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We study the evolution of satellite galaxies in clusters of the c-eagle simulations, a suite of 30 high-resolution cosmological hydrodynamical zoom-in simulations based on the eagle code. We find that the majority of galaxies that are quenched at z  = 0 (≳80 |${{\ \rm per\ cent}}$|⁠) reached this state in a dense environment (log10M200[M⊙] ≥13.5). At low redshift, regardless of the final cluster mass, galaxies appear to reach their quenching state in low-mass clusters. Moreover, galaxies quenched inside the cluster that they reside in at z  = 0 are the dominant population in low-mass clusters, while galaxies quenched in a different halo dominate in the most massive clusters. When looking at clusters at z > 0.5, their in situ quenched population dominates at all cluster masses. This suggests that galaxies are quenched inside the first cluster they fall into. After galaxies cross the cluster's r 200 they rapidly become quenched (≲1 Gyr). Just a small fraction of galaxies (⁠|$\lesssim 15{{\ \rm per\ cent}}$|⁠) is capable of retaining their gas for a longer period of time, but after 4 Gyr, almost all galaxies are quenched. This phenomenon is related to ram pressure stripping and is produced when the density of the intracluster medium reaches a threshold of |$\rho _{\rm ICM}\, \sim 3 \times 10 ^{-5}$| nH (cm−3). These results suggest that galaxies start a rapid-quenching phase shortly after their first infall inside r 200 and that, by the time they reach r 500, most of them are already quenched. [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 a model to track the orbital evolution of 'unresolved subhaloes' (USHs) in cosmological simulations. USHs are subhaloes that are no longer distinguished by halo finders as self-bound overdensities within their larger host system due to limited mass resolution. These subhaloes would host 'orphan galaxies' in semi-analytic models of galaxy formation and evolution (SAMs). Predicting the evolution of the phase-space components of USHs is crucial for the adequate modelling of environmental processes, interactions, and mergers implemented in SAMs that affect the baryonic properties of orphan satellites. Our model takes into account dynamical friction drag, mass-loss by tidal stripping and merger with the host halo, involving three free parameters. To calibrate this model, we consider two DM-only simulations of different mass resolution (MultiDark simulations). The simulation with higher mass resolution (smdpl ; |$m_{\rm DM} = 9.6 \times 10^7\, h^{-1}\, \mathrm{M_{\odot }}$|⁠) provides information about subhaloes that are not resolved in the lower mass resolution one (mdpl2 ; |$m_{\rm DM} = 1.5 \times 10^9\, h^{-1}\, \mathrm{M_{\odot }}$|⁠); the orbit of those USHs is tracked by our model. We use as constraining functions the subhalo mass function (SHMF) and the two-point correlation function (2PCF) obtained from smdpl , being the latter a novel aspect of our approach. While the SHMF fails to put tight constraints on the efficiency of dynamical friction and the merger condition, the addition of clustering information helps us to specify the parameters of the model related to the spatial distribution of subhaloes. Our model allows to achieve good convergence between the results of simulations of different mass resolution, with a precision better than 10 per cent for both SHMF and 2PCF. [ABSTRACT FROM AUTHOR]

We present a new analytic fitting profile to model the ram pressure (RP) exerted over satellite galaxies on different environments and epochs. The profile is built using the information of the gas particle distribution in hydrodynamical simulations of groups and clusters of galaxies to measure the RP directly. We show that predictions obtained by a previously introduced β -profile model cannot consistently reproduce the dependence of the RP on halocentric distance and redshift for a given halo mass. It features a systematic underestimation of the predicted RP at high redshifts (z > 1.5), which increases towards the central regions of the haloes and it is independent of halo mass, reaching differences larger than two decades for satellites at r < 0.4 R vir. This behaviour reverses as redshift decreases, featuring an increasing overestimation with halocentric distance at z  = 0. As an alternative, we introduce a new universal analytic model for the profiles that can recover the RP dependence on halo mass, halocentric distance, and redshift. We analyse the impact of our new profile on galaxy properties by applying a semi-analytic model of galaxy formation and evolution on top of the simulations. We show that galaxies experiencing large amounts of cumulative RP stripping typically have low stellar masses (M ⋆ ≤ 109.5 M⊙). Besides, their specific star formation histories depend on the RP modelling applied, particularly at high redshifts (z > 1.5). [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]

We use the semi-analytic model of galaxy formation sag  to study the relevance of mass and environmental quenching on satellite galaxies. We find that environmental processes dominate the star formation (SF) quenching of low-mass satellites (⁠|$M_{\star } \lesssim 10^{10.5}\, {\rm M}_{\odot }$|⁠), whereas high-mass galaxies typically quench as centrals. High-mass galaxies that remain actively forming stars while being accreted are found to be mainly affected by mass quenching after their first infall. For a given stellar mass, our model predicts SF quenching to be less efficient in low-mass haloes both before and after infall, in contradiction with common interpretations of observational data. Our model supports a two-stage scenario to explain the SF quenching. Initially, the SF of satellites resembles that of centrals until the gas cooling rate is reduced to approximately half its value at infall. Then, the SF fades through secular processes that exhaust the cold gas reservoir. This reservoir is not replenished efficiently due to the action of either ram-pressure stripping of the hot gas in low-mass satellites, or feedback from the active galactic nucleus in high-mass satellites. The delay times for the onset of SF quenching are found to range from |${\approx } 3$| to |${\approx } 1\, {\rm Gyr}$| for low-mass (⁠|$M_{\star } \approx 10^{10}\, {\rm M}_{\odot }$|⁠) and high-mass (⁠|$M_{\star } \approx 10^{11}\, {\rm M}_{\odot }$|⁠) satellites, respectively. SF fades in |${\approx } 1\, {\rm Gyr}$|⁠, largely independent of stellar mass. We find that the SF quenching of low-mass satellites supports the so-called delay-then-rapid quenching scenario. However, the SF history of |$z$|  = 0 passive satellites of any stellar mass is better described by a delay-then-fade quenching scenario. [ABSTRACT FROM AUTHOR]

We present the public release of the MultiDark-Galaxies: three distinct galaxy catalogues derived from one of the Planck cosmology MultiDark simulations (i.e. MDPL2, with a volume of (1 h−1 Gpc)3 and mass resolution of 1.5 × 109 h−1 M⊙) by applying the semi-analytic models galacticus, sag, and sage to it. We compare the three models and their conformity with observational data for a selection of fundamental properties of galaxies like stellar mass function, star formation rate, cold gas fractions, and metallicities – noting that they sometimes perform differently reflecting model designs and calibrations. We have further selected galaxy subsamples of the catalogues by number densities in stellar mass, cold gas mass, and star formation rate in order to study the clustering statistics of galaxies. We show that despite different treatment of orphan galaxies, i.e. galaxies that lost their dark-matter host halo due to the finite-mass resolution of the N-body simulation or tidal stripping, the clustering signal is comparable, and reproduces the observations in all three models – in particular when selecting samples based upon stellar mass. Our catalogues provide a powerful tool to study galaxy formation within a volume comparable to those probed by ongoing and future photometric and redshift surveys. All model data consisting of a range of galaxy properties – including broad-band SDSS magnitudes – are publicly available. [ABSTRACT FROM AUTHOR]