The Evolution of Galaxies in Clusters (original) (raw)

Interactions and the Evolution of Cluster Galaxies

2001

We have developed model predictions for the morphological distribution of cluster galaxies as a function of the cluster-centric distance and the local galaxy density, using a semi-analytical code. This code allows us to obtain magnitudes and colours for cluster galaxies at different redshifts, and thus to study in detail the evolution of the colour-magnitude relation of specific distant clusters.

On the survival and destruction of spiral galaxies in clusters

Monthly Notices of the Royal Astronomical Society, 1999

We follow the evolution of disk galaxies within a cluster that forms hierarchically in a cold dark matter N-body simulation. At a redshift z = 0.5 we select several dark matter halos that have quiet merger histories and are about to enter the newly forming cluster environment. The halos are replaced with equilibrium high resolution model spirals that are constructed to represent examples of low surface brightness (LSB) and high surface brightness (HSB) galaxies. Varying the disk and halo structural parameters reveals that the response of a spiral galaxy to tidal encounters depends primarily on the potential depth of the mass distribution and the disk scale length. LSB galaxies, characterised by slowly rising rotation curves and large scale lengths, evolve dramatically under the influence of rapid encounters with substructure and strong tidal shocks from the global cluster potential -galaxy harassment. We find that up to 90% of their stars are tidally stripped and congregate in large diffuse tails that trace the orbital path of the galaxy and form the diffuse intra-cluster light. The bound stellar remnants closely resemble the dwarf spheroidals (dE's) that populate nearby clusters. HSB galaxies are stable to the chaos of cluster formation and tidal encounters. These disks lie well within the tidally limited dark matter halos and their potentials are more concentrated. Although very few stars are stripped, the scale height of the disks increases substantially and no spiral features remain, therefore we speculate that these galaxies would be identified as S0 galaxies in present day clusters.

Numerical Simulations of Merging Clusters of Galaxies

The Astrophysical Journal Supplement Series, 1997

We present results from three-dimensional numerical simulations of head-on mergers between two clusters of galaxies using a hybrid hydro/N-body code. In these simulations, the gaseous intracluster medium (ICM) is evolved as a massless Ñuid within a changing gravitational potential deÐned by the collisionless dark matter component. The ICM is represented by the equations of hydrodynamics which are solved by an Eulerian, Ðnite-di †erence method. The cluster dark matter component is represented by the N-body particle distribution. A series of simulations have been conducted in which we have systematically varied the cluster-subcluster mass ratio between 8 : 1 and 1 : 1. We Ðnd that cluster-subcluster mergers result in an elongation of both the cluster dark matter and gas distributions. The dark matter distribution is elongated parallel to the merger axis and accompanied by anisotropy in the dark matter velocity dispersion. Both the elongation and corresponding velocity anisotropy are sustained for more than 5 Gyr after the merger. The elongation of the gas distribution is also generally along the merger axis, although shocks and adiabatic compressions produce elongations perpendicular to the merger axis at various times during the merger. We also Ðnd a signiÐcant o †set between dark matter and gas centroids in the period following core passage. The gasdynamics is also severely a †ected by the cluster-subcluster merger. In these simulations, the subcluster enters the primary at supersonic speeds initiating bulk Ñows that can exceed 2000 km s~1. The width of the bulk Ñows are seen to range between several hundred kiloparsecs to nearly 1 Mpc. We believe the bulk Ñows can produce the bending of wide-angle tailed (WAT) radio sources. The most signiÐcant gasdynamics is seen to subside on timescales of 2 Gyr, although still signiÐcant dynamics is seen even after 5 Gyr. The merger-induced gasdynamics may also play a role in the formation of radio halo sources, and, consequently, the sustained nature of the gasdynamics may extend the lifetime of halos beyond the canonical synchrotron lifetime of the source. Substructure, shocks, and adiabatic cooling during the merger can result in a very complex temperature structure within the intracluster medium. As a result of these mergers, we Ðnd temperature inhomogeneities of several keV on linear scales of ¹0.5 Mpc. Finally, these simulations indicate that even relatively high mass-ratio mergers (e.g., 8 : 1) result in nonequilibrium conditions for an extended period of time. The period of time with the most signiÐcant dynamical evolution is within 2 Gyr after core passage. The nonequilibrium conditions have implications for cluster mass estimates. The observable consequences of cluster mergers and their inÑuence on cluster mass estimates are addressed in Roettiger, Burns, & Loken (1996).

