טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentAvishai Gilkis
SubjectHeating of the ICM by Jets through Mixing and Inflation of
Bubbles
DepartmentDepartment of Physics
Supervisor Full Professor Soker Noam
Full Thesis textFull thesis text - English Version


Abstract

The radiative cooling time of the intra cluster medium (ICM) at the centers of many galaxy clusters is much shorter than their ages. Therefore, the ICM hot atmospheres are expected to cool, flow inward, and to form stars. This process is termed a cooling flow. Cold gas and star formation are observed in central cluster galaxies but at levels below those expected from an unimpeded cooling flow. It is widely accepted that a negative feedback heating mechanism offsets cooling to some degree, but the exact details remain unclear. By simulating jet-inflated bubbles in cooling flows with the PLUTO hydrodynamic code I show that mixing of high entropy shocked jet's material with the ICM is the major heating process along, as well as perpendicular to, the jets' axis. Heating by the forward shock is not significant. The mixing is very efficient in heating the ICM in all directions, to distances of 10 kpc and more. Although the jets in my simulations are active for a time period of only 20 Myr, the mixing and heating near the equatorial plane, as well as along the symmetry axis, continue to counter radiative cooling for times of more than 100 Myr after the jets have ceased to exist. I discuss some possible implications of the results. (i) The vigorous mixing is expected to entangle magnetic field lines, hence to suppress any global heat conduction in the ICM near the center. (ii) The vigorous mixing forms multi-phase ICM in the inner cluster regions, where the coolest parcels of gas will eventually cool first, flow inward, and feed the active galactic nucleus to set the next jet-activity episode. This further supports the cold feedback mechanism. (iii) In cases where the medium outside the inner region is not as dense as in groups and clusters of galaxies, like during the process of galaxy formation, the forward shock and the high pressure of the shocked jets' material might expel gas from the system.