123 research outputs found
Recommended from our members
Studies of broad emission line profiles in QSOs - I. Observed, high-resolution profiles
High-resolution spectra of nine high-redshift QSOs are presented. The various emission line profiles of each QSO are intercompared in order to gain information on the kinematics of the emitting gas in the broad-line region (BLR). A small number of these profiles, which are either typical of the sample or of special interest, are presented diagrammatically. A full presentation of all the line profiles can be obtained from the author. The main results are summarized and their implications regarding the kinematics of the BLR discussed.Astronom
Recommended from our members
The Lyman-alpha emission-line profiles in high-redshift QSOs
High-resolution (~ 1 Å) spectra of six high-redshift QSOs were utilized in a study of the profile of the Lyα λ 1215.67 Å emission line. The symmetry of the prof:tle was studied after removing any absorption lines, which are mostly resolved at this resolution and after subtraction of N V λ1240 and Si II λ1263 emission from the observed blend. With one exception, Q2204 – 408, the Lyα profiles are symmetric to within the uncertainties of the procedure. It also became clear during the analysis that the profiles of the emission lines are not identical, in particular C IV λ 1549 generally has weaker wings and peak than Lyα λ 1216.
It is argued that either the motion of the broad-line region gas is not purely radial, or else most of the Lyα photons originate in optically-thin gas. Further implications of these results are discussed.Astronom
Recommended from our members
Comparison of high- and low-state X-ray spectra in the type 1.5 quasi-stellar object 2MASS 0918+2117
When observed by XMM–Newton in 2003, the type 1.5 quasi-stellar object 2MASS 0918+2117 was found to be in a low state, with an X-ray flux approximately four to five times fainter than during an earlier Chandra observation. The 2–6 keV spectrum was unusually hard (photon index Γ∼ 1.25), with evidence for a reflection-dominated continuum, while a soft excess visible below ∼1 keV prevented confirmation of the anticipated low energy absorber. In a second XMM–Newton observation in 2005, the X-ray flux is found to have recovered, with a 2–10 keV continuum spectrum now typical of a broad-line active galaxy (Γ∼ 2) and a deficit of flux below ∼1 keV indicative of continuum absorption in a column NH∼ 4 × 1021 cm−2. We find the preferred ionization state of the absorbing gas to be low, which then leaves a residual soft excess of similar spectral form and flux to that found in the 2003 XMM–Newton observation. Although observed at different epochs, we note that dust in the absorbing column could also explain the red nucleus and strong optical polarization of 2MASS 0918+2117.Astronom
Recommended from our members
The H-beta emission line profile of Arakelian 120
A high-quality (S/N in the range from 30 to 100), high-resolution (approximately 1.8 A) spectrum of the photometrically and spectroscopically variable Seyfert 1 galaxy Arakelian 120 has been obtained in the wavelength region including H-beta. The observed H-beta line profile can be considered as a benchmark for future line profile studies of this interesting object. The origin of the extended red wing of H-beta is discussed.Astronom
Recommended from our members
X-ray absorption toward the red quasar 3C 212
A Roentgen Satellite (ROSAT) X-ray spectrum of the z = 1.049 'red quasar' 3C 212 has a strong low-energy cutoff. The spectrum can be fitted with a power law (of energy index 1.4(+0.8, -0.6) with low-energy photoelectric absorption in excess of the Galactic value that, if at the redhsift of the quasar, would have a column density of (0.9(+0.8, -0.6)) x 1022 atoms/sq cm. Possible sites for the absorption are a nuclear torus, an intervening damped Lyman-alpha system, or intracluster material (e.g., a cooling flow) around the quasar. The implied absorbing column density is sufficient to redden a normal quasar spectrum to the observed steep optical slope. The observed continuum, if dereddened by this amount, can produce the observed emission line fluxes and ratios. The absence of the graphite lambda-2175 feature in 3C 212 however, requires dust different from the local Milky Way composition, or an intervening absorber with z less than 0.4. Alternative acceptable fits to the X-ray spectrum are (1) a blackbody with a temperature of 0.7 keV (in the quasar frame) modified only by Galactic absorption, and (2) an optically thin thermal plasma with excess absorption. Although a blackbody spectrum would be unprecedented, the model is consistent with all the available X-ray and optical data and cannot be ruled out. We discuss possible observations that can discriminate among the above models.Astronom
Recommended from our members
What Do the Ultraviolet Spectra of Narrow‐Line Seyfert 1 Galaxies Tell Us about Their Broad‐Line Regions?
