arXiv subjects

M. Contini

Publications and source records attributed to M. Contini.

At least 37 records · Page 2Linked to original sources

arXiv2012

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 $10^{-11}$ photons cm$^{-2}$ s$^{-1}$ eV$^{-1}$ 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$^{-3}$. 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.

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arXiv2012

Evidences of merging in the Seyfert galaxy NGC 3393 revealed by modelling the spectra

The discovery of two active black holes in the Seyfert galaxy NGC 3393, separated by about 490 light years, revealed a merging event. This led us to look for other evidences of galaxy collision and merging through the analysis of the observed spectra in different frequency ranges. We found preshock densities higher by a factor of about 10 in the NGC 3393 NLR than in other AGN and patches of ionized matter beyond the observed NLR bulk. They can be explained by compression and heating of the gas downstream of shock waves created by collision. Metallicity in terms of the O/H relative abundance, is about 0.78 solar. Mg/H depletion by a factor of about 3 compared with solar cannot be explained by Mg trapping into dust grains, due to rather high shock velocities. The low O/H and Mg/H abundances indicate mixing with external matter during collision. Twice solar N/H is predicted by modelling the spectra of high shock velocity clouds reached by a Ts =8.6 10^4 K black-body flux. This suggests that Wolf-Rayet stars could be created by galaxy collision in the central region.

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arXiv2011

The LLAGN in the centre of the Galaxy

The observations of FIR line and continuum spectra throughout the Galactic centre and in some regions of the disc are analysed in order to determine the physical conditions (densities, shock velocities, radiation parameters, etc.) and the relative abundances of some elements (C, N, and O). The models account for the coupled effect of photoionization and shocks. Consistent model calculations of the line and continuum spectra show that, although the radiation from the stars dominates, an active galactic nucleus (AGN) is clearly present, with a radiation maximum in the Sgr A* region. The flux, similar to that found for low luminosity AGN (LLAGN), is lower by a factor of about 100 than that of AGN.

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arXiv2011

The symbiotic system Z Andromedae : a spectral analysis of the anomalous 1984-1986 outburst

The visual magnitude profile of the symbiotic system Z And during the 1984-1986 activity period appears double peaked and the flux intensity is low compared to outbursts in other epochs. The detailed modeling of the observed spectra, accounting for the shells ejected by the red giant star, shows that the outburst is intrinsically single but distorted by the collision at different phases of the white dwarf wind with two close shells.

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arXiv2010

Spectra from the shocked nebulae revealing turbulence near the Galactic Centre

The spectra emitted from clouds near the Galactic Centre are investigated calculating the UV-optical-IR lines using the physical parameters and the element abundances constrained by the fit of mid-IR observations. The characteristic line ratios are compared with those observed in active galaxies. We have found that the physical conditions in the nebulae near the GC are different from those of starburst galaxies and AGN, namely, gas velocities and densities as well as the photoionization fluxes are relatively low. The geometrical thickness of the emitting nebulae is particularly small suggesting that matter is strongly fragmented by instabilities leading to an underlying shock-generated turbulence.

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arXiv2009

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.

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arXiv2009

An analysis of infrared emission spectra from the regions near the Galactic Center

We present consistent modelling of line and continuum IR spectra in the region close to the Galactic center. The models account for the coupled effect of shocks and photoionization from an external source. The results show that the shock velocities range between 65 and 80 km/s, the pre-shock densities between 1 cm-3 in the ISM to 200 cm-3 in the filamentary structures. The pre-shock magnetic field increases from 5. 10^{-6} gauss in the surrounding ISM to ~8. 10^{-5} gauss in the Arched Filaments. The stellar temperatures are ~38000 K in the Quintuplet cluster and ~27000 K in the Arches Cluster. The ionization parameter is relatively low (<0.01) with the highest values near the clusters, reaching a maximum >0.01 near the Arches Cluster. Depletion from the gaseous phase of Si is found throughout the whole observed region, indicating the presence of silicate dust. Grains including iron, are concentrated throughout the Arched Filaments. The modelling of the continuum SED in the IR range, indicates that a component of dust at temperatures of ~100-200 K is present in the central region of the Galaxy. Radio emission appears to be thermal bremsstrahlung in the E2-W1 filaments crossing strip, however a synchrotron component is not excluded. More data are necessary to resolve this questions.

