143 research outputs found
Hubble Space Telescope Imaging of Bright Lyman-break Galaxy Candidates from the Sloan Digital Sky Survey: Not LBGs After All
We present deep Hubble Space Telescope ACS and NICMOS images of six bright
Lyman-break galaxy candidates that were previously discovered in the Sloan
Digital Sky Survey. We find that five of the objects are consistent with
unresolved point sources. Although somewhat atypical of the class, they are
most likely LoBAL quasars, perhaps FeLoBALs. The sixth object, J1147, has a
faint companion galaxy located ~0.8 arcsec to the southwest. The companion
contributes ~8% of the flux in the observed-frame optical and infrared. It is
unknown whether this companion is located at the same redshift as J1147.Comment: 16 pages, 8 figures, 3 tables; accepted for publication in A
Constraints on the broad line region from regularized linear inversion: Velocity-delay maps for five nearby active galactic nuclei
Reverberation mapping probes the structure of the broad emission-line region
(BLR) in active galactic nuclei (AGN). The kinematics of the BLR gas can be
used to measure the mass of the central supermassive black hole. The main
uncertainty affecting black hole mass determinations is the structure of the
BLR. We present a new method for reverberation mapping based on regularized
linear inversion (RLI) that includes modelling of the AGN continuum light
curves. This enables fast calculation of velocity-resolved response maps to
constrain BLR structure. RLI allows for negative response, such as when some
areas of the BLR respond in inverse proportion to a change in ionizing
continuum luminosity. We present time delays, integrated response functions,
and velocity-delay maps for the broad emission line in five
nearby AGN, as well as for and in Arp 151,
using data from the Lick AGN Monitoring Project 2008. We find indications of
prompt response in three of the objects (Arp 151, NGC 5548 and SBS 1116+583A)
with additional prompt response in the red wing of . In SBS
1116+583A we find evidence for a multimodal broad prompt response followed by a
second narrow response at 10 days. We find no clear indications of negative
response. The results are complementary to, and consistent with, other methods
such as cross correlation, maximum entropy and dynamical modelling. Regularized
linear inversion with continuum light curve modelling provides a fast,
complementary method for velocity-resolved reverberation mapping and is
suitable for use on large datasets.Comment: 20 pages, 13 figures, accepted to MNRA
Correlated X-ray/Ultraviolet/Optical Variability in NGC 6814
We present results of a 3-month combined X-ray/UV/optical monitoring campaign
of the Seyfert 1 galaxy NGC 6814. The object was monitored by Swift from June
through August 2012 in the X-ray and UV bands and by the Liverpool Telescope
from May through July 2012 in B and V. The light curves are variable and
significantly correlated between wavebands. Using cross-correlation analysis,
we compute the time lag between the X-ray and lower energy bands. These lags
are thought to be associated with the light travel time between the central
X-ray emitting region and areas further out on the accretion disc. The computed
lags support a thermal reprocessing scenario in which X-ray photons heat the
disc and are reprocessed into lower energy photons. Additionally, we fit the
lightcurves using CREAM, a Markov Chain Monte Carlo code for a standard disc.
The best-fitting standard disc model yields unreasonably high super-Eddington
accretion rates. Assuming more reasonable accretion rates would result in
significantly under-predicted lags. If the majority of the reprocessing
originates in the disc, then this implies the UV/optical emitting regions of
the accretion disc are farther out than predicted by the standard thin disc
model. Accounting for contributions from broad emission lines reduces the lags
in B and V by approximately 25% (less than the uncertainty in the lag
measurements), though additional contamination from the Balmer continuum may
also contribute to the larger than expected lags. This discrepancy between the
predicted and measured interband delays is now becoming common in AGN where
wavelength-dependent lags are measured.Comment: 11 pages, 8 figures, accepted for publication in MNRA
Reverberation Mapping of IC4329A
We present the results of a new reverberation mapping campaign for the
broad-lined active galactic nucleus (AGN) in the edge-on spiral IC4329A.
Monitoring of the optical continuum with band photometry and broad
emission-line flux variability with moderate-resolution spectroscopy allowed
emission-line light curves to be measured for H, H, and HeII
. We find a time delay of days for H,
a similar time delay of days for H, and an
unresolved time delay of days for HeII. The time delay for
H is consistent with the predicted value from the relationship between
AGN luminosity and broad line region radius, after correction for the
mag of intrinsic extinction at 5100A. Combining the measured time
delay for H with the broad emission line width and an adopted value of
, we find a central supermassive black hole mass of
. Velocity-resolved time
delays were measured across the broad H emission-line profile and may be
consistent with an ''M''-like shape. Modeling of the full reverberation
response of H was able to provide only modest constraints on some
parameters, but does exhibit agreement with the black hole mass and average
time delay. The models also suggest that the AGN structure is misaligned by a
large amount from the edge-on galaxy disk. This is consistent with expectations
from the unified model of AGNs, in which broad emission lines are expected to
be visible only for AGNs that are viewed at relatively face-on inclinations.Comment: 12 pages, 6 figures, 3 tables; accepted for publication in Ap
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