摘要:

A ‘‘standard’’ model of Active Galactic Nuclei (AGN), based upon a massive black hole surrounded by a thin accretion disk, is defined. It is argued that, although there is good evidence for the presence of black holes and orbiting gas, most of the details of this model are either inadequate or controversial. Magnetic field may be responsible for the confinement of continuum and line‐emitting gas, for the dynamical evolution of accretion disks and for the formation of jets. It is further argued that gaseous fuel is supplied in molecular form and that this is responsible for thermal re‐radiation, equatorial obscuration and, perhaps, the broadline gas clouds. Stars may also supply gas close to the black hole, especially in low power AGN and they may be observable in discrete orbits as probes of the gravitational field. Recent observations suggest that magnetic field, stars, dusty molecular gas and orientation effects must be essential components of a complete description of AGN. The discovery of quasars with redshifts approachingz∼5 is an important clue to the mechanism of galaxy formation.

ISSN:0094-243X    

DOI:10.1063/1.42258

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

High‐resolution surface photometry and stellar‐kinematic measurements reveal central dark objects of massM•&bartil;1017to 109M⊙in M31 and NGC 3115 (the best cases), M32, NGC 4594, and NGC 3377. NGC 3115 is discussed in detail to illustrate the search technique. Uncertainties in the volume brightness distribution, the rotation and velocity dispersion curves, velocity dispersion anisotropy, internal absorption, and the possible presence of an end‐on bar allow no escape from the conclusion that the mass‐to‐light ratioM/Lrises atr<2‘by more than a factor of 10. Then the remarkable consistency ofM/Lin old stellar populations suggests that we are detecting a black hole (BH). New observations imply thatM•∼108M⊙in the low‐luminosity, rotating elliptical NGC 3377. However, it is difficult to detect BHs in giant ellipticals; they do not rotate and so are maximally sensitive to velocity anisotropy, and their large cores give low luminosity weight to any central region dominated by a BH. The BH survey is being extended to 14, E‐Sb galaxies closer than 13 Mpc and brighter thanMB=−18 (H0=50 km s−1 Mpc−1). Evidence for BHs is seen in ≳30% of these galaxies. Failures often occur where detection is unlikely because of nuclear starbursts (Fornax A) or because the galaxy is too face‐on. In one galaxy we can rule out a massive BH: M33 hasM•≲5×104M⊙. Despite detection difficulties, we already find approximately as much mass in nuclear dark objects as energy arguments predict is present in dead quasars.

ISSN:0094-243X    

DOI:10.1063/1.42179

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This contribution to the discussion is relevant to the two talks by J. Kormendyand T. Lauer about the possible presence of supermassive black holes (SBH) in the central regions of early‐type galaxies. Several aspects of our work on this topic are presented in a poster at this conference (Nieto et al.). Here, we want to concentration on the SBH candidate, M32, and its non‐trivial central structure, uncovered by high‐resolution (FWHM‐0.4–0.5 arcsec) imaging at red‐near IR wavelengths (8000 A˚−1&mgr;m) at CFHT. The data show, within the 10 central arcsec, i)a slight isophotal twist, ii) strong color gradients (Figure), iii) a clumpy structure and iv) evidence for the presence of a disk. The three last points are dueto a population of AGB stars located within the central 20 arcsec and preferentially confined within a disk. A preliminary report is in Nieto et al. (1991); a more detailed discussion will be published elsewhere. These features have to be linked to the high‐resolution stellar velocity map (Bacon et al., 1991 and Nieto et al., this conference). All these data infer that even in the center of M32 once believed to be a simple, structureless galaxy, complex phenomena are taking place, that require sophisticated modeling.

ISSN:0094-243X    

DOI:10.1063/1.42213

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We present a critical discussion on the recent results claiming the presence of Supermassive Black Holes (SBH) in the centers of some galaxies. It is based on two‐dimensional high‐resolution imaging and spectroscopic data obtained at CFHT with the High‐Resolution Camera (HRCam) and the TIGER integral field spectrograph.

ISSN:0094-243X    

DOI:10.1063/1.42253

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A review is given of methods to constrain the mass of a putative black hole at the center of the Milky Way galaxy. These approaches are based on: (i) tidal disruption of stars by a massive black hole; (ii) displacement between Sgr A* and either of the IRS 16 components; (iii) electron‐positron pair production by a blackhole, and (iv) mass outflow centered on IRS 16/Sgr A* complex.

ISSN:0094-243X    

DOI:10.1063/1.42260

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Although there are some flaws in each of the methods to constrain the black holemass, which are described in the above paper, all of them unambiguously indicate that the mass of a putative black hole at the Galactic center is much smaller than a widely quoted value, ∼106M⊙. Possibly, the mass of the black hole, if any, does not exceed ∼102M⊙or so. Further work is needed in order to distinguish between such a modest‐mass black hole and its potential rival such as a very massive star of about the same mass. Anyway,the Galactic nucleus seems to be a tracer of a past star burst rather than a remnant of a Seyfert galaxy activity.

ISSN:0094-243X    

DOI:10.1063/1.42269

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The analysis of stars in galactic nuclei that are captured and tidally disrupted by a black hole of mass <106M⊙requires the inclusion of general relativistic effects. We present the first numerical study of tidal breakup of a 1M⊙main sequence star by a 107M⊙black hole. We use a smoothed particle code to solve the hydrodynamic equations for a relativistic fluid in a static curved spacetime geometry to analyze, among other things, the fraction of the debris captured by the hole and the velocity of fragments escaping the hole.

ISSN:0094-243X    

DOI:10.1063/1.42277

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Relativistic magnetohydrodynamics plays an important role in accretion processes. Unfortunately, a complete and rigorous study of this subject is indeed very difficult. It involves, for example, hydromagnetic flows in evolving spacetimes as well as the interaction of charged fluids with electromagnetic fields. Nonetheless, by making a set of restrictive assumptions, analytical and numerical relativistic hydrodynamics solutions for the vacuum Schwarzschild and Kerr spacetimes were found. We propose an extension of this work by considering as a fixed background the magnetized Schwarzchild metric. Two cases (in the equatorial plane) are considered. The geodesic infall (pressure neglected), and the accretion (including pressure) of apolytropic gas.

ISSN:0094-243X    

DOI:10.1063/1.42232

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The Bondi accretion approach can give useful constraints to the mass of a blackhole in luminous starburst galaxies.

ISSN:0094-243X    

DOI:10.1063/1.42241

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

One model for double‐peaked emission lines in AGNs is the double‐lined spectroscopic binary consisting of two black holes, each with its own broad‐lineregion. We are continuing to monitor the H&agr; line profiles of the two AGNs which will provide the most sensitive test of this theory. Arp 102B and 3C 332. The absence of orbital motion can be translated into alowerlimit on the mass of the hypothesized binary. As of 1991, we have obtained lower limits of 4×109M⊙and 2×1010M⊙for Arp 102B and 3C 332, respectively, rendering this theory highly unlikely. We cannot rule out theexistenceof a supermassitve binary, but only the model in which the emission‐line peaks are attributed to the two different nuclei. Alternatively, long‐term monitoring might reveal small‐amplitude radial velocity variations to anunseencompanion.

ISSN:0094-243X    

DOI:10.1063/1.42243

出版商:AIP    

年代:1992

数据来源: AIP