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 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 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 Corda, Christian
9 pages, 2 figures, published in Modern Physics Letters A. arXiv admin note: substantial text overlap with arXiv:0901.1193

The cosmological bound of the stochastic background of gravitational waves is analyzed with the aid of the WMAP data, differently from lots of works in literature, where the old COBE data were used. From our analysis, it will result that the WMAP bounds on the energy spectrum and on the characteristic amplitude of the stochastic background of gravitational waves are greater than the COBE ones, but they are also far below frequencies of the earth-based antennas band. At the end of this letter a lower bound for the integration time of a potential detection with advanced LIGO is released and compared with the previous one arising from the old COBE data. Even if the new lower bound is minor than the previous one, it results very long, thus for a possible detection we hope in the LISA interferometer and in a further growth in the sensitivity of advanced projects.

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 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 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 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 Schawinski, Kevin and Urry, Meg and Treister, Ezequiel and Simmons, Brooke and Natarajan, Priyamvada and Glikman, Eilat
Accepted for publication in ApJ Letters. 6 pages, 4 figures, 1 table

One of the key open questions in cosmology today pertains to understanding when, where and how super massive black holes form, while it is clear that mergers likely play a significant role in the growth cycles of black holes, how supermassive black holes form, and how galaxies grow around them. Here, we present Hubble Space Telescope WFC3/IR grism observations of a clumpy galaxy at z=1.35, with evidence for 10^6 – 10^7 Msun rapidly growing black holes in separate sub-components of the host galaxy. These black holes could have been brought into close proximity as a consequence of a rare multiple galaxy merger or they could have formed in situ. Such holes would eventually merge into a central black hole as the stellar clumps/components presumably coalesce to form a galaxy bulge. If we are witnessing the in-situ formation of multiple black holes, their properties can inform seed formation models and raise the possibility that massive black holes can continue to emerge in star-forming galaxies as late as z=1.35 (4.8 Gyr after the Big Bang).

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 Pepe, C. and Pellizza, L. J. and Romero, G. E.
5 pages, 3 figures, accepted for publication in MNRAS

In this work we investigate the accretion of cosmological fluids onto an intermediate-mass black hole at the centre of a globular cluster, focusing on the influence of the parent stellar system on the accretion flow. We show that the accretion of cosmic background radiation and the so-called dark energy onto an intermediate-mass black hole is negligible. On the other hand, if cold dark matter has a nonvanishing pressure, the accretion of dark matter is large enough to increase the black hole mass well beyond the present observed upper limits. We conclude that either intermediate-mass black holes do not exist, or dark matter does not exist, or it is not strictly collisionless. In the latter case, we set a lower limit for the parameter of the cold dark matter equation of state.

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 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 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 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 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 Li, Yuexing
8 pages, 4 figures. Submitted to ApJ

The origin of the supermassive black holes that power the most distant quasars observed is largely unknown. One hypothesis is that they grew rapidly from intermediate-mass seeds (~100 M_sun) left by the first stars. However, some previous studies argued that accretion onto these black holes was too low to build up the mass due to strong suppression by radiative feedback. Here, we re-exam the accretion process of such a black hole embedded in a primordial gas cloud, by considering a wide range of physical and numerical parameters not explored before. We find that, while radiative heating and pressure indeed suppress accretion effectively, self-gravity of the gas eventually overcomes the feedback effects and boosts the accretion to the Eddington rate after one free-fall timescale of the cloud. Moreover, for a given black hole mass, there exists a critical density above which the accretion can reach Eddington limit. Furthermore, we find a universal correlation between black hole accretion rate and ambient gas density, which may serve as a realistic recipe for black hole growth in simulations.

