34 research outputs found
The AGN Outflow in the HDFS Target QSO J2233-606 from a High-Resolution VLT/UVES Spectrum
We present a detailed analysis of the intrinsic UV absorption in the central
HDFS target QSO J2233-606, based on a high-resolution, high S/N (~25 -- 50)
spectrum obtained with VLT/UVES. This spectrum samples the cluster of intrinsic
absorption systems outflowing from the AGN at radial velocities v ~ -5000 --
-3800 km/s in the key far-UV diagnostic lines - the lithium-like CNO doublets
and H I Lyman series. We fit the absorption troughs using a global model of all
detected lines to solve for the independent velocity-dependent covering factors
of the continuum and emission-line sources and ionic column densities. This
reveals increasing covering factors in components with greater outflow
velocity. Narrow substructure is revealed in the optical depth profiles,
suggesting the relatively broad absorption is comprised of a series of multiple
components. We perform velocity-dependent photoionization modeling, which
allows a full solution to the C, N, and O abundances, as well as the velocity
resolved ionization parameter and total column density. The absorbers are found
to have supersolar abundances, with [C/H] and [O/H] ~0.5 -- 0.9, and [N/H] ~
1.1 -- 1.3, consistent with enhanced nitrogen production expected from
secondary nucleosynthesis processes. Independent fits to each kinematic
component give consistent results for the abundances. The lowest-ionization
material in each of the strong absorbers is modeled with similar ionization
parameters. Components of higher-ionization (indicated by stronger O VI
relative to C IV and N V) are present at velocities just redward of each
low-ionization absorber. We explore the implications of these results for the
kinematic-geometric-ionization structure of the outflow.Comment: 12 pages, 10 figures, emulateapj, accepted for publication in Ap
Variable Intrinsic Absorption in Mrk 279
We examine the variability in the intrinsic absorption in the Seyfert 1
galaxy Mrk 279 using three epochs of observations from the Far Ultraviolet
Spectroscopic Explorer (FUSE) and two epochs of observations with the Space
Telescope Imaging Spectrograph on the Hubble Space Telescope. Rather than
finding simple photoionization responses of the absorbing gas to changes in the
underlying continuum, the observed changes in the absorption profiles can be
understood more clearly if the effective covering fraction of the gas in all
emission components, continuum and broad and intermediate velocity width
emission lines, is accounted for. While we do not uniquely solve for all of
these separate covering fractions and the ionic column densities using the
spectral data, we examine the parameter space using previously well-constrained
solutions for continuum and single emission component covering fractions.
Assuming full coverage of the continuum, we find that of the two velocity
components of the Mrk 279 absorption most likely associated with its outflow,
one likely has zero coverage of the intermediate line region while the other
does not. For each component, however, the broad line region is more fully
covered than the intermediate line region. Changes in the O VI column densities
are unconstrained due to saturation, but we show that small changes in the
nonsaturated C IV and N V column densities are consistent with the outflow gas
having zero or partial covering of the intermediate line region and an
ionization parameter changing from ~0.01 to ~0.1 from 2002 to 2003 as the UV
continuum flux increased by a factor of ~8. The absence of a change in the C
III absorbing column density is attributed to this species arising outside the
Mrk 279 outflow.Comment: 36 pages, 18 figures, accepted to Ap
Chemical Abundances in AGN Environment: X-Ray/UV Campaign on the MRK 279 Outflow
We present the first reliable determination of chemical abundances in an AGN
outflow. The abundances are extracted from the deep and simultaneous FUSE and
HST/STIS observations of Mrk 279. This data set is exceptional for its high
signal-to-noise, unblended doublet troughs and little Galactic absorption
contamination. These attributes allow us to solve for the velocity-dependent
covering fraction, and therefore obtain reliable column densities for many
ionic species. For the first time we have enough such column densities to
simultaneously determine the ionization equilibrium and abundances in the flow.
