1,043 research outputs found
Classifying broad absorption line quasars: metrics, issues and a new catalogue constructed from SDSS DR5
No full textWe apply a recently developed method for classifying broad absorption line quasars (BALQSOs) to the latest quasi-stellar object (QSO) catalogue constructed from Data Release 5 of the Sloan Digital Sky Survey. Our new hybrid classification scheme combines the power of simple metrics, supervised neural networks and visual inspection. In our view, the resulting BALQSO catalogue is both more complete and more robust than all previous BALQSO catalogues, containing 3552 sources selected from a parent sample of 28 421 QSOs in the redshift range 1.7 < z < 4.2 . This equates to a raw BALQSO fraction of 12.5 per cent.In the process of constructing a robust catalogue, we shed light on the main problems encountered when dealing with BALQSO classification, many of which arise due to the lack of a proper physical definition of what constitutes a BAL. This introduces some subjectivity in what is meant by the term BALQSO, and because of this, we also provide all of the meta-data used in constructing our catalogue, for every object in the parent QSO sample. This makes it easy to quickly isolate and explore subsamples constructed with different metrics and techniques. By constructing composite QSO spectra from subsamples classified according to the meta-data, we show that no single existing metric produces clean and robust BALQSO classifications. Rather, we demonstrate that a variety of complementary metrics are required at the moment to accomplish this task. Along the way, we confirm the finding that BALQSOs are redder than non-BALQSOs and that the raw BALQSO fraction displays an apparent trend with signal-to-noise ratio steadily increasing from 9 per cent in low signal-to-noise ratio data up to 15 per cent
The intrinsic fraction of broad-absorption line quasars
No full textWe carefully reconsider the problem of classifying broad-absorption line quasars (BALQSOs) and derive a new, unbiased estimate of the intrinsic BALQSO fraction from the Sloan Digital Sky Survey (SDSS) DR3 quasi-stellar object (QSO) catalogue. We first show that the distribution of objects selected by the so-called 'absorption index' (AI) is clearly bimodal in log AI, with only one mode corresponding to definite BALQSOs. The surprisingly high BALQSO fractions that have recently been inferred from AI-based samples are therefore likely to be overestimated. We then present two new approaches to the classification problem that are designed to be more robust than the AI, but also more complete than the traditional 'balnicity index' (BI). Both approaches yield observed BALQSO fractions around 13.5 per cent, while a conservative third approach suggests an upper limit of 18.3 per cent. Finally, we discuss the selection biases that affect our observed BALQSO fraction. After correcting for these biases, we arrive at our final estimate of the intrinsic BALQSO fraction. This is fBALQSO= 0.17 ± 0.01 (stat) ± 0.03 (sys) with an upper limit of fBALQSO? 0.23 . We conclude by pointing out that the bimodality of the log AI distribution may be evidence that the BAL-forming region has clearly delineated physical boundaries
The optical counterpart of the ultraluminous X-ray source NGC 5204 X-1
No full textWe use archival HST/WFPC2 V and I band images to show that the optical counterpart to the ultra-luminous x-ray source NGC 5204 X-1, reported by Roberts et al., is composed of two sources separated by 0.5" We have also identified a third source as a possible counterpart, which lies 0.8" from the nominal x-ray position. PSF fitting photometry yields V-band magnitudes of 20.3, 22.0 and 22.4 for the three sources. The V-I band colours are 0.6, 0.1, and -0.2, respectively (i.e. the fainter sources are bluer). We find that all V-I colours and luminosities are consistent with those expected for young stellar clusters (age <10 Myr)
Modelling the AGN broad line region using single-epoch spectra II. Nearby AGN
No full textThe structure of the broad line region (BLR) is an essential ingredient in the determination of active galactic nuclei (AGN) virial black hole masses, which in turn are important to study the role of black holes in galaxy evolution. Constraints on the BLR geometry and dynamics can be obtained from velocity-resolved studies using reverberation mapping data (i.e. monitoring data). However, monitoring data are observationally expensive and only available for a limited sample of AGN, mostly confined to the local Universe. Here we explore a new version of a Bayesian inference, physical model of the BLR which uses an individual spectrum and prior information on the BLR size from the radius-luminosity relation, to model the AGN BLR geometry and dynamics. We apply our model to a sample of 11 AGN, which have been previously modelled using monitoring data. Our single-epoch BLR model is able to constrain some of the BLR parameters with inferred parameter values that agree within the uncertainties with those determined from the modelling of monitoring data. We find that our model is able to derive stronger constraints on the BLR for AGN with broad emission lines that qualitatively have more substructure and more asymmetry, presumably as they contain more information to constrain the physical model. The performance of this model makes it a practical and cost-effective tool to determine some of the BLR properties of a large sample of low and high redshift AGN, for which monitoring data are not available
Grasping at straws: a ratings downgrade for the emerging international financial architecture