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 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.

by Rafferty, D. A. and Brandt, W. N. and Alexander, D. M. and Xue, Y. Q. and Bauer, F. E. and Lehmer, B. D. and Luo, B. and Papovich, C.
25 pages, 14 figures, accepted for publication in ApJ

We present an analysis of deep multiwavelength data for z ~ 0.3-3 starburst galaxies selected by their 70 um emission in the Extended-Chandra Deep Field-South and Extended Groth Strip. We identify active galactic nuclei (AGNs) in these infrared sources through their X-ray emission and quantify the fraction that host an AGN. We find that the fraction depends strongly on both the mid-infrared color and rest-frame mid-infrared luminosity of the source, rising to ~ 50-70% at the warmest colors and highest mid-infrared luminosities (corresponding to ultraluminous infrared galaxies), similar to the trends found locally. Additionally, we find that the AGN fraction depends strongly on the star formation rate of the host galaxy (inferred from the observed 70 um luminosity after subtracting the estimated AGN contribution), particularly for more luminous AGNs (L_X > 10^43 erg/s). At the highest star formation rates (~ 1000 M_sun/yr), the fraction of galaxies with an X-ray detected AGN rises to ~ 30%, roughly consistent with that found in high-redshift submillimeter galaxies. Assuming that the AGN fraction is driven by the star formation rate (rather than stellar mass or redshift, for which our sample is largely degenerate), this result implies that the duty cycle of luminous AGN activity increases with the star formation rate of the host galaxy: specifically, we find that luminous X-ray detected AGNs are at least ~ 5-10 times more common in systems with high star formation rates (> 300 M_sun/yr) than in systems with lower star formation rates (< 30 M_sun/yr). Lastly, we investigate the ratio between the supermassive black hole accretion rate and the growth rate of the host galaxy and find that, for sources with detected AGNs and star formation, this ratio in distant starbursts agrees well with that expected from the local scaling relation assuming the black holes and bulges grew at the same epoch.

by Montero, Pedro J. and Janka, Hans-Thomas and Mueller, Ewald
12 pages, 8 figures, submitted to the Astrophysical Journal

We present results of general relativistic simulations of collapsing supermassive stars with and without rotation using the two-dimensional general relativistic numerical code Nada, which solves the Einstein equations written in the BSSN formalism and the general relativistic hydrodynamics equations with high resolution shock capturing schemes. These numerical simulations use an equation of state which includes effects of gas pressure, and in a tabulated form those associated with radiation and the electron-positron pairs. We also take into account the effect of thermonuclear energy released by hydrogen and helium burning. We find that objects with a mass of 5×10^{5} solar mass and an initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating, while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001 for objects uniformly rotating. The critical initial metallicity for a thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For those stars that do not explode we follow the evolution beyond the phase of black hole formation. We compute the neutrino energy loss rates due to several processes that may be relevant during the gravitational collapse of these objects. The peak luminosities of neutrinos and antineutrinos of all flavors for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and ~10^{45}-10^{46} ergs for models exploding.

by Natarajan, Priyamvada and Volonteri, Marta
7 pages, 4 figures, submitted to MNRAS

In this paper, we compare the observationally derived black hole mass function (BHMF) of luminous broad-line quasars (BLQSOs) at 1<z<4.5 drawn from the Sloan Digital Sky Survey (SDSS) presented in Kelly et al. (2010), with models of merger driven BH growth in the context of standard hierarchical structure formation models. In the models, we explore two distinct black hole seeding prescriptions at the highest redshifts: "light seeds" – remnants of Population III stars and "massive seeds" that form from the direct collapse of pre-galactic disks. The subsequent merger triggered mass build-up of the black hole population is tracked over cosmic time under the assumption of a fixed accretion rate as well as rates drawn from the distribution derived by Merloni & Heinz. Our model snapshots are compared to the SDSS derived BHMFs of BLQSOs. Our key findings are that the duty cycle of SMBHs powering BLQSOs increases with increasing redshift for all models and models with Pop III remnants as black hole seeds are unable to fit the observationally derived BHMFs for BLQSOs, lending strong support for the massive seeding model (abridged).

by Berti, Emanuele and Gair, Jonathan and Sesana, Alberto
5 pages, 3 figures, 2 tables

