On the emptiness of voids

Abstract

The observability of a galaxy population inside of voids is estimated by assuming a void population similar to t h e one of nearby field galaxies in density as well as in morphological mixture. Obviously an extension to apparent magnitudes beyond rn = 22 for a complete sample of galaxies in a sufficient large field is needed to get reliable information on a void population.Iiey words: galaxy voids -field galaxies A A A subject classification: 157; 160 1. IntroductionSince the discovery of the cellular structure of the Universe and the presence of voids (Joeveer et al. 1978, Joeveer & Einasto 1978, Tarenghi et al. 1978, Tifft & Gregory 1978, Tully & Fisher 1978, Zeldovich et al. 1982) the knowledge on tlhe distribution of the visible matter in space is grown enormously owing to extensive redshift surveys. These observational data (Huchra et al. 1983, de Lapparent et al. 1986, Geller et al. 1987, Geller & Huchra 1989) reveal a general picture in which the galaxies are organized in shells and filaments enclosing large empty regions, the voids, which occupy more than 80 per cent of the whole space. An early review on voids is given by Rood (1988), while comprehensive lists of voids have been published by Kauffmann & Fairall (1991), Haque-Copilah &Basu (1992), andLindner et al. (1995).Some uncertainties exist on the exact definition of a void: whether a void should be defined as a volume which is completely empty of galaxies, or if it is merely a very low-dense region in the sample of galaxies under investigation. In the second case the existence and the properties, e.g. the diameter, of a void may depend on the richness and the completeness of the used sample of galaxies. Indeed, in a recent paper Lindner et al. (1995) have shown that the dimensions of voids are not only determined by these two factors but also depend on the luminosity of the investigated galaxies: bright galaxies show the more large-scale void structure, faint galaxies reveal detailed substructures. Thus, there seems to be a hierarchical structure of voids. Moreover, the size of a void presumably depends on the mean density of galaxies of the environment in the sense that the smaller voids are located in denser regions, on the average. Furthermore, the faint galaxies are found mainly in the outskirts of the shells defined by luminous systems.From a theoretical point of view some models like the galaxy formation scenario in biased cold dark-matter dominated cosmologies (Dekel & Silk 1986, Hoffman et al. 1992) predict a smoother distribution of dwarf galaxies in comparison to bright systems. In this context the distribution of absolute faint galaxies, especially irregular and low-surface brightness objects, have been investigated by several authors (Bothun et al. 1986, Eder et al. 1989, Salzer et al. 1990, Binggeli et al. 1990, Schombert et al. 1992) who all find similar distributions of these galaxies and of the bright systems. But all these surveys are restricted to objects not fainter than about m g = 17 in apparent magnitude.Several previous stud...

Merger Effects on the Spin and Shape Alignments of Galaxy Stellar, Cold Gas, Hot Gas, and Dark Matter Components

“…where k = |k| and R f is the filtering radius; (iv) performing the inverse Fourier transformation of T ij (k) to obtain T ij (x). As in Lee et al (2022), we set the filtering radius at R f = 1.5 Mpc; the median size of cluster environments in which the majority of the galaxies are embedded (e.g., Schmidt et al 1997;Tempel et al 2014). At the grid that matches the position of each galaxy, we carry out the similarity transformation of T ij (x) to find its major, intermediate, and minor principal axes (e 1 , e 2 , and e 3 , respectively), corresponding to the largest, second largest, and smallest eigenvalues (λ 1 , λ 2 , and λ 3 , respectively).…”

Merger Effects on the Spin and Shape Alignments of Galaxy Stellar, Cold and Hot Gas, and Dark Matter Components

“…(iv) Performing the inverse Fourier transformation of T ij (k) to obtain T ij (x). As in Lee et al (2022), we set the filtering radius at R f = 1.5 Mpc, the median size of cluster environments in which the majority of the galaxies are embedded (e.g., Schmidt et al 1997;Tempel et al 2014) . At the grid that matches the position of each galaxy, we carry out the similarity transformation of T ij (x) to find its major, intermediate and minor principal axes (e 1 , e 2 and e 3 , respectively), corresponding to the largest, second largest and smallest eigenvalues (λ 1 , λ 2 and λ 3 , respectively).…”

Multi-wavelength structure analysis of local cluster galaxies

“…Having observed and statistically analysed a large fraction of the galaxies in the local Universe it is widely accepted that only few galaxies are found isolated in the field, while the majority of them are preferentially located in denser environments such as groups or clusters (Schmidt et al 1997;Robotham et al 2011). Clusters of galaxies are described as dense peaks in the galaxy distribution across the sky, which were slowly created when the first massive dark matter halos were decoupled from the nearly homogeneous expanding Universe, and they contain hundreds up to thousands member galaxies.…”