Hole Mass Ratio Research Articles

The X+ trion in a system with spatial separation of the charge carriers

A system composed of two heavy holes located in a two-dimensional (2D) quantum well (QW) and bound via mediation of an electron in a neighboring 2D QW is considered. Using a simple qualitative trial wave function, the ground-state energy of this kind of X+ trion is determined in the infinite-hole-mass approximation as a function of the QW spacing. Coordinate dependence of the effective potential binding the holes to each other is calculated for different values of QW spacing. In the adiabatic approximation, a set of dependences describing the X+ trion binding energy as a function of the electron mass to the hole mass ratio is obtained. Several estimates for the trion binding energy in GaAs-and ZnSe-based double-QW heterostructures are given.

Searching for the physical drivers of eigenvector 1: influence of black hole mass and Eddington ratio

We compute the virial mass (M) of the central black hole and the luminosity-to-mass (L/M) ratio of ≈300 low-z quasars and luminous type 1 Seyfert nuclei. We analyse the following: (1) whether radio-quiet and radio-loud objects show systematic differences in terms of M and L/M; (2) the influence of M and L/M on the shape of the Hβ broad component line profile; and (3) the significance of the so-called ‘blue outliers’, i.e. sources showing a significant blueshift of the [O iii]λλ4959,5007 lines with respect to the narrow component of Hβ, which is used as an estimator of the quasar reference frame. We show that M and L/M distributions for radio-quiet and radio-loud sources are probably different for samples matched in luminosity and redshift, in the sense that radio-quiet sources have systematically smaller masses and larger L/M. However, the L/M ratio distributions become indistinguishable if 8.5 < log M < 9.5. Line profile comparisons for median spectra computed over narrow ranges of M and L/M indicate that a Lorentz function provides a better fit for higher L/M sources and a double Gaussian for lower L/M values. A second (redshifted) Gaussian component at low L/M appears as a red asymmetry frequently observed in radio-loud and radio-quiet sources with broader (full width at half-maximum ≳4000 km s−1) Hβ broad component profiles. This component becomes stronger in larger mass and lower L/M sources. No specific influence of radio loudness on the Hβ broad component profile is detected, although equivalent widths of Hβ broad component and especially of [O iii]λλ4959,5007 are larger for radio-loud sources. We identify five more ‘blue outlier’ sources. Since these sources are, on average, one magnitude brighter than other active galactic nuclei with similar mass, their resulting Eddington ratio is 2–3 times higher. We hint at evolutionary effects that explain some of these results, and reinforce the ‘eigenvector 1’ correlations.

The Baldwin Effect and Black Hole Accretion: A Spectral Principal Component Analysis of a Complete Quasar Sample

We have performed a spectral principal component analysis (SPCA) for an essentially complete sample of 22 low-redshift QSOs with spectral data from Lyto H� . SPCA yields a set of independent principal compo- nent spectra, each of which represents a set of relationships among QSO continuum and line properties. We find three significant principal components, which account for � 78% of the total intrinsic variance. The first component, carrying � 41% of the intrinsic variance, represents Baldwin relationships: anticorrelations between equivalent widths of broad emission lines and continuum luminosity. The narrow-line core (FWHM � 2000 km s � 1 ) of the broad emission lines dominate this component. The second component, accounting for � 23% of the intrinsic variance, represents the variations in UV continuum slope, which is probably the result of dust reddening, with possible contributions from starlight. The third principal component is directly related to the Boroson & Green '' eigenvector 1 '' (their first principal component), clearly showing the anti- correlation between strengths of optical Fe ii and (O iii) � 5007, and other relationships previously found in the H� -(O iii) region. This third component shows the expected strong correlation with soft X-ray spectral index. The widths of C iii) � 1909, Mg ii � 2798, and Balmer emission lines are also involved and clearly corre- lated, relating this component to black hole mass or Eddington accretion ratio. We find an inverse correlation between the strengths of the UV and optical Fe ii blends, as suggested by some photoionization models. We also find correlations of the strengths of several low-ionization UV lines with Fe ii(opt), and a strong positive correlation of C iv � 1549 with (O iii) strength. The wide wavelength coverage of our data enables us to see clearly the relationships between the UV and optical spectra of QSOs. The Baldwin effect and Boroson & Green's eigenvector 1 relationship are clearly independent. We demonstrate how Baldwin relationships can be derived using our first principal component, virtually eliminating the scatter caused by the third principal component. This rekindles the hope that the Baldwin relationships can be used for cosmological study. Subject headings: galaxies: active — galaxies: nuclei — quasars: emission lines — ultraviolet: galaxies

