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Chapter 23
Milky Way and Galaxies
Virginia Trimble
23.1
23.1.1
23.1
Milky Way Galaxy . . . . . . . . . . . . . . . . . . . . 569
23.2
Normal Galaxies . . . . . . . . . . . . . . . . . . . . . . 576
MILKY WAY GALAXY
Overall Properties
Details of the location of the Sun in the Galaxy are given in Table 23.1.
Table 23.1. Milky Way parameters.
Solar galactocentric distance (kpc)
LSR rotation speed (km/s)
Oort constant A (km/s kpc)
Oort constant B (km/s kpc)
A + B = 0.0 for a flat rotation curve
IAU 1964
Standard
[1]
IAU 1985
Standard
[2]
Other values
[3–5]
10
250
+15
−10
8.5 ± 1.1
220
+14.4 ± 1.2
−12.0 ± 2.8
7.0 ± 0.8
190
+13.0
−13.0
References
1. Allen, C.W. Astrophysical Quantities, 3rd ed. (Athlone Press, London), p. 283
2. Kerr, F.J., & Lynden-Bell, D. 1986, MNRAS, 221, 1023
3. Gilmore, G., & Carswell, B., editors, 1987, The Galaxy (Reidel, Dordrecht)
4. Allen, C., & Santillan, A. 1991, Rev. Mexicana Astron. Af., 22, 255
5. Merrifield, M. 1992, AJ, 103, 1442
At the solar circle, the rotation period is 2.4 × 108 yr; the epicyclic period is 1.7 × 108 yr; the
vertical period is 6.2 × 107 yr [1].
569
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M ILKY WAY AND G ALAXIES
The total luminosity in the B color band, the integrated color, and the total bolometric luminosity
are [1–4]:
L B = (2.3 ± 0.6) × 1010 L ,
B − V = 0.68 − 0.80,
10
L bol = 3.6 × 10 L of which 1/3 is in infrared radiation.
The extent of luminous disk, r , is 20–25 kpc [5].
The total mass and M/L B are [6]:
M = 9.5 × 1010 M ,
M = 4 × 1011 M ,
M = 13 × 1011 M ,
M/L B = 4.2 to R0 = 8.5 kpc,
M/L B = 18 to R = 35 kpc,
M/L B = 56 to R = 230 kpc.
The escape velocity [6, 7] at R is 450–650 km/s, at the edge of the Galaxy is 311 km/s, and at the
galactic center is 650–700 km/s.
23.1.2
Galactic Populations
Contents of the components of the Galaxy are given in Table 23.2.
23.1.3
Galactic Backgrounds
Energy densities near the Sun in magnetic fields, galactic cosmic rays, gas cloud turbulence, starlight,
and microwave background are each 0.5–2 eV/cm3 .
Cosmic Rays [8]: The flux of particles with energies greater than E (eV) is 1020 E −1.74
particles/m2 s sr for E = 10–107 GeV/nucleon. The grammage traversed is 3–6 g/cm2 (from secondary
to primary ratios). The confinement time is 3 × 107 yr (from radioactive nuclides).
In soft X-rays (0.25 kev), the local background is 40–70 keV/cm2 s sr keV [9].
The ultraviolet (1400–1800 Å) flux [10] is 300–400 photons/(cm2 s sr Å) at high latitudes and
1200 ± 200 photons/(cm2 s sr Å) at low latitudes.
The visible light intensity, in units of 1.1 × 10−9 erg/cm2 s sr Å [11], for sky-averaged starlight
in the galactic plane is 200; toward the poles is 50, and in diffuse optical emission is 20. The light
absorption in the V band A V = 0.11 ± 0.02 toward poles [4].
The infrared surface brightness of the Galaxy [4] is 10−4.35 W/m2 sr at 100 µm, 10−5.35 W/m2 sr
at 25 µm, and 10−5.1 W/m2 sr at 12 µm.
In the ultraviolet to infrared range, 1000 Å–100 µm, the interstellar radiation field averaged over
all directions, d I /d ln ν, is 10−6 –10−7 W/m2 sr and is smaller toward poles by a factor of 10.
Total galactic luminosities [4, 12]: L(> 100 MeV) = (1–2) × 1039 erg/s, L(2–10 keV) =
40
10 erg/s, and L(4–100 µm) = 1.2 × 1010 L = 4.8 × 1043 erg/s.
The B band central surface brightness is 22.1 mag. mag./arcsec2 [13].
2.9
4–5
Bulge [1, 2]
Spheroid [2–6]
Disk [2, 4–6]
Thick disk [7–10]
2–3
325 pc
1?
20–25
≥ 100
1.3 kpc
0.6–1
≥ 40
20–25
20–25?
0.4
Vertical
scale
height
or c/a a
1
Radial
extent
(kpc)
0.009
0.124
0.15
0.026
0.000 26
—
Density
near Sun
(M pc−3 )
4.5
1.7 × 1010
(3–6) × 1010
≥ 650
4.6
10?
