Galaxies/cosmology Exam

Front 1

Hot Dark Matter

Back 1

Big objects fragment into smaller pieces

Front 2

Cold Dark Matter

Back 2

Large particles forming big clouds of slow gasses that dont interact

Front 3

WIMP

Back 3

Weakly interacting massive particle hypothesis
- elementary particle

- dont interact with photons, or electrostatic forces

Front 4

MACHO

Back 4

Black hole, neutron star, brown dwarf

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Neutrino

Back 5

Elementary particles that change type. Have some mass... previously a candidate for DM

Front 6

Isotropy Problem

Back 6

Universe is basically the same everywhere

No preferred directions in the universe

Front 7

Flatness Problem

Back 7

Universe has no curvature

No preferred

Front 8

Monopole Problem

Back 8

We don't see exotic stable particles around... They should have been created at high temps

Front 9

Inflation

Back 9

Solves 3 problems
Universe underwent rapid early expansion, (ie a balloon expanding) then reheated

Front 10

Reheating

Back 10

At end of inflation, potential energy of inflation field was converted into Standard Model particles

Front 11

CMB Polarization

Back 11

E-Mode -> Density Fluctuations

B-Mode -> Gravitational waves and lensing

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Big Bang 3 Tenets

Back 12

1. Universe was hot

2. Universe was dense

3. Universe is expanding

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Planck Era

Back 13

Before 10^-43 second

All forces had same strength

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Grand Unification Epoch

Back 14

10^-43 to 10^-36

Gravity separates

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Inflationary Epoch

Back 15

10^-36 to 10^-32

Rapid Expansion

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Electroweak Epoch

Back 16

10^-32 to 10^-12

Strong separates from Weak Forces & Electromagnetism

Front 17

Baryogenesis

Back 17

Why are there so many baryons (normal matter), but so few anti-baryons?

Likely there was asymmetry, so what we have is what was left over after annihilation

Front 18

CMB Fluctuations

Back 18

Small fluctuations grow with gravity to form structures in universe

Temp variations = density variations

Photons become slightly redshifted travelling through overdense areas

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Power Spectrum

Back 19

Angular Power spectrum of CMB fluctuations

Plots Temp variation throughout sky vs angular scale

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Late Time Anisotropy

Back 20

CMB photons scatter off of free electrons

Rare at z=0

Common at high z

- erases small structure, polarizes photons

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Polarization

Back 21

Two types

- Electric field mode from scattering

- Magnetic field mode from gravity

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Big Bang Nucleosynthesis

Back 22

Early universe rapidly cooled

- 98% of all helium produced in first few minutes

Universe then cooled

- particle fusion

- Baryon density explains observed abundances

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Deuterium

Back 23

No known process that makes it

Fragile element, burns at low T

Relative amounts of H, He, Deu and Li depend on density of baryonic matter

Front 24

Cosmic Shear

Back 24

Distortion of images of distant galaxies due to weak G-lensing

Angles look uniform from lensing "smearing"

- can constrain DM and DE amounts, w=DE equation of state

Front 25

WMAP

Back 25

5 year NASA mission to measure CMB

Front 26

Dark Matter

Back 26

Any type of mass that doesn't emit light

Front 27

Dark Energy

Back 27

Pure energy, doesn't produce gravity

Front 28

Cosmological Constant Problem

Back 28

Vacuum energy density is very small

Front 29

Cosmic Coincidence PRoblem

Back 29

Why is Dark Energy density only now comparable to Matter density

Front 30

Measuring Dark Energy

Back 30

see how it affects universe expansion rate

Expansion was slower in the past

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Standard Candle

Back 31

Object with known luminosity. Measuring Flux gives distance

ie Supernovae type SN1a

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SN1a

Back 32

Supernovae type 1a
- Search for SN1a galaxies

- compare expected flux with observed

- measure redshift

- - Low redshift gives H0

- - high redshift gives deceleration

If universe is accelerating, candles have smaller flux at redshift z

Result: SN1a dimmer, = acceleration

Front 33

Evidence for Dark Energy

Back 33

- Supernovae standard candles to measure expansion rate

- Cosmic microwave shows universe has threshold density

- weak lensing

- distribution of matter

Front 34

General Relativity

Back 34

Gravity replaced by Spacetime

- light follows straightest path through spacetime

Front 35

Grav Lensing

Back 35

- Deflection of lgiht as it passes massive objects

- Probes matter by its gravitational influence

- No orbital assumptions

Front 36

Einstein Rign

Back 36

If source, lens, and observer are perfectly aligned, will form a ring

Front 37

Multiply Imaged Quasars

Back 37

Example of strong lensing

- Detect high redshift (far) quasars

- look at other objects nearby, see if they're the same object!
- Can estimate constant H

