Broad Absorption Line Systems Research Articles

Outlier Detection in the DESI Bright Galaxy Survey

We present an unsupervised search for outliers in the Bright Galaxy Survey (BGS) data set from the DESI Early Data Release. This analysis utilizes an autoencoder to compress galaxy spectra into a compact, redshift-invariant latent space, and a normalizing flow to identify low-probability objects. The most prominent outliers show distinctive spectral features, such as irregular or double-peaked emission lines or originate from galaxy mergers, blended sources, and rare quasar types, including one previously unknown broad absorption line system. A significant portion of the BGS outliers are stars spectroscopically misclassified as galaxies. By building our own star model trained on spectra from the DESI Milky Way Survey, we have determined that the misclassification likely stems from the principle component analysis of stars in the DESI pipeline. To aid follow-up studies, we make the full probability catalog of all BGS objects and our pretrained models publicly available.

The WISSH quasars project

We report on the variability of a multi-component broad absorption line (BAL) system observed in the hyper-luminous quasar J1538+0855 at z = 3.6. Observations from the Sloan Digital Sky Survey (SDSS), Very Large Telescope (VLT), Large Binocular Telescope (LBT), and Subaru telescope taken at five different epochs, spanning 17 yr in the observed frame, are presented. We detect three (A, B, and C) CIV variable troughs exhibiting extreme velocities (∼40 000–54 000 km s−1) similar to the ultra-fast outflows (UFOs) typically observed in the X-ray spectra. The A component of the BAL UFO (vufo ∼ 0.17c) shows strength variations, while B (vufo ∼ 0.15c) and C (vufo ∼ 0.13c) components show changes both in shape and strength, appearing and disappearing at different epochs. In addition, during the last observation on June 2021, the entire BAL system disappeared. The variability trends observed during the first two epochs (1.30 yr rest frame) in the CIV, SiIV, OVI, and NV absorption spectral regions are the same for B and C troughs, while the A component of the BAL varies independently. This suggests a change in the ionization state of the absorbing gas for B and C components and tangential motion for the A component, as the cause of this temporal behaviour. Accordingly, it is possible to provide an upper limit for distance of the gas responsible for the A component of RoutA ≤ 58 pc and, in turn, a kinetic power of ĖK,ufo ≤ 1.37 × 1045 erg s−1. We also obtain RoutB,C ≤ 1.9 kpc for B and C components, which implies an upper limit estimation of ĖK,ufo ≤ 1.94 × 1046 erg s−1 and ĖK,ufo ≤ 1.33 × 1046 erg s−1, respectively. Future spectral monitoring with high-resolution instruments is mandatory to accurately constrain physical properties of the BAL UFO discovered in the UV spectrum of J1538+0855 and investigate its role as a promising mechanism for the origin of the extended (∼75 kpc) CIV nebula surrounding this hyper-luminous quasar.

VLT/UVES observation of the outflow in quasar SDSS J1439-0106

ABSTRACT We analyse the VLT/UVES spectrum of the quasar SDSS J143907.5-010616.7, retrieved from the UVES Spectral Quasar Absorption Database. We identify two outflow systems in the spectrum: a mini broad absorption line (mini-BAL) system and a narrow absorption line (NAL) system. We measure the ionic column densities of the mini-BAL ($v$ = −1550 km s−1) outflow, which has excited state absorption troughs of ${\rm Fe\, \rm {\small {ii}}}$. We determine that the electron number density $\log {n_e}=3.4^{+0.1}_{-0.1}$, based on the ratios between the excited and ground state abundances of ${\rm Fe\, \rm {\small {ii}}}$, and find the kinetic luminosity of the outflow to be ${\lesssim}0.1\,\hbox{per cent}$ of the quasar’s Eddington luminosity, making it insufficient to contribute to AGN feedback.

