Nahum Arav

Properties of Radio-selected Broad Absorption Line Quasars from the First Bright Quasar Survey

In a spectroscopic follow-up to the VLA FIRST survey, the FIRST Bright Quasar Survey (FBQS) has found 29 radio-selected broad absorption line (BAL) quasars. This sample provides the first opportunity to study the properties of radio-selected BAL quasars. Contrary to most previous studies, we establish that a significant population of radio-loud BAL quasars exists. Radio-selected BAL quasars display compact radio morphologies and possess both steep and flat radio spectra. Quasars with low-ionization BALs have a color distribution redder than that of the FBQS sample as a whole. The frequency of BAL quasars in the FBQS is significantly greater, perhaps by as much as a factor of 2, than that inferred from optically selected samples. The frequency of BAL quasars appears to have a complex dependence on radio loudness. The properties of this sample appear to be inconsistent with simple unified models in which BAL quasars constitute a subset of quasars seen edge-on.

Keck HIRES Observations of the QSO FIRST J104459.6+365605: Evidence for a Large-Scale Outflow

This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 A. The line of sight toward the QSO contains two clusters of outflowing clouds that give rise to broad blue-shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km s-1 and from -3400 to -5200 km s-1, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km s-1. The most prominent absorption lines are those of Mg II, Mg I, and Fe II, and Mn II is also present. The low-ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I, and Mg II line-forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low-lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE and imply an electron density in the Fe II line-forming regions of ne ~ 4 × 103 cm-3. Modeling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line-forming region and the continuum source is ~7 × 102 pc. From the correspondence in velocity between the Fe II, Mg I, and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for broad absorption lines defined by Weymann and coworkers. Therefore, the distance we find between the Mg II line-forming region and the continuum source is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.

Radiative acceleration in outflows from broad absorption line quasi-stellar objects. 2: Wind models

We investigate the dynamics of radiatively driven broad absorption-line (BAL) outflows in quasi-stellar objects (QSOs) by developing radial and time-independent numerical models. Two limits are explored. The first assumes that the absorbing matter is not forced to comove with the substrate, which provides pressure confinement. This assumption allows us to explore in detail a case in which the acceleration is entirely due to radiation pressure. Using the parameters inferred from observations, we find that under these conditions radiative acceleration (mainly due to resonance line scattering) can readily accelerate the flow to the observed velocities. An important feature of the noncoupled flow is that the line profiles tend to stay relatively flat throughout the velocity interval covered by the line. We discuss how relaxing the assumptions of radial symmetry and time independent may help to explain the structures observed in BALs. In the second class of models, the absorbing flow is assumed to be completely coupled to the substrate in which it is embedded. Aside from being more plausible physically, these models produce line profiles that trail off at higher velocities, a behavior observed in some BALs. We show that, even if the substrate is massless, we have to assume a starting radius very close to the inferred radius of the broad emission-line region (approximately 0.1 pc) in order to obtain a significant contribution from radiative acceleration, given a typical active galactic nucleus (AGN) spectrum. The reason is that the energy input needed to pressurize the substrate, allowing the flow to become supersonic and to retain a reasonable ionization equilibrium, at the same time contributes appreciably to the acceleration. A way to relax the small starting radius constraint is to use a softer ionizing spectrum.

Simultaneous X-ray and UV spectroscopy of the Seyfert galaxy NGC 5548. II. Physical conditions in the X-ray absorber

We present the results from a 500 ks Chandra observation of the Seyfert 1 galaxy NGC 5548. We detect broadened (full width half maximum = 8000 km s −1 ) emission lines of O  and C  in the spectra, similar to those observed in the optical and UV bands. The source was continuously variable, with a 30% increase in luminosity in the second half of the observation. The gradual increase in luminosity occurred over a timescale of ∼300 ks. No variability in the warm absorber was detected between the spectra from the first 170 ks and the second part of the observation. The longer wavelength range of the LETGS resulted in the detection of absorption lines from a broad range of ions, in particular of C, N, O, Ne, Mg, Si, S and Fe. The velocity structure of the X-ray absorber is consistent with the velocity structure measured simultaneously in the ultraviolet spectra. We find that the highest velocity outflow component, at −1040 km s −1 , becomes increasingly important for higher ionization parameters. This velocity component spans at least three orders of magnitude in ionization parameter, producing both highly ionized X-ray absorption lines (Mg  ,S i) as well as UV absorption lines. A similar conclusion is very probable for the other four velocity components. Based upon our observations, we argue that the warm absorber probably does not manifest itself in the form of photoionized clumps in pressure equilibrium with a surrounding wind. Instead, a model with a continuous distribution of column density versus ionization parameter gives an excellent fit to our data. From the shape of this distribution and the assumption that the mass loss through the wind should be smaller than the accretion rate onto the black hole, we derive upper limits to the solid angle as small as 10 −4 sr. From this we argue that the outflow occurs in density-stratified streamers. The density stratification across the stream then produces the wide range of ionization parameter observed in this source. We determine an upper limit of 0.3 Myr −1 for the mass loss from the galaxy due to the observed outflows.

