Quasars at z=6: the survival of the fittest

The Sloan Digital Sky survey detected luminous quasars at very high redshift, z>6. Follow-up observations indicated that at least some of these quasars are powered by supermassive black holes (SMBHs) with masses in excess of billion solar masses. SMBHs, therefore, seem to have already existed when the Universe was less than 1 Gyr old, and the bulk of galaxy formation still has to take place. We investigate in this paper to which extent accretion and dynamical processes influence the early growth of SMBHs. We assess the impact of (i) black hole mergers, (ii) the influence of the merging efficiency and (iii) the negative contribution due to dynamical effects which can kick black holes out of their host halos (gravitational recoil). We find that if accretion is always limited by the Eddington rate via a thin disc, the maximum radiative efficiency allowed to reproduce the LF at z=6 is of order 12%, when the adverse effect of the gravitational recoil is taken into consideration. Dynamical effects cannot be neglected in studies of high-redshift SMBHs. If black holes can accrete at super-critical rate during an early phase, reproducing the observed SMBH mass values is not an issue, even in the case that the recoil velocity is in the upper limits range, as the mass ratios of merging binaries are skewed towards low values, where the gravitational recoil effect is very mild. We propose that SMBH growth at early times is very selective, and efficient only for black holes hosted in high density peak halos.Comment: Accepted for publication in the ApJ. 9 pages, 6 b/w figure

The Assembly and Merging History of Supermassive Black Holes in Hierarchical Models of Galaxy Formation

We assess models for the assembly of supermassive black holes (SMBHs) at the center of galaxies that trace their hierarchical build-up far up in the dark halo `merger tree'. We assume that the first `seed' black holes (BHs) formed in (mini)halos collapsing at z=20 from high-sigma density fluctuations. As these pregalactic holes become incorporated through a series of mergers into larger and larger halos, they sink to the center owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become supermassive, form a binary system, and eventually coalesce. The merger history of dark matter halos and associated BHs is followed by cosmological Monte Carlo realizations of the merger hierarchy. A simple model, where quasar activity is driven by major mergers and SMBHs accrete at the Eddington rate a mass that scales with the fifth power of the velocity dispersion, is shown to reproduce the optical LF of quasars in the redshift range 1<z<4. Binary and triple BH interactions are followed in our merger tree. The assumptions underlying our scenario lead to the prediction of a population of massive BHs wandering in galaxy halos and the intergalactic medium at the present epoch, and contributing <10% to the total BH mass density. At all epochs the fraction of binary SMBHs in galaxy nuclei is of order 10%, while the fraction of binary quasars is less than 0.3%Comment: revised version, accepted for publication in the ApJ, emulateapj, 15 pages, 16 figure

Reconstructing the massive black hole cosmic history through gravitational waves

The massive black holes we observe in galaxies today are the natural end-product of a complex evolutionary path, in which black holes seeded in proto-galaxies at high redshift grow through cosmic history via a sequence of mergers and accretion episodes. Electromagnetic observations probe a small subset of the population of massive black holes (namely, those that are active or those that are very close to us), but planned space-based gravitational-wave observatories such as the Laser Interferometer Space Antenna (LISA) can measure the parameters of ``electromagnetically invisible'' massive black holes out to high redshift. In this paper we introduce a Bayesian framework to analyze the information that can be gathered from a set of such measurements. Our goal is to connect a set of massive black hole binary merger observations to the underlying model of massive black hole formation. In other words, given a set of observed massive black hole coalescences, we assess what information can be extracted about the underlying massive black hole population model. For concreteness we consider ten specific models of massive black hole formation, chosen to probe four important (and largely unconstrained) aspects of the input physics used in structure formation simulations: seed formation, metallicity ``feedback'', accretion efficiency and accretion geometry. For the first time we allow for the possibility of ``model mixing'', by drawing the observed population from some combination of the ``pure'' models that have been simulated. A Bayesian analysis allows us to recover a posterior probability distribution for the ``mixing parameters'' that characterize the fractions of each model represented in the observed distribution. Our work shows that LISA has enormous potential to probe the underlying physics of structure formation.Comment: 24 pages, 16 figures, submitted to Phys. Rev.

Structural and functional stabilization of protein entities

XI Reunião Regional Nordeste da SBBq | 4th International Symposium in Biochemistry of Macromolecules and BiotechnologyStabilization of protein and protein-like molecules translates into preservation of both structure and functionality during storage and/or targeting, and such stabilization is mostly attained through establishment of a thermodynamic equilibrium with the (micro)environment. The basic thermodynamic principles that govern protein structural transitions and the interactions of the protein and/or peptide molecule with its (micro)environment will, therefore, be tackled. Protein stabilization is based upon dampening the molecular motions and, therefore, eliminating conformational transitions while the molecule is still in the native 3D (folded) state. The 3D structure of a protein molecule depends mostly on two types of interactions: intramolecular interactions between aminoacid moieties and intermolecular interactions with solute and/or solvent molecules present in its microenvironment. Stabilizing a biomolecule (aiming at preserving its function) involves dampening its molecular motions, and this can be achieved by reducing the chemical activity of the water present in its microenvironment, thus stabilizing both its structure and functionality. Recently, the simultaneous entrapment-stabilization of proteins and enzymes based on nanoencapsulation in a nanoemulsion (W/O/W) matrix with an hydrophilic core has started to gain momentum. Similarly to the stabilization mechanism of osmolytes, in nanoencapsulation the water activity is altered thus affecting the molecular motions of the proteins. Highlights will also be given to structural and functional stabilization of protein entities (viz. enzymes, (macro)peptides, (recombinant) proteins, and bacteriophages) by chemical methodologies. Modification of the biomolecules microenvironment via multipoint covalent attachment onto a solid surface followed by hydrophylic polymer coimmobilization, are some of the (latest) strategies that will be discussed.info:eu-repo/semantics/publishedVersio

