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

TL;DR

This study investigates whether cosmic voids influence the evolution of giant galaxies on their surfaces by inducing perpendicular intrinsic alignments between galaxy shapes and the directions to void centres. Using TNG300-1 simulations and the Void-Finder HV02, it identifies giant void-surface galaxies with $M_{ m \star} \ge 10^{10.5} h^{-1} M_{\odot}$ across $z=0$, $0.5$, and $1$, and finds significant perpendicular alignments quantified by $p(\cos\theta)$ that are well described by the one-parameter Lee model with correlation parameter $d_t$. The strength of the alignment correlates with galaxy morphology, colour, and sSFR (stronger for elliptical, redder, and more quenched galaxies; weak with stellar age), and persists under robustness tests including alternative void identification (HV02 vs VIDE) and redshift-space considerations, though 2D projections in redshift space reduce detectability. The authors speculate that void formation and expansion can stall and quench nearby galaxies by compressing adjacent matter and hindering radial infall, with potential implications for interpreting dark-energy-driven void dynamics and for developing observational strategies to detect such effects.

Abstract

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.

Figures (17)

• Figure 1: Schematic representation of two-fold effects of the void expansion on the void-surface galaxies. After a long exposure of a void-surface galaxy to the void expansion, it becomes stalled and quiescent, exhibiting strong perpendicular alignment of its shape axis with the direction to the void center.
• Figure 2: Illustrations of the galaxies located on the surfaces of three voids, each being identified as an assembly of maximal spheres that fit large empty regions among the spatial distributions of the galaxies from the TNG 300-1 simulations tng1tng2tng3tng4tng5tng6 via the Void-Finder algorithm HV02 at $z=0$. The vertical bar displays the range and variation of the $g$-$r$ colors of the void-surface galaxies.
• Figure 3: Mean values of the cosines of the angles between the shape axes of the TNG galaxies and the directions toward the void centers in three different ranges of separation distances, $r$, as a function of stellar masses
• Figure 4: Same as figure \ref{['fig:mcost']} but with the galaxies embedded in six different spherical shells of same thickness, $R_{\rm v}/5$ with void effective radii $R_{\rm v}$.
• Figure 5: Probability density function of the cosines of the angles with Poisson errors between the shape axes of the giant void-surface galaxies and the directions toward the void centers from the TNG 300-1 simulations, and its comparison with the best-fit analytic model, eq. (\ref{['eqn:pcost']}). The best-fit value of the correlation parameter $d_{t}$ in eq. \ref{['eqn:eiej']} is determined via $\chi^{2}$-minimization method and its associated error corresponds to the interval, $\Delta d_{t}$, over which the integral of the $\chi^{2}$-distribution satisfies the condition of $\int_{\Delta d_{t}} p(\chi^{2})d\chi^{2} \approx 0.683$.