clusters - Announcements Open house this Friday, Dec 2,...

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1 Announcements Open house this Friday, Dec 2, 7-9pm Review Next Friday, Dec 9 at 1:00pm? To be confirmed Test #4 Next Tuesday, Dec 13 at 7:30am (ugh) • Notes about your grade in this class: • Everything is on Mastering Astronomy • The only "extra credit" is on the homeworks • I will drop the lowest test score (best 3 of 4) • I will drop the lowest homework (best 9 of 10) • Participation score will be 12% * (score / 24) (allows for full credit even with 3 missed lectures) Going Solar! Clusters of Galaxies and Large Scale Structure Outline 1. Classifying Clusters 2. Morphology-Density Relation 3. Intracluster Gas 4. Dark Matter and Gravitational Lensing 5. Superclusters Most galaxies are in clusters or groups. Clusters contain hundreds to thousands of galaxies. Cluster Abell 1185 showing a galaxy interaction Classifying clusters: 1) “rich” clusters vs. “poor” clusters Poor clusters include galaxy groups (few to a few dozen members) and clusters with 100’s of members. Masses are 10 12 to 10 14 solar masses. Rich clusters have 1000’s of members. Masses are 10 15 to 10 16 solar masses. Higher density of galaxies. 2) “regular” vs. “irregular” clusters Regular clusters have spherical shapes. Tend to be the rich clusters. Irregular clusters have irregular shapes. Tend to be the poor clusters. Example: Distribution of galaxies (2500 or so) in the Virgo cluster. It is moderately rich but not very regular. Large extension to the south makes it irregular. Also, these galaxies have velocities offset from the main cluster. This is a whole subcluster that is merging with the main cluster. Despite great age of universe, most clusters are still evolving!
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2 The Morphology – Density Relation The higher the density of galaxies, the higher the fraction of ellipticals. Coma cluster: thousands of galaxies, high elliptical fraction Hercules cluster: about a hundred galaxies, high spiral fraction Spirals dominate isolated galaxies, groups, poor clusters. Ellipticals and SO’s dominate rich clusters, especially dense central parts. Fraction of giant galaxies Explanation: denser environment => more mergers => more ellipticals made as bulges grew. Most mergers happened long ago when galaxies were closer together. At cluster centers lie the largest ellipticals: “cD” galaxies. They have digested many companions. Masses up to 10 14 solar masses (remember: Milky Way about 6 x 10 11 solar masses)! Are these cores of
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clusters - Announcements Open house this Friday, Dec 2,...

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