by Li, Shuo and Liu, F. K. and Berczik, Peter and Chen, Xian and Spurzem, Rainer
38 pages, 10 figues; accepted for publication in ApJ

Supermassive black hole binaries (SMBHBs) are the products of frequent galaxy mergers. The coalescence of the SMBHBs is a distinct source of gravitational wave (GW) radiation. The detections of the strong GW radiation and their possible electromagnetic counterparts are essential. Numerical relativity suggests that the post-merger supermassive black hole (SMBH) gets a kick velocity up to 4000 km/s due to the anisotropic GW radiations. Here we investigate the dynamical co-evolution and interaction of the recoiling SMBHs and their galactic stellar environments with one million direct N-body simulations including the stellar tidal disruption by the recoiling SMBHs. Our results show that the accretion of disrupted stars does not significantly affect the SMBH dynamical evolution. We investigate the stellar tidal disruption rates as a function of the dynamical evolution of oscillating SMBHs in the galactic nuclei. Our simulations show that most of stellar tidal disruptions are contributed by the unbound stars and occur when the oscillating SMBHs pass through the galactic center. The averaged disruption rate is ~10^{-6} M_\odot yr^{-1}, which is about an order of magnitude lower than that by a stationary SMBH at similar galactic nuclei. Our results also show that a bound star cluster is around the oscillating SMBH of about ~ 0.7% the black hole mass. In addition, we discover a massive cloud of unbound stars following the oscillating SMBH. We also investigate the dependence of the results on the SMBH masses and density slopes of the galactic nuclei.

by Hayasaki, Kimitake and Yagi, Kent and Tanaka, Takahiro and Mineshige, Shin
10 pages, 2 figures, submitted to ApJ

When binary black holes are embedded in a gaseous environment, a rotating disk surrounding them, the so-called circumbinary disk, will be formed. The binary exerts a gravitational torque on the circumbinary disk and thereby the orbital angular momentum is transferred to it, while the angular momentum of the circumbinary disk is transferred to the binary through the mass accretion. The binary undergoes an orbital decay due to both the gravitational wave emission and the binary-disk interaction. This causes the phase evolution of the gravitational wave signal. The precise measurement of the gravitational wave phase thus may provide information regarding the circumbinary disk. In this paper, we assess the detectability of the signature of the binary-disk interaction using the future space-borne gravitational wave detectors such as DECIGO and BBO by the standard matched filtering analysis. We find that the effect of the circumbinary disk around binary black holes in the mass range $latex 6M_sun\le{M}\lesssim3\times10^3M_sun$ is detectable at a statistically significant level in five year observation, provided that gas accretes onto the binary at a rate greater than $latex \dot{M}\sim1.4\times10^{17} [gs^{-1}] j^{-1}(M/10M_sun)^{33/23}$ with 10% mass-to-energy conversion efficiency, where j represents the efficiency of the angular momentum transfer from the binary to the circumbinary disk. We show that $latex O(0.1)$ coalescence events are expected to occur in sufficiently dense molecular clouds in five year observation. We also point out that the circumbinary disk is detectable, even if its mass at around the inner edge is by over 10 orders of magnitude less than the binary mass.

by Johnson, Jarrett L. and Whalen, Daniel J. and Fryer, Christopher L. and Li, Hui
14 pages, 4 figures; submitted to ApJ

The collapse of baryons into extremely massive stars with masses exceeding 10^4 M_Sun in a small fraction of protogalaxies at z > 10 is a promising candidate for the origin of supermassive black holes, some of which grow to a billion solar masses by z ~ 7. We determine the maximum masses such stars can attain by accreting primordial gas. We find that at relatively low accretion rates the strong ionizing radiation of these stars limits their masses to M_* ~ 10^3 M_Sun (dM_acc/dt / 10^-3 M_Sun yr^-1)^8/7, where dM_acc/dt is the rate at which the star gains mass. However, at the higher central infall rates usually found in numerical simulations of protogalactic collapse (>~ 0.1 M_Sun yr^-1), the lifetime of the star instead limits its final mass to >~ 10^6 M_Sun. Furthermore, for the spherical accretion rates at which the star can grow, its ionizing radiation is confined deep within the protogalaxy, so the evolution of the star is decoupled from that of its host galaxy. Lyman alpha emission from the surrounding H II region is trapped in these heavy accretion flows and likely reprocessed into strong Balmer series emission, which may be observable by the James Webb Space Telescope. This, along with strong He II 1640 Angstrom and continuum emission, are likely to be the key observational signatures of the progenitors of supermassive black holes at high redshift.

by Marx, Jay and Danzmann, Karsten and Hough, James and Kuroda, Kazuaki and McClelland, David and Mours, Benoit and Phinney, Sterl and Rowan, Sheila and Sathyaprakash, B. and Vetrano, Flavio and Vitale, Stefano and Whitcomb, Stan and Will, Clifford
116 pages. Original document in higher resolution can be found at https://gwic.ligo.org/roadmap/

Gravitational wave science is on the verge of direct observation of the waves predicted by Einstein’s General Theory of Relativity and opening the exciting new field of gravitational wave astronomy. In the coming decades, ultra-sensitive arrays of ground-based instruments and complementary spaced-based instruments will observe the gravitational wave sky, inevitably discovering entirely unexpected phenomena while providing new insight into many of the most profound astrophysical phenomena known. in July 2007 the Gravitational Wave International Committee (GWIC) initiated the development of a strategic roadmap for the field of gravitational wave science with a 30-year horizon. The goal of this roadmap is to serve the international gravitational wave community and its stakeholders as a tool for the development of capabilities and facilities needed to address the exciting scientific opportunities on the intermediate and long-term horizons.

by Sesana, A.
21 pages, 4 figures, accepted for publication in Advances in Astronomy

I review our current understanding of massive black hole (MBH) formation and evolution along the cosmic history. After a brief introductory overview of the relevance of MBHs in the hierarchical structure formation paradigm, I discuss the main viable channels for seed BH formation at high redshift and for their subsequent mass growth and spin evolution. The emerging hierarchical picture, where MBHs grow through merger triggered accretion episodes, acquiring their mass while shining as quasars, is overall robust, but too simplistic to explain the diversity observed in MBH phenomenology. I briefly discuss which future observations will help to shed light on the MBH cosmic history in the near future, paying particular attention to the upcoming gravitational wave window.

by Blandford, Roger D.
10 pages, 10 figures, to be submitted to MNRAS

In this paper we consider Roche accretion in an Extreme Mass-Ratio Inspiral (EMRI) binary system formed by a star orbiting a massive black hole. The ultimate goal is to detect the mass and spin of the black hole and provide a test of general relativity in the strong-field regime from the resultant quasi-periodic signals. Before accretion starts, the stellar orbit is presumed to be circular and equatorial, and shrinks due to gravitational radiation. New fitting formulae are presented for the inspiral time and the radiation-reaction torque in the relativistic regime. If the inspiralling star fills its Roche lobe outside the Innermost Stable Circular Orbit (ISCO) of the hole, gas will flow through the inner Lagrange point (L1) to the hole. We give new relativistic interpolation formulae for the volume enclosed by the Roche lobe. If this mass-transfer happens on a time scale faster than the thermal time scale but slower than the dynamical time scale, the star will evolve adiabatically, and, in most cases, will recede from the hole while filling its Roche lobe. We calculate how the stellar orbital period and mass-transfer rate will change through the “Roche evolution” for various types of stars in the relativistic regime. We envisage that the mass stream eventually hits the accretion disc, where it forms a hot spot orbiting the hole and may ultimately modulate the luminosity with the stellar orbital frequency. The observability of such a modulation is discussed along with a possible interpretation of an intermittent 1 hour period in the X-ray emission of RE J1034+396.

