Circumgalactic Medium, Interstellar Medium and Free-Free Radiation - Astrophysics

Research Project - Institute for Particle Physics and Astrophysics, ETH Zürich

Prof. Sebastiano Cantalupo and Dr. Gabriele Pezzulli

Motivation:

Study of the impact on the ionisation state of the Circumgalactic Medium of the free-free radiation (Bremmstrahlung) produced by the hot phase of the Interstellar Medium

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We gained an understanding of the rate of energy emission from an electron of some velocity v, more precisely of the emissivity (the rate of radiation energy per time, per volume, per photon solid angle and per photon frequency interval) expressed as a ’classical’ formula times a ’quantum correction’ to the classical formula (justified in some regimes) known as the (free-free) Gaunt factor. The idea stemmed from one of the latest S. Weinberg’s paper where he proposed a more generalised formula (simple and analytical) of the Gaunt factor and analysed how it behaves in different regimes (defined for different photon frequencies and electron velocities) and whether it reduces to the analytical formulas (and approximations) which have been known and used so far. In fact, one of the formulas had been widely misused given the more stringent validity conditions than previously thought. However, this issue can be numerically bypassed using a set of more complicated numerical formulas (in terms of confluent hypergeometric functions), which have been implemented in the spectral synthesis code called Cloudy (for simulating conditions in interstellar matter), and which I worked with to investigate the impact of the free-free radiation on the ionisation state of the circumgalactic medium (CGM), when the hot phase of the interstellar gas produces the soft free-free radiation.

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More on the topic concerning the 'Soft Bremsstrahlung" :

https://inspirehep.net/files/fd5a27130a065483b0e9704d898d0137 The Cloudy code to simulate conditions in interstellar matter:

https://trac.nublado.org/