Fifth Workshop on Millimetre Astronomy in Italy

Giovanni Sabatini - First ALMA maps of cosmic ray ionization rate in high-mass star-forming regions

13 Jun 2023, 12:25

20m

Milky Way

Description

Low-energy cosmic rays (<1 TeV) are a pivotal source of ionisation of the interstellar medium, where they play a central role in determining the chemical gas composition and, in turn, in influencing the formation of stars and planets. Observations of H${}_3^{+}$ absorption lines in diffuse clouds -- n(H${}_2$)~10${}^2$ cm${}^{-3}$ -- have been used for decades to provide reliable estimates of the cosmic ray ionisation rate relative to molecular hydrogen (ζ${}_{H2}$). However, in denser clouds where stars and planets form, this method is often inefficient since H${}_3^{+}$, similar to H${}_2$, does not emit rotational lines as it does not have a permanent electric dipole. The ζ${}_{H2}$ estimates are, therefore, still provisional in this context, and represent one of the least understood ingredients when it comes to defining general models of star formation. Recently, a new analytical approach to estimate ζ${}_{H2}$ in the densest regions of molecular clouds has been proposed by Bovino et al. (2020), based on observations of ortho-H${}_2$D${}^{+}$ as the main observational constraint to derive the amount of H${}_3^{+}$. This has been applied by Sabatini et al. (2020) in a large sample of high-mass star-forming regions. Exploiting the exceptional observational capabilities of ALMA, in this talk I will present the first high-resolution maps of ζ${}_{H2}$ in two massive clumps. I will present these results and the way they provide crucial constraints for the chemical/physical modelling of star-forming regions.

Presentation materials

CRIR_Sabatini_Bologna23.pdf