2,599 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
The Cambridge-Cambridge ROSAT Serendipity Survey - I. X-ray-luminous galaxies
We report on the first results obtained from a new optical identification
programme of 123 faint X-ray sources with (0.5--2ergscm serendipitously detected in {\it ROSAT}
PSPC pointed observations. We have spectroscopically identified the optical
counterparts to more than 100 sources in this survey. Although the majority of
the sample (68 objects) are QSOs, we have also identified 12 narrow emission
line galaxies which have extreme X-ray luminosities (ergs). Subsequent spectroscopy reveals them to be a
mixture of starburst galaxies and Seyfert 2 galaxies in approximately equal
numbers. Combined with potentially similar objects identified in the {\it
Einstein} Extended Medium Sensitivity Survey, these X-ray-luminous galaxies
exhibit a rate of cosmological evolution, , consistent with that derived for X-ray QSOs. This
evolution, coupled with the steep slope determined for the faint end of the
X-ray luminosity function (), implies
that such objects could comprise 15--35 per cent of the soft (1--2keV)Comment: Accepted for publication in MNRAS. 7 pages including 5 figures;
uuencoded compressed postscript; RGO-21
The Velocity Field of Quasar Broad Emission Line Gas
In this Letter, the broad emission line (BEL) profiles of superluminal
quasars with apparent jet velocities, , (ultraluminal QSOs, or
ULQSOs hereafter) are studied as a diagnostic of the velocity field of the BEL
emitting gas in quasars. The ULQSOs are useful because they satisfy a very
strict kinematical constraint, their parsec scale jets must be propagating
within of the line of sight. We know the orientation of these
objects with great certainty. The large BEL FWHM, , in ULQSOs tend to indicate that the BEL gas has a larger
component of axial velocity (either random or in a wind) along the jet
direction than previously thought.Comment: To appear in ApJ Letter
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
Quasar x-ray spectra revisited
A sample of 45 quasars observed by the Imaging Proportional Counter (IPC) on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We found the following: (1) the tendency for radio-loud quasars to have systematically flatter X-ray slopes than radio-quiet quasars (RQQ's) is confirmed with the soft X-ray excess having negligible effect; (2) there is a tendency for the flatness of the X-ray slope to correlate with radio core-dominance for radio-loud quasars, suggesting that a component of the X-ray emission is relativistically beamed; (3) for the RQQ's the soft X-ray slopes, with a mean of approximately 1.0, are consistent with the slopes found at higher energies (2-10 keV) although steeper than those observed for Seyfert 1 galaxies (also 2-10 keV) where the reflection model gives a good fit to the data; (4) the correlation of FeII emission line strength with X-ray energy index is confirmed for radio-quiet quasars using a subset of 18 quasars. The radio-loud quasars show no evidence for a correlation. This relation suggests a connection between the ionizing continuum and the line emission from the broad emission line region (BELR) of radio-quiet quasars, but in the opposite sense to that predicted by current photoionization models; and (5) the correlations of X-ray slope with radio core dominance and FeII equivalent width within the radio-loud and radio-quiet sub-classes respectively imply that the observed wide range of X-ray spectral slopes is real rather than due to the large measuring uncertainties for individual objects
Blob ejection from advection-dominated accretion flow: observational consequences
There is increasing evidence for the presence of an optically thin
advection-dominated accretion flow (ADAF) in low luminosity active galactic
nuclei and radio-loud quasars. The present paper is devoted to explore the fate
of a blob ejected from an ADAF, and to discuss its observational consequences.
It is inevitable for the ejected blob to drastically expand into its
surroundings. Consequently, it is expected that a group of relativistic
electrons should be accelerated, which may lead to nonthermal flares, since a
strong shock will be formed by the interaction between the blob and its
surroundings. Then the blob cools down efficiently, leading to the appearance
of recombination lines about s after its ejection from an ADAF. We apply
this model to NGC 4258 for some observational prediction, and to PKS 2149--306
for the explanation of observational evidence. Future simultaneous observations
of recombination X-ray lines and continuum emission are highly desired to test
the present model.Comment: 4 pages in emulateapj.sty, no figure. Accepted by ApJ Letter
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