  Submillimetre galaxies (SMGs) are bright sources at submillimetre
wavelengths. Made up of mostly of high-z galaxies, SMGs are amongst the most
luminous dusty galaxies in the Universe. Studying their environments and
clustering strength is thus important to put these galaxies in a cosmological
context. We present an environmental study of a sample of 116 SMGs in 96 ALMA
observation fields, which were initially discovered with the AzTEC camera on
ASTE and identified with high-resolution ALMA imaging within the COSMOS survey
field, having either spectroscopic or unambiguous photometric redshift. We
analysed their environments making use of the latest release of the COSMOS
photometric catalogue, COSMOS2015, a catalogue that contains precise
photometric redshifts for more than half a million objects over the 2deg2
COSMOS field. We searched for dense galaxy environments computing the so-called
overdensity parameter as a function of distance within a radius of 5 arcmin
from the SMG. We validated this approach spectroscopically for those SMGs for
which spectroscopic redshift is available. As an additional test, we searched
for extended X-ray emission as a proxy for the hot intracluster medium,
performing an X-ray stacking analysis in the 0.5-2 keV band with a 32 arcsec
aperture and our SMG position using all available XMM-Newton and Chandra X-ray
observations of the COSMOS field. We find that 27% (31 out of 116) of the SMGs
in our sample are located in a galactic dense environment; a fraction that is
similar to previous studies. The spectroscopic redshift is known for 15 of
these 31 sources, thus this photometric approach is tested using spectroscopy.
We are able to confirm that 7 out of 15 SMGs lie in high-density peaks.
However, the search for associated extended X-ray emission via an X-ray
stacking analysis leads to a detection that is not statistically significant.
