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mkhernquist - create a two-component, isotropic, spherical galaxy+halo

Hernquist model


mkhernquist [parameter=value]


mkhernquist generates a two-component, isotropic, spherical galaxy/halo model using a superposition of two Hernquist models. The galaxy is assumed to be a unit Hernquist model with M=a=1 while the halo mass and scale radius are free parameters specified on the command line. The distribution function is calculated on the fly using Eddington’s formula and then sampled to generate a N-body realization of a galaxy. The galaxy and halo particles are dumped in succession -- first half are galaxy particles.

If a single component model is needed, use m=a=1 (which is the default).

Hernquist models are a special case of Dehnen models with gamma=1. See mkdehnen(1NEMO) .


The following parameters are recognized in order; they may be given in any order if the keyword is also given. Use --help to confirm this man page is up to date.
Output snapshot(5NEMO) file name. No default.
Total number of particles. This needs to be an even number, as an equal number of particles is used for each component. No default.
Mass of Halo (where the galaxy has mass=1) [1]
Scale length of Halo (where the galaxy has radius=1) [1]
Standard seed [0]
Add (as negative) potentials to snapshot. [f]
Mass fraction used of Hernquist distribution. A value of 1.0 will result in particles at large radii. See CAVEATS below. [1.0]
Radius where to cut the mass model, which will override the mfrac value. Default: not used.
Centrate snapshot (t/f)? See CAVEATS below. [t]
Optional verbiage []


mkhernquist is one of the programs in NEMO that does not quite use virial units, though is in virial equilibrium. The total mass is 2 by default, if halo mass m=1 is used.


Due to the relatively large number of particles at large radii, setting zerocm=t will cause the center to be significantly shifted from the origin. This will depend on the value for nbody= and mfrac=. Setting mfrac=0.95 will thus a more reasonably looking model, at the cost of a model that is not quite relaxed.

See Also

mkplummer(1NEMO) , mkommod(1NEMO) , mkdehnen(1NEMO)


@ads 1990ApJ...356..359H


Peter Teuben, John Dubinski (original version)

Update History

27-Mar-03    V1.1 man pages finally created      PJT
15-may-2015    V1.2 clarified docs, potential negative now    PJT

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