by Shankar, F. and Marulli, F. and Mathur, S. and Bernardi, M. and Bournaud, F.
9 pages, 4 Figures. Accepted by A&A

There is mounting evidence that a significant fraction of Black Holes (BHs) today live in late-type galaxies, including bulge-less galaxies and those hosting pseudobulges, and are significantly undermassive with respect to the scaling relations followed by their counterpart BHs in classical bulges of similar stellar (or even bulge) mass. Here we discuss the predictions of two state-of-the-art hierarchical galaxy formation models in which BHs grow via mergers and, in one, also via disk instability. Our aim is to understand if the wealth of new data on local BH demography is consistent with standard models. We follow the merger trees of representative subsamples of BHs and compute the fractional contributions of different processes to the final BH mass. We show that the model in which BHs always closely follow the growth of their host bulges, also during late disk instabilities (i.e., bars), produces too narrow a distribution of BHs at fixed stellar mass to account for the numerous low-mass BHs now detected in later-type galaxies. Models with a looser connection between BH growth and bar instability instead predict the existence of a larger number of undermassive BHs, in better agreement with the observations. The scatter in the updated local BH-bulge mass relation (with no restriction on galaxy type) appears to be quite large when including later-type systems, but it can still be managed to be reproduced within current hierarchical models. However, the fuelling of BHs during the late bar-instability mode needs to be better quantified/improved to properly fit the data. We conclude discussing how the possibly large number of BHs in later type galaxies demands for an in-depth revision of the local BH mass function and its modelling.

by Barausse, Enrico
25 pages, 15 figures

[Abridged] [...] In this paper, we study the mass and spin evolution of massive black holes within a semianalytical galaxy-formation model that follows the evolution of dark-matter halos along merger trees, as well as that of the baryonic components (hot gas, stellar and gaseous bulges, and stellar and gaseous galactic disks). This allows us to study the mass and spin evolution of massive black holes in a self-consistent way, by taking into account the effect of the gas present in galactic nuclei both during the accretion phases and during mergers. Also, we present predictions, as a function of redshift, for the fraction of gas-rich black-hole mergers — in which the spins prior to the merger are aligned due to the gravito-magnetic torques exerted by the circumbinary disk — as opposed to gas-poor mergers, in which the orientation of the spins before the merger is roughly isotropic. These predictions may be tested by LISA or similar spaced-based gravitational-wave detectors such as eLISA/NGO or SGO.

by Devecchi, B. and Volonteri, M. and Rossi, E. M. and Colpi, M. and Zwart, S. Portegies
12 pages, MNRAS, accepted

We present results of simulations aimed at tracing the formation of nuclear star clusters (NCs) and black hole (BH) seeds, in a cosmological context. We focus on two mechanisms for the formation of BHs at high redshifts: as end-products of (1) Population III stars in metal free halos, and of (2) runaway stellar collisions in metal poor NCs. Our model tracks the chemical, radiative and mechanical feedback of stars on the baryonic component of the evolving halos. This procedure allows us to evaluate when and where the conditions for BH formation are met, and to trace the emergence of BH seeds arising from the dynamical channel, in a cosmological context. BHs start to appear already at z~30 as remnants of Population III stars. The efficiency of this mechanism begins decreasing once feedbacks become increasingly important. Around redshift z~15, BHs mostly form in the centre of mildly metal enriched halos inside dense NCs. The seed BHs that form along the two pathways have at birth a mass around 100-1000M\odot. The occupation fraction of BHs is a function of both halo mass and mass growth rate: at a given z, heavier and faster growing halos have a higher chance to form a native BH, or to acquire an inherited BH via merging of another system. With decreasing z, the probability of finding a BH shifts toward progressively higher mass halo intervals. This is due to the fact that, at later cosmic times, low mass systems rarely form a seed, and already formed BHs are deposited into larger mass systems due to hierarchical mergers. Our model predict that at z=0, all halos above 10^11M\odot should host a BH (in agreement with observational results), most probably inherited during their lifetime. Halos less massive then 10^9M\odot have a higher probability to host a native BH, but their occupation fraction decreases below 10%.

by Harko, Tiberiu and Mocanu, Gabriela
10 pages, 8 figures, accepted for publication in MNRAS

We analyze the general relativistic oscillations of thin accretion disks around compact astrophysical objects interacting with the surrounding medium through non-gravitational forces. The interaction with the external medium (a thermal bath) is modeled via a friction force, and a random force, respectively. The general equations describing the stochastically perturbed disks are derived by considering the perturbations of trajectories of the test particles in equatorial orbits, assumed to move along the geodesic lines. By taking into account the presence of a viscous dissipation and of a stochastic force we show that the dynamics of the stochastically perturbed disks can be formulated in terms of a general relativistic Langevin equation. The stochastic energy transport equation is also obtained. The vertical oscillations of the disks in the Schwarzschild and Kerr geometries are considered in detail, and they are analyzed by numerically integrating the corresponding Langevin equations. The vertical displacements, velocities and luminosities of the stochastically perturbed disks are explicitly obtained for both the Schwarzschild and the Kerr cases.

by Lousto, Carlos O. and Zlochower, Yosef and Dotti, Massimo and Volonteri, Marta
17 pages, 10 tables, 14 figures, revtex 4

We explore the newly discovered “hangup-kick” effect, which greatly amplifies the recoil for configuration with partial spin- orbital-angular momentum alignment, by studying a set of 48 new simulations of equal-mass, spinning black-hole binaries. We propose a phenomenological model for the recoil that takes this new effect into account and then use this model, in conjunction with statistical distributions for the spin magnitude and orientations, based on accretion simulations, to find the probabilities for observing recoils of several thousand km/s. In addition, we provide initial parameters, eccentricities, radiated linear and angular momentum, precession rates and remnant mass, spin, and recoils for all 48 configurations. Our results indicate that surveys exploring peculiar (redshifted or blueshifted) differential line-of-sight velocities should observe at least one case above 2000 km/s out of four thousand merged galaxies. The probability that a remnant BH receives a total recoil exceeding the ~2000 km/s escape velocity of large elliptical galaxies is ten times larger. Probabilities of recoils exceeding the escape velocity quickly rise to 5% for galaxies with escape velocities of 1000 km/s and nearly 20% for galaxies with escape velocities of 500 km/s. In addition the direction of these large recoils is strongly peaked toward the angular momentum axis, with very low probabilities of recoils exceeding 350 km/s for angles larger than 45 deg. with respect to the orbital angular momentum axis.

by King, Andrew
to appear in proceedings of `The Golden Age of Cataclysmic Variables’, Memorie Societa’ Astronomica Italiana, 2012 (F. Giovannelli and L. Sabau-Graziati eds.)