Space-based gravitational-wave detectors, such as LISA or a similar ESA-led mission, will offer unique opportunities to test general relativity. We study the bounds that space-based detectors could place on the graviton Compton wavelength \lambda_g=h/(m_g c) by observing multiple inspiralling black hole binaries. We show that while observations of individual inspirals will yield mean bounds \lambda_g~3×10^15 km, the combined bound from observing several events in a two-year mission is about ten times better: \lambda_g~3×10^16 km (m_g~4×10^-26 eV). This result is only mildly dependent on details of black hole formation and detector characteristics. The bound achievable in practice should be one order of magnitude better than this figure (and hence almost competitive with the static, model-dependent bounds from gravitational effects on cosmological scales), because our calculations ignore the merger/ringdown portion of the waveform. The observation that an ensemble of events can sensibly improve the bounds that individual binaries set on \lambda_g applies to any theory whose deviations from general relativity are parametrized by a set of global parameters.

by Lang, Meagan and Holley-Bockelmann, Kelly and Bogdanovic, Tamara and Amaro-Seoane, Pau and Sesana, Alberto
9 pages, 1 figure, submitted to ApJ. Comments are welcome and may be incorporated into the paper with attribution

Observations of the Galactic Center (GC) have accumulated a multitude of “forensic” evidence indicating that several million years ago the center of the Milky Way galaxy was teaming with starforming and accretion-powered activity — this paints a rather different picture from the GC as we understand it today. We examine a possibility that this epoch of activity could have been triggered by the infall of a satellite galaxy into the Milky Way which began at the redshift of 10 and ended few million years ago with a merger of the Galactic supermassive black hole with an intermediate mass black hole brought in by the inspiralling satellite.

by Volonteri, Marta and Stark, Daniel P.
MNRAS in press

Motivated by recent observational results that focus on high redshift black holes, we explore the effect of scatter and observational biases on the ability to recover the intrinsic properties of the black hole population at high redshift. We find that scatter and selection biases can hide the intrinsic correlations between black holes and their hosts, with ‘observable’ subsamples of the whole population suggesting, on average, positive evolution even when the underlying population is characterized by no- or negative evolution. We create theoretical mass functions of black holes convolving the mass function of dark matter halos with standard relationships linking black holes with their hosts. Under these assumptions, we find that the local MBH – sigma correlation is unable to fit the z = 6 black hole mass function proposed by Willott et al. (2010), overestimating the number density of all but the most massive black holes. Positive evolution or including scatter in the MBH – sigma correlation makes the discrepancy worse, as it further increases the number density of observable black holes. We notice that if the MBH – sigma correlation at z = 6 is steeper than today, then the mass function becomes shallower. This helps reproducing the mass function of z = 6 black holes proposed by Willott et al. (2010). Alternatively, it is possible that very few halos (of order 1/1000) host an active massive black hole at z = 6, or that most AGN are obscured, hindering their detection in optical surveys. Current measurements of the high redshift black hole mass function might be underestimating the density of low mass black holes if the active fraction or luminosity are a function of host or black hole mass. Finally, we discuss physical scenarios that can possibly lead to a steeper MBH – sigma relation at high redshift.

by Kulkarni, Girish and Loeb, Abraham
18 pages, 14 figures, 2 tables; submitted to MNRAS; comments welcome

