Abstracts of the Talks and Posters

Black Holes in X-ray Binaries

P.A. Charles
University of Oxford, Oxford, UK

The number of strong black-hole candidates in X-ray binaries has increased dramatically during the 1990s, and almost all of these reside in the sub-class known as ``soft X-ray transients'' or ``X-ray novae''. I will describe how the transient nature of these sources allows for detailed study of the mass-losing secondaries from which accurate dynamical mass estimates are possible. I will then summarise our understanding of the X-ray and optical properties of the ~dozen best-studied systems.

The Dark Mass in the Center of the Milky Way

A. Eckart
Max-Planck-Institut für Extraterrestrische Physik, Garching bei München, Germany

The dark mass at the center of the Milky Way is currently one of the most compelling cases for a massive black hole. The initial evidences for such an object have now been confirmed after over 7 years of high spatial resolution, near-infrared imaging and spectroscopy.
The sky-projected radial and tangential velocities of all 104 proper motion stars are consistent with overall isotropic spherical stellar cluster. However, for the young, early type stars - probably as a remnant of the original angular momentum pattern in the interstellar cloud from which these stars were formed - there are indications now for some significant deviations from isotropy. Leonard-Merritt projected mass estimators and Jeans equation modeling including the velocity anisotropy confirm previous conclusions (from isotropic models) that a compact central mass (central density >= 10^12.6 Msun pc^-3) is present and dominates the potential between 0.01 and 1 pc. The best value of the point mass is 2.9(±0.4) · 10⁶ Msun for Rsun = 8.0 kpc.
Very recent `lambda' / `Delta lambda' >= 3000 K-band spectroscopy 2.29 µm CO bandhead absorption line carried out with ISAAC at the ESO VLT UT1 now prove that there is no CO bandhead absorption originating in the northern part (S1/S2 area) of the central stellar cluster at the position of Sgr A^*. This makes it very likely that these K ~ 14.5 stars are O9 - B0.5 stars with masses of 15 to 20 Msun. Balance of momentum and/or energy suggests that at least 10³ to 10⁵ solar masses must be associated with Sgr A^* itself and likely is enclosed within less than 15 Schwarzschild (8 light minutes) radii of a million solar mass black hole.

On the Maximum Mass of Neutron Stars

G. Srinivasan
Raman Research Institute, Bangalore, India

The concept of a limiting mass for neutron stars is important in the context of the formation of stellar mass black holes. In their pioneering study Oppenheimer and Volkoff found that neutron stars cannot have masses exceeding 0.7 solar mass. During the last three decades there have been many attempts to improve upon this estimate. This talk will aim to highlight the difficulties encountered, and also summarize the more recent results pertaining to the limiting mass of neutron stars.

Observed Neutron Star Masses

M.H. van Kerkwijk
Astronomical Institute, University of Utrecht, Utrecht, the Netherlands

I will review attempts made to determine the properties of neutron stars. The focus will be on the maximum mass that a neutron star can have, or, conversely, the minimum mass required for the formation of a black hole. There appears to be only one neutron star for which there is strong evidence that its mass is well above the canonical 1.4 solar masses, viz., Vela X-1, for which a mass close to 1.9 solar masses is found. Prospects for progress appear brightest for studies of systems in which the neutron star should have accreted substantial amounts of matter.

Weighing Black Holes using the Largest Optical Telescopes

E.T. Harlaftis and A.V. Filippenko
National Observatory of Athens, Athens, Greece

The advent of the large effective apertures of the Keck telescopes has resulted in the determination with unprecedented accuracy of the mass functions and mass ratios of 3 faint (R ~ 21 mag) X-ray transients (GS 2000+25, GRO J0422+32, H1705-25). We describe the technique and the results of the analysis.

Recent Results on the Orbital Structure around Supermassive Black Holes

K. Gebhardt
UCO/Lick Observatory, Santa Crux, USA

As the data quality increases due to better spatial resolution and dynamical models become more sophisticated, the need for a central massive black-hole has not gone away in any galaxy. Every galaxy that has been observed with HST spectrographs requires a central massive black hole. I will present recent results from HST/STIS observations of nuclei in early-type galaxies. Although the need for black holes remains, the measured masses have changed as a result of better modeling and higher resolution data. Once larger samples become available, we will be able to determine how black holes effect global galaxy properties. In particular, I will present the stellar orbital structures near the black hole and correlate those properties with black hole masses.

