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The number and distribution of dwarf satellite galaxies remain a criticaltest of cold dark matter-dominated structure formation on small scales. Untilrecently, observational information about galaxy formation on these scales hasbeen limited mainly to the Local Group. We have searched for faint analogues ofLocal Group dwarfs around nearby bright galaxies, using a spatial clusteringanalysis of the photometric catalog of the Sloan Digital Sky Survey (SDSS) DataRelease 8. Several other recent searches of SDSS have detected clusteredsatellite populations down to $\Delta m_r \equiv ({m}_{r,\, {\rm sat}} -\,{m}_{r,\, {\rm main}}) \sim 6$-$8$, using photometric redshifts to reducebackground contamination. SDSS photometric redshifts are relatively imprecise,however, for faint and nearby galaxies. Instead we use angular size to selectpotential nearby dwarfs, and consider only the nearest isolated bright galaxiesas primaries. As a result, we are able to detect an excess clustering signalfrom companions down to $\Delta m_r = 12$, four magnitudes fainter than mostrecent studies. We detect an over-density of objects at separations $< 400$kpc, corresponding to about $4.6 \pm 0.5$ satellites per central galaxy,consistent with the satellite abundance expected from the Local Group given ourselection function. Although the sample of satellites detected is incomplete byconstruction, since it excludes the least and most compact dwarfs, thisdetection provides a lower bound on the average satellite luminosity function,down to luminosities corresponding to the faintest "classical" dwarfs of theLocal Group.

Faint Dwarfs in Nearby Groups