Recent Talks

I will describe cosmological simulations of Axion-like Dark Matter, motivated by string theory, providing  a well motivated cold dark matter alternative to the standard heavy particle interpretation. Standing de-Broglie scale waves and other interference effects are predicted within galaxies that we test with QSO lensing, pulsar timing and via stellar dynamics. Galaxy formation is delayed in this context relative to LCDM and examined with deep Hubble imaging of the earliest known galaxies.

This fundamental question has challenged space scientists for decades. At temperatures of several million degrees, the corona is hundreds of times hotter than the solar surface, and heat cannot simply flow upward against the temperature gradient. (The same is true on other stars.) It is widely believed that the energy responsible for the extreme temperatures is extracted from stressed magnetic fields that permeate the corona. This likely occurs in the form of small impulsive energy bursts called nanoflares, but the details of how they work are still a matter of vigorous debate. Understanding these details is crucial, since the basic mechanisms are central to many phenomena--on the Sun, within the heliosphere, and throughout the universe. I will review our current understanding of the coronal heating problem from both the observational and theoretical perspectives.

Mechanical feedback by jets from Active Galactic Nucei (AGN) is a key process in galaxies and galaxy clusters: the energy input from the jets (in literature often addressed as radio-mode feedback) is crucial in determining the properties of the hot gas (especially in cool-core galaxy clusters), as well as inflating the large cavities we observe in the X-ray gas. The interaction of AGN outflows (both jets and radiation) with cold gas in galactic environment  (quasar-mode feedback) can instead impact the cosmic star formation rate, as well as power galaxy-wide atomic and molecular outflows. Finally, AGN can affect its own proximity, regulating central gas accretion and giving rise to (sometimes) self-sustained feeding/feedback cycles.

I will follow the interaction of AGN with intergalactic and interstellar gas from large to small scales (radio-mode) with the use of numerical simulations. As radio-mode feedback, I will discuss the properties and the energetics​ of the hot gas bubbles inflated by multiple jet events in a galaxy ​cluster, with the aid of synthetic but realistic X-ray observations. On galactic scales, I will discuss the mechanical coupling of jets and radiation with a clumpy galactic disc, show how AGN can trigger dense and fast outflows, and briefly describe the impact on galactic star formation.

I will finally discuss "backflows" --- i.e. galaxy-wide gas circulation patterns that "flow back" to the circum-nuclear region --- as a mechanism for AGN self-regulation. I will show, complementing the simulations with a small-scale analytical model, how backflows are able to convey large amounts of cold gas to the central region, that can boost the AGN power by even a factor of ten.

MOSAIC is the proposed visible and near-infrared multi-object spectrograph (MOS) for ESO’s forthcoming ELT.  The instrument is currently in the initial project stage known as Phase A. When operational MOSAIC will give the ELT the ability to obtain spectra for large samples of faint astronomical sources which are simply out of reach of ESO’s current facilities--from stars at the very heart of the Milky Way, out to the most distant galaxies at the edge of the observable Universe. I will discuss the top science cases for MOSAIC and identify the key technical requirements for each case. I will then present the instrument concept design and architecture that comply with these requirements, and will end by outlining the next steps for the project.

I will review my past and current research, mainly focussed on  the interactions between stellar dynamics, hot ISM, AGN feedback, black hole accretion in early-type galaxies. In particular, I have investigated the evolution of the X-ray hot halo and star formation in early type-galaxies, their correlation with galaxy shape and kinematics to explain the X-ray observed under-luminosity of flat objects and fast-rotators,their cold gas content and kinematics. Moreover I studied the effects due to AGN radiative and mechanical feedback, including positive feedback in a large sample of simulated ETGs, and the consequences of the BH sub-grid physics commonly employed in cosmological hydrodynamical simulations. Currently, I am mainly interested in both quasar and radio mode feedback and their effects on BH accretion rate and star formation. At the same time, I am working on the EAGLE and C-EAGLE simulations, studying the evolution of galaxy luminosity function with redshift. Due to large observational community at the Institute, future projects will involve the production of synthetic observations in different bands and spectral signatures from cosmological zoom-in simulations, in order to be compared with real observations.

The assembly history of the stellar halo of our Galaxy might be encoded in the kinematics, metallicities, ages and spatial distribution of the tidal streams, remnants of accreted galaxies. Globular clusters have also played an important role in the study of the processes that led to the formation of our Galaxy. Moreover, the dual Galactic globular cluster system is considered a manifestation of its hierarchical formation in the context of the Lambda-CDM scenario. Wide-field imaging and spectroscopy are crucial tools to unveil the remnants of their progenitor dwarf galaxies, already assimilated by the Milky Way. In this talk, I will summarize the evidence on the presence of accreted globulars in the Galactic halo, gathered during the last decades. I will also present our results probing that the surroundings of Galactic globular clusters are still one of the best places to detect and characterize tidal streams in the Milky Way halo.