A sensitive search for CO emission from faint blue galaxies at Z ~ 0.5

We have obtained sensitive upper limits on the CO J=2-1 and CO J=3-2 emission lines for ve faint blue galaxies with redshifts z 0:5 using the IRAM 30 m telescope. These observations would have been able to detect the luminous in- frared galaxy IRAS F10214+4724 if it were located at this red- shift and unlensed. However, they are not sensitive enough to detect the prototype starburst galaxy M82 or the HII galaxy UM448 if they were located at this redshift. Our upper limits for the CO emission are consistent with between 19% and 66% of the total galactic mass being in the form of molecular hy- drogen, and thus shed little light on the ultimate fate of these galaxies.