Lec 8: Prof. Sarah Higdon1 GEARS Workshop Galaxies Sarah Higdon

Lec 8: Prof. Sarah Higdon 1

GEARS Workshop

GalaxiesSarah

Higdon

Lec 8: Prof. Sarah Higdon 2

Galaxy Evolution

We will test some of the GEARS Galaxy Evolution Unit. There are two goals

1: For everyone to be comfortable with presenting the material in the classrooms.

2: For me to be able to revise/add to the material presented here using your expertise.

Sarah Higdon p 3

Schedule:

1. 45 min WHAT DO GALAXIES LOOK LIKE – A bird’s-eye view2. 45 min WHAT DO GALAXIES LOOK LIKE - More than the eye can see

15mins Coffeeeeeeeeeeeeeeeeeee Break ~ 09:45 3. 45 min MAJOR GALAXY COMPONENTS 4. 90 min GALAXY BUILDING BLOCKS

LUNCH BREAK 1 hr ~ 12:155. 45 mins COLLIDING GALAXIES- CLOSE ENCOUNTERS AND TIDES 6. 45-90 min GAL CRASH applet

15 min Coffee Break ~15:00 7. 60 min CAPSTONE IDEAS/DEBRIEFING & COMMON

MISCONCEPTIONS REVISITED/SUGGESTIONS ON HOW TO IMPROVE THIS UNIT.

8. NASA ONLINE EVALUATIONS

Sarah Higdon p 4

Units/Jargon:

1. Distance: 1 parsec = 3.26 light years = 3 x 1016 m = 19 trillion miles (trillion = 1012) 1 Astronomical unit = 1.5 x108 km 93 million miles

2. We have sun centered view-point solopomorphic?Mass usually quoted in solar masses 1 solar mass = 2 x 1030 kg

Luminosity – again solar units Lsun = 4 x 1026 W

Lecture 8: Prof. Sarah Higdon p 5

Essential Questions What are the major components of a galaxy? What are the main types of galaxy? How can a spiral galaxy form from a giant cloud? How can an elliptical galaxy form from a giant cloud? Where do you look for the oldest stars in our galaxy? Where do you look for stellar nurseries? What do galaxies looks like at different wavelengths ranging from radio to

X-rays? Is Hubble’s Tuning Fork Diagram Useful? What are the basic building blocks for a galaxy and where is the material located

in the galaxy? How empty is the space between stars in a galaxy? How big are galaxies? How far apart are galaxies? What types of telescope do I need in order to see the galaxy building blocks? What happens when galaxies collide? Why is the tidal force so important? What types of systems can be formed from merging galaxies? What are the basic model parameters needed in the GAlCrash applet in order to

make a merger system of a given type. For example how can you make a supermassive blackhole? A galaxy with a long tidal tail? A ring galaxy

Sarah Higdon p 6

WHAT DO GALAXIES LOOK LIKE – A bird’s-eye view (45mins)

1a: Imagine you are an alien and you have one photo of the people in this classroom.

In groups design a classification scheme based on your visual data ONLY. [5mins]

each group has 1min to present their scheme. [5mins]


Discussion of schemes [5mins]

i. What makes a scheme good, what makes it bad?ii. Can you use absolutes or only relative information eg heights

of people or does that require distance?iii.Imagine comparing two images of a room full of people one

taken from the ceiling one from the doorway – does you classification scheme still work?

iv.Why do we use classification schemes?v. Can you think of some everyday examples of classification

schemes that you use? Clothes in wardrobes/drawers, kitchen cupboards, shopping list, etc..

vi.List some other scientific classification schemes –e.g. forms of energy, periodic table of elements, tree types, bird types, geometry


1b 15mins Again in groups classify this set of galaxy images using your own scheme. Revise your scheme if necessary.

The galaxy images were taken with telescopes operating at optical wavelengths – if our eyes were good enough this is what we would see. (Why are our eyes poor observers of the Universe?)

The images are available as a handout (electronic copies also available).

1c: Optical Galaxy ClassificationThe Hubble Tuning Fork Diagram

100-inch reflectingtelescope, Mt. Wilson

Edwin P. Hubble

Edwin Hubble

Lec 15: Prof Sarah Higdon p10

Types of GalaxiesDespite all the apparent variety of shapes, there are really only a few types of galaxies.


