About this Image

These XMM-Newton spectra are averages of several X-ray spectra of type-1 (top panel) and type-2 (bottom panel) active galactic nuclei (AGN) in the Lockman Hole. EPIC-pn data is shown in black, MOS in red colour. The cosmic X-ray background is the light emitted from material as it was accreted into black holes during the black holes' growth phase. Recently it has become possible to resolve a significant fraction of the X-ray background into discrete sources. The Lockman Hole is a region where along the line of sight from Earth the number of galactic hydrogen atoms is very low. This allows the distant, high-redshift AGNs of interest, containing the early black holes, to be observed. In this investigation the observed spectrum was compared to a model, which was divided into the observed spectrum. The resultant spectra clearly show a broad feature at around 6.4 keV, which the investigators presume to be a Fe K_α emission line. In the type-2 AGN there appears to be a narrow line feature also. The line profile suggests high abundances of iron, and relativistic disks around spinning black holes for the observed AGN. From this discovery it can be inferred that these are the average properties for the black holes' accretion disks from which the X-ray background was emitted.

Investigator(s): A. Streblyanska, G. Hasinger, A. Finoguenov, X. Barcons, S. Mateos, A. Fabian

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Detailed description of this image

Instrument	EPIC
Observing Mode	Full Frame
Filter	N/A
Date of Observation	2002-12-06
Detailed Caption	In this investigation the spectra of over 100 AGN sources in the Lockman Hole were taken with XMM-Newton and divided into type-1 and type-2 on the basis of their optical spectral properties using data from the Keck telescopes. 53 type-1 AGN, 41 type-2 AGN and 10 galaxies were found. The spectrum of each object was fitted with a single power law with intrinsic absorption, which was then shifted to the rest frame. The spectra shown above are the resultant spectra of the ratio of the data to the model, averaged for all the type-1 (top panel) and type-2 (bottom panel) AGN. EPIC-pn data is plotted in black, MOS data in red colour. A feature is visible at around 6.4 keV, with an equivalent width of 560 eV for the type-1 AGN and 455 eV for type-2 AGN. A feature such as this could be caused by complex absorption or a broad emission line. This feature is believed by the investigators to be a Fe K_α emission line due to low and moderate iron ionization states, below Fe XVI. It is indicated that there is some component of spin for the average black hole by the strong red line wing. The line profile is consistent with a relativistic disk line for type-1 systems and a narrow line component is also visible for type-2 systems. The Lockman Hole was observed for a total of 770 ks in 16 observations from 2000-2002, with the MOS and pn cameras, using full-frame mode and with various filters.

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XMM-Newton spectra of the X-ray background, showing relativistic iron lines

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