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We study the population of backsplash galaxies at z  = 0 in the outskirts of massive, isolated clusters of galaxies taken from the mdpl 2- sag semi-analytical catalogue. We consider four types of backsplash galaxies according to whether they are forming stars or passive at three stages in their lifetimes: before entering the cluster, during their first incursion through the cluster, and after they exit the cluster. We analyse several geometric, dynamic, and astrophysical aspects of the four types at the three stages. Galaxies that form stars at all stages account for the majority of the backsplash population (58 per cent) and have stellar masses typically below |$M_\star \sim 3\times 10^{10} \ h^{-1}\, {\rm {M_\odot }}$| that avoid the innermost cluster's regions and are only mildly affected by it. In a similar mass range, galaxies that become passive after exiting the cluster (26 per cent) follow orbits characterized by small pericentric distance and a strong deflection by the cluster potential well while suffering a strong loss of both dark matter and gas content. Only a small fraction of our sample (4 per cent) becomes passive while orbiting inside the cluster. These galaxies have experienced heavy pre-processing and the cluster's tidal stripping and ram pressure provide the final blow to their star formation. Finally, galaxies that are passive before entering the cluster for the first time (12 per cent) are typically massive and are not affected significantly by the cluster. Using the bulge/total mass ratio as a proxy for morphology, we find that a single incursion through a cluster does not result in significant morphological changes in all four types. [ABSTRACT FROM AUTHOR]

We use the roger code by de los Rios et al. to classify galaxies around a sample of X-ray clusters into five classes according to their positions in the projected phase space diagram: cluster galaxies, backsplash galaxies, recent infallers, infalling galaxies, and interlopers. To understand the effects of the cluster environment to the evolution of galaxies, we compare across the five classes: stellar mass, specific star formation rate, size, and morphology. Following the guidelines of Coenda et al. a separate analysis is carried out for red and blue galaxies. For red galaxies, cluster galaxies differ from the other classes, having a suppressed specific star formation rate, smaller sizes, and are more likely to be classified as ellipticals. Differences are smaller between the other classes, however backsplash galaxies have significantly lower specific star formation rates than early or recent infalling galaxies. For blue galaxies, we find evidence that recent infallers are smaller than infalling galaxies and interlopers, while the latter two are comparable in size. Our results provide evidence that, after a single passage, the cluster environment can diminish a galaxy's star formation, modify its morphology, and can also reduce in size blue galaxies. We find evidence that quenching occurs faster than morphological transformation from spirals to ellipticals for all classes. While quenching is evidently enhanced as soon as galaxies get into clusters, significant morphological transformations require galaxies to experience the action of the physical mechanisms of the cluster for longer time-scales. [ABSTRACT FROM AUTHOR]

We connect galaxy properties with their orbital classification by analysing a sample of galaxies with stellar mass M ⋆ ≥ 108.5 h −1M⊙ residing in and around massive and isolated galaxy clusters with mass M 200 > 1015 h −1M⊙ at redshift z  = 0. The galaxy population is generated by applying the semi-analytic model of galaxy formation sag  on the cosmological simulation MultiDark Planck 2. We classify galaxies considering their real orbits (3D) and their projected phase-space position using the roger   code (2D). We define five categories: cluster galaxies, galaxies that have recently fallen into a cluster, backsplash galaxies, infalling galaxies, and interloper galaxies. For each class, we analyse the 0.1(g − r) colour, the specific star formation rate (sSFR), and the stellar age, as a function of the stellar mass. For the 3D classes, we find that cluster galaxies have the lowest sSFR, and are the reddest and the oldest, as expected from environmental effects. Backsplash galaxies have properties intermediate between the cluster and recent infaller galaxies. For each 2D class, we find an important contamination by other classes. We find it necessary to separate the galaxy populations in red and blue to perform a more realistic analysis of the 2D data. For the red population, the 2D results are in good agreement with the 3D predictions. Nevertheless, when the blue population is considered, the 2D analysis only provides reliable results for recent infallers, infalling galaxies and interloper galaxies. [ABSTRACT FROM AUTHOR]

