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(LSBGs) using the JCMT 15-meter telescope and observed Ha images using the 2.16-meter telescope of NAOC. As no CO has been detected, only upper limits on the H2 masses are given. The upper limits of total molecular hydrogen masses are about (1.2-82.4) x 10^7 Msun. Their star formation rates are mainly lower than 0.4 Msun/yr and star formation efficiencies are lower than 1.364 x 10^10 /yr. 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 HI gas transforming to H2 gas.