Lack of Dwarf Galaxies in the Local Volume
The sample of the Local Volume galaxies (distance smaller than 10 Mpc)
gives a unique opportunity to study the properties of galaxies including
the weakest objects: the absolute magnitude MB≈-10
and the virial mass Mvir≈109M☼.
We found out that the standard ΛCDM model precisely describes
the distribution function of galactic circular velocities for massive objects
(Vcirc>~70 km s-1 and
but five times overestimates the number of dwarf galaxies with circular
velocities of Vcirc~30-40 km s-1.
Such a considerable overabundance of predicted big dwarf field galaxies
with masses Mvir≈1010M☼
causes a complicated problem: to prove they are lost, these galaxies
should be of extremely low surface brightness, with no star formation
processes and no neutral hydrogen. Up to now, there has been no such
Fig.1. Luminosity function of the Local Volume galaxies. Black circles correspond to the sample within 10 Mpc, blue circles - 8 Mpc, red triangles - 6 Mpc. The luminosity functions for galaxies are presented: red dashed line - from the 2dFGRS survey (Norberg et al. 2002); blue dash-dotted line - from the SDSS survey (Blanton et al. 2005). Black solid line denotes the distribution approximation with the Schechter function with an inclination of α=1.3 and M*=-20.0+5log(h). It can be seen from the figure that the Local Volume is complete up to -14 MB. At weaker magnitudes, the incompleteness of the sample of the Local Volume galaxies is shown. Black dashed line shows the approximation of the luminosity function in the range from -10 to -14 mag. The upper panel shows the fraction of early-type galaxies in the sample within 10 Mpc. The fraction is almost constant, ~10% for the galaxies brighter MB=-13 and starts growing for weaker galaxies due to dwarf spheroidal satellites around bright galaxies.
Fig.2. Comparison of the width distribution for the Local Volume galaxies with the theoretical predictions of ΛCDM (left panel) and WDM (right panel) models. Black dots and black dashed line show the velocity function for the 10 Mpc sample. In the left panel, the colored solid lines show theoretical predictions for the ΛCDM: red curve - with the Planck cosmological parameters; blue curve - with the WMAP7. Red dashed line denotes the predictions of the model with dark matter only without including the baryons' contribution. The increased mass of baryons in the halo centers leads to increasing the circular velocity of galaxies