We examine the formation of groups of multiple supermassive black holes (SMBHs) in gas-poor galactic nuclei due to the high merger rate of galaxies at high redshifts. We calculate the relative likelihood of binary, triple, and quadruple SMBH systems, by considering the timescales for relevant processes and combining merger trees with N-body simulations for the dynamics of stars and SMBHs in galactic nuclei. Typical haloes today with mass $latex M_0\approx 10^{14}$ M$latex _\odot$ have an average mass $latex M_{z=6}=5\times 10^{11}$ M$latex _\odot$ at $latex z\sim 6$, while rare haloes with current mass $latex M_0\gtrsim 10^{15}$ M$latex _\odot$ have an average mass $latex M_{z=6}=5\times 10^{12}$ M$latex _\odot$ at that redshift. These cluster-size haloes are expected to host single galaxies at $latex z\sim 6$. We expect about 30% galaxies within haloes with present-day mass $latex M_0\approx 10^{14}$ M$latex _\odot$ to contain more than two SMBHs at redshifts $latex 2\lesssim z\lesssim 6$. For larger present-day haloes, with $latex M_0\gtrsim 10^{15}$ M$latex _\odot$, this fraction is almost 60%. The existence of multiple SMBHs at high redshifts can potentially explain the mass deficiencies observed in the cores of massive elliptical galaxies, which are up to 5 times the mass of their central BHs. Multiple SMBHs would also lead to an enhanced rate of tidal disruption of stars, modified gravitational wave signals compared to isolated BH binaries, and slingshot ejection of SMBHs from galaxies at high speeds in excess of 2000 km s$latex ^{-1}$.

by Davies, Melvyn B. and Miller, M. Coleman and Bellovary, Jillian M.
5 pages, 2 figures, submitted to ApJ letters

Black holes exceeding a billion solar masses have been detected at redshifts greater than six. The rapid formation of these objects may suggest a massive early seed or a period of growth faster than Eddington. Here we suggest a new mechanism along these lines. We propose that in the process of hierarchical structure assembly, dense star clusters can be contracted on dynamical time scales due to the nearly free-fall inflow of self-gravitating gas with a mass comparable to or larger than that of the clusters. This increases the velocity dispersion to the point that the few remaining hard binaries can no longer effectively heat the cluster, and the cluster goes into a period of homologous core collapse. The cluster core can then reach a central density high enough for fast mergers of stellar-mass black holes and hence the rapid production of a black hole seed that could be $latex 10^5 M_\odot$ or larger.

by Natarajan, Priyamvada
28 pages, 9 figures, Proceedings of the XVth Congress of Philosophy & Foundations of Science to be published by the American Institute of Physics

We track the growth and evolution of high redshift seed black holes over cosmic time. This population of massive, initial black hole seeds form at these early epochs from the direct collapse of pre-galactic gas discs. Populating dark matter halos with seeds formed in this fashion, we follow their mass assembly history to the present time using a Monte-Carlo merger tree approach. Using this formalism, we predict the black hole mass function at the present time; the integrated mass density of black holes in the Universe; the luminosity function of accreting black holes as a function of redshift and the scatter in observed, local Mbh{\sigma}s relation. Signatures of these massive seed models appear predominantly at the low mass end of the present day black hole mass function. In fact, our prediction of the shape of the Mbh{\sigma}s relation at the low mass end and increased scatter has recently been corroborated by observations. These models predict that low surface brightness, bulge-less galaxies with large discs are least likely to be sites for the formation of massive seed black holes at high redshifts. The efficiency of seed formation at high redshifts also has a direct influence on the black hole occupation fraction in galaxies at z = 0. This effect is more pronounced for low mass galaxies today as we predict the existence of a population of low mass galaxies that do not host nuclear black holes. This is the key discriminant between the models studied here and the Population-III remnant seed model.

by Liu, Xin and Shen, Yue and Strauss, Michael A.
ApJL submitted

Hierarchical galaxy mergers will lead to the formation of binary and, in particular, triple SMBHs, given that most massive galaxies harbor central SMBHs. A triple of SMBHs becomes visible as a triple Active Galactic Nucleus (AGN) when the BHs accrete large amounts of gas at the same time. Here we report the discovery of a kpc-scale triple AGN, SDSSJ1027+1749 at z = 0.066, from our systematic search for hierarchical mergers of AGNs. The galaxy contains three emission-line nuclei, two of which are offset by ~ 450 and 110 km/s in velocity and by 2.4 and 3.0 kpc in projected separation from the central nucleus. All three nuclei are classified as obscured AGNs based on optical diagnostic emission line ratios, with black hole mass estimates M_BH >~ 10^8 M_sun from stellar velocity dispersions measured in the associated stellar components. Based on dynamical friction timescale estimates, the three stellar components in SDSSJ1027+1749 will merge in ~ 40 Myr, and their associated SMBHs may evolve into a gravitationally interacting triple system in ~ 200 Myr. Our result sets a lower limit of ~ 5 x 10^(-5) for the fraction of kpc-scale triples in optically selected AGNs at z ~ 0.1.

