Do the Herschel cold clouds in the Galactic halo embody its dark matter?

Abstract

Recent Herschel/SPIRE maps of the Small and Large Magellanic Clouds (SMC, LMC) exhibit in each thousands of clouds. Observed at 250 microns, they must be cold, T ~ 15 K, hence the name "Herschel cold clouds" (HCCs). From the observed rotational velocity profile and the assumption of spherical symmetry, the Galactic mass density is modeled in a form close to that of an isothermal sphere. If the HCCs constitute a certain fraction of it, their angular size distribution has a specified shape. A fit to the data deduced from the SMC/LMC maps supports this and yields for their radius 2.5 pc, with a small change when allowing for a spread in HCC radii. There are so many HCCs that they will make up all the missing Halo mass density if there is spherical symmetry and their average mass is of order 15,000 Mo. This compares well with the Jeans mass of circa 40,000 Mo and puts forward that the HCCs are in fact Jeans clusters, constituting all the Galactic dark matter and much of its missing baryons, a conclusion deduced before from a different field of the sky (Nieuwenhuizen, Schild and Gibson 2011). A preliminary analysis of the intensities yields that the Jeans clusters themselves may consist of some billion MACHOs of a few dozen Earth masses. With a size of dozens of solar radii, they would mostly obscure stars in the LMC, SMC and towards the Galactic center, and may thus have been overlooked in microlensing.