289 research outputs found
Winds in the AGN environment : new perspectives from high resolution X-ray spectroscopy
In recent years, winds were recognized as an important
ingredient in the AGN picture. Outflows of photoionized gas,
which produce blueshifted absorption features
detectable in the X-ray and in the UV band,
are present in about 50% of Seyfert 1 galaxies.
Combining observations at high spectral
resolution with photoionization modeling
techniques, the kinetics, and the ionization conditions
of the outflowing gas can be diagnosed with high accuracy.
In this thesis, we applied these methods
to three cases of study, obtaining a variety of results.
In the X-ray spectrum of the
Seyfert 1 galaxy 1H 0419-577,
we detected the absorption lines from
a galactic scale outflow already observed in the UV.
In the case of the prototypical type 1 AGN NGC 5548,
we discovered a lowly-ionized, patchy wind located
in the nuclear region. We show that
the emergence of this obscuring wind
have drastically changed the
spectral appearance of the source
in the soft X-ray and in the UV band.
Finally, we characterized
a photoionized gas outflow in 4C +74.26,
which is one of the few radio-loud AGN in which
signatures of photoionized gas could be detected.High Energy Astrophysic
Chandra imaging of the kpc extended outflow in 1H 0419-577
The Seyfert 1 galaxy 1H 0419-577 hosts a kpc extended outflow that is
evident in the [\ion{O}{iii}] image and that is also detected as a warm
absorber in the UV/X-ray spectrum. Here, we analyze a 30 ks Chandra-ACIS
X-ray image, with the aim of resolving the diffuse extranuclear X-ray emission
and of investigating its relationship with the galactic outflow. Thanks to its
sub-arcsecond spatial resolution, Chandra resolves the circumnuclear X-ray
emission, which extends up to a projected distance of at least 16 kpc
from the center. The morphology of the diffuse X-ray emission is spherically
symmetrical. We could not recover a morphological resemblance between the soft
X-ray emission and the ionization bicone that is traced by the [\ion{O}{iii}]
outflow. we argue that the photoionized gas nebula must be distributed mostly
along the polar directions, outside our line of sight. In this geometry, the
X-ray/UV warm absorber must trace a different gas component, physically
disconnected from the emitting gas, and located closer to the equatorial plane.Comment: accepted for publications A&
Edge-weighting of gene expression graphs
In recent years, considerable research efforts have been directed to micro-array technologies and their role in providing simultaneous information on expression profiles for thousands of genes. These data, when subjected to clustering and classification procedures, can assist in identifying patterns and providing insight on biological processes. To understand the properties of complex gene expression datasets, graphical representations can be used. Intuitively, the data can be represented in terms of a bipartite graph, with weighted edges corresponding to gene-sample node couples in the dataset. Biologically meaningful subgraphs can be sought, but performance can be influenced both by the search algorithm, and, by the graph-weighting scheme and both merit rigorous investigation. In this paper, we focus on edge-weighting schemes for bipartite graphical representation of gene expression. Two novel methods are presented: the first is based on empirical evidence; the second on a geometric distribution. The schemes are compared for several real datasets, assessing efficiency of performance based on four essential properties: robustness to noise and missing values, discrimination, parameter influence on scheme efficiency and reusability. Recommendations and limitations are briefly discussed
Simultaneous XMM-\textit{Newton} and HST-COS observation of 1H0419-577: II. Broadband spectral modeling of a variable Seyfert galaxy
In this paper we present the longest exposure (97 ks) XMM-Newton EPIC-pn
spectrum ever obtained for the Seyfert 1.5 galaxy 1H 0419-577. With the aim of
explaining the broadband emission of this source, we took advantage of the
simultaneous coverage in the optical/UV that was provided in the present case
by the XMM-Newton Optical Monitor and by a HST-COS observation. Archival FUSE
flux measurements in the FUV were also used for the present analysis. We
successfully modeled the X-ray spectrum together with the optical/UV fluxes
data points using a Comptonization model. We found that a blackbody temperature
of eV accounts for the optical/UV emission originating in the
accretion disk. This temperature serves as input for the Comptonized components
that model the X-ray continuum. Both a warm ( keV,
) and a hot corona ( keV,
) intervene to upscatter the disk photons to X-ray
wavelengths. With the addition of a partially covering () cold
absorber with a variable opacity (), this model can well explain also the historical spectral
variability of this source, with the present dataset presenting the lowest one
(). We discuss a scenario where
the variable absorber, getting ionized in response to the variations of the
X-ray continuum, becomes less opaque in the highest flux states. The lower
limit for the absorber density derived in this scenario is typical for the
broad line region clouds. Finally, we critically compare this scenario with all
the different models (e.g. disk reflection) that have been used in the past to
explain the variability of this sourceComment: 12 pages, 9 figure
Anatomy of the AGN in NGC 5548: V. A clear view of the X-ray narrow emission lines
Context. Our consortium performed an extensive multi-wavelength campaign of
the nearby Seyfert 1 galaxy NGC 5548 in 2013-14. The source appeared unusually
heavily absorbed in the soft X-rays, and signatures of outflowing absorption
were also present in the UV. He-like triplets of neon, oxygen and nitrogen, and
radiative recombination continuum (RRC) features were found to dominate the
soft X-ray spectrum due to the low continuum flux.
