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Phase-space diagram for satellites in the hostcentric frame at the instant of first pericentre. Leaver satellites classified as pre-pericentre are indicated with blue triangles, early leavers that leave 0.5 Gyr or more prior to first pericentric passage are indicated with dark blue squares, and those classified as remainers post-pericentre are indicated with red diamonds. The grey region highlights the binding region. Note that only the satellites in hosts having a pericentric passage by z = 0 in the cluster are included here.
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The disruption of substructure in galaxy clusters likely plays an important role in shaping the cluster population given that a significant fraction of cluster galaxies today have spent time in a previous host system, and thus may have been pre-processed. Once inside the cluster, group galaxies face the combined environmental effects from group and...
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... addition, we also checked where the satellites are located in their hosts when they are at the first pericentric passage in the cluster. Fig. 6 shows the phase-space diagram in their hostcentric frame at this time. The colour scheme follows that established in Fig. 3, with pre-pericentre leavers shown in blue (triangle symbols) and early leavers shown in dark blue (square symbols). For completeness we also include the remainer (post-pericentre) satellites that, despite passing ...
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... their hosts as shown in Fig. 7. It can be seen that they leave with a wide range of velocities, from ∼10 km s −1 up to an extreme ∼580 km s −1 . However, even with a more modest central value of 150 km s −1 , it can easily be shown that satellites will move a considerable distance with respect to their host over a short time period, as seen in Fig. 6. Therefore, this implies that it will quickly become difficult to identify them within the cluster population at later times. We analyse the causes and implications that this result has for the satellites and their hosts further in Section ...
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... before pericentre, while the bars to the right correspond to satellites leaving during or after this moment. Phase-space for satellites in the hostcentric frame at the cluster infall time (time when we measure our binding criterion). The colours and symbols highlight the different subsamples of satellites following the same colour scheme as in Fig. 6 with the addition of several other subsamples; leaver post-pericentre (green dots), remainer pre-pericentre (orange pentagon symbols), and grey crosses correspond to satellites that are destroyed in the cluster. Figure 9. Distribution of the clustercentric distances of leaver satellites normalized by the cluster R 200 radius at the ...
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... It is apparent from these plots that the chances of a SFG surviving during its infall into a cluster is a balance of two factors: at high local densities, pre-processing by this local environment quenches most SFGs; at low local densities, the influence of the cluster starts to win out at larger radii, also quenching SFGs; so it is at intermediate local densities that the fraction of SFGs stays high to the smallest radii. However, in all cases eventually the cluster wins, quenching almost all SFGs at small radii, irrespective of their local environment (Choque-Challapa et al. 2019;Haggar et al. 2023). ...
In order to examine where, how and why the quenching of star formation begins in the outskirts of galaxy clusters, we investigate the de-projected radial distribution of a large sample of quenched and star-forming galaxies (SFGs) out to $30R_{500}$ around clusters. We identify the SFG sample using radio continuum emission from the Low-Frequency Array Two-metre Sky Survey. We find that the SFG fraction starts to decrease from the field fraction as far out as $10R_{500}$, well outside the virial radius of the clusters. We investigate how the SFG fraction depends on both large-scale and local environments, using radial distance from a cluster to characterise the former, and distance from 5th nearest neighbour for the latter. The fraction of SFGs in high-density local environments is consistently lower than that found in low-density local environments, indicating that galaxies' immediate surroundings have a significant impact on star formation. However, for high-mass galaxies -- and low mass galaxies to a lesser extent -- high-density local environments appear to act as a protective barrier for those SFGs that survived this pre-processing, shielding them from the external quenching mechanisms of the cluster outskirts. For those galaxies that are not in a dense local environment, the global environment causes the fraction of SFGs to decrease toward the cluster centre in a manner that is independent of galaxy mass. Thus, the fraction of SFGs depends on quite a complex interplay between the galaxies' mass, their local environment, and their more global cluster-centric distance.