Anaerobic digestion of OMW : intermittent feeding strategy and LCFA oxidation profile

ManuscriptAn intermittent feeding strategy was applied to the anaerobic treatment of raw olive mill wastewater (OMW). Two reactors were operated under influent concentrations of 5 to 50 g COD L-1. Two and one batch (feed-less) periods were applied to reactor R1 and R2, respectively, operating in continuous thenceforth. It was demonstrated that the intermittent feeding of OMW improved the mineralization of accumulated Long Chain Fatty Acids (LCFA) inside the reactor. Nevertheless, LCFA accumulated again when the organic loading rate was increased from 2 to 3 and 5 kg COD m-3 d-1. The profiles of LCFA, obtained with OMW digestion, were different from previous studies with synthetic effluents. At the beginning of reactors operation, oleate was the main LCFA compound (~50%) followed by palmitate. Afterwards, a shift in the LCFA pattern accumulation was noticed for both reactors. At periods with higher OMW concentrations (30-50 g COD L-1, 3-5 kg COD m-3 d-1) palmitate was the main LCFA accumulated with 69% at R1 and 54% at R2. For real oily wastewaters, a periodically batch period could be a practical solution to maintain low values of LCFA inside the reactor. The addition of a nitrogen source was essential to enhance the methane yield

Strategies for lipids and phenolics degradation in the anaerobic treatment of olive mill wastewater

Strategies are proposed for the anaerobic treatment of lipid and phenolic-rich effluents, specifically the raw olive mill wastewater (OMW). Two reactors were operated under OMW influent concentrations from 5 to 48 g COD L-1 and Hydraulic Retention Time between 10 and 5 days. An intermittent feeding was applied whenever the reactors showed a severe decay in the methane yield. This strategy improved the mineralization of oleate and palmitate, which were the main accumulated Long Chain Fatty Acids (LCFA), and also promoted the removal of resilient phenolic compounds, reaching remarkable removal efficiencies of 60% and 81% for two parallel reactors at the end of a feed-less period. A maximum biogas production of 1.4 m3 m-3 d-1 at an Organic Loading Rate of 4.8 kg COD m-3 d-1 was obtained. Patterns of individual LCFA oxidation during the OMW anaerobic digestion are presented and discussed for the first time. The supplementation of a nitrogen source boosted immediately the methane yield from 21 and 18 to 76 and 93% in both reactors. The typical problems of sludge flotation and washout during the anaerobic treatment of this oily wastewater were overcome by biomass retention, according to the Inverted Anaerobic Sludge Blanket (IASB) reactor concepts. This work demonstrates that it is possible to avoid a previous detoxification step by implementing adequate operational strategies to the anaerobic treatment of OMW.The authors acknowledge the financial support of the “Fundação para a Ciência e a Tecnologia”, FCT/MCTES, through the project PTDC/ENR/69755/2006 and also through the grants given to Marta Gonçalves SFRH/BD/40746/2007 and José Carlos Costa SFRH/BDP/ 48962 /2008. The authors thank Tânia Ferreira for the help in LCFA analysis and Ana Cavaleiro for her scientific support

Compact massive objects in Virgo galaxies: the black hole population

We investigate the distribution of massive black holes (MBHs) in the Virgo cluster. Observations suggest that AGN activity is widespread in massive galaxies (M>1e10 solar masses), while at lower galaxy masses star clusters are more abundant, which might imply a limited presence of central black holes in these galaxy-mass regimes. We explore if this possible threshold in MBH hosting, is linked to nature, nurture, or a mixture of both. The nature scenario arises naturally in hierarchical cosmologies, as MBH formation mechanisms typically are efficient in biased systems, which would later evolve into massive galaxies. Nurture, in the guise of MBH ejections following MBH mergers, provides an additional mechanism that is more effective for low mass, satellite galaxies. The combination of inefficient formation, and lower retention of MBHs, leads to the natural explanation of the distribution of compact massive ob jects in Virgo galaxies. If MBHs arrive to the correlation with the host mass and velocity dispersion during merger-triggered accretion episodes, sustained tidal stripping of the host galaxies creates a population of MBHs which lie above the expected scaling between the holes and their host mass, suggesting a possible environmental dependence.Comment: MNRAS letter

Scaling approach to order-parameter fluctuations in disordered frustrated systems

We present a constructive approach to obtain information about the compactness and shape of large-scale lowest excitations in disordered systems by studying order-parameter fluctuations (OPF) at low temperatures. We show that the parameter $G$ which measures OPF is 1/3 at T=0 provided the ground state is unique and the probability distribution for the lowest excitations is gapless and with finite weight at zero-excitation energy. We then apply zero-temperature scaling to describe the energy and volume spectra of the lowest large-scale excitations which scale with the system size and have a weight at ze ro energy $\hat{P}_v(0)\sim l^{-\theta'}$ with $v=l^d$. A low-temperature expansion reveals that, OPF vanish like $L^{-\theta}$, if $\theta> 0$ and remain finite for space filling lowest excitations with $\theta=0$. The method can be extended to extract information about the shape and fractal surface of the large-scale lowest excitations.Comment: 4 pages, REVTeX. Some modifications; final version accepted for publication in J. Phys. A: Math. and General (Letters