Mapping the star formation history of Mrk 86 II. Stellar populations and global interpretation

In this paper, continuation of Gil de Pat et al. (Paper I), we derive the m ain properties of the stellar populations in the Blue Compact Dwarf galaxy Mrk 86. Ages, stellar masses, metallicites and burst strengths have been ob tained using the combination of Monte Carlo simulations, a maximum likeliho od estimator and Cluster and Principal Component Analysis. The three stella r populations detected show well defined properties. We have studied the un derlying stellar population, which shows an age between 5-13 Gyr and no sig nificant color gradients. The intermediate aged (30 Myr old) central starbu rst show a very low dust extinction with high burst strength and high stell ar mass content (similar to 9x10(6) M-circle dot). Finally, the properties of 46 low-metallicity (similar to 1/10Z(circle dot)) star-forming regions w ere also studied. The properties derived suggest that the most recent star-forming activity i n Mrk 86 was triggered by the evolution of a superbubble originated at the central starburst by the energy deposition of stellar winds and supernova e xplosions. This superbubble produced the blowout of a fraction of the inter stellar medium at distances of about 1 kpc with high gas surface densities, leading to the activation of the star formation. Finally, different mechanisms for the star formation triggering in this mas sive central starburst are studied, including the merging with a low mass c ompanion and the interaction with UGC 4278. We have assumed a distance to M rk 86 of 6.9 Mpc.