Steward Observatory – Gregory Rudnick

Sept 2006

RECIPE FOR A GALAXY CLUSTER: A LOT OF DARK

MATTER, A BUNCH OF HOT GAS, AND A SPRINKLING OF

GALAXIES

Dr. Gregory Rudnick(NOAO/Kitt Peak)

Steward Observatory – Gregory Rudnick

Sept 2006

Some BIG questions about galaxy clusters?

What are they? How do they form? Where do they live? Why are they interesting? What are some current efforts to study them?

Steward Observatory – Gregory Rudnick

Sept 2006

A review of gravityGravity is a forceEverything attracts everything elseWithout gravity everything would move in straight lines

Steward Observatory – Gregory Rudnick

Sept 2006

What are galaxy clusters?Large groups of galaxies held together by gravity.

6 Million light years

Steward Observatory – Gregory Rudnick

Sept 2006

What are galaxy clusters?

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Ben Moore

Large groups of galaxies held together by gravity.

Steward Observatory – Gregory Rudnick

Sept 2006

What are clusters made of?

galaxies

Hercules cluster

Steward Observatory – Gregory Rudnick

Sept 2006

An Interlude: Galaxies 101 (in 3 minutes)

There are hundreds of billions of stars in every galaxy

That’s about 200,000,000,000 stars!!

Galaxies are large collections of stars with gas and dust

Steward Observatory – Gregory Rudnick

Sept 2006

Hundreds of galaxiesThat’s trillions of stars!!

Elliptical and S0 galaxies are the most common types of galaxies

Steward Observatory – Gregory Rudnick

Sept 2006

How massive are clusters?

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Use motions of galaxies.Calculate how much mass you need to hold cluster together.

clusters are 1015 times as massive as the sun

Stars make up only 5% of cluster mass!

Where is the missing mass?

Steward Observatory – Gregory Rudnick

Sept 2006

Stars aren’t the only game in town

Matter emits at other wavelengths too.Hot (10 million degree) gas emits in the x-ray

Twice as much hot intra-cluster gas as starsHot gas makes up 10% of total mass

Steward Observatory – Gregory Rudnick

Sept 2006

Where is the rest of the mass?

Only 5% stars + 10% hot gas has been seenWhere is other 85%?Can we verify the large mass?

Gravitational lensing

Galaxy clusters are mostly made of “Dark Matter”

Steward Observatory – Gregory Rudnick

Sept 2006

What do we know

Clusters are made of: galaxies (5%) hot gas (10%) dark matter (85%)

Steward Observatory – Gregory Rudnick

Sept 2006

How do they form?

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volker springel

Steward Observatory – Gregory Rudnick

Sept 2006

Where do clusters live?The nearest two clusters

Coma (260 million light years)

Virgo (55 million light years)

Steward Observatory – Gregory Rudnick

Sept 2006

The Big Picture

Steward Observatory – Gregory Rudnick

Sept 2006

The Big Picture

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Steward Observatory – Gregory Rudnick

Sept 2006

Why are clusters interesting and useful?

Providing evidence for dark matter

Gravitational lensing

Steward Observatory – Gregory Rudnick

Sept 2006

Steward Observatory – Gregory Rudnick

Sept 2006

The Bullet Cluster - testing the existence of Dark Matter

Douglas Clowe

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If gravity is stronger on large scales and dark matter doesn’t exist then the gravitational force should be located at the center of the “visible” matter.

Steward Observatory – Gregory Rudnick

Sept 2006

The Bullet Cluster

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Douglas Clowe

Use gravitational lensing to measure total mass.

Steward Observatory – Gregory Rudnick

Sept 2006

Clusters as Laboratories of Galaxy Evolution

Can clusters tell us how galaxies might transform their types?

How can a spiral turn into an elliptical?

Steward Observatory – Gregory Rudnick

Sept 2006

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What happens to gas in a galaxy when it flies through the hot intra-cluster gas

Ram Pressure Stripping

Steward Observatory – Gregory Rudnick

Sept 2006

Galaxy Harassment

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Steward Observatory – Gregory Rudnick

Sept 2006

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Galaxy Harassment

Steward Observatory – Gregory Rudnick

Sept 2006

Observing the Evolution of Clusters

How can we see clusters when they were younger?

Astronomy is like archaeology.

increasing distance

back in time

Steward Observatory – Gregory Rudnick

Sept 2006

CL1202.4-12244.3 Billion years

CL1232.3-12505.1 Billion years

CL1037.5-12435.3 Billion years

CL1054.4-12456.3 Billion years

CL1354.1-12316.3 Billion years

Clusters through cosmic time

Steward Observatory – Gregory Rudnick

Sept 2006

Galaxies in Young Clusters

cl1037-1243 5.3 Billion years

cl1216-12016.5 Billion years

Steward Observatory – Gregory Rudnick

Sept 2006

Summary Galaxies don’t matter: Clusters are dominated by Dark Matter (5% stars, 10% hot gas, 85% dark matter)

Cosmic meeting points: Clusters are concentrations of galaxies at the intersection of filaments of cosmic structure

Cosmic Laboratories: Clusters are useful in studying dark matter and the evolution of galaxies