IRAS F10257-4339 is a merging system from WiGS. As explained in Chapter 3, the WiGS galaxies are a subset of 30 galaxies from the GOALS sample (Great Observatory All-Sky LIRG Survey; Armus et al., 2009), chosen to be observable by the WiFeS (Dopita et al., 2007) instrument on the ANU 2.3m telescope with redshifts z < 0.05. This subset of galaxies concentrates on U/LIRGs (Ultra/Luminous Infra-Red Galaxies) at different stages of merging, from isolated galaxies to late stage mergers. Specific wavelength coverage and resolutions for WiGS are presented in Table 3.1, Chapter 3.
The HST (Hubble Space Telescope) image of IRAS F10257-4339 is presented in Figure 4.1 in the F450W and F814W bands. The red box in the top left panel indicates the WiFeS FoV overlaid on the HST image. Note that the HST observation does not fill the entire WiFeS FOV and may cause a truncation to the HST colour calculated in the south- west corner. The bottom left panel of Figure 4.1 is the HST image convolved to the spatial scale of the WiFeS instrument (100/pix). The bottom right panel is the continuum image produced by the WiFeS observation. Note a slight difference in the position of the brightest point between the HST convolved image and the IFS observation. The HST observations do not overlap the wavelength coverage of the WiFeS observation, creating a slight difference in the brightest spaxel between the two bottom panels. The x and y axes of each panel represent the kpcs from the centre of the galaxy, as defined in Rich et al.
Figure 4.1: HST colour image of IRAS F10257-4339. Top left presents the HST image (F450W+F814W) with the FoV outlined in red. Top right present the FoV of our WiFeS ob- servations. Bottom left is the HST image convolved to the same pixel scale as the WiFeS instru- ment (100/pix). Bottom right presents the continuum extracted from the WiFeS datacube itself. The cross represents the position of the northern nucleus identified through the WiFeS continuum image. The red circle is the position of the southern nucleus (Neff et al., 2003).
(2011) for the northern nucleus and identified by the black cross in the bottom panels. The position of the southern nucleus has been highlighted with a red circle.
4.2.1 Emission line fitting
Before IRAS F10257-4339 can be analysed the pre-analysis steps of emission line fit- ting and absorption line fitting must be completed. The excitation mechanisms of IRAS F10257-4339 were determined in Chapter 3 by analysing the emission line maps defined by the emission line fitting of Rich et al. (2011). The emission line values were extracted using continuum and emission line fitting with UHSPECFIT(Zahid et al., 2011) and MPFIT
(Markwardt, 2009). See Rich et al. (2011, 2015) for a detailed description of the fitting process.
The WiFeS observation of IRAS F10257-4339 has ∼ 500 spaxels all fit with stellar con- tinuum models and emission line models of up to three separate Gaussians to describe the multiple physical processes hosted by this galaxy (Rich et al., 2010). The requirement of multiple components implies that IRAS F10257-4339 is a complex galaxy system of ionised gas and may also be a complex system of neutral gas.
4.2.2 Absorption line fitting
For IRAS F10257-4339 this chapter used the same continuum fit as defined by Rich et al. (2011), for consistency between the emission line and absorption line analysis. The absorp- tion line fitting uses the IDL code ifsfit(Rupke, 2014). The IDL code and description are located on GitHub at http://github.com/drupke/ifsfit. This analysis has only utilised the absorption fitting part of ifsfit, using the datacube and continuum fit of IRAS F10257-4339 produced by Rich et al. (2011). ifsfit uses the spectra from each individual spaxel, divides through by the continuum fit and scales the resulting spectrum to a continuum level of one. Each spectrum is then fit for the NaiD absorption feature.
The NaID absorption feature is a doublet line, however in this study no distinction has been made between the two as they are blended in wavelength space. Fitting 2-components to the NaiD feature means fitting 2-components to both of the lines in the NaiD absorption
feature. In spaxels where the Heiλ5876 line is present, the line is simultaneously fit using
to remove any contribution to the NaiD. ifsfit calculates the following parameters, along with Monte Carlo errors (Rupke et al., 2005b, section 6.3); Equivalent width Weq, velocity, width of absorption lineσ, covering factor Cf, and optical depthτ. Each of these parameters are discussed in detail in Section 4.3.
NaiD absorption can also be present due to the underlying stellar continuum. To ensure the absorption fit by ifsfit is not due to stellar contributions the NaiD absorption
feature is compared to the Mgibλλλ5167,5173,5185 absorption feature. The Mgib stellar
absorption line is twice the strength of the NaiD stellar absorption (Heckman et al., 2000;
Rupke et al., 2005b). No Mgib absorption was detected, which is consistent with previous
studies of IRAS F10257-4339. The stellar continuum is dominated by young stars and thus does not have strong absorption in the Mgib and consequently no stellar NaiD
contribution. An example of the spectra is presented in Figure 4.2. The top panel is the NaiD fitting, the middle panel indicates the continuum fit in comparison to the data with
the NaiD and Helium lines highlighted by the green dashed lines and the bottom panel
highlights the Mgib absorption lines. No Mgib absorption is observed in the data that is
used to fit the NaiD absorption features and so no stellar component has been included
in the analysis.