Deep CO Observations and the CO-to-H_2 Conversion Factor in DDO 154, a Low Metallicity Dwarf Irregular Galaxy

TL;DR

This study conducted deep spectroscopic observations of the low-metallicity dwarf galaxy DDO 154 to measure its CO emission and constrain the CO-to-H2 conversion factor, finding it to be significantly higher than the Galactic standard.

Contribution

First direct deep spectroscopic search for CO in DDO 154, establishing a lower limit on the CO-to-H2 conversion factor at very low metallicity.

Findings

No CO detected despite sensitive observations

Lower limit on conversion factor at least 10 times the Galactic value

Supports the hypothesis of higher conversion factors in low-metallicity environments

Abstract

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.