Broad Absorption Line Regions Research Articles

New Constraints on Quasar Broad Absorption and Emission Line Regions from Gravitational Microlensing

Gravitational microlensing is a powerful tool allowing one to probe the structure of quasars on sub-parsec scale. We report recent results, focusing on the broad absorption and emission line regions. In particular microlensing reveals the intrinsic absorption hidden in the P Cygni-type line profiles observed in the broad absorption line quasar H1413+117, as well as the existence of an extended continuum source. In addition, polarization microlensing provides constraints on the scattering region. In the quasar Q2237+030, microlensing differently distorts the H$\alpha$ and CIV broad emission line profiles, indicating that the low- and high-ionization broad emission lines must originate from regions with distinct kinematical properties. We also present simulations of the effect of microlensing on line profiles considering simple but representative models of the broad emission line region. Comparison of observations to simulations allows us to conclude that the H$\alpha$ emitting region in Q2237+030 is best represented by a Keplerian disk.

A Structure for Quasars

This paper proposes a simple, empirically derived, unifying structure for the inner regions of quasars. This structure is constructed to explain the broad absorption line regions (BALRs) and the narrow associated ultraviolet and X-ray (NALs) and is also found to explain the broad emission line regions (BELRs) and several scattering features, including a substantial fraction of the broad X-ray Fe-K emission line and the biconical extended narrow emission line region (ENLR) structures seen on large kiloparsec scales in Seyfert images. The model proposes that a funnel-shaped thin shell outflow creates all of these features. The wind arises vertically from a narrow range of radii on a disk at BELR velocities. Radiation force then accelerates the flow radially, so that it bends outward to a cone angle of ~60° and has a divergence angle of ~6°, to give a covering factor of ~10%. When the central continuum is viewed from the side, through this wind, narrow high-ionization associated ultraviolet absorption lines and the X-ray absorbers are seen, as in many low-luminosity active galactic nuclei (AGNs). When viewed end-on, the full range of velocities is seen in absorption with a large total column density, giving rise to the broad absorption line systems seen in a minority of quasars, the BAL QSOs. The wind is both warm (~106 K) and highly ionized. This warm highly ionized medium (WHIM) has a density of ~109 cm-3, putting it in pressure equilibrium with the BELR clouds; the BELR is then a cool phase embedded in the overall outflow, avoiding cloud destruction through shear. The wind has the correct ionization parameter and filling factor for this. The high- and low-ionization zones of the BELR correspond to the cylindrical and conical regions of the wind, since the former is exposed to the full continuum while the latter receives only the continuum filtered by the former. The warm wind is significantly Thomson thick along the radial flow direction, producing the polarized optical continuum found in BALs, but is only partially ionized, creating a broad fluorescent 6.4 keV Fe-K emission line and greater than 10 keV Compton hump. The conical shell outflow can produce a biconical matter-bounded NELR. Luminosity-dependent changes in the structure, reducing the cylindrical part of the flow or increasing the mean angle to the disk axis and decreasing the wind opening angle, may explain the UV and X-ray Baldwin effects and the greater prevalence of obscuration in low-luminosity AGNs.

Red Quasars and Quasar Evolution: The Case of BAL QSO FIRST J155633.8+351758

We present the first near-infrared spectroscopic observations of the radio-loud broad absorption line quasi-stellar object (QSO), FIRST J155633.8+351758. The spectrum is similar to that of a reddened QSO and shows strong emission lines of H? and H?, as well as strong Fe II emission blends near H?. The redshift of the object, measured from the H? and H? lines, is zBLR = 1.5008 ? 0.0007, slightly larger than the redshift of zmetal = 1.48, estimated from the broad metal absorption features. Thus, the broad metal absorption features are blue shifted with respect to the systemic velocity. The width of the H? emission line (FWHM ? 4100 km s -1) is typical of that observed in QSO broad-line regions, but the Balmer decrement (H?/H? ? 5.8) is larger than that of most optically selected QSOs. Both the Balmer decrement and the slope of the rest-frame UV?optical continuum independently suggest a modest amount of extinction along the line of sight to the broad-line region (EB-V ? 0.5 for SMC-type screen extinction at the redshift of the QSO). The implied gas column density along the line of sight is much less than that implied by the weak X-ray flux of the object, suggesting that either the broad emission and absorption line regions have a low dust-to-gas ratio or that the rest-frame optical light encounters significantly lower mean column density lines of sight than the X-ray emission. From the rest-frame UV-optical spectrum, we are able to constrain the stellar mass content of the system (<3 ? 1011 M?). Comparing this mass limit with the black hole mass estimated from the bolometric luminosity of the QSO, we find it possible that the ratio of the black hole to stellar mass is comparable to the Magorrian value, which would imply that the Magorrian relation is already in place at z = 1.5. However, multiple factors favor a much larger black hole?to?stellar mass ratio. This would imply that if the Magorrian relation characterizes the late history of QSOs and if the situation observed for F1556+3517 is typical of the early evolutionary history of QSOs, central black hole masses develop more rapidly than bulge masses.