Hubble Space Telescope Observations of the Broad Absorption Line QuasarPG 0946+301

We analyze HST and ground based spectra of the brightest BALQSO in the UV: PG~0946+301. A detailed study of the absorption troughs as a function of velocity is presented, facilitated by the use of a new algorithm to solve for the optical depth as a function of velocity for multiplet lines. We find convincing evidence for saturation in parts of the troughs. This supports our previous assertion that saturation is common in BALs and therefore cast doubts on claims for very high metallicity in BAL flows. Due to the importance of BAL saturation we also discuss its evidence in other objects. In PG~0946+301 large differences in ionization as a function of velocity are detected and our findings supports the hypothesis that the line of sight intersects a number of flow components that combine to give the appearance of the whole trough. Based on the optical depth profiles, we develop a geometrical-kinematical model for the flow. We have positively identified 16 ions of 8 elements (H~I, C~III, C~IV, N~III, N~IV, N~V, O~III, O~IV, O~V, O~VI, Ne~V, Ne~VIII, P~V, Si~IV, S~V, S~VI) and have a probable identifications of Mg~X and S~IV. Unlike earlier analysis of IUE data, we find no evidence for BALs arising from excited ionic states in the HST spectrum of PG~0946+301.

A fast and long-lived outflow from the supermassive black hole in NGC 5548

Gas jets block extragalactic x-rays Supermassive black holes at the heart of active galaxies produce powerful gas outflows. NGC 5548 is one such source known to sustain a persistent outflow of ionized gas. However, its associated x-ray and ultraviolet (UV) emission seem to have been suppressed in recent years. Kaastra et al. conducted a multiwavelength monitoring campaign throughout 2013 to characterize the systems behavior. They suggest that an additional faster jet component has been launching clumps of gas that obscure both the x-ray and UV radiation. The timing of this phenomenon indicates a source only a few light-days away from the nucleus. This proximity suggests that the outflow could be associated with a wind from the supermassive black holes accretion disk. Even more powerful outflows could also influence their host galaxies, and this finding demonstrates how that feedback might work. Science, this issue p. 64 Prolonged suppression of high-energy emission from an active galactic nucleus is attributed to fast expulsion of ionized gas. Supermassive black holes in the nuclei of active galaxies expel large amounts of matter through powerful winds of ionized gas. The archetypal active galaxy NGC 5548 has been studied for decades, and high-resolution x-ray and ultraviolet (UV) observations have previously shown a persistent ionized outflow. An observing campaign in 2013 with six space observatories shows the nucleus to be obscured by a long-lasting, clumpy stream of ionized gas not seen before. It blocks 90% of the soft x-ray emission and causes simultaneous deep, broad UV absorption troughs. The outflow velocities of this gas are up to five times faster than those in the persistent outflow, and, at a distance of only a few light days from the nucleus, it may likely originate from the accretion disk.

Quasar outflows and AGN feedback in the extreme UV: HST/COS observations of HE 0238−1904

Spectroscopic observations of quasar outflows at rest-frame 500-1000 Angstrom have immense diagnostic power. We present analyses of such data, where absorption troughs from three important ions are measured: first, O IV and O IV* that allow us to obtain the distance of high ionization outflows from the AGN; second, Ne VIII and Mg X that are sensitive to the very high ionization phase of the outflow. Their inferred column densities, combined with those of troughs from O VI, N IV, and H I, yield two important results: 1) The outflow shows two ionization phases, where the high ionization phase carries the bulk of the material. This is similar to the situation seen in x-ray warm absorber studies. Furthermore, the low ionization phase is inferred to have a volume filling factor of 10^(-5)-10^(-6). 2) From the O IV to O IV* column density ratio, and the knowledge of the ionization parameter, we determine a distance of 3000 pc. from the outflow to the central source. Since this is a typical high ionization outflow, we can determine robust values for the mass flux and kinetic luminosity of the outflow: 40 solar masses per year and 10^45 ergs/s, respectively, where the latter is roughly equal to 1% of the bolometric luminosity. Such a large kinetic luminosity and mass flow rate measured in a typical high ionization wind suggests that quasar outflows are a major contributor to AGN feedback mechanisms.

