1,876 research outputs found
Line Shifts, Broad-Line Region Inflow, and the Feeding of AGNs
Velocity-resolved reverberation mapping suggests that the broad-line regions
(BLRs) of 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, 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 MHD 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.Comment: 10 pages, 7 figures, Astrophysical Journal in press. The only changes
from the previous version are to include some additional discussion of the
plausibility of supersonic inflow velocities (see section 5.2) and some
additional reference
The case for inflow of the broad-line region of active galactic nuclei
The high-ionization lines of the broad-line region (BLR) of thermal active
galactic nuclei (AGNs) show blueshifts of a few hundred km/s to several
thousand km/sec with respect to the low-ionization lines. This has long been
thought to be due to the high-ionization lines of the BLR arising in a wind of
which the far side of the outflow is blocked from our view by the accretion
disc. Evidence for and against the disc-wind model is discussed. The biggest
problem for the model is that velocity-resolved reverberation mapping
repeatedly fails to show the expected kinematic signature of outflow of the
BLR. The disc-wind model also cannot readily reproduce the red side of the line
profiles of high-ionization lines. The rapidly falling density in an outflow
makes it difficult to obtain high equivalent widths. We point out a number of
major problems with associating the BLR with the outflows producing broad
absorption lines. An explanation which avoids all these problems and satisfies
the constraints of both the line profiles and velocity-resolved
reverberation-mapping is a model in which the blueshifting is due to scattering
off material spiraling inwards with an inflow velocity of half the velocity of
the blueshifting. We discuss how recent reverberation mapping results are
consistent with the scattering-plus-inflow model but do not support a disc-wind
model. We propose that the anti-correlation of the apparent redshifting of
H with the blueshifting of CIV is a consequence of contamination of the
red wings of H by the broad wings of [O III].Comment: 15 pages, 15 figures. To appear in special issue of Astrophysics and
Space Science, "Spectral Line Shapes in Astrophysics
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Line Shifts, Broad-Line Region Inflow, And The Feeding Of Active Galactic Nuclei
Velocity-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
Large scale topography of Io
To investigate the large scale topography of the Jovian satellite Io, both limb observations and stereographic techniques applied to landmarks are used. The raw data for this study consists of Voyager 1 images of Io, 800x800 arrays of picture elements each of which can take on 256 possible brightness values. In analyzing this data it was necessary to identify and locate landmarks and limb points on the raw images, remove the image distortions caused by the camera electronics and translate the corrected locations into positions relative to a reference geoid. Minimizing the uncertainty in the corrected locations is crucial to the success of this project. In the highest resolution frames, an error of a tenth of a pixel in image space location can lead to a 300 m error in true location. In the lowest resolution frames, the same error can lead to an uncertainty of several km
Spectrophotometry of 2 complete samples of flat radio spectrum quasars
Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the CIV wavelength 1550 emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for q (sub o) is approximately 1. Alternatively, luminosity evolution can be invoked to give compact distributions for q (sub o) is approximately 0 models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of CIV wavelength 1550 in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts for 4 quasars are given
Setting UBVRI Photometric Zero-Points Using Sloan Digital Sky Survey ugriz Magnitudes
We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread
function (PSF) photometry for setting the zero points of UBVRI CCD images. From
a comparison with the Landolt (1992) standards and our own photometry we find
that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i
~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where
there is significant interpolation due to saturation in the SDSS PSF fluxes.
There also seems to be another, much smaller systematic effect for stars with
g, r > 19.5. The latter effect is consistent with a small Malmquist bias.
Because of the difficulties with PSF fluxes of brighter stars, we recommend
that comparisons of ugriz and UBVRI photometry should only be made for
unsaturated stars with g, r and i in the range 14.5 - 19.5, and u in the range
16 - 19.5. We give a prescription for setting the UBVRI zero points for CCD
images, and general equations for transforming from ugriz to UBVRI.Comment: 13 pages. 6 figures. Accepted for publication in the Astronomical
Journa
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