5. Global analysis

  
Figure 45: H luminosity versus B absolute magnitude. The dashed lines represent Phillips et al. (1986) sample

  
Figure 46: Surface brightness of the ionized gas and the stars. The vertical dashed line represent the effective radius. Cross represent the gas brightness and continue line is the stellar brightness

  
Figure 47: Normalized gas extension (in unit of ) versus the intensity gradient index

5.1. Photometry

In this section we have tried to get an overall idea of the sample. Informations given previously allow us to investigate the spatial gas distribution and ionized gas mass/total mass ratio. We first look at H luminosity repartition with respect to the B absolute magnitude. This is shown in Fig. 45 (click here) H has been derived from monochromatic maps and using H/[NII] ratio found on literature (Phillips et al. 1986; Goudfrooij et al. 1994). It appears that H luminosity is 10 to 100 times more important than Phillips et al (1986) sample of emission line ellipticals detected by spectroscopy, which is consistent with Buson et al. (1993) study.
Monochromatic maps give us the gas distribution along the major axis. This extension varies considerably for the different galaxies. Figure 46 (click here) shows the radial surface brightness of the 11 galaxies for the gas and stars. The extension is different and the slope is different too, between the gas and the stars and between galaxies. In order to compare the gas surface brightness slope, an intensity gradient index has been introduced. It is derived from the intensity profile with as I=f(r^-n) with n in the range 1-2. Figure 47 (click here) shows the normalized gas extension ([NII] 6584 Å) versus the intensity gradient index. We can see that for a given gradient index, SO galaxies seem to have a larger gas extension.

5.2. Geometry

The geometrical aspect is the other major point of our study. Table 6 (click here) summarizes possible viewing angles ( and ) and possible axis ratios (I/L and S/L) derived from velocity fields and using de Zeeuw & Franx model (1989). Our sample can be divided in 3 parts for the geometrical point of view.

• Galaxies with 2 gas components: NGC 708, NGC 1052 and NGC 7332.
  NGC 708 shows a component almost aligned with the stars and another strongly decoupled. For the first component angle is not strongly constrained but it is enough to think that the gas disk is lying on the ZY plane (perpendicular to the long axis). For the second component the angle is not constrained at all and only the prolate shape seems to be possible. In that condition it is difficult to give gas disks location.
  NGC 1052 and NGC 7332 cases have been discussed in a previous paper (Plana & Boulesteix 1996). To summarize, component 1 of NGC 1052 have high probability to be located on XY plane but it is doubtly to have the second component on ZY plane, because of the none common values of axis ratios for that hypothesis. Situation for NGC 7332 is quite the same with simple way to find both components in the two perpendicular planes.
• Galaxies with no constrained angle: NGC 404, NGC 2974, NGC 5866 and NGC 5898.
  For that objects, the gas velocity field MA is almost aligned with the stellar MA. The consequence is a wide region allowed for the angle.
• Galaxies with good constraint on angle: NGC 4546, NGC 5846, NGC 6868 and NGC 7014.
  In that case several possibilities are encountered:
  Good determination and one possibility for the gas location: NGC 4546 in a Prolate case.
  Good determination but two possibilities for the gas location: NGC 5846 in a Prolate case and in a Oblate case.
  Good determination, two possibilities for gas location but one more probable than the other:
  NGC 6868 in a Prolate case.
  NGC 7014 in a Prolate case.
  As we can see, the viewing angle determination is strongly dependant of the misalignment between gas and stars MA.

   

Name Viewing Angles Axis Ratios

I/L S/L NGC 404 Prolate:

Oblate: - - NGC 708 Compo #1

Prolate: - - - - Oblate: Compo #2 Prolate:

Oblate: - - - - NGC 1052 Compo #1 Prolate: Oblate: Compo #2 Prolate: Oblate: NGC 2974 Prolate:

Oblate: - - - - NGC 4546 Prolate:

Oblate: - - - - NGC 5846 Prolate: Oblate: NGC 5866 Prolate:

Oblate: - - - - NGC 5898 Prolate:

Oblate: - - - - NGC 6868 Prolate: Oblate: NGC 7014 Prolate: Oblate: NGC 7332 Compo #1 Prolate: Oblate: Compo #2 Prolate:

Oblate: - - - -