Astronomical Applications Department, U.S. Naval Observatory thesis Page 54
40
4.1.2 Optical Surface Brightness Pro les
In contrast to the lack of FUV pro les, there have been numerous studies char-
acterizing the optical light pro les of low surface brightness galaxies Karachent-
seva
et
al.
1996; Patterson & Thuan 1996; Vader & Chaboyer 1994. A compar-
ison is made between the B-band surface brightness pro les of the three galaxies
and published pro les to determine if they demonstrate typical behavior for their
class. The B-band surface brightness pro les of the three galaxies are shown in
Fig. 4.5. The pro les of the two irregular galaxies in the sample, HoII and Sextans
A, are relatively similar and can be characterized as exponential with a central
depression. This behavior is typical of late-type low surface brightness galaxies.
The underlying exponential component indicates the presence of an optical disk
that is superimposed on bright star forming knots while the central trough demon-
strates that star formation is not centrally organized around a nucleus in these
systems. On the other hand, the IC2574 pro le does show central organization
of star formation along with the characteristic exponential shape at larger radii.
Note that the pro le is not complete; the outer 15 of the galaxy including the
brightest knot, is not shown due to the limited aperture size of the CCD compared
to the galaxy size. Despite the premature truncation of the pro le, its shape can
be compared to B-band pro les of the six dS-type galaxies in the Patterson &
Thuan 1996 study. The sample contains three galaxies with a central Gaussian
component accompanied by the characteristic exponential similar to the IC2574
pro le. Unlike the central trough in the irregular pro les, the IC2574 pro le shows
organization around a central nucleus.
A rough estimate of the central surface brightness of the HoII and Sextans A
pro les are made by tting each pro le with a pure exponential:
=
e
+ 1
:
8225
,
1
4.1
where = r r
e
. The e ective surface brightness,
e
, is the surface brightness
