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

TL;DR

This study analyzes XMM-Newton spectra of 38 nearby Seyfert galaxies to determine the distribution of X-ray absorption, revealing that a significant fraction are absorbed, including some Compton-thick sources, with implications for understanding the local AGN population.

Contribution

First comprehensive X-ray absorption distribution analysis of a complete local Seyfert galaxy sample using XMM-Newton data, highlighting the prevalence of absorbed and Compton-thick AGN.

Findings

Up to 55% of sources are absorbed with N_H > 10^22 cm^-2.

Approximately 15-20% are Compton-thick AGN.

The observed fraction of Compton-thick AGN is lower than model predictions.

Abstract

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 2-10 keV luminosity range ~10^38-10^43 ergs/s. 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 10^24 cm^-2 and high equivalent width FeKa lines (>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 N_H~10^23 cm^-2. Therefore the fraction of absorbed sources (>10^22 cm^-2 could be as high as 55+/-12%. A number of Seyfert-2 appear to host unabsorbed nuclei. These are associated with low-luminosity sources Lx < 3x10^41 ergs/s. Their stacked spectrum again shows no absorption while inspection of the \chandra images, where available, shows that contamination from nearby sources does not affect the {\it XMM-Newton} spectra in most cases. Nevertheless, such low luminosity sources are not contributing significantly to the X-ray background flux. When we consider only the brighter, $>10^{41}$ \lunits, 21 sources, we find that the fraction of absorbed nuclei rises to $75\pm19 $ % while that of Compton-thick sources to 15-20%. The fraction of Compton-thick AGN is lower than that predicted by the X-ray background synthesis model in the same luminosity and redshift range.}