1.9 × 1010
2 × 108
(3–6) × 1010
(2–4) × 109
(6–10) × 1011
1–5
(1–2) × 109
5
2 × 109
1010
(2–10) × 109
M/L
within
2R
L tot
B
(units of L )
Mtot
(units of M )
−0.1 ± 0.2
−0.3 ± 0.3
−0.6 ± 0.3
−1.5+0.5
−3.0
+0.3 ± 0.2
Metallicity
[Fe/H]
References
1. Frogel, J.A. 1988, ARA&A, 26, 51
2. Bahcall, J.N. 1986, ARA&A, 24, 577 and references therein, also private communication
3. Freeman, K.C. 1987, ARA&A, 25, 603
4. van der Kruit, P. 1987, in IAU Symposium 139, The Galaxy, edited by G. Gilmore and B. Carswell (Reidel, Dordrecht)
5. Merrifield, M. 1992, AJ, 103, 1442
6. Gilmore, G., & Kuiken, K. 1989, MNRAS, 239, 571
7. Gilmore, G., & Reid, N. 1983, MNRAS, 202, 1025
8. Gilmore, G., & Wyse, R. 1987, in IAU Symposium 139, The Galaxy, edited by G. Gilmore and B. Carswell (Reidel, Dordrecht)
9. van der Kruit, P. 1984, A&A, 140, 470
10. Gilmore, G., Wyse, R., & Kuikjen, K. 1989, ARA&A, 27, 555
Note
a The ratio of the smallest to the largest axis.
Dark halo [2, 4, 5, 6]
3.5–5
0.2
Component
Thin disk [2, 4, 8, 10]
Radial
scale
length
(kpc)
Table 23.2. Galactic population components.
0?
220
180
0–50
Vrotation
at R
(km/s)
Metal-rich globular
clusters, old stars; hot gas
Population I stars, atomic,
molecular gas
Unknown
Old stars (not population
II); molecular gas
Metal-poor globular
clusters; old stars
(population II)
Contents
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23.1.4
M ILKY WAY AND G ALAXIES
Galactic Center [14]
The inner parsec contains M ≈ 3 × 106 M in some combination of dense star cluster and a
supermassive black hole, with compact sources of radio, X-ray, and infrared radiation. Other compact
sources, including gamma-ray sources are nearby. The central magnetic field B ≈ 1 mG, largely
perpendicular to the disk.
23.1.5
Spiral Arms [15, 16]
The Milky Way is not a grand design spiral, with two discrete arms extending 360◦ or more. The
magnetic field follows the arms with an ordered component of 2–6 µG and a comparable chaotic
component. The arms that cut the radius vector through the Sun are Scutum, at 5 kpc from the
galactic center; Sagittarius, at 7.5 kpc; Orion, Carina-Cygnus, at 8.8 kpc (the local arm); and Perseus,
at 12.3 kpc.
23.1.6
Age [17, 18]
The age of the oldest spheroid (globular cluster) stars and onset of nucleosynthesis can be placed at
13–17 Gyr BP (before present). The oldest disk stars formed 6–13.5 Gyr ago.
23.1.7
Star Formation Rate [19]
The local rate is (3.5–5)M /pc3 Gyr. The global rate is (0.8–13)M /yr (most likely value 3M /yr).
23.1.8
Gas Content [4, 19–21]
HI: n(HI) = 2.9 × 1020 csc b atoms cm−2 = 3.25M pc−2 , or 0.44 atoms cm−3 with a scale height
of 130 ± 20 pc (at the solar circle).
H2 : H2 = 2M pc−2 or 0.013M pc−3 with a scale height of 65 ± 25 pc; the maximum
n(H2 ) = 3 × 1022 cm−2 at the galactic center and in the 4–6 kpc ring.
The total amount of gas is (5.7–7.5)M pc−2 = (2–6) × 109 M ; M(H2 )/M(HI) ≈ 1.
23.1.9
Galactic Rotation Curve
The basic shape (rapid central rise, extended flat part) has been decomposed into central bulge plus
spheroid, disk, and dark halo (corona) in two rather different ways. Table 23.3 shows a version where
the disk is the largest contributor between 3 and 11 kpc [22–24]. Figure 23.1 shows a version where
the disk is less massive and never dominates [25, 26].
Table 23.3. Galactic rotation (km/sec).
R (kpc)
V (bulge + spheroid)
V (disk)
V (halo)
0.25
0.50
0.75
1.0
235.1
247.3
245.3
232.5
22.0
38.5
52.5
64.8
11.4
22.5
32.9
42.5
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23.1 M ILKY WAY G ALAXY / 573
Table 23.3. (Continued.)
