  The process of cometary activity continues to pose a challenging question in
cometary science. The activity modeling of comet 67P/Churyumov-Gerasimenko,
based on data from the Rosetta mission, has significantly enhanced our
comprehension of cometary activity. But thermophysical models have difficulties
in simultaneously explaining the production rates of various gas species and
dust. It has been suggested that different gas species might be responsible for
the ejection of refractory material in distinct size ranges. This work focuses
on investigating abundance and the ejection mechanisms of large ($\gtrsim$ 1
cm) aggregates from the comet nucleus. We aim to determine their properties and
map the distribution of their source regions across the comet surface. This can
place constraints on activity models for comets. We examined 189 images
acquired at five epochs by the OSIRIS/NAC instrument. Our goal was to identify
bright tracks produced by individual aggregates as they traversed the camera
field of view. We generated synthetic images based on the output of dynamical
simulations involving various types of aggregates. By comparing these synthetic
images with the observations, we determine the characteristics of the simulated
aggregates that most closely resembled the observations. We identified over
30000 tracks present in the OSIRIS images, derived constraints on the
characteristics of the aggregates and mapped their origins on the nucleus
surface. The aggregates have an average radius of $\simeq5$ cm, and a bulk
density consistent with that of the comet's nucleus. Due to their size, gas
drag exerts only a minor influence on their dynamical behavior, so an initial
velocity is needed in order to bring them into the camera field of view. The
source regions of these aggregates are predominantly located near the
boundaries of distinct terrains on the surface.