The Kozai Mechanism and the Evolution of Binary Supermassive Black Holes

We consider the dynamical evolution of bound, hierarchical triples of supermassive black holes that might be formed in the nuclei of galaxies undergoing sequential mergers. The tidal force of the outer black hole on the inner binary produces eccentricity oscillations through the Kozai mechanism, and this can substantially reduce the gravitational wave merger time of the inner binary. We numerically calculate the merger time for a wide range of initial conditions and black hole mass ratios, including the effects of octupole interactions in the triple as well as general relativistic periastron precession in the inner binary. The semimajor axes and the mutual inclination of the inner and outer binaries are the most important factors affecting the merger time. We find that for a random distribution of inclination angles and approximately equal mass black holes, it is possible to reduce the merger time of a near circular inner binary by more than a factor of 10 in over 50% of all cases. We estimate that a typical exterior quadrupole moment from surrounding matter in the galaxy may also be sufficient to excite eccentricity oscillations in supermassive black hole binaries and to accelerate black hole mergers.

Ultraluminous Infrared Galaxies: Mergers of Sub‐L* Galaxies?

A sample of 27 low-redshift, mostly cool, ultraluminous infrared galaxies (ULIRGs) has been imaged at 1.6 μm with the Hubble Space Telescope (HST) Near-Infrared Camera and Multi-Object Spectrometer (NICMOS). The majority (67%) of the sample's galaxies are multiple-nucleus galaxies with projected separations of up to 17 kpc, and the rest of the sample (33%) are single-nucleus galaxies, as determined by the NICMOS angular resolution limit. The average observed, integrated (host+nucleus) H magnitude of our HST H sample ULIRGs is -24.3, slightly above that of an L* galaxy (MH = -24.2), and 52% of the sample's galaxies have sub-L* luminosities. The ULIRGs in the HST H sample are not generated as a result of the merging of two luminous (i.e., ≥L*) spiral galaxies. Instead, the interactions and mergers occur in general between two, or in some cases more, less massive sub-L* (0.3-0.5L*) galaxies. Only one out of the 49 nuclei identified in the entire HST H sample has the properties of a bright quasar-like nucleus. On average, the brightest nuclei in the HST H sample galaxies (i.e., cool ULIRGs) are 1.2 mag fainter than warm ULIRGs and low-luminosity Bright Quasar Survey quasars (BQS QSOs) and 2.6 mag fainter than high-luminosity BQS QSOs. Since the progenitor galaxies involved in the merger are sub-L* galaxies, the mass of the central black hole in these ULIRGs would be only about (1-2) × 107 M☉, if the bulge-to-black hole mass ratio of nearby galaxies holds for ULIRGs. The estimated mass of the central black hole is similar to that of nearby Seyfert 2 galaxies but at least 1 order of magnitude lower than the massive black holes thought to be located at the center of high-luminosity QSOs. Massive nuclear starbursts with constant star formation rates of 10-40 M☉ yr-1 could contribute significantly to the nuclear H-band flux and are consistent with the observed nuclear H-band magnitudes of the ULIRGs in the HST H sample. An evolutionary merging scenario is proposed for the generation of the different types of ULIRGs and QSOs on the basis of the masses of the progenitors involved in the merging process. According to this scenario, cool ULIRGs would be the end product of the merging of two or more low-mass (0.3L*-0.5L*) disk galaxies. Warm ULIRGs and low-luminosity QSOs would be generated by a merger involving intermediate-mass (0.5 L*) disk galaxies. Under this scenario, warm ULIRGs could still be the dust-enshrouded phases of UV-bright low-luminosity QSOs, but cool ULIRGs, which are most ULIRGs, would not evolve into QSOs.

Excitons and excitonic molecules in mixed Zn(P 1− xAs x) 2 crystals

Low-temperature (1.8 K) excitonic absorption, reflection and photoluminescence spectra of mixed Zn(P 1− x As x ) 2 crystals have been studied at x=0.01, 0.02, 0.03 and 0.05. Energy gap and rydbergs of excitonic B-, C- and A-series decrease monotonically with increasing of x. The spectral half-widths of the absorption n=1 lines of the B- and A-series increase monotonically with increase in x due to fluctuations of crystal potential. Emission lines of excitonic molecules have been observed in photoluminescence spectra of Zn(P 1− x As x ) 2 crystals. The binding energy of the molecule increases with increase in x due to the decrease of the electron–hole mass ratio.