Centaurus A: The Supermassive Black Hole in the Nearest AGN

E. Schreier
Space Telescope Science Institute, Baltimore, USA

Centaurus A (NGC5128) is the nearest and one of the first active galaxies identified, via radio and X-ray observations, even before AGNs became a major subject of research. Although its proximity should make it an ideal test case of the standard model invoking massive black holes, the heavy obscuration due to the dust lane makes it very difficult to study the AGN at high spatial resolution in the optical. Observations with HST and with the VLT are now penetrating the dust lane, providing high resolution images and spectra of the nuclear region and new insights into the region around the black hole. We will summarize what is known about Cen A, discuss the implications of recent HST optical and infrared imaging and polarimetry, and present some preliminary results from VLT/ISAAC.

Gas/Stars Coupling in the Nuclei of Early-type Galaxies: Diagnostics for Supermassive Black Holes

E. Emsellem
Centre de Recherche Astronomique de Lyon, Lyon, France

Gaseous and/or stellar kinematics obtained via long-slit spectrography are routinely used to reveal the presence of supermassive black holes (SBHs) in galactic nuclei. Both have their advantages and drawbacks, including the difficulty of building realistic stellar kinematical models or to deal with the contribution of non-gravitational forces in the gas kinematics. I will present 2D spectrographic and some HST/WFPC2 observations of the gas and stellar components in a sample of early-type galaxies, demonstrating the need of both high resolution and bidimensional spatial coverage to understand the structure and dynamics of their central regions, and in particular to test the existence of a SBH.

Quasi-Silent Supermassive Black Holes: the Case of NGC 4552

A. Renzini
European Southern Observatory, Garching bei München, Germany

There is now ample evidence that most - perhaps all - galactic spheroids host a supermassive BH at their center. This has been assessed using a variety of observational techniques, from stellar and/or gas dynamics to megamasers. Yet another promising technique is offered by the case of the Virgo elliptical NGC 4552, in which early HST/FOC observations revealed a central low-luminosity flare. Subsequent HST/FOS observations with a 0.2 arcsec aperture have revealed a rich emission-line spectrum with broad and narrow components with FWHM of 3000 and 700 km/s, respectively. This variable, mini-AGN at the center of NGC 4552 has a luminosity of only ~10,000 solar luminosities, making it the likely, intrinsically faintest AGN known today. Only thanks to the superior resolution of HST such a faint object has been discovered and studied in detail, but adaptive optics systems on large ground-based telescopes may reveal in the future that a low level of accretion onto central massive BHs is an ubiquitous phenonenon among galactic spheroids.

X-ray variability of Neutron Stars and Black Holes

T. Belloni
Brera Observatory, Merate, Italy

The study of time variability is a useful and model-independent way to probe the innermost regions of accretion disks around compact objects. In the recent years a large wealth of data on the rapid X-ray variability of accreting binaries has been obtained. I review the main results from low-field neutron star systems and black hole candidates. A complex yet relatively ordered phenomenology is observed in neutron star systems, while black hole candidates are less easily classified in terms of their aperiodic variability. Recently, a number of works indicated that there might be more in common between these two classes of sources than most of the current models predict, indicating that we are dealing with basic properties of accretion disks.

X-ray Spectra of Neutron Stars vs. Black Holes

Y. Tanaka
Max-Planck Institut für Extraterrestrische Physik, Garching bei München, Germany

This paper presents an overview of X-ray specta of X-ray binaries powered by mass accretion. Binary X-ray pulsars with a strongly magnetized neutron star show a characteristic hard spectrum often associated with cyclotron resonance features. Here we shall discuss mainly the systems in which the compact object is either a weakly magnetized neutron star (low-mass X-ray binaries) or a black hole. At high luminosities (above 10³⁷ erg/s), the X-ray spectra are generally soft, but distinctly different between the neutron-star systems and the black-hole systems. The spectral properties of both systems will be discussed. Some specific spectral features of interest such as emission lines, absorption lines, and absorption edge structures will also be presented.