R (kpc)
V (bulge + spheroid)
V (disk)
V (halo)
2.0
3.0
4.0
5.0
6.0
7.0
7.7
8.0
8.3
9.0
10.0
12.0
14.0
16.0
18.0
20.0
25.0
30.0
40.0
60.0
165.6
134.8
117.2
105.3
96.6
89.8
85.8
84.3
82.8
79.7
75.7
69.4
64.4
60.4
57.1
54.2
48.6
44.5
38.6
31.5
101.4
125.1
140.5
149.9
155.2
157.5
157.7
157.5
157.2
156.0
153.5
146.4
138.2
129.9
122.1
115.0
100.6
90.2
76.5
61.7
73.3
94.3
109.0
119.9
128.3
135.0
139.0
140.5
142.0
145.2
149.2
155.8
161.0
165.3
169.0
172.1
178.5
183.5
191.1
201.2
Figure 23.1. A second version of the Galaxy rotation in which the disk is nowhere the dominant component [25, 26].
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23.1.10
M ILKY WAY AND G ALAXIES
Acceleration Perpendicular to the Galactic Disk
The high- and low-mass disks of Sec. 23.1.9 correspond to different force laws perpendicular to the
disk at the solar position as presented in Figure 23.2. The data are in Table 23.4.
Table 23.4. Force per unit mass versus height z above galaxy plane.
z (pc)
K z (10−9 cm/s2 )
K z [(km/s)2 /pc]
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
2000
2500
3000
0.00
2.46
4.17
5.19
5.81
6.21
6.50
6.72
6.90
7.05
7.19
7.31
7.42
7.52
7.62
7.71
8.11
8.42
8.66
0.00
0.76
1.29
1.60
1.79
1.92
2.01
2.07
2.13
2.18
2.22
2.26
2.29
2.32
2.35
2.38
2.50
2.60
2.67
Figure 23.2. Force laws in direction perpendicular to the Galaxy disk versus height above Galaxy disk.
Sp.-V/AQuan/1999/10/11:12:03
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23.1 M ILKY WAY G ALAXY / 575
The corresponding mass densities are (0.10–0.29)M pc−3 in the solar neighborhood and
(48–89)M pc−2 perpendicular to the plane.
The mass density and potential anywhere in the Galaxy can be calculated by summing the
components that enter into these models [7, 27].
23.1.11
Galactic Coordinates
1. The old system [28] was defined by a North Galactic Pole (NGP) (bI = 90◦ ) at
RA = 12h 40m = 190.◦ 0,
declination = +28.◦ 0
(1900).
The ascending node on the equator, at RA = 280.◦ 00 + 1.◦ 23T (T is the time in centuries after 1900.0),
defines l I = 0◦ .
2. The new system [28–30] has been defined for Besselian year 1950 and Julian year 2000 by the
coordinates, l II bII , of the NGP:
RA = 12h 49.m 0 = 192◦ 15
,
RA = 12h 51m 26s 2755 = α3 ,
= 192.◦ 859 481 23,
declination = +27◦ 24.
0 (B1950),
declination = +27◦ 7
41.
704 = δ3
= +27.◦ 128 251 20 (J2000).
The corresponding values of l I , bI = 327.◦ 41, −1◦ 24
.
The position of the galactic center defines l II = 0◦ :
RA = 17h 42.m 4 = 265◦ 36
,
RA = 17h 45m 37.s 1991 = α1 ,
= 266.◦ 404 996 25,
declination = −28◦ 55
(B1950),
declination = −28◦ 56
10.
221 = δ1
= −28.◦ 936 172 42.
(J2000).
The galactic longitude of the North Celestial Pole is
θ = 123.◦ 00 (1950),
θ = 122.◦ 931 918 6 = l3
(J2000).
The ascending node of the galactic plane on the J2000 equator has the position
RA = α3 + 6h = 282.◦ 86,
l II = 3 − 90◦ = 32.◦ 93.
The mutual angle of inclination of the two planes is 90◦ − δ3 = 62.◦ 87.
The conversion between equatorial and new galactic coordinates for (J2000) is given approximately
by [31]
sin bII = sin δ cos 62.◦ 87 − cos δ sin(α − 282.◦ 86) sin 62.◦ 87,
cos bII cos(l II − 32.◦ 93) = cos δ cos(α − 282.◦ 86),
but see [29] for a more precise formulation.
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23.2
M ILKY WAY AND G ALAXIES
NORMAL GALAXIES
23.2.1
E
S0
S
Irr
dSph
Classification
Elliptical (spheroidal component dominates), from E0 (round) to E7 (most flattened).
b/a = 1 − n/10; e.g., b/a = 0.3 is E7. gE and dE denote giants and dwarfs, respectively.
Lenticular (spheroid and disk, but no recent star formation).
Spiral (spheroid and disk with arms of young stars) from S0a (least dominant arms)
through Sa, Sb, Sc, Sd (most dominant arms) to Sm (Magellanic faint spirals).
SA = unbarred; SB = barred.
Irregular (little or no spheroid; young stars are not in coherent arms). The Magellanic type
(intrinsically irregular) called IrrI, Im, or IBm (barred). Merger products, disturbed, and
active galaxies are labeled Irr II or I0. dIrr denotes dwarf irregulars.
Dwarf spheroidals (masses and luminosities much less than ellipticals, but much less
centrally condensed than globular clusters; many are companions). Probably the
commonest kind of galaxy in a volume-limited sample.
