Broad Absorption Line QSOs Research Articles

PKS 1004+13: A High-Inclination, Highly Absorbed Radio-loud QSO—the First Radio-loud Broad Absorption Line QSO at Low Redshift?

The existence of broad absorption line (BAL) outflows in only radio-quiet QSOs was thought to be an important clue to mass ejection and the radio-loud-radio-quiet dichotomy. Recently, a few radio-loud BAL QSOs have been discovered at high redshift. We present evidence that PKS 1004+13 is a radio-loud BAL QSO. It would be the first known at low redshift (zem = 0.24) and one of the most radio-luminous. For PKS 1004+13, there appear to be broad absorption troughs of O VI, N V, Si IV, and C IV, indicating high-ionization outflows up to ~10,000 km s-1. There are also two strong, broad (~550 km s-1), high-ionization associated absorption systems that show partial covering of the continuum source. The strong UV absorption we have detected suggests that the extreme, soft X-ray weakness of PKS 1004+13 is primarily the result of absorption. The large radio-lobe dominance indicates BAL and associated gas at high inclinations to the central engine axis, perhaps in a line of sight that passes through an accretion disk wind.

ExploratoryASCAObservations of Broad Absorption Line Quasi‐stellar Objects

We present the analysis and interpretation of a sample of eight ASCA observations of Broad Absorption Line Quasi-Stellar Objects (BALQSOs). This is the first moderate-sized sample of sensitive BALQSO observations above 2 keV, and the BALQSOs in our sample are among the optically brightest known (B=14.5-18.5). Despite the ability of 2-10 keV X-rays to penetrate large column densities, we find BALQSOs to be extremely weak sources above 2 keV, and we are only able to add two new 2-10 keV detections (0226-104 and IRAS 07598+6508) to those previously reported. By comparison with non-BALQSOs of similar optical continuum magnitudes, we derive the column densities needed to suppress the expected X-ray fluxes of our BALQSOs. In several cases we derive column densities > 5x10^{23} cm^{-2} for a neutral absorber with solar abundances. These are the largest X-ray column densities yet inferred for BALQSOs, and they exceed ROSAT lower limits by about an order of magnitude. Optical brightness does not appear to be a good predictor of 2-10 keV brightness for BALQSOs, but our data do suggest that the BALQSOs with high optical continuum polarizations may be the X-ray brighter members of the class. For example, the highly polarized object PHL 5200 appears to be unusually X-ray bright for a BALQSO given its optical magnitude. We discuss the implications of our results for future observations with AXAF and XMM. If the objects in our sample are representative of the BALQSO population, precision X-ray spectroscopy of most BALQSOs will unfortunately prove difficult in the near future.

On the Continuum Shape of Broad Absorption Line Quasars

The continuum shape of 26 broad absorption line (BAL) QSOs is shown to be virtually identical to that of non-BAL QSOs when the spectra of the former are dereddened. A procedure for dereddening of BAL QSO spectra is introduced, based on measurement of the flux in three bands and determination of the colour excess in comparison with an unreddened spectrum. This method allows us to derive the type and amount of extinction. We show that reddening in high-ionization BAL QSOs is comparatively small and the range of extinction laws varies from Milky Way, LMC to SMC type. On the other hand, low-ionization BAL QSOs seem to experience reddening which can be attributed to SMC type extinction alone. Comparison of the colour indices of composite spectra from Francis et al. (1991) and Zheng et al. (1997) with those derived from individual BAL QSO spectra shows that the Francis et al. (1991) composite might be a more suitable representative of an unreddened spectrum. In general, we conclude that the spectral energy distribution of normal QSOs can be used as an incident continuum shape for BAL QSOs.