I briefly review the progress of accretion disc theory since the seminal paper of Shakura and Sunyaev.

by Zubovas, Kastytis and King, Andrew R.
6 pages, 1 figure, 2 tables; accepted for publication in ApJ Letters

It is widely suspected that AGN activity ultimately sweeps galaxies clear of their gas. We work out the observable properties required to achieve this. Large-scale AGN-driven outflows should have kinetic luminosities $latex \sim \eta\le/2 \sim 0.05\le$ and momentum rates $latex \sim 20\le/c$, where $latex \le$ is the Eddington luminosity of the central black hole and $latex \eta\sim 0.1$ its radiative accretion efficiency. This creates an expanding two-phase medium in which molecular species coexist with hot gas, which can persist after the central AGN has switched off. This picture predicts outflow velocities $latex \sim 1000 – 1500$ km\,s$latex ^{-1}$ and mass outflow rates up to $latex 4000 \msun\,{\rm yr}^{-1}$ on kpc scales, fixed mainly by the host galaxy velocity dispersion (or equivalently black hole mass). All these features agree with those of outflows observed in galaxies such as Mrk231. This strongly suggests that AGN activity is what sweeps galaxies clear of their gas on a dynamical timescale and makes them red and dead. We suggest future observational tests of this picture.

by Johannsen, Tim and Psaltis, Dimitrios and Gillessen, Stefan and Marrone, Daniel P. and Ozel, Feryal and Doeleman, Sheperd S. and Fish, Vincent L.
7 pages, 4 figures, 2 tables, submitted to ApJ

Dynamical mass measurements to date have allowed determinations of the mass M and the distance D of the galactic center black hole Sgr A* as well as those of other nearby supermassive black holes. In the case of Sgr A*, these measurements are limited by a degeneracy between the mass and distance scaling roughly as M ~ D^2. Future very-long baseline interferometric observations will image a bright and narrow ring surrounding the shadow of the supermassive black hole, if its accretion flow is optically thin. In this paper, we show that the combination of dynamical measurements and VLBI imaging of the ring of Sgr A* breaks the degeneracy between mass and distance. We estimate the signal to noise ratio of near-future VLBI arrays consisting of five to six stations and simulate measurements of the mass and distance of Sgr A* using the expected size of the ring image and existing data of stellar ephemerides. We demonstrate that VLBI observations at 1 mm can already improve the error on the mass by a factor of three compared to the results from the monitoring of stellar orbits alone; observations at 0.5 mm can reduce the error by as much as a factor of 7.5. In addition, we calculate the angular sizes of the bright rings of a number of other nearby supermassive black holes and identify the optimal targets besides Sgr A* that could be imaged by a ground-based VLBI array or a future space-VLBI mission allowing for refined mass measurements.

by Binétruy, Pierre and Bohé, Alejandro and Caprini, Chiara and Dufaux, Jean-François
46 pages, 12 figures

We review the main cosmological backgrounds of gravitational waves accessible to detectors in space sensitive to the range $latex 10^{-4}$ to $latex 10^{-1}$ Hz, with a special emphasis on those backgrounds due to phase transitions or networks of cosmic strings. We apply this to identify the scientific potential of the NGO/eLISA mission of ESA, regarding the detectability of such cosmological backgrounds.

by Nixon, Chris and King, Andrew
8 pages, 9 figures. Accepted for publication in MNRAS

We simulate the viscous evolution of an accretion disc around a spinning black hole. In general any such disc is misaligned, and warped by the Lense-Thirring effect. Unlike previous studies we use effective viscosities constrained to be consistent with the internal fluid dynamics of the disc. We find that nonlinear fluid effects, which reduce the effective viscosities in warped regions, can promote the breaking of the disc into two distinct planes. This occurs when the Shakura & Sunyaev dimensionless viscosity parameter alpha is ~ 45 degrees. The break can be a long-lived feature, propagating outwards in the disc on the usual alignment timescale, after which the disc is fully co- or counter-aligned with the hole. Such a break in the disc may be significant in systems where we know the inclination of the outer accretion disc to the line of sight, such as some X-ray binaries: the inner disc, and so any jets, may be noticeably misaligned with respect to the orbital plane.

by Vasiliev, E. and Athanassoula, E.
13 pages, 10 figures

We use both N-body simulations and integration in fixed potentials to explore the stability and the long-term secular evolution of self-consistent, equilibrium, non-rotating, triaxial spheroidal galactic models. More specifically, we consider Dehnen models built with the Schwarzschild method. We show that short-term stability depends on the degree of velocity anisotropy (radially anisotropic models are subject to rapid development of radial-orbit instability). Long-term stability, on the other hand, depends mainly on the properties of the potential, and in particular, on whether it admits a substantial fraction of strongly chaotic orbits. We show that in the case of a weak density cusp (gamma=1 Dehnen model) the N-body model is remarkably stable, while the strong-cusp (gamma=2) model exhibits substantial evolution of shape away from triaxiality, which we attribute to the effect of chaotic diffusion of orbits. The different behaviour of these two cases originates from the different phase space structure of the potential; in the weak-cusp case there exist numerous resonant orbit families that impede chaotic diffusion. We also find that it is hardly possible to affect the rate of this evolution by altering the fraction of chaotic orbits in the Schwarzschild model, which is explained by the fact that the chaotic properties of an orbit are not preserved by the N-body evolution. There are, however, parameters in Schwarzschild modelling that do affect the stability of an N-body model, so we discuss the recipes how to build a `good’ Schwarzschild model.

by Crocker, Roland M.
30 pages, 35 figures

We construct a simple model of the star-formation- (and resultant supernova-) driven mass and energy flows through the inner ~200 pc (in diameter) of the Galaxy. Our modelling is constrained, in particular, by the non-thermal radio continuum and {\gamma}-ray signals detected from the region. The modelling points to a current star-formation rate of 0.04 – 0.12 M\msun/year at 2{\sigma} confidence within the region with best-fit value in the range 0.08 – 0.12 M\msun/year which – if sustained over 10 Gyr – would fill out the ~ 10^9 M\msun stellar population of the nuclear bulge. Mass is being accreted on to the Galactic centre (GC) region at a rate ~0.3M\msun/year. The region’s star-formation activity drives an outflow of plasma, cosmic rays, and entrained, cooler gas. Neither the plasma nor the entrained gas reaches the gravitational escape speed, however, and all this material fountains back on to the inner Galaxy. The system we model can naturally account for the recently-observed ~> 10^6 ‘halo’ of molecular gas surrounding the Central Molecular Zone out to 100-200 pc heights. The injection of cooler, high-metallicity material into the Galactic halo above the GC may catalyse the subsequent cooling and condensation of hot plasma out of this region and explain the presence of relatively pristine, nuclear-unprocessed gas in the GC. The plasma outflow from the GC reaches a height of a few kpc and is compellingly related to the recently-discovered Fermi Bubbles. Our modelling demonstrates that ~ 10^9 M\msun of hot gas is processed through the GC over 10 Gyr. We speculate that the continual star-formation in the GC over the age of the Milky Way has kept the SMBH in a quiescent state thus preventing it from significantly heating the coronal gas, allowing for the continual accretion of gas on to the disk and the sustenance of star formation on much wider scales in the Galaxy [abridged].

by Barai, Paramita and Proga, Daniel and Nagamine, Kentaro
23 pages, 11 figures, submitted. Uploaded version contains low-resolution color figures. Version with high-resolution figures can be found at: http://www.physics.unlv.edu/~barai/AllPages/Images-Movies/BHaccr_MultiPhase.pdf

