2,247 research outputs found
An Empirical Ultraviolet Iron Spectrum Template Applicable to Active Galaxies
Iron emission is often a severe contaminant in optical-ultraviolet spectra of
active galaxies. Its presence complicates emission line studies. A viable
solution, already successfully applied at optical wavelengths, is to use an
empirical iron emission template. We have generated FeII and FeIII templates
for ultraviolet active galaxy spectra based on HST archival 1100 - 3100 A
spectra of IZw1. Their application allows fitting and subtraction of the iron
emission in active galaxy spectra. This work has shown that in particular CIII]
lambda 1909 can be heavily contaminated by other line emission, including iron
transitions. Details of the data processing, generation, and use of the
templates, are given by Vestergaard & Wilkes (2001).Comment: 4 pages, including 1 figure, to appear in "Spectroscopic Challenges
of Photoionized Plasmas", ASP Conf. Series, Eds. Gary Ferland and Daniel Wolf
Savi
Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships
We present four improved empirical relationships useful for estimating the
central black hole mass in nearby AGNs and distant luminous quasars alike using
either optical or UV single-epoch spectroscopy. These mass-scaling
relationships between line widths and luminosity are based on recently improved
empirical relationships between the broad-line region size and luminosities in
various energy bands and are calibrated to the improved mass measurements of
nearby AGNs based on emission-line reverberation mapping. The mass-scaling
relationship based on the Hbeta line luminosity allows mass estimates for
low-redshift sources with strong contamination of the optical continuum
luminosity by stellar or non-thermal emission, while that based on the C IV
lambda 1549 line dispersion allows mass estimates in cases where only the line
dispersion (as opposed to the FWHM) can be reliably determined. We estimate
that the absolute uncertainties in masses given by these mass-scaling
relationships are typically around a factor of 4. We include in an Appendix
mass estimates for all the Bright Quasar Survey (PG) quasars for which direct
reverberation-based mass measurements are not available.Comment: 48 pages including 12 figures and 7 tables. Accepted by Ap
Parsec-scale radio morphology and variability of a changing-look AGN: the case of Mrk 590
We investigate the origin of the parsec-scale radio emission from the
changing-look active galactic nucleus (AGN) of Mrk 590, and examine whether the
radio power has faded concurrently with the dramatic decrease in accretion
rates observed between the 1990s and the present. We detect a compact core at
1.6 GHz and 8.4 GHz using new Very Long Baseline Array observations, finding no
significant extended, jet-like features down to 1 pc scales. The flat
spectral index () and high brightness temperature
() indicate self-absorbed synchrotron emission
from the AGN. The radio to X-ray luminosity ratio of , similar to that in coronally active stars, suggests
emission from magnetized coronal winds, although unresolved radio jets are also
consistent with the data. Comparing new Karl G. Jansky Very Large Array
measurements with archival and published radio flux densities, we find ,
, and (insignificantly) flux density decreases between the 1990s
and the year 2015 at 1.4 GHz, 5 GHz and 8.4 GHz respectively. This trend,
possibly due to the expansion and fading of internal shocks within the
radio-emitting outflow after a recent outburst, is consistent with the decline
of the optical-UV and X-ray luminosities over the same period. Such correlated
variability demonstrates the AGN accretion-outflow connection, confirming that
the changing-look behaviour in Mrk 590 originates from variable accretion rates
rather than dust obscuration. The present radio and X-ray luminosity
correlation, consistent with low/hard state accretion, suggests that the black
hole may now be accreting in a radiatively inefficient mode.Comment: 14 pages, 5 tables, 5 figures, accepted for publication in MNRA
MUSE observations of a changing-look AGN I: The re-appearance of the broad emission lines
Optical changing-look Active Galactic Nuclei (AGN) are a class of sources
that change type within a short timescale of years or decades. This change is
characterised by the appearance or disappearance of broad emission lines, often
associated with dramatic AGN continuum flux changes that are orders of
magnitude larger than those expected from typical AGN variability. In this work
we study for the first time the host galaxy of a changing-look AGN, Mrk 590,
using high spatial resolution optical and near-infrared observations. We
discover that after ~ 10 yr absence, the optical broad emission lines of Mrk
590 have reappeared. The AGN optical continuum flux however, is still ~ 10
times lower than that observed during the most luminous state in the 1990s. The
host galaxy shows a 4.5 kpc radius star-forming ring with knots of ionised and
cold molecular gas emission. Extended ionised and warm molecular gas emission
are detected in the nucleus, indicating that there is a reservoir of gas as
close as 60 pc from the black hole. We observe a nuclear gas spiral between
radii r ~ 0.5 - 2 kpc, which has been suggested as a dynamical mechanism able
to drive the necessary gas to fuel AGN. We also discover blue-shifted and high
velocity dispersion [O III] emission out to a radius of 1 kpc, tracing a
nuclear gas outflow. The gas dynamics in Mrk 590 suggest a complex balance
between gas inflow and outflow in the nucleus of the galaxy.Comment: Accepted for publication in MNRA
Supermassive Black Hole Mass Estimates Using Sloan Digital Sky Survey Quasar Spectra at 0.7 < z < 2
We present MgII-based black hole mass estimates for 27,602 quasars with
rest-frame UV spectra available in the Sloan Digital Sky Survey Data Release
Three. This estimation is possible due to the existence of an empirical
correlation between the radius of the broad line region and the continuum
luminosity at 3000 Angstroms. We regenerate this correlation by applying our
measurement method to UV spectra of low-redshift quasars in the HST/IUE
databases which have corresponding reverberation mapping estimates of the Hbeta
broad line region's radius. Our mass estimation method uses the line dispersion
rather than the full width at half maximum of the low-ionization MgII emission
line. We measure MgII line dispersions for quasars whose spectra have been
reconstructed using the most significant eigenspectra produced through
Principal Component Analysis. We have tested the reliability of using
reconstructed spectra in black hole mass estimation using a Monte Carlo
simulation and by comparing the results from original and reconstructed Data
Release Three spectra. We show that using reconstructed spectra not only makes
bias-free mass estimation possible for quasars with low spectroscopic
signal-to-noise ratio, but also reduces the intrinsic scatter of the
distribution of the black hole masses to lower than 0.15 dex.Comment: 38 Pages, 12 figures, 3 Tables, 1 hyperlink to catalogue data.
