Density and temperature of cosmic-web filaments on scales of tens of megaparsecs

Abstract

We study physical properties of matter in 23,950 filaments ranging from 30 to 100 Mpc length identified in the SDSS survey. We stack the Comptonization y map produced by the Planck Collaboration around the filaments, excluding all the resolved galaxy groups and clusters above the mass of 10 13 M . We detect for the first time the tSZ signal at a significance of 3.7 σ in filamentary gas on such a large scale. We also stack the Planck CMB lensing convergence map in the same manner and detect the lensing signal at a significance of 7.1 σ. To estimate physical properties of the matter, we consider an isothermal, cylindrical filament model with a density distribution following a β-model (β=2/3). Assuming that the gas distribution follows the dark matter distribution, the central gas and matter overdensity δ and gas temperature T e are estimated to be δ = 25.3 +34.6 −15.1 and T e = 1.2 +0.4 −0.4 × 10 6 K, which results in a measured baryon fraction of 0.071 +0.097 −0.042 × Ω b .

Characterising filaments in the SDSS volume from the galaxy distribution

“…4 but leaves the shape unaltered. After an initial peak, the number density in the survey volume is rather flat, especially in the redshift range covered by Bonjean et al (2020) Tanimura et al (2020)…”

“…(which can be identified with the centres of voids). While in the analyses described in Malavasi et al (2020), Tanimura et al (2020), and Bonjean et al (2020) we only focused on maxima, type 2 saddle points, and bifurcations and in the present catalog we only distribute filaments and disregard walls for the moment, type 1 saddle points, and minima (voids), these types of critical points are still included in the numbers given in Table 5 and are included in some of the distributions presented below to provide a complete overview of the properties of the catalogue. Red lines refer to a 3σ persistence threshold, and blue lines refer to a 5σ persistence threshold.…”

“…14), the interpolated density field is not reliable and the detected filaments are spurious. Tanimura et al (2020) performed the analysis at z > 0.2 and discarded all the filaments at lower redshifts and outside of the footprint of the SDSS DR12. Bonjean et al (2020) also applied the SDSS DR12 mask, but they did not take the large holes in the footprint at low redshift (z 0.15) into account.…”

“…They are probably due to spurious critical points created at the edge of the survey volume. The cuts in length of the filaments that were applied to the samples in Tanimura et al (2020) and Bonjean et al (2020) serve the purpose of eliminating these features. Figure 17 shows the distributions of the number of filaments that is connected to maxima.…”

“…DisPerSE can work with sparse datasets or with distributions of galaxies in which the density of tracers changes dramatically within the sampled volume). The catalogues of filaments described here have been used in Malavasi et al (2020), Tanimura et al (2020), Bonjean et al (2020) and represent the first published general-purpose catalogues of filaments in the SDSS obtained with the DisPerSE method. We study the systematic uncertainties deriving from the DisPerSE method and the SDSS survey characteristics.…”