The Polarized Spectrum of APM 08279+5255

We report the discovery of significant linear polarization (p>1%) in the hyperluminous z=3.87 broad absorption line (BAL) QSO APM 08279+5255. The polarization spectrum is complex, with properties similar to those of other, lower redshift but more highly polarized BALQSOs. The resonance emission lines are unpolarized, while the absorption troughs show polarization similar to or higher than the continuum. In particular, an apparent increase of polarization in the trough covering 1000-1030 Å (rest) supports the interpretation of this feature as a broad absorption component associated with O VI/Lyβ local to the QSO, as opposed to an intervening damped Lyα absorption system. The elevated polarization in some of the absorption features implies that we view the scattered (polarized) spectrum through a sight line with less absorbing material than the direct spectrum. Therefore, the complex structure of the polarization spectrum in this brilliant lensed BALQSO suggests that it will be an important laboratory for studying the structure of QSOs at high redshift.

Hubble Space TelescopeObservations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Modeling the Lens

We investigate gravitational lens models for the quadruply lensed Cloverleaf broad absorption line QSO H1413+1143 based on the Hubble Space Telescope (HST) WFPC/WFPC2 astrometric and photometric data of the system by Turnshek et al. and the HST NICMOS-2 data by Falco et al. The accurate image positions and the dust-extinction-corrected relative amplifications, along with a possible detection of the lensing galaxy in the infrared, permit more accurate lens models than were previously possible. While more recent models are qualitatively consistent with the HST data, none of the previous models considered the dust-extinction-corrected relative amplifications of the image components. We use the power-law elliptical mass model to fit the HST data. We find that a single elliptical galaxy perturbed by an external shear can fit the image positions within the observational uncertainties; however, the predicted relative magnifications are only roughly consistent with the observational relative amplifications. We find that a primary galaxy combined with a secondary galaxy in the vicinity of the Cloverleaf or a cluster centered (south-) west of the Cloverleaf can fit both the image positions and relative amplifications within the observational uncertainties. We discuss future observations that could be used to test and/or further constrain lens models of the Cloverleaf.

The Polarization of Broad Absorption Line QSOs

We present the combined results of optical polarization surveys of QSOs showing broad absorption lines (BALQSOs) conducted at the Steward and McDonald Observatories. The merged list of 53 objects provides the first statistical justification for claims of the tendency of BALQSOs to show stronger than average polarization, with a typical BALQSO being polarized a factor 2.4 times greater than a QSO from an optical survey selected without regard for absorption lines. Spectropolarimetry of sufficient quality to distinguish the polarization of emission lines versus absorption troughs versus continuum is also presented for six objects from the survey. When taken together with published data on other sources, the results lead to several significant correlations that can be used to gain insight into the structure of a BALQSO. These include: (1) a reduced degree of polarization in the broad emission lines, (2) enhanced polarization in the absorption troughs, and (3) an increase in the degree of polarization toward shorter wavelengths. In addition, BALQSOs with more prominent absorption systems tend to be more strongly polarized, and there is evidence that the subclass of low-ionization absorbers is more strongly polarized than other BALQSOs. If the increased polarization of BALQSOs is due to attenuation of direct, as opposed to scattered, lines of sight to the nucleus, absorption-line objects are underrepresented in optical surveys, and their true incidence is 20%-30% that of all UV-bright QSOs. Nevertheless, BALQSOs on average are not as highly polarized as their more obscured radio-quiet cousins, the IRAS QSOs/hyperluminous IR galaxies. We are led to a consistent picture in which broad absorption is observed in BALQSOs because they are inclined at intermediate inclinations, where our line of sight passes through gas clouds located near the surface of a dusty torus.

The Host Galaxy of the Broad Absorption Line QSO PG 1700+518 and Its Ring Galaxy Companion: NICMOS 1.6 Micron Imaging

The 1.6 μm Near Infrared Camera and Multiobject Spectrometer image of the broad absorption line QSO PG 1700+518 clearly resolves the QSO host galaxy and a ringlike companion. The companion is most likely a ring galaxy produced in a collision with the QSO galaxy ~5×10^7 yr ago. The morphology of the PG 1700+518 system is very similar to IRAS 04505-2958 (Boyce et al. 1996). Both objects were identified in a sample of eight QSOs selected by warm far-IR colors and extreme IR luminosities (Low et al. 1988). All eight QSOs show signs of strong interaction, and the presence of two head-on colliding systems in this sample may suggest that small impact parameters favor the energizing of IR-luminous QSOs.