Subrelativistic Jets from Black Hole Accretion Vortices. II. The Broad Absorption Lines in Quasars

This article is an analysis of the broad absorption line properties of a theory of quasars described in a companion paper (Paper I) that differentiates radio-loud quasars from radio-quiet quasars by the magnetic field structure, or lack thereof, in the vortex of an accretion flow around a supermassive rapidly rotating black hole. Nonmagnetic vortices (the radio-quiet case) can initiate radiation pressure-driven jets, as shown in Paper I and these bipolar outflows are candidate broad absorption line regions. The primary emphases of this article are the far-field dynamics and the observational implications of the radiation-driven jets from accretion vortices conjectured to exist in radio-quiet quasars. The well-known confinement problem of the broad line absorbing gas is solved by these hypersonic underexpanded jets as they are collimated kinematically with an opening angle of the order of the inverse of the Mach number. The asymptotic jet velocities are found by a detailed analysis of the force of gravity, continuum radiation pressure, and line-driving forces on the jet plasma. The dynamics are explored through time stationary solutions. However, the general solution is considered to be a superposition of episodic quasistationary funnel ejecta as the accretion flow is most likely dynamically unsteady. The final state outflow is a series of geometrically thin clouds with a distribution of velocities ranging from 0 to ? 35,000 km s-1. The most significant implication of this model is that radio-loud quasars (magnetic flux filled accretion vortices) do not have broad absorption line outflows.

The Extraordinary Abundances of Quasar Broad Absorption Line Regions: A Matter of Novae?

The broad absorption lines (BALs) of QSOs indicate abundances of heavy elements, relative to hydrogen, that are 1-2 orders of magnitude higher than the solar values. In at least one QSO, an especially large enhancement of phosphorus is observed. These abundances resemble those in Galactic novae, and this suggests that novae may produce the BAL gas. The needed rate of nova outbursts may come from single white dwarfs that accrete gas as they pass through a supermassive accretion disk around a central black hole.

Instability of evaporation-dominated flows

Abstract Hydrodynamical stability of steady flows of two-phase media with a domination of cloud evaporation is studied. Steady state flows dominated by evaporation effects are demonstrated to be intrinsically nonuni-form with characteristic spatial scale inversely proportional to the evaporation mass rate gain. In the short-wavelength limit small perturbations are shown to be stable in subsonic regions of such flows and unstable in supersonic ones. The bulk hydrodynamical motion in broad-absorption line regions of QSOs and in the interstellar medium of the Galaxy are estimated to be influenced considerably by evaporating clouds. As a consequence, stability of these motions is argued to be affected by evaporation effects.

On Correlations between the Broad Absorption Lines and Adjacent Broad Emission Lines in QSO Spectra

We compare the C IV broad absorption line (BAL) and broad emission line (BEL) properties in the sample of 72 BAL QSOs which have been studied by Korista and coworkers. A principal-component analysis and subsequent fits to some of the measured properties are utilized to derive quantitatively, for the first time, some empirical relationships between BAL properties and the adjacent BEL properties. The most interesting result stems from a correlation between the FWHM of the C IV BEL and both (1) the minimum outflow velocity of the generally detached BAL trough and (2) the outflow velocity at minimum BAL intensity. These correlations suggest that at least some type of secondary physical relationship exists between the gases in the BAL and BEL regions. This must be explained by any successful model for these regions. However, we find no correlation between continuum luminosity and BAL properties. This suggests that radiation pressure may not be a dominant force in driving the outflowing BAL region clouds.

On the Geometry, Covering Factor, and Scattering-Emission Properties of QSO Broad Absorption-Line Regions

view Abstract Citations (134) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Geometry, Covering Factor, and Scattering-Emission Properties of QSO Broad Absorption-Line Regions Hamann, Fred ; Korista, Kirk T. ; Morris, Simon L. Abstract We analyze line profiles of the 40 broad absorption-line (BAL) QSOs measured by Weymann et al. (1991) to estimate the geometry, covering factor, and scattering-emission properties of the BAL regions (BALRs). If the line photons are not selectively destroyed, the ratio of emission to absorption equivalent widths in C IV 1550 Å indicate that the BALR cannot completely envelope the continuum source. Detailed models of the C IV profiles formed in isotropic, conical, or disk-shaped winds strongly reinforced the requirement for generally low covering factors. Simultaneous modeling of the C IV and N V 1240 Å profiles argues again for low covering factors, and shows further that the ∼1265 Å bump near N V is generally not scattered Lyα flux, as previously suggested, but rather an unrelated emission line. We conclude that the covering factors are usually small and therefore all radio-quiet QSOs have BALRs. These results apply equally for the sources with low-ionization BALs (Mg II) as long as the line photons are not selectively destroyed. If QSOs are observable over 4π sr, the mean covering factor for the entire population equals the detection rate of BAL sources, i.e., ∼12%. Low covering factors imply that the emission lines form mostly in the underlying broad emission-line region (BELR) and not the BALR. As a result, the geometry and orientation of the BALRs cannot be constrained by modeling the profiles of individual sources. However, we test the wind models by generating hypothetical mean spectra for randomly oriented BAL and non-BAL samples, and comparing the results to the mean spectra derived by Weymann et al. The observed ∼25% larger N V equivalent width in the mean BALQSO spectrum could be caused by mean covering factors that are ∼0.2 (i.e., 20% of 4π sr) larger in QSOs with BALRs in our line of sight. However, the narrow profile of the N V excess in BALQSOs is inconsistent with all of the isotropic, conical, and disk-shaped winds considered here. This result holds for a wide range of scattering-emission properties in the BALRs and is not sensitive to any details of the profile calculations. We conclude that (1) the observed N V excess results from differences (possibly orientation effects) in the BELRs and not the BALRs, and (2) the mean BALR covering factors in QSOs with and without observed BALs differ by less than 0.2. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173185 Bibcode: 1993ApJ...415..541H Keywords: GALAXIES: QUASARS: ABSORPTION LINES; RADIATIVE TRANSFER full text sources ADS | data products NED (40) SIMBAD (35)