1,312 research outputs found
The Infrared-X-ray continuum correlation in Active Galactic Nuclei
The correlation between the soft X-ray and near infrared emission from AGN is
analysed using composite models by the code SUMA. We find new evidences for
differences in ranges of parameters which characterize the NLR of Seyfert
galaxies and LINERs. Results obtained by modelling the Einstein and the ROSAT
samples of galaxies are in full agreement. In order to fit the infrared and
X-ray continua, an eta factor is defined, which accounts for the emitting area
of the cloud. If the infrared emission is due to bremsstrahlung and comes from
the same cloud producing the soft X-rays, the eta values obtained from both
emissions must be the same. Therefore, if eta_IR < eta_soft-X there must be a
strong contribution of soft X-rays from the active centre. From the eta values
we expect to identify the objects that could present strong variability. \Comment: 11 pages,13 figures, in press in MNRAS. in press in MNRA
The symbiotic star H1-36. A composite model of line and continuum spectra from radio to ultraviolet
In this paper we analyse the spectra of D-type SS H1-36 within a
colliding-wind scenario. We aim to analyse the properties of this object taking
into account the observational data along the whole electromagnetic spectrum,
in order to derive a self-consistent picture able to interpret the nature of
the system as a whole. After constraining the relative physical conditions by
modelling more than 40 emission lines from radio to UV, we are able to explain
the continuum spectral energy distribution by taking into account all the
emitting contributions arising from both the stars, the dust shells and the
gaseous nebulae. A comprehensive model of the radio spectra allows to reproduce
the different slopes of the radio profile and the turnover frequency, as well
as the different size of the observed shocked envelope at different frequencies
in the light of the different contributions from the expanding and reverse
nebulae. The IR continuum unveils the presence of two dust shells with
different radii and temperatures, which might be a distinctive feature of
D-type symbiotic systems as a class of objects. The broad profiles of IR lines
direct us to investigate whether an X-ray jet may be present. This insight
leads us to indicate H1-36 as a promising X-ray target and to encourage
observations and studies which consistently take into account the complex
nature of symbiotic stars throughout the whole electromagnetic spectrum.Comment: 8 pages, 3 figures, 5 tables, accepted for publication in A&A on 2th
May 200
The spectral energy distribution of D-type symbiotic stars: the role of dust shells
We have collected continuum data of a sample of D-type symbiotic stars. By
modelling their spectral energy distribution in a colliding-wind theoretical
scenario we have found the common characteristics to all the systems: 1) at
least two dust shells are clearly present, one at \sim 1000 K and the other at
\sim 400 K; they dominate the emission in the IR; 2) the radio data are
explained by thermal self-absorbed emission from the reverse shock between the
stars; while 3) the data in the long wavelength tail come from the expanding
shock outwards the system; 4) in some symbiotic stars, the contribution from
the WD in the UV is directly seen. Finally, 5) for some objects soft X-ray
emitted by bremsstrahlung downstream of the reverse-shock between the stars are
predicted. The results thus confirm the validity of the colliding wind model
and the important role of the shocks. The comparison of the fluxes calculated
at the nebula with those observed at Earth reveals the distribution throughout
the system of the different components, in particular the nebulae and the dust
shells. The correlation of shell radii with the orbital period shows that
larger radii are found at larger periods. Moreover, the temperatures of the
dust shells regarding the sample are found at 1000 K and <=400 K, while, in the
case of late giants, they spread more uniformly throughout the same range.Comment: 14 pages, 7 figures, 5 tables. Accepted for publication in MNRA
Shock fronts in the symbiotic system BI Crucis
We investigate the symbiotic star BI Crucis through a comprehensive and
self-consistent analysis of the spectra emitted in three different epochs:
60's, 70's, and late 80's. In particular, we would like to find out the
physical conditions in the shocked nebula and in the dust shells, as well as
their location within the symbiotic system, by exploiting both photometric and
spectroscopic data from radio to UV. We suggest a model which, on the basis of
optical imaging, emission line ratios and spectral energy distribution profile,
is able to account for collision of the winds, formation of lobes and jets by
accretion onto the WD, as well as for the interaction of the blast wave from a
past, unrecorded outburst with the ISM. We have found that the spectra observed
throughout the years show the marks of the different processes at work within
BI Cru, perhaps signatures of a post-outburst evolution. We then call for new
infrared and millimeter observations, potentially able to resolve the inner
structure of the symbiotic nebula.Comment: 13 pages, 9 figures, 2 tables; accepted for publication in MNRA
The symbiotic star CH Cygni. II. The broad Ly alpha emission line explained by shocks
Context. In 1985, at the end of the active phase 1977-1986, a broad (4000
km/s) Ly alpha line appeared in the symbiotic system CH Cygni that had never
been observed previously. Aims. In this work we investigate the origin of this
anomalous broad Ly alpha line. Methods. We suggest a new interpretation of the
broad Ly alpha based on the theory of charge transfer reactions between ambient
hydrogen atoms and post-shock protons at a strong shock front. Results. We have
found that the broad Ly alpha line originated from the blast wave created by
the outburst, while the contemporary optical and UV lines arose from the nebula
downstream of the expanding shock in the colliding wind scenario.Comment: 5 pages, 2 figures, accepted for publication in A&A on 7th April 200
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
Properties of Faint Distant Galaxies as seen through Gravitational Telescopes
This paper reviews the most recent developments related to the use of lensing
clusters of galaxies as Gravitational Telescopes in deep Universe studies. We
summarize the state of the art and the most recent results aiming at studying
the physical properties of distant galaxies beyond the limits of conventional
spectroscopy. The application of photometric redshift techniques in the context
of gravitational lensing is emphasized for the study of both lensing structures
and the background population of lensed galaxies. A presently ongoing search
for the first building blocks of galaxies behind lensing clusters is presented
and discussed.Comment: Review lecture given at "Gravitational Lensing: a unique tool for
cosmology",Aussois, France, January 2003. To appear in ASP Conf. S., eds. D.
