2.3-2.4 Power Laws and Morphology Flashcards
How can surface brightness profiles at small radii be described?
As power laws
What do we call steeper and shallower power-law profiles?
Steeper - Cusps
Shallower - Cores
What can be said about the relationship for surface brightness, luminosity and mass?
They are all proportional to eachother
I(R) ∝ L(R) ∝ M(R)
What structure does the milky way have?
A flat 2D distribution of stars in a disk structure
Also has patches of blue stars (star formation)
How are the star formation regions distributed in our milky way?
Along the spiral arms
What type of spiral is the milky way?
A late-type spiral between the b and c types
When can we see evidence of a bulge in a galaxy?
When there is an overdensity of stars when compared to the rest of the disk
Can also see when looking at the surface brightness profile
What type of bulge and disk does the milky way show?
An exponential disk (n=1) and a steeper bulge (n = 3) as other spirals do
How does the density of stars change with distance from the centre of the galaxy?
It decreases exponentially
What are the two populations in the vertical distribution of stars?
The thick disk: Older, redder stars with low gas content and a scale height of 1kpc
The thin disk: Younger, bluer stars, solar metallicity and a scale height upto 0.3kpc
How does the distribution of stars change at large radii for our galaxy?
It flattens to a power law which is an indication of spherical mass distribution
What has been observed about the motion in the plane of the sky of stars?
Generally very small on the order of marcsec per year
- Measured with space instruments
What has been observed about the motion in the radial direction of the sky of stars?
Along line of sight
- Measured via the Dopper shift of the spectrum
What is the galactic bar?
The “boxy” orbits of stars near the bulge confined in a bar like shape
- Not evident morphologically, only dynamically
What is the evidence of a SMBH at the centre of our galaxy?
There is a group of 50 stars moving very close to the galactic centre
- Have a fast pmotion both on the plane of the sky and radially
3-4E6 M_solar within 0.015pc
