Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation...
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Transcript of Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation...
![Page 1: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/1.jpg)
Decomposition of rotation curves into disk, bulge, halo componentsTwo basic types of rotation curves.
Grand design spirals vs. flocculent spiralsLeading vs trailing spirals & how to tell one from the otherMaterial arms & the winding problemStochastic star formation Kinematic waves: a step in the right direction
![Page 2: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/2.jpg)
(next slide)
(superpositionprinciple for gravitation)
![Page 3: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/3.jpg)
Decomposition of the rotation curve of NGC 7331 giving the bestfit to the observations
If there are several subsystems (e.g. gas, stars in a disk, halo)contributing to M(<R), then the rotation curve is a sum of squaresof several rotation curves.
![Page 4: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/4.jpg)
A spherically-symmetric dark halo density-velocity model often used for spiral galaxies
![Page 5: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/5.jpg)
The dots are the observed rotational data. The fit to these is indicated by the full drawn line. Individual contributions of the bulge (dotted line), disc (long dashed line), gas (short dashed line), and dark halo (dash - dot line) are also given.
a) All the mass is assumed to be in a disk-like distribution. The best fit is for a disk contributing 60% at most to the total rotation.
b) As a), but now for a secondary minimum in the least squares fitting procedure. This is a maximum disk fit, but other fits are of better quality
c) For a separate bulge and disk mass distribution, where the M/L ratios of both are constrained to be equal.
d) As c), but the M/L ratios of bulge and disk are both unconstrained.
NGC 3992 radial velocity curve decompositions using different assumptions
stellar disk
gas disk
dark halo
bulge
![Page 6: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/6.jpg)
Decomposition of the rotation curve of NGC 3992.
(D = disk, B = bulge)
Situation panel in red disk (M/L)dsk bulge (M/L)bulge Rcore Vmax
Fig. 13 chi^2 mass mass dark halo
(1e9Msun) (solar u.) (1e9) (solar u.) (kpc) (km s-1)
D only, best fit a 1.22 73.7 1.79+-0.19 - - 1.16+-0.35 230+-98
D only, max disc b 1.94 194.1 4.71+-0.11 - - 44.9+-17 482+-188
D + B, equal M/L c 1.22 64.9 2.03+-0.21 18.7 2.03 1.79+-0.35 230+-64
D + B, = 240 - 1.25 71.3 2.23+-0.26 36.9 4.0 3.7+_0.6 233+-57
D + B, max d 1.08 134.6 4.2+-0.3 47.1 5.1+-0.5 23.2 5.7 327+-91
As in this sample decomposition of rotation curve. In general, it isdifficult to obtain a unique model, because we don’t know a priori the M/Lratios (‘exchange rate’ of light to mass) for the disk and the bulge
http://aanda.u-strasbg.fr:2002/papers/aa/full/2002/24/aah3038/node8.html
![Page 7: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/7.jpg)
![Page 8: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/8.jpg)
Dark mattercontents
Gradual riseof rotation curve:a sign of largecore of DM halo
Asymptoticvelocity
Notice how the three aspects of dark matter vary with galaxy type
![Page 9: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/9.jpg)
Tully-Fisher relationship, a correlation between the luminosityand rotation.
![Page 10: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/10.jpg)
Tully-Fisher
![Page 11: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/11.jpg)
SPIRAL STRUCTURE
![Page 12: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/12.jpg)
A typical radio-map of HI at 20cm
Optical image, for comparison:(not to scale)
A grand-design spiral: M51
![Page 13: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/13.jpg)
RR
Notice two different types of rotation curves
![Page 14: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/14.jpg)
About 1/3 of spiral galaxies are very regular (so-calledgrand design spirals)
but most galaxies are flocculent, with short, torn arms
NGC 2841 (cf. Fig 5.26 in textbook) M33
M81 M51
![Page 15: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/15.jpg)
Most barred galaxies show regular spirals, often attached to the bar’s ends. Bars areproducing those spirals, according to theory,via the so-called Lindblad resonances
(cf. L18)
![Page 16: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/16.jpg)
![Page 17: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/17.jpg)
One idea is that the arms we see are material spiral arms, made of concentrations of stars and gas, which never leave thearms. It has the winding problem: if the rotation curve is flat, the angular speed is ~1/R, and the pitch angle decreasesapprox. as i~1/t to i~0 too fast, in just several galactic years.
![Page 18: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/18.jpg)
Another idea: spirals as kinematic waves
It’s a nice idea but to make it work, we would need to assure that all the orbits precess (turn) at the same rate: only an additional, dynamical force can do this: self-gravity! This effect can only beproperly calculated in a density wave theory
![Page 19: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/19.jpg)
The best idea: spirals = density waves, or traffic jams in which new stars are born
![Page 20: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/20.jpg)
![Page 21: Decomposition of rotation curves into disk, bulge, halo components Two basic types of rotation curves. Grand design spirals vs. flocculent spirals Leading.](https://reader035.fdocuments.in/reader035/viewer/2022070413/5697bfe41a28abf838cb5666/html5/thumbnails/21.jpg)
Finally, galactic encounters can also generate grand-designs