We present the ROGER (Reconstructing Orbits of Galaxies in Extreme Regions) code, which uses three different machine learning techniques to classify galaxies in, and around, clusters, according to their projected phase-space position. We use a sample of 34 massive, M 200 > 1015 h −1 M ⊙, galaxy clusters in the MultiDark Planck 2 (MDLP2) simulation at redshift zero. We select all galaxies with stellar mass M ⋆ ≥ 108.5 h −1 M ⊙, as computed by the semi-analytic model of galaxy formation SAG, that are located in, and in the vicinity of, these clusters and classify them according to their orbits. We train ROGER to retrieve the original classification of the galaxies from their projected phase-space positions. For each galaxy, ROGER gives as output the probability of being a cluster galaxy, a galaxy that has recently fallen into a cluster, a backsplash galaxy, an infalling galaxy, or an interloper. We discuss the performance of the machine learning methods and potential uses of our code. Among the different methods explored, we find the K-Nearest Neighbours algorithm achieves the best performance. [ABSTRACT FROM AUTHOR]

Aims. We explore the effects of environment in the evolution of late-type galaxies by studying the radial profiles of light- and mass-weighted metallicities of galaxies in two discrete environments: field and groups. Methods. We used a sample of 167 late-type galaxies with stellar masses of 9 ≤ log(M⋆/M⊙) ≤ 12 drawn from the Calar Alto Legacy Integral Field Area (CALIFA) survey. Firstly, we obtained light- and mass-weighted stellar metallicity profiles and stellar mass density profiles of these galaxies using publicly available data. We then classified them according to their environment into field and group galaxies. Finally, we studied the metallicity of galaxies in these two environments, including a comparison of the metallicity as a function of radius, at a characteristic scale, and as a function of stellar mass surface density. As metallicity depends on galaxy mass, we took special care throughout the study to compare, in all cases, subsamples of galaxies in groups and in the field that have similar masses. Results. We find significant differences between group and field late-type galaxies in terms of their metallicity: group galaxies are systematically higher in metallicity than their field counterparts. We find that field galaxies, in general, have metallicity profiles that show a negative gradient in their inner regions and a shallower profile at larger radii. This is in contrast to the metallicity profiles of galaxies in groups, which tend to be flat in the inner regions and to have a negative gradient in the outer parts. Regarding the metallicity at the characteristic radius of the luminosity profiles, we consistently find that it is higher for group galaxies irrespective of galaxy mass. At fixed local stellar surface mass density, group galaxies are again higher in metallicity, also the dependence of metallicity on surface density is less important for group galaxies. Conclusions. The evidence of a clear difference in metallicity between group and field galaxies as a function of mass, spatial scale, and local stellar mass density is indicative of the different evolutionary paths followed by galaxies in groups and in the field. We discuss some possible implications of the observed differences. [ABSTRACT FROM AUTHOR]

We study the effects of the environment on galaxy quenching in the outskirts of clusters at 0.04 < z < 0.08. We use a subsample of 14 WINGS and OmegaWINGS clusters that are linked to other groups/clusters by filaments and study separately galaxies located in two regions in the outskirts of these clusters according to whether they are located towards the filaments' directions or not. We also use samples of galaxies in clusters and field as a comparison. Filamentary structures linking galaxy groups/clusters were identified over the Six Degree Field Galaxy Redshift Survey Data Release 3. We find a fraction of passive galaxies in the outskirts of clusters intermediate between that of the clusters and the field's. We find evidence of a more effective quenching in the direction of the filaments. We also analyse the abundance of post-starburst (PS) galaxies in the outskirts of clusters focusing our study on two extreme sets of galaxies according to their phase-space position: backsplash and true infallers. We find that up to |$\sim 70{{\ \rm per\ cent}}$| of PS galaxies in the direction of filaments are likely backsplash, while this number drops to |$\sim 40{{\ \rm per\ cent}}$| in the isotropic infall region. The presence of this small fraction of galaxies in filaments that are falling into clusters for the first time and have been recently quenched, supports a scenario in which a significant number of filament galaxies have been quenched long time ago. [ABSTRACT FROM AUTHOR]

