Although the currently favored cold dark matter plus cosmological constant model ( LCDM ) has proven to be remarkably successful on large scales , on subgalactic scales it faces some potentially fatal difficulties ; these include over-producing dwarf satellite galaxies and predicting excessive central densities in dark halos .
Among the most natural cosmological solutions to these problems is to replace cold dark matter with a warm species ( LWDM ) .
The warm component acts to reduce the small-scale power , resulting in fewer galactic subhalos and lower halo central densities .
An alternative model with a mild “ tilt ” in the inflationary power spectrum ( TLCDM ; n = 0.9 ) similarly reduces the central densities of dark halos , although the substructure abundance remains relatively high .
Here I argue that because dwarf galaxy formation should be suppressed in the presence of a strong ionizing background , favored LWDM models will generally under -predict the observed abundance of dwarf galaxies .
The satellite count for TLCDM fairs much better , as long as the photoionization effect is taken into account .
TLCDM provides a more successful alternative to LWDM on subgalactic scales with the added attraction that it relies on only a minor , natural adjustment to the standard framework of CDM .