Discovery of a Fast Iron Low-ionization Outflow in the Early Evolution of the Nearby Tidal Disruption Event AT 2019qiz

Abstract We report the results of ultraviolet (UV) and optical photometric and spectroscopic analysis of the tidal disruption event (TDE) AT 2019qiz. Our follow-up observations started <10 days after the source began to brighten in the optical and lasted for a period of six months. Our late-time host-dominated spectrum indicates that the host galaxy likely harbors a weak active galactic nucleus. The initial Hubble Space Telescope (HST) spectrum of AT 2019qiz exhibits an iron and low-ionization broad absorption line (FeLoBAL) system that is seen for the first time in a TDE. This spectrum also bears a striking resemblance to that of Gaia16apd, a superluminous supernova. Our observations provide insights into the outflow properties in TDEs and show evidence for a connection between TDEs and engine-powered supernovae at early phases, as originally suggested by Metzger & Stone. In a time frame of 50 days, the UV spectra of AT 2019qiz started to resemble those of previous TDEs with only high-ionization broad absorption lines. The change in UV spectral signatures is accompanied by a decrease in the outflow velocity, which began at 15,000 km s−1 and decelerated to ∼10,000 km s−1. A similar evolution in the Hα emission-line width further supports the speculation that the broad Balmer emission lines are formed in TDE outflows. In addition, we detect narrow absorption features on top of the FeLoBAL signatures in the early HST UV spectrum of AT 2019qiz. The measured H i column density corresponds to a Lyman-limit system, whereas the metal absorption lines (such as N v, C iv, Fe ii, and Mg ii) are likely probing the circumnuclear gas and interstellar medium in the host galaxy.

Ultradense Gas Tracked by Unshifted Broad Absorption Lines in a Quasar

Abstract We present a detailed analysis of the broad absorption line system in the quasar SDSS J122017.06+454941.1, which are clearly detected in hydrogen Lyman series and metal lines, such as C iv, Si iv, Si iii, Al iii, and C ii, with a similar velocity as that of the broad emission lines. We reliably measured the column densities of H i, Al iii, and C ii, and obtained a low limit to Si iv and Si iii. With the help of the photoionization simulations, we found that the absorption gas has a hydrogen number density n H ≈ 1011.03 cm−3 and a hydrogen column density N H ≈ 1021.0 cm−2, and is exposed to the radiation with an ionization parameter U ≈ 10−1.25, and thus located the absorber at ∼0.3 pc from the central supermassive black hole, remarkably similar to the radius of the broad-line region (BLR; 0.17–0.84 pc as estimated by the luminosity–radius relation) of the quasar. It is likely that our line of sight may happen to intercept the low-column part of the BLR with a high density similar to that of the inferred value of the absorber. We suggest that detection of Al iii absorption line doublet in moderate quality quasar spectra could be a good indicator of dense gases, provided that the neutral hydrogen column density of the absorber is .

Probing the Line-locking Signatures within the C iv Broad Absorption Line in Quasar SDSS J092345+512710

Abstract Quasar SDSS J092345.19+512710.1 (hereafter J0923+5127) shows two broad absorption line (BAL) systems. The blue one at ∼14,000 km s−1, called BAL system A, has been reported to show a synchronized kinematic shift of its C iv and Si iv BALs. In this paper, we mainly concentrate on the red one at ∼4000 km s−1, called BAL system B, which can be resolved into multiple narrow absorption lines (NALs). We identify 11 NAL systems from BAL system B and find that these blended NALs show complex line-locking phenomena, which offers evidence for the idea that radiation pressure plays an important role in the dynamics of these clumpy outflow clouds.

A Kinematic Shift of the C iv Broad Absorption Line in Quasar SDSS J120819.29+035559.4

Abstract We report the kinematic shift of the C iv broad absorption line (BAL) in quasar SDSS J120819.29+035559.4 (hereafter J1208+0355). This quasar shows two BAL systems, including a blue component of system A at ∼23,500 km s−1 that shows a kinematic shift of 1166 ± 65 km s−1, and a red component of system B at ∼7000 km s−1 that can be decomposed into several narrow absorption lines (NALs). First, we confirm that the most likely cause for the equivalent width variations of the absorption lines (at least for system B) in J1208+0355 is the ionization change scenario as a response to the changes in the ionization continuum according to the following observational factors: (1) coordinated multiple absorption lines strengthening; (2) the continuum flux shows an obvious weakening. Second, we find line-locking phenomena from the blended NALs within system B, indicating that these outflow clouds are driven by a radiative force caused by resonance lines. The above two research aspects convincingly reveal that the BAL outflows of J1208+0355 are affected by the background radiation energy. Therefore, we infer that the kinematic shift shown in system A may be produced by actual line-of-sight acceleration of the outflow clouds, which is driven by radiation pressure from the background light source.