by Fabian, A. C. and Zoghbi, A. and Wilkins, D. and Dwelly, T. and Uttley, P. and Schartel, N. and Miniutti, G. and Gallo, L. and Grupe, D. and Komossa, S. and Santos-Lleo, M.
9 pages, 19 figures, MNRAS in press

The Narrow Line Seyfert 1 Galaxy 1H0707-495 went in to a low state from 2010 December to 2011 February, discovered by a monitoring campaign using the X-Ray Telescope on the Swift satellite. We triggered a 100 ks XMM-Newton observation of the source in 2011 January, revealing the source to have dropped by a factor of ten in the soft band, below 1 keV, and a factor of 2 at 5 keV, compared with a long observation in 2008. The sharp spectral drop in the source usually seen around 7 keV now extends to lower energies, below 6 keV in our frame. The 2011 spectrum is well fit by a relativistically-blurred reflection spectrum similar to that which fits the 2008 data, except that the emission is now concentrated solely to the central part of the accretion disc. The irradiating source must lie within 1 gravitational radius of the event horizon of the black hole, which spins rapidly. Alternative models are briefly considered but none has any simple physical interpretation.

by Haas, Jaroslav and Subr, Ladislav and Vokrouhlicky, David
Accepted for publication in MNRAS; 11 pages, 6 figures

We investigate the orbital evolution of a system of N mutually interacting stars on initially circular orbits around the dominating central mass. We include perturbative influence of a distant axisymmetric source and an extended spherical potential. In particular, we focus on the case when the secular evolution of orbital eccentricities is suppressed by the spherical perturbation. By means of standard perturbation methods, we derive semi-analytic formulae for the evolution of normal vectors of the individual orbits. We find its two qualitatively different modes. Either the orbits interact strongly and, under such circumstances, they become dynamically coupled, precessing synchronously in the potential of the axisymmetric perturbation. Or, if their mutual interaction is weaker, the orbits precess independently, interchanging periodically their angular momentum, which leads to oscillations of inclinations. We argue that these processes may have been fundamental for the evolution of the disc of young stars orbiting the supermassive black hole in the centre of the Milky Way.

by Broderick, Avery E. and Loeb, Abraham and Reid, Mark J.
18 pages, 4 figures, Accepted for publication in ApJ

With the advent of the Event Horizon Telescope (EHT), a millimeter/sub-millimeter very-long baseline interferometer (VLBI), it has become possible to image a handful of black holes with sub-horizon resolutions. However, these images do not translate into microarcsecond absolute positions due to the lack of absolute phase information when an external phase reference is not used. Due to the short atmospheric coherence time at these wavelengths, nodding between the source and phase reference is impractical. However, here we suggest an alternative scheme which makes use of the fact that many of the VLBI stations within the EHT are arrays in their own right. With this we show that it should be possible to absolutely position the supermassive black holes at the centers of the Milky Way (Sgr A*) and M87 relative to nearby objects with precisions of roughly 1 microarcsecond. This is sufficient to detect the perturbations to Sgr A*’s position resulting from interactions with the stars and stellar-mass black holes in the Galactic cusp on year timescales, and severely constrain the astrophysically relevant parameter space for an orbiting intermediate mass black hole, implicated in some mechanisms for producing the young massive stars in the Galactic center. For M87, it allows the registering of millimeter images, in which the black hole may be identified by its silhouette against nearby emission, and existing larger scale radio images, eliminating present ambiguities in the nature of the radio core and inclination, opening angle, and source of the radio jet.

by Rafiee, Alireza and Hall, Patrick B.
38 Pages, 12 figures, 3 Tables, 1 hyperlink to catalogue data. Accepted for publication in ApJS

We present MgII-based black hole mass estimates for 27,602 quasars with rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release Three. This estimation is possible due to the existence of an empirical correlation between the radius of the broad line region and the continuum luminosity at 3000 Angstroms. We regenerate this correlation by applying our measurement method to UV spectra of low-redshift quasars in the HST/IUE databases which have corresponding reverberation mapping estimates of the Hbeta broad line region’s radius. Our mass estimation method uses the line dispersion rather than the full width at half maximum of the low-ionization MgII emission line. We measure MgII line dispersions for quasars whose spectra have been reconstructed using the most significant eigenspectra produced through Principal Component Analysis. We have tested the reliability of using reconstructed spectra in black hole mass estimation using a Monte Carlo simulation and by comparing the results from original and reconstructed Data Release Three spectra. We show that using reconstructed spectra not only makes bias-free mass estimation possible for quasars with low spectroscopic signal-to-noise ratio, but also reduces the intrinsic scatter of the distribution of the black hole masses to lower than 0.15 dex.

by Hénon, Michel
Originally published in 1965. 7 pages, 5 figures

This paper is an English translation of Michel H\’enon’s article, “Sur l’\'evolution dynamique des amas globulaires. II- L’amas isol\’e” originally published in French in the Annales d’Astrophysique, Vol. 28, p.62 (1965). A translation of the first paper of this series (”Sur l’\'evolution dynamique des amas globulaires”, H\’enon 1961, Annales d’Astrophysique, Vol. 24, p.369) is also available.

by Hénon, Michel
Originally published in 1961. 44 pages, 23 figures

This paper is an English translation of Michel H\’enon’s thesis, “Sur l’\'evolution dynamique des amas globulaires” originally published in French in the Annales d’Astrophysique, Vol. 24, p.369 (1961).

by Khan, Fazeel and Just, Andreas and Merritt, David
9 pages, 11 figures. Accepted for publication in The Astrophysical Journal

In spherical galaxies, binary supermassive black holes (SMBHs) have difficulty reaching sub-parsec separations due to depletion of stars on orbits that intersect the massive binary – the final-parsec problem. Galaxies that form via major mergers are substantially nonspherical, and it has been argued that the centrophilic orbits in triaxial galaxies might provide stars to the massive binary at a high enough rate to avoid stalling. Here we test that idea by carrying out fully self-consistent merger simulations of galaxies containing central SMBHs. We find hardening rates of the massive binaries that are indeed much higher than in spherical models, and essentially independent of the number of particles used in the simulations. Binary eccentricities remain high throughout the simulations. Our results constitute a fully stellar-dynamical solution to the final-parsec problem and imply a potentially high rate of events for low-frequency gravitational wave detectors like LISA.

by Stovall, Kevin and Creighton, Teviet and Price, Richard H. and Jenet, Fredrick A.
18 pages, 16 figures

According to some models, there may be a significant population of radio pulsars in the Galactic center. In principle, a beam from one of these pulsars could pass close to the supermassive black hole (SMBH) at the center, be deflected, and be detected by Earth telescopes. Such a configuration would be an unprecedented probe of the properties of spacetime in the moderate- to strong-field regime of the SMBH. We present here background on the problem, and approximations for the probability of detection of such beams. We conclude that detection is marginally probable with current telescopes, but that telescopes that will be operating in the near future, with an appropriate multiyear observational program, will have a good chance of detecting a beam deflected by the SMBH.