Microquasars in our Galaxy

I.F. Mirabel
Sap. C-E Saclay. France

Black holes of stellar mass and neutron stars in binary systems are first detected as hard X-ray sources using high-energy space telescopes. Relativistic jets in these compact sources are found by means of multiwavelength observations with ground-based telescopes. The X-ray emission probes the inner accretion disk and immediate surroundings of the black-hole, whereas the synchrotron emission from the jets is observed in the radio and infrared bands, and in the future could be detected at even shorter wavelengths. X-ray binaries with relativistic jets mimic, on a much smaller scale, many of the phenomena seen in quasars and are thus called microquasars. Their study opens the way for a better understanding of the relativistic jets seen elsewhere in the Universe. >From the observation of two-sided moving jets it is inferred that the ejecta in microquasars move with relativistic speeds similar to those estimated for quasars. Furthermore, the simultaneous multiwavelength approach to these sources reveals the close connection between instabilities in the accretion disk seen in the X-rays and the ejection of relativistic clouds of plasma observed as synchrotron emission at longer wavelengths. Besides contributing to a deeper comprehension of jets and disks, microquasars may serve in the future to test general relativity in the strong field limit.

Models for Jet Formation

R.D. Blandford and A. Celotti
SISSA, Trieste, Italy

The phenomenology of jets associated with a variety of black hole systems is summarized, emphasising the constraints imposed on their origin. Recent ideas concerning MHD models of jet formation will be briefly reviewed and the potential of forthcoming X-ray missions for advancing our understanding of jets will be highlighted.

Super-Eddington Mass Transfer, Jet Sources, and SS 433

A.R. King
Astronomy Group, University of Leicester, Leicester, UK

Recent work on systems such as Cygnus X-2 strongly suggests that neutron-star and black-hole binaries can survive highly super-Eddington mass transfer rates without undergoing common-envelope evolution. Such rates occur in systems where the companion star fills its Roche lobe as it expands across the Hertzsprung gap, particularly where this star is more massive than the compact accretor. I suggest that some of the Galactic jet sources are probably either currently in this phase, or descendants of it. Common-envelope evolution is avoided probably because radiation pressure is able to remove the excess matter from a region smaller than the accretor's Roche lobe. The jets may simply be the densest and most collimated part of this mass loss. Jet sources thus represent a short but rather common phase in the lifetime of many X-ray binaries. The end-products of this evolution include black-hole plus neutron-star binaries which will merge within the age of the Galaxy, and are thus candidate gamma-ray burst sources.

Black Holes and AGN at the Highest Redshifts

S. Phinney
California Institute of Technology, Pasadena, USA

Though nuclear activity peaks around z=2, some accreting black holes and their galactic nuclei appear fully formed at z=6. We discuss the problems posed by the birth and growth of nuclear black holes. We suggest that many AGN may exist at redshifts much higher than 6, and describe prospects for their detection.

Black Hole Accretion Discs

A.C. Fabian
Institute of Astronomy, University of Cambridge, UK

Strong evidence for thin, disc-like accretion flows immediately around black holes in many active galaxies is provided by X-ray observations of broad iron lines together with Compton reflection continuua. I will review the evidence obtained so far from ASCA and show how it will improve with the better data expected from Chandra, XMM, Astro-E and later missions. An exciting prospect is that reverberation of the line will be observed which will enable the flow to be mapped and for the mass and spin to be clearly measured. The evidence for thin disc accretion close to the black hole in many binary Black Hole Candidates is confused. I shall show how ionization of the iron in the outer layers of the disc may explain the observations there and resolve the confusion.

Radio Cores in Low-Luminosity AGN and Binary Black Holes: ADAFs or Jets?

H. Falcke, N. Nagar, A.S. Wilson, L.C. Ho and J.S. Ulvestad
Max-Planck-Institut für Radioastronomie, Bonn, Germany

We have surveyed a well-defined sample of the 96 closest low-luminosity AGN with the VLA to search for flat-spectrum radio cores, similar to Sgr A* in the Galactic Center. Roughly one third of all galaxies are detected (roughly one half if LINER/HII-transition objects are excluded), many of which have flat spectrum cores. Follow-up observations with the VLBA have confirmed that these cores are non-thermal in origin, with brightness temperatures of >= 10⁸ K. Some of the cores are resolved into linear structures. The radio core properties are compared to the x-ray, emission-line, and host galaxy properties of the galaxies. Specifically, we discuss the origin of these radio cores, i.e. whether they are better explained by radio jets or ADAFs. If the radio emission is largely due to emission from jets, this has significant implications for the SED fitting of low-luminosity AGN with the currently fashionable ADAF model. Finally, we put the radio cores we have detected into the larger context of accreting black holes, e.g., quasars, Seyferts, and especially Sgr A* and X-ray binaries. This comparison provides one with an interesting order-of-magnitude estimate for the radiative efficiency of accreting black holes as a function of accretion rate and black hole mass.