Aims. Here we focus on characterising these narrow emission features using
data obtained from the XMM-Newton RGS (770 ks stacked spectrum).
Methods. We use SPEX for our initial analysis of these features.
Self-consistent photoionisation models from Cloudy are then compared with the
data to characterise the physical conditions of the emitting region.
Results. Outflow velocity discrepancies within the O VII triplet lines can be
explained if the X-ray narrow-line region (NLR) in NGC 5548 is absorbed by at
least one of the six warm absorber components found by previous analyses. The
RRCs allow us to directly calculate a temperature of the emitting gas of a few
eV ( K), favouring photoionised conditions. We fit the data with a
Cloudy model of log erg cm s, log cm and log v km s for the emitting
gas; this is the first time the X-ray NLR gas in this source has been modelled
so comprehensively. This allows us to estimate the distance from the central
source to the illuminated face of the emitting clouds as pc,
consistent with previous work.Comment: Accepted by A&A, 15 pages, 6 figure
Sloshing cold fronts in galaxy groups and their perturbing disk galaxies: an X-ray, Optical and Radio Case Study
We present a combined X-ray, optical, and radio analysis of the galaxy group
IC 1860 using the currently available Chandra and XMM data, literature
multi-object spectroscopy data and GMRT data. The Chandra and XMM imaging and
spectroscopy reveal two surface brightness discontinuities at 45 and 76 kpc
shown to be consistent with a pair of cold fronts. These features are
interpreted as due to sloshing of the central gas induced by an off-axis minor
merger with a perturber. This scenario is further supported by the presence of
a peculiar velocity of the central galaxy IC 1860 and the identification of a
possible perturber in the optically disturbed spiral galaxy IC 1859. The
identification of the perturber is consistent with the comparison with
numerical simulations of sloshing. The GMRT observation at 325 MHz shows faint,
extended radio emission contained within the inner cold front, as seen in some
galaxy clusters hosting diffuse radio mini-halos. However, unlike mini-halos,
no particle reacceleration is needed to explain the extended radio emission,
which is consistent with aged radio plasma redistributed by the sloshing. There
is strong analogy of the X-ray and optical phenomenology of the IC 1860 group
with two other groups, NGC 5044 and NGC 5846, showing cold fronts. The evidence
presented in this paper is among the strongest supporting the currently favored
model of cold-front formation in relaxed objects and establishes the group
scale as a chief environment to study this phenomenon.Comment: 22 pages, 21 figures, accepted for publication in the Astrophysical
Journa
Anatomy of the AGN in NGC 5548: I. A global model for the broadband spectral energy distribution
An extensive multi-satellite campaign on NGC 5548 has revealed this
archetypal Seyfert-1 galaxy to be in an exceptional state of persistent heavy
absorption. Our observations taken in 2013-2014 with XMM-Newton, Swift, NuSTAR,
INTEGRAL, Chandra, HST and two ground-based observatories have together enabled
us to establish that this unexpected phenomenon is caused by an outflowing
stream of weakly ionised gas (called the obscurer), extending from the vicinity
of the accretion disk to the broad-line region. In this work we present the
details of our campaign and the data obtained by all the observatories. We
determine the spectral energy distribution of NGC 5548 from near-infrared to
hard X-rays by establishing the contribution of various emission and absorption
processes taking place along our line of sight towards the central engine. We
thus uncover the intrinsic emission and produce a broadband continuum model for
both obscured (average summer 2013 data) and unobscured ( 2011) epochs of
NGC 5548. Our results suggest that the intrinsic NIR/optical/UV continuum is a
single Comptonised component with its higher energy tail creating the 'soft
X-ray excess'. This component is compatible with emission from a warm,
optically-thick corona as part of the inner accretion disk. We then investigate
the effects of the continuum on the ionisation balance and thermal stability of
photoionised gas for unobscured and obscured epochs.Comment: Accepted for publication in A&A, 19 pages, 13 figure
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