An Active Galactic Nucleus (AGN) is the core of a galaxy powered by accretion onto a super-massive black hole (SMBH). The resulting energy output is distributed over a wide range of the electro-magnetic spectrum, from Radio to IR, UVup to X-ray and Gamma-Ray bands.
The team working on Active Galactic Nuclei (AGNs) at ESAC is extremely versatile on various aspects of AGN research.
In particular, even if individual members of the AGN group have specific interests, the team has the main focus on high-energy emission through the extensive use of the X-ray data collected by the XMM-Newton satellite.
We gather to discuss anything interesting about AGNs, i.e. new papers, technical issues, ongoing works, conferences, future visitors, observing proposals etc.
During the last 15 years members of the ESAC AGN group were always successful in proposing for observing time on XMM-Newton and other X-ray missions.
Currently active research topics are:
- reverberation mapping of the direct environment of the SMBH and high velocity outflows
The two main types of relativistic X-ray spectroscopy in AGN are X-ray reflection and ultra-fast outflows. In both cases, atomic lines from photoionised gas are red- and blueshifted because of the extreme velocities found in the vicinity of massive black holes.
Relativistic reflection produces photoionized emission lines from the accretion disk, which are broadened and shifted by the high velocities and strong gravity. This gives us a powerful probe of the close environment of the black hole, which can be used to measure the black hole spin and test accretion physics on the smallest scales. My measuring the delay between the primary emission and the reflection spectrum, we can measure the light-travel time around the inner accretion disk, essentially reverberation mapping the black hole system on the smallest possible scales.
Ultra-fast outflows are the highest velocity winds launched from accretion disks, with velocities between a few percent of the speed of light to around 30 to 40 percent. They extract a huge amount of power from accretion and transfer it to their host galaxies, potentially shutting off star-formation and regulating the growth of the galaxy. By detecting and studying these outflows we hope to understand how they are launched and the impact they can have over cosmological timescales.
Parker, M. L., et al., 2018, MNRAS.tmpL 98: Constraining the geometry of AGN outflows with reflection spectroscopy
Parker, M. L., et al., 2018, MNRAS 474, 1538: X-ray reflection from the inner disc of the AGN Ton S180
Parker, M. L., et al., 2018, MNRAS 474, 108: Using principal component analysis to understand the variability of PDS 456
Dauser, T., et al., 2012, MNRAS 422, 1914: Spectral analysis of 1H 0707-495 with XMM-Newton
- AGN in deep minimum states and bursting AGNs
The deep minimum state of AGNs is characterized by a strongly suppressed or even absent primary continuum. As the continuum disappears weak spectral features like relativistic iron lines or narrow soft X-ray emission lines from ionised plasmas become highly significant and their parameters can be determined. Therefore deep minimum states offer unique possibilities to investigate in detail the physics of the reprocessed components in AGN, including the immediate vicinity of the supermassive black hole. We have two TOO campaigns accepted which aim to observe deep minimum states in combination with quasi-simultaneous NuSTAR and HST observations.
XMM-Newton observations of Seyfert galaxies establish outbursts of radio quiet AGNs as a poorly explored discovery space for AGN physics with an enormous potential to learn. We have one TOO XMM-Newton/NuSTAR observations accepted which will be accompanied by SALT/HET optical spectroscopy of the next suited AGN outburst(s), triggered with XMM-Newton slews, Swift, Gaia and others. True AGN outbursts will allow us to trace accretion physics, X-ray spectral complexity connected with dramatic emission-line changes and possibly elusive stellar tidal disruption events probing an even more extreme accretion regime. With the detection of a new rare ``Changing Look AGN'' in July 2014 we demonstrated successful search strategy and organization of follow-up campaigns with broad wavelength coverage (Parker et al. 2016, MNRAS 461, 1927).
Parker, M. L. et al., 2016, MNRAS 461, 1927: The detection and X-ray view of the changing look AGN HE 1136-2304
Kollatschny, W., et al., 2016, A&A 585, 18: The peculiar optical-UV X-ray spectra of the X-ray weak quasar PG 0043+039
Kollatschny, W., et al., 2015, A&A 577, L1: Proving strong magnetic fields near to the central black hole in the quasar PG0043+039 via cyclotron lines
Parker, M. L. et al., 2014, MNRAS 445, 1039: A partial eclipse of the heart: the absorbed X-ray low state in Mrk 1048
- AGN at highest redshifts and SMBH seeds formation
The AGN group recently started research on AGN at highest redshifts and SMBH seeds formation.
With the paper "A Hubble Diagram for Quasars" Risaliti and Lusso (2015) established quasars as a kind of standard candles to measure cosmological parameters. This method is of utmost importance as it allows to measure the cosmological parameters for different redshift ranges and to test for an evolution of the parameters over cosmological time. We proposed successfully to observe quasars at a redshift higher than 5.6 (Banados et al., 2016) not yet observed in X-ray. The aim is to measure the cosmological parameters with high precision in the redshift range from 5.6 to 7.0 for the first time. This redshift range is not accessible with any other method, e.g. supernovae, clusters of galaxies, microwave back ground or baryon oscillation.
Super-massive black holes (SMBHs) at redshift z>7 pose a serious challenge to our understanding of black hole (BH) formation and evolution. Most likely SMBHs at high redshift require massive seed black holes (BHs) (10^5 solar masses) created in the gravitational collapse of large gas clouds with subsequent merging. We applied successfully to observe 5 extreme metal-poor blue compact dwarf galaxies, which are the best (local) laboratory for massive BH seed formation and star formation under low metallicity conditions.
Kalfountzou, E., Schartel, N., Maria Santos-Lleo M.: Quasars at Z>6.5 (in preparation)
- Dual AGN as probe of the galaxy merging process