N. Roche, A. Humphrey, J. M. Gomes, P. Papaderos, P. Lagos, S. F. Sánchez

Abstract
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. H α 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 ×10⁸ yr ago, triggered by the previous perigalacticon. The $// <![CDATA[ m [N,small {II}]6584/H,alpha // ]]>$ ratio is high in the nucleus, reaching 0.63 at the centre, which we interpret as related to high electron density (n_e ≃ 750 cm^{− 3} from the $// <![CDATA[ m [S,small {II}]{6717over 6731} // ]]>$ ratio). We find a central region of strong and blueshifted Na i(5890,5896) absorption, indicative of a starburst-driven outflow from the nucleus at an estimated velocity ∼223 km s^{− 1}. The CALIFA data also show an annular region at radii 2.25–4 kpc from the nucleus, with elevated ratios of [N ii], [O i]6300 etc. to the Balmer lines – this is evidence of shock excitation, which might be the result of interaction-triggered gas inflow.

Keywords
galaxies: evolution, galaxies: individual: NGC 5394, galaxies: interactions, galaxies: starburst

Monthly Notices of the Royal Astronomical Society
Volume 453, Issue 3, Page 2349
2015 November

>> ADS>> DOI