Front 38

Microlensing

Back 38

Lensing by stars, causes temporary brightening for background stars
- Used for MACHO searches

Front 39

weak lensing

Back 39

slight image distortions

- measure tangential component of shape and average in bins

Front 40

Gravitational Telescopes

Back 40

Light from distant sources magnified and distorted

- Use magnification to find most distant high redshift galaxies

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Lyman Alpha Forest

Back 41

Very distant quasars have some absorption lines i ntheir spectra (from neutral Hydrogen between distant quasar)

Front 42

Reionization

Back 42

Early universe was hot plasma
Galaxies start forming and ionizing universe
- atoms form, universe becomes neutral

Front 43

Radiative Cooling

Back 43

If gas can dissipate energy faster than any heating process, it'll sink towards center of potential

1. Star formation

2. Gas and stars more tightly bound than DM

Tcool, Tdynamic

if Tc < Td, Temp dropts and contracts into disk

if Tc > Td, Cloud contracts and is pressure supported

Front 44

Radiative Cooling mechanisms

Back 44

- Compton Cooling

- - Cold microwave photons scatter off hot electrons

- Bremsstrahlung Cooling

- - Free-free emission

- - charge particles deflected by others

- Line Cooling

- - Ionization of bound-bound transition

Front 45

Cooling Catastrophe

Back 45

Cooling times in centres of massive halos are SHORT.

- Should lead to massive central galaxies...

must be some kind of feedback

Front 46

Heating Feedback

Back 46

- Supernovae

- - strip gas from low mass halos

- - SNe explosion heats gas preventing feedback

- Stellar winds

- - young stars have energetic winds of particles

- AGN

- - stop contraction and cooling of gas

- ionizing radiation

- Galaxy Merger

- - Disrupt cooling of gas
- - drives cold gas to centre, cause star formation

Front 47

Ionizing Radiation

Back 47

In the presense of UV ionizing background, small systems unable to accrete gas
systems with small dispersions, gas can be boiled out

Cooling is suppressed at low mass

Front 48

Main Free Parameters

Back 48

Star Formation

- efficiency of converting gas to stars

Feedback Efficiency

- increase feedback, decrease L

Efficiency of metal production

- more metals, more cooling in small halos, more L at small mass

Front 49

Issues in Modelling

Back 49

Satellite/Substructive problem

Details of star formation
Details of feedback

Evolution of dust

Reproducing observables

Front 50

Chemical Self-Enrichment

Back 50

In young-stellar systems

- massive system, SN ejects are retained and reused

- small system, SN shocks and star winds expell enriched gas... supress star formation!

Front 51

Luminosity Bias

Back 51

As we look far away, we only see the most luminous galaxies

Front 52

Photometric Redshifts

Back 52

Find flux from different filters, compare against library of spectral energy distributions... find best fit

Front 53

Dusty Star Formation

Back 53

Many galaxies starbusting in dense dusty environments, light is absorbed

Optical doesn't show much, need to look in IR

Front 54

Active Galactic Nuclei (AGN)

Back 54

Supermassive Black Holes
Highly Variable
Short variation time scale
Small size
Huge velocity dispersion

Front 55

Seyfert Galaxies

Back 55

Type 1 and Type 2
Strong emission lines, highly ionized gas

Strong radio, IR, UV, Xray

radio = synchrotron

IR = radiation in other bands reprocessed by dust

High energy photons = inverse compton scattering

Front 56

Seyfert 1

Back 56

Broad + narrow emission lines

Front 57

Seyfert 2

Back 57

ONLY narrow emission liens

Front 58

Synchrotron Emissions

Back 58

Electrons spin in helical motion when under magnetic field, create radio emissions

Front 59

Quasars

Back 59

Stellar-looking

Radio loud or Quiet
Outshine host galaxies
high redshift

Front 60

Eddington Limit

Back 60

Limit where radiation pressure of light emitting body exceeds body gravitational attraction