by Merritt, David and Alexander, Tal and Mikkola, Seppo and Will, Clifford
28 pages, 16 figures

Inspiral of compact stellar remnants into massive black holes (MBHs) is accompanied by the emission of gravitational waves at frequencies that are potentially detectable by the proposed laser interferometer space antenna. Event rates computed from statistical (Fokker-Planck, Monte-Carlo) approaches span a wide range due to uncertaintities about the rate coefficients. Here we present results from direct integration of the post-Newtonian N-body equations of motion descrbing dense clusters of compact stars around Schwarzschild and Kerr MBHs. These simulations embody an essentially exact (at the post-Newtonian level) treatment of the interplay between stellar dynamical relaxation, relativistic precession, and gravitational-wave energy loss. The rate of capture of stars by the MBH is found to be greatly reduced by relativistic precession, which limits the ability of torques from the stellar potential to change orbital angular momenta. Penetration of this “Schwarzschild barrier” does occasionally occur, resulting in capture of stars onto orbits that gradually inspiral due to gravitational wave emission; we discuss two mechanisms for barrier penetration and find evidence for both in the simulations. We derive an approximate formula for the capture rate, which predicts that captures would be strongly disfavored from orbits with semi-major axes below a certain value; this prediction, as well as the predicted rate, are verified in the N-body integrations. Adding spin to the MBH does not substantially change the capture rate; the back-reaction of the stellar torques on the spin of the MBH is evaluated and shown to be potentially observable. We discuss the implications of our results for the detection of extreme-mass-ratio inspirals from galactic nuclei with a range of physical properties.

by Preto, Miguel and Berentzen, Ingo and Berczik, Peter and Spurzem, Rainer
6 pages, 4 figures, 1 table. Submitted to ApJL

We investigate a purely stellar dynamical solution to the Final Parsec Problem. Galactic nuclei resulting from major mergers are not spherical, but show some degree of triaxiality. With $latex N$-body simulations, we show that massive black hole binaries (MBHB) hosted by them will continuously interact with stars on centrophilic orbits and will thus inspiral—in much less than a Hubble time—down to separations at which gravitational wave (GW) emission is strong enough to drive them to coalescence. Such coalescences will be important sources of GWs for future space-borne detectors such as the {\it Laser Interferometer Space Antenna} (LISA). Based on our results, we expect that LISA will see between $latex \sim 10$ to $latex \sim {\rm few} \times 10^2$ such events every year, depending on the particular MBH seed model as obtained in recent studies of merger trees of galaxy and MBH co-evolution. Orbital eccentricities in the LISA band will be clearly distinguishable from zero with $latex e \gtrsim 0.001-0.01$.

by Jia, Jianjun and Ptak, Andrew and Heckman, Timothy M. and Overzier, Roderik A. and Hornschemeier, Ann and LaMassa, Stephanie M.
Accepted for publication in ApJ

We have used XMM-Newton to observe six Lyman Break Analogs (LBAs): members of the rare population of local galaxies that have properties that are very similar to distant Lyman Break Galaxies. Our six targets were specifically selected because they have optical emission-line properties that are intermediate between starbursts and Type 2 (obscured) AGN. Our new X-ray data provide an important diagnostic of the presence of an AGN. We find X-ray luminosities of order 10^{42} erg/s and ratios of X-ray to far-IR luminosities that are higher than values in pure starburst galaxies by factors ranging from ~ 3 to 30. This strongly suggests the presence of an AGN in at least some of the galaxies. The ratios of the luminosities of the hard (2-10 keV) X-ray to [O III]\lambda 5007 emission-line are low by about an order-of-magnitude compared to Type 1 AGN, but are consistent with the broad range seen in Type 2 AGN. Either the AGN hard X-rays are significantly obscured or the [O III] emission is dominated by the starburst. We searched for an iron emission line at ~ 6.4 keV, which is a key feature of obscured AGN, but only detected emission at the ~ 2\sigma level. Finally, we find that the ratios of the mid-infrared (24\mu m) continuum to [O III]\lambda 5007 luminosities in these LBAs are higher than the values for Type 2 AGN by an average of 0.8 dex. Combining all these clues, we conclude that an AGN is likely to be present, but that the bolometric luminosity is produced primarily by an intense starburst. If these black holes are radiating at the Eddington limit, their masses would lie in the range of 10^5 to 10^6 M_{sun}. These objects may offer ideal local laboratories to investigate the processes by which black holes grew in the early universe.

by Martinez-Sansigre, Alejo and Rawlings, Steve
Accepted for publication by MNRAS. 30 Pages, 14 Figures, 5 Tables

We use recent progress in simulating the production of magnetohydrodynamic jets around black holes to derive the cosmic spin history of the most massive black holes, with masses >~10^8 Msol. Assuming the jet efficiency depends on spin a, we can approximately reproduce the observed `radio loudness’ of quasars and the local radio luminosity function. Using the X-ray luminosity function and the local mass function of supermassive black holes, SMBHs we can reproduce the individual radio luminosity functions of radio sources showing high- and low-excitation narrow emission lines. The data favour spin distributions that are bimodal, with one component around spin zero and the other close to maximal spin. In the low-excitation galaxies, the two components have similar amplitudes. For the high-excitation galaxies, the amplitude of the high-spin peak is typically much smaller than that of the low-spin peak. A bimodality should be seen in the radio loudness of quasars. We predict that the low-excitation galaxies are dominated by SMBHs with masses >~10^8 Msol, down to radio luminosity densities ~10^21 W Hz-1 sr-1 at 1.4~GHz. Our model is also able to predict the radio luminosity function at z=1, and predicts it to be dominated by high-excitation galaxies above luminosity densities >~10^26 W Hz-1 sr-1, in full agreement with the observations. From our parametrisation and using the best fitting jet efficiencies there is marginal evidence for evolution in spin: the mean spin increases slightly from ~0.25 at z=1 to ~0.35 at z=0, and the fraction of SMBHs with a>=0.5 increases from 0.16+-0.03 at z=1 to 0.24+-0.09 at z=0. Our results are in excellent agreement with the mean radiative efficiency of quasars, as well as recent cosmological simulations. We discuss the implications in terms of accretion and SMBH mergers, and galactic black holes (Abridged).

by Inogamov, N. A. and Sunyaev, R. A.
Full text of the paper with two Appendices is published in Astronomy Letters, Vol. 36, p. 835 (2010)

The accretion of hot slowly rotating gas onto a supermassive black hole is considered. Rotation velocities at the Bondi radius r_B are small in comparison with speed of sound c_s. The centrifugal barrier at a depth r_c = l^2/G M_BH <r_c) and inner (r<r_c) disks are formed. The gas enters the zone of the internal ADAF flow along the accretion disk (r<r_c). Since the angular momentum is conserved, the outer disk removes outward an excess of angular momentum along with part of the matter falling into the torus. Such outer Keplerian disk was observed by Hubble Space Telescope around the nucleus of the M87 galaxy in the optical emission lines. Turbulence causes rotation. We discuss the characteristic times during which the turbulence should lead to the changes in the orientation of the torus, accretion disk and, possibly, of the jet.