“Face-on” v “Edge-on”Spiral galaxies are large: 30-40 kpc indiameter (90-120 thousand light-years).Globular clusters are centered on their cores.

Face-on view: beautiful “pinwheel” appearance.

Edge-on view: disk-like, and the disks are often very thin and full ofdust.


Spirals: Sa smooth broad arms & large bulge, arms tightly wound

Sc narrow well defined arms and small central bulge, arms loosely wound

Spiral Galaxies

Spiral - large (3-30 kpc), massive(109 - 1012 M), and rich in gas & dust. Large spiral galaxies may form 2-5 stars like the Sun each year. The Milky Wayis a spiral.


Barred Spiral Galaxies (SB)About 1/3 spiral galaxies have a elongatedconcentration of stars at their cores. Theseare called stellar “bars”, and these galaxiesare called Barred Spirals.

The Milky Way galaxy has a small bar, andso is a type SB galaxy.

Often gas & dust travels down the bar to theinner-nucleus (to feed a Super MassiveBlack Hole?). This can be seen in the “dustlanes” visible along the stellar bars (lowerleft).

Bars may arise from collisions with othergalaxies. Bars may also arise spontaneouslyif the halo is not very massive.


Spirals: SBa smooth broad arms, tightly wound &large bulge

SBc narrow well defined arms, loosely wound and small central bulge

Barred Spiral Galaxies


Elliptical GalaxiesThese are large centrally concentrated balls of (typically) older stars.

Unlike spiral galaxies, Elliptical galaxies (1) have very little atomic or cold molecularGas, (2) have essentially no ongoing star formation, (3) tend to be reddish in color, and (4) show little or no rotation.

Elliptical galaxies often have many more globular clusters than spirals. They can bemuch more massive than spiral galaxies. And while they may look “dull” in the optical, they can be spectacular sources of radio emission!


Elliptical Galaxies

E0 (spherical) => E7 (American football) NOTE THIS CAN BE ORIENTATION DEPENDANT think about how the football changes depending on how it is angled towards you


Virgo Cluster 2000 Galaxies - here we see the Giant Elliptical Galaxy at the core

(M86 is an S0 see next bit…)


Leo I - Dwarf Elliptical Galaxy

So few stars gas and dust you can see through its center


S0 GalaxiesS0 galaxies have properties intermediate between Spirals and Ellipticals: they have disks (no discernable arms) otherwise they look like ellipticals. Very little gas fluffy disks.

S0 galaxies (like NGC 1201 at left) have very littlegas - atomic or cold molecular - and so very littlestar formation.

Roughly 1/3 of all S0 galaxies show some signs ofa bar component (like NGC 2859 at left), just likespiral galaxies.


Irregular Galaxies

Lec 17: Prof Sarah Higdon p 21

The Hubble Tuning Fork DiagramHubble found that most galaxies could be organized by how large their bulges are, if they have bars, and how “wound up” their arms are..

The meaning of this diagram (or even if it has a meaning) is still being debated to this day!

Hubble’s Tuning-Fork DiagramRe-classify the galaxies according to the Hubble Scheme

How does it differ from your scheme?

Galaxies to Classify: 1 - 3

1

23


4

5

6


7 8 9


11

10


1312

Galaxies to Classify: 14-17

14

15

17

16


1819

Galaxies to Classify: 20-23 20

21

22

23

Galaxies to Classify: 24 - 25 24

25

Galaxies to Classify: 26-29

26

27

2928


30 31


1d: There are plenty of websites that offer classification activities if you are already planning your capstone project you can select activities from the capstone sites:

Faulkes: this gives practice with their archive and you can make false color images. If you observe with Faulkes you could revisit this activity later in the semester and add your own observations): http://lcogt.net/en/education/activity/create-hubble-tuning-fork-diagram The Sloan Digital Sky Survey: http://cas.sdss.org/runs/en/proj/advanced/galaxies/classification.asp

NASA/Hubble Galaxy Hunter a cosmic safari http://amazing-space.stsci.edu/resources/explorations/

http://lcogt.net/en/education/activity/create-hubble-tuning-fork-diagram

http://lcogt.net/en/education/activity/create-hubble-tuning-fork-diagram

http://cas.sdss.org/runs/en/proj/advanced/galaxies/classification.asp

http://cas.sdss.org/runs/en/proj/advanced/galaxies/classification.asp

http://amazing-space.stsci.edu/resources/explorations/

Sarah Higdon p 35

2: 45 min WHAT DO GALAXIES LOOK LIKE - More than the eye can see

2a 5mins Look at some images of people in the infrared from Spitzer. http://coolcosmos.ipac.caltech.edu/image_galleries/ir_portraits.html

Does your classification scheme for the people from part 1a still work? Make notes on your worksheet as to why/why not.