by Sereno, M. and Jetzer, Ph. and Sesana, A. and Volonteri, M.
10 pages, 10 figures, in press on MNRAS

LISA might detect gravitational waves from mergers of massive black hole binaries strongly lensed by intervening galaxies (Sereno et al. 2010). The detection of multiple gravitational lensing events would provide a new tool for cosmography. Constraints on cosmological parameters could be placed by exploiting either lensing statistics of strongly lensed sources or time delay measurements of lensed gravitational wave signals. These lensing methods do not need the measurement of the redshifts of the sources and the identification of their electromagnetic counterparts. They would extend cosmological probes to redshift z = 10 km s^{-1}Mpc^{-1}. With prior knowledge of H_0, lensing statistics and time delays might constrain the dark matter density (delta Omega_M >= 0.08, due to parameter degeneracy). Inclusion of our methods with other available orthogonal techniques might significantly reduce the uncertainty contours for Omega_M and the dark energy equation of state.

by Power, C. and Zubovas, K. and Nayakshin, S. and King, A. R.
6 pages, no figures, accepted for publication in MNRAS

We show that star formation in galaxy bulges is self-regulating through momentum feedback, limiting the stellar bulge mass to M_b ~ sigma^4. Together with a black hole mass M_BH ~ sigma^4 set by AGN momentum feedback, this produces a linear M_BH – M_b relation. At low redshift this gives M_BH/M_b ~ 0.001, close to the observed ratio. We show that AGN feedback can remove any remaining gas from the bulge and terminate star formation once the central black hole reaches the M_BH – sigma value, contrary to earlier claims. We find a mild upward deviation from the sigma^4 law at higher redshift and at higher sigma.

by Volonteri, Marta and Natarajan, Priyamvada and Gultekin, Kayhan
Submitted to ApJ Letters

In this letter we examine if the properties of central black holes in galactic nuclei correlate with their host dark matter halo. We analyze the entire sample of galaxies where black hole mass, velocity dispersion, sigma, and asymptotic circular velocity, Vc, have all been measured. We fit MBH-sigma and MBH-Vc to a power law, and find that in both relationships the scatter and slope are very similar. This model independent analysis suggests that the MBH-Vc correlation is as strong (or as weak) as the correlation between MBH-sigma given current samples. The correlation worsens for both sigma and Vc below ~100 km/s. This is not unexpected given our current understanding of galaxy and black hole assembly. In fact, there are several compelling reasons that account for this: (i) SMBH formation is likely less efficient in low-mass galaxies with large angular momentum content; (ii) SMBH growth is less efficient in low-mass disk galaxies that have not experienced major mergers; (iii) dynamical effects, such as gravitational recoil, increase scatter preferentially at the low-mass end. Therefore, the absence of central SMBHs in bulge-less, low mass galaxies, or deviations from the correlations defined by high-mass black holes in large galaxies today does not necessarily indicate a lack of correlation between the dark matter halo and the central object; in fact, this is a prediction of models that do predicate such a correlation at high redshifts.

by DeGraf, Colin and Oborski, Matthew and Di Matteo, Tiziana and Chatterjee, Suchetana and Nagai, Daisuke and Zheng, Zheng and Richardson, Jonathan
10 pages, 7 figures, submitted to MNRAS

