683 research outputs found
Near-infrared spectroscopy of nearby Seyfert galaxies - II. Molecular content and coronal emission
We present sub-arcsec near-infrared 1.5 - 2.5 micron moderate resolution
long-slit spectra of eight nearby Seyfert galaxies (z<0.01), both parallel to
the ionization cone and perpendicular to it. These spectra complement similar
data on six Seyferts, presented in Reunanen, Kotilainen & Prieto (2002). Large
concentrations of molecular gas (H2) are present in the nucleus regardless of
the Seyfert type. The spatial extent of the H2 emission is larger perpendicular
to the cone than parallel to it in 6/8 (75 %) galaxies, in agreement with the
unified models of Active Galactic Nuclei. Broad BrGamma was detected in nearly
half of the optically classified Seyfert 2 galaxies, including two objects with
no evidence for hidden polarized Broad Line Region. Nuclear [FeII] emission is
generally blueshifted which together with high BrGamma/[FeII] ratios suggests
shocks as the dominant excitation mechanism in Seyfert galaxies. Bright coronal
emission lines [SiVI] and [SiVII] are common in Seyferts, as they are detected
in ~60 % of the galaxies. In three galaxies the coronal lines are extended only
in the direction parallel to the cone. This could be explained by shock
excitation due to the jet or superwind interacting with the interstellar
medium.Comment: 19 pages, accepted for publication in MNRA
Multi-wavelength properties of the high-energy bright Seyfert 1 galaxy IGR J18027-1455
A new sample of hard X-ray sources in the Galactic Plane is being revealed by
the regular observations performed by the INTEGRAL satellite. The full
characterization of these sources is mandatory to understand the hard X-ray
sky. Here we report new multifrequency radio, infrared and optical observations
of the source IGR J18027-1455, as well as a multi-wavelength study from radio
to hard X-rays. The radio counterpart of IGR J18027-1455 is not resolved at any
observing frequency. The radio flux density is well fitted by a simple power
law with a spectral index alpha=-0.75+/-0.02. This value is typical of
optically thin non-thermal synchrotron emission originated in a jet. The NIR
and optical spectra show redshifted emission lines with z=0.034, and a broad
Halpha line profile with FWHM ~3400 km/s. This suggests an Active Galactic
Nucleus (AGN) of type 1 as the optical counterpart of IGR J18027-1455. We
confirm the Seyfert 1 nature of the source, which is intrinsically bright at
high energies both in absolute terms and when scaled to a normalized 6 cm
luminosity. Finally, comparing its X-ray luminosity with isotropic indicators,
we find that the source is Compton thin and AGN dominated. This indicates that
INTEGRAL might have just seen the tip of the iceberg, and several tens of such
sources should be unveiled during the course of its lifetime.Comment: 6 pages, 6 figures. Accepted for publication in A&A. Minor changes
according to referee repor
Avatar Based Multiplayer Functionalities in Next Generation Communication and Learning in Virtual Reality Social Platforms – Case MarISOT Room
Virtual Reality Social Platforms are
increasingly in use in conferences, and exhibitions. COVID19 pandemic is the main reason for a rapid growth but there
are reasons such as climate change to believe these
technologies will be used widely once we will enter to the post
pandemic era. In this paper, we will introduce our vision to
combine social functioning and hands-on-training features in
one package. We have participated in and organized various
events using existing virtual reality social platforms. We will
analyze in this paper their pros and cons plus introduce our
own technology trials. As a result, we have better
understanding what development tools and how much
resources would be needed to be able to create the first
minimal viable product combining social functioning and
hands-on-training features
VLT diffraction-limited imaging at 11 and 18 micron of the nearest active galactic nuclei
Mid-infrared imaging at resolutions of 300 mas of the central kpc region of
13 nearby, well-known active galaxies is presented. The bulk of the mid-IR
emission is concentrated on an unresolved central source within a size of less
than 5 to 130 pc, depending on the object distance. Further resolved emission
is detected in 70% of the sample in the form of circumnuclear star-forming
rings or diffuse nuclear extended emission. In the three cases with
circumnuclear star formation, the stellar contribution is at least as important
as that of the AGN. In those with extended nuclear emission -- a third of the
sample -- this emission represents a few per cent of the total measured;
however, this contribution may be underestimated because of the chopped nature
of these observations. This extended emission is generally collimated in a
preferential direction often coinciding with that of the extended ionized gas
or the jet.