The Galactic Distribution of Wolf-Rayet Stars, Possible Supernova Progenitors

K.A. van der Hucht
Space Research Organization Netherlands (SRON-Utrecht), Utrecht, the Netherlands

With the appearance of the VIth Catalogue of Galactic Wolf-Rayet Stars (van der Hucht, Conti, Lundström & Stenholm 1981) almost two decades ago, the new VIIth Catalogue (van der Hucht 1999) documents the discovery of 62 new galactic WR stars, bringing the number of known galactic WR stars to 218. Comprehensive general reviews on the WR phenomenon have been presented, e.g, in IAU Symposium No. 193 (1999, Eds. K.A. van der Hucht, G. Koenigsberger & P.R.J. Eenens). It is important to discover and monitor WR stars, where individually each one of them is an unique physics laboratory, each is a tracer of star formation in spiral arms, and each represents a very evolved phase in the evolution of massive stars, to be followed possibly by a Type Ib/Ic supernova apocalypse (Woosley et al. 1993; Maeder & Conti 1994; Langer & Woosley 1996; Garcia-Segura et al. 1996). And where statistically the next Galactic supernova is overdue for already more than a century, it is of paramount importance to gather as much as possible detailed knowledge about its potential progenitor. In this paper the galactic distribution of the 218 WR stars in the VIIth Catalogue of Galactic Wolf-Rayet Stars is discussed.

Constraints on the Presence of a Central Black Hole in M15

R.P. van der Marel
Space Telescope Science Institute, Baltimore, USA

M15 is one of the densest globular clusters. This makes it unique for probing the structure and evolution of globular clusters. HST images reveal a central cusp in the star count distribution that is consistent with either core collapse or the presence of a central black hole. Dynamical information is required to unambiguously constrain the central mass distribution. M15 has been the subject of many intense kinematical studies in the past decade, and velocities for more than 1600 individual stars are now known. However, in the central few arcseconds crowding has long prevented the measurement of velocities of enough stars to accurately determine a velocity dispersion. Significant progress is now being made on this issue with state-of-the-art Keck HIRES spectra, CFHT adaptive optics Fabry-Perot observations, and HST/STIS spectroscopy. I will review these advances, and discuss the implications for the possible presence of a black hole in M15.

Black holes in dense star clusters

S.F. Portegies Zwart
Department of Astronomy, Boston University, Boston, USA

Black holes are the end-products of the evolution of very massive stars. In dense star clusters, they become the most massive objects within a few tens of millions of years; dynamical relaxation then causes them to sink to the cluster core, where they form binaries. These black-hole binaries become more tightly bound by superelastic encounters with other cluster members, and are ultimately ejected from the cluster. The majority of escaping black-hole binaries have orbital periods short enough and eccentricities high enough that the emission of gravitational radiation causes them to coalesce within a few billion years. The merger rate of such dynamically ejected black hole binaries is about 1.6 · 10^-7 per year per cubic megaparsec. This results in one or two detections during the first two years of operation for the first generation Laser Interferometer Gravitational-Wave Observatory (LIGO-I). For its successor LIGO-II, we expect a few daily detections.

The Black Hole versus Bulge Mass Relationship in Spiral Galaxies

A. Marconi
Osservatorio Astrofisico di Arcetri, Firenze, Italy

I will describe an on-going HST program aimed at determining the relationship between the nuclear black hole mass and bulge mass in spiral galaxies. We have selected a volume limited sample of 54 nearby spiral galaxies for which we already have ground based emission line rotation curves, CCD surface photometry and radio maps. We are now obtaining STIS longslit observations of each of the galaxies in the sample in order to determine the nuclear Halpha rotation curve with high (0.1'') spatial resolution. We will then use these data to measure the unresolved dark mass concentration at the nuclues of each object. After presenting the program, I will show the first results from observations of a few object in the sample.

Dynamical Evolution of Galactic Central Clusters Hosting Massive Black Holes.

