SAMI - The Sydney-AAO Multi-object IFU

SAMI is an exciting new instrument borne of a fruitful collaboration between the Sydney Institute for Astronomy (SIfA) and the Australian Astronomical Observatory (AAO). SAMI is a multiplexed integral field instrument based on hexabundle technology.

Traditional astronomical spectrographs use a single slit or optical fibre to gather light from a single object. This means that an astronomer can measure only one spectrum from one object at a time. Some multiplexed instruments (such as 2dF) use many slits or fibres to measure the spectrum of many objects at once, greatly improving the efficiency of spectroscopic observations.

For spatially resolved objects, such as galaxies, an astronomer would often like to measure a spectrum at various different points on the object. It is possible to do this by stepping the single slit or fibre across the object of interest and measuring a spectrum at each position of interest. This technique has been used with some success but is very time consuming and prone to inaccuracies, especially when trying to study many objects in this way.

An integral field unit (or IFU) is a device that enables spectroscopy to be performed in a spatially resolved manner in one exposure, negating the need to step across the object. The SAMI IFUs are hexabundles – bundles of 61 optical fibres lightly fused together to form and imaging bundle with a high fill factor. Each of these 61 fibres can gather light from a different part of a galaxy. SAMI has 13 hexabundles, deployable over a wide (1 degree) field of view, each of which can simultaneously observe a different galaxy in the field.

The spatially resolved spectroscopy enabled by the SAMI instrument allows astronomers to measure a wide range of key physical parameters, such as dynamical mass, angular momentum, the location of star formation and many others. It also removes the biases inherent in single fibre studies of the same kind.

SAMI was built at the University of Sydney and the AAO and commissioned at the Anglo-Australian Telescope (AAT) in July 2011. The commissioning was a huge success with SAMI observing both stars and galaxies. The galaxy data was used to demonstrate that SAMI is capable of measuring internal kinematics of galaxies and resolving spatial variations in key diagnostic emission lines.

These results bode extremely well for the prospect of carrying out major new surveys with SAMI, potentially targeting thousands of galaxies with spatially resolved spectroscopy.


People

A/Prof. Scott Croom, Prof. Joss Bland-Hawthorn, Dr. Julia Bryant, Dr. Lisa Fogarty, Prof. Geraint Lewis, Mr. Sam Richards

Publications

  • Instrument Paper
  • Science Letter