Correlation between H$α$ emitters and their cosmic web environment at $z \sim 1$

TL;DR

This work investigates how Hα emitters at z ~ 1 trace the cosmic web using an environment metric based on tidal and strain anisotropy, rather than density, by applying a physically grounded Hα emission model to IllustrisTNG simulations. It demonstrates that luminous ELGs preferentially occupy knot and filament regions and that their large-scale bias increases with environmental anisotropy. The study also characterizes weak but meaningful correlations between ELG properties and the anisotropy, offering physical interpretations in terms of accretion shocks and AGN influence, and shows that the environment-induced bias has implications for upcoming near-infrared surveys and multi-tracer cosmological analyses. Overall, the results advocate incorporating environmental anisotropy into ELG clustering models to improve cosmological constraints from future surveys.

Abstract

Future near-infrared spectroscopic galaxy surveys will target high-redshift emission-line galaxies (ELGs) to test cosmological models. Deriving optimal constraints from emission-line galaxy clustering hinges on a robust understanding of their environmental dependence. Using the TNG300-1 simulation, we explore the correlation between properties of H$α$ emitters and their environment anisotropy rather than traditional density-based measures. Our galactic H$α$ emission model includes contributions from the warm interstellar medium. The environment anisotropy and type are assigned using a halo mass-dependent smoothing scale. We find that most luminous ELGs ($L_{\rm{H}α}>10^{42}\ \rm{erg\ s^{-1}}$) reside in filaments and knots. More generally, ELGs are more biased in strongly anisotropic environments. While correlations with galactic properties are found to be weak, they are statistically significant for host halo masses $M\lesssim 10^{12}\ M_\odot/h$. Our analysis motivates further investigation into how environmental anisotropy influences galaxy evolution, and highlights the potential for leveraging these effects in the analyses of upcoming cosmological surveys.

Figures (13)

• Figure 1: The average central and satellite occupation numbers $\langle N_c|M\rangle$, $\langle N_s|M\rangle$ computed for our $\mathrm{H}\rm{\alpha}$ emission model for TNG300-1 at $z=1$.
• Figure 2: Spearman rank correlation coefficient $\rho_s$ between the anisotropy parameter $\alpha_{\rm T}$ and the smoothed overdensity $\delta_{\rm R}$ at the location $\Vec{x}_h$ of dark matter halos for Gaussian filters with different prescriptions of the smoothing radius $\text{R}_\text{G}$. Results are shown as a function of the halo mass $M$. The dot-dashed line shows the correlation extracted from TNG50-1. The thin vertical line marks the minimum mass $M= 2\times 10^{11}\ {\rm {\it h}}^{-1}M_\odot$ below which $\rm{R_G}$ is poorly resolved with TNG300-1 (see text).
• Figure 3: A two-dimensional slice extracted from the $z=1$ snapshot of TNG300-1. The points indicate the positions of halos with $M>2\times 10^{11}\ {\rm {\it h}}^{-1}M_\odot$, and are colored progressively according to their $\log_{10} \alpha_{\text{T}}$, as indicated by the color bar. The background gray scale shows the dark matter overdensity $\log \ (\rho_{\text{DM}}/\bar{\rho}_{\text{DM}})$.
• Figure 4: Top: Measurements of the scale-dependent bias $b(k)$ of mock ELGs with $\mathrm{H}\rm{\alpha}$ luminosity $L_{\mathrm{H}\rm{\alpha}}>10^{41}\ {\rm erg\, s^{-1}}$ when split into terciles of $\rm{\alpha_T}$. Results are shown separately for central (solid curves) and satellite galaxies (dashed curves). Bottom: Same as the top panel but for $\rm{\alpha_V}$.
• Figure 5: Left panel: Comoving differential halo mass function, conditioned on environment. Solid and dashed curves indicate the classification obtained from the V- and T-tensors, respectively. Vertical line indicates, as in Fig. \ref{['fig:rho_S_alpha_delta']}, the mass $M\sim 2\times 10^{11}\ {\rm {\it h}}^{-1}M_\odot$ below which the smoothing scale $\rm{R_G}$ is poorly resolved. Right panel: Fraction of ELGs in voids, sheets, filaments and knots as a function of $\mathrm{H}\rm{\alpha}$ luminosity (color and linestyle conventions same as left panel). The classification obtained from DisPerSE (dotted) predicts fewer ELGs in knots and more in sheets. Due to the limited resolution of the grid, ELGs with parent halo mass smaller than $2\times 10^{11} \ {\rm {\it h}}^{-1}M_\odot$ are not included here.