Radiation Pressure Supported Starburst Disks and AGN Fueling

We consider the structure of marginally Toomre-stable starburst disks under the assumption that radiation pressure on dust grains provides the dominant vertical support against gravity. This is particularly appropriate when the disk is optically thick to its own IR radiation, as in the central regions of ULIRGs. Because the disk radiates at its Eddington limit, the Schmidt-law for star formation changes in the optically-thick limit, with the star formation rate per unit area scaling as Sigma_g/kappa, where Sigma_g is the gas surface density and kappa is the mean opacity. We show that optically thick starburst disks have a characteristic flux and dust effective temperature of F ~ 10^{13} L_sun/kpc^2 and T_eff ~ 90K, respectively. We compare our predictions with observations and find good agreement. We extend our model from many-hundred parsec scales to sub-parsec scales and address the problem of fueling AGN. We assume that angular momentum transport proceeds via global torques rather than a local viscosity. We account for the radial depletion of gas due to star formation and find a strong bifurcation between two classes of disk models: (1) solutions with a starburst on large scales that consumes all of the gas with little fueling of a central AGN and (2) models with an outer large-scale starburst accompanied by a more compact starburst on 1-10 pc scales and a bright central AGN. The luminosity of the latter models is in many cases dominated by the AGN. We show that the vertical thickness of the starburst disk on pc scales can approach h ~ r, perhaps accounting for the nuclear obscuration in some Type 2 AGN. We also argue that the disk of young stars in the Galactic Center may be the remnant of such a compact nuclear starburst.Comment: 26 pages, 9 figures, emulateapj, accepted to ApJ, minor changes, discussion tightened, references adde

Stellar disk in the galactic center -- a remnant of a dense accretion disk?

Observations of the galactic center revealed a population of young massive stars within 0.4 pc from Sgr A* -- the presumed location of a supermassive black hole. The origin of these stars is a puzzle as their formation in citu should be suppressed by the black hole's tidal field. We find that out of 13 stars whose 3-dimensional velocities have been measured by Genzel et. al. (2000), 10 lie in a thin disk. The half-opening angle of the disk is consistent with zero within the measurement errors, and does not exceed 10 degrees. We propose that a recent burst of star formation has occurred in a dense gaseous disk around Sgr A*. Such a disk is no longer present because, most likely, it has been accreted by the central black hole. The three-dimensional orbit of S2, the young star closest to Sgr A*, has been recently mapped out with high precision. It is inclined to the stellar disk by 75 degrees. We find that the orbit should undergo Lense-Thirring precession with the period of (5/a) Myr, where a<1 is the dimensionless spin of the black hole. Therefore it is possible that originally S2 orbit lay in the disk plane. If so, we can constrain the black hole spin $a$ be greater than 0.2(t_{S2}/5 Myr), where t_{S2} is the age of S2.Comment: submitted to ApJ Letter

The Link between Warm Molecular Disks in Maser Nuclei and Star Formation near the Black Hole at the Galactic Center

The discovery of hundreds of young, bright stars within a parsec from the massive black hole at the center of the Galaxy presents a challenge to star formation theories. The requisite Roche densities for the gravitational collapse of gas clouds are most naturally achieved in accretion disks. The water maser sources in Keplerian rotation in the nuclei of NGC4258, NGC1068, and the Circinus galaxy indicate the presence of warm, extended, molecular accretion disks around black holes similar in mass to the one at the Galactic center. Here we argue that the current conditions in the maser nuclei, and those near the Galactic center, represent two consecutive, recurrent phases in the life cycle of the nucleus of a typical gas-rich spiral bulge. The warm molecular disks that give rise to the observed maser emission fragment into stellar-size objects. The stellar masses, their orbital geometry, and the total number of stars thus formed are consistent with the values identified at the Galactic center. The stars tend to form in compact groups resembling the IRS 13 complex that dominates the stellar light in the neighborhood of the black hole.Comment: ApJ Letters, in pres

An axisymmetric hydrodynamical model for the torus wind in AGN. II: X-ray excited funnel flow

