A deeper look into the structure of {Lambda}CDM haloes: correlations between halo parameters from Einasto fits. (arXiv:1811.04955v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Udrescu_S/0/1/0/all/0/1">Silviu M. Udrescu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dutton_A/0/1/0/all/0/1">Aaron A. Dutton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maccio_A/0/1/0/all/0/1">Andrea V. Macciò</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Buck_T/0/1/0/all/0/1">Tobias Buck</a>
We used high resolution dark matter only cosmological simulations to
investigate the structural properties of Lambda Cold Dark Matter ($Lambda$CDM)
haloes over cosmic time. The haloes in our study range in mass from $sim
10^{10}$ to $sim 10^{12} mathrm{M}_odot$, and are resolved with $10^5$ to
$10^7$ particles. We fit the spherically averaged density profiles of DM haloes
with the three parameter Einasto function. For our sample of haloes, the
Einasto shape parameter, $alpha$, is uncorrelated with the concentration, $c$,
at fixed halo mass, and at all redshifts. Previous reports of an
anti-correlation are traced to fitting degeneracies, which our fits are less
sensitive to due to our higher spatial resolution. However, for individual
haloes the evolution in $alpha$ and $c$ is anti-correlated: at redshift $z=7$,
$alpha simeq 0.4$ and decreases with time, while $csimeq 3$ and increases
with time. The evolution in structure is primarily due to accretion of mass at
larger radii. We suggest that $alpha$ traces the evolutionary state of the
halo, with dynamically young haloes having high $alpha$ (closer to a top-hat:
$alpha^{-1}=0$), and dynamically relaxed haloes having low $alpha$ (closer to
isothermal: $alpha=0$). Such an evolutionary dependence reconciles the
increase of $alpha$ vs peak height, $nu$, with the dependence on the slope of
the power spectrum of initial density fluctuations found by previous studies.
We used high resolution dark matter only cosmological simulations to
investigate the structural properties of Lambda Cold Dark Matter ($Lambda$CDM)
haloes over cosmic time. The haloes in our study range in mass from $sim
10^{10}$ to $sim 10^{12} mathrm{M}_odot$, and are resolved with $10^5$ to
$10^7$ particles. We fit the spherically averaged density profiles of DM haloes
with the three parameter Einasto function. For our sample of haloes, the
Einasto shape parameter, $alpha$, is uncorrelated with the concentration, $c$,
at fixed halo mass, and at all redshifts. Previous reports of an
anti-correlation are traced to fitting degeneracies, which our fits are less
sensitive to due to our higher spatial resolution. However, for individual
haloes the evolution in $alpha$ and $c$ is anti-correlated: at redshift $z=7$,
$alpha simeq 0.4$ and decreases with time, while $csimeq 3$ and increases
with time. The evolution in structure is primarily due to accretion of mass at
larger radii. We suggest that $alpha$ traces the evolutionary state of the
halo, with dynamically young haloes having high $alpha$ (closer to a top-hat:
$alpha^{-1}=0$), and dynamically relaxed haloes having low $alpha$ (closer to
isothermal: $alpha=0$). Such an evolutionary dependence reconciles the
increase of $alpha$ vs peak height, $nu$, with the dependence on the slope of
the power spectrum of initial density fluctuations found by previous studies.
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