Molecular Gas and Star-formation in Low Surface Brightness Galaxies

We have obtained CO(J = 2-1) spectra of nine face-on low surface brightness galaxies using the JCMT 15 m telescope and observed Ha images using the 2.16 m telescope of NAOC. As no CO has been detected, only upper limits on the H-2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) x 10(7) M-circle dot. Their star-formation rates are mainly lower than 0.4 M-circle dot yr(-1) and star-formation efficiencies are lower than 1.364 x 10(-10) yr(-1). Our results show that the absence of molecular gas content is the direct reason for the low star-formation rate. The low star -formation efficiency probably resulted from the low efficiency of H I gas transforming to H-2 gas.