Galaxy Type
Sersic Index (n)
n=1: exponential disk
n=4: de Vaucouleurs (elliptical)
n=4: de Vaucouleurs (elliptical)
Effective Radius
Ellipticity
e = 1 - b/a (axis ratio)
Galaxy Properties
Sersic Profile
I(r) = Ie exp{-bn[(r/re)1/n - 1]}
re: effective radius
bn ≈ 2n - 1/3
Surface brightness:
μ(r) = -2.5 log I(r) + constant
re: effective radius
bn ≈ 2n - 1/3
Surface brightness:
μ(r) = -2.5 log I(r) + constant
Hubble Sequence
Ellipticals (E): n ≈ 4
Smooth, featureless, old stars
Spirals (S): n ≈ 1 (disk)
Young stars, gas, dust
Lenticulars (S0):
Bulge + disk, little gas
Smooth, featureless, old stars
Spirals (S): n ≈ 1 (disk)
Young stars, gas, dust
Lenticulars (S0):
Bulge + disk, little gas
Instructions
- Top: 2D galaxy image
- Bottom: radial profile μ(r)
- Adjust n to change morphology
- Bulge+Disk: dual component fit
- Yellow circle shows re