by Cen, Renyue
29 pages, 3 figures, submitted to the Astrophysical Journal

A model for coevolution of galaxies and supermassive black holes (SMBH) is presented that is physically based. The starting point is a gas-rich major merger that triggers a starburst and the endpoint is a quiescent elliptical galaxy many gigayears later. There is an approximate coevolution between starburst galaxies and elliptical galaxies, although it is not exact in several important ways. Starburst precedes the onset of main SMBH growth with a gap of time equal to ~100Myr and is responsible for shutting down its own activities; AGN has little to do with it. While starburst occurs earlier and lasts for only about 100Myrs, the AGN accretion occurs later and lasts for ~1 Gyr or longer with a diminishing Eddington ratio. The main AGN growth in post-starburst phase is fueled by recycled gas from inner bulge stars and self-regulated. The predicted relation between SMBH mass and bulge mass/velocity dispersion is consistent with observations. A suite of testable and falsifiable predictions and implications with respect to relationships between various types of galaxies and AGN are made. Where comparisons to extant observations are possible, the model is in agreement with them.

by Zamaninasab, M. and Eckart, A. and Dovciak, M. and Karas, V. and Schoedel, R. and Witzel, G. and Sabha, N. and Garcia-Marin, M. and Kunneriath, D. and Muzic, K. and Straubmeier, C. and Valencia-S, M. and Zensus, J. A.
12 pages, 13 figures, accepted for publication in MNRAS

Several massive black holes exhibit flux variability on time scales that correspond to source sizes of the order of few Schwarzschild radii. We survey the potential of near-infrared and X-ray polarimetry to constrain physical properties of such black hole systems, namely their spin and inclination. We have focused on a model where an orbiting hot spot is embedded in an accretion disk. A new method of searching for the time-lag between orthogonal polarization channels is developed and applied to an ensemble of hot spot models that samples a wide range of parameter space. We found that the hot spot model predicts signatures in polarized light which are in the range to be measured directly in the near future. However, our estimations are predicted upon the assumption of a Keplerian velocity distribution inside the flow where the dominant part of the magnetic field is toroidal. We also found that if the right model of the accretion flow can be chosen for each source (e.g. on the basis of magnetohydrodynamics simulations) then the black hole spin and inclination can be constrained to a small two-dimensional area in the spin-inclination space. The results of the application of the method to the available near-infrared polarimetric data of Sagittarius A* (Sgr A*) is presented. It is shown that even with the currently available data the spin and inclination of Sgr A* can be constrained. Next generations of near-infrared and X-ray polarimeters should be able to exploit this tool.

by Marsh, T. R.
11 pages, 2 figures, in press Classical and Quantum Gravity. Summary of talk given at 8th LISA Symposium, Stanford, July 2010

Close pairs of white dwarfs are potential progenitors of Type~Ia supernovae and they are common, with of order 100 — 300 million in the Galaxy. As such they will be significant, probably dominant, sources of the gravitational waves detectable by LISA. In the context of LISA’s goals for fundamental physics, double white dwarfs are a source of noise, but from an astrophysical perspective, they are of considerable interest in their own right. In this paper I discuss our current knowledge of double white dwarfs and their close relatives (and possible descendants) the AM~CVn stars. LISA will add to our knowledge of these systems by providing the following unique constraints: (i) an almost direct measurement of the Galactic merger rate of DWDs from the detection of short period systems and their period evolution, (ii) an accurate and precise normalisation of binary evolution models at the shortest periods, (iii) a determination of the evolutionary pathways to the formation of AM~CVn stars, (iv) measurements of the influence of tidal coupling in white dwarfs and its significance for stabilising mass transfer, and (v) discovery of numerous examples of eclipsing white dwarfs with the potential for optical follow-up to test models of white dwarfs.

by Kormendy, John and Bender, Ralf
12 pages, 9 Postscript figures, 1 table; published in Nature (20 January 2011)

Supermassive black holes have been detected in all galaxies that contain bulge components when the galaxies observed were close enough so that the searches were feasible. Together with the observation that bigger black holes live in bigger bulges, this has led to the belief that black hole growth and bulge formation regulate each other. That is, black holes and bulges “coevolve”. Therefore, reports of a similar correlation between black holes and the dark matter halos in which visible galaxies are embedded have profound implications. Dark matter is likely to be nonbaryonic, so these reports suggest that unknown, exotic physics controls black hole growth. Here we show – based in part on recent measurements of bulgeless galaxies – that there is almost no correlation between dark matter and parameters that measure black holes unless the galaxy also contains a bulge. We conclude that black holes do not correlate directly with dark matter. They do not correlate with galaxy disks, either. Therefore black holes coevolve only with bulges. This simplifies the puzzle of their coevolution by focusing attention on purely baryonic processes in the galaxy mergers that make bulges.

by Dayal, Pratika
PhD Thesis

We are in the golden age for the search for high-redshift galaxies, made possible by a combination of new instruments and innovative search techniques. One of the major aims of such searches is to constrain the epoch of reionization (EoR), which marks the second major change in the ionization state of the Universe. Understanding the EoR is difficult since whilst it is galaxy evolution which drives reionization, reionization itself influences galaxy evolution through feedback effects. Unraveling the interplay of reionization and galaxy evolution is further complicated by of a lack of understanding of the metal enrichment and dust distribution in high redshift galaxies. To this end, a class of galaxies called Lyman Alpha Emitters (LAEs) have been gaining enormous popularity as probes of all these three processes. In this thesis, we couple state of the art cosmological SPH simulations (GADGET-2) with a physically motivated, self-consistent model for LAEs, so as to be able to understand the importance of the intergalactic medium (IGM) ionization state, dust and peculiar velocities in shaping their observed properties. By doing so, the aim is to gain insight on the nature of LAEs, put precious constraints on their elusive physical properties and make predictions for future instruments such as the Atacama Large Millimeter Array (ALMA). Using our LAE model in conjunction with a code that builds the MW merger tree (GAMETE), we build a bridge between the high-redshift and the local Universe. We also use SPH simulations (GADGET-2) to study the nature of the earliest galaxies that have been detected as of yet, place constraints on their contribution to reionization, and predict their detectability using the next generation of instruments, such as the James Web Space Telescope (JWST).

by Lodato, Giuseppe and Clarke, Cathie C.
7 pages, 2 figures. Accepted by MNRAS

Stimulated by recent results by Meru and Bate (2010a,b), we revisit the issue of resolution requirements for simulating self-gravitating accretion discs with Smoothed Particle Hydrodynamics (SPH). We show that the results by Meru and Bate (2010a) are consistent with those of Meru and Bate (2010b) if they are both interpreted as driven by resolution effects, therefore implying that the resolution criterion for cooling gaseous discs is a function of the imposed cooling rate. We discuss two possible numerical origins of such dependence, which are both consistent with the limited number of available data. Our results tentatively indicate that convergence for current simulations is being reached for a number of SPH particles approaching 10 millions (for a disc mass of order 10 per cent of the central object mass), which would set the critical cooling time for fragmentation at about $latex 15\Omega^{-1}$, roughly a factor two larger than previously thought. More in general, we discuss the extent to which the large number of recent numerical results are reliable or not. We argue that those results that pertain to the dynamics associated with gravitational instabilities (such as the locality of angular momentum transport, and the relationship between density perturbation and induced stress) are robust, while those pertaining to the thermodynamics of the system (such as the determination of the critical cooling time for fragmentation) can be affected by poor resolution.

