Infrared mergers and infrared quasi-stellar objects with galactic winds - II. NGC 5514 : two extranuclear starbursts with LINER properties and a supergiant bubble in the rupture phase

Abstract

A study of the morphology, kinematics and ionization structure of the infrared (IR) merger NGC5514 is presented. This study is based mainly on INTEGRAL two-dimensional (2D) spectroscopy (obtained at the 4.2-m William Herschel Telescope, WHT), plus optical and near-IR images. Clear evidence of two extranuclear starbursts with young outflows (OFs) and low-ionization nuclear emission region (LINER) activity are reported. One of these OFs has generated a supergiant bubble and the other is associated with an extended complex of H II regions. In the galactic bubble it was found that: (i) the [S II], Hα, [NII], [O I] and [O III] emissionline maps show a bubble with a distorted ellipsoidal shape, with major and minor axes of ~ 6.5 kpc [13.6 arcsec; at position angle (PA) = 120◦ ± 10◦] and ~ 4.5 kpc (9.6 arcsec); (ii) these maps depict four main knots, a very strong one and three others more compact and located at the border; (iii) the centre of the bubble is located at ~ 4.1 kpc (8.5 arcsec) to the west of the main nucleus; (iv) the WHT spectra show, in this area, two strong components: blue and red emission-line systems, probably associated with emission from the near and far side of the external shell, for which the mean OF velocities were measured as VOF blue = (−320 ± 20) km s−1 and V OF red = (+265 ± 25) km s−1; (v) these two components depict LINER properties, probably associated with large-scale OF + shocks; (vi) at the east border, the kinematics of the ionized gas and the [S II] emission-line maps show an extended ejection of 4 kpc aligned with the PA of the major axis; (vii) three other ejections were found, two of them perpendicular to the extended one. Each ejection starts in one of the knots. These results suggest that the bubble is in the rupture phase. For the complex of giant H II regions it was found that: (i) the Hα, [N II] and [S II] emissionline maps show a compact strong emission area (peaking at ~ 810 pc ~ 1.7 arcsec, to the east of the second nucleus) and faint extended emission with an elongated shape, and major and minor axes of ~ 5.1 kpc (10.8 arcsec; at PA ~ 20◦) and ~ 2.9 kpc (6.0 arcsec); (ii) inside this complex, the spectra show H II region and transition LINER/H II characteristics; (iii) at the border of this extended HII area the spectra have outflow components and LINER properties. INTEGRAL 2D [N II], Hα, [S II] and [O III] velocity fields (VFs) are presented. These VF maps show results consistent with an expansion of the bubble, plus four ejections of ionized gas. The U, B, V, I, J, H and KS images show a pre-merger morphology, from which faint filaments of emission emerge, centred on the bubble. The ionization structure and the physical conditions were analysed using the following 2D emission-line ratio and width maps: [S II]/Hα, [NII]/Hα, [O I]/Hα, [O III]/Hβ and FWHM–[N II]. In the region of the bubble, 100 per cent of the [N II]/Hα and [S II]/Hα ratios show very high values (>0.8) consistent with LINER processes associated with high-velocity shocks. These new results support the previous proposition that extreme nuclear and ‘extranuclear’ starbursts with galactic winds + shocks play an important role in the evolution of IR mergers/quasi-stellar objects.