Special types:
cD
BCD
Supergiant diffuse galaxies at cluster centers,
Blue compact dwarf galaxies, dIrr with very active star formation.
For additional criteria and refinements, see [32, 33]. Table 23.5 gives more details. Table 23.6 lists
the local group members. Table 23.7 gives the local bright galaxies.
23.2.2
Galaxy Counts
Integral Counts
The number of galaxies per square degree brighter than m B (for apparent magnitude m B = 12–15) in
the South Galactic Polar Cap [34]:
log N (m) = 0.62m − 9.7.
The number in the North Galactic Polar Cap is larger by log N (m) = 0.4 at m B = 12.0, tapering
to log N (m) = 0.0 at m B = 14. Here logarithms to the base 10 are used, as elsewhere in this chapter.
Differential Counts
The number per square degree of galaxies with magnitude in the J color band of m = b J ± 0.25 in the
South Galactic Polar Cap [b J = B − 0.28(B − V )] [35] is given in Table 23.8.
15.5
14.0–18.0
≤ 14.0–18.0
15.0–20.0
17.5
15.5
16.5–21.0
19.5
20.0
16.5–21.5
?–18.0
7.6–15.5
16.5–21.5
≤ 14.0
20.0
22.5–25.0
15.5–22.0
23.0
20.0
[3, 4]
0.46
0.37
0.37
0.69
0.54
0.47
0.78
0.87
0.93
0.91
[5]
B − Vc
1–5
8.9; 0.6–8.9
13.6; 1.8–32.8
22.4; 5.3–50.9
21.5; 2.8–47.5
16.2; 4.2–52.3
16.5; 4.7–48.5
30–1000
20.5;
30–60
1–5
0.5–3
17.5; 5.5–71.7
1037 –1039
1038 –1041
1039 –1042
1043
Lx
[6]
0.1–10.0
0.1–0.2
0.03–3.0
< 0.01–0.1
0.01–0.1
[7]
L FIR /L B d
HI; 0.2
HI+H2 ; 0.1–0.5
HI+H2 ; 0.25
HI+H2 ; 0.08
HI+H2 ; 0.15
HI+H2 ; 0.25
0.5 ± 0.2
0.5 ± 0.2
1.2 ± 0.2
2–6
X-ray; (109 –1010 )
HI+H2 ; (107 –109.5 )
HI+H2 ; 0.04
2–6
4.8 ± 1
15 ± 3
Specific freq.
globular
clusters f
[9]
X-ray; (108 –1011 )
X-ray; (1011 –1012 )
Gas contente
phase; amount
(M ), or fraction
[8]
10–80
2–5
3.1; 0.7–7.0
5.8; 1.4–17.3
4.2; 1.3–13.9
4.7; 1.0–10.3
6.5; 1–23
10–80
4.0; 1–7
5–15
5–15
5–15
M/L
(solar units)
Mean; range
[4]
1010 –1012
1011.5 –1013
1012 –1013
Mtot
(M)
[6, 10]
10–20
10–90
180
M/L
Total
[6, 10]
References
1. Faber, S.M., editor, 1987, Nearly Normal Galaxies (Springer-Verlag, New York)
2. Kron, R.G., editor, 1989, Evolution of the Universe of Galaxies, Astronomical Society of the Pacific Conference Series
3. Bingelli, B., Sandage, A., & Tammann, G.A. 1988, ARA&A, 26, 509
4. Tully, R.B. 1987, Nearby Galaxies Catalog (Cambridge University Press, Cambridge); generally to 25m /sq.
5. de Vaucouleurs, G., & Mitra, S. 1991, unpublished
6. Fabbiano, G. 1987, ARA&A, 27, 87
7. Soifer, B.T., Houck, J.R., & Neubebauer, G. 1989, ARA&A, 25, 187
Notes
a All quantities are given on the “short” distance scale. None of them is so precisely known that it matters whether this means H = 85 or H = 100 (km/s)/Mpc.
For the “long” scale, distances and masses go up by a factor of 2, luminosities by a factor of 4, and M/L by a factor of 2.
b Limits containing galaxies down to 0.1 of the peak space density.
c Mean for type, corrected for inclination and internal reddening.
d Starburst S galaxies extend up to 2 × 1012 L .
e Most giant galaxies have (109 –1010 )M of gas, but it is a cool (HI + H ) disk component in spirals, a hot (keV, X-ray emitting) component in cD and elliptical
2
galaxies, and a mixture of these in S0 galaxies. Young and Scoville give ratios of the mass of disk gas to the total disk mass of the galaxies.
f Units are the number of globular clusters per unit of luminosity corresponding to visual absolute magnitude M = −15.
V
g Luminosity and size of cD galaxies includes the extended halo, much of which lies below the 25m /sq.
contour.
h Properties on intermediate lines are averages for Sa + Sb, etc.
dIrr
BCD [13]
Sm
Irr
Im
Sb
Sc
Sd
S
Sah
E
gE
dE
dSph [12]
S0
cDg [11]
Type
−M B
[3, 4]
−M B , rangeb
Diameter (kpc)
Mean; range
[4]
Table 23.5. Representative properties of galaxies by type [1, 2].a
Sp.-V/AQuan/1999/10/11:12:03
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23.2 N ORMAL G ALAXIES / 577
8.
