The Coma supercluster (100h −1 Mpc) offers an unprecedented contiguous range of environments in the nearby Universe. In this paper we present a catalogue of spectroscopically confirmed galaxies in the Coma supercluster detected in the ultraviolet (UV) wavebands. We use the arsenal of UV and optical data for galaxies in the Coma supercluster covering ∼ 500 square degrees on the sky to study their photometric and spectroscopic properties as a function of environment at various scales. We identify the different components of the cosmic-web: large-scale filaments and voids using Discrete Persistent Structures Extractor, and groups and clusters using Hierarchical Density-based spatial clustering of applications with noise, respectively. We find that in the Coma supercluster the median emission in Hα inclines, while the g − r and FUV − NUV colours of galaxies become bluer moving further away from the spine of the filaments out to a radius of ∼ 1 Mpc. On the other hand, an opposite trend is observed as the distance between the galaxy and centre of the nearest cluster or group decreases. Our analysis supports the hypothesis that properties of galaxies are not just defined by its stellar mass and large-scale density, but also by the environmental processes resulting due to the intrafilament medium whose role in accelerating galaxy transformations needs to be investigated thoroughly using multi-wavelength data.

We use an analytical approach to study ram pressure stripping with simple models for discs and halo gas distribution to study the phenomena in cluster, group and galaxy halos. We also study variations with galaxy properties and redshift. In each case we model the worst case scenario (i.e., maximum effect due to ram pressure). We show that there is little variation in the worst case scenario with redshift. We find that gas discs in galaxies with a higher spin parameter get stripped sooner than galaxies with a smaller spin parameter. Galaxies in cluster halos get stripped of gas more efficiently as compared to group and galaxy halos: this is due to the higher infall speed and a higher density of gas in the ICM due to a greater retention of baryons. We comment on the limitations of our model and situations where a significant amount of gas may be retained in galaxy disc and also give an illustration for the same. Lastly, we discuss implications for star formation in galaxies as these fall into halos.

We use data from the Evolution and Assembly of GaLaxies in their Environment (eagle) cosmological simulation to study properties of galaxies in the cosmic web. Galaxies become more redder and form stars at a lower rate relative to their counterparts further away from the cylindrical axis of the large-scale filaments. These trends are particularly strong for galaxies with M*/M⊙ ≲ 1010. We also find that at distances <0.5 Mpc from the spine of the filaments, the median gas and stellar mass fraction in filament galaxies rises sharply with decreasing distance from the spine of the filament. These results, together with matching trends in the SFR/M* and the g − r colour of filament galaxies suggest that (i) the intrafilamentary gas condenses into the filament galaxies thus fuelling star formation in them, and (ii) increased number density of galaxies closer to the central axis of the filament enhances the rate of gravitational interactions among filament galaxies closer to the spine.

We use the Horizon Run 5 cosmological simulation to study the effect of galaxy intrinsic properties and the local environment on active galactic nuclei (AGNs) characterized by their threshold of the accretion rate. We select galaxies in the stellar mass range 10 9.5 ≤ M * / M ⊙ ≤ 10 10.5 in the snapshot at redshift z = 0.625. Among various intrinsic properties, we find that the star formation rate of the host galaxy is most correlated to the AGN activity. To quantify the environment, we use background galaxy number density (large-scale environment) and distance and morphological type of the nearest neighbors (small-scale environment), and study their relative effects on the AGN properties. We find that, compared to the background density, the nearest neighbor environment is the dominant quantity determining the bolometric luminosity, star formation rate, and kinematic properties of AGNs and better dictates the gas mass of the host galaxy. We show that the cold gas content in the host galaxies is crucial in triggering AGN activity. However, when the nearest neighbor environment effects start to act at the neighbor distance of less than about half the virial radius of the neighbor, the neighbor environmental effects are the most dominant factor for quasar activity.

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