In all cases, the nuclear fluxes measured at 11.8 and 18.7 micron represent a
minor contribution of the flux levels measured by large aperture IRAS data at
the nearest energy bands of 12 and 25 micron. This contribution ranges from 30%
to less than 10%. In only three cases do the AGN fluxes agree with IRAS to
within a factor of 2. In the AGNs with strong circumnuclear star formation,
this component can well account for most of the IRAS flux measured in these
objects. But in all other cases, either a low surface brightness component
extending over galactic scales or strong extra-nuclear IR sources -- e.g. HII
regions in spiral arms -- have to be the main source of the IRAS emission. In
either case, the contribution of these components dwarfs that of the AGN at
mid-IR wavelengths.Comment: 17 pages, 10 figures. Accepted for publication in MNRA
Determining appropriate approaches for using data in feature selection
Feature selection is increasingly important in data analysis and machine learning in big data era. However, how to use the data in feature selection, i.e. using either ALL or PART of a dataset, has become a serious and tricky issue. Whilst the conventional practice of using all the data in feature selection may lead to selection bias, using part of the data may, on the other hand, lead to underestimating the relevant features under some conditions. This paper investigates these two strategies systematically in terms of reliability and effectiveness, and then determines their suitability for datasets with different characteristics. The reliability is measured by the Average Tanimoto Index and the Inter-method Average Tanimoto Index, and the effectiveness is measured by the mean generalisation accuracy of classification. The computational experiments are carried out on ten real-world benchmark datasets and fourteen synthetic datasets. The synthetic datasets are generated with a pre-set number of relevant features and varied numbers of irrelevant features and instances, and added with different levels of noise. The results indicate that the PART approach is more effective in reducing the bias when the size of a dataset is small but starts to lose its advantage as the dataset size increases
Unveiling the central parsec region of an AGN: the Circinus nucleus in the near infrared with the VLT
VLT J- to M\p-band adaptive optics observations of the Circinus Galaxy on
parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9
0.6 pc. This source is only visible at wavelengths longward of 1.6 m
and coincides in position with the peak of the [Si VII]~2.48 m coronal
line emission. With respect to the peak of the central optical emission, the
source is shifted by 0.15\arcsec (2.8 pc) to the south-east. Indeed, it
defines the vertex of a fairly collimated beam which extends for 10 pc,
and which is seen in both continuum light shortward of 1.6 m and in
H line emission. The source also lies at the center of a 19 pc
size [Si VII] ionization {\it bicone}.
Identifying this source as the nucleus of Circinus, its size is compatible
with a putative parsec-scale torus. Its spectral energy distribution,
characterized by a prominent narrow peak, is compatible with a dust temperature
of 300 K. Hotter dust within a 1 pc radius of the center is not detected. The
AGN luminosity required to heat this dust is in the range of X-ray luminosities
that have been measured toward the central source. This in turn supports the
existence of highly obscuring material, with column densities of
cm, that must be located within 1 pc of the core.Comment: 15 pages, 4 figures; To appear in The Astrophysical Journa
Radio structures of the nuclei of nearby Seyfert galaxies and the nature of the missing diffuse emission
We present archival high spatial resolution VLA and VLBA data of the nuclei
of seven of the nearest and brightest Seyfert galaxies in the Southern
Hemisphere. At VLA resolution (~0.1 arcsec), the nucleus of the Seyfert
galaxies is unresolved, with the exception of MCG-5-23-16 and NGC 7469 showing
a core-jet structure. Three Seyfert nuclei are surrounded by diffuse radio
emission related to star-forming regions. VLBA observations with parsec-scale
resolution pointed out that in MRK 1239 the nucleus is clearly resolved into
two components separated by ~30 pc, while the nucleus of NGC 3783 is
unresolved. Further comparison between VLA and VLBA data of these two sources
shows that the flux density at parsec scales is only 20% of that measured by
the VLA. This suggests that the radio emission is not concentrated in a single
central component, as in elliptical radio galaxies, and an additional
low-surface brightness component must be present. A comparison of Seyfert
nuclei with different radio spectra points out that the ``presence'' of
undetected flux on milli-arcsecond scale is common in steep-spectrum objects,
while in flat-spectrum objects essentially all the radio emission is recovered.
In the steep-spectrum objects, the nature of this ``missing'' flux is likely
due to non-thermal AGN-related radiation, perhaps from a jet that gets
disrupted in Seyfert galaxies because of the denser environment of their spiral
hosts.Comment: 13 pages, 9 figures; paper accepted for publication in MNRA
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