Abstract
Context. The properties of galaxies are known to be affected by their environment, but although galaxies in clusters and groups have been quite thoroughly investigated, little is known about galaxies belonging to filaments of the cosmic web, or about the properties of the filaments themselves. Aims. Here we investigate the properties of the rich cluster MACS J0717.5+3745 and its extended filament by analyzing the distribution and fractions of intra-cluster light (ICL) in its core and by trying to detect intra-filament light (IFL) in the filament. We analyze the galaxy luminosity function (GLF) of the cluster core and of the filament. We also study the orientations of galaxies in the filament to better constrain the filament properties. Methods. This work is based on Hubble Space Telescope (HST) archive data, both from the Hubble Frontier Fields in the F435W, F606W, F814W, and F105W bands, and from a mosaic of images in the F606W and F814W bands. The spatial distribution of the ICL was determined with our new wavelet-based software, DAWIS. The GLFs were extracted in the F606W and F814W bands, with a statistical subtraction of the background, and fit with Schechter functions. The galaxy orientations in the filaments were estimated with SExtractor after correction for the point spread function. Results. We detect a large amount of ICL in the cluster core, but no IFL in the cosmic filament. The fraction of ICL in the core peaks in the F606W filter before decreasing with wavelength. Though relatively noisy, the GLFs in the filament are notably different from those of field galaxies, with a flatter faint end slope and an excess of bright galaxies. We do not detect a significant alignment of the galaxies in the filament region analyzed.
Highlights
Already by the early 1980s, Zeldovich et al (1982) had predicted through theoretical models of structure formation that small fluctuations from the early universe would lead to a distribution of matter condensed along filaments, sheets, and voids
We retrieve galaxy spectroscopic redshifts from the NASA Extragalactic Database5 (NED) and select only galaxies in the field of view (FoV) of the Hubble Frontier Fields Survey (HFF) and with 0.53 < zspec < 0.56, assuming galaxies in this range of redshift are associated with MACS J0717
We looked for tidal streams in the cosmic filament of MACS J0717, as simulations have shown that significant portions of intra-cluster light (ICL) could be formed in such structures
Summary
Already by the early 1980s, Zeldovich et al (1982) had predicted through theoretical models of structure formation that small fluctuations from the early universe would lead to a distribution of matter condensed along filaments, sheets, and voids. While the inner part is by far the most luminous one, the wings are important These wings can be a source of contamination for low-surface-brightness features (Sandin 2014, 2015), bringing light from the inner parts of galaxies to their outer halo and modifying their color properties and luminosity profile at large radii (Capaccioli & de Vaucouleurs 1983; de Jong 2008; Trujillo & Fliri 2016). This effect impacts the ICL, since light from galaxies can be artificially brought to the intergalactic medium, simulating flux emitted by diffuse low-surfacebrightness sources and polluting real ICL
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