296 research outputs found
Physical Conditions in Quasar Outflows: VLT Observations of QSO 2359-1241
We analyze the physical conditions of the outflow seen in QSO 2359-1241 (NVSS
J235953-124148), based on high resolution spectroscopic VLT observations. This
object was previously studied using Keck/HIRES data. The main improvement over
the HIRES results is our ability to accurately determine the number density of
the outflow. For the major absorption component, level population from five
different Fe II excited level yields n_H=10^4.4 cm^-3 with less than 20%
scatter. We find that the Fe ii absorption arises from a region with roughly
constant conditions and temperature greater than 9000 K, before the ionization
front where temperature and electron density drop. Further, we model the
observed spectra and investigate the effects of varying gas metalicities and
the spectral energy distribution of the incident ionizing radiation field. The
accurately measured column densities allow us to determine the ionization
parameter log(U) = -2.4 and total column density of the outflow (log(N_H) =
20.6 cm^-2). Combined with the number density finding, these are stepping
stones towards determining the mass flux and kinetic luminosity of the outflow,
and therefore its importance to AGN feedback processes.Comment: 21 pages, 3 figures (accepted for publication in the ApJ
Anatomy of the AGN in NGC 5548 II. The spatial, temporal, and physical nature of the outflow from HST/COS Observations
Context. AGN outflows are thought to influence the evolution of their host galaxies and of super massive black holes. Our deep multiwavelength campaign on NGC 5548 has revealed a new, unusually strong X-ray obscuration, accompanied by broad UV absorption troughs observed for the first time in this object. The X-ray obscuration caused a dramatic decrease in the incident ionizing flux on the outflow that produces the long-studied narrow UV absorption lines in this AGN. The resulting data allowed us to construct a comprehensive physical, spatial, and temporal picture for this enduring AGN wind.
Aims. We aim to determine the distance of the narrow UV outflow components from the central source, their total column-density, and the mechanism responsible for their observed absorption variability.
Methods. We study the UV spectra acquired during the campaign, as well as from four previous epochs (1998â2011). Our main analysis tools are ionic column-density extraction techniques, photoionization models based on the code CLOUDY, and collisional excitation simulations.
Results. A simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. The main component of the enduring outflow is situated at 3.5 ± 1.1 pc from the central source, and its distance and number density are similar to those of the narrow-emitting-line region in this object. Three other components are situated between 5â70 pc and two are farther than 100 pc. The wealth of observational constraints and the anti-correlation between the observed X-ray and UV flux in the 2002 and 2013 epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows.
Conclusions. This campaign, in combination with prior UV and X-ray data, yields the first simple model that can explain the physical characteristics and the substantial variability observed in an AGN outflow
Magnetic Confinement, MHD Waves, and Smooth Line Profiles in AGN
In this paper, we show that if the broad line region clouds are in
approximate energy equipartition between the magnetic field and gravity, as
hypothesized by Rees, there will be a significant effect on the shape and
smoothness of broad emission line profiles in active galactic nuclei. Line
widths of contributing clouds or flow elements are much wider than their
thermal widths, due to the presence of non-dissipative MHD waves, and their
collective contribution produce emission line profiles broader and smoother
than would be expected if a magnetic field were not present. As an
illustration, a simple model of isotropically emitting clouds, normally
distributed in velocity, is used to show that smoothness can be achieved for
less than 80,000 clouds and may even be as low as a few hundred. We conclude
that magnetic confinement has far reaching consequences for observing and
modeling active galactic nuclei.Comment: to appear in MNRA
The XMM-Newton RGS spectrum of the high luminosity Seyfert 1 galaxy Markarian 509
We present a detailed analysis of the soft X-ray spectrum of the Seyfert 1
galaxy Markarian 509 taken with the XMM-Newton Reflection Grating Spectrometer.
