arXiv subjects

M. Contini

Publications and source records attributed to M. Contini.

47 records · Page 3Linked to original sources

arXiv2003

The Infrared Continuum of Active Galaxies

We discuss the different physical processes contributing to the infrared continuum of AGN, assuming that both photoionization from the active center and shocks ionize and heat the gas and dust contained in an ensemble of clouds surrounding the nucleus. Radiation transfer of primary and secondary radiation throughout a cloud is calculated consistently with collisional processes due to the shock. We consider that the observed continuum corresponds to reprocessed radiation from both dust and gas in the clouds. The model is applied to the continuum of Seyfert galaxies from which best estimate of the nuclear, stellar subtracted, emission is available. The results show that radiation-dominated high velocity clouds are more numerous in Seyfert 1-1.5 whereas shock-dominated low velocity clouds are dominant in Seyfert type 2 in full agreement with the unified model for AGN. In type 2 objects, radiation is partly suppressed by a central dusty medium with a high dust-to-gas ratio. A grid of models is used to provide a phenomenological analysis of the observed infrared spectral energy distribution.

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arXiv2003

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. \

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arXiv2003

2-D spectroscopy and modeling of the biconical ionized gas in NGC 4388

We present recent results from spectroscopic data and modeling of the biconical ionized gas in the Seyfert-2 galaxy NGC 4388. A field of ~2.6 x 2.4 kpc centered on the nucleus has been observed by means of the modern technique of integral field spectroscopy. The analysis of more than two hundred spectra allowed to study the physical characteristics of the gas in the surroundings of the active nucleus. The South-West ionization cone, revealed by the [O III]5007/H-beta excitation map, shows high emission line ratios not completely supported by simple photoionization. Composite models which account for the combined effects of photoionization and shock show that such high [O III]/H-beta line ratios are emitted by low density (n_0=30 cm^-3) gas inside large (D > 1 pc) shocked clouds (V_s=100 km/s) reached by a relatively low flux from the active nucleus. The data of the VEELR in the North-East cone by Yoshida et al. (2002) have been modeled. The results confirm that photoionization is the prevailing mechanism, but nontheless weak shocks are under way between colliding clouds with small (< 1 pc) sizes and low densities n_0 <= 100 cm^-3, moving outward at relatively low velocities (V_s=100 km/s).

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arXiv2002

The interpretation of the emission spectra of the Seyfert 2 galaxy NGC 7130. Determination of the AGN and starburst contributions

Detailed modeling of the different regions of NGC 7130 is presented, accounting for its composite nature of AGN and starburst galaxy. Shock waves, created by stellar winds from hot massive stars and by supernova ejecta, are evident in the continuum and line spectra emitted from the clouds. The AGN starburst connection is discussed on the basis of model results, considering in particular the distribution of densities and velocities throughout the galaxy.

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arXiv2002

The signature of high velocity gas in the spectra of NGC 4151

The multiwavelength emission spectrum and associated velocity field of the Seyfert prototype NGC 4151 is modeled. HST data has impressively revealed the existence of a large range of velocities (100 - 1500 \kms) dominating the emitting clouds in the extended emission line region of the galaxy. Following this observational result, a revision of the photoionization modeling approach applied to NGC 4151 is presented. It is concluded that a mixture of radiation dominated clouds and shock dominated clouds are required to explain the multiwavelength line and continuum spectra of the galaxy.

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arXiv2001

Internal and external shock fronts in He2-104

The spectra of both the inner and outer nebulae in He2-104 are modelled by composite models which accounts consistently for photoionisation and shocks. The temperature of the hot star results Ts = 130 000 K. We suggest that the characteristic "crab legs" in He2-104 are produced by R-T instability at the shock front. The calculated X-ray flux is below the detection limit of ROSAT.

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arXiv2001

A grid of Composite Models for the Simulation of Starburst Galaxy and HII Region Spectra

A grid of models for starburst spectra is presented and compared with power-law models which represent AGNs. The models are composite, i.e., they account for the radiation from the starburst and for the shocks created by super-winds. Some interesting fit of models to observations are also discussed. In particular, it is found that [OIII]/Hb ~can reach values as high as for the AGN when the emitting clouds are close to the starburst region. Moreover CIV lines can be high even if SiIV lines are relatively low. It is found that for some line ratios, which have similar values for starburst and AGN models, the width of the lines can distinguish between the two types.

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arXiv2000

A grid of composite models for the simulation of the emission-line spectra from the NLR of active galaxies

A grid of composite models for the narrow line region of active galaxies, which consistently account for both the effect of a photoionizing radiation from the active center and of a shock front, is presented. Theoretical results, calculated with the SUMA code, are given for different values of shock velocities, preshock densities, geometrical thickness of the clouds, and, particularly, for the ionizing radiation intensity in a large range. The input parameters are chosen within the ranges indicated by previous fits of several observed emission-line and continuum spectra from active galaxies. Shock velocities from 100 \kms ~to 1500 \kms ~and preshock densities from 100 \cm3 to 1000 \cm3 are considered. The line intensities of the most important ultraviolet, optical and infrared transitions are obtained and are listed in several tables.

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arXiv2000

The optical-ultraviolet continuum of Seyfert 2 galaxies

This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting the single galaxies in the sample of Heckman et al. (1995) with composite models (shock+ photoionization from the active center), we show that five main components characterize the SED of the continuum. Shocks play an important role since they produce a high temperature zone where soft X-rays are emitted. We show that in the optical-UV range, the slope of the NLR emission reproduces the observed values, and may be the main component of the featureless continuum. The presence of star forming regions cannot be excluded in the circumnuclear region of various Seyfert galaxies. An attempt is made to find their fingerprints in the observed AGN spectra. Finally, it is demonstrated that multi-cloud models are necessary to interpret the spectra of single objects, even in the global investigation of a sample of galaxies.

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arXiv1999

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.

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arXiv1998

Gas and Dust Emission from the Nuclear Region of the Circinus Galaxy

Simultaneous modeling of the line and continuum emission from the nuclear region of the Circinus galaxy is presented. Composite models which include the combined effect of shocks and photoionization from the active center and from the circumnuclear star forming region are considered. The effects of dust reradiation, bremsstrahlung from the gas and synchrotron radiation are treated consistently. The proposed model accounts for two important observational features. First, the high obscuration of Circinus central source is produced by high velocity and dense clouds with characteristic high dust-to-gas ratios. Their large velocities, up to 1500 km\s, place them very close to the active center. Second, the derived size of the line emitting region is well in agreement with the observed limits for the coronal and narrow line region of Circinus.

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