The Ubiquitous Imprint of Radiative Acceleration in the Mean Absorption Spectrum of Quasar Outflows

Abstract Observational evidence revealing the main mechanisms that accelerate quasar outflows has proven difficult to obtain due to the complexity of the absorption features that this gas produces in the spectra of the emission sources. We build 36 composite outflow spectra, covering a large range of outflow and quasar parameters, by stacking broad absorption line systems in the spectra of SDSS-III/BOSS DR12 quasars. The two lines of the atomic doublet of C iv, with a separation of ≈497 km s−1, as well as those of other species, appear well resolved in most of our composites. This agrees with broad outflow troughs consisting of the superposition of narrow absorbers. We also report on the ubiquitous detection of the radiative-acceleration signature known as line-locking in all our composite outflow spectra, including one spectrum that was strictly built from broad absorption line (BAL) systems. This is the first line-locking detection in BAL composite spectra. Line-locking is driven by the C iv atomic doublet and is visible on the blue side of most strong absorption transitions. Similar effects from the doublets of O vi, Si iv, or N v, however, seem to not be present. Our results confirm that radiation pressure is a prevalent mechanism for accelerating outflows in quasars.

Broad Emission and Absorption Line Outflows in the Quasar SDSS J163345.22+512748.4

Abstract We present a detailed study of the optical and near-infrared (NIR) emission and absorption line spectrum of the quasar SDSS J163345.22+512748.4. We discovered on the newly acquired NIR spectrum a highly metastable neutral helium broad absorption line (BAL) He i* λ10830 with a width of ∼2000 km s−1 and a blueshift of ∼7000 km s−1 in the velocity space. The BAL system is also significantly detected in Mg ii and He i* λ3889. We estimate a column density of (5.0 ± 1.7) × 1014 cm−2 for the He i*(2 3S) level and infer an ionization parameter of U A  = 10−1.9±0.2 for the BAL outflow, assuming that the BAL region is thick enough for a full development of an ionization front. The total column density of the BAL outflow is constrained in the range N H ∼ 1021–1021.4 cm−2. We also found that the bulk of both Mg ii and UV Fe ii, as well as of Hα broad emission lines (BELs), are blueshifted with a velocity of ∼2200 km s−1 with respect to the quasar systemic redshift. We constrain the blueshifted BEL region to have a covering factor C f  ≈ 16%, density n H ∼ 1010.6–1011.3 cm−3, column density N H ≳ 1023 cm−2, and ionization parameter U E  ∼ 10−2.1–10−1.5. The outflow gas is located at ∼0.1 pc away from the central ionization source, at a scale comparable to the broad-line region. A toy kinetic model has been proposed to reproduce the profile of Mg ii BEL well if a partial obscured axisymmetric geometry of the outflow with a radial velocity as observed from the BALs is assumed.

Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event

Abstract We report the discovery of nonstellar hydrogen Balmer and metastable helium absorption lines accompanying a transient, high-velocity (0.05c) broad absorption line (BAL) system in the optical spectra of the tidal disruption event (TDE) AT2018zr (z = 0.071). In the Hubble Space Telescope UV spectra, absorption of high- and low-ionization lines is also present at this velocity, making AT2018zr resemble a low-ionization BALQSO. We conclude that these transient absorption features are more likely to arise in fast outflows produced by the TDE than absorbed by the unbound debris. In accordance with the outflow picture, we are able to reproduce the flat-topped Hα emission in a spherically expanding medium without invoking the typical prescription of an elliptical disk. We also report the appearance of narrow (∼1000 kms−1) N iii λ4640, He ii λ4686, Hα, and Hβ emission in the late-time optical spectra of AT2018zr, which may be a result of UV continuum hardening at late times, as observed by Swift. Including AT2018zr, we find a high association rate (three out of four) of BALs in the UV spectra of TDEs. This suggests that outflows may be ubiquitous among TDEs and less sensitive to viewing angle effects compared to QSO outflows.