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arXiv2009

MASYS. The AKARI spectroscopic survey of Symbiotic Stars in the Magellanic Clouds

MASYS is the AKARI spectroscopic survey of Symbiotic Stars in the Magellanic Clouds, and one of the European Open Time Observing Programmes approved for the AKARI (Post-Helium) Phase-3. It is providing the first ever near-IR spectra of extragalactic symbiotic stars. The observations are scheduled to be completed in July 2009.

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arXiv2009

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.

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arXiv2008

The symbiotic star CH Cygni. I. An analysis of the shocked nebulae at different epochs

Context. We analyse the line and continuum spectra of the symbiotic system CH Cygni. Aims. To show that the colliding-wind model is valid to explain this symbiotic star at different phases. Methods. Peculiar observed features such as flickering, radio variation, X-ray emission, as well as the distribution of the nebulae and shells throughout the system are investigated by modelling the spectra at different epochs. The models account consistently for shock and photoionization and are constrained by absolute fluxes. Results. We find that the reverse shock between the stars leads to the broad lines observed during the active phases, as well as to radio and hard X-ray emission, while the expanding shock is invoked to explain the data during the transition phases.

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arXiv2008

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.

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arXiv2007

Comparison of dust-to-gas ratios in luminous, ultraluminous, and hyperluminous infrared galaxies

The dust-to-gas ratios in three different samples of luminous, ultraluminous, and hyperluminous infrared galaxies are calculated by modelling their radio to soft X-ray spectral energy distributions using composite models which account for the photoionizing radiation from HII regions, starbursts, or AGNs, and for shocks. The models are limited to a set which broadly reproduces the mid-IR fine structure line ratios of local, IR bright, starburst galaxies. The results show that two types of clouds contribute to the IR emission. Those characterized by low shock velocities and low preshock densities explain the far-IR dust emission, while those with higher velocities and densities contribute to mid-IR dust emission. An AGN is found in nearly all of the ultraluminous IR galaxies and in half of the luminous IR galaxies of the sample. High IR luminosities depend on dust-to-gas ratios of about 0.1 by mass, however, most hyperluminous IR galaxies show dust-to-gas ratios much lower than those calculated for the luminous and ultraluminous IR galaxies.

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arXiv2007

Gas and dust spectra of the D' type symbiotic star HD330036

We present a comprehensive and self-consistent modelling of the D' type symbiotic star (SS) HD330036 from radio to UV. Within a colliding-wind scenario, we analyse the continuum, line and dust spectra by means of SUMA, a code that simulates the physical conditions of an emitting gaseous cloud under the coupled effect of ionization from an external radiation source and shocks. We find that the UV lines are emitted from high density gas between the stars downstream of the reverse shock, while the optical lines are emitted downstream of the shock propagating outwards the system. As regards with the continuum SED, three shells are identified in the IR, at 850K, 320 K and 200 K with radii r = 2.8 10^13 cm, 4 10^14$ cm, and 10^15 cm, respectively, adopting a distance to Earth d=2.3 kpc: interestingly, all these shells appear to be circumbinary. The analysis of the unexploited ISO-SWS spectrum reveals that both PAHs and crystalline silicates coexist in HD330036, with PAHs associated to the internal shell at 850 K, and crystalline silicates stored into the cool shells at 320 K and 200 K. Strong evidence that crystalline silicates are shaped in a disk-like structure is derived on the basis of the relative band strengths. Finally, we suggest that shocks can be a reliable mechanism in activating the annealing and the consequent crystallization processes. We show that a consistent interpretation of gas and dust spectra emitted by SS can be obtained by models which accounts for the coupled effect of the photoionizing flux and of shocks. The VLTI/MIDI proposal recently accepted by ESO aims to verify and better constrain some of our results by means of IR interferometric observations.

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arXiv2007

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.

