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Galaxies > 5: GALAXY DYNAMICS > Flashcards

5: GALAXY DYNAMICS Flashcards

1
Q

What is the signature of a rotating galaxy?

A

Tilted spectral lines, indicating changing doppler velocities with position

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2
Q

How are velocity dispersions measured?

A

From observing the width of the galaxy’s spectral lines

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3
Q

Does general velocity dispersion vary with position?

A

Yes, if not, we have an isothermal distribution.

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4
Q

What type of velocity dispersion do ellipticals have?

A

Anisotropic velocity

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5
Q

Do ellipticals rotate fast enough to be rotationally flattened?

A

Some of them, usually the lower luminosity ones

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6
Q

Why are more luminous Es redder?

A

Because redder populations generate less light per unit mass

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7
Q

How can the x-ray emitting gas be used to measure the gravitational potential energy?

A

Via the standard equation of hydrostratic equilibrium

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8
Q

In massive black holes, when does velocity dispersion increase?

A

As we appraoch the centre

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9
Q

Define Magorrian relation

A

Evidence for a close connection between the growth of a black hole and formation of the galaxy

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10
Q

Why are some ellipticals strong radio sources?

A

Because they’re powered by accretation onto a central black hole.

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11
Q

How do you measure the dynamical feature of disks in external galaxies?

A

From the relative Doppler shift of lines in the galaxy’s spectrum at different points along the major axis

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12
Q

When can you approximate M(R) to get Keplerian orbits?

A

If the mass is centrally concentrated at large R

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13
Q

Outside central regions, disks show differential rotation. What does this mean?

A

Stars further out take longer to orbit

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14
Q

What does Oort’s constant A measure?

A

The gradient of angular velocity near the sun

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15
Q

What does Oort’s constant B measure?

A

The angular momentum gradient

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16
Q

Why is spatial resolution not good in the optical?

A

Because of the diffraction limit lambda/D for radiation of wavelength observed with telescope of diameter D

17
Q

What is the Tully-Fisher relation?

A

It’s the relation between luminosity and line width analogue for spirals.

18
Q

When does the bar end?

A

Where bar stars corotate with disk stars

19
Q

What forms a bar?

A

Probably due to an instability of the rotating disk, if the surface density is too high

20
Q

Why are bars important?

A

For ferrying matterial towards the centres of galaxies as the non-central gravitational forces allow angular momentum to be lost

21
Q

How do we know spiral arms aren’t material?

A

Because the differential rotation of the disk would wind them up in few rotation periods (less than ten to the nine years)

22
Q

What suggests the spiral is a wave?

A

Different particles must be in arms at different times

23
Q

What is the density wave theory?

A

The gravitational attraction between stars at different radii counteracts the tendency of a spiral to wind up and reinforces a pattern which rotates with a pattern speed

24
Q

What form is the missing mass in?

A

Non-baryonic form. Possible that some is supplied by invisible but macroscopic objects known as MACHOs. MACHOs could be small black holes, planet sixed bodies or dim stars such as brown dwarfs

25
Q

How could MACHOs be observed?

A

Might be detectable by gravitational effects. According to general relativity, light passing close to a large mass will be deflected

26
Q

What are signs galaxies have merged?

A

tails, shells, dust lanes, polar rings, decoupled cores

27
Q

What are kinematically decoupled cores and what do they indicate?

A

Where central regions rotate independently of the stars further out and probably indicate where the relaxation of stars in the merged system to equilibrium isn’t complete yet

28
Q

What happens in a galaxy merger if one of the galaxies is gas rich?

A

The interaction may funnel interstellar material towards the centre of the merger product and drive a burst of SF

29
Q

What is a by-product of mergers?

A

The creation of new GCs

30
Q

What is the deceleration effect called and what does it do?

A

Dynamical friction and operates like actual frictional forces in depending on the galacy’s velocity

31
Q

What is galactic cannibalism?

A

Larger mass galaxies are slowed more so a galaxy will swallow its larger neighbours first

32
Q

What are indications of interactions in the Galaxy-LMC-SMC system?

A

There is a bridge of gas between the clouds, plus a more tenuous trail of gas ahead of and behind the smc in its orbit - the Magellanic stream.

33
Q

Why could SMC merge with our galaxy?

A

SMC has been affected by tidal forces and may now be gravitationally bound. Tidal friction from the galaxy will bring about the decay of the cloud’s orbits and eventually lead to its merging.q

34
Q

What supplies a substantial fraction of halo stars?

A

Streams around the Galaxy suggest that the remains of completely accreted dwarf galaxies do

Galaxies (6 decks)

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