confidence: 99%

“…Evidence for masing circumnuclear disks has been found also in other galaxies. The most compelling case is the rotating structure in NGC 1068 (Gallimore et al 1996;Greenhill et al 1996). It is delineated by high-velocity H 2 O maser emission (≃ 300 km s −1 at ≃ 0.7 pc) where, again, the red-shifted features are much stronger and more numerous than the blue-shifted ones, being even stronger than the features with the systemic velocity of the galaxy (hereafter, the "systemic" features).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Doppler Shift Asymmetry in High‐Velocity Maser Emission from Shocks in Circumnuclear Disks

Maoz

McKee

1998

ApJ

View full text Add to dashboard Cite

The rapidly rotating, masing circumnuclear disk in the central subparsec region of the galaxy NGC 4258 is remarkably circular and Keplerian, yet a striking asymmetry appears in the maser spectrum : the redshifted, high-velocity sources are much more numerous and signiÐcantly more intense than the blueshifted ones. A similar strong asymmetry also appears in the recently discovered, masing, circumnuclear disks in NGC 1068 and NGC 4945, thus suggesting it may be a general phenomenon.We show that the observed Doppler shift asymmetry can naturally arise due to spiral shocks in circumnuclear disks. We argue that population inversion can largely be quenched in these systems because of IR photon trapping, and that the high-velocity maser emission originates within thin slabs of postshock gas, where the physical conditions are conducive to maser action. The high-velocity masers with the longest gain paths appear where the line of sight is tangent to shock fronts. Since the spirals have a trailing geometry due to the action of di †erential rotation, the locations of the masers make the blueshifted radiation travel through a column of noninverted gas that maintains close velocity coherence with the maser source, where absorption occurs. The resulting asymmetry in the high-velocity maser spectrum, where the redshifted emission appears systematically stronger, is independent of the existence of a warp in the disk or the azimuthal direction to the observer, and is insensitive to small distortions in the velocity Ðeld in the disk.The high velocities of these features reÑect the rotational velocities in the disk and have nothing to do with the shock speed. The low-velocity emission arises within a narrow annulus near the inner edge of the disk, where direct irradiation by a central source may provide the energy that ultimately powers these masers. In NGC 4258Ècurrently the most well-deÐned masing diskÈthe proposed scenario can also account for the intriguing clustering of the high-velocity maser spots in distinct clumps, the restricted radial distribution of the low-velocity sources, and the dip in the maser spectrum at the systemic velocity of the disk. In this case, we infer a molecular density of D109 cm~3, a disk mass of D104 and a mass accretion rate of order D7 ] 10~3 yr~1, which is consistent with an advection-M _ , M _ dominated accretion Ñow. These results di †er signiÐcantly from those of the Neufeld and Maloney model (^107.5 cm~3, D100and D7 ] 10~5a yr~1, respectively). M _ , M _ The predicted maser luminosities of the blueshifted and redshifted, high-velocity features in NGC 4258 are consistent with the observations, both in the case of C-type (MHD) shocks and dissociative J-type shocks, where the shock speed is about 20 km s~1. The high-velocity features arise nearly along a diameter through the disk that makes an angle of about 2¡ with the midline. It does not introduce any noticeable deviation from a Keplerian rotation curve (the velocity gradient across the shock is always perpendicular to the line of si...

show abstract

AGN Obscuring Tori Supported by Infrared Radiation Pressure

Krolik

2007

ApJ

110

128

View full text Add to dashboard Cite

Explicit 2-d axisymmetric solutions are found to the hydrostatic equilibrium, energy balance, and photon diffusion equations within obscuring tori around active galactic nuclei. These solutions demonstrate that infrared radiation pressure can support geometrically thick structures in AGN environments subject to certain constraints: the bolometric luminosity must be roughly 0.03--1 times the Eddington luminosity; and the Compton optical depth of matter in the equatorial plane should be order unity, with a tolerance of about an order of magnitude up or down. Both of these constraints are at least roughly consistent with observations. In addition, angular momentum must be redistributed so that the fractional rotational support against gravity rises from the inner edge of the torus to the outer in a manner specific to the detailed shape of the gravitational potential. This model also predicts that the column densities observed in obscured AGN should range from about 10^{22} to about 10^{24} cm^{-2}.Comment: ApJ, in pres

show abstract

Ahumada, J. C., Chevalier, R. M., and Sammartino, R.: Actinomycosis of the Ovary

Cited by 4 publications

References 0 publications

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

Doppler Shift Asymmetry in High‐Velocity Maser Emission from Shocks in Circumnuclear Disks

AGN Obscuring Tori Supported by Infrared Radiation Pressure

Contact Info

Product

Resources

About

Ahumada, J. C., Chevalier, R. M., and Sammartino, R.: Actinomycosis of the Ovary

Cited by 4 publications

References 0 publications

A Survey for H 2 O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

A Survey for H 2 O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

Doppler Shift Asymmetry in High‐Velocity Maser Emission from Shocks in Circumnuclear Disks

AGN Obscuring Tori Supported by Infrared Radiation Pressure

Contact Info

Product

Resources

About

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies

A Survey for H ₂ O Megamasers in Active Galactic Nuclei. II. A Comparison of Detected and Undetected Galaxies