Letters of Intent received in 2016

LoI 2018-1914
NON-GA SYMPOSIUM - Perseus in Sicily: from black hole to cluster outskirts

Topics

Black Hole:
- approaching the Schwarzschild radius (mass, spin, magnetosphere)
- methods to measure BH mass and spin
- sphere of gravitational influence
- BH-galaxy coevolution
Accretion:
- Hot accretion, cold accretion
- RIAF vs. REAF
- role of B-field
Outflow:
- Production mechanism
- collimation and acceleration
- role of B-field
- structures in the jet: radial vs transverse, winds
High energy emission:
- site of HE emission
- leptonic vs. hadronic processes
- particle acceleration
Feedback:
- jet-ISM interaction
- cavities (jet-hot gas interaction)
- heating and cooling
- radio source evolution

Rationale

The inflow and outflow processes associated to supermassive black holes (SMBH) constitute a complex system. The astrophysical environments associated to this complex system are varied and span linear scales from AU to Mpc. The SMBH located at the center of active galaxies efficiently releases the gravitational energy of the intergalactic- and interstellar-medium accreting onto it. The gravitational energy is converted and released in different forms, including kinematic energy of relativistic outflows, magnetosphere of the accretion flow and/or rotational energy of the black hole itself. The outflows form in the vicinity of the SMBH and propagate up to galaxy cluster scale, interacting with the interstellar and intergalactic medium. The relativistic outflows completely dissipate, and it results in the radio bubbles/cavities in the intergalactic hot plasma. Mass circulates between intergalactic and Schwarzschild radius scale through those process, and it influences the galaxy and galaxy cluster evolution in a process known as feedback.

The Perseus cluster is an outstanding example of such systems, as it contains prominent examples of each one of the key ingredients associated with SMBH activity. For the past decade, Perseus A has been showing a dramatic increase in radio flux density, which is now approaching its historical maximum. This active state coincides with the formation of compact radio lobes in the central parsec, which provides a wealth of information on the interaction between the jet and ISM deep within the host galaxy; the jet morphology on parsec scales has at the same time evolved from centrally- to limb-brightened. Extensive monitoring in space by Fermi-LAT and by imaging Cherenkov arrays from ground has detected and characterised Per A at high and very high gamma-ray energy. Serendipitously, it has led to the discovery of extremely short time scale activity in the other Perseus galaxy IC 310. On larger angular scales, deep X-ray observations have provided a wealth of information on the properties of the intracluster gas and of its interaction with the relativistic plasma ejected from the SMBH (bubbles/cavities interaction). Finally, Hitomi surprisingly revealed the evidence of very small amounts of turbulence, which poses a new interesting and difficult question how to sustain the hot gas at the center of the Perseus cluster. Therefore, the Perseus cluster can be considered as the perfect testbed to investigate all aspects associated with black hole inflow/outflow system. A high-level understanding of the inflow/outflow system in this source will be beneficial to address those long-standing questions.

The aim of this symposium is to bring together experts in several fields, including observations, theory and numerical simulations, in a very special time for both the source activity state and richness in observational datasets: 

- Observers from radio through optical and X-ray to very high energy gamma rays will report on the most recent highlights. Space- and mm-VLBI observations provide angular resolution down to few tens of Schwarzschild radii. The spectral and variability properties at high and very high energy (including those of IC 310) will address further more on the origin of the high energy emission. At intermediate wavelength, there will be developments thanks to new techniques to estimate the black hole mass of nearby galaxies based on cold and hot gas dynamics by ALMA and optical observations. Those new observation on gas will also probe interaction of outflow and ISM, and will address the star formation efficiency. The physics of the intracluster medium based on the X-ray results on the large-scale structure will be revisited, including the legacy observation from Hitomi. 

- Theorists will report on the framework for hot and cold mass accretion process on to the SMBH, particle acceleration, jet composition and acceleration, with particular emphasis on the jet launching mechanism, the role of the magnetic field, the mass accretion process within the sphere of the gravitational influence of the SMBH.   Numerical simulation with large computation time based on GR- and SR- MHD from 1 to 10^6-8 Schwarzschild radius scale are awaited to address on the interactions of inflow and outflow in self-consistent manner.

The proposed host city for the symposium is Noto, in the province of Siracusa of the mediterranean island of Sicily (Italy). Noto is the site of a 32m radio telescope that operates as an element of several VLBI arrays. In particular, the Noto radio telescope is the southernmost station of the European VLBI Network and it has participated in the space VLBI observations that allowed the highest angular resolution images of the black hole vicinity in PerA. Moreover, Noto is one of the “Late Baroque Towns of the Val di Noto" listed in the UNESCO world heritage list. It is a beautiful city, with nice weather, excellent food, and unique hospitality. It is served by Catania Fontanarossa international airport. The Noto radio telescope is operated by INAF Istituto di Radioastronomia, a historical institution of Italian astronomy, with a long tradition in the organisation of conferences and workshops, including IAU Symposia IAUS 100 (VLBI and Compact Radio Sources, as early as 1983) and IAUS 175 (Extragalactic Radio Sources, in 1995).