We study the quenching of galaxies in different environments and its evolution in the redshift range 0.43 ≤ |$z$| ≤ 0.89. For this purpose, we identify galaxies inhabiting filaments, the isotropic infall region of groups, the field, and groups in the VIMOS Public Extragalactic Redshift Survey (VIPERS). We classify galaxies as quenched (passive), through their NUV − r versus r − K colours. We study the fraction of quenched galaxies (Fr) as a function of stellar mass and environment at two redshift intervals. Our results confirm that stellar mass is the dominant factor determining galaxy quenching over the full redshift range explored. We find compelling evidence of evolution in the quenching of intermediate mass galaxies (9.3 ≤ log (M ⋆/ M ⊙) ≤ 10.5) for all environments. For this mass range, Fr is largest for galaxies in groups and smallest for galaxies in the field, while galaxies in filaments and in the isotropic infall regions appear to have intermediate values with the exception of the high redshift bin, where the latter show similar fraction of quenched galaxies as in the field. Galaxies in filaments are systematically more quenched than their counterparts infalling from other directions, in agreement to similar results found at low redshift. The least massive galaxies in our samples do not show evidence of internal or environmental quenching. [ABSTRACT FROM AUTHOR]

Aims. We explore the effects of environment on star formation in late-type galaxies by studying the dependence of the radial profiles of specific star formation rate (sSFR) on environment and the stellar mass, using a sample of 275 late-type galaxies drawn from the CALIFA survey. Methods. We consider three different discrete environments: field galaxies, galaxies in pairs, and galaxies in groups, with stellar masses 9 ≤ log(M⋆/M⊙) ≤ 12, and compare their sSFR profiles across the environments. Results. Our results suggest that the stellar mass is the main factor determining the sSFR profiles of late-type galaxies; the influence of AGNs and bars are secondary. We find that the relative size of the bulge plays a key role in depressing star formation towards the center of late-type galaxies. The group environment determines clear differences in the sSFR profiles of galaxies. We find evidence of an outside-in action upon galaxies with stellar masses 9 ≤ log(M⋆/M⊙) ≤ 10 in groups. We find a much stronger suppression of star formation in the inner regions of massive galaxies in groups, which may be an indication of a different merger history. [ABSTRACT FROM AUTHOR]

We perform a comparative analysis of the properties of galaxies infalling into groups classifying them accordingly to whether they are: falling along filamentary structures; or they are falling isotropically. For this purpose, we identify filamentary structures connecting massive groups of galaxies in the SDSS. We perform a comparative analysis of some properties of galaxies in filaments, in the isotropic infall region, in the field, and in groups. We study the luminosity functions (LF) and the dependence of the specific star formation rate (SSFR) on stellar mass, galaxy type, and projected distance to the groups that define the filaments. We find that the LF of galaxies in filaments and in the isotropic infalling region are basically indistinguishable between them, with the possible exception of late-type galaxies. On the other hand, regardless of galaxy type, their LFs are clearly different from that of field or group galaxies. Both of them have characteristic absolute magnitudes and faint end slopes in between the field and group values. More significant differences between galaxies in filaments and in the isotropic infall region are observed when we analyse the SSFR. We find that galaxies in filaments have a systematically higher fraction of galaxies with low SSFR as a function of both, stellar mass and distance to the groups, indicating a stronger quenching of the star formation in the filaments compared to both, the isotropic infalling region, and the field. Our results suggest that some physical mechanisms that determine the differences observed between field galaxies and galaxies in systems, affect galaxies even when they are not yet within the systems. [ABSTRACT FROM AUTHOR]