M. Freitag
Observatoire de Genève, Sauverny, Switzerland

As observational evidences for massive 10^6-9 Msun black holes lurking in the center of most luminous galaxies are getting more and more compelling, the time is ripe for a systematic study of the dynamical interplay between the central object and the surrounding stellar cluster. Of key observational interest are disruptive processes, namely stellar collisions and tidal disruptions, that could feed with gas the otherwise starved black hole, thus initiating bright activity phases.
Realistic simulations of the long term (10¹⁰ years) evolution of such a galactic central cluster impose to take into account many physical processes: 2-body relaxation, collisions, tidal disruptions, stellar evolution.... When applied to relaxational systems, N-body methods are both very time consuming and restricted to values of `N' much smaller than those of actual systems. This motivated our efforts to develop a cluster evolution simulation program based on a Monte Carlo algorithm originally proposed by Hénon in the 70's. This stellar dynamical approach will be complemented with the results of thousands of hydrodynamical simulations of stellar collisions.
As a first application of our code, we focus on a better understanding of the relative importance of two-body relaxation, stellar collisions and tidal disruptions on the dynamics of stellar clusters in galactic centers.

Black Hole Formation in Gamma-Ray Bursts and Supernovae

S.E. Woosley
Astronomy Department, UCSC, Santa Cruz, USA

A variety of observational phenomena may be associated with the formation of a black hole at the end of the life of a massive star. These range from relatively innocuous occurrences, such as the disappearance of the radioactive tail from the light curve of a Type IIp supernova that swallowed its ⁵⁶Ni in a collapsed remnant, to the tremendous explosions like the gamma-ray bursts (GRBs) of 971214 and 990123 produced when a stellar mass black hole forms promptly in a rotating massive helium star.
The nature of the event depends upon the mass of the star, its angular momentum distribution, whether the star has or lacks a hydrogen envelope, and the energy of the shock that is initially launched when the star's iron core collapses to a neutron star. It also depends sensitively upon the uncertain physics of jet formation by hyper-accreting black holes ( = 10^-4 - 1 Msun s^-1), either by neutrino energy transport or MHD processes. As time allows, I will discuss 1) models for classical GRBs - beamed highly relativistic jets of up to 10⁵² erg and Gamma ~ 100 with half-angles of about 10 degrees; 2) models for longer gamma-ray bursts and deformed, energetic supernova - jet powered supernovae resulting from delayed fall back and black hole formation minutes to hours after the initial explosion; 3) models for ``smothered gamma-ray bursts'' like GRB 980425 and SN 1998bw; and 4) mixing in SN 1987A.

Formation of BH X-ray Binaries with Low-mass Donor Stars

V. Kalogera
Harvard-Smithsonian Center for Astrophysics, Cambridge, USA

The characteristics of the observed sample of black-hole X-ray binaries can be used to obtain information about their evolutionary history and the process of black-hole formation. In this talk I will focus on systems with donor masses lower than the inferred black-hole masses. The short orbital periods at present dictate that the progenitors have experienced a common envelope phase in a way similar to the formation of low-mass X-ray binaries with neutron stars. I will show that limits derived from this prior evolution and the properties of the donor stars in these systems can be used to constrain the masses of possible black-hole progenitors (at most twice the black-hole mass) and the strength of winds in helium stars (fractional amount of mass lost smaller than about 50%). Additional constraints on common-envelope evolution and the properties of massive stars are obtained. I will also discuss the dependence on models for single, mass-losing massive stars and the possible role of black-hole kicks.

Empirical Lower Mass Limit for Black-hole Formation in a Massive Binary

L. Kaper
Astronomical Institute, University of Amsterdam, Amsterdam, the Netherlands

The mass of the OB star in a high-mass X-ray binary provides an important constraint on the initial progenitor mass of the neutron-star or black-hole companion. In case the binary system hosts an X-ray pulsar (i.e., a neutron star), a lower limit on the present mass of the OB-star companion can be derived. When the orbital parameters of both stars are known, as well as the inclination of the binary orbit, the masses of both the massive star and the compact companion are determined. Since the initially most massive star in the binary formed the compact companion, and the system remained bound after the supernova explosion, the present mass of the OB star sets a limit to the initial mass of the compact companion. Obviously, details on the evolutionary scenario of the binary system (e.g. the amount of material transferred to the companion and the amount lost from the system) have to be known to make a definitive statement on the initial masses of the two stars. An overview will be given of the stellar parameters of the massive stars in high-mass X-ray binaries, including the ones hosting a black-hole candidate. The most massive star with an X-ray pulsar companion is Wray 977 (GX301-2); its present mass is at least 40 Msun, but its companion formed a neutron star and not a black hole. The consequences of these observations for the progenitor masses of black holes formed in massive binaries will be discussed.

