Filament hunting: integrated H i 21 cm emission from filaments inferred by galaxy surveys

Abstract

Large scale filaments, with lengths that can reach tens of Mpc, are the most prominent features in the cosmic web. These filaments have only been observed indirectly through the positions of galaxies in large galaxy surveys or through absorption features in the spectra of high-redshift sources. In this study, we propose to go one step further and directly detect intergalactic medium filaments through their emission in the HI 21 cm line. We make use of high-resolution cosmological simulations to estimate the intensity of this emission in low-redshift filaments and use it to make predictions for the direct detectability of specific filaments previously inferred from galaxy surveys, in particular the Sloan Digital Sky Survey. Given the expected signal of these filaments, our study shows that HI emission from large filaments can be observed by current and next-generation radio telescopes. We estimate that gas in filaments of length l 15 h −1 Mpc with relatively small inclinations to the line of sight ( 10 • ) can be observed in ∼ 100 h with telescopes such as Giant Metrewave Telescope or Expanded Very Large Array, potentially providing large improvements over our knowledge of the astrophysical properties of these filaments. Due to their large field of view and sufficiently long integration times, upcoming HI surveys with the Apertif and Australian Square Kilometre Array Pathfinder instruments will be able to detect the brightest independently of their orientation and curvature. Furthermore, our estimates indicate that a more powerful future radio telescope like Square Kilometre Array can be used detect even the faintest of these filaments with integration times of ∼ 10 − 40 h.

Deforming black hole and cosmological solutions by quasiperiodic and/or pattern forming structures in modified and Einstein gravity

“…The predominantly accepted ΛCDM paradigm predicts for the cosmological structure that dark matter is organized as a cosmic web structure of walls, filaments and halos [46,47,48,49,50,51,52,53,54,55]. Numerous images of the visually striking cosmic web have been created and studied theoretically in a framework of research of the large-scale structure of the universe.…”

“…The most general class of nonholonomic stationary quasiperiodic deformations of BHs is determined by corresponding nonlinear quaisperiodic functionals both for the generating functions and (effective) sources. Nonlinear superpositions of solutions of type (55) and (57) are determined by coefficients of (55) computed…”

“…On relevant former results, we cite a series of papers for the physics of quasicrystals and Penrose-like telings, see [32,33,34,35,36,37,38,39,40,41,42,43,44,45]). It is considered that various web like, filament, quasiperiodic, aperiodic, singular and nonsigular cosmological evolution, solitonic like distributions and nonlinear wave structures are distinguished /found in modern cosmological observational data [46,47,48,49,50,51,52,53,54,55]. Such generic locally anisotropic and inhomogeneous cosmological configurations can not be explained exhaustively using only higher symmetry solutions (for instance, Friedmann-Lemaître-Roberstson-Walker, FLRW, and/or Bianchi type metrics) depending only on time like coordinates and constructed following methods of the theory of ODEs.…”

Searching for H i imprints in cosmic web filaments with 21-cm intensity mapping

“…In order to match the estimates in Ω (f) HI and N HI reported in Table 2 the filament thickness is constrained to ∼ 3 Mpc. There is no universal definition for the typical filament radial extension; galaxies are usually considered filament members up to a radial distance of 0.5 h −1 Mpc (Tempel et al 2014) or 1 h −1 Mpc (Kooistra et al 2017) from the filament spine. The latter is consistent with our constraint if we take ∆s to represent the diametral filament size.…”

“…The present study, conversely, targets specifically the cosmic web filaments, and aims at searching for the 21-cm signature from the neutral gas fraction in the WHIM. The feasibility of a direct detection of 21-cm emission from the filamentary gas has been explored in Kooistra et al (2017). In this work, however, we adopt a methodology very similar to the one used by T19 and DG19, based on the stacking of galaxy pairs to enhance the signal coming from the large-scale filaments, and we employ the same data set used by A18, namely the 21-cm maps from the Parkes telescope and the galaxy catalogue from the Two-Degree-Field (2dF) survey.…”