53 research outputs found
An X-ray/SDSS sample (II): outflowing gas plasma properties
Galaxy-scale outflows are nowadays observed in many active galactic nuclei
(AGNs); however, their characterisation in terms of (multi-) phase nature,
amount of flowing material, effects on the host galaxy, is still unsettled. In
particular, ionized gas mass outflow rate and related energetics are still
affected by many sources of uncertainties. In this respect, outflowing gas
plasma conditions, being largely unknown, play a crucial role.
Taking advantage of the spectroscopic analysis results we obtained studying
the X-ray/SDSS sample of 563 AGNs at z presented in our companion paper,
we analyse stacked spectra and sub-samples of sources with high signal-to-noise
temperature- and density-sensitive emission lines to derive the plasma
properties of the outflowing ionized gas component. For these sources, we also
study in detail various diagnostic diagrams to infer information about
outflowing gas ionization mechanisms. We derive, for the first time, median
values for electron temperature and density of outflowing gas from medium-size
samples ( targets) and stacked spectra of AGNs. Evidences of shock
excitation are found for outflowing gas.
We measure electron temperatures of the order of K and
densities of cm for faint and moderately luminous AGNs
(intrinsic X-ray luminosity in the 2-10 keV band). We
caution that the usually assumed electron density ( cm) in
ejected material might result in relevant overestimates of flow mass rates and
energetics and, as a consequence, of the effects of AGN-driven outflows on the
host galaxy.Comment: 16 pages, 10 figures. Accepted for publication in A&
Multi-phase outflows in Mkn 848 observed with SDSS-MaNGA Integral Field Spectroscopy
The characterisation of galaxy-scale outflows in terms of their multi-phase
nature, amount, and effects of flowing material is crucial to place constraints
on models of galaxy evolution. This study can proceed only with the detailed
investigation of individual targets.
We present a spatially resolved spectroscopic optical data analysis of Mkn
848, a complex system consisting of two merging galaxies at z~0.04 that are
separated 7.5 kpc (projected distance). Motivated by the presence of a
multi-phase outflow in the north-west system revealed by the SDSS integrated
spectrum, we analysed the publicly available MaNGA data, which cover almost the
entire merging system, to study the physical properties of cool and warm gas in
detail.
Galaxy-wide outflowing gas in multiple phases is revealed for the first time
in the two merging galaxies. We also detect spatially resolved resonant NaID
emission associated with the outflows. The derived outflow energetics may be
consistent with a scenario in which both winds are accelerated by stellar
processes and AGN activity, although we favour an AGN origin given the high
outflow velocities and the ionisation conditions observed in the outflow
regions. Deeper observations are required, however, to better constrain the
nature of these multi-phase outflows. Outflow energetics in the north-west
system are strongly different between the ionised and atomic gas components,
the latter of which is associated with mass outflow rate and kinetic and
momentum powers that are 1-2 dex higher; those associated with the south-east
galaxy are instead similar.
Strong kp-scale outflows are revealed in an ongoing merger system, suggesting
that feedback can potentially impact the host galaxy even in the early merger
phases. The characterisation of the neutral and ionised gas phases has proved
to be crucial for a comprehensive study of the outflow phenomena.Comment: 19 pages, 14 figures, accepted for publication in A&
The MUSE view of He 2-10: no AGN ionization but a sparkling starburst
We study the physical and dynamical properties of the ionized gas in the
prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The
large scale dynamics is dominated by extended outflowing bubbles, probably the
results of massive gas ejection from the central star forming regions. We
derive a mass outflow rate dMout/dt~0.30 Msun/yr, corresponding to mass loading
factor eta~0.4, in range with similar measurements in local LIRGs. Such a
massive outflow has a total kinetic energy that is sustainable by the stellar
winds and Supernova Remnants expected in the galaxy. We use classical emission
line diagnostic to study the dust extinction, electron density and ionization
conditions all across the galaxy, confirming the extreme nature of the highly
star forming knots in the core of the galaxy, which show high density and high
ionization parameter. We measure the gas phase metallicity in the galaxy taking
into account the strong variation of the ionization parameter, finding that the
external parts of the galaxy have abundances as low as 12 + log(O/H)~8.3, while
the central star forming knots are highly enriched with super solar
metallicity. We find no sign of AGN ionization in the galaxy, despite the
recent claim of the presence of a super massive active Black Hole in the core
of He~2-10. We therefore reanalyze the X-ray data that were used to propose the
presence of the AGN, but we conclude that the observed X-ray emission can be
better explained with sources of a different nature, such as a Supernova
Remnant.Comment: 11 pages, 8 Figures, Accepted for publication in A&
Compton thick AGN in the NuSTAR era
We present the 2-100 keV spectral analysis of 30 candidate Compton thick
(CT-) active galactic nuclei (AGN) selected in the Swift-BAT 100-month survey.