Our analysis uses the full spectral information embedded in these
high-resolution data. Slicing a given trough into many independent outflow
elements yields the extra constraints needed for a physically meaningful
abundances determination. We find that relative to solar the abundances in the
Mrk 279 outflow are (linear scaling): carbon 2.2+/-0.7, nitrogen 3.5+/-1.1 and
oxygen 1.6+/-0.8. Our UV-based photoionization and abundances results are in
good agreement with the independent analysis of the simultaneous Mrk 279 X-ray
spectra. This is the best agreement between the UV and X-ray analyses of the
same outflow to date.Comment: 28 pages, 7 figures, accepted on 29 Nov 2006 for publication in the
ApJ (submission date: 27 Jul 2006
The Ionized Gas and Nuclear Environment in NGC 3783 V. Variability and Modeling of the Intrinsic Ultraviolet Absorption
We present results on the location, physical conditions, and geometry of the
outflow in the Seyfert 1 galaxy NGC 3783 from a study of the variable intrinsic
UV absorption. Based on 18 observations with HST/STIS and 6 observations with
FUSE, we find: 1) The absorption from the lowest-ionization species in each of
the three strong kinematic components varied inversely with the continuum flux,
indicating the ionization structure responded to changes in the photoionizing
flux over the weekly timescales sampled by our observations. 2) A multi-
component model with an unocculted NLR and separate BLR and continuum
line-of-sight covering factors predicts saturation in several lines, consistent
with the lack of observed variability. 3) Column densities for the individual
metastable levels are measured from the resolved C III *1175 absorption complex
observed in one component. Based on our computed metastable level populations,
the electron density of this absorber is ~3x10^4 cm^-3. Photoionization
modeling results place it at ~25 pc from the central source. 4) Using
time-dependent calculations, we are able to reproduce the detailed variability
observed in this absorber, and derive upper limits on the distances for the
other components of 25-50 pc. 5) The ionization parameters derived for the
higher ionization UV absorbers are consistent with the modeling results for the
lowest-ionization X-ray component, but with smaller total column density. They
have similar pressures as the three X-ray ionization components. These results
are consistent with an inhomogeneous wind model for the outflow in NGC 3783. 6)
Based on the predicted emission-line luminosities, global covering factor
constraints, and distances derived for the UV absorbers, they may be identified
with emission- line gas observed in the inner NLR of AGNs. (abridged)Comment: 30 pages, 18 figures (7 color), emulateapj, accepted for publication
in The Astrophysical Journa
The Ionized Gas and Nuclear Environment in NGC 3783. I. Time-Averaged 900 ks Chandra Grating Spectroscopy
We present results from a 900 ks exposure of NGC 3783 with the High-Energy
Transmission Grating Spectrometer on board the Chandra X-ray Observatory. The
resulting X-ray spectrum has the best combination of signal-to-noise and
resolution ever obtained for an AGN. This spectrum reveals absorption lines
from H-like and He-like ions of N, O, Ne, Mg, Al, Si, and S. There are also
possible absorption lines from H-like and He-like Ar and Ca. We also identify
inner-shell absorption from lower-ionization ions such as Si_VII-Si_XII and
S_XII-S_XIV. The iron absorption spectrum is very rich; L-shell lines of
Fe_XVII-Fe_XXIV are detected, strong complex of M-shell lines, and probable
resonance lines from Fe_XXV. The absorption lines are blueshifted relative to
the systemic velocity by a mean velocity of -590+-150 km/s. We resolve many of
the absorption lines, and their mean FWHM is 820+-280 km/s. We do not find
correlations between the velocity shifts or the FWHMs with the ionization
potentials of the ions. Most absorption lines show asymmetry, having more
extended blue wings than red wings. In O_VII we have resolved this asymmetry to
be from an additional absorption system at ~ -1300 km/s. The two X-ray
absorption systems are consistent in velocity shift and FWHM with the ones
identified in the UV lines of C IV, N V, and H I. Equivalent width measurements
for all lines are given and column densities are calculated for several ions.
We resolve the narrow Fe_K\alpha line at 6398.2+-3.3 eV to have a FWHM of
1720+-360 km/s, which suggests that this narrow line may be emitted from the
outer part of the broad line region or the inner part of the torus. We also
detect a `Compton shoulder' redward of the narrow Fe_K\alpha line which
indicates that it arises in cold, Compton-thick gas.Comment: 19 pages, 12 figures (2 in color), emulateapj5, accepted for
publication in The Astrophysical Journal Supplement
Hubble Space Telescope Ultraviolet Spectroscopy of Fourteen Low-Redshift Quasars
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8)
quasars observed with HST/STIS as part of a Snap project to understand the
relationship between quasar outflows and luminosity. By design, all
observations cover the CIV emission line. Nine of the quasars are from the
Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from
the Parkes catalog. The sample contains a few interesting quasars including two
broad absorption line (BAL) quasars (HE0143-3535, HE0436-2614), one quasar with
a mini-BAL (HE1105-0746), and one quasar with associated narrow absorption
(HE0409-5004). These BAL quasars are among the brightest known (though not the
most luminous) since they lie at z<0.8. We compare the properties of these BAL
quasars to the z1.4 Large Bright Quasar samples. By
design, our objects sample luminosities in between these two surveys, and our
four absorbed objects are consistent with the v ~ L^0.62 relation derived by
Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak
emission lines and our spectrum is consistent with a simple power-law
continuum. The quasar is radio-loud, but has a steep spectral index and a
