Galaxy filaments as pearl necklaces

Abstract

Context. Galaxies in the Universe form chains (filaments) that connect groups and clusters of galaxies. The filamentary network includes nearly half of the galaxies and is visually the most striking feature in cosmological maps. Aims. We study the distribution of galaxies along the filamentary network, trying to find specific patterns and regularities. Methods. Galaxy filaments are defined by the Bisous model, a marked point process with interactions. We use the two-point correlation function and the Rayleigh Z-squared statistic to study how galaxies and galaxy groups are distributed along the filaments. Results. We show that galaxies and groups are not uniformly distributed along filaments, but tend to form a regular pattern. The characteristic length of the pattern is around 7 h −1 Mpc. A slightly smaller characteristic length 4 h −1 Mpc can also be found, using the Z-squared statistic. Conclusions. We find that galaxy filaments in the Universe are like pearl necklaces, where the pearls are galaxy groups distributed more or less regularly along the filaments. We propose that this well-defined characteristic scale could be used to test various cosmological models and to probe environmental effects on the formation and evolution of galaxies.Key words. methods: numerical -methods: observational -large-scale structure of Universe IntroductionMany cosmological probes have been developed and used to estimate the parameters of the cosmological models describing our Universe. Most of them rely on some aspects of the large-scale structure. The most common probe used to quantify galaxy clustering is the two-point correlation function which was first used decades ago (Davis & Geller 1976;Groth & Peebles 1977;Davis et al. 1988;Hamilton 1988;White et al. 1988;Boerner et al. 1989;Einasto 1991) It is well known that galaxy filaments are visually the most dominant structures in the galaxy distribution, being part of the so-called cosmic network (Jõeveer et al. 1978;Bond et al. 1996). Presumably, nearly half (∼40%) of the galaxies (or mass in simulations) are located in filaments. This number is based on morphological or dynamical classification of the cosmic web (e.g. Jasche et al. 2010;Tempel et al. 2014b;Cautun et al. 2014). Properties of the three-point correlation function also indicate that galaxies tend to populate filamentary structures (Guo et al. 2014a) and, indeed, filaments have been found between galaxy clusters (e.g. Dietrich et al. 2012). Tempel et al. (2014a) show Appendices are available in electronic form at

On the angular momentum history of galactic discs

“…Qualitatively, we may expect the baryonic gas to rotate around the axis of a filament, as it is attracted by the filament gravitational pull, while roughly conserving the AM it may have acquired from tidal interactions with other forming structures nearby. A gradient in specific AM, perpendicular to the filament, will also naturally arise, as the more distant material is expected to have experienced stronger tidal interactions with its surroundings, hough the cross section of filaments is typically of the order of a Mpc (Tempel et al 2014), much larger than galaxies. Such a rotating baryonic cylinder would quite naturally administer to galaxies the raw material for their growth, with increasing AM, hence growing disks whose rotational vector should align with the filament.…”

The alignment of galaxy spin with the shear field in observations

“…µ = 0 implies that the rotation axis of the galaxy is perpendicular to the respective eigenvector and µ = 1 implies the two are parallel. We use kernel density estimation technique (see appendix of Tempel et al 2014b) to obtain a histogram of the probability distribution.…”

The orientation of galaxy pairs with filamentary structures: dependence on morphology

“…Clusters, filaments, sheets and voids are the building blocks of the cosmic web. It is believed that galaxies in filaments represent about the half of the baryon mass in the universe (Tempel et al 2014b, and references therein). In addition, Libeskind et al (2018) performed a comparative analysis of twelve different methods devised to classify the cosmic web finding a good agree between the most of the thechinque with a mass fraction in filaments between ≈ 10% and ≈ 60%.…”