We study molecular outflows in a sample of 25 nearby (z< 0.17, d<750 Mpc)
ULIRG systems (38 individual nuclei) as part of the "Physics of ULIRGs with
MUSE and ALMA" (PUMA) survey, using ~400 pc (0.1-1.0" beam FWHM) resolution
ALMA CO(2-1) observations. We used a spectro-astrometry analysis to identify
high-velocity (> 300 km/s) molecular gas disconnected from the galaxy rotation,
which we attribute to outflows. In 77% of the 26 nuclei with logLIR/L⊙>11.8, we identifid molecular outflows with an average
vout=490 km/s, outflow masses 1−35×107M⊙, mass
outflow rates M˙out=6−300M⊙ yr−1, mass-loading factors
η=M˙out/SFR=0.1−1, and an average outflow mass escape fraction
of 45%. The majority of these outflows (18/20) are spatially resolved with
radii of 0.2-0.9 kpc and have short dynamical times (tdyn=Rout/vout)
in the range 0.5-2.8 Myr. The outflow detection rate is higher in nuclei
dominated by starbursts (SBs, 14/15=93%) than in active galactic nuclei (AGN,
6/11=55%). Outflows perpendicular to the kinematic major axis are mainly found
in interacting SBs. We also find that our sample does not follow the
M˙out versus AGN luminosity relation reported in previous works. In
our analysis, we include a sample of nearby main-sequence galaxies (SFR =
0.3-17 M⊙ yr−1) with detected molecular outflows from the
PHANGS-ALMA survey to increase the LIR dynamic range. Using these two
samples, we find a correlation between the outflow velocity and the SFR, as
traced by LIR (vout∝SFR0.25±0.01), which is consistent
with what was found for the atomic ionised and neutral phases. Using this
correlation, and the relation between Mout/Rout and vout, we
conclude that these outflows are likely momentum-driven.Comment: 27 pages, 23 figures; Appendix: 49 pages, 41 figures. Accepted for
publication in Astronomy & Astrophysic