(Abridged) We investigate non-spherical behavior of gas accreting onto a central supermassive black hole performing simulations using the SPH code GADGET-3 including radiative cooling and heating by the central X-ray source. As found in earlier 1D studies, our 3D simulations show that the accretion mode depends on the X-ray luminosity (L_X) for a fixed density at infinity and accretion efficiency. In the low L_X limit, gas accretes in a stable, spherically symmetric fashion. In the high L_X limit, the inner gas is significantly heated up and expands, reducing the central mass inflow rate. The expanding gas can turn into a strong enough outflow capable of expelling most of the gas at larger radii. For some intermediate L_X, the accretion flow becomes unstable developing prominent non-spherical features, the key reason for which is thermal instability (TI) as shown by our analyses. Small perturbations of the initially spherically symmetric accretion flow that is heated by the intermediate L_X quickly grow to form cold and dense clumps surrounded by overheated low density regions. The cold clumps continue their inward motion forming filamentary structures; while the hot infalling gas slows down because of buoyancy and can even start outflowing through the channels in between the filaments. We found that the ratio between the mass inflow rates of the cold and hot gas is a dynamical quantity depending on several factors: time, spatial location, and L_X; and ranges between 0 and 4. We briefly discuss astrophysical implications of such TI-driven fragmentation of accreting gas on the formation of clouds in narrow and broad line regions of AGN, the formation of stars, and the observed variability of the AGN luminiosity.

by Healy, James and Bode, Tanja and Haas, Roland and Pazos, Enrique and Laguna, Pablo and Shoemaker, Deirdre M. and Yunes, Nicolás
4 pages, 5 figures, 1 table

Gravitational wave observations will probe non-linear gravitational interactions and thus enable strong tests of Einstein’s theory of general relativity. We present a numerical relativity study of the late inspiral and merger of binary black holes in scalar-tensor theories of gravity. We consider black hole binaries in an inhomogeneous scalar field, specifically binaries inside a scalar field bubble, in some cases with a potential. We calculate the emission of dipole radiation. We also show how these configurations trigger detectable differences between gravitational waves in scalar-tensor gravity and the corresponding waves in general relativity. We conclude that, barring an external mechanism to induce dynamics in the scalar field, scalar-tensor gravity binary black holes alone are not capable of awaking a dormant scalar field, and are thus observationally indistinguishable from their general relativistic counterparts.

by Gillessen, S. and Genzel, R. and Fritz, T. K. and Quataert, E. and Alig, C. and Burkert, A. and Cuadra, J. and Eisenhauer, F. and Pfuhl, O. and Dodds-Eden, K. and Gammie, C. F. and Ott, T.
in press at Nature

Measurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* at the Galactic Centre is a black hole four million times the mass of the Sun. With the exception of modest X-ray and infrared flares, Sgr A* is surprisingly faint, suggesting that the accretion rate and radiation efficiency near the event horizon are currently very low. Here we report the presence of a dense gas cloud approximately three times the mass of Earth that is falling into the accretion zone of Sgr A*. Our observations tightly constrain the cloud’s orbit to be highly eccentric, with an innermost radius of approach of only ~3,100 times the event horizon that will be reached in 2013. Over the past three years the cloud has begun to disrupt, probably mainly through tidal shearing arising from the black hole’s gravitational force. The cloud’s dynamic evolution and radiation in the next few years will probe the properties of the accretion flow and the feeding processes of the super-massive black hole. The kilo-electronvolt X-ray emission of Sgr A* may brighten significantly when the cloud reaches pericentre. There may also be a giant radiation flare several years from now if the cloud breaks up and its fragments feed gas into the central accretion zone.

by Dubois, Yohan and Pichon, Christophe and Haehnelt, Martin and Kimm, Taysun and Slyz, Adrianne and Devriendt, Julien and Pogosyan, Dmitry
16 pages, 12 figures, submitted to MNRAS

We use cosmological hydrodynamical simulations to show that a significant fraction of the gas in high redshift rare massive halos falls nearly radially to their very centre on extremely short timescales. This process results in the formation of very compact bulges with specific angular momentum a factor 5-30$latex smaller than the average angular momentum of the baryons in the whole halo. Such low angular momentum originates both from segregation and effective cancellation when the gas flows to the centre of the halo along well defined cold filamentary streams. These filaments penetrate deep inside the halo and connect to the bulge from multiple rapidly changing directions. Structures falling in along the filaments (satellite galaxies) or formed by gravitational instabilities triggered by the inflow (star clusters) further reduce the angular momentum of the gas in the bulge. Finally, the fraction of gas radially falling to the centre appears to increase with the mass of the halo; we argue that this is most likely due to an enhanced cancellation of angular momentum in rarer halos which are fed by more isotropically distributed cold streams. Such an increasingly efficient funnelling of low-angular momentum gas to the centre of very massive halos at high redshift may account for the rapid pace at which the most massive supermassive black holes grow to reach observed masses around $10^9$latex M$_\odot$ at an epoch when the Universe is barely 1 Gyr old.

by Erwin, Peter and Gadotti, Dimitri
pdflatex, 10 pages, 4 figures. Invited paper for Advances in Astronomy special issue: “Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes”

Studies have suggested that there is a strong correlation between the masses of nuclear star clusters (NSCs) and their host galaxies, a correlation which said to be an extension of the well-known correlations between supermassive black holes (SMBHs) and their host galaxies. But careful analysis of disk galaxies — including 2D bulge/disk/bar decompositions — shows that while SMBHs correlate with the stellar mass of the bulge component of galaxies, the masses of NSCs correlate much better with the total galaxy stellar mass. In addition, the mass ratio M_nsc/M_star,tot for NSCs in spirals (at least those with Hubble types Sc and later) is typically an order of magnitude smaller than the mass ratio M_bh/M_star, bulge of SMBHs. The absence of a universal “central massive object” correlation argues against common formation and growth mechanisms for both SMBHs and NSCs. We also discuss evidence for a break in the NSC-host galaxy correlation: galaxies with Hubble types earlier than Sbc appear to host systematically more massive NSCs than do types Sc and later.

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 Alexander, David M. and Hickox, Ryan C.
42 pages, 8 figures; Extensive review to appear in New Astronomy Reviews

Massive black holes (BHs) are at once exotic and yet ubiquitous, residing in the centers of massive galaxies in the local Universe. Recent years have seen remarkable advances in our understanding of how these BHs form and grow over cosmic time, during which they are revealed as active galactic nuclei (AGN). However, despite decades of research, we still lack a coherent picture of the physical drivers of BH growth, the connection between the growth of BHs and their host galaxies, the role of large-scale environment on the fueling of BHs, and the impact of BH-driven outflows on the growth of galaxies. In this paper we review our progress in addressing these key issues, motivated by the science presented at the “What Drives the Growth of Black Holes?” workshop held at Durham on 26th-29th July 2010, and discuss how these questions may be tackled with current and future facilities.

by Liu, K. and Wex, N. and Kramer, M. and Cordes, J. M. and Lazio, T. J. W.
12 pages, 10 Figures, accepted for publication in ApJ

