Title: THE ROLE OF SHOCKS IN THE EMISSION OF THE SINGLY IONIZED CARBON  IN GALAXIES

SUMMARY:

The fine structure [CII] line at 157.7um is considered a good tracer of star formation because it is unaffected by dust attenuation and it is bright enough to be detected in high-z galaxies. This happens because the singly ionized carbon C+ collisionally excited by the surrounding neutral atomic and molecular hydrogen acts as the main coolant for the molecular clouds heated by young bright stars in galaxies. In this talk I will present a few cases of nearby galaxies where shocks are instead the reason for the [CII] emission. In particular I will talk about galaxies where jets from the central AGN affect the interstellar medium at great distance from the nucleus and about a few other cases where shocks from galaxy interactions are at the origin of a [CII] emission excess.

Cometary emission processes: fingerprints of their physical and chemical behavior

I will discuss key atomic and molecular processes in cometary atmospheres.  Like comets in our solar system, it will be difficult if not impossible to directly study the physical and chemical properties of comets around other stars. Instead, we have to infer these properties from the gas and dust surrounding them. Atomic and molecular reaction such as dissociation, ionization, and charge exchange both alter gases surrounding comets. Because many reactions result in the emission of light, they also offer insight into the composition and radiation environment exocomets are exposed to. In this presentation I will provide a broad review of radiative processes in cometary atmospheres, with a particular focus on spectral modeling, observational opportunities, and anticipated challenges in the interpretation of new observations, based on our current understanding of the atomic and molecular processes occurring in the atmospheres of small, icy bodies. Close to the surface, comet atmospheres form a thermalized atmosphere tracing the irregular shape of the nucleus. Gravity is too low to retain the gas, which flows out to form a large collisionless exosphere. As such, cometary comae represent conditions that are both familiar, as well as unattainable in laboratories on Earth, necessitating state-of-the-art theoretical treatments of the relevant microphysical processes. Radiative processes offer direct diagnostics of the local conditions, as well as the macroscopic coma properties. Finally, measurements of cometary compositions are uniquely valuable because they provide information on the formation and evolution of our solar system, but extracting chemical abundances from spectroscopic measurements of the coma requires detailed models that span a broad range of physical regimes (both macroscopic and microscopic).

Cometary emission processes: fingerprints of their physical and chemical behavior

I will discuss key atomic and molecular processes in cometary atmospheres.  Like comets in our solar system, it will be difficult if not impossible to directly study the physical and chemical properties of comets around other stars. Instead, we have to infer these properties from the gas and dust surrounding them. Atomic and molecular reaction such as dissociation, ionization, and charge exchange both alter gases surrounding comets. Because many reactions result in the emission of light, they also offer insight into the composition and radiation environment exocomets are exposed to. In this presentation I will provide a broad review of radiative processes in cometary atmospheres, with a particular focus on spectral modeling, observational opportunities, and anticipated challenges in the interpretation of new observations, based on our current understanding of the atomic and molecular processes occurring in the atmospheres of small, icy bodies. Close to the surface, comet atmospheres form a thermalized atmosphere tracing the irregular shape of the nucleus. Gravity is too low to retain the gas, which flows out to form a large collisionless exosphere. As such, cometary comae represent conditions that are both familiar, as well as unattainable in laboratories on Earth, necessitating state-of-the-art theoretical treatments of the relevant microphysical processes. Radiative processes offer direct diagnostics of the local conditions, as well as the macroscopic coma properties. Finally, measurements of cometary compositions are uniquely valuable because they provide information on the formation and evolution of our solar system, but extracting chemical abundances from spectroscopic measurements of the coma requires detailed models that span a broad range of physical regimes (both macroscopic and microscopic).

Black hole accretion flows: from nearby stellar binaries to quasars at cosmic dawn

Accretion onto black holes transforms the darkest objects in the universe into the brightest. I will review what we know about the emission from the accretion flow, starting with the stellar mass black holes in binary systems in our own galaxy. Scaling up to the supermassive black holes in active galaxies and quasars reveals both similarities and differences. One of the key similarities is the 'changing look' phenomena in active galaxies, where the UV continuum associated with an optically thick accretion flow drops over a few months/years, triggering the disappearance of the characteristic broad emission lines, analogous to the state transition in binaries. One of the key differences is the nature of the accretion flow above the transition luminosity, where the stellar mass black holes look like standard discs and have variability timescales like standard discs while the supermassive ones do not. Only at the highest luminosities (extreme narrow line Seyfert 1 galaxies and the weak line quasars) does the accretion flow match to the disc models. I will speculate on the physics underlying all the behavior, and give a united picture of the accretion flow.

Black hole accretion flows: from nearby stellar binaries to quasars at cosmic dawn

Accretion onto black holes transforms the darkest objects in the universe into the brightest. I will review what we know about the emission from the accretion flow, starting with the stellar mass black holes in binary systems in our own galaxy. Scaling up to the supermassive black holes in active galaxies and quasars reveals both similarities and differences. One of the key similarities is the 'changing look' phenomena in active galaxies, where the UV continuum associated with an optically thick accretion flow drops over a few months/years, triggering the disappearance of the characteristic broad emission lines, analogous to the state transition in binaries. One of the key differences is the nature of the accretion flow above the transition luminosity, where the stellar mass black holes look like standard discs and have variability timescales like standard discs while the supermassive ones do not. Only at the highest luminosities (extreme narrow line Seyfert 1 galaxies and the weak line quasars) does the accretion flow match to the disc models. I will speculate on the physics underlying all the behavior, and give a united picture of the accretion flow.