The Study of Nebular Emission on Nearby Spiral Galaxies in the IFU Era
Figure 4
(a) BPT diagnostic diagram for HII regions coded according to the geometric position (quadrants) with respect to the an arbitrary axis drawn across the galaxy surface. The locus of different sectors does not show a clear trend or do not populate a clearly visible region on any diagram, compared to the rest of the quadrants. Points from all the regions are equally distributed within the cloud of points on each diagnostic diagram, indicating that the emission line ratios of the HII regions are not a function of azimuthal angle across the disc. (b) Radial gradients of the ionization parameter log for morphologically selected HII regions of NGC 628. The panel shows the log versus relation for the regions belonging to the north and south spiral arms of the galaxy. The difference between the two spiral arms resides in the slope of the gradient of log , for the north arm, and the values of log increase moderately with galactocentric distance, while, for the south arm, the ionization parameter increases with a steeper slope, although within the errors of the linear fittings. Figure adapted from Rosales-Ortega et al. [30].
