Ismael Ferrero, Mario G. Abadi, Julio F. Navarro, Laura V. Sales, Sebastian Gurovich
The cold dark matter halo mass function is much steeper than the galaxy
stellar mass function on galactic and subgalactic scales. This difference is
usually reconciled by assuming that the galaxy formation efficiency drops
sharply with decreasing halo mass, so that galaxy formation is effectively
suppressed below a threshold mass, M_th ~ 10^10 M_sun . A halo mass threshold
implies that, at any given radius, the dark mass enclosed by a galaxy must
exceed a certain minimum. We use rotation curves of dwarf galaxies compiled
from the literature to explore whether their enclosed mass is consistent with
this constraint. We find that almost one half of the dwarfs in our sample with
stellar mass between 10^6-10^7 Msun violate this restriction: either they live
in halos with masses substantially below the threshold or there is a mechanism
capable of reducing the dark mass enclosed by some of the faintest dwarfs.
Neither possibility is easily accommodated within the standard LCDM scenario.
Extending galaxy formation to halos well below 10^10 M_sun would lead to severe
disagreement with the low mass end of the galaxy stellar mass function; at the
same time, the extremely low stellar mass of the systems involved make it
unlikely that baryonic effects may be responsible for reducing their dark
matter content. Resolving this challenge seems to require new insights into
dwarf galaxy formation, or else a radical revision of the prevailing paradigm.
View original:
http://arxiv.org/abs/1111.6609
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