Mass-loss, episodic star formation and the HI envelope of blue compact dwarfs

Abstract

The star formation history of a class of dwarf galaxies like BCDs (blue compact dwarfs) is episodic and/or intermit- tent. Episodic star formation is theoretically supported by the limit-cycle model of the interstellar medium (ISM). This model describes the cyclic change among some components of the multi-phased ISM and the total mass of the ISM is conserved. However, the gravitational potential of dwarfs is very shallow. Then, the effect of mass-loss from dwarfs should be examined to investigate the limit-cycle of the ISM. In this paper, we study how the limit-cycle is affected by mass-loss. According to our results, when the time-scale of mass-loss is comparable to the covering time-scale of supernova remnants over a dwarf, the limit-cycle is delayed and an episodic star-formation history is inhibited. Inversely, if the mass-loss is gradual, our model predicts an HI-rich ISM and possible episodic star formation. This prediction is consistent with the typical images of BCDs which are composed of a large amount of HI and on-going star forming regions.