Implications of Massive Close Binaries for Black Hole Formation and Supernovae

S. Wellstein and N. Langer
Institut für Physik, Potsdam, Germany

The progenitor evolution of the massive X-ray binary Wray 977 is investigated using new models of massive close binary evolution. These models yield constraints on the mass limit for neutron star/black hole formation in single stars, M_BH. We argue for quasi-conservative evolution in this system, and we find M_BH > 13..21 Msun from the existence of a neutron star in Wray 977, with the uncertainty being due to uncertainties in the treatment of convection. Our results revise earlier published much larger values of M_BH derived from the parameters of Wray 977. Then, on the basis of a grid of 37 evolutionary models for massive close binaries with various initial masses, mass ratios and periods, we derive primary initial-final mass, initial mass-final helium core mass, and initial mass-final CO-core mass relations for the various mass transfer cases of close binary evolution. From these models we derive for single stars that M_BH <= 25 Msun, independent of whether most black hole binaries formed through the Case A/B or the Case C binary channel. Using our grid of binary models, we obtain a consistent scenario for the formation of black holes in binary systems. We emphasize that in binaries the critical initial mass limits for neutron star/black hole formation and for white dwarf/neutron star formation are very different from the corresponding values in single stars. While the first may well be above 100 Msun in Case A/B binaries, the latter is found to be in the range 12...15 Msun instead of the canonical value of 8...10 Msun usually quoted for single stars. This effect should not be neglected in population synthesis studies of massive binary systems. Also, neutron star and black hole mass functions obtained for single stars can not per se compared to the masses of compact objects in binary systems.

Black Hole Formation: Predictions from Core-collapse and Accretion Induced Collapse Mechanisms

C. Fryer
UCO/Lick Observatory, Santa Crux, USA

The number of strong candidates for stellar mass black holes has increased dramatically over the last ten years and it is now possible to estimate the mass distribution of these black holes. In addition, core-collapse simulations have now progressed to a stage where they can predict the formation (and mass distribution) of these black holes. Similarly, population synthesis models are now able to make some predictions on those stellar mass black holes formed via accretion induced collapse. I will review these two black hole formation mechanisms and present results of both core-collapse and population synthesis simulations. Using these simulations as a guideline, we predict trends and explain the biases in the observed set of black holes.

Accreting Black Holes in Asymmetric Supernovae and Gamma Ray Bursts

A. MacFadyen
UCO/Lick Observatory, Santa Crux, USA

When the iron core of a very massive star collapses, a black hole may form in either of two ways - promptly owing to a failure of neutrino energy deposition to generate an outwardly propagating shock, or delayed because of the fall back of ejecta that fails to reach terminal escape velocity. In either case the newly formed black hole will accrete at an enormous rate, typically 0.1 solar masses per second in the prompt case, 0.001 to 0.01 solar masses per second in the delayed case. Provided the accreting material has angular momentum, j, greater than a few times 10¹⁶ cm² s^-1, accretion will occur by way of a disk giving rise to the possibility of jet formation. The jet may be powered, for very high accretion rates, by neutrino energy transport, or by magnetic energy dissipation in the disk, or by extracting some of the rotational energy of the black hole. Jets having total energies of 10⁵⁰ to 10⁵³ ergs are expected. Depending on the duration of the jet and the presupernova star, diverse phenomena may result ranging from bright beamed gamma-ray bursts like GRB 990123, to supernovae and gamma-ray bursts like GRB 980425 and SN 1998bw, to ordinary appearing supernovae that exhibit anomalous mixing and non-spherical appearance. Each of these possibilities will be illustrated by numerical calculation.

High-redshift Galaxies, their Active Nuclei and Central Black Holes

M. Hähnelt
Max-Planck-Institut für Astrophysik, Garching bei München, Germany

I will discuss the formation of supermassive black holes within hierarchical cosmogonies. I will thereby pay particular attention to the role which mergers play for the accretion history of supermassive black holes. I will further show that a consistent picture for the evolution of AGN, their host galaxies and the resulting remnant black holes arises.

