Deep CO Observations and the CO-to-H_2 Conversion Factor in DDO 154, a
  Low Metallicity Dwarf Irregular Galaxy
  We present a deep spectroscopic search for CO emission in the dwarf irregular
galaxy DDO154, which has an Oxygen abundance of only 1/20 the solar value. The
observations were conducted in order to constrain the CO-to-$\mathrm{H_2}$
conversion factor at low metallicity. No CO was detected, however, despite
being one of the sensitive observations done towards galaxies of this type. We
succeed in putting a strong lower limit on the conversion factor, at least 10
times the Galactic value. Our result supports previous studies which argue for
a high conversion factor at low metallicity.
