ACCESS: NIR luminosity function and stellar mass function of galaxies in the Shapley supercluster environment

We present the near-infrared luminosity and stellar mass functions (SMFs) of galaxies in the core of the Shapley supercluster at z = 0.048, based on new K-band observations carried out at the United Kingdom Infrared Telescope with the Wide Field Infrared Camera in conjunction with B- and R-band photometry from the Shapley Optical Survey, and including a subsample (similar to 650 galaxies) of spectroscopically confirmed supercluster members. These data sets allow us to investigate the supercluster galaxy population down to M(K)(star) + 6 and M = 10(8.75) M(circle dot). For the overall 3 deg(2) field, the K-band luminosity function (LF) is described by a Schechter function with M(K)(star) = -24.96 +/- 0.10 and alpha = -1.42 +/- 0.03, a significantly steeper faint-end slope than that observed in field regions. We investigate the effect of environment by deriving the LF in three regions selected according to the local galaxy density and observe a significant (2 sigma) increase in the faint-end slope going from high-density (alpha = -1.33) to low-density (alpha = -1.49) environments, while a faint-end upturn at M(K) > -21 becomes increasingly apparent in the lower density regions. The galaxy SMF is fitted well by a Schechter function with log(10)(M(star)) = 11.16 +/- 0.04 and alpha = -1.20 +/- 0.02. The SMF of supercluster galaxies is also characterized by an excess of massive galaxies that are associated with the brightest cluster galaxies. While the value of M* depends on the environment, increasing by 0.2 dex from low- to high-density regions, the slope of the galaxy SMF does not vary with the environment. By comparing our findings with cosmological simulations, we conclude that the environmental dependences of the LF are not primarily due to variations in the merging histories, but to processes which are not treated in the semi-analytical models, such as tidal stripping or harassment. In field regions, the SMF shows a sharp upturn below M = 10(9) M(circle dot), close to our mass limit, suggesting that the upturns seen in our K-band LFs, but not in the SMF, are due to this dwarf population. The environmental variations seen in the faint end of the K-band LF suggest that these dwarf galaxies, which are easier to strip than their more massive counterparts, are affected by tidal/gas stripping upon entering the supercluster environment.