Galaxies: Starburst Galaxies

M82 is the prototypical starburst galaxy. There has been a recent massive burst of star-formation in the heart of the galaxy. The combined action of supersonic winds and supernovae leads to the formation of a hot, X-ray emitting superbubble. This bubble expands and eventually breaks out of the galaxy to give rise to a spectacular bipolar superwind. In this picture X-ray contours are superimposed on an optical picture of M82, showing how the superwind has burst out of the galaxy perpendicular to the galactic plane.

Starburst galaxies are common throughout the Universe, and are the seats of massive bursts of star-formation that can dramatically alter the structure of the host galaxy and input large amounts of energy and mass into the intergalactic medium via a superwind. Understanding this feedback mechanism, particularly at high redshifts, is a key topic in understanding the structure and development of the Universe. With the recent launch of both the Chandra and XMM X-ray observatories we are studying the properties of starbursts and superwinds in a range of nearby galaxies, at X-ray, optical and radio wavelengths.

Research in this area at Birmingham includes:

• The X-ray emission properties of M82 and other starburst galaxies with superwinds. Density and temperature profiles can be derived through the wind, allowing estimates of mass and energy loss rates to be derived.  New data from the XMM-Newton and Chandra X-ray observatories will greatly advance our capabilities in this area. The observed properties can also be compared with the results of hydrodynamic modelling to explore the physical properties of starbursts and winds. 
  
  
• The study of Wolf-Rayet galaxies - a class of very young starbursts containing large populations of massive Wolf-Rayet stars. Here one is observing the very earliest stages of the evolution of starbursts, in which a superbubble is expanding around the star-clusters. We can examine the spatial and spectral properties of the X-ray emission, and are performing a survey of nearby systems.
  
  
• Merging galaxies, such as the Antennae, can be the sites of spectacular starbursts. Simulations suggest that the end product of a spiral-spiral merger should be an elliptical galaxy, and it may be that the entire interstellar medium in the spirals is heated and ejected during this process. We have scheduled observations of a sequence of merging and post-merger galaxies with both XMM and Chandra to explore the evolution of the hot gas through the merger process.
  
  
• We are also studying super-star clusters (SSCs) both in our own neighbourhood (objects such NGC3603 and 30 Doradus) and in external galaxies (such as in dwarf starbursts like NGC1569 and NGC5253). SSCs are very massive and dense clusters of stars - possibly 1 million solar masses in a cluster only a few pc in diameter, and are very common in starburst galaxies.