Black Hole Mass and Eddington Ratio as Drivers for the Observable Properties of Radio‐loud and Radio‐quiet QSOs

Recent studies of black holes in the nuclei of both active and normal galaxies have yielded relationships that permit a physical interpretation of the principal components of the spectra of QSOs. It is shown that principal component (or eigenvector) 1 (PC1) is driven predominantly by L/LEdd, and principal component 2 (PC2) is driven by accretion rate. This results in a PC2 versus PC1 diagram in which lines of constant black hole mass are diagonal. Using a sample consisting of the low-redshift PG objects supplemented by 75 radio-loud QSOs, it is shown that such a diagram effectively distinguishes radio-loud from radio-quiet objects and demonstrates that both narrow-line Seyfert 1 galaxies and broad absorption line QSOs lie at the high L/LEdd extreme, although these two types of objects are well separated in the PC2 direction. A simple picture that ties together physical parameters (black hole mass and Eddington ratio) and classification of active galactic nuclei is presented. Based on the location of core-dominated and lobe-dominated radio-loud QSOs, orientation can be modeled as a third parameter in this scheme, implying an enhancement in the radio flux of core-dominated objects.

Excited states of the positronium molecule

We investigate the spectrum of the positronium (Ps) molecule consisting of two electrons and two positrons by the stochastic variational method (SVM). By calculating the energies of states with L π=0 ±,1 ± and 2 ±, we confirm that only four states, 0 +( A 1), 0 +( B 2), 0 +( E) and 1 −( B 2), are bound. We investigate the various properties of these bound states as well as the decay probabilities for the 2γ emission by electron–positron annihilation leaving a particular Ps final state. The binding energies of a biexciton, a Coulomb four-body system analogous to Ps 2, are also examined as a function of the electron–hole mass ratio.

Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei.

We identify a correlation space involving optical and UV emission-line parameters as well as the soft X-ray spectral index that provides optimal discrimination between all principal classes of active galactic nuclei (AGNs). Most of the sources in our three high-quality data samples show a strong intercorrelation with narrow-line Seyfert 1 (NLSy1) galaxies and steep-spectrum radio galaxies occupying opposite extrema in the space. NLSy1 sources show a clear continuity with broader line sources, indicating that they are not a disjoint class of AGN as is sometimes suggested. We interpret the principal intercorrelation in the parameter space as being driven by the AGN luminosity-to-black hole mass ratio (L&solm0;M is proportional to the Eddington ratio). Source orientation no doubt also plays an important role, but it is not yet clear whether FWHM Hbeta or C iv lambda1549 line shift is the better indicator. We tentatively identify two radio-quiet populations: an almost pure radio-quiet population A, with FWHM</=4000, and population B, which occupies the same parameter domain as the flat-spectrum radio-loud sources. A possible interpretation sees population A/NLSy1 as lower mass/high accretion rate sources and population B/radio-loud sources as the opposite.

Black Hole-Neutron Star Mergers as Central Engines of Gamma-Ray Bursts.

Hydrodynamic simulations of the merger of stellar mass black hole-neutron star binaries are compared with mergers of binary neutron stars. The simulations are Newtonian but take into account the emission and back-reaction of gravitational waves. The use of a physical nuclear equation of state allows us to include the effects of neutrino emission. For low neutron star-to-black hole mass ratios, the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted, whereas for ratios near unity the neutron star is destroyed during its first approach. A gas mass between approximately 0.3 and approximately 0.7 M middle dot in circle is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several times 1053 ergs s-1 during an estimated accretion timescale of about 0.1 s. The emitted neutrinos and antineutrinos annihilate into e+/- pairs with efficiencies of 1%-3% and rates of up to approximately 2x1052 ergs s-1, thus depositing an energy Enunu&d1; less, similar1051 ergs above the poles of the black hole in a region that contains less than 10-5 M middle dot in circle of baryonic matter. This could allow for relativistic expansion with Lorentz factors around 100 and is sufficient to explain apparent burst luminosities Lgamma approximately Enunu&d1;&solm0;&parl0;fOmegatgamma&parr0; up to several times 1053 ergs s-1 for burst durations tgamma approximately 0.1-1 s, if the gamma emission is collimated in two moderately focused jets in a fraction fOmega=2deltaOmega&solm0;&parl0;4pi&parr0; approximately 1&solm0;100-(1/10) of the sky.

