Probing the gas in the outer Galaxy: Molecular or AtomicquestionMark

Despite of all theoretical speculations and various observationalconstraints, the nature of the dark matter in the outer Galaxy isstill unknown. Herschel/HIFI offers the unique opportunity to detector set a significant upper limit to a potential component of baryonicmatter in the form of cold gas, which is molecular in hydrogen, butdoes not form CO. Such gas can be potentially be traced through CII150 um and HF J10 absorption against continuum backgroundsources. We propose a set of 7 the brightest outer Galaxy dustcontinuum sources, for which we will determine the positions of peakemission by PACS mapping. Deep integrations in CII and HF towardsthe 4 brightest peaks in these sources will potentially detect a coldgas component and will, in any case, give significant upper limits toits column density. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]