Abstract :
The Euclid mission is transforming our view of the low-mass Universe by
enabling the systematic exploration of ultracool dwarfs (UCDs), from late-M
dwarfs to free-floating planetary-mass objects, across diverse Galactic
environments. Within the Euclid SUBSTELLAR project, we are building the
largest homogeneous census of brown dwarfs and free-floating planets to
date, expecting to increase the known population by two orders of
magnitude. Euclid’s combination of wide-area, deep, high-resolution
near-infrared imaging and low-resolution near-infrared spectroscopy enables
the identification of UCDs over unprecedented volumes of the Galaxy,
reaching masses of ~4 MJup at the distance of Orion. Using Early Release
Observations (ERO) data, we illustrate this potential through studies of
the σ Orionis cluster and the neighboring Horsehead Nebula region. In σ
Orionis, Euclid observations have improved the characterization of the
initial mass function (IMF) in the substellar regime, while complementary
infrared data are allowing us to extend the search for UCDs into the highly
reddened environments of the Orion B molecular cloud. Preliminary results
reveal numerous new embedded UCD candidates, opening a window onto the
formation of very low-mass objects in environments shaped by ionization
fronts and stellar feedback.
We are also taking the first steps toward constraining the very low-mass
field IMF using Euclid Quick Data Release 1 (Q1) and Data Release 1 (DR1).
UCD candidates are selected by combining Euclid photometry and spectroscopy
while accounting for contamination and survey completeness, providing the
statistically robust samples needed to probe the poorly constrained
lowest-mass end of the IMF. Field measurements offer a crucial counterpart
to studies in young clusters, enabling us to investigate how the formation
environment and subsequent dynamical evolution shape the present-day
substellar population. Together, these complementary approaches demonstrate
Euclid’s potential to bridge stellar and planetary populations and to
facilitate discussions on fundamental questions about the shape, low-mass
cutoff, and universality of the IMF, laying the foundation for the
mission’s broader legacy in substellar astrophysics.
