High resolution imaging of galaxy cores

Crane, P. C.; Stiavelli, M.; King, Ivan R.; Deharveng, J. M.; Albrecht, R.; Barbieri, C.; Blades, J. C.; Boksenberg, A.; Disney, M. J.; Jakobsen, P.; Kamperman, T. M.; Machetto, F.; Mackay, C. D.; Paresce, Francesco; Weigelt, G.; Baxter, D.; Greenfield, P.; Jędrzejewski, R.; Nota, A.; Sparks, W. B.

doi:10.1086/116733

Cited by 152 publications

(123 citation statements)

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“…The Plummer model is easy to set up and interpret, but is a poor model for real galaxies: they are much more concentrated, many with densities that continue rising to the innermost observable radius (Crane et al, 1993;Ferrarese et al, 1994;Forbes et al, 1995;Lauer et al, 1995). We therefore used two models with density cusps from the family considered by Dehnen (1993) and Tremaine et al (1994):…”

Section: Initial Conditions and Units Of Measurementmentioning

confidence: 99%

The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

1996

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We use a hybrid N-body program to study the evolution of massive black hole binaries in the centers of galaxies, mainly to understand the factors affecting the binary eccentricity, the response of the galaxy to the binary merger, and the effect of loss-cone depletion on the merger time. The scattering experiments from paper I showed that the merger time is not sensitive to the eccentricity growth unless a binary forms with at least a moderate eccentricity. We find here that the eccentricity can become large under some conditions if a binary forms in a galaxy with a flat core or with a radial bias in its velocity distribution, especially if the dynamical friction is enhanced by resonances as suggested by Rauch and Tremaine (1996). But the necessary conditions all seem unlikely, and our prediction from paper I remains unchanged: in most cases the eccentricity will start and remain small. As a binary hardens it ejects stars from the center of a galaxy, which may explain why large elliptical galaxies have weaker density cusps than smaller galaxies. If so, the central velocity distributions in those galaxies should have strong tangential anisotropies. The wandering of a binary from the center of a galaxy mitigates the problems associated with loss-cone depletion and helps the binary merge.

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Section: Initial Conditions and Units Of Measurementmentioning

confidence: 99%

The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

1996

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“…NGC 6251 (1637+826, J1632+8232, z ¼ 0:024) is an elliptical galaxy containing an apparently edge-on dust lane (Nieto et al 1983;Crane & Vernet 1997) and a central stellar cusp and blue continuum light source (Young et al 1979;Crane 1993). Spectroscopic observations with Hubble Space Telescope (HST) indicate the presence of a central black hole with a mass of ð6 AE 2Þ Â 10 8 M (Ferrarese & Ford 1999).…”

Section: Introductionmentioning

confidence: 99%

What Happened to the NGC 6251 Counterjet?

Jones

Wehrle

2002

ApJ

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We have used the Very Long Baseline Array to produce a high dynamic range image of the nucleus of NGC 6251 at 1.6 GHz and snapshot images at 5.0, 8.4, and 15.3 GHz to search for emission from a parsecscale counterjet. Previous VLBI images at 1.6 GHz have set a lower limit for the jet/counterjet brightness ratio near the core at about 80:1, which is larger than expected, given the evidence that the radio axis is fairly close to the plane of the sky. A possible explanation is that the inner few parsecs of the counterjet are hidden by free-free absorption by ionized gas associated with an accretion disk or torus. This would be consistent with the nearly edge-on appearance of the arcsecond-scale dust disk seen in the center of NGC 6251 by Hubble Space Telescope (HST). We detect counterjet emission close to the core at 1.6 GHz, but not at the higher frequencies. Given that the optical depth of free-free absorption falls off more rapidly with increasing frequency than the optically thin synchrotron emission from a typical radio jet, this result implies that the absence of a detectable parsec-scale counterjet at high frequencies is not due to free-free absorption unless the density of ionized gas is extremely high and we have misidentified the core at 1.6 GHz. The most likely alternative is a large jet/counterjet brightness ratio caused by relativistic beaming, which in turn requires the inner radio axis to be closer to our line of sight than the orientation of the HST dust disk would suggest.

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“…The inclusion of central singularities, containing a large fraction of galaxy mass, has a substantial inÑuence on the dynamics and evolution of the surrounding stars, mainly a †ecting the box orbits present in triaxial systems (Gerhard & Binney 1985). These models are supported by Hubble Space T elescope observations (Crane et al 1993 ;Ja †e et al 1994 ;Ferrarese et al 1994 ;Lauer et al 1995) that show that elliptical galaxies and bulges of spiral galaxies exhibit a variety of cusp strengths and possible central black holes Miyoshi et al 1995). For the spiral barred galaxies, the chaotic trajectories may be important owing to the rotation of the Ðgure and the bar perturbation (Contopoulos & Papayannopoulos 1980 ;Contopoulos 1983 ;Athanassoula et al 1983 ;Pfenniger 1984) and to the e †ects of the gas that joins the bar and the spiral arms (Contopoulos & Grosbol 1989).…”

Section: Introductionmentioning

confidence: 74%

On the Effect of Chaotic Orbits on Dynamical Friction

Cora

Vergne

Muzzio

2001

ApJ

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Chaotic orbits su †er signiÐcant changes as a result of small perturbations. One can thus wonder whether the dynamical friction su †ered by a satellite on a regular orbit, and interacting with the stars of a galaxy, will be di †erent if the bulk of the stars of the galaxy are in regular or chaotic orbits. In order to check that idea, we investigated the orbital decay (caused by dynamical friction) of a rigid satellite moving within a larger stellar system (a galaxy) whose potential is nonintegrable. We performed numerical experiments using two kinds of triaxial galaxy models : (1) the triaxial generalization of DehnenÏs spherical mass model (Dehnen ; Merritt & Fridman) ; (2) a modiÐed Satoh model (Satoh ; Carpintero, Muzzio, & Wachlin). The percentages of chaotic orbits present in these models were increased by perturbing them. In the Ðrst case, a central compact object (black hole) was introduced ; in the second case, the perturbation was produced by allowing the galaxy to move on a circular orbit in a logarithmic potential. The equations of motion were integrated with a nonÈself-consistent code. Our results show that the presence of chaotic orbits does not a †ect signiÐcantly the orbital decay of the satellite.

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High resolution imaging of galaxy cores

Cited by 152 publications

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The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

What Happened to the NGC 6251 Counterjet?

On the Effect of Chaotic Orbits on Dynamical Friction

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