What Determines the Depth of Broad Absorption Lines? Keck HIRES Observations of BALQSO 1603+3002

We find that the depth and shape of the broad absorption lines (BALs) in BALQSO 1603+3002 are determined largely by the fraction of the emitting source which is covered by the BAL flow. In addition, the observed depth of the BALs is poorly correlated with their real optical depth. The implication of this result is that abundance studies based on direct extraction of column densities from the depth of the absorption troughs are unreliable. Our conclusion is based on analysis of unblended absorption features of two lines from the same ion (in this case the Si IV doublet), which allows unambiguous separation of covering factor and optical depth effects. The complex morphology of the covering factor as a function of velocity suggests that the BALs are produced by several physically separated outflows. The covering factor is ion dependent in both depth and velocity width. We also find evidence that in BALQSO 1603+3002 the flow does not cover the broad emission line region.

MAJOR CONTRIBUTOR TO AGN FEEDBACK: VLT X-SHOOTER OBSERVATIONS OF S IV BALQSO OUTFLOWS*

We present the most energetic BALQSO outflow measured to date, with a kinetic luminosity of at least 10{sup 46} erg s{sup -1}, which is 5% of the bolometric luminosity of this high Eddington ratio quasar. The associated mass-flow rate is 400 solar masses per year. Such kinetic luminosity and mass-flow rate should provide strong active galactic nucleus feedback effects. The outflow is located at about 300 pc from the quasar and has a velocity of roughly 8000 km s{sup -1}. Our distance and energetic measurements are based in large part on the identification and measurement of S IV and S IV* broad absorption lines (BALs). The use of this high-ionization species allows us to generalize the result to the majority of high-ionization BALQSOs that are identified by their C IV absorption. We also report the energetics of two other outflows seen in another object using the same technique. The distances of all three outflows from the central source (100-2000 pc) suggest that we observe BAL troughs much farther away from the central source than the assumed acceleration region of these outflows (0.01-0.1 pc).

X-RAY/ULTRAVIOLET OBSERVING CAMPAIGN OF THE MARKARIAN 279 ACTIVE GALACTIC NUCLEUS OUTFLOW: A GLOBAL-FITTING ANALYSIS OF THE ULTRAVIOLET ABSORPTION

We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy Mrk 279 based on simultaneous long observations with the Hubble Space Telescope (41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the line-of-sight covering factors and ionic column densities, we separately fit two groups of absorption lines: the Lyman series and the CNO lithium-like doublets. For the CNO doublets we assume that all three ions share the same covering factors. The fitting method applied here overcomes some limitations of the traditional method using individual doublet pairs; it allows for the treatment of more complex, physically realistic scenarios for the absorption-emission geometry and eliminates systematic errors that we show are introduced by spectral noise. We derive velocity-dependent solutions based on two models of geometrical covering: a single covering factor for all background emission sources, and separate covering factors for the continuum and emission lines. Although both models give good statistical fits to the observed absorption, we favor the model with two covering factors because (1) the best-fit covering factors for both emission sources are similar for the independent Lyman series and CNO doublet fits; (2) the fits are consistent with full coverage of the continuum source and partial coverage of the emission lines by the absorbers, as expected from the relative sizes of the nuclear emission components; and (3) it provides a natural explanation for variability in the Lyα absorption detected in an earlier epoch. We also explore physical and geometrical constraints on the outflow from these results.We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy Mrk 279 based on simultaneous long observations with the Hubble Space Telescope (41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the line-of-sight covering factors and ionic column densities, we separately fit two groups of absorption lines: the Lyman series and the CNO lithium-like doublets. For the CNO doublets we assume that all three ions share the same covering factors. The fitting method applied here overcomes some limitations of the traditional method using individual doublet pairs; it allows for the treatment of more complex, physically realistic scenarios for the absorption-emission geometry and eliminates systematic errors that we show are introduced by spectral noise. We derive velocity-dependent solutions based on two models of geometrical covering – a single covering factor for all background emission sources, and separate covering factors for the continuum and emission lines. Although both models give good statistical fits to the observed absorption, we favor the model with two covering factors because: (a) the best-fit covering factors for both emission sources are similar for the independent Lyman series and CNO doublet fits; (b) the fits are consistent with full coverage of the continuum source and partial coverage of the emission lines by the absorbers, as expected from the relative sizes of the nuclear emission components; and (c) it provides a natural explanation for variability in the Lyα absorption detected in an earlier epoch. We also explore physical and geometrical constraints on the outflow from these results. Subject headings: galaxies: individual (Mrk 279) — galaxies: active — galaxies: Seyfert — ultraviolet: galaxies