2b 15mins Sort some multi-wavelength images – try and group each object together. Fill out table

2c 20 mins Pick a galaxy set and view the images at each wavelength in DS9 using the mosaic view. Make notes on the differences. Look up some basic parameters about your galaxytry http://nedwww.ipac.caltech.edu

2d 5 mins Discuss the limits of the Hubble classification scheme

http://coolcosmos.ipac.caltech.edu/image_galleries/ir_portraits.html

http://coolcosmos.ipac.caltech.edu/image_galleries/ir_portraits.html

http://nedwww.ipac.caltech.edu/


Coffee Break 15mins

Sarah Higdon p 37

3 MAJOR GALAXY COMPONENTS 45 mins

3a 20mins We will review the major components and identify them in your galaxies and fill in a table – also discuss the major component that cannot be seen – dark matter halo, super-massive black holes. Briefly discuss ways of inferring the presence of hidden components – which is covered in more detail in another parrot of the galaxy unit.


2 x1011 stars 3 components:

Disk: gas, dust, Young, Metal Rich Population I stars 0.6 kpc (2000 ly) thick

50kpc across (160,000ly)

Bulge: Population I & II stars. 2kpc across (6500 ly)

Halo: Old Metal Poor Population II stars - Globular clusters but mainly isolated stars

Milky Way Structure


90% of matter in our galaxy is

dark matter only 10% is stars, gas & dust!

What is Dark Matter ?


Any theory of galaxy formation should be able to account for all the properties below:

Milky Way Components

Ellipticals!!While elliptical galaxies often appear to be just a big ball o’ stars, many are shootingout extremely high energy electrons + magnetic fields millions of parsecs into space.

Blue: optical Red: radio

3c 83Fornax A

White: optical Orange: radio

Radio Images: What kind of Galaxies?A detailed look at the radio emission shows that it commonly consists of 3 components: (a) bright core, (b) two skinny “jets”, and (c ) expansive “lobes” at the ends of the jets.

Cygnus A

3c 353

Sarah Higdon p 43

3 MAJOR GALAXY COMPONENTS :NASA In The Media

3b 25mins Find a NASA press release discussing one of the major components

relay the story to the group - 2 mins allowed per presentation.

Prize for best presentation!


4 GALAXY BUILDING BLOCKS 90min:4a: How To make a Spiral/Lenticular galaxy

0. Subgalactic Units merge to make a protogalaxy.


4a: How To Make an Elliptical Galaxy0. Subgalactic Units merge to make a protogalaxy.

\



Sarah Higdon p 48

4 GALAXY BUILDING BLOCKS :

4b 20 mins Make a list of what you think are the basic building blocks in each of the main galaxy components

Is it easy to see with a telescope when you are looking at our galaxy or when you are looking at another galaxy (far away)? At what wavelength is it brightest?

Refer back to the multi-wavelength images for inspiration

Compare our lists – did we miss anything?

Sarah Higdon p 49

GALAXY BUILDING BLOCKS 90min:

4c 15 mins On a white board: Sort your components in relative sizes – guess a factor of 10 between each object from smallest largest. And masses again with a factor of 10

Sarah Higdon p 50

GALAXY BUILDING BLOCKS 90min:

4d: 35 mins Exactly how empty is space? We will end up with a roadmap of how far apart stars are how big/how massive each component is e.g. gas in a given volume amount of dust etc.. Review the building blocks masses and sizes,

Revise parts 4 b/c/ can you make some analogies keeping the correct scale factors. You have the solar system walk tonight is it possible to do a galaxy or cluster walk?

Lec 6 : Prof Sarah Higdon p51

First lets get a feel for how big our solar system is…


Now how big is our “dwarf” Sun


Guess Which Star is the Brightest? Which is the most Luminous?