We investigate the halo occupation distribution (HOD) of black holes within a hydrodynamic cosmological simulation that directly follows black hole growth. Similar to the HOD of galaxies/subhalos, we find that the black hole occupation number can be described by the form N_BH proportional to 1+ (M_Host)^alpha where alpha evolves mildly with redshift indicating that a given mass halo (M_Host) at low redshift tends to host fewer BHs than at high redshift (as expected as a result of galaxy and BH mergers). We further divide the occupation number into contributions from black holes residing in central and satellite galaxies within a halo. The distribution of M_BH within halos tends to consist of a single massive BH (distributed about a peak mass strongly correlated with M_Host), and a collection of relatively low-mass secondary BHs, with weaker correlation with M_Host. We also examine the spatial distribution of BHs within their host halos, and find they typically follow a power-law radial distribution (i.e. much more centrally concentrated than the subhalo distribution). Finally, we characterize the host mass for which BH growth is feedback dominated (e.g. star formation quenched). We show that halos with M_Host > 3 * 10^12 M_sun have primary BHs that are feedback dominated by z~3 with lower mass halos becoming increasingly more affected at lower redshift.

by Micic, Miroslav and Holley-Bockelmann, Kelly and Sigurdsson, Steinn
25 pages, 19 figures, accepted for publication in MNRAS

We explore the growth of < 10^7 Msun black holes that reside at the centers of spiral and field dwarf galaxies in a Local Group type of environment. We use merger trees from a cosmological N-body simulation known as Via Lactea II (VL-2) as a framework to test two merger-driven semi-analytic recipes for black hole growth that include dynamical friction, tidal stripping, and gravitational wave recoil in over 20,000 merger tree realizations. First, we apply a Fundamental Plane limited (FPL) model to the growth of Sgr A*, which drives the central black hole to a maximum mass limited by the Black Hole Fundamental Plane after every merger. Next, we present a new model that allows for low-level Prolonged Gas Accretion (PGA) during the merger. We find that both models can generate a Sgr A* mass black hole. We predict a population of massive black holes in local field dwarf galaxies – if the VL-2 simulation is representative of the growth of the Local Group, we predict up to 35 massive black holes (< 10^6 Msun) in Local Group field dwarfs. We also predict that hundreds of < 10^5 Msun black holes fail to merge, and instead populate the Milky Way halo, with the most massive of them at roughly the virial radius. In addition, we find that there may be hundreds of massive black holes ejected from their hosts into the nearby intergalactic medium due to gravitational wave recoil. We discuss how the black hole population in the Local Group field dwarfs may help to constrain the growth mechanism for Sgr A*.

by Petiteau, Antoine and Babak, Stanislav and Sesana, Alberto
12 pages, 8 figures, revised version to address referee’s comments, submitted to ApJ

Gravitational wave signals from coalescing Massive Black Hole (MBH) binaries could be used as standard sirens to measure cosmological parameters. The future space based gravitational wave observatory Laser Interferometer Space Antenna (LISA) will detect up to a hundred of those events, providing very accurate measurements of their luminosity distances. To constrain the cosmological parameters we also need to measure the redshift of the galaxy (or cluster of galaxies) hosting the merger. This requires the identification of a distinctive electromagnetic event associated to the binary coalescence. However, putative electromagnetic signatures may be too weak to be observed. Instead, we study here the possibility of constraining the cosmological parameters by enforcing statistical consistency between all the possible hosts detected within the measurement error box of a few dozen of low redshift (z<3) events. We construct MBH populations using merger tree realizations of the dark matter hierarchy in a LambdaCDM Universe, and we use data from the Millennium simulation to model the galaxy distribution in the LISA error box. We show that, assuming that all the other cosmological parameters are known, the parameter w describing the dark energy equation of state can be constrained to a 4-8% level (2sigma error), competitive with current uncertainties obtained by type Ia supernovae measurements, providing an independent test of our cosmological model.

by Yagi, Kent and Tanahashi, Norihiro and Tanaka, Takahiro
19 pages, 10 figures; submitted to PRD

