OBSERVED ROTATION CURVE OF HAM I 3" E

In document The dynamics of galactic bulges (Page 154-168)

r (arc sec) V (S)b v (N) 0 121 121 2.5 99 - 102 5.1 50 - 102 7.6 33 - 74 10 132 - 86 13 179 66 15 135 - 138 18 143 - 138 20 143 - 165

a relative to corrected systemic velocity of 4050 km.s"!

Figure 4.18 Observed rotation curve of NGC 4179 with the slit displaced 5" NE and parallel to the major axis. The data have been plotted relative to a corrected systemic velocity of 1251 km.s ^ . The error associated with each observation is also shown. The open circle shows the measured velocity dispersion on the minor axis 5" from the centre, taken from Figure 4.19.

NGC 4179

_ 100

Figure 4.19 Fit of the best fitting power spectrum from the velocity broadened template star grid (thin solid line) to the smoothed power spectrum of NGC 4179 (thick solid line), at z=5". The units of velocity dispersion are km.s The dashed lines show for comparison, fits 50 km.s ^ above and below the adopted value of 150 + 20 km.s ^ .

L o g P o w e r NGC 4179 ' 200 Frequency (cycles.A"1)

The corrected systemic radial velocity was found to be 1251 + 20 km.s-^ in good agreement with 1279 km.s ^ from RC2. The

rotation curve, plotted relative to the systemic velocity is shown in Figure 4.18 and tabulated in Table 4.11. The rotation curve gives an observed V Qf 160 + 20 km.s ^ • The best estimate of

m

the velocity dispersion 5" from the centre along the minor axis was found to be 150 + 20 km.s Figure 4.19 shows the fit of the velocity broadened star power spectrum (thin solid line) to the smoothed galaxy power spectrum (thick solid line). Combining these two datum gives V y a (z=5") = 1.07 + 0.02 where the error is formal. No corrections for inclination have been made. The surface photometry gave a value of e = 0.57 + 0.05 for the maximum

IDaX

ellipticity in B. However, NGC 4179 is not quite edge on so this value may be smaller than its intrinsic value.

(iv) Ham I

Ham I (named due to its similarity to a edge-on ham­ burger ), situated only 9° from the south celestial pole, is an unusual and interesting object. Morphologically it resembles both a highly flattened elliptical galaxy with a very distinct dust lane along the major axis and a late type SO galaxy with little evidence of a luminous disc - see Figure 4.20. This at first seems contra­ dictory, since by definition an SO galaxy has a luminous disc. The kinematics reveal the latter interpretation is probably correct. The rotation curve and velocity dispersion were derived from a 3000s exposure with the slit displaced 3” in a perpendicular direction on the east side from the major axis and parallel to the major axis to avoid the dust lane. The rotation curve is shown in Figure 4.21 and

r_ ^

Figure 4.20 Upper Panel The galaxy Ham I from a 4 30 B band (IIa-0+GG385) exposure taken at the f/8 focus of the 1.0m telescope. North is up and east is to the right.

Lower Panel Pseudo isodensity contours of the above plate to accentuate the outer bulge.

%

%

/ J

1

.

Piüü.

Figure 4.21 Observed rotation curve of Ham I with the slit displaced 3" E and parallel to the major axis. The data have been plotted relative to a corrected systemic velocity of 4050 km.s ^ . The error associated with each observation is also shown. The open circle shows the measured velocity dispersion on the minor axis 3" from the centre, taken from Figure 4.22.

Ham I

Figure 4.22 Fit of the best fitting power spectrum from the velocity broadened template star grid (thin solid line) to the smoothed power spectrum of Ham I (thick solid line) at z=3". The units of velocity dispersion are km.s ^ . The dashed lines show for comparison, fits 50 km.s ^ above and below the adopted value of 150 + 20 km.s ^ .

L o q P o w e r j a n 0.5 0.0 - 0.5 - 1.0 Ham • 1 F r e q u e n c y ( c y c l e s . A ' )

Figure 4.23 Observed surface brightness distribution in B of Ham I. The isophotes are in arbitrary units of log I spaced 0.5 mag apart. The faintest isophote is 1.0 mag below the next brightest. The data was smoothed with a two-dimensional Gaussian beam of halfwidth 2"x2" before the isophotes were plotted. Note the strong absorption on the major axis.

due to the apparent faintness of the galaxy and the relatively short exposure. However, there is still clear indication of significant rotation with V (z=3") of about 200 + 50 km.s_1* Ham I is the

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second most distant object in the sample, with a corrected systemic velocity of 4050 + 30 km.s 1 . This places the galaxy at a distance of 54 Mpc (H = 75 km.s Mpc ^), similar to NGC 128

(55.4 Mpc; this work). The velocity dispersion from Figure 4.22 was found to be 150 + 20 km.s"*1 , giving an observed V / a ( z=3") = 1.33 + 0.38, the most highly rotating galaxy in the sample. Most of the formal error results from the uncertainty in V .

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Figure 4.23 shows the isophotes of Ham I in B on an arbitrary log I scale, with an isophote spacing of 0.5 mag. The faintest isophote is 1.0 mag below the next brightest. The data has been taken from a 4.5 hour exposure using a IIa-0 + GG385 plate- filter combination (plate 4029), and reduced using the techniques described in Chapter III. The map was firstly smoothed with a two- dimensional Gaussian filter of halfwidth 3" before plotting the isophotes. The distribution of ellipticities give e = 0.67 +

max

0.05.

Ham I is interesting because it is morphologically like a

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