XMM-Newton observations of Seyfert galaxies from the Palomar spectroscopic survey: the X-ray absorption distribution

摘要

We present XMM-Newton spectral analysis of all 38 Seyfert galaxies from the Palomar spectroscopic sample of galaxies. These are found at distances of up to 67 Mpc and cover the absorbed 2-10keV luminosity range 1038-1043 .Our aim is to determine the distribution of the X-ray absorption in the local Universe. Three of these are Compton-thick with column densities just above 1024 and high equivalent width FeKlines (>700 eV). Five more sources have low values of the X-ray to [OIII] flux ratio suggesting that they could be associated with obscured nuclei. Their individual spectra show neither high absorbing columns nor flat spectral indices. However, their stacked spectrum reveals an absorbing column density of .Therefore the fraction of absorbedsources (>1022 )could be as high as %. A number of Seyfert-2 appear to host unabsorbed nuclei. These are associated with low-luminosity sources .Their stacked spectrum again shows no absorption while inspection of the Chandraimages, where available, shows that contamination from nearby sources does not affect the XMM-Newton spectrain most cases. Nevertheless, such low luminosity sources are not contributing significantly to the X-ray background flux. When we consider only the brighter, >1041 ,21 sources, we find that the fraction of absorbed nuclei rises to % while that of Compton-thick sources to15-20%. The fraction of Compton-thick AGN is lower than that predicted by the X-ray background synthesis modelin the same luminosity and redshift range.Key words: surveys - X-rays: galaxies - X-rays: general