The galaxy density field

The galaxy density field has been profusely used to study the impact of environment in galaxy properties, such as the luminosity, the colour, the stellar mass, or the star formation rate. Thus, a robust and unbiased estimation of the density field is needed to track the role of environment from z = 1 to the local Universe.

The galaxy density field will be estimated by the weighted counting of tracer objects inside an aperture R around a given galaxy. Following Kovac+10, N = Σi mi W(|r – ri|, R), where mi is a physical weight (e.g. the inverse of the galaxy bias), W the window function (e.g. a top-hat or a Gaussian function), ri = (RAi, Deci) the position of the tracer galaxies, and R (Mpc) the radial aperture. Several efforts have been made in the literature to compute the density field from photometric redshifts (e.g. Darvish+15, Lai+15), but a complete PDF-based technique is still missing. We note that N depends on z, since the physical aperture R translates to a variable angular distance and the contribution of PDF(z) varies with z. We will apply our PDF techniques to estimate N(z), taking into account the border effects and the selection function of the tracer galaxies.

PHASE: Definition phase.