Of all the alternatives presented above, none is simpler than our scenario for the formation of the nearby SBNGs. It has many advantages: it explains the origin of the bursts in these galaxies (the galaxies are in a burst phase because they are still forming), and it fits their star formation history (Coziol 1996), their chemical evolution (Coziol et al. 1998; 1999) and the properties of their bars (Considère et al. 2000).
According to this scenario, bulges of galaxies form first and the disks form later mostly through gas accretion. It predicts that young galaxies initially look like unbarred early-type spirals with small disks. Then, as the disk grows, they change into late-type and giant barred spiral galaxies (Kauffmann et al. 1993; Baugh et al. 1996; Andredakis 1998). This transformation may explain why Markarian starburst galaxies are so frequent among Sa and Sb galaxies (see Fig. 1). The fact that we do not see many Sc galaxies in the sample of Markarian starburst galaxies suggests that these galaxies forms differently (Andredakis 1998).
© European Southern Observatory (ESO) 2000
Online publication: March 28, 2000