... On the other hand, if we look at clusters in the optical, we can often find substructures traced by the cluster galaxies themselves, which can share common positions and velocities. Optical substructures are indeed recently accreted haloes that can lose 25-45 per cent of their mass per pericentric passage (Taylor & Babul 2004 ), getting mostly disrupted within 1-3 Gyr after infall (Choque-Challapa et al. 2019 ;Benavides, Sales & Abadi 2020 ). ...
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... It is important to bear in mind that galaxies arriving in clusters within groups will also face what is called post-processing , a combination of the environmental effects from the parent group and the cluster. Ho we ver, it is dif ficult to disentangle this effect, which has not been deeply investigated (an exception is found in Choque-Challapa et al. 2019 ). ...
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We present clear and direct evidence of the pre-processing effect of group galaxies falling into clusters in the local Universe (z ≲ 0.1). We start with a sample of 238 clusters, from which we select 153 with N200 ≥ 20. We considered 1641 groups within the turnaround radius (∼ 5×R200) of these 153 clusters. There are 6654 individual cluster galaxies and 4133 group galaxies within this radius. We considered two control samples of galaxies, in isolated groups and in the field. The first comprises 2601 galaxies within 1606 isolated groups, and the latter has 4273 field objects. The fraction of star forming galaxies in infalling groups has a distinct clustercentric behavior in comparison to the remaining cluster galaxies. Even at 5 ×R200 the group galaxies already show a reduced fraction of star forming objects. At this radius, the results for the individual cluster galaxies is actually compatible to the field. That is strong evidence that the group environment is effective to quench the star formation prior to the cluster arrival. The group star forming fraction remains roughly constant inwards, decreasing significantly only within the cluster R200 radius. We have also found that the pre-processing effect depends on the group mass (indicated by the number of members). The effect is larger for more massive groups. However, it is significant even for pairs an triplets. Finally, we find evidence that the time scale required for morphological transformation is larger than the one for quenching.
... This condition is the same previously used by Han et al. (2018) and Choque-Challapa et al. (2019) to find galaxy groups. In Eq. (1), Φ( ) represents the gravitational potential due to the primary galaxy at a distance from its centre, and is the relative velocity of a secondary galaxy with respect to this primary galaxy. ...
Using the data set of The Three Hundred project, i.e. 324 hydrodynamical resimulations of cluster-sized haloes and the regions of radius 15 $h^{-1}$Mpc around them, we study galaxy pairs in high-density environments. By projecting the galaxies' 3D coordinates onto a 2D plane, we apply observational techniques to find galaxy pairs. Based on a previous theoretical study on galaxy groups in the same simulations, we are able to classify the observed pairs into "true" or "false", depending on whether they are gravitationally bound or not. We find that the fraction of true pairs (purity) crucially depends on the specific thresholds used to find the pairs, ranging from around 30 to more than 80 per cent in the most restrictive case. Nevertheless, in these very restrictive cases, we see that the completeness of the sample is low, failing to find a significant number of true pairs. Therefore, we train a machine learning algorithm to help us to identify these true pairs based on the properties of the galaxies that constitute them. With the aid of the machine learning model trained with a set of properties of all the objects, we show that purity and completeness can be boosted significantly using the default observational thresholds. Furthermore, this machine learning model also reveals the properties that are most important when distinguishing true pairs, mainly the size and mass of the galaxies, their spin parameter, gas content and shape of their stellar components.
... Additionally, the definition of a 'galaxy group' is not standardised, and different definitions can lead to different conclusions. Various studies have identified group members as galaxies that lie within the radius of a host group halo (Arthur et al. 2019;Donnari et al. 2021), that satisfy a boundness criterion (Han et al. 2018;Choque-Challapa et al. 2019), or by using a Friends-of-Friends algorithm (Benavides et al. 2020), all of which can result in different selections of group members. Furthermore, Berrier et al. (2009) found that, although 30% of cluster members (with dark matter halo masses greater than 10 11.5 h −1 M ) 2 The relative velocities of merging galaxies are usually < 500 km s −1 (Lotz et al. 2008;An et al. 2019), but dark matter haloes with masses greater than 10 14 M typically have velocity dispersions greater than 500 km s −1 (McClintock et al. 2019;Wetzell et al. 2021). ...