HST and ground-based spectroscopy of quasar outflows: from mini-BALs to BALs

Quasar outflows have been posited as a mechanism to couple supermassive black holes to evolution in their host galaxies. We use multi-epoch spectra from the Hubble Space Telescope (HST) and ground-based observatories to study the outflows in seven quasars that have C iv outflow lines ranging from a classic broad absorption line (BAL) to weaker/narrower ‘mini-BALs’ across rest wavelengths of at least 850–1650 Å. The C iv outflow lines all varied within a time frame of ≤1.9 yr (rest). This includes equal occurrences of strengthening and weakening plus the emergence of a new BAL system at −38 800 km s−1 accompanied by dramatic strengthening in a mini-BAL at −22 800 km s−1. We infer from ∼1:1 doublet ratios in P v and other lines that the BAL system is highly saturated with line-of-sight covering fractions ranging from 0.27 to 0.80 in the highest to lowest column density regions, respectively. Three of the mini-BALs also provide evidence for saturation and partial covering based on ∼1:1 doublet ratios. We speculate that the BALs and mini-BALs form in similar clumpy/filamentary outflows, with mini-BALs identifying smaller or fewer clumps along our lines of sight. If we attribute the line variabilities to clumps crossing our lines of sight at roughly Keplerian speeds, then a typical variability time in our study, ∼1.1 yr, corresponds to a distance ∼2 pc from the central black hole. Combining this with the speed and minimum total column density inferred from the P v BAL, NH ≳ 2.5 × 1022 cm−2, suggests that the BAL outflow kinetic energy is in the range believed to be sufficient for feedback to galaxy evolution.

QUASAR OUTFLOW CONTRIBUTION TO AGN FEEDBACK: OBSERVATIONS OF QSO SDSS J0838+2955

We present a detailed analysis of the Astrophysical Research Consortium 3.5 m telescope spectrum of QSO SDSS J0838+2955. The object shows three broad absorption line (BAL) systems at 22,000, 13,000, and 4900 km s^-1 blueshifted from the systemic redshift of z=2.043. Of particular interest is the lowest velocity system that displays absorption from low-ionization species such as Mg II, Al II, Si II, Si II*, Fe II and Fe II*. Accurate column densities were measured for all transitions in this lowest velocity BAL using an inhomogeneous absorber model. The ratio of column densities of Si II* and Fe II* with respect to their ground states gave an electron number density of log n_e (cm^-3) = 3.75 +/- 0.22 for the outflow. Photoionization modeling with careful regards to chemical abundances and the incident spectral energy distribution predicts an ionization parameter of log U_H = -1.93 +/- 0.21 and a hydrogen column density of log N_H (cm^-2) = 20.80 +/- 0.28. This places the outflow at 3.3+1.5-1.0 kpc from the central AGN. Assuming that the fraction of solid angle subtended by the outflow is 0.2, these values yield a kinetic luminosity of (4.5+3.1-1.8) x 10^45 erg s^-1, which is (1.4+1.1-0.6)% the bolometric luminosity of the QSO itself. Such large kinetic luminosity suggests that QSO outflows are a major contributor to AGN feedback mechanisms.

The quasar-frame velocity distribution of narrow C iv absorbers

We report on a survey for narrow (full widths at half-minimum <600 km s−1) C iv absorption lines in a sample of bright quasars at redshifts 1.8 ≤z < 2.25 in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow C iv absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad Mg ii emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find that a substantial number (≥43 ± 6 per cent) of absorbers with Wλ15480 > 0.3Å in the velocity range +750 ≲v≲+ 12 000 km s−1 are intrinsic to the active galactic nucleus outflow. This ‘outflow fraction’ peaks near v=+2000 km s−1 with a value of foutflow≃ 0.81 ± 0.13. At velocities below v≈+ 2000 km s−1, the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disc. Furthermore, we find that outflow absorbers are on average broader and stronger than cosmologically intervening systems. Finally, we find that ∼14 per cent of the quasars in our sample exhibit narrow, outflowing C iv absorption with Wλ15480 > 0.3Å, slightly larger than that for broad absorption line systems.