Discovery of Radio-Loud Broad Absorption Line Quasars Using Ultraviolet Excess and Deep Radio Selection

We report the discovery of five broad-absorption-line (BAL) QSOs in a complete sample of 111 ultraviolet excess (UVX) QSO candidates also detected in the NRAO VLA Sky Survey. All five BAL QSOs, which include two high-ionization BAL QSOs and three low-ionization BAL QSOs, are formally radio-loud. Of QSOs with z > 0.4, 3+/-2% show low-ionization BALs, and of QSOs with z > 1.5, all radio-loud, 9+/-5% show BALs; these frequencies are consistent with those of optical surveys. While the first reported radio-loud BAL QSO, FIRST J155633.8+351758, is likely to be heavily dust reddened and thus less radio-loud than indicated by its observed radio-to-optical luminosity, these QSOs are UVX selected and probably free of significant dust along the line of sight. We point out unusual features in two of the BAL QSOs and discuss the significance finding these heretofore rare objects.

Broad PvAbsorption in the QSO PG 1254+047: Column Densities, Ionizations, and Metal Abundances in Broad Absorption Line Winds

This paper discusses the detection of P V λλ1118, 1128 and other broad absorption lines (BALs) in archival Hubble Space Telescope spectra of the low-redshift BAL QSO PG 1254+047. The P V identification is secured by excellent redshift and profile coincidences with the other BALs, such as C IV λλ1548, 1550 and Si IV λλ1393, 1403, and by photoionization calculations showing that other lines near this wavelength, e.g., Fe III λ1123, should be much weaker than P V. The observed BAL strengths imply that either (1) there are extreme abundance ratios such as [C/H] ≳ +1.0, [Si/H] ≳ +1.8, and [P/C] ≳ +2.2, or (2) at least some of the lines are much more optically thick than they appear. I argue that the significant presence of P V absorption indicates severe line saturation, which is disguised in the observed (moderate-strength) BALs because the absorber does not fully cover the continuum source(s) along our line(s) of sight. The variety of observed BAL strengths and profiles results from a complex mixture of ionization, optical depth, and coverage fraction effects, making useful determinations of the abundance ratios impossible without a specific physical model. Computed optical depths for all UV resonance lines show that the observed BALs are consistent with solar abundances if (1) the ionization parameter is at least moderately high, log U ≳ -0.6, (2) the total hydrogen column density is log NH (cm-2) ≳ 22.0, and (3) the optical depths in strong lines like C IV and O VI λλ1032, 1038 are ≳25 and ≳80, respectively. These optical depths and column densities are at least an order of magnitude larger than expected from the residual intensities in the BAL troughs, but they are consistent with the large absorbing columns derived from X-ray observations of BAL QSOs. In particular, a nominal X-ray column density of log NH (cm-2) ~ 23 could produce the observed BAL spectrum if +0.4 ≲ log U ≲ +0.7 in a simple one-zone medium. The outflowing BAL region, at velocities from -15,000 to -27,000 km s-1 in PG 1254+047, is therefore a strong candidate for the X-ray absorber in BAL QSOs.

Detection of the Galaxy Lensing the Doubly Imaged Quasar SBS 1520+530

H-band observations with a spatial resolution of 015 carried out with the Canada-France-Hawaii Telescope adaptive optics system show a galaxy between the components of the double broad absorption line QSO SBS 1520+530, thereby confirming this system as a gravitational lens. The galaxy is located 040 from the fainter of the two QSO images and is offset 012 from the line joining them. The H magnitude of the lensing galaxy is ∼1 mag fainter than expected from the velocity dispersion derived for the lensing galaxy were it at z = 0.72 or z = 0.81, the redshifts of the two absorption-line systems.

