The X-ray evolving universe: (ionized) absorption and dust, from nearby Seyfert galaxies to high-redshift quasars

TL;DR

This paper reviews the role of ionized absorption and dust in active galactic nuclei across redshifts, highlighting how future X-ray observations with XEUS can address key questions about gas, dust evolution, and cosmology.

Contribution

It presents a comprehensive review of X-ray absorbers in AGN and outlines new scientific opportunities with XEUS for high-redshift studies.

Findings

Detection of metal absorption edges in X-ray spectra.

Resolution of dust and gas composition through K-edge analysis.

Potential to measure gas velocity fields and evolution over cosmic time.

Abstract

(Abridged) Cold and warm absorbers have beeen detected in all types of active galaxies (AGN) from low to high redshift. This gas, located in the black hole region of AGN, is thought to play an important role in AGN unification scenarios, in explaining the X-ray background, in black hole growth and AGN evolution. We provide a review of the observations of dusty and dust-free warm and cold absorbers at low and high redshift, including most recent results and exciting questions still open. Emphasis is on the science issues that we will be able to address with XEUS for the first time, particularly at high redshift, including: (i) determination of metal abundances of X-ray (cold) absorbers by detection of metal absorption edges, (ii) analysis of the composition of dust mixed with cold and ionized gas (K-edges of metals in cold dust and cold gas will be resolvable from each other for the first time), (iii) measurement of the velocity field of the gas, (iv) utilization of these results to investigate the evolution of gas and dust in AGN from high to low redshift: the evolution of abundances, dust content, ionization state, amount and velocity of gas, and its role in feeding the black hole. We emphasize the importance of iron absorption measurements with XEUS at high redshift for two key issues of cosmology: the early star formation history of the universe, and the measurement of cosmological parameters. As an example, we discuss recent XMM-Newton observations of the high-redshift BAL quasar APM 08279+5255.