lobe-dominated morphology, which argues against it being a blazar. The unusual
spectrum of this quasar resembles the spectra of the quasars PG1407+265,
SDSSJ1136+0242, and PKS1004+13 for which several possible explanations have
been entertained.Comment: Uses aastex.cls, 21 pages in preprint mode, including 6 figures and 2
tables; accepted for publication in The Astronomical Journal (projected vol
133
The Ionized Gas and Nuclear Environment in NGC 3783. IV. Variability and Modeling of the 900 ks CHANDRA Spectrum
We present a detailed spectral analysis of the data obtained from NGC 3783
during the period 2000-2001 using Chandra. This analysis leads us to the
following results. 1) NGC 3783 fluctuated in luminosity by a factor ~1.5 during
individual observations (~170 ks duration). These fluctuations were not
associated with significant spectral variations. 2) On a longer time scale
(20-120 days), we found the source to exhibit two very different spectral
shapes. The main difference between these can be well-described by the
appearance and disappearance of a spectral component that dominates the
underlying continuum at the longest wavelengths. The spectral variations are
not related to the brightening or the fading of the continuum at short
wavelengths in any simple way. 3) The appearance of the soft continuum
component is consistent with being the only spectral variation, and there is no
need to invoke changes in the opacity of the absorbers. 4) Photoionization
modeling indicates that a combination of three ionized absorbers, each split
into two kinematic components, can explain the strengths of almost all the
absorption lines and bound-free edges. All three components are thermally
stable and seem to have the same gas pressure. 5) The only real discrepancy
between our model and the observations concerns the range of wavelengths
absorbed by the iron M-shell UTA feature. This most likely arises as the result
of our underestimation of the poorly-known dielectronic recombination rates
appropriate for these ions. 6) The lower limit on the distance of the absorbing
gas in NGC 3783 is between 0.2 and 3.2 pc. The assumption of pressure
equilibrium imposes an upper limit of about 25 pc on the distance of the
least-ionized component from the central source. (abridged)Comment: 16 pages, 12 figures (9 in color), emulateapj5, accepted for
publication in The Astrophysical Journa
X-ray/UV Observing Campaign on the Mrk 279 AGN Outflow: A Global Fitting Analysis of the UV Absorption
We present an analysis of the intrinsic UV absorption in the Seyfert 1 galaxy
Mrk 279 based on simultaneous long observations with the Hubble Space Telescope
(41 ks) and the Far Ultraviolet Spectroscopic Explorer (91 ks). To extract the
line-of-sight covering factors and ionic column densities, we separately fit
two groups of absorption lines: the Lyman series and the CNO lithium-like
doublets. For the CNO doublets we assume that all three ions share the same
covering factors. The fitting method applied here overcomes some limitations of
the traditional method using individual doublet pairs; it allows for the
treatment of more complex, physically realistic scenarios for the
absorption-emission geometry and eliminates systematic errors that we show are
introduced by spectral noise. We derive velocity-dependent solutions based on
two models of geometrical covering -- a single covering factor for all
background emission sources, and separate covering factors for the continuum
and emission lines. Although both models give good statistical fits to the
observed absorption, we favor the model with two covering factors because: (a)
the best-fit covering factors for both emission sources are similar for the
independent Lyman series and CNO doublet fits; (b) the fits are consistent with
full coverage of the continuum source and partial coverage of the emission
lines by the absorbers, as expected from the relative sizes of the nuclear
emission components; and (c) it provides a natural explanation for variability
in the Ly absorption detected in an earlier epoch. We also explore
physical and geometrical constraints on the outflow from these results.Comment: 17 pages, 15 figures (9 color), emulateapj, accepted for publication
in The Astrophysical Journa
The Ionized Gas and Nuclear Environment in NGC 3783 II. Averaged HST/STIS and FUSE Spectra
We present observations of the intrinsic absorption in the Seyfert 1 galaxy
NGC 3783 obtained with the STIS/HST and FUSE. We have coadded multiple STIS and
FUSE observations to obtain a high S/N averaged spectrum spanning 905-1730 A.
The averaged spectrum reveals absorption in O VI, N V, C IV, N III, C III and
the Lyman lines up to LyE in the three blueshifted kinematic components
previously detected in the STIS spectrum (at radial velocities of -1320, -724,
and -548 km/s). The highest velocity component exhibits absorption in Si IV. We
also detect metastable C III* in this component, indicating a high density in
this absorber. We separate the individual covering factors of the continuum and
emission-line sources as a function of velocity in each kinematic component
using the LyA and LyB lines. Additionally, we find that the continuum covering
factor varies with velocity within the individual kinematic components,
decreasing smoothly in the wings of the absorption by at least 60%. The
covering factor of Si IV is found to be less than half that of H I and N V in
the high velocity component. Additionally, the FWHM of N III and Si IV are
narrower than the higher ionization lines in this component. These results
indicate there is substructure within this absorber. We derive a lower limit on
the total column (N_H>=10^{19}cm^{-2}) and ionization parameter (U>=0.005) in
the low ionization subcomponent of this absorber. The metastable-to-total C III
column density ratio implies n_e~10^9 cm^{-3} and an upper limit on the
distance of the absorber from the ionizing continuum of R<=8x10^{17} cm.Comment: 29 pages, 8 figures (Figures 1-3 are in color), Accepted for
pulication in the Astrophysical Journa