In this contribution we report on the study of the optical emission lines and X-ray spectra of a sample of Type 1 AGNs, collected at the Sloan Digital Sky Survey database and observed by the XMM Newton satellite. Exploiting the different instruments carried onboard XMM, we identify the spectral components of the soft and hard energy bands (in the range from 0.3 keV up to 10 keV). The properties of the X-ray continuum and of the Fe Kalpha line feature are investigated in relation to the optical broad emission line profiles and intensity ratios. The resulting picture of emission, absorption and reflection processes is interpreted by means of a BLR structural model that was developed on the basis of independent optical and radio observations.
The spectra of Type 1 Seyfert galaxies are characterised by prominent emission lines and by a strong continuum of ionizing radiation. In general, it is accepted that such spectral components descend from our direct view of the central engine of an Active Galactic Nucleus (AGN), where accretion of matter onto a Super Massive Black Hole results in the emission of large amounts of energy (typically 10 41 erg s -1 ≤ L ≤ 10 46 erg s -1 ). The mass of the SMBH can be estimated from the width of the broad emission lines, which are produced very close to the continuum source, in the so called Broad Line Region (BLR):
where v is an estimate of the plasma velocity (usually connected to the width of the emission lines), R BLR is the size of the region, G is the gravitational constant, and f is a geometrical factor, accounting for the influence of the source structure on the formation of the line profiles.
In this work we present a combined analysis of Type 1 AGN optical and Xray spectra, devoted to the investigation of the intrinsic properties of the central engine and their influence on the BLR plasma.
If we consider an emission line, originated by the transition from an upper level u to a lower level l, we can express the associated intensity as:
where A ul is the probability of a spontaneous radiative decay, N u (r) the number density of the emitting ions, τ (r) is the optical depth of the layer, h, c, and λ ul represent the Planck constant, the speed of light, and the line wavelength, while R 1 and R 2 are the boundaries of the emitting region. In the case of an optically thin plasma, with the population of the high excitation energy levels following the Saha-Boltzmann distribution (plasma in a Partial Local Thermodynamic Equilibrium, or PLTE; see Popović 2003Popović , 2006)), we can introduce a normalized line intensity, with respect to the atomic transition constants, and write Eq. ( 2) in the form of:
in which g u is the statistical weight of the upper level, ℓ is the spatial extension of the emitting region, N 0 is the number density of the ions in their unexcited configuration, while E u0 , k B , and T are the excitation energy of the level, the Boltzmann constant, and the plasma electron temperature, respectively. If we take into account a series of transitions originated by a particular ion species, the normalized intensity of each line is a function of the upper level energy, that we can express as:
where it has been assumed that the line emitting region is the same for the whole transition series. Eq. ( 4) defines the Boltzmann Plot (BP) of the transition series. This formalism was originally developed for high density plasmas, but in La Mura et al. (2007) it was tested on a statistically relevant sample of type 1 AGNs, extracted from the 3 rd data release of the Sloan Digital Sky Survey (SDSS). As it is illustrated in Fig. 1, the technique led to the identification different physical scenarios in the line emitting plasma.
In general, it is observed that a satisfactory match with the underlying assumptions is achieved in approximately 30% of the selected objects, with an improved statistics in the domain of sources with very broad emission lines. This result is also illustrated in Fig. 1, where the coefficient A = -log e/k B T , corresponding to the slope of the linear function defined in Eq. ( 4), is compared with the width of the broad emission line components. In the range of narrow line emitting objects, instead, the BP finds indications of a higher degree of plasma ionization, probably due to a stronger interaction with the ionizing radiation field.
The profiles of broad lines are influenced by the effects of complex kinematics within the source and of radiation transfer from the source to the observer. For this reason it is hardly conceivable that a simple analytic expression might be used to fit the outcome. If the line emitting region results from the combination of several kinematical components, multiple Gaussian functions provide reasonable fits to the observed profiles. However, the presence of distinct kinematical components may affect the profiles in a non-Gaussian form. A good way to estimate the importance of non-Gaussian contributions is to parameterize the observed line shapes by means of a Gauss-Hermite orthonormal expansion (see Van Der Marel & Franx 1993). If we call α(v) the normal Gaussian function, the emission line profile in velocity units can be expressed as:
in which we call F 0 the profile normalization factor, V sys the systemic radial velocity offset between the line and the adopted reference frame, H i (v -V sys ) the i th order Hermite polynomial, and h i the corresponding coefficient.
As we show in Fig. 2, the symmetric component of the non-Gaussian contribution h 4 shows a remarkable decrease for increasing line profile width. Such an effect can be explained assuming that the BLR velocity field includes an ordered kinematical component, consistent with a flatte
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