What are the 4 morphological categories in the Hubble sequence?
- S-galaxies (normal spirals)
- SB-galaxies (barred spirals)
- E-galaxies (elliptical galaxies)
- Irr-galaxies (irregular galaxies)
What are the subclasses of spiral galaxies in the Hubble sequence?
- Sa/SBa to Sb/SBb to Sc/SBc (late type galaxies)
- decreasing bulge size
- increasing opening angle of spiral windings
What are the subclasses of elliptical galaxies in the Hubble sequence?
- E0 - E7 (early type galaxies)
- larger number -> flatter
(
- Flattening of spheroid Ex (intrinsic ellipticity ≥ Ex)
- x = 10 (a-b) / a (a,b long and short axis)
)
What is the frequency of galaxies in the NGC-catalog?
- S/SB: ≈ 70%
- E: ≈ 20%
- Irr: ≈ 7%
What is the typical luminosity MB of galaxies?
- M_B = -20m is ≈ 1010 L⊙
- S-galaxies: -17m to -23m
- E-galaxies:
– gE: ≈ -21m, E: ≈ -19m
– dE: -14m to -18m
– dSph: -10m to -15m
– cD: -22m to -25m - Irr-galaxies: Irr: -17m, dIrr: -10m to -17m
largest range indicated in bold
they stand for different types of elliptical, so: giat, dwarf, spherical, and cd is some kind of extra giant hahah
Describe elliptical galaxies. (5+1)
- Homogeneous appearance
- No cold gas
- No star formation
- Spectrum of cool stars (5000 K)
- Random stellar orbits
-> red and dead
Describe spiral galaxies. (7)
- Central bulge
- Disk
– Cold gas (dust lanes, HI and CO emission, HII-regions)
– Spiral arms
– More young stars and HII-regions - Gas and stars follow disk rotation
- Trailing spirals
- Spectrum like hot star with emission lines
What are the velocity-luminosity relations for elliptical and disk galaxies?
+ qualitative description
- Elliptical galaxies: Faber-Jackson relation, σv ≈ 220(L/L*)0.25km/s
- Disk galaxies: Tully-Fisher relation, vc ≈ 220(L/L*)0.22 km/s
L* is characteristic galaxy luminosity
-> the brigher, the faster the velocities of the stars
