Previous PhD OATs

Research Themes

Borsa 1
The impact of a variable Initial Mass Function on galaxy evolution

Supervisors:  F. Fontanot, G. De Lucia


Abstract: This PhD project is aimed at a detailed characterization of the impact of a variable Initial Mass Function (IMF) on the chemical and physical properties of galaxies. Different lines of evidence have recently suggested a non-universality of the IMF, with the strongest deviations found for the most massive early type galaxies (e.g. La Barbera et al. 2013, Cappellari et al. 2012). Results from different studies are often inconsistent, and the subject remain heavily debated in the community. The increase of available resolved dynamical information and high resolution spectroscopy is also making the subject of a variable IMF a
popular one. It is therefore timely to assess the theoretical expectations of such a scenario.
The recently developed GAEA model (Hirschmann, De Lucia & Fontanot 2016) represents an ideal tool to carry out this investigation, thanks to the improved modeling of chemical enrichment (which explicitly includes the differential contribution of SNeII, SNeIa and AGB stars) and stellar feedback (which allows us to reproduce the differential assembly of galaxy populations over cosmic epochs). In Fontanot et al. (2017, 2018), we have included in GAEA some of the proposed models for IMF variation (Weidner et al. 2013, and Papadopoulos et al., 2011), and analysed the basic predictions of these specific theories.
PhD fellowship outline The student will focus on three different aspects of the modeling:

  • Characterization of the properties of galaxy populations in the variable IMF theories.
    Moving from the basic predictions in Fontanot et al. (2017, 2018), we expect the student to study the physical properties, environment and star formation histories associated with different galaxy populations, and connect them with the observed evidences for a non-universal IMF. This analysis will allow us to get insight on the mechanisms determining the chemical and physical properties of model galaxies (and their redshift evolution). In this phase, the student will accustom with the GAEA code and its outputs.

  • Expand the range of tested theories for IMF variation. The modules currently available in GAEA represent just some of the possible approaches to IMF variation which have been proposed in the literature. We expect the student to implement new prescriptions, calibrate them and analyse their predictions, both in comparison with observed data and with previous models. The new prescriptions will allow us to study common trends among the proposed theories as well as to highlight possible discrepancies. In this phase, the student will need to modify the available semi-analytic model.

  • Quantitative comparison with observed samples. Many observational studies of IMF variations are based on detailed modelling of spectral indices sensitive to the dwarf to giant stars ratio (Conroy & van Dokkum 2012, La Barbera et al., 2013). By coupling our galaxy formation model with the latest generation population synthesis models, it will be possible to predict how the strength of these spectral features varies as a function of galaxy properties and as a function of e.g. the environment. This will allow a quantitative comparison with available data, as well as the possibility to formulate specific predictions for future observational programmes.


Borsa 2
Lo studente vincitore avrà facoltà di scegliere tra uno dei seguenti temi di ricerca

2.a - Rosetta data fusion

Supervisor:  M. Fulle

Context: Comets provide constraints on the first phases of the planetesimal growth in the protoplanetary discs, whose models are also being applied to the observations of exoplanets and ALMA protosolar nebulae. Refereed papers devoted to the Rosetta mission to the Jupiter Family Comet 67P/Churyumov-Gerasimenko (67P hereafter) are about one thousand, but most of them concern the analysis and models of data obtained by a single instrument. These data are in general affected by large uncertainties, which can be reduced and disentangled from bias by inter-instrumental comparisons. Up to now, it is hard to infer which processes drive the ejection of gas and refractories, and how the nucleus evolves both on short time scales (a single orbit) and on long ones (the typical nucleus lifetime lasting thousands of orbits). In particular, the Rosetta mission has pointed out the importance of fallout processes occurring at perihelion, in form of the heaviest aggregates ejected from the southern hemisphere, which require new models both to the inter-instrumental data analysis and to predict the past and future nucleus evolution.

Work Plan: Fallout processes point out the importance of feedback in models of 67P activity. All the physical processes at work on the nucleus surface are strongly linked. We list here the general topics, which will be necessarily faced at different levels of detail according to the specific task selected by the candidate.
1. Inter-instrumental analysis of the data on the 67P perihelion activity, done on available papers by comparing the obtained results to infer the nucleus parameter uncertainties and their bias:
   1a. Gas emission (ROSINA, MIRO, VIRTIS data)
   1b. Refractory emission (ROSINA, MIRO, VIRTIS, OSIRIS, GIADA, COSIMA data)
2. Models of perihelion activity:
   2a. Models of the nucleus structure.
   2b. Ejection of gas and of sub-millimeter dust.
   2c. Ejection of gas and of “chunks” (90% of the nucleus mass is ejected in form of ice and dust aggregates of bulk density of about 0.5 g/cc and of average mass of about 1 kg, named “chunks”).
   2d. Constraints on the nucleus properties derived from the perihelion activity (e.g. dust/ice ratio).
3. Fallout processes:
   3a. Injection of chunks in metastable orbits (rockets effects, gravity field and gas flux in non-spherical symmetry).
   3b. Frictions collapsing the bound orbits on the nucleus.
   3c. Fallout mass, its distribution on the nucleus, data comparison (images by ROLIS, OSIRIS).
4. Evolution of the 67P nucleus:
   4a. Perihelion erosion, mass transfer from south to north and/or big/small lobes.
   4b. Long term evolution of the nucleus shape and mass.
   4c. How activity is sustained (minimal ice content in the fallout consistent with continuing activity, both on short and long timescales).
   4d. Constraints on the nucleus homogeneity versus depth (CONSERT and RSI data).
   4e. Constraints on the models of nucleus accretion in a protoplanetary disc.

2.b - Atmospheric radiative transfer in climate models of habitable exoplanets

Supervisors:  G. Vladilo, M. Fulle

Description: Statistical surveys of exoplanets indicate that terrestrial-type, rocky planets are relatively frequent around late-type stars. Planets of this type will soon be discovered and characterized in relatively large numbers with cutting-edge instrumentation, such as ESPRESSO, in which INAF-OATs is involved both in technological and scientific areas. However, even with the most advanced instrumentation, the amount of experimental data for the newly detected rocky planets will be relatively scarce, and a significant effort of modelization will be required to cast light on their physical properties. The aim of the present PhD project is to model the surface physical conditions of these planets as an essential contribution to the study of their habitability. As a starting point, a climate model tailored for terrestrial-type exoplanets (ESTM) will be employed (Vladilo et al. 2013, 2015). The model has been developed at INAF-OATs in the framework of an ongoing collaboration with climatologists working at ISAC-CNR (Torino) and IGG-CNR (Pisa). The possibility of using ESTM for exploring the climate impact of a wide spectrum of planetary parameters has been demonstrated for the exoplanet Kepler- 452b (Silva et al. 2017). However, the atmospheric radiative transfer module currently used in ESTM does not have sufficient flexibility for simulating significant departures from Earth-like atmospheric conditions. The specific goal of this PhD project is to implement a radiative transfer module able to treat planetary atmospheres in a broad range of atmospheric pressure, chemical composition and stellar spectral distribution.
In particular, the plan is to incorporate the effect of Collision Induced Absorption, fundamental at high pressure, and an updated set of molecular cross-sections. As a subsequent step of the work, the radiative transfer module could be implemented in the global climate model of intermediate complexity PlaSim (Fraedrich et al. 2005 ), which provides the possibility to study tidally-locked exoplanets in the proximity of M-type stars. Other potential applications of the radiative transfer module include the modelization of the outer layers of Jupiter, taking advantage of upcoming data of the Juno mission.