Star-forming galaxies are surrounded by a multiphase, low-density gas component built by a combination of material accreting onto their disc from the intergalactic medium and gas expelled from their disc by supernova feedback. Studying this disc-halo interplay is important to understand how galaxies replenish their ‘fuel’ for star formation. In my research I have shown how the Milky Way is able to sustain its star formation by harvesting gas from its hot circumgalactic medium via the galactic fountain mechanism. This analysis was based on the modelling of the available emission and absorption-line data. We are currently working to extend this study to nearby disc galaxies from the HALOGAS HI Survey.
Galactic fountain: data vs models
Comparison between a representative HI channel map (v=-45 km/s) of the Milky Way and those predicted by our models (bottom panels). The models are, from the left: a thin disc model, a disc model plus a slow rotating and inflowing layer of extraplanar HI, a dynamical model of the galactic fountain without condensation of coronal gas, and the fountain model with condensation. The latter is in better agreement with the data (see regions A and B).
Extraplanar HI and galactic fountain
Comparison between the mass of extraplanar HI in late-type galaxies (from the HALOGAS survey) and that predicted by a simple model of supernova feedback-powered galactic fountain. The model matches the data remarkably well.
Galactic fountain in the Milky Way
Scheme of the galactic fountain framework: fountain clouds are ejected from the disc by stellar feedback and interact with the galactic hot corona, triggering its condensation and subsequent accretion. This process can be observed in emission (cold gas in the front and in condensing knots) and ionised absorption lines (in the warm-hot wakes).
Dark and luminous bars in APOSTLE
Dark matter halos can be significantly prolate at their centre, producing a bar-line morphology in the stellar component and strong non-circular motions in the gas. This is an example from the APOSTLE hydrodynamical simulations.
Environmental HI stripping in EAGLE
Stellar and HI morphology for satellite galaxies in the EAGLE simulations. The top row shows satellites affected by ram-pressure stripping processes, the middle row shows tidally stripped satellites, the bottom row shows satellite-satellite flybys. The magnitude of the three environmental effects increases from left to right.
Numerical simulations are powerful tools to study the physics of gas in galaxies. In my work I have used state-of-the art hydrodynamical simulations, both in a cosmological (EAGLE, APOSTLE) and in an isolated framework to study different aspects associated to the galactic HI physics, like how stellar feedback affects the kinematics and morphology of HI discs, how the HI kinematics of dwarf galaxies is influenced by the shape of their dark matter halo, and the mode by which the environment regulates the HI content of galaxies. All these studies were accompanied by a detailed comparison with the observations.
Galaxies obey to simple scaling laws that link their luminous mass to their rotational speed, specific angular momentum and dark matter content. These empirical kinematic scaling laws are particularly informative of the co-evolution between galaxies, their host dark matter halos and the material accreting from the intergalactic space. I have participated in several studies aimed at the characterisation and theoretical understanding of these scaling laws and their evolution with cosmic time.
Star formation efficiency in spirals
Star formation efficiency in late-type galaxies from the SPARC sample. Contrary to popular abundance matching models, the most massive spirals are the most efficient at forming stars and have virtually no missing baryons.
Fall relation at z=1
Stellar mass - specific angular momentum relation (or "Fall relation") for a sample of regularly rotating, main sequence galaxy at z=1. The data indicate that the Fall relation has not evolved from z=1 to z=0 (~8 Gyr).
SuperStar vs DAOPHOT
Comparing the performance of SuperStar and DAOPHOT on an artificial image (see text). Left panels: zoomed view on a corner of the synthetic image (on top), DAOPHOT residuals (middle) and SuperStar residuals (bottom). Right panels: photo and astro-metric precision as a function of the input stellar magnitude for the entire image.
Photometric and astrometric measurements on images from single and multi-conjugated adaptive optics suffer from the variability of the PSF in time and across the field of view. In collaboration with Prof. E. Tolstoy and Dr. D. Massari I am developing SuperStar, a new software for photo/astro-metric measurements in stellar fields. The software processes the image while iteratively building a grid of numerical PSFs using as an input the image itself.
Stay tuned for further updates...