by Gebhardt, Karl and Adams, Joshua and Richstone, Douglas and Lauer, Tod R. and Faber, S. M. and Gultekin, Kayhan and Murphy, Jeremy and Tremaine, Scott
12 pages, accepted for publication in the Astrophysical Journal

We present the stellar kinematics in the central 2″ of the luminous elliptical galaxy M87 (NGC 4486), using laser adaptive optics to feed the Gemini telescope integral-field spectrograph, NIFS. The velocity dispersion rises to 480 km/s at 0.2″. We combine these data with extensive stellar kinematics out to large radii to derive a black-hole mass equal to (6.6+-0.4)x10^9 Msun, using orbit-based axisymmetric models and including only the NIFS data in the central region. Including previously-reported ground-based data in the central region drops the uncertainty to 0.25×10^9 Msun with no change in the best-fit mass; however, we rely on the values derived from the NIFS-only data in the central region in order to limit systematic differences. The best-fit model shows a significant increase in the tangential velocity anisotropy of stars orbiting in the central region with decreasing radius; similar to that seen in the centers of other core galaxies. The black-hole mass is insensitive to the inclusion of a dark halo in the models — the high angular-resolution provided by the adaptive optics breaks the degeneracy between black-hole mass and stellar mass-to-light ratio. The present black-hole mass is in excellent agreement with the Gebhardt & Thomas value, implying that the dark halo must be included when the kinematic influence of the black hole is poorly resolved. This degeneracy implies that the black-hole masses of luminous core galaxies, where this effect is important, may need to be re-evaluated. The present value exceeds the prediction of the black hole-dispersion and black hole-luminosity relations, both of which predict about 1×10^9 Msun for M87, by close to twice the intrinsic scatter in the relations. The high-end of the black hole correlations may be poorly determined at present.

by Snyder, Gregory F. and Hopkins, Philip F. and Hernquist, Lars
7 pages, 2 figures, accepted for publication in ApJL

We analyze the relation between the mass of the central supermassive black hole (Mbh) and the number of globular clusters (Ngc) in elliptical galaxies and bulges as a ramification of the black hole fundamental plane, the theoretically predicted and observed multi-variable correlation between Mbh and bulge binding energy. Although the tightness of the Mbh-Ngc correlation suggests an unlikely causal link between supermassive black holes and globular clusters, such a correspondence can exhibit small scatter even if the physical relationship is indirect. We show that the relatively small scatter of the Mbh-Ngc relation owes to the mutual residual correlation of Mbh and Ngc with stellar mass when the velocity dispersion is held fixed. Thus, present observations lend evidence for feedback-regulated models in which the bulge binding energy is most important; they do not necessarily imply any `special’ connection between globular clusters and Mbh. This raises the question of why Ngc traces the formation of ellipticals and bulges sufficiently well to be correlated with binding energy.

by Schawinski, Kevin and Treister, Ezequiel and Urry, C. Megan and Cardamone, Carolin N. and Simmons, Brooke and Yi, Sukyoung K.
7 pages, 3 figures, 2 tables. Accepted for publication in the Astrophysical Journal Letters

We present the rest-frame optical morphologies of active galactic nucleus (AGN) host galaxies at 1.5<z<3, using near-infrared imaging from the Hubble Space Telescope Wide Field Camera 3, the first such study of AGN host galaxies at these redshifts. The AGN are X-ray selected from the Chandra Deep Field South and have typical luminosities of 1E42 < L_X < 1E44 erg/s. Accreting black holes in this luminosity and redshift range account for a substantial fraction of the total space density and black hole mass growth over cosmic time; they thus represent an important mode of black hole growth in the universe. We find that the majority (~80%) of the host galaxies of these AGN have low Sersic indices indicative of disk-dominated light profiles, suggesting that secular processes govern a significant fraction of the cosmic growth of black holes. That is, many black holes in the present-day universe grew much of their mass in disk-dominated galaxies and not in early-type galaxies or major mergers. The properties of the AGN host galaxies are furthermore indistinguishable from their parent galaxy population and we find no strong evolution in either effective radii or morphological mix between z~2 and z~0.05.

by Plotkin, Richard M. and Markoff, Sera and Trager, Scott C. and Anderson, Scott F.
9 pages, 5 figures, 1 table. Accepted for publication in MNRAS

We measure black hole masses for 71 BL Lac objects from the Sloan Digital Sky Survey with redshifts out to z~0.4. We perform spectral decompositions of their nuclei from their host galaxies and measure their stellar velocity dispersions. Black hole masses are then derived from the black hole mass – stellar velocity dispersion relation. We find BL Lac objects host black holes of similar masses, ~10^{8.5} M_sun, with a dispersion of 0.4 dex, similar to the uncertainties on each black hole measurement. Therefore, all BL Lac objects in our sample have the same indistinguishable black hole mass. These 71 BL Lac objects follow the black hole mass – bulge luminosity relation, and their narrow range of host galaxy luminosities confirm previous claims that BL Lac host galaxies can be treated as standard candles. We conclude that the observed diversity in the shapes of BL Lac object spectral energy distributions is not strongly driven by black hole mass or host galaxy properties.

by Harris, William E.
6 pages, 4 figures

A new revision of the McMaster catalog of Milky Way globular clusters is available. This is the first update since 2003 and the biggest single revision since the original version of the catalog published in 1996. The list now contains a total of 157 objects classified as globular clusters. Major upgrades have been made especially to the cluster coordinates, metallicities, and structural profile parameters, and the list of parameters now also includes central velocity dispersion.

NB: This paper is a stand-alone publication available only on the astro-ph archive; it will not be published separately in a journal.

by Chen, Xian and Sesana, Alberto and Madau, Piero and Liu, Fukun
16 pages, 20 figures, accepted for publication in the Astrophysical Journal

Tidal stellar disruptions have traditionally been discussed as a probe of the single, massive black holes (MBHs) that are dormant in the nuclei of galaxies. In Chen et al. (2009), we used numerical scattering experiments to show that three-body interactions between bound stars in a stellar cusp and a non-evolving “hard” MBH binary will also produce a burst of tidal disruptions, caused by a combination of the secular “Kozai effect” and by close resonant encounters with the secondary hole. Here we derive basic analytical scalings of the stellar disruption rates with the system parameters, assess the relative importance of the Kozai and resonant encounter mechanisms as a function of time, discuss the impact of general relativistic (GR) and extended stellar cusp effects, and develop a hybrid model to self-consistently follow the shrinking of an MBH binary in a stellar background, including slingshot ejections and tidal disruptions. In the case of a fiducial binary with primary hole mass M_1=10^7\msun and mass ratio q=M_2/M_1=1/81, embedded in an isothermal cusp, we derive a stellar disruption rate \dot{N_*} ~ 0.2/yr lasting ~ 3X10^5 yr. This rate is 3 orders of magnitude larger than the corresponding value for a single MBH fed by two-body relaxation, confirming our previous findings. For q<~10% of the tidal-disruption events may originate in MBH binaries.

