Population Of Supermassive Black Holes Research Articles

Testing Models of Supermassive Black Hole Seed Formation through Gravity Waves

We study the gravitational wave background produced from the formation and assembly of supermassive black holes within the cosmological paradigm of hierarchical structure formation. In particular, we focus on a supermassive black hole formation scenario in which the present-day population of supermassive black holes is built from high-mass seed black holes and we compute the concomitant spectrum of gravitational radiation produced by mergers of the seed black holes. We find that this scenario predicts a large, gravitational wave background that should be resolved into individual sources with space interferometers such as the proposed Laser Interferometric Space Antenna (LISA). The number of inspiral, merger and ringdown events above a signal to noise ratio of 5 that result from massive black hole seeds is of order 10^3. This prediction is robust and insensitive to several of the details of the model. We conclude that an interferometer such as LISA will be able to effectively rule out or confirm a class of models where supermassive black holes grow from high-mass seed black holes and may be able to place strong limits on the role of mergers as a channel for supermassive black hole growth. Supermassive black hole seeds likely form in the earliest proto-galactic structures at high redshift and the masses of supermassive black holes are known to be strongly correlated with the potentials of the spheroids in which they reside, therefore these results imply that space interferometers can be used as a powerful probe of the physics of galaxy formation and proto-galaxy formation at very high redshift.

Primordial structure of massive black hole clusters

We describe a mechanism of the primordial black holes formation that can explain the existence of a population of supermassive black holes in galactic bulges. The mechanism is based on the formation of black holes from closed domain walls. The origin of such domain walls could be a result of the evolution of an effectively massless scalar field during inflation. The initial non-equilibrium distribution of the scalar field imposed by background de Sitter fluctuations gives rise to the spectrum of black holes, which covers a wide range of masses—from superheavy ones down to deeply subsolar. The primordial black holes of smaller masses are concentrated around the most massive ones within a fractal-like cluster.

Modeling the Counts of Faint Radio‐Loud Quasars: Constraints on the Supermassive Black Hole Population and Predictions for High Redshift

We use a physically motivated semianalytic model, based on the mass function of dark matter halos, to predict the number of radio-loud quasars as a function of redshift and luminosity. Simple models in which the central black hole (BH) mass scales with the velocity dispersion of its host halo as MBH ∝ σ have been previously found to be consistent with a number of observations, including the optical and X-ray quasar luminosity functions. We find that similar models, when augmented with an empirical prescription for radio emission, overpredict the number of faint (~10 μJy) radio sources by 1-2 orders of magnitude. This translates into a more stringent constraint on the low-mass end of the quasar BH mass function than is available from the Hubble and Chandra Deep Fields. We interpret this discrepancy as evidence that BHs with masses ≲107 M☉ either are rare or are not as radio-loud as their more massive counterparts. Models that exclude BHs with masses below 107 M☉ are in agreement with the deepest existing radio observations but still produce a significant tail of high-redshift objects. In the 1-10 GHz bands at the sensitivity of ~10 μJy, we find surface densities of ~100, ~10, and ~0.3 deg-2 for sources located at z > 6, 10, and 15, respectively. The discovery of these sources with instruments such as the Allen Telescope Array, Extended Very Large Array, and the Square Kilometer Array would open a new window for the study of supermassive BHs at high redshift. We also find surface densities of ~0.1 deg-2 at z > 6 for millijansky sources that can be used to study 21 cm absorption from the epoch of reionization. We suggest that, although they are not yet optically identified, the FIRST survey may have already detected ~103-104 such sources.

Supermassive black hole demography: the match between the local and accreted mass functions