Acceptor states in cubic semiconductors having a large hole-mass ratio

In cubic semiconductors the hole-mass ratio is small, which makes it possible to use the zero light-hole-mass limit. It was found that variational methods in this popular limit are not necessary to solve the Luttinger equation and not only the entire energy spectrum for the bound states of an acceptor and the eigenfunctions, including in momentum space, but also the behavior of the eigenfunctions at large radii can be determined to a high degree of accuracy. This approach made it possible to suggest comparatively simple relations for the lowest states of each series having different angular momenta, covering the entire range of possible mass ratios for semiconductors.

Simulations of Coalescing Neutron Star and Black Hole Binaries

We investigate the dynamics and evolution of merging neutron stars, of neutron stars coalescing with stellar-mass black holes, and the formation and properties of accretion tori around the (remnant) black holes. The three-dimensional Newtonian hydrodynamics equations are integrated by a Eulerian PPM code on four nested Cartesian grids. The code includes the emission and backreaction of gravitational waves as well as a physical nuclear equation-of-state (Lattimer & Swesty 1991) and the neutrino emission from the hot matter. Lepton number and energy losses of the gas due to neutrino emission are treated by an elaborate neutrino leakage scheme which takes into account neutrinos and antineutrinos of all flavors. Neutrino-antineutrino annihilation in the vicinity of the merger is evaluated in a post-processing step. The gravity of the black hole is described with a Newtonian or, alternatively, with a Paczynski-Wiita potential. The hydrodynamic effect of the black hole is simulated by extracting all matter that flows into a sphere with radius equal to the Schwarzschild radius of the black hole or, in accretion simulations, twice the Schwarzschild radius. The NS/NS and BH/NS merging models yield information about gravitational wave and neutrino emission. Also, they allow us to determine the physical properties (masses, densities, temperatures, estimated life times) of the remnants of the mergers: a black hole surrounded by an accretion torus. In the NS/NS case, a thick disk with a mass around 0.1 Mforms after the massive and very compact central object that contains most of the mass of the merged neutron stars, has collapsed to a black hole, presumably on a dynamical time scale. The dynamics of BH/NS mergers is very sensitive to the neutron star to black hole mass ratio. For low ratios the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted, whereas for ratios near unity the neutron star is already destroyed during its first approach. Agas mass of about 0.5 Mis left in an accretion torus around the black hole. The accretion tori radiate neutrinos at luminosities of up to several 10 53 erg/s. Higher luminosities are found for larger disk masses and smaller black holes. The emitted neutrinos and antineutrinos annihilate into e ± pairs with efficiencies of a few percent and rates of up to ∼ 2 × 10 52 erg/s, releasing an estimated energy of up to ∼ 10 51 erg in a pair-plasma fireball. The torus geometry favors relativistic expansion of the pair plasma along the baryon depleted system axis. The occurrence of moderately beamed jets with opening angles of several ten degrees is therefore likely. The jet energies and short accretion times of the tori of about 0.1 s are in the right range to account for the subclass of short and less energetic gamma-ray bursts.

Magnetic moment of an acceptor center in cubic semiconductors

The magnetic field-induced splitting of the ground-state spin levels of an acceptor center, described by superposition of the Coulomb and the central-cell potentials, has been calculated for diamond-type. An analytic expression for the g factor obtained in the zero-radius potential approximation depends only on the light to heavy hole mass ratio. It is shown that the differences between the values of the g factor for the limiting cases of purely Coulomb and zero-radius potentials do not exceed 5%, thus permitting one to use this analytic expression for estimates.

Bloated stars as AGN broad-line clouds: the emission-line profiles

The Bloated Stars Scenario proposes that AGN broad line emission originates in the winds or envelopes of bloated stars (BS). Alexander and Netzer (1994) established that ~ 5e4 BSs with dense, decelerating winds can reproduce the observed emission line spectrum and avoid rapid collisional destruction. Here, we use the observed properties of AGN line profiles to further constrain the model parameters. In the BS model, the origin of the broad profiles is the stellar velocity field in the vicinity of the central black hole. We use a detailed photoionization code and a model of the stellar distribution function to calculate the BS emission line profiles and compare them to a large sample of AGN CIV, CIII] and MgII profiles. We find that the BSs can reproduce the general shape and width of typical AGN profiles as well as the line ratios if (i) The ionizing luminosity to black hole mass ratio is low enough. (ii) The broad line region size is limited by some cutoff mechanism. (iii) The fraction of the BSs in the stellar population falls off roughly as r^-2. (iv) The wind density and/or velocity are correlated with the black hole mass and ionizing luminosity. Under these conditions the strong tidal forces near the black hole play an important role in determining the line emission properties of the BSs. Some discrepancies remain: the calculated BS profiles tend to have weaker wings than the observed ones, and the differences between the profiles of different lines are somewhat smaller than those observed.

