Sub-arcsecond imaging of Arp\,299-A at 150 MHz with LOFAR: Evidence for
  a starburst-driven outflow
  We report on the first sub-arcsecond (0.44 $\times$ 0.41 arcsec$\rm ^2$)
angular resolution image at 150 MHz of the A-nucleus in the Luminous Infrared
Galaxy Arp$\,$299, from International Low Frequency Array (LOFAR) Telescope
observations. The most remarkable finding is that of an intriguing two-sided,
filamentary structure emanating from A-nucleus, which we interpret as an
outflow that extends up to at least 14 arcseconds from the A-nucleus in the N-S
direction ($\approx$ 5 kpc deprojected size) and accounts for almost 40% of the
extended emission of the entire galaxy system. We also discuss HST/NICMOS
[FeII] 1.64 $\rm \mu m$ and H$\rm_2$ 2.12 $\rm \mu m$ images of Arp$\,$299-A,
which show similar features to those unveiled by our 150 MHz LOFAR
observations, thus giving string morphological support for the outflow
scenario. Finally, we discuss unpublished NaI D spectra that confirm the
outflow nature of this structure. From energetic arguments, we rule out the
low-luminosity active galactic nucleus in Arp$\,$299-A as a driver for the
outflow. On the contrary, the powerful, compact starburst in the central
regions of Arp$\,$299-A provides plenty of mechanical energy to sustain an
outflow, and we conclude that the intense supernova (SN) activity in the
nuclear region of Arp299-A is driving the observed outflow. We estimate that
the starburst wind can support a mass-outflow rate in the range (11-63) $\rm
M_{\odot} yr^{-1}$ at speeds of up to (370 - 890) $\rm km \, s^{-1}$, and is
relatively young, with an estimated kinematic age of (3 - 7) Myr. Those results
open an avenue to the use of low-frequency (150 MHz), sub-arcsecond imaging
with LOFAR to detect outflows in the central regions of local luminous infrared
galaxies.