The Galaxy Formation Connection

S.D.M. White
Max-Planck-Institut für Astrophysik, Garching bei München, Germany

Observational constraints on the assembly of galaxies have improved dramatically over the last few years. There is now strong direct evidence that the spheroids of massive galaxies did not form through early monolithic collapse, but rather were assembled relatively recently from smaller pieces. In addition we now know that the global gas to star ratio of galaxies was more than an order of magnitude higher at z>2 than it it is locally; at such redshifts HI, rather than stars, was the dominant baryonic component of galaxies. These facts have important implications for our ideas about how massive black holes grew in galactic nuclei. They are easily accommodated in current hierarchical galaxy formation theories which therefore form a natural framework for interpreting not only the flood of new data on the evolution and clustering of the galaxy population, but also the demographics of the growth and fuelling of nuclear black holes.

Black Hole Results from STIS

R. Olling, C. Joseph, D. Merritt and M. Valluri
Rutgers University, Piscataway, USA

The Space Telescope Imaging Spectrograph (STIS) has obtained 0.1-0.2'' resolution spectra from the nuclei of about 15 nearby galaxies in a search for supermassive black holes. Here we present the nuclear kinematics for several galaxies for which Rutgers astronomers are lead investigators, including M32, M87, NGC 2842, and NGC 4552. In M32 we reproduce the van der Marel et al. (1998) FOS results but with approximately 7 times higher velocity resolution, and 2 times higher spatial resolution. In NGC2841 we obtain a clear signature in the stellar motions of a black hole with mass ~ 10^7.7 solar masses, the first black hole detection in this galaxy. In M87 we measure the stellar velocity dispersion at a radius of ~ 0.3'', a factor of ~ 2 higher spatial resolution than existing, ground-based data. In each of these galaxies, the STIS stellar data extend well within r_g, the radius of gravitational influence of the black hole, making the interpretation of the black hole mass essentially independent of the stellar anisotropy.

SINFONI - Galaxy Dynamics at 0.05'' Resolution with the VLT

N. Thatte
Max-Planck-Intitut für Extraterrestrische Physik, Garching bei München, Germany

Stellar dynamics (velocity dispersion, rotation and anisotropies) provides the most robust method for measuring central dark masses in galaxy nuclei, since the stars, unlike gas, respond only to gravitational forces. However, the radius of influence of the central black hole is small, and very high spatial resolution spectroscopic observations are called for. To date, such high resolution studies have been carried out with space telescopes at visible wavelengths.
We present SINFONI, an adaptive optics assisted integral field spectrometer for the ESO VLT, which provides near-infrared (1 to 2.5 µm) spectroscopy at spatial resolutions of 0.05'' (diffraction limit at the K band). LOSVD measurements of the nuclear regions will use the deep stellar absorption features of CO at 2.3 µm, with an instrumental resolution of ~ 70 km s^-1. Operating at near-infrared wavelengths, SINFONI will be able to see through significant extinction, making measurements of spiral galaxies feasible. SINFONI is an integral field instrument, delivering data cubes which can be used to place hard constraints on anisotropic effects.
We present the features of the instrument, its design concept, and its promise for black hole searches.

Gamma Ray Observations of Black Hole Candidates: The Prospect of Integral

N. Trams
ESTEC, Noordwijk, The Netherlands

Many Black Hole candidates and BH binaries have been observed at gamma ray energies by the Gamma Ray Observatory (GRO). GRO has shown that this energy range provides important information for modelling of the spectra and variability of these sources. Currently a new gamma ray observatory, the International Gamma Ray Astrophysics Laboratory (INTEGRAL), is being prepared for launch in 2001. With a complement of 4 scientific instruments (a gamma ray spectrograph, a gamma ray imager, and X-ray and optical monitoring cameras) this satellite will provide unprecedented imaging and spectroscopic capabilities at gamma ray energies as well as simultaneous observation in X-rays and the optical. The sensitivity will be an order of magnitude better than GRO. The INTEGRAL Call for Proposals will be issued in spring of next year. In this talk a brief overview of INTEGRAL and its scientific capabilities will be given, specifically with respect to Black Hole candidates (galactic and extragalactic).