We have calculated a series of models of outflows from the obscuring torus in active galactic nuclei (AGN). Our modeling assumes that the inner face of a rotationally supported torus is illuminated and heated by the intense X-rays from the inner accretion disk and black hole. As a result of such heating a strong biconical outflow is observed in our simulations. We calculate 3-dimensional hydrodynamical models, assuming axial symmetry, and including the effects of X-ray heating, ionization, and radiation pressure. We discuss the behavior of a large family of these models, their velocity fields, mass fluxes and temperature, as functions of the torus properties and X-ray flux. Synthetic warm absorber spectra are calculated, assuming pure absorption, for sample models at various inclination angles and observing times. We show that these models have mass fluxes and flow speeds which are comparable to those which have been inferred from observations of Seyfert 1 warm absorbers, and that they can produce rich absorption line spectra.Comment: 32 pages, 11 figures Accepted for publication in Ap

An Eccentric Circumbinary Accretion Disk and the Detection of Binary Massive Black Holes

We present a two-dimensional grid-based hydrodynamic simulation of a thin, viscous, locally-isothermal corotating disk orbiting an equal-mass Newtonian binary point mass on a fixed circular orbit. We study the structure of the disk after multiple viscous times. The binary maintains a central hole in the viscously-relaxed disk with radius equal to about twice the binary semimajor axis. Disk surface density within the hole is reduced by orders of magnitude relative to the density in the disk bulk. The inner truncation of the disk resembles the clearing of a gap in a protoplanetary disk. An initially circular disk becomes elliptical and then eccentric. Disturbances in the disk contain a component that is stationary in the rotating frame in which the binary is at rest; this component is a two-armed spiral density wave. We measure the distribution of the binary torque in the disk and find that the strongest positive torque is exerted inside the central low-density hole. We make connection with the linear theory of disk forcing at outer Lindblad resonances (OLRs) and find that the measured torque density distribution is consistent with forcing at the 3:2 (m=2) OLR, well within the central hole. We also measure the time dependence of the rate at which gas accretes across the hole and find quasi-periodic structure. We discuss implications for variability and detection of active galactic nuclei containing a binary massive black hole.Comment: 10 pages; replaced to match ApJ version; includes new physical interpretation of torque density (Sec. 4.1); large mpeg animation is available at http://www.tapir.caltech.edu/~milos/circBinaryEccDisk.mp

21cm Absorption by Compact Hydrogen Disks Around Black Holes in Radio-Loud Nuclei of Galaxies

The clumpy maser disks observed in some galactic nuclei mark the outskirts of the accretion disk that fuels the central black hole and provide a potential site of nuclear star formation. Unfortunately, most of the gas in maser disks is currently not being probed; large maser gains favor paths that are characterized by a small velocity gradient and require rare edge-on orientations of the disk. Here we propose a method for mapping the atomic hydrogen distribution in nuclear disks through its 21cm absorption against the radio continuum glow around the central black hole. In NGC 4258, the 21cm optical depth may approach unity for high angular-resolution (VLBI) imaging of coherent clumps which are dominated by thermal broadening and have the column density inferred from X-ray absorption data, ~10^{23}/cm^2. Spreading the 21cm absorption over the full rotation velocity width of the material in front of the narrow radio jets gives a mean optical depth of ~0.1. Spectroscopic searches for the 21cm absorption feature in other galaxies can be used to identify the large population of inclined gaseous disks which are not masing in our direction. Follow-up imaging of 21cm silhouettes of accelerating clumps within these disks can in turn be used to measure cosmological distances.Comment: 4 page

