1,032 research outputs found
Distribution of the heavy elements throughout the extended narrow line region of the Seyfert galaxy NGC 7212
The latest observations of line and continuum spectra emitted from the
extended narrow line region (ENLR) of the Seyfert 2 galaxy NGC 7212 are
analysed using models accounting for photoionization from the active nucleus
and shocks. The results show that relatively high (500--800 \kms) shock
velocities appear on the edge of the cone and outside of it. The model-inferred
AGN flux, which is lower than photons cm s eV
at the Lyman limit, is more typical of low-luminosity AGN, and less so for
Seyfert 2 galaxies. The preshock densities are characteristic of the ENLR and
range between 80--150 cm. Nitrogen and sulphur are found depleted by a
factor lower than 2, particularly at the eastern edge. Oxygen is depleted at
several locations. The Fe/H ratio is approximately solar, whereas the Ne/H
relative abundance is unusually high, 1.5--2 times the solar value. Modelling
the continuum spectral energy distribution (SED), we have found radio
synchrotron radiation generated by the Fermi mechanism at the shock front,
whereas the X-rays are produced by the bremsstrahlung from a relatively high
temperature plasma.Comment: 17 pages, 14 figures, accepted for publication in A&
A Multi-Cloud Warm-Absorber Model for NGC 4051
A multi-cloud model is presented which explains the soft X-ray excess in NGC
4051 and, consistently, the optical line spectrum and the SED of the continuum.
The clouds are heated and ionized by the photoionizing flux from the active
center and by shocks. Diffuse radiation, partly absorbed throughout the clouds,
nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation
from the gaseous clouds contribute to the fit of the continuum SED. Debris of
high density fragmented clouds are necessary to explain the absorption oxygen
throats observed at 0.87 keV and 0.74 keV. The debris are heated by shocks of
about 200-300 km/s. Low velocity (100 km/s)-density (100 cm-3) clouds
contribute to the line and continuum spectra, as well as high velocity (1000
km/s)-density (8000 cm-3) clouds which are revealed by the FWHM of the line
profiles. The SED in the IR is explained by reradiation of dust, however, the
dust-to-gas ratio is not particularly high. Radio emission is well fitted by
synchrotron radiation created at the shock front by Fermi mechanism.Comment: 19 pages + 3 figures PostScrip
Evolution of the mass, size, and star formation rate in high-redshift merging galaxies MIRAGE - A new sample of simulations with detailed stellar feedback
We aim at addressing the questions related to galaxy mass assembly through
major and minor wet merging processes in the redshift range 1<z<2. A consequent
fraction of Milky Way like galaxies are thought to have undergone an unstable
clumpy phase at this early stage. Using the adaptive mesh refinement code
RAMSES, with a recent physically-motivated implementation of stellar feedback,
we build the Merging and Isolated high-Redshift Adaptive mesh refinement
Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized
disks simulations with global physical properties in accordance with the 1<z<2
mass complete sample MASSIV. The numerical hydrodynamical resolution reaches 7
parsecs in the smallest Eulerian cells. Our simulations include: star
formation, metal line cooling, metallicity advection, and a recent
implementation of stellar feedback which encompasses OB-type stars radiative
pressure, photo-ionization heating, and supernovae. The initial conditions are
set to match the z~2 observations, thanks to a new public code DICE. The
numerical resolution allows us to follow the formation and evolution of giant
clumps formed in-situ from Jeans instabilities triggered by high initial gas
fraction. The star formation history of isolated disks shows stochastic star
formation rate, which proceeds from the complex behavior of the giant clumps.
