| Name: | AYAN NANDA |
| Affiliation: | National Institute of Science Education and Research |
| Conference ID: | ASI2025_163 |
| Title: | Self-Similarity of Halo Shapes in Cosmological Simulations |
| Authors: | Ayan Nanda 1,2, Nishikanta Khandai 1,2, Jasjeet Singh Bagla 3, Swati Gavas 3 |
| Authors Affiliation: | 1 Ayan Nanda, Nishikanta Khandai (School of Physical Sciences, National Institute of Science Education and Research, Jatni 752050, India)
2 Ayan Nanda, Nishikanta Khandai(Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai 400094, India)
3 Jasjeet Singh Bagla, Swati Gavas(IISER Mohali, Knowledge city, Sector 81, SAS Nagar, Manauli PO 140306, Pujab, India) |
| Mode of Presentation: | Oral |
| Abstract Category: | Galaxies and Cosmology |
| Abstract: | We investigate the shapes of dark matter halos in cosmological
$N$-body simulations in scale free Einstein-De Sitter (EdS)
and $\Lambda$CDM cosmologies.
We use two halo finders, SUBFIND (SF) and ROCKSTAR (RS), to identify bound structures.
We compute the shape tensor of well-resolved central halos and obtain
their principle axes ($a \geq b \geq c)$.
We find that at fixed mass, halos become more spherical
with decreasing redshift.
The distribution of axis ratios ($q=b/a,s=c/a$) show self-similar behaviour
when the mass $M$ is scaled by the non-linear mass $M_{\mathrm{nl}}$,
$\left( \frac{M}{M_{\mathrm{nl}}}\right)$, across power-law spectral indices.
This leads to the average value of the axis ratios($\bar{q},\bar{s}$) also
showing self-similar behaviour as a function
of $\frac{M}{M_{\mathrm{nl}}}$ across spectral indices, within uncertainties.
However $\bar{q},\bar{s}$ show a tighter self-similar behaviour as a function
of peak height $\left(\nu=\frac{\delta_c}{\sigma(M,z)}\right)$. We find
that $(\bar{q}(\nu),\bar{s}(\nu)$) are consistent with a universal function,
$y=a-b \tanh \left[ c \left(\log_{10}(\nu) - d\right)\right]$
across the spectral indices ranging from $n=-1.0$ to $n=-2.2$.
When comparing halo finders we see that
the the results with RS show a tighter self-similar behaviour compared to those with SF.
We extend our analysis of halo shapes for the standard $\Lambda$CDM cosmology.
However we find a different universal function describing
$(\bar{q}(\nu),\bar{s}(\nu)$). The width of the distributions of $(q,s)$ in
both, scale-free and $\Lambda$CDM, classes of simulations can be reduced
further by classifying halos as oblate, triaxial or prolate, each of
which are described by self-similarity. |