A combined model for the X-ray to gamma-ray emission of Cyg X-1

We use recent data obtained by three (OSSE, BATSE, and COMPTEL) of four instruments on board the Compton Gamma Ray Observatory, to construct a model of Cyg X-1 which describes its emission in a broad energy range from soft X-rays to MeV gamma-rays self-consistently. The gamma-ray emission is interpreted to be the result of Comptonization, bremsstrahlung, and positron annihilation in a hot optically thin and spatially extended region surrounding the whole accretion disk. For the X-ray emission a standard corona-disk model is applied. We show that the Cyg X-1 spectrum accumulated by the CGRO instruments during a ~4 year time period between 1991 and 1995, as well as the HEAO-3 gamma1 and gamma2 spectra can be well represented by our model. The derived parameters match the observational results obtained from X-ray measurements.Comment: 11 pages including 6 ps-figures and 2 tables, latex2e, uses emulateapj.sty (ver. of 18 Sep 96, enclosed), epsfig.sty, times.sty. To appear in July 20, 1998 issue of ApJ (v.502

HERPESVIRUS INFECTIONS AND CLINICAL-IMMUNOLOGIC INTERACTIONS IN PATIENTS WITH EARLY-ONSET ALZHEIMER’S DISEASE AND LATE-ONSET ALZHEIMER’S DISEASE

Alzheimer’s disease (AD) is currently the most common cause of dementia. A significant role in the pathogenesis of AD belongs to the activation of the mechanisms of neuroinflammation. There is a hypothesis that chronic infections may play a role in the maintenance of the inflammatory response in AD. The aim of this work was to study the detection rate and DNA level of herpesviruses, as well as their possible relationship with the level of the key cytokines and with clinical parameters of AD in patients with early and late onset. 30 patients with AD and 33 healthy volunteers were enrolled. The quantitative determination of DNA of CMV, EBV, HHV-6, HHV-7 was carried out by PCR. The level of cytokines and soluble IL-1β antagonist (IL-1ra) in the blood was determined by ELISA. Herpesvirus infection with increased viral load was determined if at least one of the criteria was present: 1) DNA level of EBV and/or HHV-6 &gt; 10,000 copies/ml in saliva; 2) presence of DNA of at least one of the EBV, HHV-6, HHV-7 viruses in the blood. In the subgroup of patients with early onset and increased viral load, there was a higher increase in the levels of a number of cytokines: proinflammatory IL-8 and IL-12, a Th2-cytokine IL-4, a cytokine of the adaptive immune response IL-2. However, the level of the anti-inflammatory protein IL-1ra was lower than in the controls. These changes may indicate a dysregulation of the antiviral response, with a predominance of activation of systemic inflammation and Th2-mediated reactions. Also, in early onset AD the increased viral load was associated with lower scores on Boston naming test. The results indicate that in studies of AD mechanisms and in the search for prognostic markers of the disease, it is important to take into account the heterogeneity of AD in terms of genetic predisposition factors, risk factors, immune parameters and clinical data. Such approach is necessary for the subsequent development of personalized approaches to the prevention and treatment of AD

Star Formation and Dynamics in the Galactic Centre

The centre of our Galaxy is one of the most studied and yet enigmatic places in the Universe. At a distance of about 8 kpc from our Sun, the Galactic centre (GC) is the ideal environment to study the extreme processes that take place in the vicinity of a supermassive black hole (SMBH). Despite the hostile environment, several tens of early-type stars populate the central parsec of our Galaxy. A fraction of them lie in a thin ring with mild eccentricity and inner radius ~0.04 pc, while the S-stars, i.e. the ~30 stars closest to the SMBH (<0.04 pc), have randomly oriented and highly eccentric orbits. The formation of such early-type stars has been a puzzle for a long time: molecular clouds should be tidally disrupted by the SMBH before they can fragment into stars. We review the main scenarios proposed to explain the formation and the dynamical evolution of the early-type stars in the GC. In particular, we discuss the most popular in situ scenarios (accretion disc fragmentation and molecular cloud disruption) and migration scenarios (star cluster inspiral and Hills mechanism). We focus on the most pressing challenges that must be faced to shed light on the process of star formation in the vicinity of a SMBH.Comment: 68 pages, 35 figures; invited review chapter, to be published in expanded form in Haardt, F., Gorini, V., Moschella, U. and Treves, A., 'Astrophysical Black Holes'. Lecture Notes in Physics. Springer 201