438 research outputs found
Input Elaboration, Head Faithfulness and Evidence for Representation in the Acquisition of Left-edge Clusters in West Germanic
No full textThis paper focuses on the elaboration of inputs, drawing on data from two patterns of cluster reduction in early English, Dutch and German. In the sonority pattern, the least sonorous segment survives; in the head pattern, the structurally-defined head of the cluster survives. Earlier research has shown that the sonority pattern can be arrived at using constraints that assess the sonority value of onsets only. This is not so for the head pattern: in /S/+sonorant clusters, there is a mismatch between cluster head and least sonorous segment. In this paper, a unified analysis is proposed for both patterns. It begins by adopting a structural difference between obstruent- versus /S/-initial clusters: the former are left-headed branching onsets; the latter contain an initial appendix. It is argued that faithfulness constraints must reference heads of constituents; MaxHead(Onset) plays a crucial role in the analysis. MaxHead requires inputs to be fully prosodified. This, in turn, demands knowledge of the structures that are permitted in the target language. Accordingly, it is proposed that children's inputs are initially prosodified for simplex onsets and rhymes, that is, for constituent heads only. While there is often a correlation between the head of a cluster and low sonority, it is shown that heads cannot be determined solely on the basis of relative prominence; distributional evidence must be factored in and understanding this requires knowledge that is relatively sophisticated. It is proposed that children initially make decisions about headedness on the basis of sonority until the distributional facts are understood. It is for this reason that two patterns of cluster reduction are observed: the sonority pattern represents stage 1; the head pattern, stage 2.The definitive version of this paper was published in Goad, H. & Y. Rose. (2004). Input elaboration, head faithfulness and evidence for representation in the acquisition of left-edge clusters in West Germanic. In R. Kager, J. Pater & W. Zonneveld (Eds.) Constraints in phonological acquisition (pp. 109-157). Cambridge: Cambridge University PressThis research was supported by grants from Fonds pour la formation de chercheurs et l’aide à la recherche (Québec) (FCAR) and Sonderforschungsbereich (SFB) (to H. Goad), from Social Sciences and Humanities Research Council (SSHRC) (to G.L. Piggott and H. Goad), as well as by a SSHRC doctoral fellowship (to Y. Rose)
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
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
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)
A study to determine if in-house training staff in organizations possess the key skills necessary to author web-based and computer-based training programs
No full textIncludes bibliographical references
Accretion disk reverberation with Hubble Space Telescope observations of NGC 4593 : evidence for diffuse continuum lags
No full textK.H. acknowledges support from STFC grant ST/M001296/1.The Seyfert 1 galaxy NGC 4593 was monitored spectroscopically with the Hubble Space Telescope as part of a reverberation mapping campaign that also included Swift, Kepler and ground-based photometric monitoring. During 2016 July 12 - August 6, we obtained 26 spectra across a nearly continuous wavelength range of ~1150 - 10,000 Å. These were combined with Swift data to produce a UV/optical "lag spectrum", which shows the interband lag relative to the Swift UVW2 band as a function of wavelength. The broad shape of the lag spectrum appears to follow the τ ∝ λ 4/3 relation seen previously in photometric interband lag measurements of other active galactic nuclei (AGN). This shape is consistent with the standard thin disk model but the magnitude of the lags implies a disk that is a factor of ~3 larger than predicted, again consistent with what has been previously seen in other AGN. In all cases these large disk sizes, which are also implied by independent gravitational microlensing of higher-mass AGN, cannot be simply reconciled with the standard model. However the most striking feature in this higher resolution lag spectrum is a clear excess around the 3646 Å Balmer jump. This strongly suggests that diffuse emission from gas in the much larger broad-line region (BLR) must also contribute significantly to the interband lags. While the relative contributions of the disk and BLR cannot be uniquely determined in these initial measurements, it is clear that both will need to be considered in comprehensively modeling and understanding AGN lag spectra.Peer reviewe
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
Interpreting broad emission-line variations II: Tensions between luminosity, characteristic size and responsivity
No full textWe investigate the variability behaviour of the broad H β emission-line to driving continuum variations in the best-studied AGN NGC 5548. For a particular choice of broad emission-line region (BLR) geometry, H β surface emissivity based on photoionization models, and using a scaled version of the 13-yr optical continuum light-curve as a proxy for the driving ionizing continuum, we explore several key factors that determine the broad emission-line luminosity L, characteristic size RRW, and variability amplitude (i.e. responsivity) η, as well as the interplay between them. For fixed boundary models which extend as far as the hot dust the predicted delays for H β are on average too long. However, the predicted variability amplitude of H β provides a remarkably good match to observations except during low-continuum states. We suggest that the continuum flux variations which drive the redistribution in H β surface emissivity F(r) do not on their own lead to large enough changes in RRW or ηeff. We thus investigate dust-bounded BLRs for which the location of the effective outer boundary is modulated by the continuum level and the dust-sublimation and dust-condensation time-scales. We find that in order to match the observed variability amplitude of broad H β in NGC 5548 a rather static outer boundary is preferred. Intriguingly, we show that the most effective way of reducing the H β delay, while preserving its responsivity and equivalent width, is to invoke a smaller value in the incident ionizing photon flux ΦH for a given ionizing source–cloud radial distance r, than is normally inferred from the observed UV continuum flux and typical models of the continuum spectral energy distribution
Evidence for variability timescale dependent UV/X-ray delay in Seyfert 1 AGN NGC 7469
No full textUsing a month-long X-ray light curve from RXTE/PCA and 1.5 month-long UV continuum light curves from IUE spectra in 1220–1970 Å, we performed a detailed time-lag study of the Seyfert 1 galaxy NGC 7469. Our cross-correlation analysis confirms previous results showing that the X-rays are delayed relative to the UV continuum at 1315 Å by 3.49 ± 0.22 d, which is possibly caused by either propagating fluctuation or variable Comptonization. However, if variations slower than 5 d are removed from the X-ray light curve, the UV variations then lag behind the X-ray variations by 0.37 ± 0.14 d, consistent with reprocessing of the X-rays by a surrounding accretion disc. A very similar reverberation delay is observed between Swift/XRT X-ray and Swift/UVOT UVW2, U light curves. Continuum light curves extracted from the Swift/GRISM spectra show delays with respect to X-rays consistent with reverberation. Separating the UV continuum variations faster and slower than 5 d, the slow variations at 1825 Å lag those at 1315 Å by 0.29 ± 0.06 d, while the fast variations are coincident (0.04 ± 0.12 d). The UV/optical continuum reverberation lag from IUE, Swift, and other optical telescopes at different wavelengths are consistent with the relationship: τ ∝ λ4/3, predicted for the standard accretion disc theory while the best-fitting X-ray delay from RXTE and Swift/XRT shows a negative X-ray offset of ∼0.38 d from the standard disc delay prediction
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