Properties of brightest group galaxies in cosmic web filaments
  Context. The cosmic web, a complex network of galaxy groups and clusters
connected by filaments, is a dynamical environment in which galaxies form and
evolve. However, the impact of cosmic filaments on the properties of galaxies
is difficult to study because of the much more influential local (galaxy-group
scale) environment.
  Aims. The aim of this paper is to investigate the dependence of intrinsic
galaxy properties on distance to the nearest cosmic web filament, using a
sample of galaxies for which the local environment is easily assessable.}
  Methods. Our study is based on a volume-limited galaxy sample with
$M_\mathrm{r}$ $\leq -19$ mag, drawn from the SDSS DR12. We chose brightest
group galaxies (BGGs) in groups with two to six members as our probes of the
impact of filamentary environment because their local environment can be
determined more accurately. We use the Bisous marked point process method to
detect cosmic-web filaments with radii of $0.5-1.0$ Mpc and measure the
perpendicular filament spine distance ($D_{\mathrm{fil}}$) for the BGGs. We
limit our study to $D_{\mathrm{fil}}$ values up to 4 Mpc. We use the luminosity
density field as a tracer of the local environment. To achieve uniformity of
the sample and to reduce potential biases we only consider filaments longer
than 5 Mpc. Our final sample contains 1427 BGGs.
  Results. We note slight deviations between the galaxy populations inside and
outside the filament radius in terms of stellar mass, colour, the 4000AA break,
specific star formation rates, and morphologies. However, all these differences
remain below 95% confidence and are negligible compared to the effects arising
from local environment density.
  Conclusions. Within a 4 Mpc radius of the filament axes, the effect of
filaments on BGGs is marginal. The local environment is the main factor in
determining BGG properties.
