Deep CO Observations and the CO-to-H2 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 DDO 154, which has an Oxygen abundance of only 1=20 of the solar value. The observations were conducted in order to constrain the CO-to-H2 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 that argue for a high conversion factor at low metallicity