Public Lectures for the Session 2004-2005 held in Room F14 of the Renold Building, University of Manchester.
Delivered to the Manchester Astronomical Society

18 November 2004

''A Recipe for Galaxy Soup: When Galaxies Collide. Smashing Galaxies Together and the Consequences''

Dr. Richard de Grijs
(University of Sheffield)

Dr. Richard de Grijs began his talk by taking us on a journey from the edge of the Universe to the present time. He gave an account of the current knowledge of the field of Cosmology. An image of the Hubble Ultra Deep Field displayed a multitude of galaxies which was obtained by many hours of exposure time with the Hubble Space Telescope. This image was given as an example of our most distant part of the visible known universe.

Our local universe consists of the outer part of the Solar System colliding with a shock wave of material once it hits the interstellar medium of our Milky Way. The Solar System is positioned in the Orionis spiral arm. Our position in the universe is nothing special, and we do not hold any particular important place in it. By examining infrared views from satellite observations of our Milky Way we can calculate a sense of scale when trying to compare the size of galaxies.

Our galaxy is quite large in size, and close to us are the Magellanic Clouds. There is a lot of active star formation in these dwarf galaxies which indicates that the Magellanic Clouds are growing. Our galaxy is part of the Local group which the Andromeda Galaxy is also a part of. A little further out is the Virgo Cluster. The famous galaxy with a jet, M87 is part of this group.

The size of our universe is quite overwhelming. The Hubble Ultra Deep Field is the most detailed image of the universe we have so far. At the time the images were taken the galaxies look peculiar in shape and resemble spiral type galaxies. These spirals contain a lot of material which is the key to the formation of new stars. A different type of galaxy exists where two spirals seem to merge with each other. The Antennae system consists of two colliding galaxies with a tail each which protrude outwards. The assumption that these galaxies are colliding is based on the enormous amount of blue stars which are found in this region.

The study of star clusters in these colliding galaxies points towards the evidence that these star clusters are formed through the direct interaction between galaxies. Dr de Grijs made observations using the HST to observe M81 in visible and infrared light. By using different filters astronomers can observe different wavelengths of light. In the case of M81 and M82 enormous filaments of gas have been found linking the two galaxies together. Many examples exist of similar interactions between galaxies with star formation in-between the active regions.

There is one small problem in this evolutionary scale of events though. It is not known why Irregular type galaxies should form in areas of space where they shouldn't. In the Large Magellanic Cloud an area known as 30 Doradus exhibits star formation and supernovae. These two cycles in stellar birth and death happen simultaneously in the same region.

Richard concluded his talk with an image from the new Spitzer Telescope. By observing these active star formation regions astronomers can conclude how star clusters evolve and how they play their part in the scale of the universe.

Synopsis by Sotira Trifourki (Secretary)

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