We have performed a detailed analysis of the local super-massive black-hole (SMBH) mass function based on both kinematic and photometric data and derived an accurate analytical fit in the range 10^6 <= (M_BH/M_sun) <= 5*10^9. We find a total SMBH mass density of (4.2+/-1.1)*10^5 M_sun/Mpc^3, about 25% of which is contributed by SMBHs residing in bulges of late type galaxies. Exploiting up-to-date luminosity functions of hard X-ray and optically selected AGNs, we have studied the accretion history of the SMBH population. If most of the accretion happens at constant \dot{M_BH}/M_BH the local SMBH mass function is fully accounted for by mass accreted by X-ray selected AGNs, with bolometric corrections indicated by current observations and a standard mass-to-light conversion efficiency \epsilon ~10%. The analysis of the accretion history highlights that the most massive BHs accreted their mass faster and at higher redshifts (z>1.5), while the lower mass BHs responsible for most of the hard X-ray background have mostly grown at z<1.5. The accreted mass function matches the local SMBH mass function if \epsilon ~0.09(+0.04,-0.03) and the Eddington ratio \lambda=L/L_Edd \~0.3(+0.3,-0.1) (68% confidence errors). The visibility time, during which AGNs are luminous enough to be detected by the currently available X-ray surveys, ranges from ~0.1 Gyr for present day BH masses M_BH(z=0) ~10^6 M_sun to ~0.3 Gyr for M_BH(z=0) >= 10^9 M_sun. The mass accreted during luminous phases is >= 25-30% even if we assume extreme values of \epsilon (\epsilon \~0.3-0.4). An unlikely fine tuning of the parameters would be required to account for the local SMBH mass function accomodating a dominant contribution from 'dark' BH growth (due, e.g., to BH coalescence).

Could supermassive black holes be quintessential primordial black holes?

There is growing observational evidence for a population of supermassive black holes (SMBHs) in galactic bulges. We examine in detail the conditions under which these black holes must have originated from primordial black holes (PBHs). We consider the merging and accretion history experienced by SMBHs to find that, whereas it is possible that they were formed by purely astrophysical processes, this is unlikely and most probably a population of primordial progenitors is necessary. We identify the mass distribution and comoving density of this population and then propose a cosmological scenario producing PBHs with the right properties. Although this is not essential we consider PBHs produced at the end of a period of inflation with a blue spectrum of fluctuations. We constrain the value of the spectral tilt in order to obtain the required PBH comoving density. We then assume that PBHs grow by accreting quintessence, showing that their mass scales like the horizon mass while the quintessence field itself is scaling. We find that if scaling is broken just before nucleosynthesis (as is the case with some attractive nonminimally coupled models) we obtain the appropriate PBH mass distribution. Hawking evaporation is negligible in most cases, but we also discuss situations in which the interplay of accretion and evaporation is relevant.

Limits on the cosmological abundance of supermassive compact objects from a search for multiple imaging in compact radio sources.

Using very long baseline interferometry we have searched a sample of 300 compact radio sources for examples of multiple imaging produced by gravitational lensing; no multiple images were found with separations in the angular range 1.5--50 milliarcsec. This null result allows us to place a limit on the cosmological abundance of intergalactic supermassive compact objects in the mass range approximately 10(6)M( middle dot in circle) to approximately 10(8)M( middle dot in circle); such objects cannot make up more than approximately 1% of the closure density ( 95% confidence). A uniformly distributed population of supermassive black holes forming soon after the big bang does not, therefore, contribute significantly to the dark matter content of the Universe.

Quasars from Galaxy Collisions with Naked Black Holes

Motivated by a set of new Hubble Space Telescope observations by Bahcall and collaborators, we propose that the universe contains a substantial independent population of supermassive black holes and that QSOs are a phenomenon that occurs when they collide with galaxies or gas clouds in the intergalactic medium. We argue that this new model is not in conflict with any available constraints and would also naturally explain one puzzle for the conventional model, the very rapid QSO population decline toward low redshift. The hypothesis therefore bears further investigation.

Low-frequency gravitational waves from supermassive black holes

Supermassive black holes are investigated as possible sources for low-frequency bursts of gravity waves. The event rate for `known' supermassive black holes at intermediate and high redshifts, inferred from the quasar luminosity function, is low $\sim 0.1 \yr^{-1}$. A space-based interferometer could therefore only see several events per year from supermassive black holes if an additional population of supermassive black holes existed and emitted gravitational waves efficiently. These might reside in the population of dwarf galaxies or in a transient population of small dark matter haloes that have mostly merged into larger haloes hosting the galaxies seen today. The proposed space-based gravitational-wave interferometer LISA/SAGITTARIUS should detect most gravitational-wave events involving supermassive black holes above $10^{4} \Msol$ out to redshifts of $z \sim 100$.