9.
10.
11.
12.
13.
Milky Way
M31
= NGC224
M32
= NGC221
NGC205 = M110
SMC
NGC185
NGC147
And. I
Sculptor
And. III
IC1613
= DDO8
Psc
= LGS3
NGC598
= M33
And. II
Phoenix
WLM
= DDO221
Fornax
LMC
Carina
Leo I
Sextans
Leo II
Ursa Minor
Draco
NGC6822
DDO210
Tucana
Galaxy
[1]
−149
−46
70.8
1.6
4.9
11.5
63.1
645.7
23.4
9.8
90.
12.0
30.2
35.5
15.5
2.2
5.5
+21◦ 51
+30◦ 34
+33◦ 26
−44◦ 26
−15◦ 27
−34◦ 27
−69◦ 45
−50◦ 58
+12◦ 18
−01◦ 36
+22◦ 09
+67◦ 12
+57◦ 55
−14◦ 48
−12◦ 50
−64◦ 25
01h 33.m 9
01h 16.m 5
01h 51.m 1
00h 02.m 0
02h 39.m 9
05h 23.m 7
06h 41.m 6
10h 08.m 5
10h 13.m 0
11h 13.m 5
15h 08.m 8
17h 20.m 1
19h 45.m 0
20h 46.m 8
22h 49.m 1
0.7
0.85
0.66
0.8
0.6
0.9
0.6
0.7
0.9
0.5
0.55
0.7
0.8
0.35
0.6
0.63
0.59
11.18
12.6
11.9
10.8
9.31
14.0
(14.0R)
0.01
0.43
0.31
0.47
0.67
0.82
0.36
0.73
0.78
0.75
9.04
0.91
11.03
13.5
6.27
8.92
2.70
10.10
10.47
13.5
10.50
13.5
9.88
+36
−47
−87
+44
−23
−41
+119
+13
+60
−61
−152
+115
−60
+34
−64
+28
−28
01h 03.m 8
0.5
0.6
0.85
0.6
1.0
0.8
0.4
0.9
0.88
21.9
316.2
11.7
13.2
1.4
39.8
0.75
16.2
9.03
+41◦ 41
−72◦ 49
+48◦ 20
+48◦ 30
+38◦ 02
−33◦ 42
+36◦ 31
+02◦ 08
0.74
00h 40.m 0
00h 52.m 7
00h 38.m 9
00h 33.m 2
00h 45.m 5
01h 00.m 2
00h 35.m 3
01h 04.m 8
−121
Vrg f
[2]
8.7
0.68
(B − V )0 e
[2]
+40◦ 52
4.36
BT d
[2]
00h 42.m 7
0.32
b/a c
[2]
190.5
Diam.b
[2]
+41◦ 16
Decl.
[2]
00h 42.m 7
RA
(2000.0)
dSph
SBm–Ir III-IV
dSph
dSph
dSph
dSph–E0p
dSph
dSph
IBm IV-V
IBm V
dSph–dE5
dSph
dIm/dSph
IBm IV-V
Sc,cd II-III
dIrr
Sph–E5p
Im IV-V
dSph–dE3p
dSph–dE5
dSph–E3p
dSph
dSph
IBm/Irr V
E2
Sbc I-II
Sb I-II
Type
[1–3]
131
55
107
229
87
234
69
76
495
725
890
725
417
940
795
725
725
58
620
645
725
78
725
715
725
725
Dist.
(kpc)
[1]
−13.7
−18.1
−7.6
−11.7
−10.0
−9.4
−8.9
−8.6
−16.4
−11.5
−9.5
−11.8
−9.9
−14.1
−18.9
−16.3
−16.2
−15.3
−15.1
−11.8
−10.7
−10.3
−14.9
100:
101
50:
220
254
−20.6
−21.1
−16.4
Vrotation
(km/s)
[4]
MV
[1]
1 × 1037
< 3 × 1035
6.6 × 1038
1.1 × 1039
< 9 × 1036
6.1 × 1037
5.4 × 1037
3.0 × 1039
3.6 × 1039
Lx g
(erg/s)
[5]
−1.40
−0.40
−1.52
−1.30
−1.5?
