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

(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.Comment: 8 pages, to appear in the proc. of the workshop "XEUS - studying the evolution of the universe", G. Hasinger et al. (eds), MPE Report, in press. Related papers on the high-z BAL quasar APM 08279+5255 (and MPG press release), and on ionized absorbers are available at http://www.xray.mpe.mpg.de/~skomossa

Studying the Evolving Universe with XMM-Newton and Chandra

First indications of the warm/hot intergalactic medium, tracing out the large scale structure of the universe, have been obtained in sensitive Chandra and XMM-Newton high resolution absorption line spectroscopy of bright blazars. High resolution X-ray spectroscopy and imaging also provides important new constraints on the physical condition of the cooling matter in the centers of clusters, requiring major modifications to the standard cooling flow models. XMM-Newton and Chandra low resolution spectroscopy detected significant Fe K_alpha absorption features in the spectrum of the ultraluminous, high redshift lensed broad absorption line QSO APM 08279+5255, yielding new insights in the outflow geometry indicating a supersolar Fe/O ratio. Chandra high resolution imaging spectroscopy of the nearby ULIRG/obscured QSO NGC 6240 for the first time gave evidence of two active supermassive black holes in the same galaxy, likely bound to coalesce in the course of the ongoing major merger in this galaxy. Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the X-ray background into discrete sources. Optical spectroscopic identifications show that the sources producing the bulk of the X-ray background are a mixture of obscured (type-2) and unobscured (type-1) AGNs, as predicted by the XRB population synthesis models. A class of highly luminous type-2 AGN, so called QSO-2s, has been detected in the deepest Chandra and XMM-Newton surveys. The new Chandra AGN redshift distribution peaks at much lower redshifts (z~0.7) than that based on ROSAT data, indicating that the evolution of Seyfert galaxies occurs at significantly later cosmic time than that of QSOs.Comment: 13 pages, 6 figures, review to appear in "High Energy Processes and Phenomena in Astrophysics, IAU Symposium 214, X. Li, Z. Wang, V. Trimble (eds

When Supermassive Black Holes were growing: Clues from Deep X-ray Surveys

Merging the Chandra and XMM-Newton deep surveys with the previously identified ROSAT sample, almost 1000 AGN-1 covering five orders of magnitude in 0.5-2 keV flux limit and six orders of magnitude in survey solid angle were identified with ~95% completeness. AGN-1 are by far the largest contributors to the soft X-ray samples. Their evolution is responsible for the break in the 0.5-2 keV source counts. Their soft X-ray luminosity function clearly changes shape as a function of redshift, confirming earlier reports of luminosity--dependent density evolution. The space density with redshift changes significantly for different luminosity classes, showing a strong positive evolution up to a certain redshift and then a flattening. The redshift, at which the evolution peaks, changes considerably with X-ray luminosity. The amount of density evolution also depends strongly on X-ray luminosity, more than a factor of 100 at high luminosities, but less than a factor of 10 for low luminosities. For the first time, a significant decline of the space density of X-ray selected AGN towards high redshift has been detected. No significant evolution of the X-ray to optical spectral index is found for AGN-1. The constraints from the AGN luminosity function and evolution in comparison with the mass function of black holes in local galaxies indicates, that the average supermassive black hole has built up its mass through efficient accretion and is likely rapidly spinning.Comment: Proceedings of the Conference "Growing Black Holes"; A. Merloni, S. Nayakshin and R. Sunyaev (eds.

Winds and Outflows in Starburst Galaxies and AGN

Winds and outflows in starburst galaxies and AGN provide important information on the physics of the "central engine", the presence and evolution of (nuclear) starbursts, and the metal enrichment of the nuclear environment and the intergalactic medium. Here, we concentrate on two examples, X-ray observations of the (U)LIRG NGC6240 and the BAL quasar APM08279+5255.Comment: 6 pages incl. 2 figures, to appear in "Recycling interstellar and intergalactic matter", IAU Symp. 217, P.-A. Duc et al. (eds); related papers available at http://www.xray.mpe.mpg.de/~skomossa

Chandra Observations of Six QSOs at z ≈\approx 3

We report the results of our Chandra observations of six QSOs at $z\sim 3$ from the Palomer Transit Grism Survey. Our primary goal is to investigate the possible systematic change of $\alpha_{ox}$ between $z>4$ and $z\sim 3$, between which a rapid rise of luminous QSO number density with cosmic time is observed. The summed spectrum showed a power-law spectrum with photon index of $\Gamma \approx 1.9$, which is similar to other unabsorbed AGNs. Combining our $z\sim 3$ QSOs with X-ray observations of QSOs at $z>4$ from literaure/archive, we find a correlation of $\alpha_{\rm ox}$ with optical luminosity. This is consistent with the fact that the luminosity function slope of the luminous end of the X-ray selected QSOs is steeper than that of optically-selected QSOs. We discuss an upper limit to the redshift dependence of $\alpha_{ox}$ using a Monte-Carlo simulation. Within the current statistical errors including the derived limits on the redshift dependence of $\alpha_{\rm ox}$, we found that the behaviors of the X-ray and optically-selected QSO number densities are consistent with each other.Comment: 13 Pages, 3 Figures, Astronomical Journal in press, An entry in Table 2 corrected--Log Lx for PC 1000+4751 from 44.0 (incorrect) to 45.0 (correct). A few minor errors correcte