THE ASSEMBLY OF GALAXY CLUSTERS

Astrophysical Journal, 2009

We study the formation of fifty-three galaxy cluster-size dark matter halos formed within a pair of cosmological LCDM N-body simulations, and track the accretion histories of cluster subhalos with masses large enough to host 0.1L* galaxies. By associating subhalos with cluster galaxies, we find the majority of galaxies in clusters experience no pre-processing in the group environment prior to their accretion into the cluster. On average, ~70% of cluster galaxies fall into the cluster potential directly from the field, with no luminous companions in their host halos at the time of accretion; and less than ~12% are accreted as members of groups with five or more galaxies. Moreover, we find that cluster galaxies are significantly less likely to have experienced a merger in the recent past (~6 Gyr) than a field halo of the same mass. These results suggest that local, cluster processes like ram-pressure stripping, galaxy harassment, or strangulation play the dominant role in explaining the difference between cluster and field populations at a fixed stellar mass; and that pre-evolution or past merging in the group environment is of secondary importance for setting cluster galaxy properties for most clusters. The accretion times for z = 0 cluster members are quite extended, with ~20% incorporated into the cluster halo more than 7 Gyr ago and ~20% within the last 2 Gyr. By comparing the observed morphological fractions in cluster and field populations, we estimate an approximate timescale for late-type to early-type transformation within the cluster environment to be ~6 Gyr.

The formation and evolution of clusters of galaxies in different cosmogonies

Monthly Notices of the Royal Astronomical Society, 1999

The formation of galaxy clusters in hierarchically clustering universes is investigated by means of high resolution N-body simulations. The simulations are performed using a newly developed multi-mass scheme which combines a PM code with a high resolution N-body code. Numerical effects due to time stepping and gravitational softening are investigated as well as the influence of the simulation box size and of the assumed boundary conditions. Special emphasis is laid on the formation process and the influence of various cosmological parameters. Cosmogonies with massive neutrinos are also considered. Differences between clusters in the same cosmological model seem to dominate over differences due differing background cosmogony. The cosmological model can alter the time evolution of cluster collapse, but the merging pattern remains fairly similar, e.g. number of mergers and mass ratio of mergers. The gross properties of a halo, such as its size and total angular momentum, also evolve in a similar manner for all cosmogonies and can be described using analytical models. It is shown that the density distribution of a halo shows a characteristic radial dependence which follows a power law with a slope of α = −1 at small and α = −3 at large radii, independent of the background cosmogony or the considered redshift. The shape of the density profiles follows the generic form proposed by Navarro et al. (1996) for all hierarchically clustering scenarios and retains very little information about the formation process or the cosmological model. Only the central matter concentration of a halo is correlated to the formation time and therefore to the corresponding cosmogony. We emphasise the role of non-radial motions of the halo particles in the evolution of the density profile.

Simulating galaxy clusters - II. Global star formation histories and the galaxy populations

Monthly Notices of the Royal Astronomical Society, 2005

We performed N-body + hydrodynamical simulations of the formation and evolution of galaxy groups and clusters in a cold dark matter cosmology. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metal-dependent radiative cooling, strong starbursts and (optionally) active galactic nucleus (AGN) driven galactic superwinds, effects of a meta-galactic ultraviolet field and thermal conduction. The properties of the galaxy populations in two clusters, one Virgo-like (T ∼ 3 keV) and one (sub)Coma-like (T ∼ 6 keV), are discussed. The global star formation rates of the cluster galaxies are found to decrease very significantly from redshift z = 2 to 0, in agreement with observations. The total K-band luminosity of the cluster galaxies correlates tightly with total cluster mass, and for models without additional AGN feedback, the zero-point of the relation matches the observed one fairly well. Compared to the observed galaxy luminosity function (LF), the simulations nicely match the number of intermediate-mass galaxies (−20 M B −17, smaller galaxies being affected by resolution limits) but they show a deficiency of bright galaxies in favour of an overgrown central dominant (cD) galaxy. High-resolution tests indicate that this deficiency is not simply due to numerical 'overmerging'.