If AGN has L > eddington, stops accreting

Front 61

Radio-loud quasar

Back 61

Behaves like quiet, WITH emission from jet

Front 62

Blazar

Back 62

Rapidly variable polarized emission, no lines

Front 63

Radio galaxies

Back 63

Nuclear and extended radio emission

Usually elliptical

Front 64

Source of radio emissions in galaxies

Back 64

Electrons near center of quasar accelerated -> c

In B field, electrons move helical paths

Front 65

AGN properties

Back 65

Radio Quiet
L > Lgalaxy = R-Quiet Quasar

L < Lgalaxy = Seyfert 1, 2

Radio Loud
L > Lgalaxy = R-Loud Quasar, Blazar
L < Lgalaxy = Radio galaxy

Front 66

Superluminal Motion

Back 66

Redshift formula applies only for low redshifts/velocities

Some quasars have superluminal jets

- creates optical illusion with material moving close to c

- if jet pointed at us, appears faster than light

Front 67

Virial Theorem

Back 67

For a stable, self-gravitating spherical distribution of equal mass objects, total kinetic energy = -1/2 total Gravitational potential energy

Front 68

Jean's Mass Derivation

Back 68

Exceeding this mass, gas collapses to form star
Decreases as density increases

Front 69

Initial Mass Function

Back 69

Number of stars that form per mass internal per unit volume

Front 70

Galaxy Bulge

Back 70

R = 1kpc
Spherical

Light Distribution: r^1/4

Front 71

Galaxy Disk

Back 71

R = 15kpc

Spiral Arms

Front 72

Galaxy Halo

Back 72

Globular clusters and old field stars

Younger stars contain more metals

Front 73

Luminosity Function

Back 73

How many stars of each luminosity are present in parsec cubed

Front 74

Schechter Function

Back 74

Luminosity Function, space density of galaxies as a function of their luminosity

Front 75

Proper Motion

Back 75

"Parallax Effect"

Angular motion of stars across sky... typical motion across 1 year

Smallest resolvable angle = 1arcmin

Front 76

Radial Motion

Back 76

Away vs towards us

Doppler Shifted

Front 77

Tangential Velocity

Back 77

Proper Motion * distance

Front 78

Apparent MAgnitude

Back 78

How bright it appears in the sky

Front 79

Absolute MAgnitude

Back 79

Apparent magnitude at 10 parsecs away

Front 80

Detecting Interstellar medium

Back 80

Hot ionized gas and dust

Front 81

Attributes of Stars

Back 81

Mass

Chemical Composittion

Front 82

Luminosity

Back 82

Total energy emitted by the star

Front 83

Hydrostatic Balance

Back 83

Equilibrium of gravity and radiation pressure

- small, not hot enough for nuclear reactions

- large, outer layers of star blown away

Front 84

Stellar Metallicity

Back 84

Fraction of mass in heavy elements (Z)

Front 85

Hertzsprung-Russel (HR) Diagram

Back 85

Luminosity vs Surface Temperature

Shows sequence groupings of stars

- Main Sequence

- White Dwarfs

- Giants

- Supergiants

Front 86

Stellar Age (HR Diagram)

Back 86

Main sequence is where most life is spent.
Position determined by mass

Stars evolve OFF of Main Sequence

Front 87

Star Clusters

Back 87

Open = group of stars formed in giant cloud, loosely bound

Globular = tightly bound old stars

Front 88

Stellar Evolution

Back 88

if M < 8Ms = Red Giant, Planetary nebulae, white dwarf

if 8Ms < M < 25Ms = Supernovae, neutron star

if M > 25Ms = Supernova, black hole

Front 89

Planetary nebulae

Back 89

Hydrogen in star is depleted

Front 90

White Dwarf

Back 90

Star exhausts all fuel

very dense

very faint

Front 91

Supernova

Back 91

Extremely bright stellar explosion

Type 1a = star with companion white dwarf.

Type 2 = single massive stars at the end of their lives

Front 92

Neutron Star

Back 92

Neutron degenerate material

very dense

Front 93

Black hole

Back 93

escape velocity > c

detected by hot gas swirling in and their influence

Front 94

Interstellar medium

Back 94

Gas in galaxies, "Dust"

