SAMI finds windy galaxy using spatially resolved optical spectra
SAMI, the Sydney-AAO Multi-object Integral Field Spectrograph, is a new instrument mounted on the Anglo-Australian Telescope and the first spectrograph to use hexabundles. A hexabundle is the extension of a technology that takes the light from a large optical telescope at a particular point in the focal plane and directs it down an optical fibre to a detector, such as a spectrograph. Instead of single optical fibres, hexabundles use multiple fibres fused together to cover a larger area than possible with a single fibre, allowing the spectra of extended objects to be studied efficiently and in detail. Each of SAMI’s 13 hexabundles contains 61 optical fibres of 105 µm diameter, arranged in a circular pattern and lightly fused to give a field of view of 14”.9 on sky (sampling 1”.6 per fibre).
The first SAMI science commissioning run in mid 2011 targeted a single field on the sky, selected from the 6dF Galaxy Survey. One particular object on which a hexabundle was placed (ESO 185-G031 at a redshift of z=0.016) attracted the attention of Dr Lisa Fogarty and her colleagues in Sydney and the USA (including CAASTRO co-authors) because of interesting kinematic characteristics and emission lines that were immediately seen in the spatially resolved spectra from the hexabundle. Their analysis has now been published in The Astrophysical Journal 761, 169.
Measuring seven optical gas emission lines, the team was able to construct spatially resolved maps of common line ratios that give an indication of the ionisation mechanisms at work. They found that while the disk of the galaxy was dominated by ionisation due to star formation (at a rate of 1.7 solar masses per year), the ionisation source of gas further away from the disk was likely shock excitation. Analysing the gas kinematics of ESO 185-G031, Fogarty et al. could further support their hypothesis of two different ionisation mechanisms and conclude that they have identified a gas outflow that was not rotating with the disk – i.e. a galactic wind. The detection of such phenomena can help our understanding of galaxy evolution.
SAMI and its hexabundles have also already proven very effective in characterising the morphology of galaxies, especially if these do not exhibit symmetry.
Lisa M. R. Fogarty, Joss Bland-Hawthorn, Scott M. Croom, Andrew W. Green, Julia J. Bryant, Jon S. Lawrence, Samuel Richards, James T. Allen, Amanda E. Bauer, Michael N. Birchall, Sarah Brough, Matthew Colless, Simon C. Ellis, Tony Farrell, Michael Goodwin, Ron Heald, Andrew M. Hopkins, Anthony Horton, D. Heath Jones, Steve Lee, Geraint Lewis, Angel R. Lopez-Sanchez, Stan Miziarski, Holly Trowland, Sergio G. Leon-Saval, Seong-Sik Min, Christopher Trinh, Gerald Cecil, Sylvain Veilleux, and Kory Kreimeyer, in ApJ 761, 169 (December 2012)