−1.90
−2.20
−2.10
−0.6
−2.0
−0.90
−1.20
−1.40
−1.80
−0.85
−0.75
[Fe/H]
[6]
578 / 23
Table 23.6. The Local Group.a
Young, J.S., & Scoville, N.S. 1991 ARA&A, 29, 281; ratios of the mass of disk gas to the total disk mass of the galaxies
Harris, W.E. 1991, ARA&A, 29, 543
Trimble, V. 1987, ARA&A, 25, 425
Kormendy, J., & Djorgovski, S. 1989, ARA&A, 27, 235 and references therein
van den Bergh, S. 1992, MNRAS, 255, 29pp
Thuan, T.X., in Ref. [1]
Sp.-V/AQuan/1999/10/11:12:03
Page 578
M ILKY WAY AND G ALAXIES
NGC 55
NGC 247
NGC 253
NGC 300
NGC 628 = M74
NGC 1068 = M77
NGC 1291
NGC 1313
NGC 1316
(Fornax A)
NGC 2403
NGC 2903
NGC 3031 = M81
NGC 3034 = M82
NGC 3115
NGC 3521
NGC 3627 = M66
NGC 4258 = M106
NGC 4449
NGC 4472 = M49
Galaxy
[1]
32.4
21.4
27.5
21.9
10.5
7.1
9.8
9.1
12.0
21.9
12.6
26.9
11.2
7.2
11.0
9.1
14.8
6.2
10.2
+65◦ 36
+21◦ 30
+69◦ 04
+69◦ 41
−07◦ 43
−00◦ 02
+13◦ 00
+47◦ 18
+46◦ 06
+08◦ 00
07h 37m
09h 32m
09h 56m
09h 56m
10h 05m
11h 06m
11h 20m
12h 19m
12h 28m
12h 30m
Diam.a
[2]
−39◦ 13
−20◦ 46
−25◦ 17
−37◦ 41
+15◦ 47
−00◦ 01
−41◦ 06
−66◦ 30
−37◦ 12
Decl.
(2000.0)
[2]
00h 15m
00h 47m
00h 48m
00h 54m
01h 37m
02h 43m
03h 17m
03h 18m
03h 23m
[2]
RA
0.56
0.48
0.52
0.38
0.84
0.47
0.46
0.39
0.71
0.81
0.17
0.32
0.25
0.71
0.91
0.85
0.83
0.76
0.71
b/a b
[2]
8.93
9.68
7.89
9.30
9.87
9.83
9.65
9.10
9.99
9.37
8.42
9.67
8.04
8.72
9.95
9.61
9.39
9.20
9.42
BT c
[2]
0.39
0.55
0.82
0.79
0.94
0.68
0.60
0.55
0.41
0.95
0.58
0.51
0.70
0.91
0.48
0.87
0.54
0.54
(B − V )d0
[2]
Scd III
SABbc I-II
SAab I-II
I0/amorphous
S0
SABbc II
SABb II
SABbc II-III
IB/Sm IV
E1-2/S0
SBc/m III
SABc/d III-IV
SABc II
Sc/d II-IV
SAc II
SAb II
SB0/a
SBc/d III-IV
SAB0/a pec
Type
[1, 2]
+226
+476
+69
+323
+492
+673
+643
+510
+255
+846
+94
+176
+251
+98
+753
+1144
+712
+292
+1674
Vrg e
[2]
Table 23.7. Bright Galaxies, BT < 10 (excluding Local Group galaxies).
4.2
6.3
1.4
5.2
6.7
7.2
6.6
6.8
3.0
16.8
1.3
2.1
3.0
1.2
9.7
14.4
8.6
3.7
16.9
Dist. f
(Mpc)
[3]
−19.68
−19.85
−18.29
−19.42
−19.18
−19.88
−19.66
−20.59
−17.66
−21.82
−18.13
−17.98
−20.02
−16.88
−20.32
−21.39
−20.26
−18.60
−21.47
0i g
M BT
[3]
10.67
10.91
10.73
10.99
10.74
11.17
295
188
213
10.31
9.87
10.02
10.87
9.89
log Mtot i
[3]
124
196
236
83
92
197
100
face on
face on
face on
136
Vrotn h
[3]
References
1. van den Bergh, S. 1992, MNRAS, 255, 29pp
2. de Vaucouleurs, G., de Vaucouleurs, A., Corwin, H.G., Buta, R.J., Paturel, G., & Fouque, P. 1990, Third Reference Catalogue of Bright Galaxies
(University of Texas Press, Austin)
3. Sandage, A., & Tammann, G. 1987, A Revised Shapley Ames Catalog of Bright Galaxies (Carnegie Institute of Washington, Washington, DC)
4. Tully, R.B. 1987, Nearby Galaxies Catalog (Cambridge University Press, Cambridge)
5. Fabbiano, G. 1989, ARA&A, 27, 87
6. Hodge, P. 1989, ARA&A, 27, 139; Caldwell, N. et al. 1992, AJ, 103, 840
Notes
a Other suggested Local Group members include IC10 and 1927-17 = UGC 594-04 = SagDIG [4] and And IV [Madore, B.F. in Observer’s Handbook
1992, edited by B.L. Bishop (Royal Astronomical Society Canada), p. 223].
b Arcminutes; isophotal to 25m /sq.
, except And. I, II, and III core radii.
c Axial ratio, to 25m /sq.
isophote.
d Entire galaxy, no correction for absorption.
e Entire galaxy, corrected for reddening.
f Galactocentric radial velocity.
g X-ray luminosity, 0.2–3.5 keV.