The discovery of radio pulsars in compact orbits around Sgr A* would allow an unprecedented and detailed investigation of the spacetime of the supermassive black hole. This paper shows that pulsar timing, including that of a single pulsar, has the potential to provide novel tests of general relativity, in particular its cosmic censorship conjecture and no-hair theorem for rotating black holes. These experiments can be performed by timing observations with 100 micro-second precision, achievable with the Square Kilometre Array for a normal pulsar at frequency above 15 GHz. Based on the standard pulsar timing technique, we develop a method that allows the determination of the mass, spin, and quadrupole moment of Sgr A*, and provides a consistent covariance analysis of the measurement errors. Furthermore, we test this method in detailed mock data simulations. It seems likely that only for orbital periods below ~0.3 yr is there the possibility of having negligible external perturbations. For such orbits we expect a ~10^-3 test of the frame dragging and a ~10^-2 test of the no-hair theorem within 5 years, if Sgr A* is spinning rapidly. Our method is also capable of identifying perturbations caused by distributed mass around Sgr A*, thus providing high confidence in these gravity tests. Our analysis is not affected by uncertainties in our knowledge of the distance to the Galactic center, R0. A combination of pulsar timing with the astrometric results of stellar orbits would greatly improve the measurement precision of R0.

by Berger, E. and Zauderer, A. and Pooley, G. G. and Soderberg, A. M. and Sari, R. and Brunthaler, A. and Bietenholz, M. F.
Submitted to ApJ; 22 pages, 2 tables, 9 figures

We present continued radio observations of the tidal disruption event SwiftJ164449.3+573451 extending to \sim216 days after discovery. The data are part of a long-term program to monitor the expansion and energy scale of the relativistic outflow, and to trace the parsec-scale environment around a previously-dormant supermassive black hole (SMBH). The new observations reveal a significant change in the radio evolution starting at \sim1 month, with a brightening at all frequencies that requires an increase in the energy by about an order of magnitude, and an overall density profile around the SMBH of rho \propto r^{-3/2} (0.1-1.2 pc) with a significant flattening at r\sim0.4-0.6 pc. The increase in energy cannot be explained with continuous injection from an L \propto t^{-5/3} tail, which is observed in the X-rays. Instead, we conclude that the relativistic jet was launched with a wide range of Lorentz factors, obeying E(>Gamma) \propto Gamma^{-2.5}. The similar ratio of duration to dynamical timescale for Sw1644+57 and GRBs suggests that this result may be applicable to GRBs as well. The radial density profile may be indicative of Bondi accretion, with the inferred flattening at r\sim0.5 pc in good agreement with the Bondi radius for a \sim10^6 M_sun black hole. The density at \sim0.5 pc is about a factor of 30 times lower than inferred for the Milky Way galactic center, potentially due to a smaller number of mass-shedding massive stars. From our latest observations (\sim216 d) we find that the jet energy is E_{iso}\sim5×10^{53} erg (E_j\sim2.4×10^{51} erg for theta_j=0.1), the radius is r\sim1.2 pc, the Lorentz factor is Gamma\sim2.2, the ambient density is n\sim0.2 cm^{-3}, and the projected size is r_{proj}\sim25 microarcsec. Assuming no future changes in the observed evolution we predict that the radio emission from Sw1644+57 should be detectable with the EVLA for several decades, and will be resolvable with VLBI in a few years.

by Kelly, Brandon C. and Merloni, Andrea
40 pages, 7 figures, review paper accepted for the Advances in Astronomy Special Issue “Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes”

The black hole mass function of supermassive black holes describes the evolution of the distribution of black hole mass. It is one of the primary empirical tools available for mapping the growth of supermassive black holes and for constraining theoretical models of their evolution. In this review we discuss methods for estimating the black hole mass function, including their advantages and disadvantages. We also review the results of using these methods for estimating the mass function of both active and inactive black holes. In addition, we review current theoretical models for the growth of supermassive black holes that predict the black hole mass function. We conclude with a discussion of directions for future research which will lead to improvement in both empirical and theoretical determinations of the mass function of supermassive black holes.

by Lauer, Tod R. and Bender, Ralf and Kormendy, John and Rosenfield, Philip and Green, Richard F.
29 pages, 11 figures (3 color); Astrophysical Journal accepted

We obtained U_330 and B band images of the M31 nucleus using the High Resolution Camera of the Advanced Camera for Surveys on board the Hubble Space Telescope (HST). The spatial resolution in the U_330-band, 0.03″ FWHM, or 0.1 pc at M31, is sufficient to resolve the outskirts of the compact cluster (P3) of UV-bright stars surrounding the M31 black hole. The center of the cluster is marked by an extended source that is both brighter and redder than the other point sources within P3; it is likely to be a blend of several bright stars. We hypothesize that it marks the location of the M31 black hole. Both stellar photometry and a surface brightness fluctuation analysis, show that the P3 stellar population is consistent with early-type main sequence stars formed in a ~100 – ~200 Myr old starburst population. Evolutionary tracks of post early asymptotic giant-branch stars, associated with late-stage evolution of an old population, also traverse the U and U-B domain occupied by the P3 stars; but we argue that only a few stars could be accounted for that way. PEAGB evolution is very rapid, and there is no progenitor population of red giants associated with P3. The result that P3 comprises young stars is consistent with inferences from earlier HST observations of the integrated light of the cluster. Like the Milky Way, M31 harbors a black hole closely surrounded by apparently young stars.

by Treister, Ezequiel and Urry, C. Megan
33 pages, 20 figures, review paper accepted for the Advances in Astronomy Special Issue “Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes”

Significant progress has been made in the last few years on understanding how supermassive black holes form and grow. In this paper, we begin by reviewing the spectral signatures of Active Galactic Nuclei (AGN) ranging from radio to hard X-ray wavelengths. We then describe the most commonly used methods to find these sources, including optical/UV, radio, infrared and X-ray emission and optical emission lines. We then describe the main observational properties of the obscured and unobscured AGN population. Finally, we summarize the cosmic history of black hole accretion, i.e., when in the history of the Universe supermassive black holes were getting most of their mass. We finish with a summary of open questions and a description of planned and future observatories that are going to help answer them.

by Regimbau, Tania and Giampanis, Stefanos and Siemens, Xavier and Mandic, Vuk
21 pages, 11 figures, submitted to PRD

In the era of the next generation of gravitational wave experiments a stochastic background from cusps of cosmic (super)strings is expected to be probed and, if not detected, to be significantly constrained. A popcorn-like background can be, for part of the parameter space, as pronounced as the (Gaussian) continuous contribution from unresolved sources that overlap in frequency and time. We study both contributions from unresolved cosmic string cusps over a range of frequencies relevant to ground based interferometers, such as LIGO/Virgo second generation (AdLV) and Einstein Telescope (ET) third generation detectors, the space antenna LISA and Pulsar Timing Arrays (PTA). We compute the sensitivity (at $latex 2 \sigma$ level) in the parameter space for AdLV, ET, LISA and PTA. We conclude that the popcorn regime is complementary to the continuous background. Its detection could therefore enhance confidence in a stochastic background detection and possibly help determine fundamental string parameters such as the string tension and the reconnection probability.

by Jeon, Myoungwon and Pawlik, Andreas H. and Greif, Thomas H. and Glover, Simon C. O. and Bromm, Volker and Milosavljevic, Milos and Klessen, Ralf S.
17 pages, 14 figures

