Tasca col·laborativa: paletitzat amb control de qualitat

the presence of a relativistically widened FeKα line (as in MCG-6-30-15); c) the presence of more than one emission line (as in NGC 1068); d) spectra due entirely to reflection (as in NGC 7674); e) the presence of partial and/or warm absorbers (as in NGC 3516). When warm absorbers were required, they were wfit with the ABSORI model.

The models outlined above have been used to fit the data. The criterion used has been the one of increasing complexity of the model applied in subsequent steps. As a first order approximation a best fit has been recognized for those models for which the added element of complexity corresponds to at least a 90% increase of statistical significance of the last added component. Final acceptance of a best fit has been based on inspection of the physical significance of the derived parameters by the automated fit procedure. The final results are summarized in Table A.3 and to obtain the luminosities reported in there, Ho=75 km s−1Mpc−1and q0=0.5 were

used.

2.2

The X–C f A sample

This sample of Seyfert galaxies has been derived from the Palomar optical spectroscopic survey of nearby galaxies (Ho, Filippenko, & Sargent 1985). From this survey, high-quality optical spectra of 486 bright (BT ≤ 12.5 mag), northern

(δ > 0⊙) galaxies have been taken and a comprehensive, homogeneous catalog of spectral classifications of all galaxies have been obtained (, Ho, Filippenko & sargent 1997a, herefter HFS97). The Palomar survey is complete to BT = 12.0

mag and 80% complete to BT = 12.5 mag (Sandage, Tammann, & Yahil 1979).

This sample offers the advantage to have an accurate optical classification and the opportunity of detecting weak nuclei since the AGNs included covers a large range of luminosities (Lbol∼ 1041−44erg s−1).

The spectroscopic classification system of the Palomar survey can be briefly summarized (see HFS97 for a more accurate description) as follow: the relative strength of the low-ionization optical forbidden lines ([OI] λλ6300, 6364, [NII]

λλ6548, 6583, [S II] λλ6716, 6731) compared to the hydrogen Balmer lines deter- mines the classification of emission-line nuclei into two classes: H II nuclei (pow- ered by stars) and AGN (powered by black-hole accretion). The separation between LINERs and Seyferts is instead given by the ratio [OIII]λ5007/Hβwhich corresponds

to the ionization state of the narrow-line gas in AGN, i.e. [OIII]λ5007/Hβ < 3 for LINERs and [OIII]λ5007/Hβ ≥ 3 for Seyferts. Emission line nuclei having [OI] strengths intermediate between those of H II nuclei and LINERs are classified as ”transition objects”. As such, symbols used in table B.1 are: L = LINER, T = “transition object” (LINER + HII nucleus), and S = Seyfert. The classification in “type 1” or “type 2” depends on the presence or absence of broad permitted lines. The measurement of the relative strength of the broad component of the hydrogen Balmer lines lead to subdivisions in the classification (type 1.0, 1.2, 1.5, 1.8 and 1.9; see Osterbrock 1981).

All the Seyfert galaxies presented in the original sample have been extracted to form the present sample that is formed of 60 Seyfert galaxies. The sample includes 39 type 2 (type 2 and 1.9) and 13 type 1 AGN (type 1.0, 1.2, 1.5). Eight objects, which are placed near the boundary between Seyfert and LINER, HII or transition classification, with a double classification (e.g., S2/T2, L2/S2, H/S2, etc.), have been included in the final sample. Hereafter I refer to these objects as ’mixed Seyferts’.

Seyfert galaxies classified as type 2 and 1.9 have been grouped into a more general ’type 2’ classification, while type 1.0, 1.2 and 1.5 have been grouped in the ’type 1’ class. Type 2 and type 1.9 sources are normally both absorbed objects, while the type 1 group is referred to objects which are normally not affected by heavy absorption.

Two sources of the sample, NGC 4395 and NGC 4579, which have been clas- sified by HFS97 as S1.8 and S1.9/L1.9 respectively, have been reclassified as type 1.5. A broad component is present in a number of optical (Filippenko & Sargent 1989) and ultraviolet (Filippenko, Ho & Sargent 1993) emission lines of NGC 4395. Extremely broad permitted lines have been detected in NGC 4579. HST observations have revealed an Hαcomponent with FWZI of ∼ 18000 km/s (Barth et al. 1996 and Barth et al. 2001).

In objects like NGC 3608, NGC 3941, NGC 4472 and NGC 6482, the difficulty in the starlight subtraction process has lead to uncertainties in the classification (HFS97a). Finally, the classification of NGC 185 is also uncertain, i.e., it is a dwarf spheroidal galaxy whose Seyfert-like line ratios maybe produced by stellar processes (Ho & Ulvestad 2001, hereafter HU01).

2.2 The X–C f A sample 25

Cols. (2)–(8) are taken from the compilation of HU01 and references therein. Dis- tances for a few objects have been updated with more recent estimates (references are indicated in Col. (5)). The median distance of the sample galaxies is 25.7± 17.7 Mpc. The nearest galaxy is NGC 185 (one of the companions of M 31) at D = 0.64 Mpc and the farthest is NGC 5548 at D = 70.2 Mpc, so only the local universe is sampled.

2.2.1 The X-ray data

Other than the ∼250 ks of EPIC Guaranteed Time for the distance-limited sam- ple of 27 Seyfert galaxies (see Section 2.3), five further public observations avail- able from the XMM-Newton Science Archive (XSA)1were analyzed.

The X M M–Newton data reduction and analysis willl be discussed in detail in the next section. Here it is important to stress that the objects not belonging to the X M M–Newton sample are NGC 1275, NGC 3516, NGC 3227, NGC 5548 and NGC 7479.

To complement the X-ray information on the whole sample, a search in the literature for observations with previous X-ray observatories (operating in the 2-10 keV energy range) has also been carried out. ASCA observations have been found for 8 further objects, references for those data taken from the literature are given in Table B.2, except for NGC 3982 and NGC 4235 for which ASCA fluxes have been derived in this work. Adding all these data, 47 sources out of 60 objects have X-ray data available.

The CIAO software was used for the Chandra data analysis and to perform the data processing and calibration2. Starting from level 1 files, new level 2 event files were generated. Pixel randomization introduced by the CXC (Chandra X- ray observatory Center) and standard data processing (SDP) were applied to avoid the instrumental ”gridded” appearance of the data and any possible aliasing effects associated with this spatial grid. Finally, the light curves were examinated in order to clean the datasets for periods of anomalous background rates.

Most observations have been taken in the standard mode that allows a read-out mode of the full chip every 3.2s. For many bright sources in the sample more than

1_{http://xmm.esac.esa.int/xsa}

2_{All the data processing have been carried out following analysis threads on the Chandra web}

one observation is often available. In this case, the data set without gratings was chosen and, in order to minimize pile-up effects, the data set with 1/8 or 1/2 chip sub-array mode.

It is worth recalling here that the final results of such analysis are presented in Table B.2. Finally, for the vast majority of the objects not included in the

X M M–Newton sample, the X-ray data available were not of high quality. This

was expected since many of the objects included in the present sample were al- ready known to be quite faint. Nonetheless, the possibility to create a sample quite populated for which the X-ray luminosity is known for almost all the sources, open the opportunity to perform some kind of tests that are hampered by the small num- ber of objects included in the X M M–Newton sample.