1. Lecture 27
Read before Class
Dark Matter
rotation curves e.g. p.596 & p.640
gravitational lensing e.g.
p.660
Galaxies
Hubble Types, properties Chapt 24
Interacting/merging galaxies, galaxy evolution
Milky Way Structure Chapt 23
Portions of Chapters 23 through 26.
ALL NOTES COPYRIGHT JAYANNE ENGLISH
Wednesday ~8am watch Philae land on Rosetta’s comet!

2. Supermassive BH in both spirals & ellipticals.
Types of Black Holes:
Elliptical (jet)
Spiral galaxy (disk + bulge)
Do galaxies form around black holes? Or do galaxies form and in the centre black holes accumulate? This is a question of current research.
Talk about growth mechanisms later. Merger vs local feeding.
Measure the motion of stars or gas (using spectra) in the centre of galaxies.
Become an astronomer and figure this out!
Supermassive BH in both spirals & ellipticals.
There are some pure disk galaxies without evidence of a BH.

3. Galaxies:
Discuss with your neighbour what a galaxy is, what it consists of, shapes, evolve with time?

4. Size range: several million to 100 billion stars.
Galaxies:
Definition: A large group of stars held together by the stars’ mutual gravitational attraction.
Size range: several million to 100 billion stars.

5. Spiral galaxies also contain significant amounts of gas & dust.

6. A major component of galaxies (90%) is dark matter. (DM)
Gravitational Lensing
Rotation Curves of Spirals
Using these techniques we can measure the amount of dark matter in a galaxy.
A major component of galaxies (90%) is dark matter. (DM)

7. Doppler Shift  absolute value of velocity vs radius.
Mass in Galaxies:
Ex. Of Rotation Curves
Doppler Shift  absolute value of velocity vs radius.
“rotation curves”
Same as for velocity vs distance plot for solar system?
Spiral galaxies are inclined to our line of sight by different amounts. So we calculate what the motion would be if they were edge-on and we had all the velocity along our line of sight. 6 galaxies are plotted on the diagram above.

8. Plot Velocity Equation for planets the Solar System:
sun contains 99.85% of M in solar system .
Increase r  M constant & v decreases.
Keperlian motion.
Kepler determined empirical laws about how planets moved around the sun. Using the Period of the orbit of each planet he determined the velocity. Plotting velocity of the planets against their distance from the sun gives the curve which fits the equation above.
FYI:
(note “**” means “to the power”)
Percentage = mass of sun
* 100
mass of sun+planets
Mass of planets (Jupiter + Saturn + Neptune…) ~ 3 * 10**27 kg
Mass of sun ~ 2 * 10**30 kg

9. The general shape of rotation curves is
Mass in Galaxies:
The general shape of rotation curves is
the same as the velocity vs radius plot for the solar system.
is flat or rising which is the same as for Keplerian motion.
is flat or rising which is different than Keplerian motion.

10. If radius increases, then mass is increasing!
Mass in Galaxies:
Rearranging the equation gives:
galaxy’s rotation curve, increase r  velocity is constant (the plot is flat).
If radius increases, then mass is increasing!
“dynamical mass” consists of all matter – stars, gas, dust, etc.
Got to here
Dynamic: Physics of or relating to forces producing motion.
In the solar system M is constant. In a spiral galaxy M is not constant. What does this mean that the mass is increasing?

11. Calculate the dynamical M out to the furthest measurable radius.
Mass in Galaxies:
Sum up all luminous radiation (x-ray gas, optically visible stars, IR, dust, cold HI). Convert this into mass required to produce this amount of radiation.  the luminous M.
Calculate the dynamical M out to the furthest measurable radius.
Form ratio to compare these masses.
Sum up at all wavelengths.

12. Dynamical M >> luminous M!
Mass in Galaxies:
Dynamical M >> luminous M!
90% of M is not luminous - called Dark Matter.
Since dynamical M extends beyond the disk, we say a galaxy has a DM halo.
Discuss what this matter might be with your neighbours.
We can talk more about dark matter later. Guesses in this class were black holes, planets, and (exotic) particles (like neutrinos).

13. Mass in Galaxies using GR: Gravitational Lensing
A foreground object (galaxy or cluster of galaxies) bends the fabric of spt.
Light must travel in spt so it bends around the object.
Projecting back onto the celestial sphere we see more than one image a background galaxy (e.g. quasar).

14. GR: Gravitational Lensing
A background galaxy will be made into arcs by the foreground lensing galaxy or cluster of galaxies.
All matter in the foreground galaxy (luminous & dark) bends spt.