Can the Formation of X-Ray–obscuring Tori and Jets in Active Galaxies be Determined by One Parameter?

A torus of reduced differential rotation can form in the inner 10 pc core of active galactic nuclei (AGNs), incurring a density enhancement that can account for obscuration of X-rays in Seyfert galaxies when the initial inner core-to-black hole mass ratio is 50. The same density enhancement can also lead to dynamo growth of significant poloidal magnetic fields when accreted onto the central engine. Since radio jet models often employ poloidal fields as agents in extracting power for the jet luminosity, we suggest that jetted AGNs might require this poloidal field production. Although the poloidal field would originally be produced in the obscuring torus, jetted objects could exist without obscuring tori: The poloidal field would only aid in powering jet emission after it accretes with the torus matter to the central engine. Thus, only during the relatively short torus accretion timescale could there be both a jet and a torus.

Simple formula for exciton binding energy in quantum wells with zero band offsets.

Band offsets in II-VI semiconductor quantum wells can be such as to show small or zero confinement in the conduction band while having considerable confinement in the valence band, or vice versa. By assuming purely two-dimensional motion and a simple variational exciton function, we calculate an explicit analytical expression for the 1s-exciton binding energy in this case and evaluate it for a range of electron- to hole-mass ratios.

Theory of optical orientation and alignment in quantum wells

The momentum distribution function and the average spin of photoexcited electrons in a quantum well are calculated for polarized optical excitation normal to the quantum well plane. In the case of small light hole-heavy hole mass ratio the dependencies of alignment parameter and spin on 2D motion energy are shown to have peculiarities at small energies. For the high-frequency edge of hot photoluminescence, the theoretical dependencies of linear and circular polarization on the excited electron energy are presented.

Many-body aspects of the optical spectra of bulk and low-dimensional doped semiconductors.

We discuss the many-body aspects of the optical spectra of doped semiconductors, for both bulk and low-dimensional systems. At low doping concentrations the spectra are dominated by excitonic effects, consistent with the single-particle band structure of these systems. With increasing doping atomic excitons lose their identity and eventually unbind, while the spectral weight moves continuously to the Fermi level. Depending on the electron-mass to hole-mass ratio, the spectra display a broadened singularity as well as Auger-like indirect transitions. We calculate the onset of absorption in this regime to second order in the effective interaction. We stress that a calculation of the spectra near the Fermi level is outside the scope of conventional perturbation theory and we comment on the validity of various previously proposed calculational schemes. We conclude by discussing the problem in terms of Fadeev-like equations, which describe up to three-particle correlations exactly.

Radiative decay of the bound exciton in direct-gap semiconductors: The correlation effect

We present a theory of the radiative decay of excitons bound to neutral donors and acceptors in direct-gap semiconductors within the spherical-effective-mass approximation. The calculation is carried out using a three-particle wave function which incorporates Pauli exchange and important interparticle correlation effects over the entire range of electron- to hole-mass ratios. Thus donor-and acceptor-bound excitons are treated within the same framework. Radiative lifetimes are studied and are found to be particularly sensitive to the interparticle distance between electron and hole for all mass ratios of physical interest. Calculations are carried out for the radiative decay rates of bound excitons in a number of materials and comparison is made with the measured radiative lifetimes of both donor- and acceptor-bound excitons in GaAs, InP, and CdS.

Biexcitons in crystals with large ortho—para‐exciton splitting

AbstractIt is shown that in a system of ortho‐ and para‐excitons two ortho‐excitons with total spin S = 0 interact attractively and biexcitons can be formed. The interaction potential of two ortho‐excitons is approximated by a generalized Morse potential depending on the electron—hole mass ratio σ. On this basis the energy of vibrational and rotational levels of the biexciton is obtained. The binding energy of the biexciton ground state is estimated for all values of σ.