Class Of QSOs Research Articles

AHubble Space TelescopeFaint Object Spectrograph Survey for Broad Absorption Lines in a Sample of Low‐Redshift Weak [Oiii] Quasi‐stellar Objects

The study by Boroson & Meyers led to the suggestion that radio-quiet QSOs with weak [O III] and strong Fe II emission spectra form a class of QSOs that has a high probability of exhibiting broad absorption lines (BALs) in their spectra. Furthermore, they argued that since narrow-line [O III] emission is almost certainly emitted isotropically, this indicates that such objects have relatively large BAL region covering factors. Low covering factor models are consistent with scenarios in which most QSOs have BAL regions, while higher covering factor models are consistent with scenarios in which there are special classes of QSOs with large BAL region outflows. By making Hubble Space Telescope (HST) FOS observations and using IUE or HST archival data when available, the details of the Boroson & Meyers suggestion have been explored by directly searching for classical C IV BALs in a sample of 18 QSOs with weak [O III] and often strong Fe II emission. Six of the 18 QSOs are found to exhibit C IV BALs. (In the archival sample, four of six objects have BALs, while two of the 12 new objects observed with the HST FOS have BALs.) However, there is evidence that the sample is heterogeneous, with IRAS-selected objects and high-luminosity objects having a greater tendency to exhibit BALs. If an isotropic model for [O III] emission equivalent width is considered, the results suggest that for the 18 object sample as a whole the average BAL region covering factor is ≈ 0.33 -->+ 0.20−0.09, which is significantly larger (with a more than 99% probability) than the overall fraction of QSOs observed to have BALs (normally taken as ≈ 0.1). Given possible selection effects, in the context of an isotropic model the results may indicate that some of the sample objects have covering factors 0.33, while others have covering factors 0.33. At the same time, it is impossible to rule out in a non-model-dependent way a scenario in which orientation effects are important and covering factors are generally small. Results such as these ultimately provide constraints on QSO geometries, intrinsic QSO properties, and evolutionary processes in QSOs.

A Fractal Model of the Universe: Do Large Galaxies Interact by Quasar Exchange ?

A fractal universe model has been proposed elsewhere (Driessen, 1991, 1994), based on the assumption of perfect self-similarity between some definite scales, and in particular between particles and galaxies. Its motivation rested essentially on two ideas: first, if striving for unification is justified, then the fractal idea makes sense, for in this case one single theory of particles could encompass all self-similar structures at once. Secondly, it could be demonstrated that, provided some reasonable hypothesis were made about the structure of spiral galaxy cores, they came back to the same topological state after two complete revolutions (Driessen, 1991). These ideas combined suggested that spiral galaxies might correspond to electrons on the cosmic scale. The main test of the coherence of the fractal picture was then to discover if other galaxy types and quasars do find a place in this model. Now, a small group of dissident has sustained for years that QSOs (or at least a certain class of QSOs) are local objects emitted by galaxies. This class would contain very small (d ≈ 0.3 kpc), faint (Mv≈ −12), and most often radio-quiet objects with large (non cosmological) excess redshift. The analogy between the two statements “electrons emit photons” and “galaxies emit QSOs” hinted that QSOs embody cosmic scale photons, and entails that galaxies experience quasar exchange interactions. It was claimed further that galaxy clusters reproduce atomic and molecular-like systems with one or a few central giant ellipticals (the cosmic scale nuclei) interacting via quasar exchange with their satellite spirals (the cosmic scale electrons). The flock of dwarf galaxies around large ellipticals and spirals would result from condensation of dusty gas clouds entrained by ejected QSOs.

The Soft X-Ray Properties of a Large Optical QSO Sample: ROSAT Observations of the Large Bright Quasar Survey

