1. Distribution of Galaxies
Lecture 3
Distribution of Galaxies
The Local Universe
the Milky-Way system
the Andromeda system
the Local Group of Galaxies
the Local Supercluster
the nearby superclusters
Astronomía Extragaláctica y Cosmología Observacional
Depto. de Astronomía (UGto)

2. The Local Universe: Distribution of Galaxies
Small scale:
Galaxies are not distributed at random
Concentrations of galaxies may be groups, clusters, superclusters or filaments
Regions with the lowest densities of galaxies are called voids
Distribution of galaxies of the catalogs UGC, ESO and MCG

3. The Local Universe: Distribution of Galaxies
Milky-Way
Distribution of galaxies from 2MASS catalog

4. The Local Universe: the Milky-Way system
[Faber & Gallagher 1979, ARAA 17, 135*]
Globular Clusters (R > 20 kpc)
Dwarf satellites
[W. Harris 1999, in Globular Clusters*]

5. The Local Universe: the Milky-Way and its satellites
(2MASS)
Scl dSph
For dSph
Car dSph
LeoI dSph
LeoII dSph
Dra dSph
Sex dSph
UMi dSph
Phe dIrr
SMC
LMC

6. The Local Universe: the Milky-Way and its closest satellites
Sag DEG
CMa dwarf
Sagitarius DEG (found by stellar
brightness density investigations)
[R. Ibata, G. Gilmore & M. Irwin 1994,
Nature 370, 6486]
Canis Majoris dwarf (found in
2MASS data – asymetries in red
giant population)
[Martin et al. 2004, MNRAS 348, 12]

7. The Local Universe: the Milky-Way and its closest satellites
UMa dw
Ursa Majoris dwarf (overdensity of red stars in the SDSS)
Boo dw
CVn dw
[Willman et al. 2005, ApJ 626, 85]
Bootes & Canis Venati dwarves
(stellar overdensity on SDSS data)
[Belokurov et al. 2006, ApJ 647, L111; y Zucker et al. 2006a, ApJ 643, 103]

8. The Local Universe: the Milky-Way and its closest satellites
UMa II dwarf
(found on SDSS data, Subaru)
[Zucker et al. 2006b, ApJ 650, L41]
Leo T dwarf (transition)
(found on SDSS data, INT)
[Irwin et al. 2007, ApJ 656, L13]
Leo T dw

9. The Local Universe: the Milky-Way system
Galaxy Alias Position (J2000.0) Type MV D(kpc) Size(’) [Fe/H]
Milky Way – S(B)bc
1. CMa dwarf – Irr(p)
2. Vir SS Irr(p) x –1.9
3. Sag DEG – dSph(7p) x –0.5/–1.0
4. UMa II dSph(5) –1.3
5. Coma dwarf dSph(5)
6. LMC ESO 056-G – SBm x –0.6
7. SMC NGC – Im x –1.2
8. Boo dwarf dSph(3p) x 8.7
9. UMi dwarf DDO dSph(5) x –1.9/–2.2
10. Draco dwarf DDO dSph(3) x –2.0
11. Sculptor dwarf ESO 351-G – dSph(3p) x –1.5/–1.8
12. Sextans dwarf – dSph(4) x –1.9/–1.7
13. Carina dwarf ESO 206-G – dSph(4) x –1.8/–2.0
14. UMa dwarf dSph –2.0
15. Fornax dwarf ESO 356-G – dSph(3) x –1.2/–1.3
16. Hercules dwarf dSph(5)
17. CVn II dwarf dSph(3)
18. Leo IV – dSph(2)
19. CVn dwarf dSph(4) x 5
16. Leo II DDO dSph(0) x –1.6/–1.9
17. Leo I Regulus, DDO dSph(3) x –1.4/–1.5
18. Phoenix dwarf ESO 245-G – dIrr/dSph x –1.9
19. Leo T dIrr/dSph x –1.6
3 Ibata et al. 1994, Nature 370, Zucker et al. 2006a, ApJ 643, 103
1 Martin et al. 2004, MNRAS 348, Zucker et al. 2006b, ApJ 650, L41
6 Willman et al. 2005, ApJ 626, Belokurov et al. 2007, ApJ 654, 897
2 Duffau et al. 2005, ApJ 636, L Irwin et al. 2007, ApJ 656, L13
5 Belokurov et al. 2006, ApJ 647, L111

10. The Local Universe: the Andromeda system
NGC 185
NGC 147

11. The Local Universe: the Andromeda system
[Van den Bergh 2006, AJ 132, 1571]

12. The Local Universe: the distant members (?) of the LG
Galaxy Alias Position (J2000.0) Type MV D(kpc) Size(’) [Fe/H]
Distant satellites
1. N Irr
2. LeoA DDO dIrr
3. Cetus dwarf dSph
4. Tucana dwarf dSph
5. WLM DDO Irr
6. Aquarius dwarf DDO Irr
7. Sag DIG dIrr
8. Gr DDO dIrr
9. UKS UGCA dIrr
Antlia-Sextans Group
10. NGC Irr
11. Antlia dSph
12. Sex A dIrr
13. Sex B dIrr

13. The Local Universe: The Local Group of Galaxies

14. The Local Universe: The Local Group of Galaxies

15. The Local Universe: The Local Group of Galaxies
[van den Bergh 1999, A&AR 9, 273]

16. The Local Universe: The Local Group of Galaxies
Virial mass:
MLG ≈ (7.5/G) <σ>2 RH
= (7.5/G) (61 km/s)2 (350 kpc)
 2.3  1012 M
Zero-velocity surface radius:
radius beyond which galaxies participate in the
Hubble expansion (or distance from which a
free-falling body, beginning at rest, would take
the age of the Universe to reach the center)
[Lynden-Bell 1981, Observatory 101, 111]
tcol = ¼ √ (3π / 2Gρ)
= ¼ √ (2 π2 R3 / GM)
 R3 = (8/ π2) GM tcol2
considering: MLG = 2.3  1012 M
and tcol = tH ≈ 14 Ga
RLG  1.2 Mpc

17. The Local Universe: The Local Group of Galaxies
[van den Bergh 1999, A&AR 9, 273]
[van den Bergh 2000, PASP 112, 529] 

18. The Local Universe: The vicinity of the LG
Maffei
Sculptor
Antlia-
Sextans
[Karachentsev et al. 2004, AJ 127, 2031]

19. The Local Universe: The vicinity of the LG
H0 = 72 km s-1 Mpc-1
CenA
M83
IC 342
NGC 253
M81
CnV I
M31
[Karachentsev et al. 2005,
AJ 129, 178] 

20. The Local Universe: The Local Supercluster
discovery of the Local Supercluster
[G. de Vaucouleurs 1953, AJ 58, 30]

21. The Local Universe: The Local Supercluster
[Sparke & Gallagher III,
Galaxies in the Universe:
an Introduction*]
[B. Tully 1982,
ApJ 257, 389] 

22. The Local Universe: Nearby Superclusters
the Coma-Leo Supercluster
[Gregory & Thompson 1978, ApJ 222, 784 ]
the Perseus-Pisces Supercluster
[Wegner, Haynes & Giovanelli 1993, AJ 105, 1251]

23. The Local Universe [Fairall 1998, Large Scale Structures
in the Universe*]

24. The Local Universe
[M. Hudson 1993,
MNRAS 265, 43]

25. The Local
Universe
 300 Mpc 

26. z = λo – λe = H0  d
λe c
 600 Mpc

27.  4 Gpc
The
“Observable
Universe”

28. Age of the
Universe
Quasars