578 research outputs found
Line Shifts, Broad-Line Region Inflow, And The Feeding Of Active Galactic Nuclei
No full textVelocity-resolved reverberation mapping suggests that the broad-line regions (BLRs) of active galactic nuclei (AGNs) can have significant net inflow. We use the STOKES radiative transfer code to show that electron and Rayleigh scattering off the BLR and torus naturally explains the blueshifted profiles of high-ionization lines and the ionization dependence of the blueshifts. This result is insensitive to the geometry of the scattering region. If correct, then this model resolves the long-standing conflict between the absence of outflow implied by velocity-resolved reverberation mapping and the need for outflow if the blueshifting is the result of obscuration. The accretion rate implied by the inflow is sufficient to power the AGN. We suggest that the BLR is part of the outer accretion disk and that similar magnetohydrodynamic processes are operating. In the scattering model, the blueshifting is proportional to the accretion rate so high-accretion-rate AGNs will show greater high-ionization line blueshifts, as is observed. Scattering can lead to systematically too high black hole mass estimates from the C IV line. We note many similarities between narrow-line region (NLR) and BLR blueshiftings, and suggest that NLR blueshiftings have a similar explanation. Our model explains the higher blueshifts of broad absorption line QSOs if they are more highly inclined. Rayleigh scattering from the BLR and torus could be more important in the UV than electron scattering for predominantly neutral material around AGNs. The importance of Rayleigh scattering versus electron scattering can be assessed by comparing line profiles at different wavelengths arising from the same emission-line region.US National Science Foundation AST 03-07912, AST 08-03883Space Telescope Science Institute AR-09926.01GEMINI-CONICYT Fund of Chile 32070017FONDECYT of Chile 1120957French GdR PCHECenter for Theoretical Astrophysics (CTA) through Czech Ministry of Education, Youth and Sports LC06014ANR-11-JS56-013-01Astronom
The Origin Of The Relationship Between Black Hole Mass And Host Galaxy Bulge Luminosity
No full textThere is a strong decrease in scatter in the M(circle dot) - L(bulge) relationship with increasing luminosity and very little scatter for the most luminous galaxies. It is shown that this is a natural consequence of the substantial initial dispersion in the ratio of black hole mass to total stellar mass and of subsequent galaxy growth through hierarchical mergers. >Fine-tuning> through feedback between black hole growth and bulge growth is neither necessary nor desirable.Astronom
Emission-line regions in active galactic nuclei: Structure, kinematics, physical conditions, and chemical abundances.
No full textIUE archival data are used to investigate the structure and kinematics of the broad line region (BLR) in 11 active galactic nuclei (AGNs). The cross-correlation technique advocated by Gaskell and Sparke (1986) has been applied to spectra taken between 1978 and 1988. An extensive investigation of the errors has been carried out. 3 of the objects fail to satisfy the Gaskell and Peterson (1987) sampling criterion and only yield upper limits to the sizes of the emitting region. For 8 AGNs I estimate the luminosity-weighted radii and the inner radii of the line emitting regions and obtain upper limits to their extents. It is confirmed that the high ionization lines are emitted from regions significantly smaller than had been predicted by the "standard" photoionization model and that the lower ionization lines come from further away from the central source, especially in the low luminosity sources. The cloud motions are dominated by gravity and pure radial motion (either inflow or outflow) is excluded at a high confidence level. The rapid variability of the 3C 273 BLR suggests that there might be anisotropic continuum variability. BLR sizes derived are used to estimate directly the masses of the central objects. The BLR radius is consistent with being proportional to the square root of the bolometric luminosity (L\sb{bol}). The analysis shows that L\sb{bol}\propto M\sp{1.1}. The ratio of L\sb{bol} to the Eddington luminosity (L\sb{Edd}), increases from 0.03 in the low luminosity Seyfert galaxies up to 0.06 in the most luminous objects in the sample. Intensities and variability in the emission lines along with the results of the cross-correlation analysis are used to constrain a self-consistent numerical photoionization model for the BLR in NGC 3783. The model involves two gas components, an inner optically thin cloud and an outer optically thick component, with density of 3 10\sp{10}cm\sp{-3}, and ionization parameters 0.1 and 0.01, respectively. Without any assumptions of the ionization parameter, the weak intercombination lines are used to determine the C:N:O abundances. N/C is 1.2 and O/C is 0.3 relative to solar abundances. The He II 1640 rest equivalent width indicates a covering factor of 0.2.PhDAstronomyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105222/1/9116224.pdfDescription of 9116224.pdf : Restricted to UM users only
DISCOVERY OF POLARIZATION REVERBERATION IN NGC 4151
No full textObservations of the optical polarization of NGC 4151 in 1997–2003 show variations of an order of magnitude in the polarized flux while the polarization position angle remains constant. The amplitude of variability of the polarized flux is comparable to the amplitude of variability of the total U-band flux, except that the polarized flux follows the total flux with a lag of 8 ± 3 days. The time lag and the constancy of the position angle strongly favor a scattering origin for the variable polarization rather than a non-thermal synchrotron origin. The orientation of the position angle of the polarized flux (parallel to the radio axis) and the size of the lag imply that the polarization arises from electron scattering in a flattened region within the low-ionization component of the broad-line region. Polarization from dust scattering in the equatorial torus is ruled out as the source of the lag in polarized flux because it would produce a larger lag and, unless the half-opening angle of the torus is \u3e53◦, the polarization would be perpendicular to the radio axis. We note a long-term change in the percentage of polarization at similar total flux levels, and this could be due either to changing non-axisymmetry in the optical continuum emission or a change in the number of scatterers on a timescale of years
Monitoring the Historic Environment: The Archaeological Resource
No full textThe overall aim of the project was to develop a workable methodology to monitor the condition of and threat to the archaeological resource on agricultural land in Wales based on the cost–effective use of existing data sources wherever possible.
