Appendix E
Drap
= Dr exp[-(r/ro)2/2]
(E-1)
The
apparent radial distance rap measured
by the earth observer is the integral of Eq. E-1:
rap
=
¦
drap
=
¦
exp[-(r/ro)2/2]
dr
(E-2)
Divide
this by ro, and place
limits on the integral, to obtain
rap/ro
=
¦
(0,z) exp[-(r/ro)2/2]
(dr/ro) =
¦
(0,z) exp[-x2/2]
dx (E-3)
The
subscript for the integral sign indicates that the lower limit on the integral
is zero, and the upper limit is z. The value for the upper limit z is
z
= (r/ro)
(E-4)
The integral of Eq. E-3 is related to
the normal distribution function denoted F(x),
which is used extensively in probability and statistics. As shown by Feller [4]
(p. 164), the normal distribution function is defined as
F(x) = (1/Ö
[2p])
¦(-
¥
,x) exp[-y2/2]
dy
(E-5)
The lower limit on this integral is
minus infinity (-¥) and the upper limit is zero. Values of this
function F(x) are tabulated on page 167 of Ref. [4]. The derivative of the normal
distribution function F(x)
is denoted f(x),
and is called the normal density function.
Note that the density function f(x) is denoted by the lower case Greek phi, whereas the distribution
function F(x) is denoted by the upper case Greek phi. The normal density function f(x) is defined as
f(x) = dF(x)/dx =
(1/
Ö
[2p]) exp[-x2/2]
(E-6)
This is the common bell-shaped curve
used in statistics. Since the area under this curve is unity, and the curve is
symmetric about zero, the value of its integral F(x) must be unity at x =
¥
, and must be 0.5 at x = 0. Hence, Eq. E-5 can be expressed as follows
in terms of an integral from zero to x:
F(x) = 0.5 + (1/Ö[2p])
¦(0,x) exp[-y2/2]
dy
(E-7)
Multiply Eq. E-7 by 2, and solve for
the integral. This gives
¦(0,x)exp[-y2/2]dy
=
Ö
[p/2]{ 2F(x) - 1}
= Ö
[2p]{ F(x) – 0.5} (E-8)
rap/ro
=
¦(0,z) exp[-x2/2]
dx
=
Ö2p{F[r/ro] – 0.5}
(E-9)
The
upper limit of the integration, z, is equal to
r/ro. The values of
F(x)
are obtained from tabulated data given by Feller [4] (p.167). From these one can
compute from Eq. E-9 the values of the function rap/ro
listed in Table E-1.
Table E-1:
Values of the apparent distance ratio rap/ro
of a galaxy versus the true
distance ratio r/ro derived from Eq.
E-9,
using tabulated values of the normal
distribution function F(x).
x,
r/ro
F[x]
rap/ro
x, r/ro
F[x]
rap/ro
0 .500
000
0
2.0 .977 250
1.196 288
.1 .539
828
.099 833
2.1 .982 136
1.208 535
.2 .579
260
.198 675
2.2 .986 097
1.218 464
.3 .617
911
.295 559
2.3 .989 276
1.226 433
.4 .655
422
.389 585
2.4 .991 802
1.232 765
.5 .691
462
.479 924
.6 .725
747
.565 864
.7 .758
036
.646 800
.8 .788
145
.722 272
.9 .815
940
.791 944
2.9 .998 134
1.248 637
1.0 .841 345
.855 625
3.0 .998 650
1.249 930
1.1 .864 334
.913 250
1.2 .884 930
.964 876
1.3 .903 200
1.010 673
1.4 .919 243
1.050 886
1.5 .933 193
1.085 854
1.6 .945 201
1.115 953
1.7 .955 439
1.141 616
1.8 .964 070
1.163 251
1.9 .971 283
1.181 331