NAM 16: Astronomers find ‘smoking gun’ of compact galaxy formation
A team at Bristol University have found irrevocable evidence that explains how an unusual type of galaxy, so-called compact ellipticals (cEs), are formed and have discovered two examples in which they see the process of formation in action. Team leader Dr Avon Huxor will present their work on Wednesday 20 April at the Royal Astronomical Society's National Astronomy Meeting in Llandudno, Wales.
Compact elliptical galaxies are small in size and with high brightness. There are two main theories as to how these are formed. The most popular scenario involves the stripping of a more massive galaxy, leaving a smaller remnant galaxy behind. The other scenario argues that cE galaxies are the smallest members of the standard class of elliptical galaxies.
Until now, the evidence supporting the stripping scenario has been circumstantial. The astronomers used the Sloan Digital Sky Survey (SDSS), one of the largest and deepest surveys of galaxies ever undertaken, to discover two cEs where they observed the process of stripping taking place. These images showed streams of stars being ripped from the cE galaxies, and leaving small bright remnants behind. In a serendipitous find, the scientists also discovered one of the cEs in high-quality archival data from the 4-meter Canada-France-Hawaii Telescope (CFHT).
"The stripping process is expected to be short-lived, in astronomical terms," explained Professor Steve Phillipps, a co-author of the study, "but by studying the many galaxies in the SDSS we have had the opportunity to find a couple in which this stripping has been caught in the act - we have found the 'smoking gun'."
Both of the cEs were found in small groups of galaxies. These are very different from the big galaxy cluster environments in which previous researchers had looked for them. It may be that the cEs found in galaxy clusters were actually formed in small groups that later came together to become a galaxy cluster.
However lead author Dr Huxor expressed a note of caution, "Although these cEs show that stripping is certainly one way in which these galaxies form, it does not exclude other mechanisms". An analysis of the many cE candidates found in the Bristol study will show what alternatives might also exist.
Dr Avon Huxor
NAM 2011 Press Office (0900 – 1730 BST, 18-21 April only)
Dr Robert Massey
An image of one of the cE galaxies is available from http://www.star.bris.ac.uk/avon/nam2011/
Figure caption: A CFHT/Megacam image of the newly forming cE and its host galaxy (III Zw 069). The image is about 160,000 light years on each side. The streams of stars can be seen being stripped from the cE as it interacts with its more massive neighbour. Credit: Avon Huxor
Notes for editors
Bringing together around 500 astronomers and space scientists, the RAS National Astronomy Meeting 2011 (NAM 2011: http://www.ras.org.uk/nam-2011) will take place from 17-21 April in Venue Cymru (http://www.venuecymru.co.uk), Llandudno, Wales. The conference is held in conjunction with the UK Solar Physics (UKSP: http://www.uksolphys.org) and Magnetosphere Ionosphere and Solar-Terrestrial Physics (MIST: http://www.mist.ac.uk) meetings. NAM 2011 is principally sponsored by the RAS and the Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk).
The Royal Astronomical Society
The Royal Astronomical Society (RAS: http://www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The Science and Technology Facilities Council
The Science and Technology Facilities Council (STFC: http://www.stfc.ac.uk) ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange. The Council has a broad science portfolio including Astronomy, Particle Astrophysics and Space Science. In the area of astronomy it funds the UK membership of international bodies such as the European Southern Observatory.
Venue Cymru (http://www.venuecymru.co.uk) is a purpose built conference centre and theatre with modern facilities for up to 2000 delegates. Located on the Llandudno promenade with stunning sea and mountain views; Venue Cymru comprises a stunning location, outstanding quality and exceptional value: the perfect conference package.