The ionised gas velocities have been determined through the fitting of Hαemission lines in each spaxel of the WiFeS observation and are ordered by line width (first = most narrow, etc). The analysis of the emission lines present multiple physical processes through the
Figure 4.2: Top: example of fitting NaiD absorption feature withifsfit. Middle: data around NaiD feature, the red presents the continuum which has been removed from the data before fitting, green dashed lines indicate the positions of Heiand NaiD. Bottom presents the data around the Mgib absorption feature with the continuum fit presented in red, the green dashed lines indicate the Mgib absorption lines. In all panels the blue represents the error in the flux. Bottom: shows no significant Mgib absorption, thus showing there is negligible NaiD absorption due to underlying stellar continuum.
Figure 4.3: The ionised gas velocity maps of IRAS F10257-4339 defined from emission line fitting. There are up to three Gaussian components needed to explain the emission lines observed in this galaxy. The contours represent Gaussian smoothed ionised velocity where dashed contours represent negative velocities and solid contours represent positive velocities (inclusive of zero).
velocity maps of all 3-components are presented in Figure 4.3. The first two components (left and middle panel) show similar velocity structures with a defined rotation structure as is expected of the stellar disk of a galaxy. The rotation curve defined by the first component matches the rotation curve defined by previous studies of IRAS F10257-4339 (e.g. Emonts et al., 2014; Sakamoto et al., 2014; L´ıpari et al., 2004). The third component (right panel) indicates a different picture, with velocities shifted blue-ward in comparison to the disk gas velocities shown by the first two components. This third component may trace the same ionised outflow detected by L´ıpari et al. (2004). The contours in all panels of Figure 4.3 are defined by the first component of the velocity (galaxy rotation) with dashed lines indicating negative values of velocity.
The neutral gas velocities have been determined through the fitting of the NaiD absorption
line and are ordered by velocity shift (first = smallest shift from systemic). In IRAS F10257-4339 up to two separate components of the NaiD doublet have been allowed, in
the same way 3-components were used in the fitting of the emission lines. As described in Section 4.2 the stellar component of the NaiD is not present in the fitting of the doublet
Figure 4.4: The neutral gas velocity maps of IRAS F10257-4339 defined through fitting NaiD absorption features with multiple components. The contours represent Gaussian smoothed ionised velocity where dashed contours represent negative velocities and solid contours represent positive velocities (inclusive of zero).
structure defined by the NaiD fits is presented in Figure 4.4. The velocity scale is the same as used in Figure 4.3 for comparison and the contours are derived from the first ionised velocity component. In the left panel two structures are identified in the velocity map, one mildly shifted both blue and red from systemic towards the southern nucleus and the other heavily blue-shifted towards the northern nucleus.
This picture is quantified in Figure 4.5, which shows that the neutral gas within 1 kpc of the northern nucleus is blue shifted up to -500 km/s, while within 1 kpc of the southern nucleus it is near systemic. Assuming the orientation from Sakamoto et al. (2014), the heavily blue-shifted components could be the outflow along the minor axis of the northern galaxy. The outflow described in Emonts et al. (2014); Sakamoto et al. (2014) from the southern nucleus, however, is red-shifted to the north and blue-shifted to the south in molecular gas. There is no strong evidence for this in our NaiD velocities.
The heavily blue-shifted component is correlated with the third component of the ionised gas velocity. Comparisons of the ionised (y-axis) and neutral (x-axis) velocities are pre- sented in Figure 4.6. The top and middle panels show the limits of the ionised gas between
Figure 4.5: The velocity and distances of each spaxels’ component from the north (left) and south (right) nuclei of IRAS F10257-4339. The distances are not de-projected. In the left figure we can identify the heavily blue-shifted components which are related to the north core, while the components around systemic velocity are associated with the southern core of this merger. The dashed lines in both panels indicate the distance between the two nuclei.
±200 km/s as expected from the rotation curve of the galaxy. The neutral gas velocities show groupings shifted slightly from the systemic velocity as has been indicated in the histograms of Figure 4.9. The third component of the ionised velocity has some correla- tion with the NaiD velocities suggesting the third ionised gas component is also tracing
the outflow along the minor axis of IRAS F10257-4339. This is consistent with studies by L´ıpari et al. (2000, 2004) where they observed the outflow in the ionised gas. However, velocity distributions only tell a part of the story. To determine the physical mechanisms which give rise to the two observed NaiD components this study also investigated the
equivalent width of the absorption, Weq, and hydrogen column densities, N(H).