No full textFollowing the Asia crisis of 1997-98, policymakers invested a great deal of energy in designing a new international financial architecture. However many of the policy proposals which have emerged from think tanks and the multilateral agencies have proven unworkable or politically unpalatable. The debate focuses on state-led initiatives. But the assumption that public policy is by definition an output of public institutions is difficult to sustain in an era of global change. This paper considers specialized forms of intelligence-gathering and judgment-determination which seem increasingly important as sources of governance in this era of financial market volatility. These agents - embedded knowledge networks (EKNs) - include the major bond rating agencies, Moody’s Investors Service and Standard and Poor’s, the focus of this paper. The Basel Committee has put forward a serious proposal to reform the existing capital adequacy framework which uses banks' own internal ratings and external bond ratings to calculate bank risk-weighted capital requirements. The paper shows that there are potentially unexpected consequences from using private rating agencies as a substitute for state-based regulation, due to the organizational incentives that shape the ratings industry. Cementing these organizational incentives into the emerging financial architecture will give rise to negative social and economic consequences
Approximate torus fibrations of high dimensional manifolds can be approximated by torus bundle projections
No full textIn this paper, we prove that approximate torus fibrations of high dimensional manifolds can be approximated by torus bundle projections. The principal tools are the torus trick developed by Kirby and Siebenmann, a surgery theorem concerning homotopy structures on torii due to Hsiang and Wall, a theorem on the space of homeomorphisms of the torus due to Hamstrom and a generalization of hereditary homotopy equivalence developed by the author.</p
Evaluating nineteenth-century urbanization in the Galata neighbourhood of İstanbul using the maps by Huber, d’Ostoya, and Goad
No full textİstanbul experienced significant changes in its urban pattern as a result of Westernization that took place in the nineteenth century. Galata, a neighbourhood located in the Beyoğlu District, represents the occidental and cosmopolitan face of the city during that time. This study examines the spatial effects of these social and political changesby integrating old city maps of Beyoğlu and Galata with geographic information system programmes (GIS). This methodology affords novel interpretations of historical maps thanks to these new ways of analyzing, displaying, and managing geographical information. The maps of G. d’Ostoya (1858–1860), R. Huber (1887–1891), and Charles E. Goad (1904–1906) have been coordinated with GIS software. Items such as buildings, roads, and empty spaces included as raster data have been transformed into vector data to make comparisons and superpositions possible within the GIS environment. Thus, the transformation of urban space can be revealed, and conclusions about how Galata experienced broader change across the nineteenth century can be perceived.Publisher's Versio
An anticorrelation between X-ray luminosity and H? equivalent width in X-ray binaries
No full textWe report an anticorrelation between continuum luminosity and the equivalent width (EW) of the H? emission line in X-ray binary systems. The effect is evident both in a universal monotonic increase in H? EW with time following outbursts, as systems fade, and in a comparison between measured EWs and contemporaneous X-ray measurements. The effect is most clear for black hole binaries in the low/hard X-ray state, which is prevalent at X-ray luminosities below ?1 per cent of the Eddington luminosity. We do not find strong evidence for significant changes in line profiles across accretion state changes, but this is hampered by a lack of good data at such times. The observed anticorrelation, highly significant for black hole binaries, is only marginally so for neutron star systems, for which there are far less data. Comparison with previously established correlations between optical and X-ray luminosity suggests that the line luminosity is falling as the X-ray and optical luminosities drop, but not as fast, approximately, as LH??L?0.4X?L?0.7opt . We briefly discuss possible origins for such an effect, including the optical depth, form of the irradiating spectrum and geometry of the accretion flow. Further refinement of the relation in the future may allow measurements of H? EW to be used to estimate the luminosity of, and hence the distance to, X-ray binary systems. Beyond this, further progress will require a better sample of spectrophotometric data
Space telescope and optical reverberation mapping project. II. Swift and HST reverberation mapping of the accretion disk of NGC 5548
No full textRecent intensive Swift monitoring of the Seyfert 1 galaxy NGC 5548 yielded 282 usable epochs over 125 days across six UV/optical bands and the X-rays. This is the densest extended active galactic nucleus (AGN) UV/optical continuum sampling ever obtained, with a mean sampling rate <0.5 day. Approximately daily Hubble Space Telescope UV sampling was also obtained. The UV/optical light curves show strong correlations () and the clearest measurement to date of interband lags. These lags are well-fit by a wavelength dependence, with a normalization that indicates an unexpectedly large disk radius of lt-day at 1367 Å, assuming a simple face-on model. The U band shows a marginally larger lag than expected from the fit and surrounding bands, which could be due to Balmer continuum emission from the broad-line region as suggested by Korista and Goad. The UV/X-ray correlation is weaker () and less consistent over time. This indicates that while Swift is beginning to measure UV/optical lags in general agreement with accretion disk theory (although the derived size is larger than predicted), the relationship with X-ray variability is less well understood. Combining this accretion disk size estimate with those from quasar microlensing studies suggests that AGN disk sizes scale approximately linearly with central black hole mass over a wide range of masses
Galax Savings & Loan Association v. Robert E. Goad and Joyce R. Goad
No full textSupreme Court of Virginiahttps://scholarlycommons.law.wlu.edu/va-supreme-court-records-vol226/1075/thumbnail.jp
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