7.1

Question 1

What are the 4 morphological categories in the Hubble sequence?

Answer 1

• S-galaxies (normal spirals)
• SB-galaxies (barred spirals)
• E-galaxies (elliptical galaxies)
• Irr-galaxies (irregular galaxies)

Question 2

What are the subclasses of spiral galaxies in the Hubble sequence?

Answer 2

• Sa/SBa to Sb/SBb to Sc/SBc (late type galaxies)
• decreasing bulge size
• increasing opening angle of spiral windings

Question 3

What are the subclasses of elliptical galaxies in the Hubble sequence?

Answer 3

• 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)
)

Question 4

What is the frequency of galaxies in the NGC-catalog?

Answer 4

• S/SB: ≈ 70%
• E: ≈ 20%
• Irr: ≈ 7%

Question 5

What is the typical luminosity M_B of galaxies?

Answer 5

• M_B = -20^m is ≈ 10¹⁰ L_⊙
• S-galaxies: -17^m to -23^m
• E-galaxies:
  – gE: ≈ -21^m, E: ≈ -19^m
  – dE: -14^m to -18^m
  – dSph: -10^m to -15^m
  – cD: -22^m to -25^m
• Irr-galaxies: Irr: -17^m, dIrr: -10^m to -17^m

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

Question 6

Describe elliptical galaxies. (5+1)

Answer 6

• Homogeneous appearance
• No cold gas
• No star formation
• Spectrum of cool stars (5000 K)
• Random stellar orbits

-> red and dead

Question 7

Describe spiral galaxies. (7)

Answer 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

Question 8

What are the velocity-luminosity relations for elliptical and disk galaxies?

+ qualitative description

Answer 8

• Elliptical galaxies: Faber-Jackson relation, σ_v ≈ 220(L/L_*)^0.25km/s
• Disk galaxies: Tully-Fisher relation, v_c ≈ 220(L/L_*)^0.22 km/s

L_* is characteristic galaxy luminosity

-> the brigher, the faster the velocities of the stars