Hubble Space TelescopeObservations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Spectroscopy of the Lyα Forest and Metal‐Line Systems

The intervening Lyα forest and metal-line absorbers toward the Cloverleaf gravitational lens H1413+1143 (zem = 2.54, mv ≈ 17) are examined along the four individual sight lines using HST-FOS spectra. The observations probe the Lyα forest systems on size scales of up to 4 h-1 kpc (H0 = 100 h km s-1 Mpc-1, q0 = 0.5) and metal-line systems on scales up to 6 h-1 kpc. The equivalent widths of Lyα forest lines in general are well correlated along the four different lines of sight and are consistent with the sight lines piercing the same absorbers. The heavy-element systems clearly show evidence for differences. One striking difference is seen in a system at zabs = 2.0969 in which the Lyα line possesses a column density approaching log N(H I) = 19.7 in component B but not exceeding log N(H I) = 18.4 in any of the other three components. Simulations show that a circular absorber responsible for such a scenario has a radius of ≤10 h-1 kpc with a 90% confidence level, assuming a lens redshift of zlens = 1.55. The zabs = 1.6595 system contains a probable damped Lyα line and shows evidence for rotation. A system at zabs = 1.4377 exhibits very significant Fe II absorption in only two of the components at the level of sensitivity of the observations. Examination of how the absorption-line equivalent widths are correlated between the component spectra can provide information about whether all four lines of sight to the QSO are passing through the same absorbers, placing limits on absorber sizes and shapes. The four sight lines toward H1413+1143 provide a unique geometry for this type of study.

First Results from the Las Campanas QSO Brightness Monitoring Program

We have examined optical brightness changes in 151 luminous, moderate-redshift QSOs with unknown variability properties. Short exposures were obtained using CCD detectors on the 40 inch (102 cm) Swope Telescope at Las Campanas Observatory. Some of the observations were taken as early as 1987, with the bulk of them beginning in 1990 and continuing through the beginning of 1994. Observations of individual QSOs were typically taken several times per year in V and/or Gunn r filters. Brightness variations have been determined relative to stars contained in an ≈ 6 arcmin2 field. We investigated the characteristics of the brightness variations using the ensemble structure function for three QSO object classes: radio quiet QSOs with broad absorption lines (BALs) in their spectra, radio quiet QSOs without BALs, and radio-loud quasars that systematically lack BALs. We find that ≈ 2/3 of the entire sample show very quiescent variations, with changes typically less than 0.15 mag yr-1 (proper time), corresponding to individual structure function slopes less than 0.0225 mag2 yr-1. We have designated these objects optically weak variables (OWVs), while the remainder of the sample with larger variations are designated optically strong variables (OSVs). Over the time of the observations, we were able to find only subtle statistical differences in the variability properties of radio quiet non-BAL and BAL QSOs. Although there is a slight tendency for the rate of change of continuum brightness to be larger in the radio-quiet non-BAL QSOs, to first order in both object classes the mean rate of change is similar and the characteristic timescale of variation appears to be greater than 1.2 yr (proper time). Consistent with the finding of slightly larger rates of change in radio-quiet non-BAL QSOs, we also find that the fraction of OSVs is marginally larger in the non-BAL QSOs in comparison to the BAL QSOs. However, the optical variability properties of the radio-loud quasars are clearly different. For the radio-loud quasars, while their rate of change in brightness is similar to changes observed in radio-quiet QSOs, their characteristic timescale of variation is statistically shorter, ≈ 0.6-0.8 yr (proper time). Collectively, these results have implications for models of QSO geometry and future methods of conducting QSO optical variability surveys. The results also illustrate the limitations of methods for discovering QSOs on the basis of optical variability alone.

