Thursday, June 23, 2011

Spectrum of a Active Brightest Cluster Galaxy

Our next guest post is from Dr. Ilani Loubser from North-West University in Potchefstroom, South Africa. If you are interested in collaborating on this work, please feel free to contact her at

This low resolution (pg0900 grating) spectrum was extracted from one 900 sec (major axis) exposure of a z ~ 0.05 Brightest Cluster Galaxy. This spectrum shows the area to the left of the first chip gap - and nicely illustrates SALT's efficiency in the blue! The higher order Balmer lines, as well as the diffuse weak emission lines, can clearly be identified.

This spectrum was taken as part of a program to probe activity in the most massive of elliptical galaxies – Brightest Cluster Galaxies (PI Ilani Loubser). They are believed to be sites of very interesting evolutionary phenomena (e.g. dynamical friction, galactic cannibalism, cooling flows), and may well require there to have been a special process of formation. These galaxies are normally assumed to be red and dead. However, several examples of ongoing star formation in BCGs, in particular those hosted by cooling-flow clusters, have been reported. The origin of the gas fuelling this star formation is still a mystery, and the possible explanations include processes involving cooling flows or cold gas deposited during a merging event. These BCGs often host radio-loud AGN, and can also help us to understand the role of feedback and gas accretion in galaxy and cluster evolution.

These spectra will now be analysed by extracting the underlying stellar absorption components and measuring the weak emission lines from the hot, ionised gas. The emission lines can then be analysed to determine whether they originated from AGN/Liner activity or star formation, and will be correlated to the host cluster properties (e.g. cooling flows) determined from existing X-ray data. In combination with other multi-wavelength data, the origin of the gas fuelling the star formation can then be determined.

1 comment:

  1. What a great idea to have guest posters. Super way to get exposure.