Observing Baryonic Dark Matter with ALMA

Abstract

It has recently been argued that the unidentified SCUBA objects (USOs) are a thick disk population of free-floating dense, compact galactic gas clumps at a temperature of about 7 K. The characteristic mass scale is constrained to be on the order of a Jupiter mass, and the size is about 10 AU. A typical galactic USO is located at a distance from the sun of about 300 pc. We have calculated the molecular emission lines from these low temperature clouds. We consider three molecules: HD, LiH, and CO. HD is optically thin in the cloud, LiH is a molecule with a large electric dipole moment, and CO is an abundant molecule that is observed in dusty clouds. Our estimate for the typical object shows that LiH may be detectable by the future sub-mm array project, ALMA; its expected flux is at the mJy level and the line width is about $10^5$ Hz. Although typical galactic USOs are chemically and dynamically transient, the younger USOs will be recognisable via LiH emission if about a hundred USOs are observed. If USOs are confirmed to be of galactic origin, the total baryonic budget will need to be reevaluated.