15. The rings are from 2 galaxies behind the foreground galaxy.
Can determine existence & amount of DM using GR, rather than Newton’s law.
The rings are from 2 galaxies behind the foreground galaxy.
right: Foreground galaxy subtracted.
“This is an image of gravitational lens system SDSSJ as photographed by Hubble Space Telescope's Advanced Camera for Surveys. The gravitational field of an elliptical galaxy warps the light of two galaxies exactly behind it. The massive foreground galaxy is almost perfectly aligned in the sky with two background galaxies at different distances. The foreground galaxy is 3 billion light-years away, the inner ring and outer ring are comprised of multiple images of two galaxies at a distance of 6 and approximately 11 billion light-years. The odds of seeing such a special alignment are estimated to be 1 in 10,000. The right panel is a zoom onto the lens showing two concentric partial ring-like structures after subtracting the glare of the central, foreground galaxy.”

16. The arcs are not scratches on the film or bleeding in the CCD.
Seeing Gravity:
The arcs are not scratches on the film or bleeding in the CCD.
Clusters  gravitational lenses.

17. Gravitational Lensing in the submm!
Atacama Large Millimetre/Submillimetre Array

18. Credit: Dan Marrone
“Baby Boom”
Can also use lensing to find out other characteristics of galaxies, e.g. very young dusty, gassy galaxies. Milky Way forms 1-10 stars a year. These “starburst” galaxies form up to 10,000 stars per year.
The background galaxy (coloured pink) is about 12 billion light years away. This wavelength traces gas & dust  means that rapid star formation began a mere two billion years after the Big Bang.

19. What could dark matter be?
~10% of matter is sufficiently luminous to be detected
Stars
X-ray gas in clusters of galaxies
Dust
HI gas
Discuss briefly with your neighbours what 90% of the rest of the matter could be.

20. What could dark matter be?
From measurements we estimate:
~20% from dim, distant objects made from normal atoms
Very cold gas
Black holes
Planets
Small stars like Brown Dwarfs
~10-20% are exotic particles called neutrinos
MACHOS
MAssive Compact Halo Ojects
WIMPS
Weakly
Interacting
Massive
Particles

21. What could dark matter be?
The rest is expected to be exotic particles. (e.g. Sudbury Neutrino Observatory is converting its apparatus to look for these.)

22. Galaxies: Hubble Tuning Fork Diagram
Note at the joint of the branches there is a “spheroidal” galaxy.
Main types are
Elliptical (E)
Spiral (S or SB, if they have a bar.)
Irregular (Irr)

23. Galaxies: Hubble Tuning Fork Diagram
Galaxies do not come in every shape conceivable. Why not?
E # increases with flattening; little gas
Sa –large bulge, tight arms, less gas
Sb – smaller bulge, looser arms
Sc – small bulge, loose arms, most gas

24. Stars: Stellar Populations - classification
Population I:
Age of our sun or younger.
Most enriched in chemical elements i.e. “metals” (1-2%)
Population II:
Older, previous generation.
Less enriched – “metal poor”
Population III:
Have the chemical abundances of the early universe (only H, He, Li and traces of other elements).
Died long ago so not observed.
RECALL:

25. 20% of observed galaxies (not including faint, distant dwarf E).
Galaxies: Elliptical
20% of observed galaxies (not including faint, distant dwarf E).
Population II (Pop II) & old Pop I stars (i.e. old stars).
Mass: 10**5 to 10**13 Msun
Luminosity: 3 * 10**5 to 10**11 Lsun
stars’ orbits at random orientations.
Note ** means “to the power”.
Miniscule amount of gas and dust.

26. Leo I: low surface brightness dwarf galaxy with spheroidal shape.
Galaxies: Elliptical
Miniscule amount of gas and dust.
Leo I: low surface brightness dwarf galaxy with spheroidal shape.

27. dust lanes & pink HII regions. Arms are bluish  young Pop I stars.
Galaxies: Spirals
77% of observed galaxies
dust lanes & pink HII regions.
Arms are bluish  young Pop I stars.
Nucleus & throughout disk are yellowish like E  Pop II & old Pop I stars.
AAO Malin image so this is almost “true” colour.

28. Most of stars, gas & dust orbit in a plane == disk.
Galaxies: Spirals
Mass: 10**9 to 4* 10**11 Msun.
Luminosity: 10**8 to 2 x 10**10
Most of stars, gas & dust orbit in a plane == disk.
Stars in bulge & halo orbit in random orientations, like stars do in E.
Mass neither as small nor as large as regular E. Nor as faint or as bright as E.