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We present sensitive CO (J = 1 - 0) emission line observations of threemetal-poor dwarf irregular galaxies Leo P (Z ~ 3% Z_Solar), Sextans A (Z ~ 7.5%Z_Solar), and Sextans B (Z ~ 7.5% Z_Solar), all obtained with the CombinedArray for Millimeter-wave Astronomy (CARMA) interferometer. While no COemission was detected, the proximity of the three systems allows us to placevery stringent (4 sigma) upper limits on the CO luminosity (L_CO) in thesemetal-poor galaxies. We find the CO luminosities to be L_CO < 2900 K km/s pc^2for Leo P, L_CO < 12400 K km/s pc^2 for Sextans A, and L_CO < 9700 K km/s pc^2for Sextans B. Comparison of our results with recent observational estimates ofthe factor for converting between L_CO and the mass of molecular hydrogen, aswell as theoretical models, provides further evidence that either the CO-to-H_2conversion factor increases sharply as metallicity decreases, or that stars areforming in these three galaxies very efficiently, requiring little molecularhydrogen.

CARMA CO Observations of Three Extremely Metal-Poor, Star-Forming Galaxies