Massive Star Formation and Feedback in Nearby Galaxies (#362)

Fatemeh Tabatabaei


Recent studies show the importance of the massive star formation feedback in
changing the energetic and structure of galaxies and evolution of star formation
with cosmic time.

Understanding the physics of the feedback is impossible neglecting the
environment where massive stars interact with, i.e., the ISM and its energetic
components, the magnetic fields and cosmic rays.

Full polarization radio continuum surveys provide ideal tracers of massive star
formation and feedback in galaxies. Using the SKA precursors, we have
investigated the effect of massive star formation on the ISM of nearby galaxies.
Our results show that massive star formation increases the energetics of the
cosmic ray population in a galaxy via supernova explosions and their strong
shocks. These particles could, in principle, lose their energy and being aged by
diffusion along the magnetic field lines in the ISM. However, this energy loss
is interrupted by irregularities in the field lines: In the turbulent magnetic
field, cosmic ray electrons can scatter perpendicular to the magnetic field
lines before losing their energy.

Besides injecting the cosmic rays, star forming regions are also strong sources
of the turbulent magnetic field imposing the cosmic rays to scatter off their
very many pitch angles. This causes a high-density concentration of high-energy
particles which may result in winds due to local pressure gradients. These winds
are powerful enough to re-distribute the gas in galaxies hampering or triggering
formation of new stars.

This founding/interpretation is independently confirmed by our GMRT observations
showing that clusters of massive stars are indeed strong sources of the
nonthermal synchrotron emission detected at meter-wavelengths.