It Is Lonely Out There in The Solar Neighborhood

Nearest star to the Sun: Proxima Centauri, which is a member of a 3-star system: Alpha Centauri complex

Model: Sun is a marble (2cm diameter), Earth is a grain of sand

Nearest star is another marble in Birmingham Alabama (600 km away)

Solar system: Pluto about 85 m from Sun; Oort cloud (~5 Earth Masses) about 136km (1LY)rest of distance to nearest star is basically empty

How Far away is the nearest star? How big is the solar system?.


Nebulae & The Interstellar MediumSpace between stars not completely empty, filled with atomic & ionized gas, cold molecular gas, dust grains.

<density>gas ~ 1 atom/cm3

(density air in this room ~1019 atoms/cm3 )1 dust grain for 1012 atoms

Stars form out of the ISM.

When stars die, they seed the ISM with C, O, N, etc.that they form during theirlifetimes. Stars made in thefollowing generations formout of this enriched gas.

Take 1cm3 of air in this room and put it in space – How big a cube of space would it now occupy?

What size cube of space do you need to find 1 dust grain?

1cm3 Air-from room would occupy 1019cm3 = 20kmx20kmx20km cube!

In space to find 1 dust grain you would need 1019 cm3 2football pitches for the base of your cube 100mx100mx100m


The Interstellar Medium: Stellar Nursery and

Raw Materials

What are the building blocks?


Emission Nebulae:clouds of hot excited gas

The Orion Nebula is a hot thin gas and emits an emission line spectrumTypical nebula

T ~ 104 K

Mass ~ 102 - 104 Msolar

<density>gas ~ 103 atom/cm3 (density air in this room ~1019 atoms/cm3 )

Found near O & B Stars.


Emission Nebulae also calledHII Regions

The hydrogen atom (HI) is ionized by UV photons from the hot O & B stars. The Halpha photon (and other photons) emitted when a free electron recombines with an Ionized Hydrogen (HII) ion and cascades down to the ground (n=1) state.

Halpha emitted when electron jumps from n=3 to n=2


Whiter-Than White Laundry

Detergent contains fluorescent material - remains in your clothes. Absorbs UV photons from Sun or lights at the night club, which excites the fluorescent material. Electron then cascades down to the ground state emitting blue photons - you appear to be clean! Looks can be deceiving!


Reflection Nebulae

The bluish haze is evidence of dust in the cloud.

Starlight is scattered and reflected by these small grains

The grain size ~500 nm i.e equal to wavelength of visible light

Scatter blue more efficiently than red hence the blue haze


Dark Dust Clouds: The Horsehead Nebula


Dark Dust Clouds - not holes in the heavens but more evidence for dust

This cloud is very dark, and can be seen only by its obscuration of the background stars. The image at right is the same cloud, but in the infrared.


Reddening

Dust clouds absorb/scatter blue light preferentially. NOT A Doppler Shift! - spectral lines do not shift


Dark Clouds - very cold

T = 10 - 100 K

Temperature low enough for hydrogen to form molecules

104 -109 particles/cm3 (atoms, molecules & dust)

Compared to <HII>gas ~ 103 atom/cm3 ;

density air in this room ~1019 atoms/cm3 )


Star Formation & Molecular ISM

CO OC O

HH

HHO

Stars are born in cold clouds of molecular gas & dust.

Sarah Higdon GRAM 2009

Burnt Toast in Space Spitzer 8um ImagesPAH Normal Modes

Peeters / Hony


Dust Grains

small (~10-7 m) and oblong in shape.

Core: C, Fe & silicatesMantle: ices of H2O, CO2, & NH3 Crust: simple organic (i.e., with Carbon)molecules.

This probably accounts for the lowabundance of C, Fe, & silicates in thegaseous ISM.


Dark Cloud Complex L977

Dust (Optical obscuration) = 2.5 mm CO molecular line

Dust and cold molecular gas are coincident


Cold Atomic Gas: Hydrogen 21 cm LineMuch of the ISM is in the form of cool (T ~ 100-200 K) atomic hydrogen gas. We know about this gas because of the photons it emits at radio wavelengths.

It turns out that protons & electrons have something like “spin”. In some ways resembles a Star-Planet system - the electron orbits the proton. - both “spin” on their axes.Spin and orbits QUANTIZED two states: (1) proton & electron spins “parallel” (high-energy) (2) proton & electron spins “anti-parallel” (Transition to low-energy emit a 21 cm photon i.e. radio).Takes ~ 10 million years!!