We study the UV spectra of narrow-line Seyfert 1 (NLSy1) galaxies and compare them with "normal" active galactic nuclei. Similar to their optical lines, the NLSy1s show narrower UV lines. They are also characterized by weaker C IV λ1549 and C III] λ1909 and stronger Al III λ1857 emission. These UV-line properties add to the optical and X-ray properties known to be part of the Boroson & Green eigenvector 1. We show that the steep soft X-rays, which characterize the NLSy1s SEDs, change the equilibrium of the two-phase cloud-intercloud medium, resulting in somewhat higher broad-line region cloud densities, lower ionization parameter, and larger broad-line region radii. These modified conditions can explain the unusual emission-line properties we find in NLSy1. Using a specific model of an accretion disk with corona presented by Witt, Czerny, & Życki, we also show that the steep soft and hard X-ray continua can be explained if the L/LEdd ratios are larger than in "normal" Sy1s/QSOs, strengthening earlier suggestions that the L/LEdd is the physical parameter driving this eigenvector.Astronom
Recommended from our members
The X-ray and ultraviolet absorbing outflow in 3C 351
3C 351 (z = 0.371), and X-ray-'quiet' quasar, is one of the few quasars showing signs of a 'warm absorber' in its X-ray spectrum; i.e., partially ionized absorbing material in the line of sight whose opacity depends on its ionization structure. The main feature in the X-ray spectrum is a K-edge due to O VII or O VIII. 3C 351 also shows unusually strong, blueshifted, associated, absorption lines in the ultraviolet (Bahcall et al. 1993) including O VI (lambda lambda 1031, 1037). This high ionization state strongly suggests an identification with the X-ray absorber and a site within the active nucleus. In this paper we demonstrate that the X-ray and UV absorption is due to the same material. This is the first confirmed UV/X-ray absorber. Physical conditions of the absorber are determined through the combination of constraints derived from both the X-ray and UV analysis. This highly ionized, outflowing, low-density, high-column density absorber situated outside the broad emission line region (BELR) is a previously unknown component of nuclear material. We rule out the identification of the absorber with a BELR cloud as the physical conditions in the two regions are inconsistent with one another. The effect of the X-ray quietness and IR upturn in the 3C 351 continuum on the BELR is also investigated. The strengths of the high-ionization lines of C IV lambda-1549 and O VI lambda-1034 with respect to Lyman-alpha are systematically lower (up to a factor of 10) in the material ionized by the 3C 351 continuum as compared to those produced by the 'standard' quasar continuum, the strongest effect being on the strength of O VI lambda-1034. We find that for a 3C 351-like continuum, C III) lambda-1909 ceases to be a density indicator.Astronom
Recommended from our members
X-ray and optical continua of active galactic nuclei with extreme Fe II emission
We present the results of ROSAT PSPC observations of three active galactic nuclei (AGN) with extremely strong Fe ii emission (PHL 1092, IRAS 07598 + 6508 and I Zw 1) and two AGN with very weak Fe ii emission (Mrk 10 and 110). The weak Fe ii emitters have X-ray spectra typical of Type 1 AGN (α = 1.35 and 1.41, where α is the spectral energy index). Of the strong Fe ii emitters, two have steep spectra (PHL 1092 has α = 3.5, and I Zw 1 has =2.0) and the third, IRAS 07598 + 6508, is barely detected and so is extremely X-ray-quiet (αox=2.45). During our observations, PHL 1092 varied by a factor of 4, unusually fast for such a high-luminosity object, and requiring an efficiency of matter-to-energy conversion of 2 per cent or more. Compiling recently published data on other strong Fe ii emitters, we find that they are always X-ray-quiet, and usually X-ray-steep.
Adding these data to the complete UVX-selected quasar sample of Laor et al., we find a statistical connection of Fe ii/Hβ with αx but not a simple relationship: weak Fe ii emitters always have flat spectra, but strong Fe ii emitters can be either flat or steep. A much cleaner relationship exists between Fe ii strength and X-ray loudness, as quantified by αix, the spectral index between 1 μm and 2 keV. We also confirm that Fe ii/Hβ anticorrelates with Balmer line velocity width, which in turn correlates well with both αx and αix in the sense that AGN with narrow lines are X-ray-quiet. There is also marginal evidence that Fe ii/Hβ correlates with both optical continuum slope and the curvature of the optical-UV-X-ray continuum: strong Fe ii objects tend to have steeper continua and weaker ‘blue bumps’. The amount of extinction required to explain the optical steepening compared to normal quasars [E(B − V) in the range 0.2 to 0.6] suggests absorbing columns in the range (1 – 3) × 1021 cm−2, just about the right amount to reduce the ROSAT-band X-ray flux by enough to explain the correlation with αix. However, the spectral shapes observed in the ROSAT band are not consistent with a simple absorption model.