Sp.-V/AQuan/1999/10/11:12:03
Page 579
23.2 N ORMAL G ALAXIES / 579
8.3
8.7
15.5
7.4
11.2
10.0
20.0
12.6
25.7
11.2
12.9
28.8
20.0
11.5
9.3
+32◦ 32
+11◦ 33
+41◦ 07
+21◦ 41
−49◦ 28
+42◦ 02
−43◦ 01
+47◦ 12
−29◦ 52
+54◦ 21
−63◦ 51
+60◦ 09
−32◦ 35
12h 42m
12h 44m
12h 51m
12h 57m
13h 05m
13h 16m
13h 25m
13h 30m
13h 37m
14h 03m
19h 10m
20h 35m
23h 58m
Diam.a
[2]
+12◦ 23
−11◦ 37
Decl.
(2000.0)
[2]
12h 31m
12h 40m
[2]
RA
0.62
0.89
0.93
0.65
0.85
0.68
0.17
0.81
0.81
0.54
0.19
0.58
0.79
0.79
0.41
b/a b
[2]
8.96
8.20
8.31
9.14
9.61
9.63
9.75
9.81
8.99
9.36
9.3
9.31
7.84
9.59
8.98
BT c
[2]
0.40
0.53
0.61
0.44
0.64
0.88
0.55
0.95
0.72
0.71
0.93
0.45
(B − V )d0
[2]
SAbc I-IIp
SBc II
SABcd I
Sbc II
Scd II
SAd IV
SBc/d III
S0/E2
SAab II
Sab II
SBcd IV
SAbc II-III
S0p
cD, E0p
Sa/ab
Type
[1, 2]
+551
+384
+360
+746
+277
+228
+629
+970
+360
+403
+383
+571
+398
+1229
+969
Vrg e
[2]
7.7
4.7
5.4
10.4
5.5
2.8
6.9
16.8
4.3
4.1
5.2
7.2
4.9
16.8
20.0
Dist. f
(Mpc)
[3]
−20.75
−20.31
−20.45
−21.39
−20.78
−17.69
−20.12
−21.36
−19.37
−19.15
−20.65
−20.42
−20.97
−21.64
−22.98
0i g
M BT
[3]
11.37
10.81
9.95
References
1. Sandage, A., & Tammann, G.A. 1987, A Revised Shapley Ames Catalog of Bright Galaxies (Carnegie Institute of Washington, Washington, DC)
2. de Vaucouleurs, G., de Vaucouleurs, A., Corwin, H.G., Buta, R.J., Paturel, G., & Fouque, P. 1990, Third Reference Catalogue of Bright Galaxies
(University of Texas Press, Austin) (RC3)
3. Tully, R.B. 1987, Nearby Galaxies Catalog (Cambridge University Press, Cambridge)
face on
face on
185
153
104
11.15
10.78
186
224
10.70
11.38
log Mtot i
[3]
142
369
Vrotn h
[3]
580 / 23
Notes
a Arcminutes; isophotal to 25m /sq.
b Axial ratio, to 25m /sq.
isophote.
c Entire galaxy, no correction for absorption.
d Entire galaxy, corrected for reddening; inclination corrections revised from RC3 (G. de Vaucouleurs, private communication).
e Galactocentric radial velocity, km/s.
f Distances larger by factors 1.2–2 and correspondingly brighter absolute magnitudes are given in [1].
g Entire galaxy, corrected for absorption and angle of inclination.
h 21 cm velocity width, corrected for sin i.
i From 21 cm velocity width and angular extent.
NGC 4486 = M87
NGC 4594 = M104
(Sombrero)
NGC 4631
NGC 4649 = M60
NGC 4736 = M94
NGC 4826 = M64
NGC 4945
NGC 5055 = M63
NGC 5128
(Cen. A)
NGC 5194 = M55
NGC 5236 = M83
NGC 5457 = M101
NGC 6744
NGC 6946
NGC 7793
Galaxy
[1]
Table 23.7. (Continued.)
Sp.-V/AQuan/1999/10/11:12:03
Page 580
M ILKY WAY AND G ALAXIES
Sp.-V/AQuan/1999/10/11:12:03
Page 581
23.2 N ORMAL G ALAXIES / 581
Table 23.8. Galaxy counts.
bJ
N
15.29
15.77
16.25
16.71
17.29
17.74
18.29
18.72
19.25
19.77
20.27
20.77
0.47
0.83
1.51
2.90
6.11
11.7
24.8
41.7
81.3
140.
233.
407.
The fainter counts have been corrected for galaxy spectral shapes (k correction) but generally not
for galactic extinction. The numbers at b 90◦ will be smaller by
log N = −s A(90◦ )(csc b − 1),
where A(90◦ ) is the extinction at the pole (A B = 0.13–0.20) and s is the slope of log N (m) (= 0.6 in
the Euclidean case).
Most surveys that go fainter than b J = 20 find differential counts per square degree per unit
magnitude [35]:
log N (b J ) = 0.45b J + C, with normalization C = 7.7 to 8.2.
