17/03/2004 – Auditório Principal Bloco G – IAG/USP

Msc. Claudio Melioli

IAG/USP

Título/Title: Recycling the ISM of SB galaxies: the SN heating efficiency paradigm and
the potential connection between SBs and AGN activity

Resumo/Abstract:

The interstellar medium heated by supernova explosions (SN) may acquire an expansion velocity larger than the escape velocity and leave the galaxy through a supersonic wind. Galactic winds are observed in many local starburst galaxies. SN ejecta are transported out of the galaxies by such winds, affecting the chemical evolution of the galaxies. The effectiveness of this process depends on the heating efficiency (HE) of the SNe, i.e. on the fraction of SN energy that is not radiated away. The value of HE, in particular in starburst (SB) galaxies, is a matter of debate.
We have constructed a simple semi-analytic model, considering the essential ingredients that are able to qualitatively trace the thermalisation history of the ISM in a SB region and determine the HE evolution. Our study has been accompanied by fully 3-D radiative cooling, hydrodynamical simulations of SNR-SNR and SNR-clouds interactions. We find that, as long as the typical time scale of mass-loss of the clouds, often dominated by photoevaporation, remains shorter than the time scale at which the SNRs interact to form a superbubble, the SN heating efficiency remains very small, as radiative cooling of the gas dominates. If there is a continuous production of clouds by the gas swept by the SNR shells, this occurs during the first ~ 16 Myrs of the SB activity (of ~ 30 Myrs), after which the efficiency rapidly increases to one, leading to a possible galactic wind formation. We conclude that the HE value has a time-dependent trend that is sensitive to the initial conditions of the system and cannot be simply assumed to be = 1, as in most SB galactic wind models.
Finally, we should notice that studies that search for a potential connection between SBs and AGN activity, that suggest that SBs at the nuclear regions of active galaxies could eventually trigger the development of a supermassive black hole (BH) in the center, may be favored by the results of the present analysis. The gas retained in the system may lead to new starbursts and increasing deposition of material in the centre of the SB, eventually feeding a BH.

 

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