Serendipitous Discovery of a Broad Absorption Line QSO at [CLC][ITAL]z[/ITAL][/CLC] = 2.169

We report the serendipitous discovery of a broad absorption line (BAL) QSO at z = 2.169, located 41'' southwest of 3C 48. We present Keck Low Resolution Imaging Spectrometer spectroscopy covering rest-frame wavelengths 1500–2300 A. The C IV BAL has three components, and it extends to outflow velocities of at least 12,000 km s-1. The BAL QSO has an intervening low-ionization metal-line absorption system at z = 1.667, which is likely to be a damped Lyα absorber. Hubble Space Telescope images show extended luminous material around the QSO, which could be either the host galaxy or the intervening system.

Short-Term Optical Variability in Broad Absorption Line QSO[CLC]s[/CLC

We present the first results from a pilot programme to monitor the short term optical variability in Broad Absorption Line system QSOs. Intra-night optical variations of ~5% were detected on time scales of ~ one hour in QSOs 0846+156 and 0856+172. Further, the mean magnitude level decreased in the two objects by ~0.05 and ~0.15 magnitude respectively during the period of our observations. The observed light curves are quite similar to those previously seem in the flat spectrum radio-loud sources, especially the BL Lacertae objects, and can provide important constraints for the origin of microvariability, and also a possible evolutionary link between the radio-loud and the radio-quiet QSOs.

Spectropolarimetry of FIRST Broad Absorption Line Quasars

We present Keck spectropolarimetry of two rare low-ionization broad absorption line (BAL) QSOs, FIRST J084044.5+363328 and FIRST J155633.8+351758, that also exhibit narrow absorption lines from metastable excited levels of Fe II (``Iron Lo-BALs''). These QSOs were discovered in optical follow-ups to a deep radio survey; FIRST J155633.8+351758 is radio-loud, the first BAL QSO so identified. FIRST J084044.5+363328 is highly polarized and exhibits many features found in other BAL QSOs, and the polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, suggesting that more than one mechanism is at work, or that the system geometry is complex. FIRST J155633.8+351758 may be the most highly polarized BAL QSO known, and exhibits other unusual polarization properties compared to other highly polarized BAL QSOs. Currently available data cannot yet discriminate among the possible lines of sight to BAL QSOs (edge-on, pole-on, or random).

Hubble Space TelescopeObservations of the Gravitationally Lensed Cloverleaf Broad Absorption Line QSO H1413+1143: Imaging

An analysis of Hubble Space Telescope (HST) Wide Field Planetary Camera (WFPC) and Wide Field Planetary Camera 2 (WFPC2) images of the gravitationally lensed Cloverleaf broad absorption line quasi-stellar object (QSO) H1413+1143 is presented. Astrometric and photometric measurements are derived for the four components of the lensed QSO for five different epochs over a baseline of 2.76 yr. Because of the replacement of WFPC with WFPC2 and the change in the purpose of the observation at the various epochs, the data were not always taken with the same filter. With the exception of the declination of component D, the relative positions of the four components are measured to within ≈ 3 mas; these results are consistent with but considerably more accurate than earlier measurements. The relative photometric measurements at any one epoch are typically accurate to ≈ 0.02-0.03 mag (1 σ). The initial HST WFPC images cover a baseline of 1.26 yr (1992.21-1993.47 [1992 March 16-1993 June 22]), and over this time interval there is little evidence for brightness variations of any of the components relative to one another at levels >0.06 mag (>2 σ). Photometric measurements of the more accurate WFPC2 data obtained with different filters extends this baseline an additional 1.50 yr (to 1994.97 [1994 December 22]). The WFPC2 data also fail to reveal significant brightness variations among the components. In addition, the WFPC2 data include both UV (F336W) and near-infrared (F814W) images. These color data indicate the presence of sight-line-dependent extinction, causing the F336W-F814W color index of component B (the most reddened component) to be 0.56 ± 0.04 mag redder than that of component C (the least reddened component). The lack of evidence for significant component brightness variations at all HST observation epochs suggests that the data could be reliably extinction-corrected to derive the relative amplifications of the four image components. This is done for several reasonable dust-extinction models. Thus, the derived astrometry along with the photometric analysis set clear constraints on models for the Cloverleaf. Since component D shows some evidence for microlensing, the results on its relative amplification should be used with caution. While existing models can successfully reproduce the relative positions, the relative amplifications have not yet been successfully modeled. The WFPC2 imaging data has also permitted a sensitive search for component structure and the gravitational lens itself. There is marginal evidence for elongated structure between components A and C that may be part of an Einstein ring. However, no significant evidence for the lensing object is found. The various measurements are quantified in ways useful for setting model constraints. Limits on the mass-to-light ratio and detectability of the lensing galaxy are also discussed.