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arXiv2007

Silicates in D-type symbiotic stars: an ISO overview

We investigate the IR spectral features of a sample of D-type symbiotic stars. Analyzing unexploited ISO-SWS data, deriving the basic observational parameters of dust bands and comparing them with respect to those observed in other astronomical sources, we try to highlight the effect of environment on grain chemistry and physic. We find strong amorphous silicate emission bands at 10 micron and 18 micron in a large fraction of the sample. The analysis of the 10 micron band, along with a direct comparison with several astronomical sources, reveals that silicate dust in symbiotic stars shows features between the characteristic circumstellar environments and the interstellar medium. This indicates an increasing reprocessing of grains in relation to specific symbiotic behavior of the objects. A correlation between the central wavelength of the 10 and 18 micron dust bands is found. By the modeling of IR spectral lines we investigate also dust grains conditions within the shocked nebulae. Both the unusual depletion values and the high sputtering efficiency might be explained by the formation of SiO moleculae, which are known to be a very reliable shock tracer. We conclude that the signature of dust chemical disturbance due to symbiotic activity should be looked for in the outer, circumbinary, expanding shells where the environmental conditions for grain processing might be achieved. Symbiotic stars are thus attractive targets for new mid-infrared and mm observations.

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arXiv2004

The continuum and narrow line region of the NLS1 galaxy Mrk 766

We present the first spectroscopic observations in the interval 0.8-4.0 microns, complemented with HST/UV and optical spectroscopy, of the narrow line Seyfert 1 galaxy Mrk766. The NIR spectrum is characterized by permitted lines of HI, HeI, HeII and FeII, and forbidden lines of [SII], [SIII] and [FeII] among others. High ionized species such as [SiIX], [SiX], [SIX] and [MgVII] are also observed. The continuum has a complex shape, with contribution of the central engine, circumnuclear stellar population and dust. This last component is evidenced by the presence of an excess of emission peaking at 2.25 microns, fitted by blackbody function with T_bb=1200K. That temperature is close to the evaporation temperature of graphite grains. As such, it provides strong evidence of hot dust, probably very close to the nucleus. Consistent modeling of the line and broad band continuum spectrum by composite models, which account for the photoionizing flux of the central engine and shocks, shows that the shock velocities are between 100 and 500 km/s, the preshock densities between 100 and 1000 cm^-3 and the radiation fluxes from the active centre between 10^9 and 5x10^12 photons cm^-2 s^-1 eV^-1 at 1 Ryd with spectral indices $α_{UV}$=-1.5 and $α_X$=-0.4. Adopting silicon grains, dust-to-gas ratios are between 10^-{6} and 4x10$^{-4}$ by mass. The emitting clouds are at an average distance of 160 pc from the centre, with high velocity clouds closer and low velocity clouds farther from the centre. The N/H relative abundance could be twice solar. In constrast, Fe is depleted from the gaseous phase by a factor >2. Ratios of calculated to observed line ratios to Hbeta indicate an average contribution of the broad line region to the observed Hbeta of about 40%.

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arXiv2004

The peculiar galaxy Mkn 298 revisited through integral field spectroscopy

Spectroscopic and imaging data of the peculiar galaxy Mkn 298 are presented in this paper. Narrow-band Halpha and broad-band R images are used to study the star formation rate in the galaxy and its morphology, which is typical of a merging system. Long-slit and integral field spectra are used to assess the kinematics of gas and stars, and the nature of the ionizing source at different distances from the nucleus. In particular, the nucleus of Mkn 298 is characterized by peculiar line ratios: [NII] 6583/Halpha is typical of HII-like regions, while [OI] 6300/Halpha could indicate the presence of an active galactic nucleus. We show that models where a shock component is added to photoionization from a starburst allow to reproduce the observed line ratios. Mkn 298 is thus most likely a star forming galaxy, rather than a galaxy hosting an active nucleus.

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arXiv2004

Dust-to-gas ratios in the Kepler supernova remnant

A new method to evaluate the dust-to-gas ratios in the Kepler SNR is presented. Dust emission in the infrared and bremsstrahlung are calculated consistently, considering that dust grains are collisionally heated by the gas throughout the front and downstream of both the expanding and the reverse shocks. The dust-to-gas ratios are determined by the ratio of the dust emission bump and bremsstrahlung in the infrared. A maximum dust mass < 0.16 Mo is calculated.

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