2015MNRAS.453.2349R

We investigate the spiral galaxy NGC 5394, which is strongly interacting with the larger spiral NGC 5395 (the pair is Arp 84), using optical integral-field spectroscopy from the CALIFA (Calar Alto Legacy Integral Field Area) survey. Spatially resolved equivalent widths, emission-line ratios and kinematics reveal many features related to the interaction, which has reshaped the galaxy. Hα maps (with other diagnostic emission lines) show a concentrated central (r < 1 kpc) starburst and three less luminous star-forming regions (one knot far out in the northern arm), and we estimate the dust-corrected total star-formation rate as 3.39 M_☉yr- 1. However, much of the galaxy, especially the outer tidal arms, has a post-starburst spectrum, evidence of a more extensive episode of star formation a few x10⁸ yr ago, triggered by the previous perigalacticon. The [N II]6584/H α ratio is high in the nucleus, reaching 0.63 at the centre, which we interpret as related to high electron density (ne ≃ 750 cm- 3 from the [S II]6717 / 6731 ratio). We find a central region of strong and blueshifted Nai(5890,5896) absorption, indicative of a starburst-driven outflow from the nucleus at an estimated velocity ∼ 223 kms- 1. The CALIFA data also show an annular region at radii 2.25-4 kpc from the nucleus, with elevated ratios of [Nii], [Oi]6300 etc. to the Balmer lines - this is evidence of shock excitation, which might be the result of interaction-triggered gas inflow.