Accepted for publication in ApJ
Comparison of markets for organic food in six EU states.
This report was presented at the UK Organic Research 2002 Conference. Recent research confirms that the decision to convert is now highly influenced by financial incentives arising from EU regulations but the exact mix of incentives depends on prevailing government policies and access to premium markets so that the organic sector in most countries is now referred to as either government-led or market-driven. The objective of the paper is to compare development of the sector along these two polarities but set within the context of "common elements of interest" within new agrifood methodologies: time, space, power, and meaning (Cooke, Uranga and Etxebarria 1998; Morgan and Murdoch 2000). The paper presents preliminary findings relating to six EU States: UK, Ireland, Austria, Denmark, Portugal and Italy, and through the application of "worlds of production" to market outlets and suggests discourses that define these outlets. The analysis aims to inform the further study of farmer marketing decisions and practices
Swift/UVOT grism monitoring of NGC 5548 in 2013: an attempt at MgII reverberation mapping
Reverberation-mapping-based scaling relations are often used to estimate the
masses of black holes from single-epoch spectra of AGN. While the
radius-luminosity relation that is the basis of these scaling relations is
determined using reverberation mapping of the H line in nearby AGN, the
scaling relations are often extended to use other broad emission lines, such as
MgII, in order to get black hole masses at higher redshifts when H is
redshifted out of the optical waveband. However, there is no radius-luminosity
relation determined directly from MgII. Here, we present an attempt to perform
reverberation mapping using MgII in the well-studied nearby Seyfert 1, NGC
5548. We used Swift to obtain UV grism spectra of NGC 5548 once every two days
from April to September 2013. Concurrent photometric UV monitoring with Swift
provides a well determined continuum lightcurve that shows strong variability.
The MgII emission line, however, is not strongly correlated with the continuum
variability, and there is no significant lag between the two. We discuss these
results in the context of using MgII scaling relations to estimate
high-redshift black hole masses.Comment: 8 pages, 7 figures, accepted for publication in Ap
Optical/near-infrared selection of red QSOs: Evidence for steep extinction curves towards galactic centers?
We present the results of a search for red QSOs using a selection based on
optical imaging from SDSS and near-infrared imaging from UKIDSS. For a sample
of 58 candidates 46 (79%) are confirmed to be QSOs. The QSOs are predominantly
dust-reddened except a handul at redshifts z>3.5. The dust is most likely
located in the QSO host galaxies. 4 (7%) of the candidates turned out to be
late-type stars, and another 4 (7%) are compact galaxies. The remaining 4
objects we could not identify. In terms of their optical spectra the QSOs are
similar to the QSOs selected in the FIRST-2MASS red Quasar survey except they
are on average fainter, more distant and only two are detected in the FIRST
survey. We estimate the amount of extinction using the SDSS QSO template
reddened by SMC-like dust. It is possible to get a good match to the observed
(restframe ultraviolet) spectra, but for nearly all the reddened QSOs it is not
possible to match the near-IR photometry from UKIDSS. The likely reasons are
that the SDSS QSO template is too red at optical wavelengths due to
contaminating host galaxy light and that the assumed SMC extinction curve is
too shallow. Our survey has demonstrated that selection of QSOs based on
near-IR photometry is an efficent way to select QSOs, including reddened QSOs,
with only small contamination from late-type stars and compact galaxies. This
will be useful with ongoing and future wide-field near-IR surveys such as the
VISTA and EUCLID surveys. [Abridged]Comment: 74 pages, 6 figures. Accepted for for publication in ApJ
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