We study how the first galaxies were assembled under feedback from the accretion onto a central black hole (BH) that is left behind by the first generation of metal-free stars through self-consistent, cosmological simulations. X-ray radiation from the accretion of gas onto BH remnants of Population III (Pop III) stars, or from high-mass X-ray binaries (HMXBs), again involving Pop III stars, influences the mode of second generation star formation. We track the evolution of the black hole accretion rate and the associated X-ray feedback starting with the death of the Pop III progenitor star inside a minihalo and following the subsequent evolution of the black hole as the minihalo grows to become an atomically cooling galaxy. We find that X-ray photoionization heating from a stellar-mass BH is able to quench further star formation in the host halo at all times before the halo enters the atomic cooling phase. X-ray radiation from a HMXB, assuming a luminosity close to the Eddington value, exerts an even stronger, and more diverse, feedback on star formation. It photoheats the gas inside the host halo, but also promotes the formation of molecular hydrogen and cooling of gas in the intergalactic medium and in nearby minihalos, leading to a net increase in the number of stars formed at early times. Our simulations further show that the radiative feedback from the first BHs may strongly suppress early BH growth, thus constraining models for the formation of supermassive BHs.

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 Wyithe, Stuart and Loeb, Abraham
10 pages, 4 figures. Submitted to MNRAS

We identify a physical mechanism that would have resulted in rapid, obscured growth of seed super-massive black-holes in galaxies at z>6. Specifically, we find that the density at the centre of typical high redshift galaxies was at a level where the Bondi accretion rate implies a diffusion speed of photons that was slower than the gravitational infall velocity, resulting in photons being trapped within the accretion flow and advected into the black-hole. We show that there is a range of black-hole masses (M_bh ~ 10^3-10^5 solar masses) where the accretion flow traps radiation, corresponding to black-holes that were massive enough to generate a photon trapping accretion flow, but small enough that their Bondi radii did not exceed the isothermal scale height of self-gravitating gas. Under these conditions we find that the accretion reaches levels far in excess of the Eddington rate. A prediction of this scenario is that X-ray number counts of active galactic nuclei at z>6 would exhibit a cutoff at the low luminosities corresponding to black-hole masses below ~10^5 solar masses. At low redshifts we find photon trapping to be unimportant because it could only occur in rare low spin halos, and would require black-hole masses in excess of expectations from the observed black-hole – halo mass relation. The super-Eddington growth of ~10^5 solar mass seed black-holes at high redshift may have provided a natural acceleration towards the growth of super-massive black-holes at z~6-7, less than a billion years after the Big Bang.

by Shankar, Francesco and Weinberg, David H. and Miralda-Escude’, Jordi
27 pages, 16 Figures. Submitted to MNRAS

We develop semi-empirical models of the supermassive black hole and active galactic nucleus (AGN) populations, which incorporate the black hole growth implied by the observed AGN luminosity function assuming a radiative efficiency \epsilon, and a distribution of Eddington ratios \lambda. By generalizing these continuity-equation models to allow a distribution P(\lambda|mbh,z) we are able to draw on constraints from observationally estimated P(\lambda) distributions and active galaxy fractions while accounting for the luminosity thresholds of observational samples. We consider models with a Gaussian distribution of log \lambda, and Gaussians augmented with a power-law tail to low \lambda. Within our framework, reproducing the high observed AGN fractions at low redshift requires a characteristic Eddington ratio \lambda_c that declines at late times, and matching observed Eddington ratio distributions requires P(\lambda) that broadens at low redshift. To reproduce the observed increase of AGN fraction with black hole or galaxy mass, we also require a \lambda_c that decreases with increasing black hole mass, reducing the AGN luminosity associated with the most massive black holes. Finally, achieving a good match to the high mass end of the local black hole mass function requires an increased radiative efficiency at high black hole mass. We discuss the potential impact of black hole mergers or a \lambda-dependent bolometric correction, and we compute evolutionary predictions for black hole and galaxy specific accretion rates. Despite the flexibility of our framework, no one model provides a good fit to all the data we consider.

by Lamastra, Alessandra and Menci, Nicola and Fiore, Fabrizio and Di Porto, Cinzia and Amendola, Luca
19 pages, 6 figures, accepted to MNRAS

We compute the number density of massive Black Holes (BHs) at the centre of galaxies at z=6 in different Dynamical Dark Energy (DDE) cosmologies, and compare it with existing observational lower limits, to derive constraints on the evolution of the Dark Energy equation of state parameter w. Our approach only assumes the canonical scenario for structure formation from the collapse of overdense regions of the Dark Matter dominated primordial density field on progressively larger scales; the Black Hole accretion and merging rate have been maximized in the computation so as to obtain robust constraints on w and on its look-back time derivative w_a. Our results provide independent constraints complementary to those obtained by combining Supernovae, Cosmic Microwave Background and Baryonic Acoustic Oscillations; while the latter concern combinations of w_0 and w_a leaving the time evolution of the state parameter w_a highly unconstrained, the BH abundance mainly provide upper limits on w_a, only weakly depending on w_0. Combined with the existing constraints, our results significantly restrict the allowed region in DDE parameter space, ruling out DDE models not providing cosmic time and fast growth factor large enough to allow for the building up of the observed abundance of BHs; in particular, models with -1.2 \leq w_0 \leq -1 and positive redshift evolution w_a > 0.8 – completely consistent with previous constraints – are strongly disfavoured by our independent constraints from BH abundance. Such range of parameters corresponds to “Quintom” DDE models, with w crossing -1 starting from larger values.

by Krolik, Julian H. and Piran, Tsvi

Tidal disruption of main sequence stars by black holes has generally been thought to lead to a signal dominated by UV emission. If, however, the black hole spins rapidly and the poloidal magnetic field intensity on the black hole horizon is comparable to the inner accretion disk pressure, a powerful jet may form whose luminosity can easily exceed the thermal UV luminosity. When the jet beam points at Earth, its non-thermal luminosity can dominate the emitted spectrum. The thermal and non-thermal components decay differently with time. In particular, the thermal emission should remain roughly constant for a significant time after the period of maximum accretion, beginning to diminish only after a delay, whereas after the peak accretion rate, the non-thermal jet emission decays, but then reaches a plateau. When the newly-found flare source Swift J2058 is analyzed in terms of this model, it is found to be consistent with an event in which a main sequence solar-type star is disrupted by a black hole of mass at least $latex \sim 10^7 M_{\odot}$. Swift may have already observed the beginning of the flat phase in the non-thermal emission from this source. Optical photometry over the first $latex \simeq 40$ d of this flare is also consistent with this picture, but there is a large uncertainty in the bolometric correction. We suggest that future searches for main sequence tidal disruptions use methods sensitive to jet radiation as well as to thermal UV radiation.

by Gaskell, C. Martin
SF2A-2011: Proceedings of the 2011 annual meeting of the French Society of Astronomy and Astrophysics. G. Alecian, K. Belkacem, S. Collin, R. Samadi and D. Valls-Gabaud (eds), p. 573. 6 pages, 4 figures

