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ERC

FEEDBACK Report Summary

Project ID: 340442
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Mid-Term Report Summary - FEEDBACK (ACCRETING BLACK HOLES AND COSMIC FEEDBACK)

The FEEDBACK group have published well over 100 papers in refereed journals resulting from work funded by the ERC Advanced Grant. Our work ranges over all aspects of AGN Feedback from how AGN (Active Galactic Nuclei) work, how energy is transferred to the host galaxy, to the effects on that galaxy and its environment, particularly in cluster and groups of galaxies.

We have studied X-ray reflection and reverberation in accreting black holes ranging from stellar mass binaries to supermassive AGN, using XMM and NUSTAR. This enables us to map the innermost regions around the black hole and in some cases determine the spin of the black hole. Many of the AGN studied appear to have high spin. This may be due to a selection effect caused by the higher radiative efficiency of accretion onto high spin black holes. The brightest objects in the Sky, which tend to be the ones studied, are then more likely to be the more highly spinning ones.

The temperature of the X-ray emitting corona is made accessible now by NUSTAR observations and detailed spectral modelling of the reflection component. We have shown that pair production may be responsible for the temperature distribution in sources, with the more compact ones having the lower temperatures

We have also looked at disk winds and outflows from black holes in X-ray binaries. The most striking outflows that we have discovered are in UltraLuminous X-ray Sources (ULXs). These sources typically have luminosities of a few times 1e40 erg/s, which is at least ten times more than the Eddington limit of a 10 Solar mass black hole. Our work with the XMM Reflection Grating Spectrometer (RGS) observations of several bright ULXs has revealed, for the first time, spectral emission lines from matter at rest together with absorption troughs due to high velocity (0.2c) outflowing gas. The implication is that these objects are most plausibly stellar mass black holes accreting at Super-Eddington rates. The power in the wind is very high and they may be nearby, low- mass examples showing how early quasars grow and feedback energy at high redshifts.

Radiation pressure on dust grains is a possible way to clear gas out of a galaxy with an active nucleus. The process has been considered in the case in which the matter is initially optically thick, leading to a considerable boost in energy and momentum.

How black holes at the centres of massive black holes accrete has been explored with Chandra X-ray observations of M87 in the Virgo cluster and HST narrow--band imaging of NGC4696 in the Centaurus cluster. In the latter case we see Halpha emission in a marked swirl around the Bondi accretion radius. We have also continued to make and analyse deep X-ray images of clusters, with the Centaurus cluster being a recent example. An edge detection algorithm has been applied to such images, revealing for the first time detail which had not been recognised hitherto.

The XMM RGS has been used to search spectroscopically for low temperature components in cool core clusters and groups. We found OVII emission characteristic of gas just above one million K in several objects. This has been modelled with OVI and FeXVII emission to show that the gas is complex and multiphase.

The Japanese-US observatory Hitomi was launched in February 2016 and operated for 5 weeks before breaking up. During that time its Soft X-ray Spectrometer observed the Perseus cluster with an unprecedented spectral resolution of 5eV. The turbulent velocities in the hot intracluster were measured to a precision of 10 km/s. The analysis and resulting Nature paper from these data was led by Fabian. It shows that the measured turbulence of 164 km/s is too low to explain AGN feedback in the cluster core. Sounds waves, as suggested by us 13 years ago, have been reconsidered as the energy transfer mechanism.

One goal of the work has changed, following the loss of the Hitomi spacecraft. Postdoc Dr Ciro Pinto who, with the PI AC Fabian, was a member of the Hitomi Science Team, worked in Japan and later in Cambridge on the Hitomi Science paper, published in Nature, on the Perseus cluster. Ciro is also collaborating on several further papers expected from the small amount of Hitomi data gathered before the spacecraft was lost.

Ciro is an expert on high resolution spectroscopy and has shifted his research from Hitomi back to the XMM Reflection Grating Spectrometer, working on feedback in galaxy cluster cores and on luminous accreting black holes. He is very successful and has discovered ultrafast outflows from several UltraLuminous X-ray sources (ULXs), also now published in Nature. These objects are accreting above the Eddington Limit and the results are relevant to considerations of feedback from early quasars, which may also have accreted in this way.

Reported by

THE CHANCELLOR, MASTERS AND SCHOLARS OF THE UNIVERSITY OF CAMBRIDGE
United Kingdom
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