Astronomical Applications Department, U.S. Naval Observatory thesis Page 55
41
0
1
2
3
4
25
24
23
22
HoII
0
2
4
6
8
25
24
23
22
IC2574
0
1
2
3
4
25
24
23
22
Fig. 4.5. B-band surface brightness pro les as a function of radius
level at the e ective radius, r
e
, where the total galaxy luminosity drops to half
its total value. The central surface brightness estimate is made by extrapolating
the exponential t to the center of the galaxy. Corrected for Galactic foreground
extinction,
B
0=22.3
0
:
02 mag arcsec
,2
and
B
0=22.2
0
:
01 mag arcsec
,2
for HoII and Sextans A, respectively. The range in central surface brightness of
the galaxies in the Karachentseva
et
al.
1996 sample is 22.2
B
0
24 mag
arcsec
,2
compared to the canonical value of 21.65
0
:
30 mag arcsec
,2
for disk
galaxies Freeman 1970. HoII and Sextans A fall at the brighter end of the ob-
served range for low surface brightness irregular galaxies. Other studies report an
average
h
B
0
i
=23.5
0
:
2 Ronnback and Bergvall 1994 and
h
B
0
i
=23.5
1
:
6
mag arcsec
,2
Vader and Chaboyer 1994.