Photometric evolution of galaxies in rich clusters: Numerical simulations

Astrophysics and Space Science, 1990

This paper briefly presents a numerical code which simulates the evolution of galaxies belonging to rich clusters. The evolutionary model considers both, cluster dynamics and galaxy photometry, taking into account the galaxy-cluster interactions (collisional stripping, merging and ram-pressure stripping by the ICM) and the intrinsic galaxy evolution, We use different initial mass distributions for galaxies and we briefly discuss the influence of the initial segregation in mass on the evolution of the photometrical properties.

GALICS- VI. Modelling hierarchical galaxy formation in clusters

Monthly Notices of the Royal Astronomical Society, 2005

High-resolution N-body re-simulations of 15 massive (10 14 − 10 15 M ⊙ ) dark matter haloes have been combined with the hybrid galaxy formation model GalICS (Hatton et al. 2003), to study the formation and evolution of galaxies in clusters, within the framework of the hierarchical merging scenario. This paper describes the high-resolution resimulation technique used to build the dark matter halo sample, and discusses its reliability. New features incorporated in GalICS include a better description of galaxy positioning after dark matter halo merger events, a more reliable computation of the temperature of the inter-galactic medium as a function of redshift, that also takes into account the reionisation history of the Universe, and a semi-analytic description of the ram pressure stripping of cold gas from galactic discs, suffered by galaxies during their motion through the diffuse hot intra-cluster medium. Within the multitude of available model results, we choose to focus here on the luminosity functions, morphological fractions and colour distributions of galaxies in clusters and in cluster outskirts, at z = 0. No systematic dependency on cluster richness is found either for the galaxy luminosity functions, morphological mixes, or colour distributions. Moving from higher density (cluster cores), to lower density environments (cluster outskirts), we detect a progressive flattening of the luminosity functions, an increase of the fraction of spirals and a decrease of that of ellipticals and S0s, and the progressive emergence of a bluer tail in the distributions of galaxy colours, especially for spirals. As compared to cluster spirals, early-type galaxies show a flatter luminosity function, and more homogeneous and redder colours. An overall good agreement is found between our results and the observations, particularly in terms of the cluster luminosity functions and morphological mixes. However, some discrepancies are also apparent, with too faint magnitudes of the brightest cluster members, especially in the B band, and galaxy colours tendentially too red (or not blue enough) in the model, with respect to the observations. Finally, ram pressure stripping appears to affect very little our results.

Cluster Physics with Merging Galaxy Clusters

Frontiers in Astronomy and Space Sciences, 2016

Collisions between galaxy clusters provide a unique opportunity to study matter in a parameter space which cannot be explored in our laboratories on Earth. In the standard CDM model, where the total density is dominated by the cosmological constant () and the matter density by cold dark matter (CDM), structure formation is hierarchical, and clusters grow mostly by merging. Mergers of two massive clusters are the most energetic events in the universe after the Big Bang, hence they provide a unique laboratory to study cluster physics. The two main mass components in clusters behave differently during collisions: the dark matter is nearly collisionless, responding only to gravity, while the gas is subject to pressure forces and dissipation, and shocks and turbulence are developed during collisions. In the present contribution we review the different methods used to derive the physical properties of merging clusters. Different physical processes leave their signatures on different wavelengths, thus our review is based on a multifrequency analysis. In principle, the best way to analyze multifrequency observations of merging clusters is to model them using N-body/hydrodynamical numerical simulations. We discuss the results of such detailed analyses. New high spatial and spectral resolution ground and space based telescopes will come online in the near future. Motivated by these new opportunities, we briefly discuss methods which will be feasible in the near future in studying merging clusters.