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# FLows Around Galaxies (FLAG) I -- The dependency of galaxy connectivity on cosmic environments and effects on the star-formation rate

Daniela Galárraga-Espinosa, Enrico Garaldi, Guinevere Kauffmann

Submitted on 12 September 2022

## Abstract

With the aim of bringing substantial insight to the fundamental question of how galaxies acquire their material for star-formation, we present in this work the first comprehensive characterisation of the galaxy connectivity (i.e. the number of filamentary streams connected to a galaxy) in relation with the cosmic environment, and a statistical exploration of the impact of connectivity on the star-formation rate at z=2. We detect kpc-scale filaments directly connected to galaxies by applying the DisPerSE filament finder to the dark matter (DM) density around 2977 massive central galaxies (${M}_{\ast }>{10}^{8}$ ${\mathrm{M}}_{\odot }/h$) of the TNG50-1 simulation. Our results demonstrate that more than half of the galaxies are connected to two or three streams. About $15\mathrm{%}$ of them are connected to zero streams, i.e. these galaxies are completely disconnected from the local web. We examine a variety of factors that could influence the connectivity finding out that this parameter increases with mass, decreases with local density for low mass galaxies, and does not depend on local environment, estimated by the Delaunay tessellation, for high mass galaxies. In order to better understand the relation between the small-scale streams and the large-scale environment, galaxies are further classified according to their location in different cosmic web environments. On average, we find that galaxies are connected to two streams in filaments, three in cluster cores, but are not connected to streams in cluster outskirts. Finally, we show that, at fixed local density and cosmic web environment, the specific star-formation (sSFR) of low mass galaxies is up to $7\phantom{\rule{0.167em}{0ex}}\sigma$ enhanced due to connectivity. A milder impact is found for high mass galaxies, hinting at different relative efficiencies of matter inflow via filamentary streams in galaxies of different masses.

## Preprint

Comment: submitted to A&A, abridged abstract, comments welcome

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics