Classifying Galaxies

1. Classifying Galaxies A.N. Other and N. O’Body All Saints School, Upper Nowhere, UK.

2. What are Galaxies? • Galaxies are giant groups of stars, dust and gas. • They can contain anywhere from millions to hundreds of billions of stars. • They come in lots of different shapes, sizes and colours. • Some galaxies have lots of new stars being formed inside them, but others only contain old stars. • Galaxies can be seen out to enormous distances – most of the way to the “edge” of the universe - and so are important to understand if we want to understand the universe as a whole.

3. Why Classify Galaxies? • There are many billions of galaxies in the Universe, with catalogues of several million already created. • If we want to understand the properties of galaxies, we need to classify them so that we can make the task more manageable. • Also, differences and similarities between galaxies within a class or between different classes can help us decide what to study in order to learn more.

4. The Hubble Sequence • In 1925 Edwin Hubble created a system of galaxy classification called the “Hubble Sequence” or “Tuning Fork Diagram” • The classification separates galaxies into: • Elliptical Galaxies • Spiral Galaxies • Barred Spiral Galaxies • “Irregulars” And then divides each one up by shape.

5. The Hubble Sequence Images from Zsolt Frei’s “Galaxy Catalog” - www.astro.princeton.edu/~frei/catalog.htm

6. Sky Watch Galaxies • For our project, we decided to classify 4 of the Sky Watch galaxies. • We chose the four galaxies to look very different, to try and make sure that we covered most of the Hubble diagram. • The galaxies are: NGC 524, NGC 1032, NGC 2776 and NGC 7479 • We then used the software to make images that showed the shapes well.

7. Our Galaxies

8. Detailed Exploration Observations from the telescopes have a lot of information in them – much more than can be seen in one go by the human eye. Therefore, we used false-colour imaging to bring out more details, as you can see in the example:

9. NGC 524 • An Elliptical Galaxy. • The almost-circular shape makes this an E0 or E1. • Remember that viewed from other angles, it may not be as circular.

10. NGC 1032 • A Spiral Galaxy • Seen edge-on, so detailed classification is difficult. • A dust lane can be seen running through the centre.

11. NGC 2776 • A Spiral Galaxy • The large spiral arms and smaller core mean that this is an Sc. • The Milky Way is probably rather like this.

12. NGC 7479 • A Barred-Spiral Galaxy • The long arms again make this a “c” type, so a classification of SBc. • The “negative” colours show the dust lanes very clearly.

13. Future Work • Our four galaxies have shown some interesting aspects of Galaxy Classification. • To continue the work, we could classify galaxies of other types. • However, we can also learn a lot from the colour of the galaxies since red areas will be mainly old stars and blue ones, areas where new, young stars exist

14. Future Work • We therefore would like to get more observations of our 4 galaxies using different filters. • We can then combine these filters to get colour pictures. • With these pictures we can see where the old stars are, and which parts of galaxies have new stars in them. • This will help us learn about how galaxies and stars form.

15. Future Work An example image from the Very Large Telescope showing redder, old stars near the centre and blue, young stars in the spiral arms.