Description
Organisers: Ellis Owen, Kinwah Wu
Energetic particles, particularly hadronic cosmic rays, represent a significant fraction of the energy budget in many galaxies. They can deposit substantial energy and momentum within galactic media, influence galactic outflows and the circulation of baryons, and alter the thermal properties of the interstellar medium, potentially regulating long-term galaxy evolution.
Recent theoretical and observational advancements have improved our understanding of the role energetic particles play in galaxy evolution. However, the full implications of their complex, multi-channel feedback mechanisms operating over many decades in energy and across the full hierarchy of galactic structures are yet to be fully understood.
Energetic non-photonic particles are generated by cosmic ray processes in galaxies. They directly carry information about these processes, which are not always accessible through traditional photonic observations. Adopting a multi-messenger approach can therefore reveal crucial new insights about how cosmic rays engage with galaxies. With an upcoming new generation of high-energy multi-messenger and multi-wavelength observatories and experiments, it is timely to discuss how observational strategies and theoretical approaches can be aligned to promote the development of a complete picture of cosmic ray effects in galactic ecosystems.
This session will review the current state of our understanding of cosmic ray processes in galaxies. It will explore on their role in galaxy evolution, promote synergies between photonic and non-photonic domains, and highlight emerging opportunities within the broader context of multi-messenger astronomy.
The composition of black hole jetsโwhether lepton-dominated or baryon-loadedโremains a longstanding open question, primarily due to the spectral degeneracy observed in high-energy emissions. We propose that extreme mass ratio (EMR) black hole binaries, particularly systems involving a secondary microquasar interacting periodically with the accretion flow of a primary supermassive black hole,...
A decade of gamma-ray observations from the Milky Way's centre has provided hints of the existence of a Galactic accelerator, the so-called PeVatron, capable of generating cosmic rays up to PeV energy scales. These hints are based on the observation of a gamma-ray energy spectrum from the dense gas clouds at the centre of our galaxy, which follow an energy spectrum with no detected cut-off up...
The Galactic Centre is a complex environment. It hosts many compact objects and the most massive clouds of molecular gas in our Galaxy. Neutral and charged pions are produced when cosmic rays from energetic sources collide with particles inside the molecular clouds. When the pions decay, the clouds glow in gamma-rays and neutrinos. Gamma-rays could be from other sources, but neutrinos are...
The microphysics of cosmic ray (CR) propagation in complex, magnetized interstellar media remains unsettled. CR pressure gradients can self-generate magneto-sonic turbulence, promoting diffusion, while ion-neutral damping in dense regions suppresses this turbulence, favoring ballistic transport. The interplay between these processes across the hierarchical structure of the interstellar medium...
Cosmic rays (CRs) influence the ionization, heating, and astrochemistry of interstellar molecular clouds. Their propagation through the complex structure of these clouds remains unsettled but appears to transition from diffusion in magnetized turbulent regions to ballistic streaming in dense cores. Efforts to characterize CR diffusion under varying physical conditions have produced a wide...
Recent observations indicate that galactic-scale bubbles are more prevalent than previously thought. Our Milky Way hosts the giant Fermi Bubbles, which are highly symmetric large gamma-ray structures emanating from the Galactic Centre and located both above and below the Galactic plane. The galaxy NGC 3079 also has galactic-scale bubbles, but they are considerably smaller than the Fermi...
Axions or axion-like particles (ALPs) are hypothetical particles predicted by various BSM theories, which also make one of the dark matter candidates. If ALPs exist in nature, the CMB photons as they pass through galaxy clusters will convert to ALPs (of mass range $10^{-14}$ to $10^{-11}$ eV), resulting in a polarized spectral distortion in the CMB. The probability of the resonant conversion...
Jets from active galactic nuclei (AGNs) are promising candidates for the acceleration of ultra-high-energy cosmic rays (UHECRs). If AGN jets are indeed dominant sources, the diffuse UHECR flux should trace the underlying jet power and, by extension, reflect the nature of supermassive black hole (SMBH) accretion states. In this work, we employ the cosmological semi-analytic framework JET (Jets...
Brightest cluster galaxies (BCGs) are among the most luminous and massive galaxies in the current epoch. They are expected to contribute to the cosmic ray population in galaxy clusters, yet past research on BCGs with the Fermi-LAT ฮณ-ray space telescope produced only upper limits, with a few exceptions. It is important to investigate this issue further to broaden the understanding of the...
Isolated stellar-mass black holes traversing dense regions of the interstellar medium, such as molecular clouds, are expected to accrete ambient gas. This accretion process can ionize surrounding gas, carving out a low-density ionized cavity within the cloud. The accreting black hole which possesses an accretion disc and a jet can further interacts with the cloud. Relativistic plasma from the...
Galaxies with high star-formation surface densities often host large-scale outflow winds. These winds have been observed in local starbursts, such as Arp 220 and M82. They are also widespread at high-redshifts, where galaxies are typically more compact and have higher star-formation rates relative to their stellar mass. Outflow winds play a critical role in redistributing energy, momentum,...
Rotational glitches can result from the angular momentum exchange between the curst and neutron star interiors. We study the dynamics of about 600 quantum vortices in a spinning-down two-dimensional neutron superfluid using the Gross-Pitaevskii model. For the first time, we find convincing spatial-temporal evidence of avalanching behaviour with about 10-20 vortices in each event resulting...