A simple refinement is proposed to the Dibai method for determining black hole masses in type-1 thermal AGNs. Comparisons with reverberation mapping black hole masses and host galaxy bulge properties suggest that the method is accurate to +/- 0.15 dex. Contrary to what was thought when the black hole mass – stellar velocity dispersion (”M – sigma”) relationship was first discovered, it does not have a lower dispersion than the black hole mass – bulge luminosity (”M – L”) relationship. The dispersion in the M – L relationship for AGNs decreases strongly with increasing black hole mass or bulge luminosity. This is naturally explained as a consequence of the black hole – bulge relationships being the result of averaging due to mergers. Simulations show that the decrease in dispersion in the M – L relationship with increasing mass is in qualitative agreement with being driven by mergers. The large scatter in AGN black hole masses at lower masses rules out significant AGN feedback. A non-causal origin of the correlations between black holes and bulges explains the frequent lack of supermassive black holes in late-type galaxies, and the lack of correlation of black hole mass with pseudo-bulges.

by Willott, Chris J.
4 pages, 2 figures, ApJ Letters, in press

It has been claimed that there is a large population of obscured, accreting black holes at high-redshift and that the integrated black hole density at z=6 as inferred from X-ray observations is ~100 times greater than inferred from optical quasars. I have performed a stacking analysis of very deep Chandra X-ray data at the positions of photometrically-selected z=6 galaxy candidates. It is found that there is no evidence for a stacked X-ray signal in either the soft (0.5-2 keV) or hard (2-8 keV) X-ray bands. Previous work which reported a significant signal is affected by an incorrect method of background subtraction which underestimates the true background within the target aperture. The puzzle remains of why the z=6 black hole mass function has such a flat slope and a low normalization compared to the stellar mass function.

by Banerjee, Sambaran and Kroupa, Pavel
14 pages, 4 figures. Published in The Astrophysical Journal Letters

Among the most explored directions in the study of dense stellar systems is the investigation of the effects of the retention of supernova remnants, especially that of the massive stellar remnant black holes (BHs), in star clusters. By virtue of their eventual high central concentration, these stellar mass BHs potentially invoke a wide variety of physical phenomena, the most important ones being emission of gravitational waves (GWs), formation of X-ray binaries, and modification of the dynamical evolution of the cluster. Here we propose, for the first time, that rapid removal of stars from the outer parts of a cluster by the strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster, which appears as a star cluster that is gravitationally bound by an invisible mass. We study the formation and properties of such systems through direct N-body computations and estimate that they can be present in significant numbers in the inner region of the Milky Way. We call such objects “dark star clusters” (DSCs) as they appear dimmer than normal star clusters of similar mass and they comprise a predicted, new class of entities. The finding of DSCs will robustly cross-check BH retention; they will not only constrain the uncertain natal kicks of BHs, thereby the widely debated theoretical models of BH formation, but will also pinpoint star clusters as potential sites for GW emission for forthcoming ground-based detectors such as the Advanced LIGO. Finally, we also discuss the relevance of DSCs for the nature of IRS 13E.

by Mancini, Luigi and Feoli, Antonio
11 pages, 8 figures, to appear in Astronomy & Astrophysics

Thanks to the angular resolution of modern telescopes and kinematic models, the existence of supermassive black holes (SMBHs) in the inner part of galaxies has been established on quite solid grounds. A possible correlation between the mass of SMBHs and the evolutionary state of their host galaxies is expected. Based on the recent 2D decomposition of mid-infrared Spiter/IRAC images of local galaxies with M_bh measurements, we investigated various scaling laws, studying what the best predictor of the mass of the central SMBHs is. We focused on the M_bh-M_G sigma^2 law, the relation between the mass of SMBHs and the kinetic energy of random motions of the corresponding host galaxies. In order to find the best fit for each of the scaling laws examined, we performed a least-squares regression of M_bh on x for the considered sample of galaxies, x being a whatever known parameter of the galaxy bulge. Our analysis shows that M_bh-M_G sigma^2 law fits the examined experimental data successfully as much as the other known scaling laws and shows a value of chi^2 better than the others, a result which is consistent with previous determinations. This means that a combination of sigma and M_G could be necessary to drive the correlations between M_bh and other bulge properties. This issue has been investigated by a careful analysis of the residuals of the various relations. In order to avoid rushed conclusions on galaxy activity and evolution, the indirect inferring of M_bh from the kinetic energy of random motions should be considered, especially when applied to higher redshift galaxies. This statement is suggested by a reanalysis of the SDSS data used to study the SMBH growth in the nearby Universe. Adopting the M_bh-M_G sigma^2 relation instead of the M_bh-sigma, a radio-quiet/radio-loud dichotomy appears in the SMBH mass distribution of the corresponding SDSS early-type AGN galaxies.

by Chen, Songbai and Jing, Jiliang
13 pages, 5 figures. References added, Expanded discussion of the marginally stable orbit and its consequence. arXiv admin note: substantial text overlap with arXiv:1106.5183

We study the accretion process in the thin disk around a rotating non-Kerr black hole with a deformed parameter and an unbound rotation parameter. Our results show that the presence of the deformed parameter $latex \epsilon$ modifies the standard properties of the disk. For the case in which the black hole is more oblate than a Kerr black hole, the larger deviation leads to the smaller energy flux, the lower radiation temperature and the fainter spectra luminosity in the disk. For the black hole with positive deformed parameter, we find that the effect of the deformed parameter on the disk becomes more complicated. It depends not only on the rotation direction of the black hole and the orbit particles, but also on the sign of the difference between the deformed parameter $latex \epsilon$ and a certain critical value $latex \epsilon_{c}$. These significant features in the mass accretion process may provide a possibility to test gravity in the strong field regime in future astronomical observations.

by Park, KwangHo and Ricotti, Massimo
27 pages, 10 figures, submitted to ApJ, for associated mpeg files, see http://www.astro.umd.edu/~kpark/research.html

In this paper, the second of a series on radiation-regulated accretion onto black holes(BHs) from galactic scales, we focus on the effects that radiation pressure and angular momentum of the gas have on the periodic and short-lived luminosity bursts found when thermal pressure of the ionized sphere around the BH regulates the accretion rate. Our simulations focus on intermediate-mass BH, but we derive general scaling relationships that are solutions of the classic Bondi problem when radiation feedback is considered. We find that for ambient gas densities(n) exceeding a critical value n (5×10^6 cm^{-3})/M_2, where M_2 is the mass of the BH in units of 100 solar masses, the period of the oscillations decreases rapidly and the duty cycle increases from 6% to 50%. However, the maximum and mean accretion rates become Eddington limited only if n>n_Edd n_cr/T_4 where T_4 is the ambient gas temperature in units of 10^4 K. In the sub-Eddington regime, the mean accretion rate onto BH is about 1% T_4^{2.5} of the Bondi rate, thus is proportional to the thermal pressure of the ambient medium. The period of the oscillations coincides with depletion time scale of the gas inside the hot ionized bubble surrounding the BH. For n~n_cr accretion onto the BH becomes the dominant gas depletion mechanism, explaining the rapid decrease of the period of the oscillations and increasing the duty cycle. Angular momentum of the accreting gas produces a time delay between the accretion rate near the sonic point and the luminosity output. Generally, assuming reasonable values of the time delay calculated using an alpha-model for a thin disk, angular momentum does not affect significantly the accretion rate and period of the oscillations.

