No halo catalogue found for GADGET2 snapshot

[Eric Tang]

Dear All,

My n-body simulation results are phase-space of disk/bulge/halo as follows plus masses for each particle types:

 type: 0 = gal1 halo  1 = gal1 bulge  2 = gal1 disk

 type: 3 = gal2 halo  4 = gal2 bulge, 5 = gal2 disk

 particles type, x[kpc], y[kpc], z[kpc],vx[km/s], vy[km/s], vz[km/s]

 TIMESTEP =    0.00000000

0,     -5.29833,    -31.17922,     16.55958,   -100.41090,      4.48718,   -175.37633

I converted them to Gadget2 snapshot and pynbody loads that OK and is able to identify families of particles:

[<Family dm>, <Family star>]

40000

20100

The problem is halo catalogue which pynbody cannot find:

h = f.halos(priority = ['HaloNumberCatalogue'])

RuntimeError: No halo catalogue found 

How to fix this for further analysis using pynbody?

Regards,

Eric

[PONTZEN, ANDREW P.]

What result were you expecting? This sounds like an isolated simulation, so there is no way in which you would have a halo catalogue available as far as I can tell.  If you do somehow have halo IDs stored in a number array (as suggested by your code), you may wish to pass the name of the array (something like f.halos(array='name_of_array') ) to help pynbody find it.

If you need a halo finder, see also: https://pynbody.readthedocs.io/latest/reference/_autosummary/pynbody.halo.html#supported-halo-finder-formats 

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[Eric Tang]

Hi Andrew,

I would like to have a halo with particles of family <star> for pynbody.analysis. I'll try that. Thanks.

Regards,

Eric

[Andrew Pontzen]

Just pass f.star to whatever routine within pynbody.analysis you are using, this should work fine! All the best, Andrew

[Eric Tang]

Hi Andrew,

Noted with thanks. That works.

Regards,

Eric

Sent from my iPhone

On 29 May 2025, at 21:27, Andrew Pontzen <andrew.p...@durham.ac.uk> wrote:

Just pass f.star to whatever routine within pynbody.analysis you are using, this should work fine! All the best, Andrew

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