Cold Atomic Gas - HIThis image shows the distributionof cold atomic hydrogen gas in theMilky Way galaxy.

• This gas is called “HI”.

• The Sun’s position is indicated bythe yellow-arrow; the center of theMilky Way galaxy is shown by theblue-dot.

Note: atomic HI is not uniformlydistributed: dense “arms” of gasand extended regions of lowdensity between them.

Note: center of Milky Way showslittle or no atomic hydrogen (HI).

The mass of HI in the Milky Way is enough to make several billion Suns.


The ISM Distribution in the Milky Way

This image - from the NobeyamaRadio Observatory in Japan -shows both 21cm emission from HI(red) with 2.5 cm emission fromCO (green), which by proxy showsthe distribution of H2 gas.

Note: center of the Milky Way isvery rich in molecular gas. Theouter parts has both atomic andmolecular gas (yellow & orange).

Note: there is probably enoughmolecular gas to make anotherfew billion Sun-like stars.


ISM SummaryThe Interstellar medium is concentrated in the disk of the Galaxy.

Emission Nebula or HII regions are ionized gas clouds surrounding

O & B stars. T ~ 104 K; Mass ~ 102 - 104 Msolar

<density>gas ~ 103 atom/cm3 (density air in this room ~1019 atoms/cm3 )

Reflection Nebula are produced when starlight is reflected and scattered off dust grains

Dark Nebula are so dense that they are opaque. T = 10 - 100 K (low enough for hydrogen to form molecules)

104 -109 particles/cm3

Reddening is due to the scattering of blue light - it is not due to a Doppler shift.

The eye is not sensitive enough to observe either reddening or a Doppler shift - if you perceive a star to be red it is probably a giant star or you really need to sleeeep…


Note! Stars are distributed fairly uniformly in disk - density in spiral arms only 5% higher. Arms stand out as O & B stars are here which are 104 times more luminous than average star in disk

There is not a hole at the centre of the galaxy - full of molecular gas


Spiral Galaxy Template: Milky Way

Stellar mass

Atomic gas (HI)

Molecular gas (H2)

Disk Size

Halo Size

Super massive blackhole

Dark Matter


Elliptical Galaxy Template M87

Stellar mass

Atomic gas (HI)

Molecular gas (H2)

Disk Size

Halo Size

Super massive blackhole

Dark Matter

Sarah Higdon p 76

:

LUNCH BREAK 1 hr ~ 12:15


5. Colliding GalaxiesGroups and Clusters: Bound by Gravity

• Groups – Small collection: ‘galaxy poor’– E.g The Local Group includes the Milky Way– 40+ galaxies mostly dwarf ellipticals

• Clusters– Large collection: ‘galaxy rich’– E.g. Virgo cluster – 2500 galaxies


Hercules Cluster


Virgo Cluster 2500 Galaxies - here we see the Giant Elliptical Galaxies at the core, which are bigger than our Local Group!


Colliding Galaxies: Rogues Gallery of Peculiar Galaxies

Arp Atlas 1966

What is going on here? Early guesses at what caused these galaxies to look like this

• magnetic forces?• entirely new forces at work?• gigantic explosions?• new matter being created? (Steady State Cosmology)

Answer: Gravity


Gravitational Tides1) Galaxies are very big 2) Gravitational force diminishes ~(1/d)2

disknucleus

A A

3) Gravitational force from other galaxy strongest on near-side, weakest on far-side.

Stars & gas at “A” feel reduced Fgrav. They are no longer held totheir original orbits. Stars & gas at “A” are launched into space!


Numerical Simulations of Encounters

A. Toomre 1974

The Antennae (Arp Atlas)


How Common Are Galaxy Collisions?Galaxies are found in rich clusters… … and in loose groups.

How Often Can They Collide? Separation: ~ 5 times their diameter. Diameter: ~1018 km Speed: ~300 km/s

Tcollide ~ (Separation / Speed)

~ 5 x 1018 km / 300 km/s

0.5 Billion years

Age of Universe: 14 Billion years.