by Touma, Jihad R. and Sridhar, S.
41 pages, 5 figures, Submitted to MNRAS

We formulate the collisionless Boltzmann equation (CBE) for dense star clusters that lie within the radius of influence of a massive black hole in galactic nuclei. Our approach to these nearly Keplerian systems follows that of Sridhar and Touma (1999): Delaunay canonical variables are used to describe stellar orbits and we average over the fast Keplerian orbital phases. The stellar distribution function (DF) evolves on the longer time scale of precessional motions, whose dynamics is governed by a Hamiltonian, given by the orbit-averaged self-gravitational potential of the cluster. We specialize to razor-thin, planar discs and consider two counter-rotating (”$latex \pm$”) populations of stars. To describe discs of small eccentricities, we expand the $latex \pm$ Hamiltonian to fourth order in the eccentricities, with coefficients that depend self-consistently on the $latex \pm$ DFs. We construct approximate $latex \pm$ dynamical invariants and use Jeans’ theorem to construct time-dependent $latex \pm$ DFs, which are completely described by their centroid coordinates and shape matrices. When the centroid eccentricities are larger than the dispersion in eccentricities, the $latex \pm$ centroids obey a set of 4 autonomous ordinary differential equations. We show that these can be cast as a two-degree of freedom Hamiltonian system which is nonlinear, yet integrable. We study the linear instability of initially circular discs and derive a criterion for the counter-rotating instability. We then explore the rich nonlinear dynamics of counter-rotating discs, with focus on the variety of steadily precessing eccentric configurations that are allowed. The stability and properties of these configurations are studied as functions of parameters such as the disc mass ratios and angular momentum.

by Begelman, Mitchell C.
13 pages, 8 figures, to appear in Monthly Notices of the Royal Astronomical Society

We reformulate the adiabatic inflow-outflow (ADIOS) model for radiatively inefficient accretion flows, treating the inflow and outflow zones on an equal footing. For purely adiabatic flows (i.e., with no radiative losses), we show that the mass flux in each zone must satisfy Mdot ~ R^n with n=1, in contrast to previous work in which 0<n< 1 is a free parameter but in rough agreement with numerical simulations. We also demonstrate that the resulting two-zone ADIOS models are not dynamically self-consistent without the introduction of an energy source close in to the central regions of the flow; we identify this with the energy liberated by accretion. We explore the parameter space of non-radiative models and show that both powerful winds and gentle breezes are possible. When small radiative losses (with fixed efficiency) are included, any centrally injected energy flux is radiated away and the system reverts to a power-law behavior with n < 1, where n falls in a small range determined by the fractional level of radiative losses. We also present an ADIOS model for hypercritical (super-Eddington) disk accretion, in which the radiative losses are closely related to the flow geometry. We suggest that hyperaccretion can lead to either winds or breezes.

by Wang, Yan and Li, Xiang-Dong
22 pages, 8 figures. Accepted for publication in ApJ

If an accretion disk around a black hole is illuminated by hard X-rays from non-thermal coronae, fluorescent iron lines will be emitted from the inner region of the accretion disk. The emission line profiles will show a variety of strong field effects, which may be used as a probe of the spin parameter of the black hole and the structure of the accretion disk. In this paper we generalize the previous relativistic line profile models by including both the black hole spinning effects and the non-axisymmetries of warped accretion disks. Our results show different features from the conventional calculations for either a flat disk around a Kerr black hole or a warped disk around a Schwarzschild black hole by presenting, at the same time, multiple peaks, rather long red tails and time variations of line profiles with the precession of the disk. We show disk images as seen by a distant observer, which are distorted by the strong gravity. Although we are primarily concerned with the iron K-shell lines in this paper, the calculation is general and is valid for any emission lines produced from a warped accretion disk around a black hole.

by Li, Gongjie and Conroy, Charlie and Loeb, Abraham
8 pages, 3 figures, 2 tables

We investigate the evolution of the MBH-{\sigma} relation by examining the relationship between the intrinsic scatter in the MBH-{\sigma} relation and galaxy bolometric nuclear luminosity, the latter being a probe of the accretion rate of the black hole (BH). Our sample is composed of galaxies with classical bulges when possible, of which 38 have dynamically measured BHs masses, and 17 have BHs masses measured by reverberation mapping. In order to obtain the bolometric nuclear luminosity for galaxies with low nuclear luminosity, we convert the X-ray nuclear luminosity measured by Chandra to bolometric luminosity. We find that the scatter in the MBH-{\sigma} relation is uncorrelated with nuclear luminosity over seven orders of magnitude in luminosity, with the high luminosity end approaching the Eddington luminosity. This suggests that at the present epoch galaxies evolve along the MBH-{\sigma} relation. This conclusion is consistent with the standard paradigm that BHs grow contemporaneously with their host stellar spheroids.

by Stone, Nicholas and Loeb, Abraham
4 pages, 4 figures

When a star is tidally disrupted by a supermassive black hole (SMBH), the streams of liberated gas form an accretion disk after their return to pericenter. We demonstrate that Lense-Thirring precession in the spacetime around a rotating SMBH can produce significant time evolution of the disk angular momentum vector, due to both the periodic precession of the disk and the nonperiodic, differential precession of the bound debris streams. Jet precession and periodic modulation of disk luminosity are possible consequences. The persistence of the jetted X-ray emission in the Swift J164449.3+573451 flare suggests that the jet axis was aligned with the spin axis of the SMBH during this event.

by Decarli, Roberto and Falomo, Renato and Kotilainen, Jari K. and Hyvonen, Tomi and Uslenghi, Michela and Treves, Aldo
Accepted for publication in Advances in Astronomy. To appear in the special issue: “Seeking for the Leading Actor on the Cosmic Stage: Galaxies versus Supermassive Black Holes”

The Mbh-Mhost relation in quasars has been probed only in a limited parameter space, namely at Mbh~10^9 Msun and Mhost~10^12 Msun. Here we present a study of 26 quasars lying in the low-mass end of the relation, down to Mbh~10^7 Msun. We selected quasars from the SDSS and HST-FOS archives, requiring modest Mbh (as derived through the virial paradigm). We imaged our sources in H band from the Nordic Optical Telescope. The quasar host galaxies have been resolved in 25 out of 26 observed targets. Host galaxy luminosities and stellar masses are computed, under reasonable assumptions on their star formation histories. Combining these results with those from our previous studies, we manage to extend the sampled parameter space of the Mbh-Mhost relation in quasars. The relation holds over 2 dex in both the parameters, similarly to what observed in low-luminosity AGN and in quiescent galaxies. For the first time, we are able to measure the slope of the Mbh-Mhost relation in quasars. We find that it is consistent with the linear case (similarly to what observed in quiescent galaxies). We do not find any evidence of a population of massive black holes lying below the relation.

by Gil-Merino, Rodrigo and Goicoechea, Luis J. and Shalyapin, Vyacheslav N. and Braga, Vittorio F.
21 pages, 7 text pages, 13 figures, 2 tables, accepted by The Astrophysical Journal