In Randall-Sundrum II (RS-II) braneworld model, it has been conjectured according to the AdS/CFT correspondence that brane-localized black hole (BH) larger than the bulk AdS curvature scale $latex \ell$ cannot be static, and it is dual to a four dimensional BH emitting the Hawking radiation through some quantum fields. In this scenario, the number of the quantum field species is so large that this radiation changes the orbital evolution of a BH binary. We derived the correction to the gravitational waveform phase due to this effect and estimated the upper bounds on $latex \ell$ by performing Fisher analyses. We found that DECIGO/BBO can put a stronger constraint than the current table-top result by detecting gravitational waves from small mass BH/BH and BH/neutron star (NS) binaries. Furthermore, DECIGO/BBO is expected to detect 10$latex ^5$ BH/NS binaries per year. Taking this advantage, we found that DECIGO/BBO can actually measure $latex \ell$ down to $latex \ell=0.33 \mu$m for 5 year observation if we know that binaries are circular a priori. This is about 40 times smaller than the upper bound obtained from the table-top experiment. On the other hand, when we take eccentricities into binary parameters, the detection limit weakens to $latex \ell=1.5 \mu$m due to strong degeneracies between $latex \ell$ and eccentricities. We also derived the upper bound on $latex \ell$ from the expected detection number of extreme mass ratio inspirals (EMRIs) with LISA and BH/NS binaries with DECIGO/BBO, extending the discussion made recently by McWilliams. We found that these less robust constraints are weaker than the ones from phase differences.

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 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 Sereno, M. and Sesana, A. and Bleuler, A. and Jetzer, Ph. and Volonteri, M. and Begelman, M. C.
4 pages, 6 figures, in press on Phys. Rev. Lett

We discuss strong gravitational lensing of gravitational waves from merging of massive black hole binaries in the context of the LISA mission. Detection of multiple events would provide invaluable information on competing theories of gravity, evolution and formation of structures and, with complementary observations, constraints on H_0 and other cosmological parameters. Most of the optical depth for lensing is provided by intervening massive galactic halos, for which wave optics effects are negligible. Probabilities to observe multiple events are sizable for a broad range of formation histories. For the most optimistic models, up to 4 multiple events with a signal to noise ratio >= 8 are expected in a 5-year mission. Chances are significant even for conservative models with either light (<= 60%) or heavy (<= 40%) seeds. Due to lensing amplification, some intrinsically too faint signals are brought over threshold (<= 2 per year).

by Norman, Michael L.
11 pages, 3 figures, Proceedings of “The First Stars and Galaxies: Challenges for the Next Decade”, Austin, TX, March 8-11, 2010

We provide a status report on our current understanding of the mass scales for Pop III.1 and Pop III.2 stars. Since the last review (Norman 2008), substantial progress has been made both numerically and analytically on the late stages of protostellar cloud core collapse, protostar formation and accretion, and stellar evolution taking into account cloud core properties and radiative feedback effects. Based on this, there are growing indications that primordial stars forming from purely cosmological initial conditions (Pop III.1) were substantially more massive than stars forming in preionized gas (Pop III.2) where HD cooling is important. Different stellar endpoints are predicted for these two types of Pop III stars with different chemical enrichment signatures: the former die as pair instability supernovae or intermediate mass black holes, whereas the latter die as iron core-collapse supernovae, leaving behind neutron star and stellar black hole remnants. We review recent simulations which show evidence for binary fragmentation at high densities, and comment on the significance of these results. We then summarize an attempt to directly calculate the Pop III.1 IMF taking into account the latest numerical and analytical models. We conclude with suggestions for the kind of simulations needed next to continue improving our understanding of Pop III star formation, which is a necessary input to understanding high redshift galaxy formation.