... Moreover, previous work has hinted that galaxy groups themselves can be heavily disrupted when entering a cluster. Choque-Challapa et al. (2019) found that, using dark matter-only simulations and a similar group definition as is used in this work, over 90% of group members become unbound after a group enters a cluster, and that these galaxies quickly form part of the cluster population of galaxies. Furthermore, González-Casado et al. (1994) showed that tidal ...
... a large fraction of their mass due to stripping from a cluster (Muldrew et al. 2011;Bahé et al. 2019). Similarly, galaxies can be tidally stripped from these groups (González-Casado et al. 1994;Choque-Challapa et al. 2019), although the extent of this stripping varies between different studies. For instance, Vijayaraghavan et al. (2015) found that the central regions of galaxy groups are largely unaffected by a cluster potential, and are only disrupted by dynamical friction after several Gyr. ...
Galaxy clusters grow by accreting galaxies as individual objects, or as members of a galaxy group. These groups can strongly impact galaxy evolution, stripping the gas from galaxies, and enhancing the rate of galaxy mergers. However, it is not clear how the dynamics and structure of groups are affected when they interact with a large cluster, or whether all group members necessarily experience the same evolutionary processes. Using data from The Three Hundred project, a suite of 324 hydrodynamical resimulations of large galaxy clusters, we study the properties of 1340 groups passing through a cluster. We find that half of group galaxies become gravitationally unbound from the group by the first pericentre, typically just 0.5–1 Gyr after cluster entry. Most groups quickly mix with the cluster satellite population; only $8{{\ \rm per\ cent}}$ of infalling group haloes later leave the cluster, although for nearly half of these, all of their galaxies have become unbound, tidally disrupted or merged into the central by this stage. The position of galaxies in group-centric phase space is also important – only galaxies near the centre of a group (r ≲ 0.7R200) remain bound once a group is inside a cluster, and slow-moving galaxies in the group centre are likely to be tidally disrupted, or merge with another galaxy. This work will help future observational studies to constrain the environmental histories of group galaxies. For instance, groups observed inside or nearby to clusters have likely approached very recently, meaning that their galaxies will not have experienced a cluster environment before.
... Additionally, the definition of a 'galaxy group' is not standardised, and different definitions can lead to different conclusions. Various studies have identified group members as galaxies that lie within the radius of a host group halo (Arthur et al. 2019;Donnari et al. 2021), that satisfy a boundness criterion (Han et al. 2018;Choque-Challapa et al. 2019), or by using a Friends-of-Friends algorithm (Benavides et al. 2020), all of which can result in different selections of group members. Furthermore, Berrier et al. (2009) found that, although 30% of cluster members (with dark matter halo masses greater than 10 11.5 h −1 M ) 2 The relative velocities of merging galaxies are usually < 500 km s −1 (Lotz et al. 2008;An et al. 2019), but dark matter haloes with masses greater than 10 14 M typically have velocity dispersions greater than 500 km s −1 (McClintock et al. 2019;Wetzell et al. 2021). ...
... Moreover, previous work has hinted that galaxy groups themselves can be heavily disrupted when entering a cluster. Choque-Challapa et al. (2019) found that, using dark matter-only simulations and a similar group definition as is used in this work, over 90% of group members become unbound after a group enters a cluster, and that these galaxies quickly form part of the cluster population of galaxies. Furthermore, González-Casado et al. (1994) showed that tidal forces from clusters can rapidly increase the internal energy of infalling groups, by up to a factor of 10 for the smallest groups. ...
... a large fraction of their mass due to stripping from a cluster (Muldrew et al. 2011;Bahé et al. 2019). Similarly, galaxies can be tidally stripped from these groups (González-Casado et al. 1994;Choque-Challapa et al. 2019), although the extent of this stripping varies between different studies. For instance, Vijayaraghavan et al. (2015) found that the central regions of galaxy groups are largely unaffected by a cluster potential, and are only disrupted by dynamical friction after several Gyr. ...