The specific objectives of the project identified by the project brief were to:
· Build on the work undertaken by Dwyer et al(2006),Gaskell et al (2007) and Hossell et al (2007) and review existing literature/reports on the likely impacts of Common Agricultural Policy (CAP) reform on the archaeology of Wales.
· Build on the work undertaken by DAT (2006) and evaluate the data sources that could provide indicators to monitor the condition of and threat to the archaeological resource.
· Design operational indicators to monitor the condition of and threat to the archaeological resource
Evidence for Binary Orbital Motion of a Quasar Broad-Line Region
No full textAnalysis of spectra of the quasar 3C 390.3 covering a period of over 20 yr shows that the blueshifted peak of H beta has been changing its radial velocity at an almost constant rate during this time. The radial velocity has increased by over 1500 km/s. The lower limit to the period of radial velocity changes is 210 yr. Although very long periods cannot be excluded by the radial velocity curve alone, other considerations suggest that the period is about 300 yr. If the radial velocity changes are due to orbital motion, the radius of the orbit is about 0.3 pc and the total mass of the system is about 7 * 10**9 solar masses. In the binary black-hole model the masses of the two holes are about 2.2 * 10**9 solar masses. and about 4.4 * 10**9 solar masses. A possible third peak claimed to be present in some 1974-75 spectra is shown to be an instrumental artifact. The narrowness of the displaced peaks in 3C 390.3 objects requires that the broad line region cloud motions are not governed solely by gravity. The black hole masses derived by Koratkar & Gaskell (1991) need to be increased significantly. This probably lowers accretion efficiencies to less than 1\% of the Eddington limit
THE BALDWIN EFFECT IN THE NARROW EMISSION LINES OF ACTIVE GALACTIC NUCLEI
No full textThe anti-correlations between the equivalent widths of emission lines and the continuum luminosity in active galactic nuclei (AGNs), known as the Baldwin effect, are well established for broad lines, but are less well studied for narrow lines. In this paper we explore the Baldwin effect of narrow emission lines over a wide range of ionization levels and critical densities using a large sample of broad-line, radio-quiet AGNs taken from Sloan Digital Sky Survey Data Release 4. These type 1 AGNs span three orders of magnitude in continuum luminosity. We show that most narrow lines show a similar Baldwin effect slope of about -0.2, while the significant deviations of the slopes for [NII]lambda 6583, [OII]lambda 3727, [Ne v]lambda 3425, and the narrow component of Ha can be explained by the influence of metallicity, star formation contamination, and possibly by the difference in the shape of the UV-optical continuum. The slopes do not show any correlation with either the ionization potential or the critical density. We show that a combination of 50% variations in continuum near 5100 angstrom and a lognormal distribution of observed luminosity can naturally reproduce a constant Baldwin effect slope of -0.2 for all narrow lines. The variations of the continuum could be due to variability, intrinsic anisotropic emission, or an inclination effect
A New Echo-Mapping Campaign at Intermediate Redshift
No full textEdited by C. Martin Gaskell, Ian M. McHardy, Bradley M. Peterson and Sergey G. Sergee
Domestic narratives in the transatlantic community: Elizabeth Gaskell and Louisa May Alcott
No full textMy thesis investigates the processes of reciprocal, transatlantic literary exchange between Britain and the United States in the nineteenth century. While these specific transnational relations have received much critical attention in recent years, I extend current theoretical frameworks by focusing on how women‘s domestic fiction operates as a currency for literal and ideological interchanges between Britain and the United States.
Concentrating primarily upon Elizabeth Gaskell‘s and Louisa May Alcott‘s fictions, I trace how they operate as 'transatlantic domestic narratives‘. I use this term to refer to the mobility of their material texts as they circulate within a transatlantic community, and also to articulate the generic narrative tropes on which their domestic fictions rely. I explore, therefore, how the rhetoric of domesticity – as transmitted through the transatlantic domestic narrative – becomes a shared medium through which specific localised concerns can be articulated and circulated within a transatlantic arena.
Focusing on four domestic tropes which were common on both sides of the Atlantic – home, the worker, the nurse, and the witch – I illustrate how both Gaskell and Alcott mobilise these four narrative structures in order to contribute to local and transnational debates in which national, literary and gendered identities are created and contested. Both authors‘ fictions, I demonstrate, exemplify, and have a significant impact upon, a transatlantic literary marketplace
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