46
integrated ux is converted to a SFR and listed in Table 4.2. The H luminosities
and SFR of HoII and IC2574 agree with the values derived by Miller & Hodge
1994 after di erences in distances are removed. The H luminosity for Sextans A
given by Hunter & Plummer 1996 is twice the luminosity found here. This
di erence is expected since they also derive uxes for individual HII regions that
are on average twice that of Hodge
et
al.
1994, the calibration source for the
H image.
Galaxy
LogL
H
LogL
FUV
SFR
H
SFR
FUV
SFR
FUV
SFR
H
M yr
,1
M yr
,1
HoII
39.55
38.67
0.028
0.049
1.75
IC2574
39.97
38.73
0.074
0.057
0.77
Sextans A
38.60
37.74
0.003
0.006
2.00
Table 4.2. Star Formation Rates from Observed Luminosities
A comparison between the SFR derived using the FUV and H regimes allows
a rough estimate of the recent star formation history in a given system. For exam-
ple, the ratio of SFR
FUV
SRF
H
indicates the fraction of recently formed massive
stars which the FUV observations trace as compared to the H observations. Since
internal extinction is not extreme low metallicity systems, this comparison is valid
to the rst order in estimating the recent to current formation history of massive
stars. For example, di erences in internal extinction e ects between the FUV
and H observations for a given EB-V are likely on the order of A
FUV
A
H
4,
assuming a LMC extinction curve for internal reddening this ratio doubles for
the SMC extinction curve. This di erence translates into a higher SFR
FUV
than
SFR
H
in a given system by underestimating A
FUV
to a greater degree than A
H
.
The results indicate the levels of recent 10
,
100 Myr and current 0
,
5 Myr
massive star formation in the galaxies are comparable with only slight di erences
between current and recent rates. Of the three, the FUV light in Sextans A traces