The average redshift of these objects is 0.03 and they
all lie within 500 Mpc. We used the MyTorus (Murphy et al. 2009) model to
perform X-ray spectral fitting both without and with the contribution of the
NuSTAR data in the 3-50 keV energy range. When the NuSTAR data are added to the
fit, 14 out of 30 of these objects (47% of the whole sample) have intrinsic
absorption N3 confidence level,
i.e., they are re-classified from Compton thick to Compton thin. Consequently,
we infer an overall observed fraction of CT-AGN with respect to the whole AGN
population lower than the one reported in previous works, and as low as
4%. We find evidence that this over-estimation of N is likely
due to the low quality of a subsample of spectra, either in the 2-10 keV band
or in the Swift-BAT one.Comment: 19 pages, 10 figures, accepted for publication on the Astrophysical
Journa
Large-scale clustering of buried X-ray AGN: Trends in AGN obscuration and redshift evolution
In order to test active galactic nucleus (AGN) unification and evolutionary
models, we measured the AGN clustering properties as a function of AGN
obscuration defined in terms of hydrogen column density, . In
addition to measuring the clustering of unobscured () and moderately obscured () AGNs,
we also targeted highly obscured sources () up to
redshifts of . We have compiled one of the largest samples of
X-ray-selected AGNs from a total of eight deep XMM/Chandra surveys. We measured
the clustering as a function of both AGN obscuration and redshift using the
projected two-point correlation function, . We modeled
the large-scale clustering signal, measured the AGN bias, ,
and interpreted it in terms of the typical AGN host dark matter halo, ). We find no significant dependence of AGN clustering on
obscuration, suggesting similar typical masses of the hosting halos as a
function of . This result matches expectations of AGN unification
models, in which AGN obscuration depends mainly on the viewing angle of the
obscuring torus. We measured, for the first time, the clustering of highly
obscured AGNs and find that these objects reside in halos with typical mass
() at low (high ) redshifts. We
find that irrespective of obscuration, an increase in AGN bias with redshift is
slower than the expectation for a constant halo mass and instead follows the
growth rate of halos, known as the passive evolution track. This implies that
for those AGNs the clustering is mainly driven by the mass growth rate of the
hosting halos and galaxies across cosmic time.Comment: 13 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Compton-thick AGN in the NuSTAR era III: A systematic study of the torus covering factor
We present the analysis of a sample of 35 candidate Compton thick (CT-)
active galactic nuclei (AGNs) selected in the nearby Universe (average redshift
~0.03) with the Swift-BAT 100-month survey. All sources have available
NuSTAR data, thus allowing us to constrain with unprecedented quality important
spectral parameters such as the obscuring torus line-of-sight column density
(N_{H, z}), the average torus column density (N_{H, tor}) and the torus
covering factor (f_c). We compare the best-fit results obtained with the widely
used MyTorus (Murphy et al. 2009) model with those of the recently published
borus02 model (Balokovic et al. 2018) used in the same geometrical
configuration of MyTorus (i.e., with f_c=0.5). We find a remarkable agreement
between the two, although with increasing dispersion in N_{H, z} moving towards
higher column densities. We then use borus02 to measure f_c. High-f_c sources
have, on average, smaller offset between N_{H, z} and N_{H, tor} than low-f_c
ones. Therefore, low f_c values can be linked to a "patchy torus" scenario,
where the AGN is seen through an over-dense region in the torus, while high-f_c
objects are more likely to be obscured by a more uniform gas distribution.
Finally, we find potential evidence of an inverse trend between f_c and the AGN
2-10 keV luminosity, i.e., sources with higher f_c values have on average lower
luminosities.Comment: 35 Pages, 23 Figures. Accepted for publication in Ap
A trade-off study of the WFI field of view
We performed a trade-off study of the Athena WFI field of view (f.o.v.) taking into account a square and a circular f.o.v. In the latter case, the WFI corners would not be exposed to cosmic X-rays and could be used as particle background monitors, simultaneously to the observation. The resulting loss of area would concern only regions of low sensitivity. So, how many and which kind of AGN would be lost? In this poster we report some results derived from simple computations; for both of the two f.o.v. shapes, we folded the Aird+10 XLF with the Athena sky-coverage (assuming the CDF2 configuration and Gamma=1.8) of a deep (700 ks) pointing to derive the number of detectable AGN. Although the absolute numbers are affected by huge uncertainties, the relative numbers (i.e. the fraction of AGN retrieved with the circular f.o.v. with respect to the square f.o.v.) depend only on the different sky-coverages and are therefore much more robust. <P /
An X-ray/SDSS sample. I. Multi-phase outflow incidence and dependence on AGN luminosity
Aims: The connection between the growth of super-massive black holes (SMBHs) and the evolution of their host galaxies is nowadays well established, although the underlying mechanisms explaining their mutual relations are still debated. Multi-phase fast, massive outflows have been postulated to play a crucial role in this process. The aim of this work is to constrain the nature and the fraction of outflowing gas in active galactic nuclei (AGNs) as well as the nuclear conditions possibly at the origin of such phenomena. Methods: We present a large spectroscopic sample of X-ray detected SDSS AGNs at z Results: We derive the incidence of ionized ( 40%) and atomic (42 to 1046 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained by studying high-z QSOs. Conclusions: We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (MBH), [O III], and X-ray luminosity. We show a well-defined positive trend between outflow velocity and LX, for the first time, over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at MBH> 108M☉ the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionized phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: first, an initial stage characterized by X-ray/optical obscured AGNs, in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components and, second, a later stage associated with unobscured AGNs, in which the line of sight has been cleaned and the cold components have been heated or exhausted
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