We analyze photometric data in SDSS-DR7 to infer statistical properties of faint satellites associated to isolated bright galaxies ( M _ { r } < -20.5 ) in the redshift range 0.03 < z < 0.1 .
The mean projected radial number density profile shows an excess of companions in the photometric sample around the primaries , with approximately a power law shape that extends up to \simeq 700 kpc .
Given this overdensity signal , a suitable background subtraction method is used to study the statistical properties of the population of bound satellites , down to magnitude M _ { r } = -14.5 , in the projected radial distance range 100 < r _ { p } / kpc < 3 < R _ { vir } > .
The maximum projected distance corresponds is in the range 470 - 660 kpc for the different samples .
We have also considered a colour cut consistent with the observed colours of spectroscopic satellites in nearby galaxies so that distant redshifted galaxies do not dominate the statistics .
We have tested the implementation of this background subtraction procedure using a mock catalogue derived from the Millenium simulation SAM galaxy catalogue based on a \Lambda CDM model .
We find that the method is effective in reproducing the true projected radial satellite number density profile and luminosity distributions , providing confidence in the results derived from SDSS data .
We find that the spatial extent of satellite systems is larger for bright , red primaries .
Also , we find a larger spatial distribution of blue satellites .
For the different samples analyzed , we derive the average number of satellites and their luminosity distributions down to M _ { r } = -14.5 .
The mean number of satellites depends very strongly on host luminosity .
Bright primaries ( M _ { r } < -21.5 ) host on average \sim 6 satellites with M _ { r } < -14.5 .
This number is reduced for primaries with lower luminosities ( -21.5 < M _ { r } < -20.5 ) which have less than 1 satellites per host .
We provide Schechter function fits to the luminosity distributions of satellite galaxies where the resulting faint end slopes equal to − 1.3 \pm 0.2 , consistent with the universal value .
This shows that satellites of bright primaries lack an excess population of faint objects , in agreement with the results in the Milky Way and nearby galaxies .