E. Taylor on "Star formation and the non-existence of dark galaxies

Do all DM halos have galaxies or can you somehow prevent star formation? Some galaxies form very little stars, but have much gas around them. HIPASS is a complete census of all neutral hydrogen over the sky and it found no dark galaxies.

But why do all galaxies form stars? Cooling is the key here. To cool further down than 10^4K you need H2 -cooling to get the temperature low enough to have disk-instabilities an initiate star formation. In their simulations they set up thngs to favor dark galaxies, but all but one of their models does not form stars and there is a minimal star-formation-rate (SFR) which in turn keeps the HI-could stable by heating it up again. This means star formation is self-regulated and it again boils down to the Schmitt-law of SF.

But the major point against dark galaxies still is the non-detection in HIPASS, where about 80 detections were expected.