The number of galaxies seen from outside the Milky Way would be larger than the polar cap number
N (m) by
log N = +s A(90◦ ),
where A(90◦ ) = 0 to 0.20 in this context [32, 36].
23.2.3
Luminosity Function
Away from anomalies due to the Local Supercluster, a Schechter function [37] provides a remarkably
good fit [38–41] over the range M B = −15 to −21:
φ(L) d L = φ ∗ (L/L ∗ )α exp(−L/L ∗ ) d(L/L ∗ ),
where
φ ∗ = (0.015 ± 0.001)h 3 galaxies Mpc−3 ,
L ∗ is the luminosity corresponding to M B∗ = −19.5 ± 0.2 (M B = 5.48), and α = −1.1 ± 0.1 (−1.0
in the field, −1.25 in rich clusters). Such numbers have been corrected for redshift effects (including
the k correction) and absorption in the Milky Way, using a variety of prescriptions.
The true luminosity function is a strong function of Hubble morphological type; in particular, that
for dwarf galaxies continues to rise faintward of M B = −14, though not so steeply that faint galaxies
dominate the cosmic luminosity density [2, 39].
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582 / 23
23.2.4
M ILKY WAY AND G ALAXIES
Luminosity Density
The luminosity density of the Universe, for a Schechter luminosity function, is [41]
L = φ ∗ (α + 2)L ∗ ,
L = (1.4–2.0) × 108 h L /Mpc3
in the B band.
Thus the closure density in the Universe corresponds to
M/L B = (1400–2000)h(M/L) .
Notes added in proof.
A number of things have evolved since this chapter was completed in June 1992: the distance
to the galactic center [42] and details of galactic structure [43]. New members of the Local Group
include a dwarf spheroidal galaxy in Sagittarius [44], a Pegusus dwarf [45], and the nonmembership of
Andromeda IV [46]. Galaxy properties as a function of Hubble type are discussed in [47], black holes
in the centers of normal galaxies are discussed in [48], and a number of papers on galaxy counts are
given in IAU Symposium 161 and 179 [49].
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3. Fich, M., & Tremaine, S. 1991, ARA&A, 29, 409
4. Beichman, C.A. 1987, ARA&A, 25, 521
5. van der Kruit, P. in The Galaxy, edited by G. Gilmore
and B. Carswell (Reidel, Dordrecht)
6. Kulessa, A.S., & Lynden-Bell, D. 1992, MNRAS, 255,
105
7. Allen, C., & Santillan, A. 1991, Rev. Mexicana Astron.
Af., 22, 255
8. Zombeck, M.V. 1982, Handbook of Space Astronomy
and Astrophysics (Cambridge University Press, Cambridge)
9. McCammon, D., & Sanders, W.T. 1990, ARA&A, 28,
657
10. Bowyer, S. 1991, ARA&A, 29, 59
11. Bowyer, S., & Leinert, C., editors, 1990, IAU Symposium 139, Galactic and Extragalactic Backgrounds
(Kluwer Academic, Dordrecht)
12. Bloemen, H. 1989, ARA&A, 27, 469
13. van der Kruit, P. 1987, in IAU Symposium 139,
Ref. [11]
14. Genzel, R., & Townes, C.H. 1987, ARA&A, 25, 377
15. Vallee, J.P., Simard-Normandin, M., & Bignell, R.C.
1988, ApJ, 331, 321
16. Combes, F. 1991, ARA&A, 29, 295
17. Cowan, J.J., Thielmann, F.-K., & Truran, J.W. 1991,
ARA&A, 29, 447
18. Wood, M.A. 1992, ApJ, 386, 539
19. Rana, N.C. 1991, ARA&A, 29, 129
20. Dickey, J.M., & Lockman, F.J. 1990, ARA&A, 28, 215
21. Young, J.S., & Scoville, N. 1991, ARA&A, 29, 281
22. Bahcall, J.N., Schmidt, M., & Soneira, R.M. 1983, ApJ,
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26. Merrifield, M. 1992, AJ, 103, 1552
27. Bahcall, J.N. 1986, ARA&A, 24, 577
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29. Murray, C.A. 1988, A&Ap, 218, 325
30. Murray, C.A. 1992, private communication
31. Lang, K.R. 1980, Astrophysical Formulae (SpringerVerlag, Berlin), p. 50l
32. Sandage, A., & Tammann, G. 1987, A Revised Shapley
Ames Catalog of Bright Galaxies (Carnegie Institute of
Washington, Washington, DC)
33. de Vancouleurs, G., de Vaucouleurs, A., Corwin, H.G.,
Buta, R.J., Paturel, G., & Fougue, P. 1990, Third Reference Catalogue of Bright Galaxies (University of Texas
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35. Maddox, S.J. et al. 1990, MNRAS, 247, 1p
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37. Schechter, P. 1976, ApJ, 203, 297
38. Giovanelli, R., & Haynes, M. 1991, ARA&A, 29, 499
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39. Bingelli, B., Sandage, A., & Tammann, G.A. 1988,
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Page 584