2018AJ....155..227B

We present Submillimeter Array and Northern Extended Millimeter Array observations of the host galaxy of FRB 121102 in the CO 3-2 and 1-0 transitions, respectively. We do not detect emission from either transition. We set 3σ upper limits to the CO luminosity L_CO < 2.5 x 10⁷ K km s^–1 pc^–2 for CO 3-2 and L_CO < 2.3 x 10⁹ K km s^–1 pc^–2 for CO 1-0. For Milky Way-like star formation properties, we set a 3σ upper limit on the H₂ mass of 2.5 x 10⁸ M_☉, slightly less than the predictions for the H₂ mass based on the star formation rate. The true constraint on the H₂ mass may be significantly higher, however, because of the reduction in CO luminosity that is common for low-metallicity dwarf galaxies like the FRB host galaxy. These results demonstrate the challenge of identifying the nature of FRB progenitors through study of the host galaxy molecular gas. We also place a limit of 42 µJy (3σ) on the continuum flux density of the persistent radio source at 97 GHz, consistent with a power-law extrapolation of the low-frequency spectrum, which may arise from an active galactic nucleus or other nonthermal source.