Studying the spatially resolved Schmidt-Kennicutt law in interacting
  galaxies: the case of Arp 158
  Recent studies have shown that star formation in mergers does not seem to
follow the same Schmidt-Kennicutt (KS) relation as in spiral disks, presenting
a higher star formation rate (SFR) for a given gas column density. In this
paper we study why and how different models of star formation arise. To do so
we examine the process of star formation in the interacting system Arp 158 and
its tidal debris. We perform an analysis of the properties of specific regions
of interest in Arp 158 using observations tracing the atomic and the molecular
gas, star formation, the stellar populations as well as optical spectroscopy to
determine their exact nature. We also fit their spectral energy distribution
with an evolutionary synthesis code. Finally, we compare star formation in
these objects to star formation in the disks of spiral galaxies and mergers.
Abundant molecular gas is found throughout the system and the tidal tails
appear to have many young stars compared to their old stellar content. One of
the nuclei is dominated by a starburst whereas the other is an active nucleus.
We estimate the SFR throughout the system and find that most regions follow
closely the KS relation seen in spiral galaxies with the exception of the
nuclear starburst and the tip of one of the tails. We examine whether this
diversity is due to uncertainties in the manner the SFR is determined or
whether the conditions in the nuclear starburst region are such that it does
not follow the same KS law as other regions. Observations of the interacting
system Arp 158 provide the first evidence in a resolved fashion that different
star-forming regions in a merger may be following different KS laws. This
suggests that the physics of the interstellar medium at a scale no larger than
1 kpc, the size of the largest gravitational instabilities and the injection
scale of turbulence, determines the origin of these laws.
