Project D

The mysterious [CII] emission in the interstellar medium of galaxies

Michele Ginolfi, Gergo Popping & Paola Andreani  

(email advisors)

Compile the largest dataset of [CII] observations in galaxies over the cosmic time, and discover new properties of the interstellar medium. Learn how to use ALMA, and get experienced with advanced statistical analyses.

To understand how galaxies evolve across the cosmic time, it is fundamental to study the properties of their interstellar medium (ISM), where many critical processes take place, like the formation of new stars in giant molecular clouds and the chemical enrichment of the gas. A common tool for studying the ISM is the transition of singly ionised carbon, [CII], at 158μm, a major coolant of the neutral atomic gas, and one of the brightest emission lines in nearby galaxies. Recently, ALMA, the most powerful (sub)millimeter telescope in the world, has pushed the exploration of [CII] up to the first billion years after the Big Bang, showing that [CII] can be used as a tracer of the ISM also in the early Universe.

In particular, the [CII] luminosity has been shown to correlate with (i) the rate at which new stars are formed and with (ii) the amount of molecular gas, both in local and distant galaxies, although the physical mechanisms that drive these empirical relations, as well as the exact origin of the [CII] emission itself, still remain unclear.

The aim of this project is to compile the largest dataset of [CII] observations, at any cosmic time and for any type of galaxy, combining existing samples with new/archival ALMA data, and complementing it with possible other measurements available for each object. Thus, we will explore the redshift evolution of the [CII]-based empirical relations and, through statistical techniques (e.g., principal component analysis, variables clustering etc) we will study their dependencies on other properties and physical quantities, like galaxy class, stellar mass and, when possible, metallicity, dust mass and fraction of molecular gas. The results will add precious information on the origin of [CII] and its link with galaxy properties, and will serve as a benchmark for modelling the ISM physics.

The student will have the opportunity to mine the ALMA archive, experience the handling of ALMA data, learn useful statistical tools and get some knowledge of the ISM physics and galaxy evolution.

#galaxies #gas #interstellar-medium #emission-lines #[CII] #ALMA #python #statistics

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