The star formation history of low surface brightness galaxies (LSBGs) are <br />
interesting but poorly constrained.<br />
These objects tend to be rather blue, contradicting the initial impression <br />
that they may simply be faded remnants of higher surface brightness galaxies <br />
whose star formation has finished.<br />
Other scenarios span a broad range: a young mean age, less dust, a lower <br />
metallicity, perhaps even a variable initial mass function. <br />
We have obtained near-infrared broadband photometry and H$\\alpha$ photometry <br />
of a large sample of low surface brightness galaxies to measure the current <br />
and the time-averaged star formation rate (SFR) in order to constrain their <br />
star formation histories.<br />
The current star formation rates of LSBGs generally are higher than their <br />
past star formation rate, suggesting that the mean age of their stellar <br />
population is relatively young. <br />
This may stem from either a late epoch of formation or a sluggish evolution. <br />
In the latter case, the star formation efficiency may be an increasing <br />
function of time, perhaps due in part to the slow build up of metals and dust.<br />
Nevertheless, star formation remains sporadic and is generally not well <br />
organized across the disk.<br />
We find a strong correlation between the ratio of current to past average <br />
star formation rate and the gas mass fraction. <br />
Galaxies with large reservoirs of gas have relatively high current SFRs.<br />
There is a conspicuous absence of high gas mass fraction, low SFR galaxies, <br />
suggesting that the observed trend is not driven by bursts of star formation <br />
with short duty cycles.