Galaxy clusters grow by accreting galaxies as individual objects, or as members of a galaxy group. These groups can strongly impact galaxy evolution, stripping the gas from galaxies, and enhancing the rate of galaxy mergers. However, it is not clear how the dynamics and structure of groups are affected when they interact with a large cluster, or whether all group members necessarily experience the same evolutionary processes. Using data from TheThreeHundred project, a suite of 324 hydrodynamical resimulations of large galaxy clusters, we study the properties of 1340 groups passing through a cluster. We find that half of group galaxies become gravitationally unbound from the group by the first pericentre, typically just 0.5-1 Gyr after cluster entry. Most groups quickly mix with the cluster satellite population; only 8% of infalling group haloes later leave the cluster, although for nearly half of these, all of their galaxies have become unbound, tidally disrupted or merged into the central by this stage. The position of galaxies in group-centric phase space is also important -- only galaxies near the centre of a group ($r\lesssim0.7R_{200}$) remain bound once a group is inside a cluster, and slow-moving galaxies in the group centre are likely to be tidally disrupted, or merge with another galaxy. This work will help future observational studies to constrain the environmental histories of group galaxies. For instance, groups observed inside or nearby to clusters have likely approached very recently, meaning that their galaxies will not have experienced a cluster environment before.
... dwarf irregulars), losing their interstellar medium when entering the cluster through ram pressure stripping (see e.g. Boselli & Gavazzi 2014 ;Choque-Challapa et al. 2019 ). It is in principle also possible that galaxy interactions, i.e. galaxy harassment (Moore et al. 1996 ) Figure 19. ...
We perform a detailed study of the stellar populations in a sample of massive Fornax dwarf galaxies using a set of newly defined line indices.Using data from the Integral field spectroscopic data, we study abundance ratios of eight dEs with stellar mass ranging from 108 to 109.5 M⊙ in the Fornax cluster. We present the definitions of a new set of high-resolution Lick-style indices to be used for stellar population studies of unresolved small stellar systems. We identify 23 absorption features and continuum regions, mainly dominated by 12 elements (Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Y, Ba and Nd) in the wavelength range 4700–5400 Å and characterise them as a function of age, metallicity and alpha element abundance ratios. We analyse eight dEs and interpret the line strengths, measured in our new high resolution system of indices, with the aid of stellar population models with high enough spectral resolution. We obtain abundance ratio proxies for a number of elements that have never been studied before for dwarf ellipticals outside the Local Group. These proxies represent relative deviations from predicted index-strengths of base stellar population models built-up following the abundance pattern of The Galaxy. The abundance proxy trend results are compared to abundance ratios from resolved stars in the Local Group, and indices from integrated light of larger early-type galaxies. We find that all our dwarfs show a pattern of abundance ratios consistent with the disk of the Milky Way, indicative of slow formation in comparison to their high mass counterparts.
... We note again that this definition of "good" is only a measure of 3D proximity, rather than physically testing if the galaxies are bound. Previous works like Haggar et al. (2021) or Choque-Challapa et al. (2019) associate galaxies with a host galaxy based on their relative velocity and the host gravitational potential. In future works following this study we aim at using a more theoretical approach to distinguish between these physical pairs and galaxies that are just passing by. ...
Close pairs of galaxies have been broadly studied in the literature as a way to understand galaxy interactions and mergers. In observations they are usually defined by setting a maximum separation in the sky and in velocity along the line of sight, and finding galaxies within these ranges. However, when observing the sky, projection effects can affect the results, by creating spurious pairs that are not close in physical distance. In this work we mimic these observational techniques to find pairs in The Three Hundred simulations of clusters of galaxies. The galaxies' 3D coordinates are projected into 2D, with Hubble flow included for their line-of-sight velocities. The pairs found are classified into "good" or "bad" depending on whether their 3D separations are within the 2D spatial limit or not. We find that the fraction of good pairs can be between 30 and 60 per cent depending on the thresholds used in observations. Studying the ratios of observable properties between the pair member galaxies, we find that the likelihood of a pair being "good" can be increased by around 40, 20 and 30 per cent if the given pair has, respectively, a mass ratio below 0.2, metallicity ratio above 0.8, or colour ratio below 0.8. Moreover, shape and stellar-to-halo mass ratios respectively below 0.4 and 0.2 can increase the likelihood by 50 to 100 per cent. These results suggest that these properties can be used to increase the chance of finding good pairs in observations of galaxy clusters and their environment.
