Two starburst galaxies selected from our sample. Left: The Hammerhead Galaxy and Right: The Ring Galaxy

Starburst galaxies are forming stars at a prodigious rate, at least ten times the quiescent rate of normal galaxies like the Milky Way. In order to understand how galaxies evolve, it is important to study starburst galaxies, since we are catching them in the stages of violent evolution. It is thought that starbursts are the progenitors of the rare post-starburst galaxies – what are also known as “E+A” galaxies, because their spectra look like that of a dormant elliptical (E) galaxy, which has the spectrum of a young (A-type) population of stars superimposed upon it. From their spectra, we can deduce that they must have undergone a recent burst of star formation, which for some unknown reason has been truncated sharply in the recent past.

Mechanisms responsible for triggering the starburst and for the sharp cessation of the star formation are not well understood, although popular explanations suggest galaxy-galaxy interactions and interaction with the tenuous, hot intra-cluster medium may be responsible. We are attempting to further elucidate these possibilities by studying both the local and global environments starburst galaxies reside in. To do this, we have selected such a sample from the Two Degree Field Galaxy Redshift Survey (2dFGRS), which contains spectra for around 225,000 galaxies. By comparing the local and global environments of the galaxies in this sample to those of a “control” sample of randomly selected galaxies, we have found the distinguishing properties of starburst galaxies is that they have a near neighbour, but tend not to reside in dense global environments such as clusters of galaxies.

To further understand the mechanisms involved in triggering and truncating a starburst, we are also gathering information on the internal astrophysical state of such objects. Using the 2.3m telescope at Siding Spring Observatory, we are obtaining spatially resolved spectroscopy for a subset of our starburst galaxy sample. This will allow us to determine the internal kinematics and star formation “geography” of these galaxies, thereby providing important clues as to the traumatic events that took place which caused them to undergo this intense and short-lived episode of star formation.

Matt Owers and Warrick Couch