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mktabdisk - create a test disk with density, circular velocity and dispersion given by a table


mktabdisk [parameter=value]


mktabdisk creates an idealized test disk with a given tabular form of density, circular velocity and velocity dispersion as function of radius. It can also optionally compute the asymmetric drift correction.

For clarity the Asymmetric Drift Correction output is split in three: a density, velocity and dispersion related component. They are linear, but recall they are added (or subtracted) in quadrature, so we print the sign of the correction as well. See EXAMPLES below. The three are (many references in the literature with some assumptions of isotropicity):

     adc_D^2 = S^2 dlnD/dlnR
     adc_V^2 = S^2 (1-dlnV/dlnR) / 2
     adc_S_2 = S^2 dS^2/dlnR
Normally only the adc_V^2 term increases the rotation curve, the other two act like an outward bound force, and subtract from the rotation curve to give the observed streaming velocity.


The following parameters are recognized in any order if the keyword is also given:
Input table (radius,density,velocity,dispersion). No default.
Output file name in standard snapshot(5NEMO) format.
Number of disk particles [2048]
Inner disk radius [min radius from table]
Outer cutoff radius [max radius from table]
Rescale total mass to this?. By default not scaled, if a positive value given, this will be the total mass [1.0]
Usual random number seed, see also xrandom(1NEMO) [0]
Sign of Z-angular momentum vector of disk. +1 means counter clock wise. [1]
Produce a table of Asymmetric Drift Corrections. If choosen, a simple ascii table with 7 columns is printed: rad, den (D), vel (V), sig (S), adc_D, adc_V, adc_S, vobs [f]
Select mode of initial conditions. 1: regular in Radius, but random in Theta. nbody= will be exact. 2: cartesian grid, but keeping within rmax. nbody= will be approximate. [1].
Scaling factor by which the vertical velocity dispersions are computed compared to the (isotropic) planar. Remember this is a toy model. The default is 3D isotropic, but use sigmaz=0 if you want a truly planar disk in all phase space coordinates [1].
Text headline for output file [default: not used].


Here is an example of producing the ADC table of an exponential disk with an isothermal halo rotation curve and constant velocity dispersion at 10% of the peak velocity:
     nemoinp 0:5:0.2 | tabmath - - ’exp(-%1),%1/sqrt(1+%1**2),0.1’ > tab1
     mktabdisk tab1 . adc=true
     # R  D          V         S    adc_D      adc_V     adc_S  Vobs
     0.2  0.818731   0.196116  0.1  -0.0447318 0.0145238 0      0.191498
     0.4  0.67032    0.371391  0.1  -0.0632403 0.0261482 0      0.3669
     0.6  0.548812   0.514496  0.1  -0.0774612 0.036386  0      0.509931
     4.6  0.0100518  0.977176  0.1  -0.214485  0.0690972 0      0.955847
     4.8  0.00822975 0.97898   0.1  -0.219031  0.0692244 0      0.956671
     5.0  0.00673795 0.980581  0.1  -0.223867  0.0693351 0      0.957199
or a colorful plot with various velocity components plotted, and where the V/sigma < 1 in the nuclear region
     nemoinp 0.001,0.1:15:0.1 | tabmath - - ’exp(-%1),%1/sqrt(1+%1**2),0.4-0.3*%1/(1+%1)’
> tab2
     mktabdisk tab2 . adc=true > tab2.adc
     tabplot tab2.adc 1 3,4,5,6,7,8 0 16 -0.5 1.1 line=1,1,1,1,1,2 color=3,4,2,3,4,3
ycoord=0 xcoord=1


The current version distributes particles regularly by radius, but randomnly in angle.

See Also

mkdisk(1NEMO) , snapshot(5NEMO)




Peter Teuben

Update History

16-may-2020    V0.1 drafted    PJT
27-may-2020    V0.5 add sigmaz=    PJT

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