Parts, Observation and Composition

Question 1

What are the types of galaxies?

Answer 1

Spiral, Elliptical, Dwarf, Irregular, Starburst, (U)LIRG, Sub mm, Seyfert 1+2, Radio, Quasar and Blazar

Question 2

What are the observational characteristics of a spiral galaxy?

Answer 2

Stars in optical wavelengths.
Dust and gas are present.
A variety of star ages.

Question 3

What are the observational characteristics of an elliptical galaxy?

Answer 3

Stars are mostly old and red.
Not much gas and dust.
More random motion of stars.

Question 4

What is a starburst galaxy, and how do you observe it?

Answer 4

It’s a bright galaxy with a large amount of star formation, typically due to a merger or gravitational event.
Visible in optical, IR and UV.
Fairly blue with ionised gas and dust.

Question 5

What is a ULIRG and a LIRG?

Answer 5

Ultra Luminous Infra-Red Galaxy
Lumiunous Infra-Red Galaxy

Question 5

What is a Seyfert Galaxy?

Answer 5

AGN galaxies, which are also observable in the optical range.
Large amounts of UV, IR and X-rays from the core.

Question 6

What are the two types of Seryfert Galaxy?

Answer 6

Type 1:
Broad permitted lines (≈10^4 km/s)(Hα, Hβ, etc). Narrow forbidden lines.
Type 2:
Narrow permitted lines (<10^3 km/s). Narrow forbidden lines.

Question 7

What is a Radio Galaxy?

Answer 7

A galaxy with a pair of large radio lobes. The jets are the result of the acceleration of charged particles by the black hole’s E and B fields.

Question 8

What is a Quasar?

Answer 8

An AGN galaxy where the rest of the galaxy isn’t visible. And a very bright radio signal, which outshines the rest of the galaxy. We pass near the radio beam, but not through.

Question 9

What is a Blazar?

Answer 9

An AGN galaxy that we pass through the radio beam of.

Question 10

What parts of the spectrum are Quasars and Blazars visible in?

Answer 10

Quasar: Strong radio signal, some X-rays.
Blazars: Strong radio and gamma signals

Question 11

What are the main components of a spiral galaxy?

Answer 11

Halo, Disc, Bulge, Core

Question 12

What is the size of the components of spiral galaxies?

Answer 12

Bulge: r = 2Kpc
Disc: r = 15Kpc
Halo: r = 150-200Kpc

Question 13

How are the proportions of mass split in a spiral galaxy?

Answer 13

Bulge: 2%
Disc: 5%
Halo: 90%
Core: 3%

Question 14

What are HI and HII gases?

Answer 14

HI: Neutral atomic hydrogen gas, 8000K warm, 25K cold

HII: Partially ionised hydrogen gas, 8000K warm

Question 15

What is the total mass of the galaxy?

Answer 15

≈10^12 M☉︎

Question 16

What wavelengths do dust and gas emit in?

Answer 16

Ionised gas: bremsstrahlung (radio), HII, Hα, synchrotron (radio), Inverse Compton (X-ray)

Dust: Thermal (IR)

Question 17

What is the vertical density of the galaxy?

Answer 17

ρ(z) = ρ0 exp(-z/h)

h = KT/mg

Question 18

What is the Local Standard of Rest?

Answer 18

The frame of reference of the sun moving in a circular orbit about the gravitational potential of the galaxy.
R0 = 8.5Kpc
V0 = 220Km/s

Question 19

What shape is the galaxy’s rotation curve?

Answer 19

Increases quickly from a small radius, then very slowly decreases.

Question 20

What shape would you expect the galaxy’s rotation curve to be?

Answer 20

1/r^2 decrease.

Question 21

In what ways are spiral and elliptical galaxies different?

Answer 21

Spiral: Most stars orbit in a defined plane, have more gas and dust and have younger (thus bluer) stars.
Elliptical: Less gas and dust, older redder stars, and stars have more random motion.

Question 22

What are the types of cluster?

Answer 22

Globular and Open

Question 23

Describe a Globular Cluster.

Answer 23

Exists in the halo.
≈150 of them
10^5 - 10^6 stars
10^5 - 10^6 L☉︎
≈1 pc radius
very old ≈11-13 Gyr
Low metallicity due to age

Question 24

What are the possible origins of the galactic bulge?