Results of Monitoring the Dramatically Variable CivMini–Broad Absorption Line System in the Quasar HS 1603+3820

We present six new and two previously published high-resolution spectra of the quasar HS 1603+3820 (z_em = 2.542) taken over an interval of 4.2 years (1.2 years in the quasar rest frame). The observations were made with the High-Dispersion Spectrograph on the Subaru telescope and Medium-Resolution Spectrograph on the Hobby-Eberly Telescope. The purpose was to study the narrow absorption lines (NALs). We use time variability as well as coverage fraction analysis to separate intrinsic absorption lines, which are physically related to the quasar, from intervening absorption lines. By fitting models to the line profiles, we derive the parameters of the respective absorbers as a function of time. Only the mini-BAL system at z_abs ~ 2.43 (v_off ~ 9,500 km/s) shows both partial coverage and time variability, although two NAL systems possibly show evidence of partial coverage. We find that all the troughs of the mini-BAL system vary in concert and its total equivalent width variations resemble those of the coverage fraction. However, no other correlations are seen between the variations of different model parameters. Thus, the observed variations cannot be reproduced by a simple change of ionization state nor by motion of a homogeneous parcel of gas across the cylinder of sight. We propose that the observed variations are a result of rapid continuum fluctuations, coupled with coverage fraction fluctuations caused by a clumpy screen of variable optical depth located between the continuum source and the mini-BAL gas. An alternative explanation is that the observed partial coverage signature is the result of scattering of continuum photons around the absorber, thus the equivalent width of the mini-BAL can vary as the intensity of the scattered continuum changes.

Evolutionary unification in composite active galactic nuclei

In this paper, we present an evolutionary unification scenario, involving supermassive black holes (SMBHs) and starbursts (SBs) with outflow (OF), that seems capable of explaining most of the observational properties (of at least part) of active galactic nuclei (AGN). The scenario includes a nuclear/circumnuclear SB closely associated with the AGN where the narrow-line region (NLR), broad-line region (BLR) and broad absorption line (BAL) region are produced in part by the OF process with shells and in compact supernova remnants (cSNRs). The OF process in BAL quasi-stellar objects (QSOs) with extreme infrared (IR) and Fe II emission is studied. In addition, the Fe II problem regarding the BLR of AGN is analysed. The correlations between the BAL, IR emission, Fe II intensity and the intrinsic properties of the AGN are not clearly understood. We suggest here that the behaviour of the BAL, IR and Fe II emission in AGN can be understood within an evolutionary and composite model for AGN. In our model, strong BAL systems and Fe II emission are present (and intense) in young IR objects. Parameters like the BALs, IR emission, Fe II/Hβ intensity ratio, Fe II equivalent width (EW), broad-line width, [O III] λ5007-A intensity and width, NLR size, X-ray spectral slope in radio quiet (RQ) AGN plus lobe separation, and lobe to core intensity ratio in radio loud (RL) AGN are proposed to be fundamentally time-dependent variables inside time-scales of the order of 10 8 yr. Orientation/obscuration effects take the role of a second parameter providing the segregation between Seyfert 1/Seyfert 2 galaxies (Sy1/Sy2) and broad-/narrow-line radio galaxies (BLRG/NLRG).