- hot ionized = Ha emission, xray

- Neutral atomic = 21cm emission, radio

- cold molecular = CO rotational emission, mm wavelenghts

- Dust = Thermal Blackbody, IR

Front 95

ISM Distribution

Back 95

Hot ionized gas = Halo

Neutral atomic gas = midplane, large radii

Cold molecular gas = spiral arms

Dust = tracks in distrubution of gas

Front 96

ISM Cycle

Back 96

Atomic HI

- Gas compressed

Molecular H2

- Stars form, ionize gas

Ionized HIII

- Stars die, electrons and nuclei recombine

Front 97

HI Regions

Back 97

Atomic hydrogen

detected by radio lines

Front 98

Star formation

Back 98

Form fro mmolecular gas

rotation leads to accretion of molecular cloud, channels material to core

Front 99

Milky Way Metallicities

Back 99

Disk = metal rich, young stars

Halo = metal poor, old

Bulge = mostly metal poor

Front 100

Velocity Dispersion

Back 100

Spread of velocities in galaxy

Front 101

Cepheid Variable Stars

Back 101

Variable He burning stars
Period linked to luminosity

Can measure distance from period

Front 102

Surface Brightntess

Back 102

How light from object is distributed

Front 103

Isophotes

Back 103

Lines of constant surface brightness

Front 104

Tully Fisher Relation

Back 104

Relation between spiral galaxy luminosity and max rotational velocity

Brighter spins faster

Front 105

Bulge to Total Ration

Back 105

Differentiate between spiral types...

Front 106

Galaxy Classification

Back 106

S = Spiral

a = big bulge, tight arms

b = med bulge, med arms

c = small bulge, loose arms

SB = bar galaxy

Front 107

Bar Galaxies

Back 107

Systems that are triaxial, many stars on radial orbits

Redistribute mass and angular momentum in disk galaxies

- drive change

- lead to starbursts

Half of galaxies have bars

Likely very old

Front 108

Winding Problem

Back 108

Why dont all stars converge from spiral?
Solution: density-wave theory

Front 109

Density-Wave Theory of Spiral Arms

Back 109

Spiral arm is where density of gas is higher
- travels slowly in circular motion

- dust and gas move faster, collide with wave

- star formation

Low mass stars move between arms

Front 110

What determines stellar disk size?

Back 110

Angular Momentum

Conversion of gas to stars

Internal redistribution of angular momentum

Front 111

Gastrophyiscs

Back 111

Adding physics of gas, stars, and dust afterwards in simulation

Front 112

Elliptical Galaxies

Back 112

cD Galaxy = big bright, center of large clusters, many mergers

Normal = condenced, high surface B

Dwarf elliptical = diameters 1-10kpc, surface B low

Dwarf spheroidal = low luminosity & SB, only seen closeby

Front 113

Isophote

Back 113

Very close to ellipses for most E galaxies

Front 114

Faber JAckson Relation

Back 114

Luminosity proportional to velicty dispersion

estimate distances

Front 115

Fundamental Plane

Back 115

Relation between SB, Re and sig

Front 116

Monolithic collapse

Back 116

Gas cloud collapses, rapid starbursts

Front 117

Tidal (Jacobi/Roche) Limit

Back 117

Where a star feels equal fgravity from its satellite and larger host

Front 118

Missing Satellite problem

Back 118

We predict 100-1000 satellites, but Milky Way only has 25

- Maybe no stars?

- Maybe only DM?

- Maybe no gas for star formation?

Front 119

Dwarfs are useful because (3 reasons)

Back 119

1. test structure formation models

2. measure extent and shapes of DM halos

3. Dwarfs have more DM

Front 120

Fritz Zwicky did what

Back 120

Estimated mass by luminosity vs Virial mass equation, didnt match, therefore more mass?

Front 121

Bremsstrahlung

Back 121

Braking Radiation = emission when a charged particle is deflected by another charged particle

Front 122

Supercluster

Back 122

Large grouping of groups and clusters

not virialized

Front 123

Schwarzschild Radius

Back 123

Size of black hole

Front 124

Friedmann Equations

Back 124

Generally, describes the expansion of space as a function of time

- Assumes homogeneous and isotropy

- Friedmann, Fluid, and Acceleration

Front 125

Angular Diameter Distance

Back 125

Proper distance to a Standard "yardstick" for measuring length between two objects

Proportional to diameter luminosity

Front 126

Temperature Fluctuations

Back 126

Universe was not perfectly homogeneous at the time of last scattering (z~1100)

Seen from dipole distortion of CMB, current Universe isn't perfectly homogenous

Angular size of Temperature fluctuations reflects size of density and velocity fluctuations

Front 127

Benchmark Model of Temp Fluctuations

Back 127

Current horizon distance set,

Angular diameter distance to the surface of last scattering = 13 Mpc