arXiv subjects

Geonwoo Kang

Publications and source records attributed to Geonwoo Kang.

4 recordsLinked to original sources

arXiv2026

The effect of dark energy on the void-halo perpendicular alignments

We report a numerical discovery that in a more rapidly accelerating spacetime, the galactic halos on void surfaces develop stronger perpendicular alignments with the directions toward the void centers. We utilize the halo catalogs from the AbacusSummit suite of simulations for $10$ different cosmologies that include one Planck $\Lambda$CDM, four $w$CDM and five $w_{0}w_{a}$CDM, which share the identical initial conditions except for the dark energy equation of state. For each cosmology, we identify the voids and void-surface galactic halos at $z=0.1$ and determine the probability density functions of the cosines of the angles, $p(\cos\theta)$, between the shape axes of void-surface galactic halos and the directions toward the void centers. The numerically obtained $p(\cos\theta)$ is fitted to an analytic single-parameter formula derived through an empirical modification of the linear perturbation theory. Eliminating spurious signals caused by the differences in the mass and sphericity distributions of void-surface galactic halos among different cosmologies, we detect a clear net effect of dark energy on the strengths of the perpendicular alignments of void-surface galactic halos, quantified by the single parameter, $d_{t}$. Noting that $d_{t}$ has higher values in the cosmologies where dark energy has more negative pressure and evolves more rapidly, we put forth a bilinear model for the difference in $d_{t}$ between the two cases of $w=-1$ and $w\ne -1$. Demonstrating that this bilinear relation excellently describes the numerical results, we conclude that the perpendicular alignments of void-surface galactic halos should in principle be a powerful independent indicator of the dynamic nature of dark energy.

astro-ph.CO↗

arXiv2026

A Universal Bilinear Model for the Dependence of Void Asymmetry Distributions on $\Omega_{m}$ and $\sigma_{8}$

$Aims$: We present a new independent diagnostics based on void properties, by which the matter density parameter ($\Omega_{m}$) and amplitude of initial density field ($\sigma_{8}$) can be constrained. This diagnostics utilizes coherent rotation of void galaxies, which can be observed as redshift asymmetry in opposite sides bisected by the projected spin axes of hosting voids. $Methods$: Identifying the voids and their member galaxies in the AbacusSummit of cosmological simulations and searching for their projected spin axes with an iterative method, we numerically determine the void asymmetry distributions both in real and redshift spaces for three different classes of the background cosmologies: the $\Lambda$CDM, the $w$CDM and the $w_{0}w_{a}$CDM. $Results$: It is discovered that the void asymmetry distributions in real and redshift spaces are well approximated by the generalized Gamma models characterized by the scale and shape parameters for all of the $33$ background cosmologies considered. It turns out that the initial conditions affect only the scale parameter of the void asymmetry distributions that exhibits an almost linear dependence on each of $\Omega_{m}$ and $\sigma_{8}$ with being insensitive to $w$. Developing a bilinear model for the dependence of void asymmetry distributions on $\Omega_{m}$ and $\sigma_{8}$, we show that its coefficients are universal constants over the three cosmological classes. $Conclusions$: Given that the void asymmetry distributions in redshift space are readily measurable properties, our universal model for the scale parameter of the void asymmetry distributions will in principle complement the standard cosmological diagnostics to break the $\Omega_{m}$-$\sigma_{8}$ degeneracy, regardless of $w$.

astro-ph.CO↗

arXiv2025

How the cosmic voids contribute to stalling and quenching the giant galaxies on their surfaces

We report a numerical hint that the formations of cosmic voids may be closely linked with the mechanism through which the giant galaxies on void surfaces establish elliptical shapes, redder colors, and lower specific star formation rates (sSFR). Identifying the voids from the TNG300-1 simulations via the Void-Finder algorithm~\cite{HV02} at $z=0$, $0.5$ and $1$, we explore if and how the shapes of the TNG galaxies located on void surfaces are aligned with the directions toward the void centers. Noting that only the giant void-surface galaxies with stellar masses $M_{\star}\ge 10^{10.5}\,h^{-1}\,M_{\odot}$ exhibit significant tendency of perpendicular alignments, we dichotomize them into two $M_{\star}$-controlled samples according to their morphologies (elliptical or spiral), colors (redder or bluer), sSFR (lower or higher) and stellar ages (older or younger). It is found at all of the three redshifts that the perpendicular alignments of void-surface galaxies become stronger for the cases that they have elliptical shapes, redder colors, and lower sSFR, but showing weak dependence on the stellar ages. It is also shown that the numerical results are well described by the analytical one-parameter model developed by Lee~\cite{lee19} under the assumption of the existence of a linear scaling between the covariance matrices of galaxy shape axes and local tidal tensors. We test the robustness of alignment signals against the variation of void-finder algorithms and its feasibility against the redshift-space and projection effects. Our results lead us to speculate that the formation and expansion of voids may have an effect of stalling and quenching the giant void-surface galaxies by compressing adjacent matter and then preventing them from radial infall/accretion.

astro-ph.CO↗

arXiv2025

Void spin distribution as a powerful probe of $\sigma_{8}$

We present a numerical proof of the concept that the void spin distributions can provide a tight constraint on the amplitude of matter density fluctuation on the scale of $8\,h^{-1}{\rm Mpc}$ ($\sigma_{8}$) without being severely deteriorated by the degeneracies of $\sigma_{8}$ with cold dark matter density parameter multiplied by the dimensionless Hubble parameter square ($\Omega_{\rm cdm}h^{2}$), total neutrino mass ($M_{\nu}$) and dark energy equation of state ($w$). Applying the Void-Finder algorithm~\cite{HV02} to a total of $15$ AbacusSummit $N$-body simulations of $15$ different cosmological models~\cite{summit1}, we identify the giant voids and measure the magnitudes of rescaled specific angular momenta of point-like void halos as their spins. The $15$ cosmologies include the Planck $\Lambda$CDM and $14$ non-Planck models, each of which differs among one another only in one of $\{\sigma_{8},\ \Omega_{\rm cdm}h^{2},\ M_{\nu},\ w\}$. We determine the probability density distribution of void spins for each model and for the first time find it to be well approximated by the generalized Gamma distribution with two characteristic parameters, $k$ and $\theta$. It turns out that the best-fit values of $k$ and $\theta$ exhibit very sensitive dependence only on $\sigma_{8}$, being almost insensitive to $\Omega_{\rm cdm}h^{2}$, $M_{\nu}$ and $w$. This exclusive $\sigma_{8}$-dependence of the void spin distributions is confirmed to be robust against the variation of the mass and number cuts of void halos. We also test an observational feasibility of estimating the void spins from real data on the galaxy redshifts.

astro-ph.CO↗