Infrared mergers and infrared quasi-stellar objects with galactic winds - III. Mrk 231: an exploding young quasi-stellar object with composite outflow/broad absorption lines (and multiple expanding superbubbles)

We present a study of outflow (OF) and broad absorption line (BAL) systems in Mrk 231, and in similar infrared (IR) quasi-stellar objects (QSOs). This study is based mainly on one-dimensional and two-dimensional spectroscopy (obtained at La Palma/William Herschel Telescope, Hubble Space Telescope, International Ultraviolet Explorer, European Southern Observatory/New Technology Telescope, Kitt Peak National Observatory, Apache Point Observatory and Complejo Astronomico El Leoncito observatories) plus Hubble Space Telescope images. For Mrk 231, we report evidence that the extreme nuclear OF process has at least three main components on different scales, which are probably associated with: (i) the radio jet, at parsec scale; (ii) the extreme starburst at parsec and kiloparsec scale. This OF has generated at least four concentric expanding superbubbles and the BAL systems. Specifically, inside and very close to the nucleus the two-dimensional spectra show the presence of an OF emission bump in the blend Hα+[Nii], with a peak at the same velocity of the main BAL-I system (VEjectionBAL-I∼−4700 km s−1). This bump was more clearly detected in the area located at 0.6–1.5 arcsec (490–1220 pc), to the south-west of the nucleus core, showing a strong and broad peak. In addition, in the same direction [at position angle (PA) ∼−120°, i.e. close to the PA of the small-scale radio jet] at 1.7–2.5 arcsec, we also detected multiple narrow emission-line components, with ‘greatly’ enhanced [Nii]/Hα ratio (very similar to the spectra of jets bow shocks). These results suggest that the BAL-I system is generated in OF clouds associated with the parsec-scale jet. The Hubble Space Telescope images show four (or possibly five) nuclear superbubbles or shells with radii r∼ 2.9, 1.5, 1.0, 0.6 and 0.2 kpc. For these bubbles, the two-dimensional Hα velocity field map and two-dimensional spectra show the following. (i) At the border of the more extended bubble (S1), a clear expansion of the shell with blueshifted velocities (with circular shape and at a radius r∼ 5.0 arcsec). This bubble shows a rupture arc – to the south – suggesting that the bubble is in the blowout phase. The axis of this rupture or ejection (at PA ∼ 00°) is coincident with the axis of the intermediate and large-scale structures detected at radio wavelengths. (ii) In addition, in the three more external bubbles (S1, S2, S3), the two-dimensional William Herschel Telescope spectra show multiple emission-line components with OF velocities, of 〈VOFBubble〉 S1, S2 and S3 =[−(650 − 420) ± 30], [−500 ± 30] and [−230 ± 30] km s−1. (iii) In the whole circumnuclear region (1.8 < r < 5 arcsec), the [Nii]/Hα and [Sii]/Hα narrow emission-line ratios show high values (>0.8), which are consistent with low-ionization nuclear emission-line region/OF processes associated with fast velocity shocks. Therefore, we suggest that these giant bubbles are associated with the large-scale nuclear OF component, which is generated – at least in part – by the extreme nuclear starburst: giant supernova/hypernova explosions. The variability of the short-lived BAL-III Nai D system was studied, covering almost all the period in which this system appeared (between ∼1984 and 2004). We have found that the BAL-III light curve is clearly asymmetric with a steep increase, a clear maximum and an exponential fall (similar to the shape of a supernova light curve). The origin of this BAL-III system is discussed, mainly in the framework of an extreme explosive event, probably associated with giant supernova/hypernova explosions. Finally, the IR colour diagram and the ultraviolet BAL systems of IR + GW/OF + Feii QSOs are analysed. This study shows two new BAL IR QSOs and suggests/confirms that these objects could be nearby young BAL QSOs, similar to those detected recently at z∼ 6.0. We propose that the phase of young QSOs is associated with accretion of a large amount of gas (by the supermassive black hole) + extreme starbursts + extreme composite OFs/BALs.