We present the results of our X-ray, UV and optical monitoring campaign of the first gravitationally lensed AGN from late 2009 to mid 2010. The trailing (B) image of the AGN 0957+561 shows the intrinsic continuum variations that were predicted in advance based on observations of the leading (A) image in the gr optical bands. This multiwavelength variability of the B image allows us to carry out a reverberation mapping analysis in the radio-loud AGN 0957+561 at redshift z = 1.41. We find that the U-band and r-band light curves are highly correlated with the g-band record, leading and trailing it by 3 +/- 1 days (U band) and 4 +/- 1 days (r band). These 1-sigma measurements are consistent with a scenario in which flares originated in the immediate vicinity of the supermassive black hole are thermally reprocessed in a standard accretion disk at about 10-20 Schwarzschild radii from the central dark object. We also report that the light curve for the X-ray emission with power-law spectrum is delayed with respect to those in the Ugr bands by about 32 days. Hence, the central driving source can not be a standard corona emitting the observed power-law X-rays. This result is also supported by X-ray reprocessing simulations and the absence of X-ray reflection features in the spectrum of 0957+561. We plausibly interpret the lack of reflection and the 32-day delay as evidence for a power-law X-ray source in the base of the jet at a typical height of about 200 Schwarzschild radii. A central EUV source would drive the variability of 0957+561.

by Fiore, F. and Puccetti, S. and Grazian, A. and Menci, N. and Shankar, F. and Santini, P. and Piconcelli, E. and Koekemoer, A. M. and Fontana, A. and Boutsia, K. and Castellano, M. and Lamastra, A. and Malacaria, C. and Feruglio, C. and Mathur, S. and Miller, N. and Pannella, M.
A&A in press

We present detection and analysis of faint X-ray sources in the Chandra deep field south (CDFS) using the 4 Msec Chandra observation and adopting a new detection algorithm, based on a targeted search at the position of known high-z galaxies. This optimized technique results in the identification of 54 z>3 AGNs, 29 of which are new detections. Applying stringent completeness criteria, we derive AGN luminosity functions in the redshift bins 3-4, 4-5 and >5.8 and for 42.75<log L(2-10 keV)3 (18+17-10%). Their optical counterparts are not strongly reddened and we thus conclude that the size of the X-ray absorber is likely smaller than the dust sublimation radius. We finally report the discovery of a highly star-forming galaxy at z=3.47. If confirmed, this would be one of the farthest objects in which stellar sources are detected in X-rays.

by Schulze, Andreas and Wisotzki, Lutz
20 pages, 20 figures, accepted for publication in A&A

We present an investigation of sample selection effects that influence the observed black hole – bulge relations and its evolution with redshift. We provide a common framework in which all kinds of selection effects on the BH-bulge relations can be investigated, but our main emphasis is on the consequences of using broad-line AGN and their host galaxies to search for evolution in the BH-bulge relation. We identified relevant sources of bias that were not discussed in the literature so far. A particularly important effect is caused by the fact that the active fraction among SMBHs varies considerably with BH mass, in the sense that high-mass BHs are less likely to be active than lower mass ones. In the connection with intrinsic scatter of the BH-bulge relation this effect implies a bias towards a low BH mass at given bulge property. This effect adds to the bias caused by working with luminosity or flux limited samples that were already discussed by others. A quantitative prediction of these biases requires (i) a realistic model of the sample selection function, and (ii) knowledge of relevant underlying distribution functions. For low-redshift AGN samples we can naturally reproduce the flattening of the relation observed in some studies. When extending our analysis to higher redshift samples we are clearly hampered by limited empirical constraints on the various relevant distribution functions. Using a best-guess approach for these distributions we estimate the expected magnitude of sample selection biases for a number of recent observational attempts to study the BH-bulge evolution. In no case do we find statistically significant evidence for an evolving BH-bulge relation. We suggest a possible practical approach to circumvent several of the most problematic issues connected with AGN selection; this could become a powerful diagnostic in future investigations (abridged).

by Martinez-Sansigre, Alejo and Rawlings, Steve
Accepted by MNRAS. 6 pages, 3 colour figures. Supplementary material can be found at: http://research.icg.port.ac.uk/~martinea/spin_suppl_fig.pdf

We use results from simulations of the production of magnetohydrodynamic jets around black holes to derive the cosmic spin history of the most massive black holes. We assume that the efficiency of jet production is a monotonic function of spin a, as given by the simulations, and that the accretion flow geometry is similarly thick for quasars accreting close to the Eddington ratio and for low-excitation radio galaxies accreting at very small Eddington rates. We use the ratio of the comoving densities of the jet power and the radiated accretion power associated with supermassive black holes with Mbh>~10^8 Msol to estimate the cosmic history of the characteristic spin a. The evolution of this ratio, which increases with decreasing z, is consistent with a picture where the z~0 active galactic nuclei have typically higher spins than those at z~2 (with typical values a~0.35-0.95 and a~0.0-0.25 respectively). We discuss the implications in terms of the relative importance of accretion and mergers in the growth of supermassive black holes with Mbh>~10^8 Msol.

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 Fiestas, Jose and Porth, Oliver and Berczik, Peter and Spurzem, Rainer
15 pages, 7 figures,accepted by MNRAS

NBody realizations of axisymmetric collisional galaxy cores (e.g. M32, M33, NGC205, Milky Way) with embedded growing black holes are presented. Stars which approach the disruption sphere are disrupted and accreted to the black hole. We measure the zone of influence of the black hole and disruption rates in relaxation time scales. We show that secular gravitational instabilities dominate the initial core dynamics, while the black hole is small and growing due to consumption of stars. Later, the black hole potential dominates the core, and loss cone theory can be applied. Our simulations show that central rotation in galaxies can not be neglected for relaxed systems, and compare and discuss our results with the standard theory of spherically symmetric systems.

by Dubois, Yohan and Devriendt, Julien and Slyz, Adrianne and Teyssier, Romain
24 pages, 18 figures, 1 table, submitted to MNRAS

We develop a new sub-grid model for the growth of supermassive Black Holes (BHs) and their associated Active Galactic Nuclei (AGN) feedback in hydrodynamical cosmological simulations. Assuming that BHs are created in the early stages of galaxy formation, they grow by mergers and accretion of gas at a Eddington-limited Bondi accretion rate. However this growth is regulated by AGN feedback which we model using two different modes: a quasar-heating mode when accretion rates onto the BHs are comparable to the Eddington rate, and a radio-jet mode at lower accretion rates. In other words, our feedback model deposits energy as a succession of thermal bursts and jet outflows depending on the properties of the gas surrounding the BHs. We assess the plausibility of such a model by comparing our results to observational measurements of the coevolution of BHs and their host galaxy properties, and check their robustness with respect to numerical resolution. We show that AGN feedback must be a crucial physical ingredient for the formation of massive galaxies as it appears to be the only physical mechanism able to efficiently prevent the accumulation of and/or expel cold gas out of halos/galaxies and significantly suppress star formation. Our model predicts that the relationship between BHs and their host galaxy mass evolves as a function of redshift, because of the vigorous accretion of cold material in the early Universe that drives Eddington-limited accretion onto BHs. Quasar activity is also enhanced at high redshift. However, as structures grow in mass and lose their cold material through star formation and efficient BH feedback ejection, the AGN activity in the low-redshift Universe becomes more and more dominated by the radio mode, which powers jets through the hot circum-galactic medium.