1. Previous Classes: This Class interacting galaxies cosmology
Phys 1830: Lecture 33
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galaxies
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interacting galaxies
cosmology
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ALL NOTES COPYRIGHT JAYANNE ENGLISH

2. 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)

3. Population II and old Population I stars (i.e. old stars).
Galaxies: Elliptical
20% of observed galaxies (not including faint, distant dwarf ellipticals).
Population II and old Population I stars (i.e. old stars).
Mass: 10**5 to 10**13 solar masses
Luminosity: 3 * 10**5 to 10**11 solar L
Stars in orbit but orbits are at random orientations.
Note ** means “to the power”.
Miniscule amount of gas and dust.

4. Leo I: A low surface brightness dwarf galaxy with a spheroidal shape.
Galaxies: Elliptical
Got to here
Miniscule amount of gas and dust.
Leo I: A low surface brightness dwarf galaxy with a spheroidal shape.

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

6. Mass: 10**9 to 4* 10**11 solar masses. Luminosity: 10**8 to 2 x 10**10
Galaxies: Spirals
Mass: 10**9 to 4* 10**11 solar masses.
Luminosity: 10**8 to 2 x 10**10
Most of the stars, gas and dust orbit in a plane.
Stars in the bulge and halo orbit in random orientations, like stars do in an elliptical.
Mass neither as small nor as large as regular E. Nor as faint or as bright as E.

7. How long for our sun to orbit the centre of the Milky Way
How long for our sun to orbit the centre of the Milky Way? The distance from the Galactic centre is 8.5 kpc and the sun orbits at 220 km/s. There are 3.09 * 10**13 km per kpc.
on order of thousands of years
on order of millions of years
on order of billions of years
It doesn’t orbit in circle so one can’t calculate this.

8. Galaxies: Hubble Tuning Fork Diagram
The appearance of gaps of empty space between arms is a misrepresentation.
The apparent gaps are actually dust lanes.

9. Spirals: No gaps in disk of galaxy.
HST
I band is near-IR
I-band image.
Dusting of stars throughout the disk.
Pop II and older Pop I stars. (Recall low mass stars live longer and are red on the MS.)

10. Spirals: No gaps in disk of galaxy.
HST
B-band image.
Dust absorbs UV and B radiation, obscuring stars.
Recall on MS massive stars are blue.

11. Spirals: No gaps in disk of galaxy.
HST
F435W(B), F555W(V), F814W(I)
Note that it is missing H_alpha filter so we don’t see pink HII regions.

12. The disk rotates. Stars and gas orbit around the centre.
Spiral Disk Galaxies:
Canada-France-Hawaii Telescope: Jean-Charles Cuillandre
If we could get outside our Milky Way galaxy, from the side it would look like the left picture and from above it would look something like the galaxy on the right.
Disk galaxies can have a spiral arm pattern of dust and hot young stars superimposed on the disk.
The disk rotates. Stars and gas orbit around the centre.

13. Galaxies: Spirals – examples and inclination.
Flocculent (like a sheep)

14. Galaxies: Spirals – examples and inclination.
Almost face-on inclination.
Grand Design Spirals have well-defined arms

15. Galaxies: Spirals – examples and inclination.
Barred galaxy.

16. Galaxies: Spirals – examples and inclination.
Edge-on.
Note the dust lane in midplane of galaxy and dust filaments rising into the halo.

17. Galaxies: Spirals – examples and inclination.
Edge-on.
Large bulge (spherical component).
Note the nucleus in the centre of the bulge.

18. Mostly Population I stars.
Galaxies: Irregular
i.e. these can have young Population I stars.
Appearance of irregular shape is often due to the distribution of regions of star formation.
Mostly Population I stars.

19. Which of these does not have young population I stars?
Review
Which of these does not have young population I stars?
A) elliptical galaxies
B) non-barred spirals
C) Irregular galaxies
D) barred spirals

20. Galaxies: HI distribution compared to stellar distribution
Optical image of M 33.

21. Galaxies: HI distribution compared to stellar distribution
Radio 21 cm image of M 33.
Notice the gas is more extended in distribution than the stars.

22. Galaxies: Evolution with time
Atoms for Peace galaxy (NGC 7252) Hibbard & van Gorkom (1996)
More spirals than ellipticals which would happen if mergers occurred (2 galaxies become 1). Gas and dust in spirals get converted into stars in the process leaving little gas and dust in E type galaxies.
HCG 31 HST English, Charlton et al.
Interacting spiral galaxies - lectures 13 & 14. (Tidal effects.)
Eventually they merge together to form elliptical galaxies.
Material around merger remnant (on right) would fall towards the central region forming elliptical orbits.

23. Galaxies: Evolution with Time.
Spiral metamorphosis at Gravitas website.
Watch for tidal tails left behind & bridges between interacting galaxies.

24. Interactions and Mergers
John Dubinski (U. of Toronto)
Note tails and bridges
Outstanding Questions:
If E form from mergers, why do E and S/SBs both co-exist at early times in the universe?
How do disk galaxies get spiral arms?
Shouldn’t there be an era of only spiral galaxies before ellipticals form?

25. Galaxies: You can participate in research
Galaxy Zoo
“In order to understand how these galaxies — and our own — formed, we need your help to classify them according to their shapes — a task at which your brain is better than even the fastest computer.”
“Based on the basic input parameters that we provide, a Java applet running in your browser will simulate some possible collision scenarios. Computers don’t do a good job comparing simulations and real astronomical images, so we need your help to find out which simulations are the most similar to the real galaxy collision.”

26. It is likely that
E galaxies fragment to become SB galaxies.
Irr galaxies are the last stage of merging galaxies.
Galaxies formed out of gas clouds at the beginning of time and remained the same since. They will never change shape.
S and SB galaxies interact, merging together to form E galaxies.

27. Cosmology
Observations of the cosmic web.
Galaxies can be used to trace the structure and evolution of the universe.
The study of the structure and evolution of the universe as a whole is called cosmology.