An Empirical Calibration of the Completeness of the SDSS Quasar Survey

Spectra of nearly 20,000 pointlike objects to a Galactic reddening–corrected magnitude of i = 19.1 have been obtained to test the completeness of the Sloan Digital Sky Survey (SDSS) quasar survey. We focus on spatially unresolved quasars, which comprise 94% of all SDSS quasars to the main survey magnitude limit. The objects were selected from all regions of color space, sparsely sampled from within a 278 deg2 area (effective area 233 deg2) of sky covered by this study. Only 10 quasars were identified that were not targeted as candidates by the SDSS quasar survey (including both color and radio source selection). The inferred density of unresolved quasars on the sky that are missed by the SDSS algorithm is 0.44 deg-2, compared with 8.28 deg-2 for the selected quasar density, giving a completeness of 94.9% to the limiting magnitude. Omitting radio selection reduces the color-only selection completeness by about 1%. Of the 10 newly identified quasars, three have detected broad absorption line systems, six are significantly redder than other quasars at the same redshift, and four have redshifts between 2.7 and 3.0 (the redshift range where the SDSS colors of quasars intersect the stellar locus). The fraction of quasars (and other unresolved sources) missed because of image defects and blends, independent of the selection algorithm, is ≈4%, but this number varies by a few percent with magnitude. Quasars with extended images comprise about 6% of the SDSS sample, and the completeness of the selection algorithm for extended quasars is approximately 81%, based on the SDSS galaxy survey. The combined end-to-end completeness for the SDSS quasar survey is ≈89%. The total corrected density of quasars on the sky to i = 19.1 is estimated to be 10.2 deg-2. The SDSS completeness restricted to z 3 quasars is expected to be considerably lower and is a strong function of redshift. The determination of the global completeness is required for the statistical properties of quasars to i = 19.1 derived from the SDSS data set, such as the luminosity function and correlation function, to be accurately determined.

BAL QSOs in the eigenvector 1 context: toward a self-consistent model of the line absorbing/emitting regions

We attempt to define the structural properties of Broad Absorption Line (BAL) QSOs and their relationship with the general quasar population using the Eigenvector 1 correlations. We identify 8 low-redshift quasars (z 1549 emission motivates us to model the BAL systems with an additional component that may share the BLR outflow and may be co-axial with the accretion disk, perhaps associated to a significant black hole spin.

The Ensemble Photometric Variability of ∼25,000 Quasars in the Sloan Digital Sky Survey

Using a sample of over 25,000 spectroscopically confirmed quasars from the Sloan Digital Sky Survey, we show how quasar variability in the rest-frame optical/UV regime depends on rest-frame time lag, luminosity, rest wavelength, redshift, the presence of radio and X-ray emission, and the presence of broad absorption line systems. Imaging photometry is compared with three-band spectrophotometry obtained at later epochs spanning time lags up to about 2 yr. The large sample size and wide range of parameter values allow the dependence of variability to be isolated as a function of many independent parameters. The time dependence of variability (the structure function) is well fitted by a single power law with an index γ = 0.246 ± 0.008, on timescales from days to years. There is an anticorrelation of variability amplitude with rest wavelength—e.g., quasars are about twice as variable at 1000 A as at 6000 A—and quasars are systematically bluer when brighter at all redshifts. There is a strong anticorrelation of variability with quasar luminosity—variability amplitude decreases by a factor of about 4 when luminosity increases by a factor of 100. There is also a significant positive correlation of variability amplitude with redshift, indicating evolution of the quasar population or the variability mechanism. We parameterize all of these relationships. Quasars with ROSAT All-Sky Survey X-ray detections are significantly more variable (at optical/UV wavelengths) than those without, and radio-loud quasars are marginally more variable than their radio-quiet counterparts. We find no significant difference in the variability of quasars with and without broad absorption line troughs. Currently, no models of quasar variability address more than a few of these relationships. Models involving multiple discrete events or gravitational microlensing are unlikely by themselves to account for the data. So-called accretion disk instability models are promising, but more quantitative predictions are needed.

A catalogue of absorption-line systems in QSO spectra

We present a new catalog of absprption-line systems identified in the quasar spectra. It contains data on 821 QSOs and 8558 absorption systems comprizing 16139 absorption lines with measured redshifts in the QSO spectra. The catalog includes absorption-line systems consisting of lines of heavy elements, lines of neutral hydrogen, Lyman limit systems, damped Ly\alpha absorption systems, and broad absorption-line systems. The catalog is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/707 and at www.ioffe.ru/astro/QC. Using the data of the present catalog we also discuss redshift distributions of absorption-line systems.