... dwarf irregulars), losing their interstellar medium when entering the cluster through ram pressure stripping (see e.g. Boselli & Gavazzi 2014;Choque-Challapa et al. 2019). It is in principle also possible that galaxy interactions, i.e., galaxy harassment (Moore et al. 1996) causes this transformation, but in such a case it would be expected considerable changes in the properties of dEs as a function of position in the cluster, which have not been seen up to now (e.g. ...
We perform a detailed study of the stellar populations in a sample of massive Fornax dwarf galaxies using a set of newly defined line indices. Using data from the Integral field spectroscopic data, we study abundance ratios of eight dEs with stellar mass ranging from 10$^8$ to 10$^{9.5}$ M$_\odot$ in the Fornax cluster. We present the definitions of a new set of high-resolution Lick-style indices to be used for stellar population studies of unresolved small stellar systems. We identify 23 absorption features and continuum regions, mainly dominated by 12 elements (Na, Ca, Sc, Ti, V, Cr, Mn, Fe, Ni, Y, Ba and Nd) in the wavelength range 4700 - 5400 \r{A} and characterise them as a function of age, metallicity and alpha element abundance ratios. We analyse eight dEs and interpret the line strengths, measured in our new high resolution system of indices, with the aid of stellar population models with high enough spectral resolution. We obtain abundance ratio proxies for a number of elements that have never been studied before for dwarf ellipticals outside the Local Group. These proxies represent relative deviations from predicted index-strengths of base stellar population models built-up following the abundance pattern of The Galaxy. The abundance proxy trend results are compared to abundance ratios from resolved stars in the Local Group, and indices from integrated light of larger early-type galaxies. We find that all our dwarfs show a pattern of abundance ratios consistent with the disk of the Milky Way, indicative of slow formation in comparison to their high mass counterparts.
... In Section 3.1, we identify galaxy groups located in the region we refer to as the 'cluster outskirts', between [R clus,h 200 , 5R clus,h 200 ] from the cluster centre at z = 0. Then, in Section 3.2, we instead identify infalling galaxy groups, at all redshifts, again using the same methods as Han et al. (2018) and Choque-Challapa et al. (2019). Using the halo merger trees, we first identify all objects that have just fallen into the cluster, taken from the whole history of the cluster; that is, we find galaxies that were at a distance greater than R clus,h 200 from the cluster centre in one snapshot, but are within R clus,h 200 in the following snapshot. ...
... Only 9 per cent of dark matter-only groups contain at least one subhalo with r < 0.3R grp,h 200 and v < v cir (excluding the host halo at the centre of each group). This is a region that previous work, such as that of Choque-Challapa et al. (2019), has also shown to contain few satellites in dark matter-only simulations. ...
Dark matter-only simulations are able to produce the cosmic structure of a Lambda cold dark matter universe, at a much lower computational cost than more physically motivated hydrodynamical simulations. However, it is not clear how well smaller substructure is reproduced by dark matter-only simulations. To investigate this, we directly compare the substructure of galaxy clusters and of surrounding galaxy groups in hydrodynamical and dark matter-only simulations. We utilize thethreeHundred project, a suite of 324 simulations of galaxy clusters that have been simulated with hydrodynamics, and in dark matter-only. We find that dark matter-only simulations underestimate the number density of galaxies in the centres of groups and clusters relative to hydrodynamical simulations, and that this effect is stronger in denser regions. We also look at the phase space of infalling galaxy groups, to show that dark matter-only simulations underpredict the number density of galaxies in the centres of these groups by about a factor of four. This implies that the structure and evolution of infalling groups may be different to that predicted by dark matter-only simulations. Finally, we discuss potential causes for this underestimation, considering both physical effects, and numerical differences in the analysis.
