Deep Near-ir Surface Photometry of 57 Galaxies in the Local Sphere of Influence

We present H-band (1.65μm) surface photometry of 57 galaxies drawn from the Local Sphere of Influence (LSI) with distances of less than 10 Mpc from the Milky Way. The images with a typical surface brightness limit 4 mag fainter than 2MASS (24.5 mag arcsec−2 < μlim < 26 mag arcsec−2 ) have been obtained with IRIS2 on the 3.9 m Anglo-Australian Telescope. A total of 22 galaxies that remained previously undetected in the near-IR and potentially could have been genuinely young galaxies were found to have an old stellar population with a star density 1− 2 magnitudes below the 2MASS detection threshold. The cleaned near-IR images reveal the morphology and extent of many of the galaxies for the first time. For all program galaxies, we derive radial luminosity profiles, ellipticities, and position angles, together with global parameters such as total magnitude, mean effective surface brightness and half-light radius. Our results show that 2MASS underestimates the total magnitude of galaxies with 〈μH〉eff between 18 − 21 mag arcsec−2 by up to 2.5 mag. The Sérsic parameters best describing the observed surface brightness profiles are also presented. Adopting accurate galaxy distances and a H-band mass-to-light ratio of Υ∗ = 1.0 ± 0.4, the LSI galaxies are found to cover a stellar mass range of 5.6 < log10(Mstars) < 11.1. The results are discussed along with previously obtained optical data. Our sample of low luminosity galaxies is found to follow closely the opticalinfrared B versus H luminosity relation defined by brighter galaxies with a slope of 1.14 ± 0.02 and scatter of 0.3 magnitudes. Finally we analyse the luminosity – surface brightness relation to determine an empirical mass-to-light ratio of Υ∗ = 0.78± 0.08 for late-type galaxies in the H-band. Subject headings: galaxies: dwarf – galaxies: stellar content – galaxies: fundamental parameters – galaxies: general – galaxies: photometry – infrared: galaxies