by Psaltis, Dimitrios and Johannsen, Tim
11 pages, 11 figures, Invited Talk in Recent Developments in Gravity XIV, June 2010

The black hole in the center of the Milky Way has been observed and modeled intensely during the last decades. It is also the prime target of a number of new experiments that aim to zoom into the vicinity of its horizon and reveal the inner working of its spacetime. In this review we discuss our current understanding of the gravitational field of Sgr A* and the prospects of testing the Kerr nature of its spacetime via imaging, astrometric, and timing observations.

by Volonteri, Marta and Dotti, Massimo and Campbell, Duncan and Mateo, Mario
Submitted to ApJ

Only a small fraction of local galaxies harbor an accreting black hole, classified as an active galactic nucleus (AGN). However, many stellar systems are plausibly expected to host black holes, from globular clusters to nuclear star clusters, to massive galaxies. The mere presence of stars in the vicinity of a black hole provides a source of fuel via mass loss of evolved stars. In this paper we assess the expected luminosities of black holes embedded in stellar systems of different sizes and properties, spanning a large range of masses. We model the distribution of stars and derive the amount of gas available to a central black hole through a geometrical model. We estimate the luminosity of the black holes under simple, but physically grounded, assumptions on the accretion flow. Finally we discuss the detectability of ‘quiescent’ black holes in the local Universe.

by Amaro-Seoane, Pau and Preto, Miguel
Submitted to Class. Quantum Grav.; based on the invited plenary talk of P. Amaro-Seoane at the LISA Symposium 2010

One of the most interesting sources of gravitational waves (GWs) for LISA is the inspiral of compact objects on to a massive black hole (MBH), commonly referred to as an “extreme-mass ratio inspiral” (EMRI). The small object, typically a stellar black hole (bh), emits significant amounts of GW along each orbit in the detector bandwidth. The slowly, adiabatic inspiral of these sources will allow us to map space-time around MBHs in detail, as well as to test our current conception of gravitation in the strong regime. The event rate of this kind of source has been addressed many times in the literature and the numbers reported fluctuate by orders of magnitude. On the other hand, recent observations of the Galactic center revealed a dearth of giant stars inside the inner parsec relative to the numbers theoretically expected for a fully relaxed stellar cusp. The possibility of unrelaxed nuclei (or, equivalently, with no or only a very shallow cusp) adds substantial uncertainty to the estimates. Having this timely question in mind, we run a significant number of direct-summation $latex N-$body simulations with up to half a million particles to calibrate a much faster orbit-averaged Fokker-Planck code. We then investigate the regime of strong mass segregation (SMS) for models with two different stellar mass components. We show that, under quite generic initial conditions, the time required for the growth of a relaxed, mass segregated stellar cusp is shorter than a Hubble time for MBHs with $latex M_\bullet \lesssim 5 \times 10^6 M_\odot$ (i.e. nuclei in the range of LISA). SMS has a significant impact boosting the EMRI rates by a factor of $latex \sim 10$ for our fiducial models of Milky Way type galactic nuclei.

by Georgakakis, A. and Tsamis, Y. G. and James, B. L. and Aloisi, A.
Submitted to MNRAS

The possibility is explored that accretion on an intermediate mass black hole contributes to the ionisation of the interstellar medium of the Compact Blue Dwarf galaxy MRK996. Chandra observations set tight upper limits (99.7 per cent confidence level) in both the X-ray luminosity of the posited AGN, Lx(2-10keV)<3e40erg/s, and the black hole mass, <1e4/\lambda Msolar, where \lambda, is the Eddington ratio. The X-ray luminosity upper limit is insufficient to explain the high ionisation line [OIV]25.89\mu m, which is observed in the mid-infrared spectrum of the MRK996 and is proposed as evidence for AGN activity. This indicates that shocks associated with supernovae explosions and winds of young stars must be responsible for this line. It is also found that the properties of the diffuse X-ray emission of MRK996 are consistent with this scenario, thereby providing direct evidence for shocks that heat the galaxy's interstellar medium and contribute to its ionisation.

by Blecha, Laura and Cox, Thomas J. and Loeb, Abraham and Hernquist, Lars
29 pages, 18 figures. Submitted to MNRAS

Gravitational-wave (GW) recoil of merging supermassive black holes (SMBHs) may influence the co-evolution of SMBHs and their host galaxies. We examine this possibility using SPH/N-body simulations of gaseous galaxy mergers in which the merged BH receives a recoil kick. This enables us to follow recoiling BHs in self-consistent, evolving merger remnants. In contrast to recent studies on similar topics, we conduct a large parameter study, generating a suite of over 200 simulations with more than 60 merger models and a range of recoil velocities (vk). Our main results are as follows. (1) BHs kicked at nearly the central escape speed (vesc) may oscillate on large orbits for up to a Hubble time, but in gas-rich mergers, BHs kicked with up to ~ 0.7 vesc may be confined to the central few kpc of the galaxy, owing to gas drag and steep central potentials. (2) vesc in gas-rich mergers may increase rapidly during final coalescence, in which case trajectories may depend on the timing of the BH merger relative to the formation of the potential well. (3) Recoil events generally reduce the lifetimes of bright active galactic nuclei (AGN), but may actually extend AGN lifetimes at lower luminosities. (4) Kinematically-offset AGN (v > 800 km s^-1) may be observable for up to ~ 10 Myr either immediately after the recoil or during pericentric passages through a gas-rich remnant. (5) Spatially-offset AGN (R > 1 kpc) generally have low luminosities and lifetimes of ~ 1 – 100 Myr. (6) Rapidly-recoiling BHs may be up to ~ 5 times less massive than their stationary counterparts. This lowers the normalization of the M-sigma relation and contributes to both intrinsic and overall scatter. (7) Finally, the displacement of AGN feedback after a recoil event enhances central star formation rates, thereby extending the starburst phase of the merger and creating a denser stellar cusp. [Abridged.]

by Amaro-Seoane, Pau and Freitag, Marc Dewi
A small note of 5 pages, submitted to MNRAS letts

Two coalescing black holes (BHs) represent a conspicuous source of gravitational waves (GWs). The merger involves 17 parameters in the general case of Kerr BHs, so that a successful identification and parameter extraction of the information encoded in the waves will provide us with a detailed description of the physics of BHs. A search based on matched-filtering for characterization and parameter extraction requires the development of some $latex 10^{15}$ waveforms. If a third additional BH perturbed the system, the waveforms would not be applicable, and we would need to increase the number of templates required for a valid detection. In this letter, we calculate the probability that more than two BHs interact in the regime of strong relativity in a dense stellar cluster. We determine the physical properties necessary in a stellar system for three black holes to have a close encounter in this regime and also for an existing binary of two BHs to have a strong interaction with a third hole. In both cases the event rate is negligible. While dense stellar systems such as galactic nuclei, globular clusters and nuclear stellar clusters are the breeding grounds for the sources of gravitational waves that ground-based and space-borne detectors like Advanced LIGO and LISA will be exploring, the analysis of the waveforms in full general relativity needs only to evaluate the two-body problem. This reduces the number of templates of waveforms to create by orders of magnitude.

by Just, A. and Khan, F. M. and Berczik, P. and Ernst, A. and Spurzem, R.
22 pages, 28 figures, accepted by MNRAS

