Bulge-disk decomposition

1
Bulge-disk decomposition

• Appears like the Dawn
• Fair as the Moon
• Bright as the Sun
• Majestic as the Stars
• by Nari Jeong 2007. 2. 14

2
The Fundamental Characterstics of Galaxics.
Ellpiticals Sprials Irregular l
Mass 105 1013 109 41011 108 31010
Absolute magnitude -9 -23 -15 -21 -13 -18
Luminosity 3105 1010 108 21010 107 109
M/L 100 2 20 1
Diameter (kpc) 1 200 5 50 1 10
Presence of dust Almost none Yes Yes
3

• What are you think about?
• lt My question gt
• Why Ellipticals larger than Spirals of diameter?
• How to determine Galaxies of classification?
• Why dont dust exist in ellipticals?
• lt Hubble developed a Spiral classification system
  gt
• 1. The size of the bulge relative to the disk
  length
• 2. The tightness of the winding of the spiral
  arms
• 3. The degree of resolution of the disk into
  stars and H ll regions

4
Discovery of Spirals

• Figure 4.47
• Average brightness around ellipses of similar
  shape to the galaxies outer isophotes.
• Images of the galaxies indicate that in most
  cases the additional brightness is contributed by
  an elliptical-like bulge, which might well obey
  the R1/4 law.
• Point
• It is different ellipticals!!! -gt New
  characteristics gt Spirals. (F4.47)

5

• Figure 4.48
• Many type ll galaxies may have holes in their
  disks. Moreover, the bumps in the profiles of
  some type I galaxies are caused by bars see
  below.
• gt caused by dust lanes.
• Figure 4.49
• The only reliable way to choose between possible
  bulge-disk decompositions is to fit the models
  directly to the two-dimensional surface
  photometry rather than to surface brightness
  profiles.
• Point
• 1. Discovery of Spirals. (F4.48)
• 2. We need to the two-dimensional surface
  photometry. (F4.49)

6
Why important edge-on Galaxies

• Why Important?
• 1. They enable us to test the conjecture that the
  surface-brightness profiles of bulges may be
  fitted with the R1/4
• 2. They enable us to study the vertical
  structures of disks.
• Dust is a major problem for both studies.
• Profiles
• line-of-sight projections of the model luminosity
  density (4.44)
• Point
• - Dust is very important of Spirals!!!
• Research
• Kruit Searle(1981b) , Freeman Hyland (1989)

7
About Spirals

• Figure 4.50
• - Rd must significantly exceed the radial scale
  length of the thin disk -gt but not all disk
  galaxies. (why? Burstein type)
• Burstein attributes to the thick disk should be
  assigned to the bugle. Not all disks have
  exponential vertical profiles
• gt physical origin chemical composition of
  the stars
• Point
• Different out side of Spirals shape -gt Spirals
  arm (F4.50)
• Research.
• Burstein(1979)

8
How to determine of Characteristics of Galaxies

• Bulge fraction
• The fraction of the total luminosity that is
  contributed by the bulge.
• -gt B/T is related to disk-to-bulge ratio
• Bulge fraction (4.46)
• Figure 4.51
• Have shown that existing data are usually unable
  to distinguish between bulges that follow the
  R1/4 law and ones that take the form of thick
  disks.
• Point
• - Used Bulge!!!

9
Star Formation,Environment .
Morphology,Stellar Mass, Mean Stellar
Age Star Formation EW(OII) Environment
R? Morphology B/T Stellar Mass from
2MASS J, K D4000 Mean Stellar Age D4000
residual correlation
hold constant
10

• Freemans law
• Figure 4.52
• Physically larger systems have lower central
  surface brightness.
• -gt low surface brightness gt it is worth
  nothing!!
• bluer at larger radii see 4.4.5
• ltReferencegt
• - Bugle-disk decomposition of 659 spiral and
  Lenticular Galaxy
• brightness profiles (W.E S.M)
• - Spiral Galaxies Requirements for accurate
  photometric Bugle-disk decomposition (M. Prieto
  ...)