Our minor and major gas-rich merger simulations do not trigger starbursts,
suggesting a saturation of the star formation in a turbulent and clumpy
interstellar medium fed by substantial accretion from the circum-galactic
medium. Our simulations are close to the normal regime of the disk-like star
formation on a Schmidt-Kennicutt diagram. The mass-size relation and its rate
of evolution matches observations, suggesting that the inside-out growth
mechanisms of the stellar disk do not necessarily require to be achieved
through a cold accretion.Comment: 18 pages, 12 figures. Accepted in A&
High resolution spectroscopy of the extended narrow-line region of IC 5063 and NGC 7212
We studied the properties of the gas of the extended narrow line region
(ENLR) of two Seyfert 2 galaxies: IC 5063 and NGC 7212. We analysed high
resolution spectra to investigate how the main properties of this region depend
on the gas velocity. We divided the emission lines in velocity bins and we
calculated several line ratios. Diagnostic diagrams and SUMA composite models
(photo-ionization + shocks), show that in both galaxies there might be evidence
of shocks significantly contributing in the gas ionization at high |V|, even
though photo-ionization from the active nucleus remains the main ionization
mechanism. In IC 5063 the ionization parameter depends on V and its trend might
be explained assuming an hollow bi-conical shape for the ENLR, with one of the
edges aligned with the galaxy disk. On the other hand, NGC 7212 does not show
any kind of dependence. The models show that solar O/H relative abundances
reproduce the observed spectra in all the analysed regions. They also revealed
an high fragmentation of the gas clouds, suggesting that the complex kinematics
observed in these two objects might be caused by interaction between the ISM
and high velocity components, such as jets.Comment: 29 pages, 32 figures, accepted for publication in MNRA
Possible development of the organic production in a moutain area of the Florence province in Tuscany
A study on the multicolour evolution of Red Sequence galaxy populations: insights from hydrodynamical simulations and semi-analytical models
By means of our own cosmological-hydrodynamical simulation and
semi-analytical model we studied galaxy population properties in clusters and
groups, spanning over 10 different bands from UV to NIR, and their evolution
since redshift z=2. We compare our results in terms of galaxy red/blue
fractions and luminous-to-faint ratio (LFR) on the Red Sequence (RS) with
recent observational data reaching beyond z=1.5. Different selection criteria
were tested in order to retrieve galaxies belonging to the RS: either by their
quiescence degree measured from their specific SFR ("Dead Sequence"), or by
their position in a colour-colour plane which is also a function of sSFR. In
both cases, the colour cut and the limiting magnitude threshold were let
evolving with redshift, in order to follow the natural shift of the
characteristic luminosity in the LF.
We find that the Butcher-Oemler effect is wavelength-dependent, with the
fraction of blue galaxies increasing steeper in optical colours than in NIR.
Besides, only when applying a lower limit in terms of fixed absolute magnitude,
a steep BO effect can be reproduced, while the blue fraction results less
evolving when selecting samples by stellar mass or an evolving magnitude limit.
We then find that also the RS-LFR behaviour, highly debated in the literature,
is strongly dependent on the galaxy selection function: in particular its very
mild evolution recovered when measured in terms of stellar mass, is in
agreement with values reported for some of the highest redshift confirmed
(proto)clusters. As to differences through environments, we find that normal
groups and (to a lesser extent) cluster outskirts present the highest values of
both star forming fraction and LFR at low z, while fossil groups and cluster
cores the lowest: this separation among groups begins after z~0.5, while
earlier all group star forming properties are undistinguishable.Comment: revised version, A&A accepted (11 pages, 6 figures
IEC 61508: Effect of test policy on the probability of failure on demand of safety instrumented systems
Standard IEC 61508 provides probabilistic equations for determining the Average Probability of Failure on Demand (PFDavg) and the Average Probability of Failure per Hour (PFHavg) for some architectures of Safety Instrumented Systems (SIS) under the hypothesis of equal redundant components, taking into account Common Cause Failures (CCF), Detection Coverage (DC) and Proof Test Coverage (PTC) parameters. Surprisingly, IEC standard does not mention the testing policy aspects of SIS redundant
components. However, from a close examination of the probabilistic equations, it is possible to recognize that the simultaneous/sequential testing policy has been implicitly assumed. This paper describes the conditions under which the staggered testing policy - which is better than all the
others in case of independent tested components - can be advantageously applied to reduce PFDavg when CCF, DC and PTC parameters are taken into account
Linear regression models and k-means clustering for statistical analysis of fNIRS data
We propose a new algorithm, based on a linear regression model, to statistically estimate the hemodynamic activations in fNIRS data sets. The main concern guiding the algorithm development was the minimization of assumptions and approximations made on the data set for the application of statistical tests. Further, we propose a K-means method to cluster fNIRS data (i.e. channels) as activated or not activated. The methods were validated both on simulated and in vivo fNIRS data. A time domain (TD) fNIRS technique was preferred because of its high performances in discriminating cortical activation and superficial physiological changes. However, the proposed method is also applicable to continuous wave or frequency domain fNIRS data sets
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