An underlying power-law continuum and three warm absorber phases provide a good
fit to the data along with a number of broad and narrow emission lines. Our
three warm absorber phases each have different ionization parameters and column
densities. We identify a low ionization, log xi=0.89, high outflow velocity
phase producing an Fe M-shell UTA feature along with absorption from O VI and N
VI. There is an intermediate phase, log xi=2.14, showing absorption from H-like
carbon and nitrogen and He-like neon and oxygen. The third, high ionization,
log xi=3.26, low outflow velocity phase contains absorption from O VIII, Ne X
and highly ionized iron. All phases are blueshifted with respect to the
systemic velocity with flow velocities ranging from -60km/s to -510km/s. The
observed broad emission features have an RMS velocity of ~8000km/s for the C VI
and O VII lines.Comment: 10 pages, 7 figures. To be published in Astronomy and Astrophysics
journa
The Evolution of Quasar CIV and SiIV Broad Absorption Lines Over Multi-Year Time Scales
We investigate the variability of CIV 1549A broad absorption line (BAL)
troughs over rest-frame time scales of up to ~7 yr in 14 quasars at redshifts
z>2.1. For 9 sources at sufficiently high redshift, we also compare CIV and
SiIV 1400A absorption variation. We compare shorter- and longer-term
variability using spectra from up to four different epochs per source and find
complex patterns of variation in the sample overall. The scatter in the change
of absorption equivalent width (EW), Delta EW, increases with the time between
observations. BALs do not, in general, strengthen or weaken monotonically, and
variation observed over shorter (<months) time scales is not predictive of
multi-year variation. We find no evidence for asymmetry in the distribution of
Delta EW that would indicate that BALs form and decay on different time scales,
and we constrain the typical BAL lifetime to be >~30 yr. The BAL absorption for
one source, LBQS 0022+0150, has weakened and may now be classified as a
mini-BAL. Another source, 1235+1453, shows evidence of variable, blue continuum
emission that is relatively unabsorbed by the BAL outflow. CIV and SiIV BAL
shape changes are related in at least some sources. Given their high
velocities, BAL outflows apparently traverse large spatial regions and may
interact with parsec-scale structures such as an obscuring torus. Assuming BAL
outflows are launched from a rotating accretion disk, notable azimuthal
symmetry is required in the outflow to explain the relatively small changes
observed in velocity structure over times up to 7 yr
Simultaneous X-ray and UV spectroscopy of the Seyfert 1 galaxy NGC 5548.II. Physical conditions in the X-ray absorber
We present the results from a 500 ks Chandra observation of the Seyfert 1
galaxy NGC 5548. We detect broadened emission lines of O VII and C VI in the
spectra, similar to those observed in the optical and UV bands. The source was
continuously variable, with a 30 % increase in luminosity in the second half of
the observation. No variability in the warm absorber was detected between the
spectra from the first 170 ks and the second part of the observation. The
velocity structure of the X-ray absorber is consistent with the velocity
structure measured simultaneously in the ultraviolet spectra. We find that the
highest velocity outflow component, at -1040 km/s, becomes increasingly
important for higher ionization parameters. This velocity component spans at
least three orders of magnitude in ionization parameter, producing both highly
ionized X-ray absorption lines (Mg XII, Si XIV) as well as UV absorption lines.
A similar conclusion is very probable for the other four velocity components.
Based upon our observations, we argue that the warm absorber probably does not
manifest itself in the form of photoionized clumps in pressure equilibrium with
a surrounding wind. Instead, a model with a continuous distribution of column
density versus ionization parameter gives an excellent fit to our data. From
the shape of this distribution and the assumption that the mass loss through
the wind should be smaller than the accretion rate onto the black hole, we
derive upper limits to the solid angle as small as 10^{-4} sr. From this we
argue that the outflow occurs in density-stratified streamers. The density
stratification across the stream then produces the wide range of ionization
parameter observed in this source. Abridged.Comment: 21 pages, 12 figures accepted for publication in A&
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
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