A Search for Warm/Hot Gas Filaments Between Pairs of SDSS Luminous Red Galaxies (1709.05024v5)

Abstract: We search the Planck data for a thermal Sunyaev-Zel'dovich (tSZ) signal due to gas filaments between pairs of Luminous Red Galaxies (LRG's) taken from the Sloan Digital Sky Survey Data Release 12 (SDSS/DR12). We identify $\sim$260,000 LRG pairs in the DR12 catalog that lie within 6-10 $h^{-1} \mathrm{Mpc}$ of each other in tangential direction and within 6 $h^{-1} \mathrm{Mpc}$ in radial direction. We stack pairs by rotating and scaling the angular positions of each LRG so they lie on a common reference frame, then we subtract a circularly symmetric halo from each member of the pair to search for a residual signal between the pair members. We find a statistically significant (5.3$\sigma$) signal between LRG pairs in the stacked data with a magnitude $\Delta y = (1.31 \pm 0.25) \times 10^{-8}$. The uncertainty is estimated from two Monte Carlo null tests which also establish the reliability of our analysis. Assuming a simple, isothermal, cylindrical filament model of electron over-density with a radial density profile proportional to $r_c/r$ (as determined from simulations), where $r$ is the perpendicular distance from the cylinder axis and $r_c$ is the core radius of the density profile, we constrain the product of over-density and filament temperature to be $\delta_c \times (T_{\rm e}/10^7 \, {\rm K}) \times (r_c/0.5h^{-1} \, {\rm Mpc}) = 2.7 \pm 0.5$. To our knowledge, this is the first detection of filamentary gas at over-densities typical of cosmological large-scale structure. We compare our result to the BAHAMAS suite of cosmological hydrodynamic simulations (McCarthy et al. 2017) and find a slightly lower, but marginally consistent Comptonization excess, $\Delta y = (0.84 \pm 0.24) \times 10^{-8}$.

• The paper demonstrates a 5.3σ detection of warm/hot gas filaments by stacking Planck tSZ data from approximately 260,000 SDSS LRG pairs.
• It isolates a residual signal (Δy = (1.31 ± 0.25)×10⁻⁸) after removing individual halo contributions, indicating the presence of intergalactic filamentary gas.
• The findings constrain filament properties, revealing lower over-densities than some hydrodynamic simulations, and call for refined cosmological models and surveys.

An Analysis of Warm/Hot Gas Filaments between SDSS Luminous Red Galaxies

The paper presents an investigation into the presence of warm/hot gas filaments connecting pairs of Luminous Red Galaxies (LRG's) using thermal Sunyaev-Zel'dovich (tSZ) effect data from the Planck satellite, combined with the Sloan Digital Sky Survey Data Release 12 (SDSS/DR12). LRG's, predominantly featuring old stellar populations, serve as critical probes of large-scale cosmological structures. The authors leveraged a sample of approximately 260,000 LRG pairs to statistically detect gas filaments over cosmological scales.

Methodology and Results

The authors implemented a stacking technique on Planck's tSZ data to identify residual signals potentially indicative of filamentary gas after accounting for the prominent halo emissions from individual LRG's. This involved observing the excess Comptonization parameter, $\Delta y$, between galaxy pairs, yielding a significant signal detected at 5.3σ with a magnitude of $(1.31 \pm 0.25) \times 10^{-8}$. Notably, the detection outperformed null-hypothesis tests across rotated LRG pair configurations and pseudo-pair analyses, enhancing confidence in the captured signal's authenticity.

The authors derived from simulations an estimate linking the observed signal to the properties of filamentary gas. The derived constraints on physical properties indicated lower filament over-densities than predictions from some current hydrodynamic simulations, calculated as $$\delta_c \times (T_{\rm e}/10^7 \, \text{K}) \times (r_c/0.5h^{-1} \, \text{Mpc}) = 2.7 \pm 0.5$$.

Implications and Theoretical Comparisons

The implications of this paper revolve around the characterization and detection of the Warm/Hot Intergalactic Medium (WHIM), pivotal in cosmological baryonic matter analysis. It provides constraints for cosmological models aiming to accurately simulate the distribution and conditions of baryonic matter. The results show a marginal consistency with BAHAMAS hydrodynamic simulations, albeit predictions from simulations exhibit a lower expected tSZ signal magnitude at $\Delta y = (0.84 \pm 0.24) \times 10^{-8}$. Therefore, while potential systematic errors could impact signal magnitude, a consensus between simulation constraints and observed data necessitated exploring beyond traditional models of baryonic distribution.

Comparisons and Future Perspectives

This research aligns with previous studies that detected the lensing signals of filaments on similar scales using weak gravitational lensing but breaks new ground with tSZ observations. The consistency across multiple simulation cosmologies and complementary findings, including those using gravitational lensing, suggests this methodology's robustness in identifying filament structures.

Future directions might involve refining resolution and depth using next-generation surveys and continual advancements in tSZ mapping technologies. Enhanced simulations that incorporate feedback mechanisms and incorporate realistic cosmic environments are vital to better reconcile theory and observation.

In conclusion, this paper successfully argues the presence of a diffuse gaseous component in large-scale structures such as warm/hot gas filaments, representing an advancement in our understanding of cosmic baryonic content and emphasizing the need for integrative approaches combining observational astrometry and refined simulation techniques in contemporary astrophysics.