Today’s outline

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Dark matter Homework due Friday Morning Galaxy Types Tonight: Public talk on Exoplanets! 7:30pm tonight Elliptical Spiral Irregular Hubble Sequence Review: Components of Galaxies Giant Ellipticals Dwarf Galaxies Tutorial on dark matter in galaxies

Galaxy Types

I Main classes

I Hubble’s system

I special types Outline

Review

Dark matter

Galaxy Types Elliptical Spiral Irregular Hubble Sequence Review: Components of Galaxies Giant Ellipticals Dwarf Galaxies Outline

Review

Dark matter

Galaxy Types Tutorial on dark matter in galaxies Elliptical Spiral Irregular Galaxy Types Hubble Sequence Giant Ellipticals I Main classes Dwarf Galaxies

I Hubble’s system

I special types Outline

Review

Dark matter

Galaxy Types Elliptical Spiral Irregular Hubble Sequence Tutorial: Orbits around Galaxies and Dark Matter Giant Ellipticals Dwarf Galaxies Dark matter halo

Outline

Review Orbital period of a star is Dark matter: Dark matter determined by the mass Galaxy Types I more like ”ghost matter” Elliptical enclosed in its orbit. Spiral I does not interact Irregular Hubble Sequence Orbital motions indicate there electromagnetically Giant Ellipticals Dwarf Galaxies is more mass than there are Most of our everyday world stars, gas and dust. (light, solid objects, In a galaxy, there is more dark chemistry) is due to matter than everything else. electromagnetic interactions The dark matter halo is much Makes dark matter very hard larger than the galaxy that to detect – only through other lives in it. forces (weak, gravity) Galaxy Types

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Dark matter

Galaxy Types Elliptical Spiral Major galaxy types Irregular Special galaxy types Hubble Sequence I Elliptical Giant Ellipticals I dwarf galaxies Dwarf Galaxies I Spiral I giant elliptical Irregular I galaxies Hubble classification Elliptical Galaxies

Outline Elliptical galaxies are a pure Review

spheroidal component Dark matter I pure spheroid component Galaxy Types Elliptical I stars and some hot gas Spiral Irregular Hubble Sequence I no star formation Giant Ellipticals Dwarf Galaxies I old stars

I wide variety of sizes

I most common type in galaxy clusters Are not necessarily ”spherical” generally more oval-shaped often due to rotational flattening, making them somewhat ”squashed” Spiral Galaxies

Outline Spiral galaxies show Review star-forming arms and Dark matter sometimes bars Galaxy Types Elliptical Also called ”disk” galaxies Spiral Irregular because the have a prominent Hubble Sequence Giant Ellipticals disk component Dwarf Galaxies

I strong disk component

I also have a spheroid

I dust

I cold gas and star formation

I most common type outside clusters Irregular Galaxies

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Dark matter Irregulars are Galaxy Types Elliptical Galaxies without a clear Spiral Irregular organization Hubble Sequence Giant Ellipticals Dwarf Galaxies I Many small galaxies

I Satellite galaxies

I Some merger products

I usually dusty and star-forming Hubble Sequence

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Dark matter

Galaxy Types Elliptical Spiral Irregular Hubble Sequence Giant Ellipticals Dwarf Galaxies

Based mostly on ”shape” of galaxy: Elliptical sequence based on ”roundness” Two spiral sequences: with and without bar ”Lenticular” are in-between: disk and spheroid, no spiral

Sequence has only modest physical meaning, mostly a conevient way to classify Galaxy Types

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Review

Dark matter

Galaxy Types Elliptical Spiral Major galaxy types Irregular Special galaxy types Hubble Sequence I Elliptical Giant Ellipticals I dwarf galaxies Dwarf Galaxies I Spiral I giant elliptical Irregular I galaxies Hubble classification Giant Elliptical Galaxies

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Review

Dark matter

Galaxy Types Elliptical Spiral Irregular Hubble Sequence Giant Ellipticals Dwarf Galaxies

At core of a cluster, galaxies merge to form one Giant elliptical Made up of lots of other galaxies put together Dwarf Galaxies

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Review Many small dwarf Dark matter

galaxies orbiting all Galaxy Types large galaxies Elliptical Spiral Irregular I mostly spheriodal Hubble Sequence Giant Ellipticals (not currently Dwarf Galaxies forming stars)

I many have been ”eaten” by the dominant galaxy in the past, thus giving their stars to the larger galaxy Galaxy Types

Outline

Review

Dark matter

Galaxy Types Elliptical Spiral Major galaxy types Irregular Special galaxy types Hubble Sequence I Elliptical Giant Ellipticals I dwarf galaxies Dwarf Galaxies I Spiral I giant elliptical Irregular I galaxies Hubble classification