Session:- SMBHs- growth and feedback
Theoretical and observational studies of astrophysical black holes have been in rapid development in recent decades. This conference will present major breakthroughs and key remaining questions concerning our fundamental understanding of astrophysical black holes, such as the formation and collimation of relativistic jets, the accretion and growth of black holes, the measurement of black hole spin, the merger of black holes, the first images of black hole shadow, the particle acceleration mechanisms and transient phenomena around black holes, and the feedback from massive black holes to galaxies.
◎Black holes regulate cold gas accretion in massive galaxies
Nearly every massive galaxy contains a supermassive Black Hole(BH) in their centers. For decades, both theories and numerical simulations suggest a central role of BHs in regulating the growth of galaxies. In particular, BH feedback through heating or blowing up the InterStellar Medium(ISM) serves as the foundation for current models of massive galaxy formation. However, direct evidence for such an impact on the galaxy-wide ISM from BHs has only been found for some most extreme objects. For general galaxy populations, it remains unclear on how BHs affect the ISM. Here based on a large sample of nearby galaxies with measurements of both BH mass and atomic hydrogen, the major component of cold ISM, the team of the speaker reveal that the atomic hydrogen content (fHI=MHI/M⋆) is tightly and inversely correlated with BH masses with fHI∝M−α,BH (α∼0.6), which is valid across five orders of magnitude in BH masses. Once this correlation is accounted for, fHI loses dependence on other galactic parameters, indicating that BHs masses serve as the primary driver of fHI. This result provides critical evidence on how the accumulated energy from BH accretion affects the surrounding ISM, which marks an important step forward in our understanding on the central role of BHs in regulating the growth and quenching of galaxies.
講者：Prof. Tao Wang (Nanjing University)
◎Active Galactic Nuclei Feedback : From Cosmological Simulation to Observation
Observations suggest that feedback from Active Galactic Nuclei(AGN) plays important role in the evolution of large scale structures of the universe. However, the exact physics of coupling the feedback energy to their surrounding medium is still not well understood. In this talk the spekaer will try to explain their work to investigate different modes of AGN feedback and their effects on the surrounding gas as well as host galaxies and dark matter halos by analysing diffuse X-ray emission from galaxy groups and clusters. Starting with careful investigation of different scaling relations between Super-Massive Black Holes(SMBH) and host halo properties using cosmological simulation, the team continues to model X-ray emission from simulated galaxy clusters with the help of Astrophysical Plasma Emission Code(APEC). Finally, they perform synthetic observation of Chandra X-ray telescope of these systems using ray-tracing simulator Model of AXAF Response to X-rays(MARX) to compare them with actual observations. Their results conclusively establish the impact of AGN feedback on their ambient medium. Besides, they show the importance of jet and X-ray mode of AGN feedback together with their detection probability at different redshifts with Chandra and propose to continue the search with upcoming X-ray missions such as Athena and XRISM
講者：Dr Rudrani Kar Chowdhury (Postdoctoral Fellow)
◎Pathway to high-z SMBHs: seed formation and growth in the statistical perspective
The early evolution of the Black Hole Mass Function(BHMF) and Quasar Luminosity Function(QLF) encodes key information on the physics determining the radiative and accretion processes of Black Holes(BHs) growing in high-redshift galaxies. Starting from the formation of seed BHs as their parent halos evolve, the speaker and her team study primordial gas collapse in the biased quasar host halos, computing gas chemical and thermal evolution, environmental UV radiation, and merger heating following halo merger trees. As gas collapses, the accretion rate onto a newly-born protostar ranges between 0.003-5 Msun/yr, leading to a top-heavy seed BH mass distribution ranging from several hundred to above 10⁵ solar mass. They then construct a theoretical BH growth model via multiple accretion bursts constrained by z~6 QLF and BHMF observations. In a statistical way, they predict that in every active episode, BHs grow with an Eddington ratio distribution function following the Schechter shape. Imposing a luminosity limit of quasar surveys, they find that the observed Eddington-ratio distribution function is skewed to a log-normal shape, preferentially selecting more active quasars. The predicted redshift evolution of the QLF and BHMF suggests a rapid decay of their number and mass density in a cosmic volume toward z>6. JWST and future devices will push BH observations to mass ranges lower than typical high-redshift quasars, and help explore the growth history of BHs in the early universe and the establishment of BH-galaxy coevolution.
講者：Li Wenxiu (KIAA, PKU)
◎Supercritical growth of seed BHs at cosmic dawn and co-evolution with host galaxies
Supercritical growth of massive/stellar mass seed BHs at high-z universe is believed to be one of the possible solutions to grow the observed SuperMassive Black Holes(SMBHs) at z~6. The speaker and his team study the long-term evolution of the global structure of axisymmetric accretion flows onto a Black Hole(BH) at rates substantially higher than the Eddington value, performing two-dimensional Radiation HydroDynamical(RHD) simulations. In the high-accretion optically thick limit, where radiation energy is efficiently trapped within the inflow, the accretion flow becomes adiabatic and comprises of turbulent gas in the equatorial region and strong bipolar outflows. As a result, the mass inflow rate decreases towards the center as a power law relation and only a small fraction of inflow gas feeds the nuclear BH. Energy transport via radiative diffusion accelerates the outflow near the poles in the inner region but does not affect the overall properties of accretion flow. Based on their simulation results, they provide a mechanical feedback model for super-Eddington accreting BHs, which can be applied to large-scale simulations that hardly resolve galactic nuclei. They applied the feedback model to the assembly of first massive BHs observed in high-redshift quasars and find that the existence of strong outflows can suppress the BH growth, while moderate outflows can coordinate the early BH-galaxy co-evolution.
講者：HU, Haojie (KIAA/DoA, Peking University)
◎Density profile of the ambient circumnuclear medium in Seyfert 1 radio-quiet galaxies
The shape of the Ambient Circumnuclear Medium(ACM) density profile can probe the history of accretion onto the central supermassive black holes in galaxies and circumnuclear environment. However, due to the limitations of instrument resolution, the density profile of the ACM for most galaxies remain largely unknown. Here the team proposes a novel method to measure the ACM density profile of Active Galactic Nuclei(AGNs) by the equilibrium between the radiation pressure on the warm absorbers (WAs, a type of AGN outflow) and the drag pressure from the ACM. They study the correlation between the outflow velocity and ionization parameter of WAs in each of the five Seyfert 1 radio-quiet galaxies, inferring that the index of ACM density profile is between -1.7 and -2.15 from 0.01 to 1 parsec scale. Their results indicate that the ACM density profile in these five Seyfert 1 radio-quiet galaxies is consistent with the prediction by the standard thin-disk model, and steeper than the prediction by the spherically symmetric Bondi accretion model and simulated results of the host accretion model.
講者：Dr Yijun Wang 王倚君 博士 (Nanjing University)
地點：香港大學 百週年校園 CPD 3.04 Centennial Campus