Nearby spiral globular cluster systems. I. Luminosity functions

We compare the near-infrared (JHK) globular cluster luminosity functions (GCLFs) of the Milky Way, M31, and the Sculptor Group spiral galaxies. We obtained near-infrared photometry with the Persson's Auxiliary Nasmyth Infrared Camera on the Baade Telescope for 38 objects ( mostly globular cluster candidates) in the Sculptor Group. We also have near-infrared photometry from the Two Micron All Sky Survey (2MASS)-6X database for 360 M31 globular cluster candidates and aperture photometry for 96 Milky Way globular cluster candidates from the 2MASS All-Sky and Second Incremental Release databases. The M31 6X GCLFs peak at absolute reddening-corrected magnitudes of M(J0) = 9.18, M(H0) = -9.73, and M(K0) = -9.98. The mean brightness of the Milky Way objects is consistent with that of M31 after accounting for incompleteness. The average Sculptor absolute magnitudes ( correcting for relative distance from the literature and foreground reddening) are M(J0) = -9.18, M(H0) = -9.70, and M(K0) = -9.80. NGC 300 alone has absolute foreground-dereddened magnitudes M(J0) = -8.87, M(H0) = -9.39, and M(K0) = -9.46 using the newest Gieren et al. distance. This implies either that the NGC 300 GCLF may be intrinsically fainter than that of the larger galaxy M31 or that NGC 300 may be slightly farther away than previously thought. Straightforward application of our M31 GCLF results as a calibrator gives NGC 300 distance moduli of 26.68 +/- 0.14 using J, 26.71 +/- 0.14 using H, and 26.89 +/- 0.14 using K.