Relation Between BCDS and Blue LSBGS

Extract

Two important questions are connected to the evolutionary history of blue compact dwarf galaxies (BCDs): the triggering mechanism of the starburst and the properties of the precursor(s) and successor. The halos of many BCDs show red colours indicating that the host galaxy is in fact of early type. But where did the gas come from? Was it there from the start in a quiescent mode or was it fed by a merger with an intergalactic gas cloud or a gas-rich dwarf? Is there a general answer to this question or are there different families of BCDs?

The BCDs generating most of the interest are those with low chemical abundances, typically 10% solar. The only plausible precursors in this case are metal-poor dis, LSBGs or pure HI clouds (e.g. Thuan & Seitzer 197, ApJ 231, 680). In a comparison between LSBGs and BCDs Taylor et al. (e.g. 1997, ApJ 480, 524; 1996, ApJS 107, 143) found an excess of HI rich companions in the environments of BCDs which they interpret as a support of tidal triggering. We have studied a few massive (~ 10⁹ M _ʘ ) metal- poor blue compact galaxies (BCGs). These are too bright to be classified as dwarfs but define an extension of the BCD family. For simplicity we will in the following use the common abbrevation BCD. In a search for possible precursors we have studied a sample of blue LSBGs with metallicities similar to BCDs (5-15%).