Dynamical friction leads to an orbital decay of massive objects like young compact star clusters or Massive Black Holes in central regions of galaxies. The dynamical friction force can be well approximated by Chandrasekhar’s standard formula, but recent investigations show, that corrections to the Coulomb logarithm are necessary. With a large set of N-body simulations we show that the improved formula for the Coulomb logarithm fits the orbital decay very well for circular and eccentric orbits. The local scale-length of the background density distribution serves as the maximum impact parameter for a wide range of power-law indices of -1 … -5. For each type of code the numerical resolution must be compared to the effective minimum impact parameter in order to determine the Coulomb logarithm. We also quantify the correction factors by using self-consistent velocity distribution functions instead of the standard Maxwellian often used. These factors enter directly the decay timescale and cover a range of 0.5 … 3 for typical orbits. The new Coulomb logarithm combined with self-consistent velocity distribution functions in the Chandrasekhar formula provides a significant improvement of orbital decay times with correction up to one order of magnitude compared to the standard case. We suggest the general use of the improved formula in parameter studies as well as in special applications.

by Plowman, Joseph E. and Hellings, Ronald W. and Tsuruta, Sachiko
32 pages, 21 Figures, 6 Tables; Submitted to MNRAS

A number of scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many such scenarios predict a high-redshift population of massive black holes (MBHs), with masses in the range 100 to 100000 times that of the Sun. When the Laser Interferometer Space Antenna (LISA) is finally operational, it is likely that it will detect on the order of 100 of these MBH binaries as they merge. The differences between proposed population models produce appreciable effects in the portion of the population which is detectable by LISA, so it is likely that the LISA observations will allow us to place constraints on them. However, gravitational wave detectors such as LISA will not be able to detect all such mergers nor assign precise black hole parameters to the merger, due to weak gravitational wave signal strengths. This paper explores LISA’s ability to distinguish between several MBH population models. In this way, we go beyond predicting a LISA observed population and consider the extent to which LISA observations could inform astrophysical modellers. The errors in LISA parameter estimation are applied with a direct method which generates random sample parameters for each source in a population realisation. We consider how the distinguishability varies depending on the choice of source parameters (1 or 2 parameters chosen from masses, redshift or spins) used to characterise the model distributions, with confidence levels determined by 1 and 2-dimensional tests based on the Kolmogorov-Smirnov test.

by McConnell, Nicholas J. and Ma, Chung-Pei and Graham, James R. and Gebhardt, Karl and Lauer, Tod R. and Wright, Shelley A. and Richstone, Douglas O.
21 pages, 17 figures; submitted to ApJ

We present the first direct measurement of the central black hole mass, M_BH, in NGC 6086, the Brightest Cluster Galaxy (BCG) in Abell 2162. Our investigation demonstrates for the first time that stellar dynamical measurements of M_BH in BCGs are possible beyond the nearest few galaxy clusters. We observed NGC 6086 with laser guide star adaptive optics and the integral-field spectrograph (IFS) OSIRIS at the W.M. Keck Observatory, and with the seeing-limited IFS GMOS-N at Gemini Observatory North. We combined the two IFS data sets with existing major-axis kinematics, and used axisymmetric stellar orbit models with an assumed dark matter halo to determine M_BH and the R-band stellar mass-to-light ratio, M*/L_R. The best-fit values of M_BH and M*/L_R strongly depend on the assumed dark matter halo mass, M_halo: more massive halos yield larger M_BH and smaller M*/L_R. For the most massive halo allowed within the gravitational potential of the host cluster, we find M_BH = 3.6(+1.7)(-1.1) x 10^9 M_Sun and M*/L_R = 4.6(+0.3)(-0.7) M_Sun/L_Sun (68% confidence). The correlation between M_BH and M_halo could extend to dynamical models of other galaxies with central stellar cores, and new measurements of M_BH from models with dark matter could steepen the empirical scaling relationships between black holes and their host galaxies. Further observations with adaptive optics will measure M_BH in a larger sample of BCGs, progressing toward a statistical understanding of black hole-bulge scaling relationships in the most massive galaxies.

by Moeckel, Nickolas and Clarke, Cathie J.
8 pages, submitted to MNRAS. Includes revisions per referee’s comments

We investigate the contraction of accreting protoclusters using an extension of n-body techniques that incorporates the accretional growth of stars from the gaseous reservoir in which they are embedded. Following on from Monte Carlo studies by Davis et al., we target our experiments toward populous clusters likely to experience collisions as a result of accretion-driven contraction. We verify that in less extreme star forming environments, similar to Orion, the stellar density is low enough that collisions are unimportant, but that conditions suitable for stellar collisions are much more easily satisfied in large-n clusters, i.e. n ~ 30,000 (we argue, however, that the density of the Arches cluster is insufficient for us to expect stellar collisions to have occurred in the cluster’s prior evolution). We find that the character of the collision process is not such that it is a route toward smoothly filling the top end of the mass spectrum. Instead, runaway growth of one or two extreme objects can occur within less than 1 Myr after accretion is shut off, resulting in a few objects with masses several times the maximum reached by accretion. The rapid formation of these objects is due to not just the post-formation dynamical evolution of the clusters, but an interplay of dynamics and the accretional growth of the stars. We find that accretion-driven cluster shrinkage results in a distribution of gas and stars that offsets the disruptive effect of gas expulsion, and we propose that the process can lead to massive binaries and early mass segregation in star clusters.

by Rusli, Stephanie P. and Thomas, Jens and Erwin, Peter and Saglia, Roberto P. and Nowak, Nina and Bender, Ralf
15 pages, 12 figures, accepted for publication in MNRAS

The masses of the most massive supermassive black holes (SMBHs) predicted by the M_BH-sigma and M_BH-luminosity relations appear to be in conflict. Which of the two relations is the more fundamental one remains an open question. NGC 1332 is an excellent example that represents the regime of conflict. It is a massive lenticular galaxy which has a bulge with a high velocity dispersion sigma of ~320 km/s; bulge–disc decomposition suggests that only 44% of the total light comes from the bulge. The M_BH-sigma and the M_BH-luminosity predictions for the central black hole mass of NGC 1332 differ by almost an order of magnitude. We present a stellar dynamical measurement of the SMBH mass using an axisymmetric orbit superposition method. Our SINFONI integral-field unit (IFU) observations of NGC 1332 resolve the SMBH’s sphere of influence which has a diameter of ~0.76 arcsec. The sigma inside 0.2 arcsec reaches ~400 km/s. The IFU data allow us to increase the statistical significance of our results by modelling each of the four quadrants separately. We measure a SMBH mass of (1.45 \pm 0.20) x 10^9 M_sun with a bulge mass-to-light ratio of 7.08 \pm 0.39 in the R-band. With this mass, the SMBH of NGC 1332 is offset from the M_BH-luminosity relation by a full order of magnitude but is consistent with the M_BH-sigma relation.