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 Eliche-Moral, M. Carmen and Prieto, Mercedes and Gallego, Jesus and Zamorano, Jaime
3 figures, 6 pages, in “Highlights of Spanish Astrophysics VI”, Proceedings of the IX Scientific Meeting of the Spanish Astronomical Society held on September 13-17 2010, in Madrid (Spain), eds. M. R. Zapatero Osorio, A. Gil de Paz, J. Maiz Apellaniz, J.R. Pardo, and J. Gorgas

Hierarchical models predict that massive early-type galaxies (mETGs) derive from the most massive and violent merging sequences occurred in the Universe. However, the role of wet, mixed, and dry major mergers in the assembly of mETGs is questioned by some recent observations. We have developed a semi-analytical model to test the feasibility of the major-merger origin hypothesis for mETGs, just accounting for the effects on galaxy evolution of the major mergers strictly reported by observations. The model proves that it is feasible to reproduce the observed number density evolution of mETGs since z~1, just accounting for the coordinated effects of wet/mixed/dry major mergers. It can also reconcile the different assembly redshifts derived by hierarchical models and by mass downsizing data for mETGs, just considering that a mETG observed at a certain redshift is not necessarily in place since then. The model predicts that wet major mergers have controlled the mETGs buildup since z~1, although dry and mixed mergers have also played an essential role in it. The bulk of this assembly took place at 0.7<z<1, being nearly frozen at z<~0.7 due to the negligible number of major mergers occurred per existing mETG since then. The model suggests that major mergers have been the main driver for the observational migration of mass from the massive end of the blue galaxy cloud to that of the red sequence in the last ~8 Gyr.

by Babak, Stanislav and Gair, Jonathan R. and Petiteau, Antoine and Sesana, Alberto
Based on the talk given at GR19. 10 pages, 2 figures

In this article we give a brief review of the fundamental physics that can be done with the future space-based gravitational wave detector LISA. This includes detection of gravitational wave bursts coming from cosmic strings, measuring a stochastic gravitational wave background, mapping spacetime around massive compact objects in galactic nuclei with extreme-mass-ratio inspirals and testing the predictions of General Relativity for the strong dynamical fields of inspiralling binaries. We give particular attention to new results which show the capability of LISA to constrain cosmological parameters using observations of coalescing massive Black Hole binaries.

by Schnittman, Jeremy D.
10 pages, 1 figure, submitted to Class. Quantum Grav. special issue: proceedings of 8th LISA Symposium

During the final moments of a binary black hole (BH) merger, the gravitational wave (GW) luminosity of the system is greater than the combined electromagnetic output of the entire observable universe. However, the extremely weak coupling between GWs and ordinary matter makes these waves very difficult to detect directly. Fortunately, the inspiraling BH system will interact strongly–on a purely Newtonian level–with any surrounding material in the host galaxy, and this matter can in turn produce unique electromagnetic (EM) signals detectable at Earth. By identifying EM counterparts to GW sources, we will be able to study the host environments of the merging BHs, in turn greatly expanding the scientific yield of a mission like LISA.

by Gair, Jonathan R and Sesana, Alberto and Berti, Emanuele and Volonteri, Marta
11 pages, 3 figures, submitted to Class. Quantum Grav. for proceedings of 8th LISA Symposium

LISA should detect gravitational waves from tens to hundreds of systems containing black holes with mass in the range from 10 thousand to 10 million solar masses. Black holes in this mass range are not well constrained by current electromagnetic observations, so LISA could significantly enhance our understanding of the astrophysics of such systems. In this paper, we describe a framework for combining LISA observations to make statements about massive black hole populations. We summarise the constraints that LISA observations of extreme-mass-ratio inspirals might be able to place on the mass function of black holes in the LISA range. We also describe how LISA observations can be used to choose between different models for the hierarchical growth of structure in the early Universe. We consider four models that differ in their prescription for the initial mass distribution of black hole seeds, and in the efficiency of accretion onto the black holes. We show that with as little as 3 months of LISA data we can clearly distinguish between these models, even under relatively pessimistic assumptions about the performance of the detector and our knowledge of the gravitational waveforms.