Off-center nuclei in galaxies

Miller, Richard H.; Smith, B. F.

doi:10.1086/171523

Cited by 54 publications

(48 citation statements)

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“…The frequency of the oscillations is close to the fundamental frequency calculated in the paper and evident in the third panel of Figure 1. We attribute these oscillations to the presence of very weakly damped coherent modes in the stellar system, of the kind reported by Miller (1992) and Miller & Smith (1992), and calculated by Mathur (1990) and Weinberg (1994).…”

Section: Tests Of the Model Using Numerical Simulationssupporting

confidence: 62%

Dynamics of a Massive Black Hole at the Center of a Dense Stellar System

Chatterjee

Hernquist

Loeb

2002

ApJ

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We develop a simple physical model to describe the dynamics of a massive pointlike object, such as a black hole, near the center of a dense stellar system. It is shown that the total force on this body can be separated into two independent parts, one of which is the slowly varying influence of the aggregate stellar system, and the other being the rapidly fluctuating stochastic force due to discrete encounters with individual stars. For the particular example of a stellar system distributed according to a Plummer model, it is shown that the motion of the black hole is then similar to that of a Brownian particle in a harmonic potential, and we analyze its dynamics using an approach akin to Langevin's solution of the Brownian motion problem. The equations are solved to obtain the average values, time autocorrelation functions, and probability distributions of the black hole's position and velocity. By comparing these results with N-body simulations, we demonstrate that this model provides a very good statistical description of the actual black hole dynamics. As an application of our model, we use our results to derive a lower limit on the mass of the black hole Sgr A* in the Galactic center.

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Section: Tests Of the Model Using Numerical Simulationssupporting

confidence: 62%

Dynamics of a Massive Black Hole at the Center of a Dense Stellar System

Chatterjee

Hernquist

Loeb

2002

ApJ

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“…Nonetheless, we estimate nuclear masses M nuke $ 10 6 10 7 M , comparable to the masses of low-luminosity star cluster nuclei derived for other late-type spirals [e.g., As a final note, we draw attention to the fact that some of the nuclei in our present sample appear to be offset from the dynamical centers of the galaxies as defined by either the optical continuum and/or the centroid of the global H i profile (see also the Appendix). The frequent displacement of compact nuclei from the dynamical centers of galaxies has been discussed previously by Miller & Smith (1992; see also Levine & Sparke 1998) and may offer an important clue to the formation mechanism of the nuclei. Higher resolution spectroscopy of more extensive samples of these types of nuclei is clearly desirable in order to better understand their natures, to improve these mass estimates, and to help us…”

Section: Kinematic Signatures Of Semi-stellar Nuclei In Extreme Late-mentioning

confidence: 66%

High‐Resolution Optical Rotation Curves of Low‐Luminosity Spiral Galaxies

Matthews¹,

Gallagher²

2002

ASTROPHYS J SUPPL S

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We present optical long-slit spectroscopic observations of 21 low-luminosity, extreme late-type spiral galaxies. Our sample is comprised of Sc-Sm Local Supercluster spirals with moderate-to-low optical surface brightnesses and with luminosities at the low end for spiral disk galaxies (M V ! À18:8). For each galaxy we have measured high spatial resolution position-velocity (P-V) curves using the H emission line, and for 15 of the galaxies we also derive major-axis rotation curves. In $50% of our sample, the P-V curves show significant asymmetries in shape, extent, and/or amplitude on the approaching and receding sides of the disk. A number of the P-V curves are still rising to the last measured point or reach a clear turnover on only one side. In most instances we find good agreement between the kinematic centers of extreme late-type spirals as defined by the global H i emission profile and by their optical continuum, although in a few cases we see evidence of possible real offsets. In spite of their shallow central gravitational potentials, at least six of the galaxies in our sample possess semi-stellar nuclei that appear to be compact nuclear star clusters; in five of these cases we see kinematic signatures in the P-V curves at the location of the nucleus. Finally, we find that like giant spirals, our sample galaxies have higher specific angular momenta than predicted by current cold dark matter models.

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“…Previous works have suggested coupling between m = 1 and m = 2 modes (Tagger & Athanassoula 1991), as well as among m = 1, 2 and 3 modes for both gaseous (Laughlin & Korchagin 1996) and stellar (Miller & Smith 1992;Quillen et al 2011) discs. We now turn our attention to the m = 3 spectra, shown in the fourth row of Fig.…”

Section: Relation Among M = 1 2 Andmentioning

confidence: 90%

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

Minchev

Famaey

Quillen

et al. 2012

A&A

191

208

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We investigate the evolution of galactic discs in N-body tree-SPH simulations. We find that discs, initially truncated at three scalelengths, can triple their radial extent, solely driven by secular evolution. At the same time, the initial radial metallicity gradients are flattened and even reversed in the outer discs. Both Type I (single exponential) and Type II (down-turning) observed disc surfacebrightness profiles can be explained by our findings. We show that profiles with breaks beyond the bar's outer Lindblad resonance, at present only explained as the effect of star-formation threshold, can occur even if no star formation is considered. We explain these results with the strong angular momentum outward transfer, resulting from torques and radial migration associated with multiple patterns, such as central bars and spiral waves of different multiplicity. We find that even for stars ending up on cold orbits, the changes in angular momentum exhibit complex structure as a function of radius, unlike the expected effect of transient spirals alone. We show that the bars in all of our simulations are the most effective drivers of radial migration through their corotation resonance, throughout the 3 Gyr of evolution studied. Focussing on one of our models, we find evidence for non-linear coupling among m = 1, 2, 3 and 4 density waves, where m is the pattern multiplicity. In this way the waves involved conspire to carry the energy and angular momentum extracted by the first mode from the inner parts of the disc much farther out than a single mode could. We suggest that the naturally occurring larger resonance widths at galactic radii beyond four scale-lengths may have profound consequences on the formation and location of breaks in disc density profiles, provided spirals are present at such large distances. We also consider the effect of gas inflow and show that when in-plane smooth gas accretion of ∼5 M /yr is included, the outer discs become more unstable, leading to a strong increase in the stellar velocity dispersion. This, in turn, causes the formation of a Type III (up-turning) profile in the old stellar population. We propose that observations of Type III surface brightness profiles, combined with an up-turn in the stellar velocity dispersions beyond the disc break, could be a signature of ongoing gas-accretion. The results of this study suggest that disc outskirts comprised of stars migrated from the inner disc would have relatively large radial velocity dispersions (>30 km s −1 at 6 scale-lengths for Milky Way-size systems), and significant thickness when seen edge-on.

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Off-center nuclei in galaxies

Cited by 54 publications

References 0 publications

Dynamics of a Massive Black Hole at the Center of a Dense Stellar System

Dynamics of a Massive Black Hole at the Center of a Dense Stellar System

High‐Resolution Optical Rotation Curves of Low‐Luminosity Spiral Galaxies

Evolution of galactic discs: multiple patterns, radial migration, and disc outskirts

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