Leo Triplet

Abell 2118


M81 Group: Tidal Streams: HI 21 cm


Galaxy Formation: Tidal Dwarf Galaxies• Blue clumps of stars often found near end of tidal tails that resemble dwarf galaxies.• Zwicky (1947) suggested that these are new galaxies formed in the tidal tail. these are “Tidal Dwarf Galaxies” (TDGs) ( 1 + 1 = 3-10! )

TDGs TDGs

TDGs

Arp 143

Blue Light Hydrogen Gas

Higdon & Higdon 2006


A Tidal Interaction May Create Spiral Arms


Large Galaxies Can Eat Small Galaxies: Cannibalism


Ellipticals: Some are Giant Cannibals

Remember, ellipticals usually have very little gas and dust. This galaxy, Centaurus A, has gained its dust lane via collision with a spiral (gas/dust rich) galaxy


M82 near-miss/less violent collision triggers Starburst


Another Peculiar Galaxy Type: Ring Galaxy

Lynds & Toomre 1976

Ring Galaxies are formed through special collisions …

Star formation Gas distribution


Cosmic Fireworks: Starbursts• Large spiral galaxies form ~ 1-3 stars like the sun each year.

SFR = 1-3 M/yr

• Some galaxies – “Starburst Galaxies” – can make 10-1000 M/yr.

Most Starburst Galaxies are peculiar/interacting

Cartwheel Ring Galaxy

Higdon (1995)

M 82


Finding the Intruder!James Higdon 1996 ApJ 467 241

G3 makes a splash

Cartwheel Ring Galaxy

Higdon (1995)


Summary1) Galaxies are found in groups & clusters, separated by ~5x diameters. Close passages can create strong gravitational tidal forces that can dramatically change their form.2) Very close passages can result in two galaxies merging into one, or the spawning of numerous dwarf-like galaxies. 3) Galaxy collisions can also trigger bursts of star formation and feed a SMBH.4) Galaxies “grew” via mergers over long times “bottom-up”: ellipticals from “major mergers”

and spirals through “minor mergers”. This process is still going on!6) Spiral/lenticular galaxies star formation relatively slowly enabling gas to settle into a disk.

Population II stars in halo, Population I stars in disk e.g. our Sun. Elliptical galaxies stars form rapidly no disk. Metal-poor Population II stars

5) Galaxies are found along vast “sheets” surrounding ~Mpc sized “voids” where few galaxies are found. Galaxy clusters appear as large (~2-5 Mpc) concentrations on these sheets.6) “Regular” galaxy clusters are ~spherical, centrally concentrated, very massive, and are dominated by large ellipticals/S0’s in their cores. Spirals are found in the outskirts. Large amounts of Hot ~107 K X-ray emitting gas is present heated by collisions.7) “Irregular” clusters are smaller, looser, and dominated by spirals.

Checkout http://burro.astr.cwru.edu/JavaLab/GalCrashWeb/main.htmlhttp://ifa.hawaii.edu/~barnes/transform.html

http://burro.astr.cwru.edu/JavaLab/GalCrashWeb/main.html

http://ifa.hawaii.edu/~barnes/transform.html

Sarah Higdon p 94

GALCrash Applet:


Coffee Break 15mins

Sarah Higdon p 96

60 min CAPSTONE IDEAS/DEBRIEFING & COMMON MISCONCEPTIONS REVISITED/SUGGESTIONS ON HOW TO IMPROVE THIS UNIT


Essential Questions What are the major components of a galaxy? What are the main types of galaxy? How can a spiral galaxy form from a giant cloud? How can an elliptical galaxy form from a giant cloud? Where do you look for the oldest stars in our galaxy? Where do you look for stellar nurseries? What do galaxies looks like at different wavelengths ranging from radio to X-rays. Is Hubble’s Tuning Fork Diagram Useful? What are the basic building blocks for a galaxy and where is the material located

in the galaxy? How empty is the space between stars in a galaxy? How big are galaxies? How far apart are galaxies? What types of telescope do I need in order to see the galaxy building blocks? What happens when galaxies collide? Why is the tidal force so important? What types of systems can be formed from merging galaxies? What are the basic model parameters needed in the GAlCrash applet in order to

make a merger system of a given type. For example how can you make a supermassive blackhole? A galaxy with a long tidal tail? A ring galaxy

Sarah Higdon p 98

1. 30 min NASA EVALUATIONS

Documents

Lec 8: Prof. Sarah Higdon1 GEARS Workshop Galaxies Sarah Higdon