by Hayasaki, Kimitake
12 pages, 2 figures, submitted to ApJL

We study an accretion flow during the gravitational-wave driven evolution of binary massive black holes. After the binary orbit decays due to interacting with a massive circumbinary disk, the binary is decoupled from the circumbinary disk because the orbital-decay timescale due to emission of gravitational wave becomes shorter than the viscous timescale evaluated at the inner edge of circumbinary disk. During the subsequent evolution, the accretion disk, which is truncated at the tidal radius because of the tidal torque, also shrinks as the orbital decay. Assuming that the disk mass changed by this process is all accreted, the whole region of the disk completely becomes radiatively inefficient when the semi-major axis is several hundred Schwarzschild radii. The disk temperature can become comparable with the virial temperature there in spite of a low disk luminosity. The prompt high-energy emission is hence expected long before black hole coalescence as well as the gravitational wave signals. Binary massive black holes finally merge without accretion disks.

by Harris, Gretchen L. H. and Harris, William E.
7 pages, 4 figures; accepted for publication in MNRAS

We explore the relation between the total globular cluster population in a galaxy (N_GC) and the the mass of its central black hole (M_BH). Using a sample of 33 galaxies, twice as large as the original sample discussed by Burkert & Tremaine (2010), we find that N_GC for elliptical and spiral galaxies increases in almost precisely direct proportion to M_BH. The S0-type galaxies by contrast do not follow a clear trend, showing large scatter in M_BH at a given N_GC. After accounting for observational measurement uncertainty, we find that the mean relation defined by the E and S galaxies must also have an intrinsic or “cosmic” scatter of +-0.2 in either logN_GC or logM_BH. The residuals from this correlation show no trend with globular cluster specific frequency. We suggest that these two types of galaxy subsystems (central black hole and globular cluster system) may be closely correlated because they both originated at high redshift during the main epoch of hierarchical merging, and both require extremely high-density conditions for formation. Lastly, we note that roughly 10% of the galaxies in our sample (one E, one S, and two S0) deviate strongly from the main trend, all in the sense that their M_BH is at least 10x smaller than would be predicted by the mean relation.

by Soria, Roberto and Zampieri, Luca and Zane, Silvia and Wu, Kinwah
10 pages, accepted by MNRAS. Corrected LZ’s affiliation and updated 1 reference

We re-assess the XMM-Newton and Swift observations of HLX1, to examine the evidence for its identification as an intermediate-mass black hole. We show that the X-ray spectral and timing properties are equally consistent with an intermediate-mass black hole in a high state, or with a foreground neutron star with a luminosity of about a few times 10^{32} erg/s ~ 10^{-6} L_{Edd}, located at a distance of about 1.5 to 3 kpc. Contrary to previously published results, we find that the X-ray spectral change between the two XMM-Newton observations of 2004 and 2008 (going from power-law dominated to thermal dominated) is not associated with a change in the X-ray luminosity. The thermal component becomes more dominant (and hotter) during the 2009 outburst seen by Swift, but in a way that is consistent with either scenario.

by Burke-Spolaor, Sarah
11 Pages, 7 figures, accepted for publication in MNRAS

Using archival VLBI data for 3114 radio-luminous active galactic nuclei, we searched for binary supermassive black holes using a radio spectral index mapping technique which targets spatially resolved, double radio-emitting nuclei. Only one source was detected as a double nucleus. This result is compared with a cosmological merger rate model and interpreted in terms of (1) implications for post-merger timescales for centralisation of the two black holes, (2) implications for the possibility of “stalled” systems, and (3) the relationship of radio activity in nuclei to mergers. Our analysis suggests that the binary evolution of paired supermassive black holes (both of masses >= 1e8 Msun) spends less than 500 Myr in progression from the merging of galactic stellar cores to within the purported stalling radius for supermassive black hole pairs. The data show no evidence for an excess of stalled binary systems at small separations. We see circumstantial evidence that the relative state of radio emission between paired supermassive black holes is correlated within orbital separations of 2.5 kpc.

by Maksym, Peter and Ulmer, Melville P. and Eracleous, Michael
24 pages, including 6 figures and 2 tables Accepted for publication in the Astrophysical Journal

Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated stellar debris falls back onto the black hole itself. We examine the first results of an ongoing archival survey of galaxy clusters using Chandra and XMM-selected data, and report a likely tidal disruption flare from SDSS J131122.15-012345.6 in Abell 1689. The flare is observed to vary by a factor of >30 over at least 2 years, to have maximum L_X(0.3-3.0 keV)> 5 x 10^{42} erg s^{-1} and to emit as a blackbody with kT~0.12 keV. From the galaxy population as determined by existing studies of the cluster, we estimate a tidal disruption rate of 1.2 x 10^{-4} galaxy^{-1} year^{-1} if we assume a contribution to the observable rate from galaxies whose range of luminosities corresponds to a central black hole mass (M_bh) between 10^6 and 10^8 M_sun.

by Strubbe, Linda E. and Quataert, Eliot
14 pages, 5 figures; submitted to MNRAS

During the tidal disruption of a star by a massive black hole (BH) of mass MBH <~ 10^7 Msun, stellar debris falls back to the BH at a rate well above the Eddington rate. A fraction of this gas is subsequently blown away from the BH, producing an optically bright flare of radiation. We predict the spectra and spectral evolution of tidal disruption events, focusing on the photoionized gas outside this outflow's photosphere. The spectrum will show absorption lines that are strongly blueshifted relative to the host galaxy, very broad (0.01-0.1c), and strongest at UV wavelengths (e.g., C IV, Ly alpha, O VI), lasting ~ 1 month for a 10^6 Msun BH. Meanwhile, supernovae in galactic nuclei are a significant source of confusion in optical surveys for tidal disruption events: we estimate that nuclear Type Ia supernovae are two orders of magnitude more common than tidal disruption events at z ~ 0.1 for ground-based surveys. Nuclear Type II supernovae occur at a comparable rate but can be excluded by pre-selecting red galaxies. Supernova contamination can be reduced to a manageable level using high-resolution follow-up imaging with adaptive optics or the Hubble Space Telescope. Our predictions should help optical transient surveys capitalize on their potential for discovering tidal disruption events.

by Wiersema, Klaas and Farrell, Sean A. and Webb, Natalie A. and Servillat, Mathieu and Maccarone, Thomas J. and Barret, Didier and Godet, Olivier
5 pages, 4 figures, submitted to ApJL on 20th May 2010, accepted for publication 20th July 2010

In this Letter we report a spectroscopic confirmation of the association of HLX-1, the brightest ultra-luminous X-ray source, with the galaxy ESO 243-49. At the host galaxy distance of 95 Mpc, the maximum observed 0.2 – 10 keV luminosity is 1.2E42 erg/s. This luminosity is ~400 times above the Eddington limit for a 20 Msun black hole, and has been interpreted as implying an accreting intermediate mass black hole with a mass in excess of 500 Msun (assuming the luminosity is a factor of 10 above the Eddington value). However, a number of other ultra-luminous X-ray sources have been later identified as background active galaxies or foreground sources. It has recently been claimed that HLX-1 could be a quiescent neutron star X-ray binary at a Galactic distance of only 2.5 kpc, so a definitive association with the host galaxy is crucial in order to confirm the nature of the object. Here we report the detection of the Halpha emission line for the recently identified optical counterpart at a redshift consistent with that of ESO 243-49. This finding definitively places HLX-1 inside ESO 243-49, confirming the extreme maximum luminosity and strengthening the case for it containing an accreting intermediate mass black hole of more than 500 Msun.