Valls-Gabaud & J.-P. Kneib, 26 pages, 8 figure
The Relation Between Activity and Environment in Compact Groups of Galaxies
We present the results of the classification of spectral activity types for
193 galaxies from a new sample of 49 compact groups of galaxies in the southern
hemisphere (SCGs). This sample was selected in automated fashion from a
digitized galaxy catalogue, covering an area of ~5200 sq deg, around the South
Galactic Pole. It is complete up to m ~14.5 in b_j for the brightest galaxy of
the group.
The spectral analysis of the SCG galaxies confirms the results previously
obtained for a smaller sample of Hickson's compact groups (HCG). We confirm the
luminosity-activity and morphology-activity relations, as well as the
predominance of AGNs (41% of SCGs galaxies). We verified also that the number
of early-type non-emission-line galaxies increases with the number of members
in the group.
The SCGs contain more star-forming galaxies (SFGs) and less non-emission-line
galaxies than HCGs, which suggests that they probe a wider range of physical
properties. The SFGs are composed in majority of HII Nucleus Galaxies, which
have less intense star formation than starburst galaxies. The star formation
activity in SCGs is, consequently, remarkably low. The SFGs show also evidence
for nuclear activity. If these results are further confirmed, 70% of the
galaxies in SCGs would then have an active nucleus, making these systems
remarkably rich in AGNs. Curiously, however, this characteristic of CGs
generally excludes Seyfert 1 galaxies.(Abridged)Comment: 53 pages, Latex, 9 encapsulated postscript figures, Accepted for
publication in The Astronomical Journa
A New Pharmacological Approach Based on Remdesivir Aerosolized Administration on SARS-CoV-2 Pulmonary Inflammation: A Possible and Rational Therapeutic Application
The new zoonotic coronavirus (SARS-CoV-2) responsible for coronavirus disease (COVID-19) is a new strain of coronavirus not previously seen in humans and which appears to come from bat species. It originated in Wuhan, Hubei Province, China, and spread rapidly throughout the world, causing over 5,569,679 global cases and 351,866 deaths in almost every country in the world, including Europe, particularly Italy. In general, based on existing data published to date, 80.9% of patients infected with the virus develop mild infection; 13.8% severe pneumonia; 4.7% respiratory failure, septic shock or multi-organ failure; 3% of these cases are fatal. Critical patients have been shown to develop acute respiratory distress syndrome (ARDS) and hospitalization in intensive care units. The average age of patients admitted to hospital is 57–79 years, with one third half with an un- derlying disease. Asymptomatic infections have also been described, but their frequency is not known. SARS- CoV-2 transmission is mainly airborne from one person to another via droplets. The data available so far seem to indicate that SARS-CoV-2 is capable of producing an excessive immune reaction in the host. The virus attacks type II pneumocytes in the lower bronchi through the binding of the Spike protein (S protein) to viral receptors, of which the angiotensin 2 conversion enzyme (ACE2) receptor is the most important. ACE2 receptor is widely expressed in numerous tissues, including the oropharynx and conjunctiva, but mostly distributed in ciliated bronchial epithelial cells and type II pneumocytes in the lower bronchi. The arrival of SARS-CoV-2 in the lungs causes severe primary interstitial viral pneumonia that can lead to the “cytokine storm syndrome”, a deadly uncontrolled systemic inflammatory response triggered by the activation of interleukin 6 (IL-6), whose effect is extensive lung tissue damage and disseminated intravascular coagulation (DIC), that are life-threatening for patients with COVID-19. In the absence of a therapy of proven efficacy, current management consists of off-label or compassionate use therapies based on antivirals, antiparasitic agents in both oral and parenteral formulation, anti-inflammatory drugs, oxygen therapy and heparin support and convalescent plasma. Like most respiratory viruses can function and replicate at low temperatures (i.e. 34–35 °C) and assuming viral thermolability of SARS- CoV-2, local instillation or aerosol of antiviral (i.e. remdesivir) in humid heat vaporization (40°–41 °C) in the first phase of infection (phenotype I, before admission), both in asymptomatic but nasopharyngeal swab positive patients, together with antiseptic-antiviral oral gargles and povidone-iodine eye drops for conjunctiva (0,8–5% conjunctival congestion), would attack the virus directly through the receptors to which it binds, significantly decreasing viral replication, risk of evolution to phenotypes IV and V, reducing hospitalization and therefore death
- …