Aims. The properties of the brightest galaxies (BCGs) are studied in both compact and loose groups of galaxies in order to better understand the physical mechanisms influencing galaxy evolution in different environments. Methods. Samples of BCGs are selected in compact and loose groups of galaxies previously identified in the Sloan Digital Sky Survey. The following physical properties of the BCGs in compact groups and in sub-samples of loose groups are compared, defined by their mass and total luminosity: absolute magnitude, colour, size, surface brightness, stellar mass, concentration and morphological information from the Galaxy Zoo. The fraction of BCGs classified as red and/or early-type as a function of galaxy luminosity is studied. The fraction of the group's total luminosity contained in the BCG and the difference in luminosity between the BCG and the second-ranked galaxy, are also analysed. Results. Some properties of BCGs in compact and loose groups are comparable. However, BCGs in compact groups are systematically more concentrated and have larger surface brightness than their counterparts in both, high- and low-mass loose groups. The fractions of red and early-type BCGs in compact groups are consistent with those of high-mass loose groups. Comparing BCGs in sub-samples of compact and loose groups selected for their similar luminosities, BCGs in compact groups are found to be, on average, brighter, more massive, larger, redder and more frequently classified as elliptical. In compact groups, the BCG contains a larger fraction of the system's total luminosity and differs more in absolute magnitude from the second-ranked galaxy. Using a simple model, which dry-merges the BCG in loose groups with a random choice among the 2nd, 3rd and 4th-ranked galaxies in the group, and allowing for some star loss in the process, we show that the absolute magnitude distributions of BCGs in compact and loose groups of similar luminosities can be made more alike. Conclusions. BCGs in compact and loose groups are found to be different. Some mechanisms responsible for transforming late-type galaxies into early types, such as mergers, may be more effective within compact groups due to their high densities and small velocity dispersion, which would lead their BCGs along somewhat different evolutionary paths. [ABSTRACT FROM AUTHOR]

The dependence of the sequence of red galaxies (RS) with the environment is investigated using volume-limited samples of field, group and cluster galaxies drawn from the Sloan Digital Sky Survey. Our work focuses on studying the mean colour and the scatter of the RS as a function of -band absolute magnitude in different environments characterized either by the mass of the system in which the galaxies are located or by the distance to the system's centre. These results are compared with the RS of field galaxies. The same analysis is carried out using subsamples of red galaxies classified as early types according to their concentration parameter. For a given luminosity, of field galaxies is bluer and is larger than their group and cluster counterparts irrespective of mass and position within the systems. Among systems of galaxies, high-mass groups and clusters have the reddest and the smallest . These differences almost disappear when red early-type galaxies alone are considered. Galaxies in the core and in the outskirts of groups have similar , whereas galaxies in clusters show a strong dependence on cluster-centric distance, the inner galaxies being the reddest objects. Red early-type galaxies in the outskirts of clusters have values as large as those of field galaxies, while galaxies in the inner regions of clusters have lower values, comparable to those of group galaxies. We find that bright red early-type galaxies have reached nearly the same evolutionary stage in all environments. Our results suggest that, although effective in drifting galaxies of intermediate luminosities towards redder colours, the cluster environment is not necessary to populate the RS. We propose a scenario in which the RS in massive systems is populated by two different star formation history galaxies: red early-type galaxies that formed the bulk of their stars during the early stages of massive halo assembly and red galaxies that passed most of their lives inhabiting poor groups or the field and fell into massive systems at lower redshifts. [ABSTRACT FROM AUTHOR]

We analyse how the properties of galaxies in groups identified in the Sloan Digital Sky Survey depend on the environment. In particular, we study the relationship between galaxy properties and group mass and group-centric distance. Among the galaxy properties we have considered here, we find that the colour is the most predictive parameter for group mass, while the most predictive pair of properties are colour and r-band absolute magnitude. Regarding the position inside the systems, the colour is the best tracer of group-centric distance and the most predictive pair of properties are colour and spectral type taken together. These results remain unchanged when a subsample of high-mass groups is analysed. The same happens if the brightest group galaxies are excluded. [ABSTRACT FROM AUTHOR]

We study the galaxy environment of active galaxies, radio-loud and radio-quiet quasars in the redshift range 0.1 &les; z. &les; 0.25. We use galaxies from the APM survey in order to explore the local galaxy overdensity and the D[SUBj] - R colour distribution of neighbouring galaxies of these target samples. For comparison, we perform similar analysis on samples of Abell clusters with X-ray emission, and samples of Abell clusters with richness R = 1 and 0. The projected cross-correlations show that the samples of quasars and active galaxies reside in regions of galaxy density enhancements lower than those typical of R = 0 clusters. We also find that in the nearby Universe the local galaxy overdensities of radio-loud and radio-quiet quasars are comparable. The analysis of the distribution of b[SUBj] - R galaxy colour indices suggests that the environment of quasars is not strongly dominated by a population of red galaxies, characteristic of rich Abell clusters, an effect that is more clearly appreciated for our sample of radio-loud quasars. [ABSTRACT FROM AUTHOR]