Answer 24

Formed with the galaxy. It's a result of galactic mergers

Question 25

What are the possible origins of the galactic bar?

Answer 25

Product of a collision with smaller galaxies. Gravitational instability slowly collected matter

Question 26

What is at the galactic centre?

Answer 26

Supermassive black hole. Large molecular, dust and gas clouds. Large open clusters Nuclear star cluster (stars very close to Sgr A* ≈1pc)

Question 27

Where does star formation occur in the galaxy?

Answer 27

Disc, Galactic centre, and a small amount in the bar

Question 28

What is the mass of different parts of the galaxy?

Answer 28

Disc: ≈10^10 M☉︎ Halo ≈10^12 M☉︎ Bar+Bulge ≈10^10 M☉︎ Galactic centre ≈10^9 M☉︎

Question 29

What is an epicycle?

Answer 29

A small orbit whose centre is making a larger orbit about a body.

Question 30

What are κ and Ω in reference to epicycles?

Answer 30

Ω: Angular frequency of large orbit. κ: Angular frequency of small orbit.

Question 31

What does the ratio of κ and Ω mean for a system?

Answer 31

κ/Ω ≠ integer: an orbit won't return to the same place. κ/Ω = integer: an orbit will return to the same place. κ = Ω: One small orbit per big orbit, and returns to the same place.

Question 32

How do κ and Ω relate for a flat rotation curve?

Answer 32

κ = sqrt(2) Ω

Question 33

Why is the Milky Way a hard galaxy to classify?

Answer 33

We cannot see its overall shape well due to being within it.

Question 34

What are the galaxies on the Hubble tuning fork?

Answer 34

Elliptical E0-E7 Lenticular S0 Bared Spiral SBa-SBc Spiral Sa-Sc

Question 35

What is the "Winding Problem"?

Answer 35

Its is how the spiral arms should wind tighter and tighter, due to the same rotation speed but different distance to travel while rotation (due to radius).

Question 36

What are solutions to the "Winding Problem"?

Answer 36

Spiral Arms are just density waves, and matter doesn't travel with them. Spiral arms are short-lived.

Question 37

What does it mean if a galaxy is flocculent?

Answer 37

Its spiral arms are patchy

Question 38

What are tracers for star formation?

Answer 38

UV (large stars) Hα (gas ionised by stars) Radio (Bremsstrahlung in HII regions) IR, Submm (dust heated by stars)

Question 39

What is the Tully-Fisher Relation?

Answer 39

It is a relation which links a spiral galaxy's luminosity and rotation rate. L ∝ Vcirc ^α α ≈ 2.5 - 4

Question 40

How do you get the distance to a galaxy using the Tully-Fisher Relation?

Answer 40

Measure a galaxy's circular velocity using Doppler shift. Convert it to a luminosity. Compar the luminosity of the galaxy with its flux and rearange fro distance.

Question 41

What is Sersic's law?

Answer 41

It's a function of a galaxy's intensity is related to its radius.

Question 42

What is De Vaucouleurs's law?

Answer 42

Sersic's Law where n=4. This best represents most elliptical galaxies.

Question 43

What are the four types of galaxy mergers?

Answer 43

Wet: the galaxies contain gas and dust Dry: No gas and dust. Only stars and dark matter. Major: The two galaxies are of similar size. Minor: One galaxy is far bigger than the other. Starburst: A large amount of star formation is started

Question 44

What is the Fundamental Plane?

Answer 44

It is a shared plane of variables on which most ellipticals exist. Re ∝ σ^1.2 Ie^-0.8

Question 45

What are the Z-shifts of CMB, the first stars, the first galaxies, peak star formation and peak AGN activity?

Answer 45

CMB ≈ 1100 First stars ≈ 20 First galaxies ≈ 5-10 Peak star formation ≈ 2-3 Peak AGN activity ≈ 2-3

Question 46

What is quenching?

Answer 46

The process in which star formation slows, and the galaxy becomes redder.

Question 47

What causes quenching?

Answer 47

Stellar feedback: AGN feedback: AGN activity heats the dust and gas, making it more diffuse.

Question 48

How is it thought that the angular momentum affects proto galaxies?

Answer 48

More angular momentum forms spirals. Less angular momentum forms elliptical