Three objects in our total sample of 19 stand out persistently in all correlations: Mrk 231, IRAS 07598 + 6508 and Mrk 507. Interestingly, two out of the three are known to have low-ionization, broad absorption lines in the UV, and the third (Mrk 507) has no UV spectrum available. Furthermore, low-ionization, broad absorption lines are at least an order of magnitude more common in strong Fe ii emitters than in quasars in general. Overall, continuum shape and blueshified absorption should be added to the intriguing cluster of properties which all vary loosely together, and which has been isolated as ‘eigenvector 1’ by Boroson & Green: Fe ii strength, velocity width, narrow-line strength and line asymmetry. We suggest that the underlying parameter is the density of an outflowing wind.Astronom
Recommended from our members
A Chandra Survey of Broad Absorption Line Quasars
We have carried out a survey with the Chandra X-Ray Observatory of a sample of 10 bright broad absorption line (BAL) quasars (QSOs). Eight of 10 sources are detected. The six brightest sources have only high-ionization BALs (hiBALs), while the four faintest all show low-ionization BALs (loBALs). We perform a combined spectral fit for hiBAL QSOs (384 counts total; 0.5-6 keV) to determine the mean spectral parameters of this sample. We derive an underlying best-fit power-law slope Γ = 1.8 ± 0.35, which is consistent with the mean slope for radio-quiet QSOs from ASCA, but BAL QSOs require a (rest-frame) absorbing column of 6.5 × 1022 cm-2, with a partial covering fraction of ~80%. The optical-to-X-ray spectral slope (αox from 2500 Å to 2 keV) varies from 1.7 to 2.4 across the full sample, consistent with previous results that BAL QSOs appear to be weak soft X-ray emitters. Removing the absorption component from our best-fit spectral model yields a range of αox from 1.55 to 2.28. All six hiBAL QSOs have deabsorbed X-ray emission consistent with non-BAL QSOs of similar luminosity. The spectral energy distributions of the hiBAL QSOs—both the underlying power-law slope and αox—provide the first conclusive evidence that BAL QSOs have appeared to be X-ray weak because of intrinsic absorption and that their underlying emission is consistent with non-BAL QSOs. By contrast, the removal of the best-fit absorption column detected in the hiBAL QSOs still leaves the four loBAL QSOs with values of αox > 2 that are unusually X-ray faint for their optical luminosities, which is consistent with other evidence that loBALs have higher column density, dustier absorbers. Important questions of whether BAL QSOs represent a special line of sight toward a QSO nucleus or rather an early evolutionary or high-accretion phase in a QSO lifetime remain to be resolved, and the unique properties of loBAL QSOs will be an integral part of that investigation.Astronom
Recommended from our members
Optical Detection of the Hidden Nuclear Engine in NGC 4258
The subparsec masing disk recently found to be orbiting a central mass of ~3.6 × 107 M☉ in the Seyfert/LINER galaxy NGC 4258 (Miyoshi and coworkers) provides the most compelling evidence to date for the existence of a massive black hole in the nucleus of a galaxy. The disk is oriented nearly edge-on, and the X-ray spectrum is heavily absorbed. Therefore, in this galaxy, the optical emission-line spectrum generally exhibited by an active galactic nucleus is perhaps best sought using polarized light: probing for light scattered off material surrounding the central source. New polarimetry of NGC 4258 has uncovered a compact polarized nucleus whose spectrum consists of a faint blue continuum similar to those of unobscured quasars (Fν ∝ ν-1.1), plus broadened (~1000 km s-1) emission lines. The lines are strongly linearly polarized (5%-10%) at a position angle (85° ± 2°) coincident with the plane of the maser disk. This result provides substantiating evidence for a weakly active central engine in NGC 4258 and for the existence of obscuring, orbiting tori, which impart many of the perceived distinctions between various types of active galaxies.Astronom
- …