Re: Newtonian simulations of dark matter only sphere

From: Cameron McBride <>
Date: Wed, 9 Sep 2020 14:38:44 -0400

My guess here is that you need to adapt your gravitational softening in
Gadget-2. I've been out of actively following the literature for the last
~5ish years, but there was a host of papers that talk about cusp - core
connection to gravitational softening that can change the cusp vs core.
It's a little bit of a numerical quagmire, as you can tune softening to act
differently (and there are tradeoffs even if you force a strict N^2
calculation, which Gadget-2 typically doesn't). I also suggest you don't
use grid, but tree only configurations.

I think Zavala et al 2019 or Kuhlen et al 2012 might discuss aspects of
this. There are some older articles, like Boylan-Kolchin et al 2005 that
might also discuss some of it.

Others might have more insight, but hopefully that might help you start
digging deeper.


On Wed, Sep 9, 2020 at 8:32 AM ABINASH KUMAR SHAW <> wrote:

> Hello,
> I am trying to study time evolution of the density profile of a single
> dark matter only halo in Newtonian space (without boundary) using Gadget-2.
> My initial condition file contains a spherical distribution of only the
> cold dark matter particle which is written in gadget format. I am following
> the example of the gassphere (provided with the code) to evolve the CDM
> halo. I expect the density profile to show the cusp at the halo centre
> whereas I am getting a core. I understand that a core forms when there are
> baryons in addition to the CDM. There are no baryons here, however I expect
> that somehow baryonic interaction is still taking place. So, do I need to
> modify the code of my simulations; or am I doing something wrong?
> Thank you in advance.
> Sincerely,
> Abinash Kumar Shaw
> *Senior Research Fellow*
> *Department of Physics*
> *Indian Institute of Technology Kharagpur*
> *Kharagpur, India -- 721302.*
Received on 2020-09-09 20:39:06

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