Interaction effects on galaxy pairs with Gemini/GMOS- I: Electron
  density
  We present an observational study about the impacts of the interactions in
the electron density of \ion{H}{ii} regions located in 7 systems of interacting
galaxies. The data consist of long-slit spectra in the range 4400-7300 A,
obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS). The
electron density was determined using the ratio of emission lines
[SII]6716/6731. Our results indicate that the electron density estimates
obtained of HII regions from our sample of interacting galaxies are
systematically higher than those derived for isolated galaxies. The mean
electron density values of interacting galaxies are in the range of $N_{\rm
e}=24-532$\,$ \rm cm^{-3}$, while those obtained for isolated galaxies are in
the range of $N_{\rm e}=40-137\: \rm cm^{-3}$. Comparing the observed emission
lines with predictions of photoionization models, we verified that almost all
the \ion{H}{ii} regions of the galaxies AM\,1054A, AM\,2058B, and AM\,2306B,
have emission lines excited by shock gas. For the remaining galaxies, only few
HII regions has emission lines excited by shocks, such as in AM\,2322B (1
point), and AM\,2322A (4 points). No correlation is obtained between the
presence of shocks and electron densities. Indeed, the highest electron density
values found in our sample do not belong to the objects with gas shock
excitation. We emphasize the importance of considering theses quantities
especially when the metallicity is derived for these types of systems.