The FIRST Radio-loud Broad Absorption Line QSO and Evidence for a Hidden Population of Quasars

We have discovered two low-ionization broad absorption line quasars in programs to obtain optical spectra for radio-selected quasar candidates from the VLA FIRST Survey (Becker, White, & Helfand 1995). Both belong to the extremely rare class of BAL QSOs that exhibit narrow absorption lines from metastable excited levels of Fe II and Fe III. Until now, there was just a single object in this class, 0059-2735 (Hazard et al. 1987). In addition, one of our new objects is the first known radio-loud BAL QSO. The properties of these three unusual objects suggest a trend of increasing radio luminosity with the amount of absorption to the quasar, and are perhaps transition objects between radio-loud and radio-quiet quasars. The two new objects are from a radio-selected sample comprising less than 200 quasars; one is heavily attenuated at optical wavelengths in the observed frame. These objects would be easily overlooked by most optical QSO searches; their abundance in the radio sample suggests that they may be representatives of a largely undetected component of the quasar population, perhaps as numerous as ordinary low-ionization BAL QSOs which constitute 1-2% of all QSOs.

On the Fraction of Broad Absorption Line Quasi‐stellar Objects

Recent evidence indicates that some, if not all, broad absorption line quasi-stellar objects (BAL QSOs) may have significantly attenuated continuum compared with normal (non-BAL) radio-quiet QSOs. This attenuation has important implications for the fraction of radio-quiet QSOs that show the BAL QSO phenomenon, implying a fraction of at least 30%, much larger than the canonical value of 10%. This also implies a covering factor for the BAL region of ≥30%. Constraints can in turn be placed on how many of the BAL QSOs are in fact heavily attenuated, if we make the reasonable assumption that scattering within the BAL region produces the polarization.

Evidence for Radiative Acceleration in Quasars

AbstractI give an overview of a promising signature for radiative acceleration in quasars “the ghost of Lyα,” which is seen in the spectra of a few broad absorption line (BAL) QSOs. The ghost appears as an absorption hump in the C IV λ1549 BAL and is centered around 5,900 km s−1 to the blue of the corresponding broad emission line (BEL). This velocity separation is the same as the velocity separation between the N V λ1240 and Lyα lines. Thus, when the N V BAL and the C IV BAL are plotted as a function of velocity (where zero velocity corresponds to the peaks of these BELs), the hump in the C IV BAL appears at the same velocity as the Lyα BEL and qualitatively resembles it. The best examples and model fits are shown and the radiative dynamics explained.

The Disk Wind Model of the Broad Line Region of Active Galactic Nuclei

AbstractIn a fashion similar to winds in O stars, the AGN disk winds may be responsible for the broad, blue-shifted absorption of resonance lines which characterize the Broad Absorption Line QSOs. The dynamical features of the disk wind may also account for many of the properties of the broad emission lines of AGN. Although the velocity field of the material responsible for the line emission is primarily that of the accretion disk, the presence of an accelerated radial wind influences the line formation so that single-peaked profiles are generic. Further, the recent reverberation mapping response of NGC 5548 is also qualitatively explained by these same radiative transfer effects.