view Abstract Citations (150) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Soft X-Ray Properties of a Large Optical QSO Sample: ROSAT Observations of the Large Bright Quasar Survey Green, Paul J. ; Schartel, Norbert ; Anderson, Scott F. ; Hewett, Paul C. ; Foltz, Craig B. ; Brinkmann, Wolfgang ; Fink, Henner ; Truemper, Joachim ; Margon, Bruce Abstract Of the more than 1000 QSOs in the Large Bright Quasar Survey (LBQS), we study the X-ray properties of 908 that were covered by the ROSAT All-Sky Survey (RASS). These data constitute among the largest, most homogeneous X-ray surveys of QSOs to date, and as such are well suited to the study of the multiwavelength properties of QSOs. Due to the ≍ 600 s RASS exposure times, only 10% of the QSOs are detected in X-rays. However, by stacking X-ray counts, we obtain effectively much more sensitive observations for an average QSO in bins of redshift or luminosity, and for several classes of QSOs. We confirm a correlation of αox with luminosity for the overall sample. For higher redshifts and optical luminosities, radio-loud QSOs appear to become progressively more luminous in X-rays than radio-quiet QSOs. The X-ray properties of a subsample of 36 broad absorption line QSOs suggest that they are strongly absorbed or underluminous in the X-rays, while a subsample of 22 Fe II-strong QSOs is anomalously X-ray bright. Publication: The Astrophysical Journal Pub Date: September 1995 DOI: 10.1086/176118 Bibcode: 1995ApJ...450...51G Keywords: GALAXIES: ACTIVE; GALAXIES: QUASARS: GENERAL; SURVEYS; X-RAYS: GALAXIES full text sources ADS | data products SIMBAD (102) NED (92) CDS (1)

Absorption features of QSOs

Absorption features shown by QSOs may be identified and measured as reported absorption redshift systems, or may remain unidentified and not measured. The features are believed to be observed in objects with high emission redshifts (z em), although no quantitative analysis exists to examine any such preferential trend, except that by Basu (1982). However, redshift data have since increased enormously both in range of the redshift spectrum and in number. Furthermore, the earlier analysis was based on only the reported absorption redshifts while unidentified absorption features were not dealt with. The present paper analyses the updated data, both identified and unidentified features. It is found that absorption features may be expressed as exponential function ofz em, and upper limits are set for the percentage of QSOs showing absorption features. Finally, an entirely new method of analysis confirms the earlier conclusion of Basu (1982) that the appearance of absorbing clouds is closely associated with the creation of the QSOs, the two may be having a common cause. It is suggested that ‘absorption QSOs’ may be a separate class of QSOs whose birth is accompanied with creation of absorbing clouds.

Optical variability of QSOs and gravitational lenses in galactic haloes

The problem of QSO-galaxy associations has been analysed1,2 by taking into account different classes of QSOs with the conclusions that: (1) the strong excess of 3C QSOs near bright galaxies3 is not confirmed by larger QSO samples, which do not show any tendency towards QSO-galaxy associations, so that the 3C QSOs appeared as a statistical fluctuation1. (2) Amongst various classes of QSOs, optically variable (OV) QSOs from a list of 41 objects4 showed a significant excess of QSOs near galaxies2. But to be considered as a physical effect this excess needed confirmation from a larger sample of QSOs. Canizares5 has used the possibility of gravitational lens effects on QSOs caused by stars in galactic haloes to explain the presence of numerous QSOs near bright galaxies6, whose statistical significance is quite controversial (see refs 7–11). Canizares attributed to such QSOs one physical characteristic--their optical variability caused by the relative motions of the Earth and of the star acting as a gravitational lens. As these theoretical considerations gave a new insight on our previous statistical study, we decided to consider a larger sample of OV QSOs. We now present this new analysis and discuss the results in the light of Canizares' considerations.

QSO evolution and the intergalactic medium

A model is developed of a cold, photoionized intergalactic medium in which only discrete, evolving sources (quasars) produce the observed extragalactic hard X-ray background. Constraints on the model are imposed by observed optical depth limits to various redshifts, far UV and visible flux measurements, X-ray background and source counts in the region 2-6 keV, and it makes use of results of the Palomar Bright Quasar Survey and the Braccesi Quasar survey to obtain expressions for the quasar evolution function, absolute luminosity, present number density and switch-on redshift. Results of computer modeling reveal an intergalactic medium with a density with respect to closure less than 0.35, temperature of 16,000 K and fractional ion abundances of approximately 0.000001 for H I and 0.001 for He II, under the assumption of a Hubble constant of 50 km/sec per Mpc. In addition, spectral indices of -0.4 and -1.3 are obtained for the regions of the emission spectrum above and below 4 x 10 to the 18th Hz.