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The star formation rate (SFR) of the current SF episode can be estimated
from the total H
luminosity. The H
flux was measured within
the slit, and was corrected for the missing light outside the slit.
A correction factor of 2.33 was calculated, using the brightness
profile along the slit and assuming circular symmetry.
For the derived total flux F(H
)=5.8
erg s-1cm-2 we obtain a total H
luminosity of 1039 erg s-1.
This H
luminosity corresponds to a current SFR
of
0.007
yr-1 (Hunter & Gallagher [1986])
assuming a Salpeter IMF with a 0.1
lower mass cutoff.
The gaseous mass converted into the stars during a
3 Myr burst is
2
104
.
The unknown contribution of the gaseous emission to the light from the LSB
component further complicates the stellar mass estimate. If only stars with age
100 Myr contribute to
the LSB luminosity, then the total mass of stars in the underlying
disc with
=-123
is 1.3
106
(from e.g., Leitherer et al.
[1999]). This is much smaller than the total
neutral gas mass of
3.0
107
,
accounting for a helium mass fraction of 0.25.
The total mass of ionized gas can
be obtained from the average mass density inside the H II
region and its volume. An average mass density corresponding to the
average electron density
of 1 cm-3 within a volume
with a diameter of 0.5 kpc yields a total ionized gas mass of 106
.
The above estimates show that baryonic matter in HS 0822+3542 is dominated by the gaseous component.