arXiv subjects

E. van Kampen

Publications and source records attributed to E. van Kampen.

83 records · Page 5Linked to original sources

arXiv2005

Simulations of galactic winds and starbursts in galaxy clusters

We present an investigation of the metal enrichment of the intra-cluster medium (ICM) by galactic winds and merger-driven starbursts. We use combined N-body/hydrodynamic simulations with a semi-numerical galaxy formation model. The mass loss by galactic winds is obtained by calculating transonic solutions of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure. The inhomogeneities in the metal distribution caused by these processes are an ideal tool to reveal the dynamical state of a galaxy cluster. We present surface brightness, X-ray emission weighted temperature and metal maps of our model clusters as they would be observed by X-ray telescopes like XMM-Newton. We show that X-ray weighted metal maps distinguish between pre- or post-merger galaxy clusters by comparing the metallicity distribution with the galaxy-density distribution: pre-mergers have a metallicity gap between the subclusters, post-mergers a high metallicity between subclusters. We apply our approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show whether they are pre- or post-merging systems. The survival time of the inhomogeneities in the metallicity distribution found in our simulations is up to several Gyr. We show that galactic winds and merger-driven starbursts enrich the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a galaxy cluster.

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arXiv2005

Metal Enrichment Processes in the Intra-Cluster Medium

We present numerical simulations of galaxy clusters which include interaction processes between the galaxies and the intra-cluster gas. The considered interaction processes are galactic winds and ram-pressure stripping, which both transfer metal-enriched interstellar medium into the intra-cluster gas and hence increase its metallicity. We investigate the efficiency and time evolution of the interaction processes by simulated metallicity maps, which are directly comparable to those obtained from X-ray observations. We find that ram-pressure stripping is more efficient than quiet (i.e. non-starburst driven) galactic winds in the redshift interval between 1 and 0. The expelled metals are not mixed immediately with the intra-cluster gas, but inhomogeneities are visible in the metallicity maps. Even stripes of higher metallicity that a single galaxy has left behind can be seen. The spatial distribution of the metals transported by ram-pressure stripping and by galactic winds are very different for massive clusters: the former process yields a centrally concentrated metal distribution while the latter results in an extended metal distribution.

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arXiv2005

Star formation rates and mass distributions in interacting galaxies

We present a systematic investigation of the star formation rate (hereafter SFR) in interacting disk galaxies. We determine the dependence of the overall SFR on different spatial alignments and impact parameters of more than 50 different configurations in combined N-body/hydrodynamic simulations. We also show mass profiles of the baryonic components. We find that galaxy-galaxy interactions can enrich the surrounding intergalatic medium with metals very efficiently up to distances of several 100 kpc. This enrichment can be explained in terms of indirect processes like thermal driven galactic winds or direct processes like 'kinetic' spreading of baryonic matter. In the case of equal mass mergers the direct -kinetic- redistribution of gaseous matter (after 5 Gyr) is less efficient than the environmental enrichment of the same isolated galaxies by a galactic wind. In the case of non-equal mass mergers however, the direct -kinetic- process dominates the redistribution of gaseous matter. Compared to the isolated systems, the integrated star formation rates (ISFRs) ($\int_{t = 0 Gyr}^{t = 5 Gyr}\textnormal{SFR(t)}dt$) in the modelled interacting galaxies are in extreme cases a factor of 5 higher and on average a factor of 2 higher in interacting galaxies. Co-rotating and counter-rotating interactions do not show a common trend for the enhancement of the ISFRs depending on the interaction being edge-on or face-on. The latter case shows an increase of the ISFRs for the counter-rotating system of about 100%, whereas the edge-on counter-rotating case results in a lower increase ($\sim$ 10%).

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arXiv2004

Metal Enrichment and Energetics of Galactic Winds in Galaxy Clusters

We investigate efficiency and time dependence of metal enrichment processes in the Intra-Cluster Medium (ICM). In this presentation we concentrate on the effects of galactic winds. The mass loss rates due to galactic winds are calculated with a special algorithm, which takes into account cosmic rays and magnetic fields. This algorithm is embedded in a combined N-body/hydrodynamic code which calculates the dynamics and evolution of a cluster. We present mass loss rates depending on galaxy properties like type, mass, gas mass fraction and the surrounding ICM. In addition we show metallicity maps as they would be observed with X-ray telescopes.

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arXiv2004

Metal Enrichment of the Intra-Cluster Medium: Ram-Pressure Stripping of Cluster Galaxies

We present numerical simulations of the dynamical and chemical evolution of galaxy clusters. X-ray spectra show that the intra-cluster medium contains a significant amount of metals. As heavy elements are produced in the stars of galaxies material from the galaxies must have been expelled to enrich the ambient medium. We have performed hydrodynamic simulations investigating various processes. In this presentation we show the feedback from gas which is stripped from galaxies by ram-pressure stripping. The efficiency, resulting spatial distribution of the metals and the time dependency of this enrichment process on galaxy cluster scale is shown.

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arXiv2002

Properties of Disk Galaxies in Phenomenological Models of Galaxy Formation

We present a phenomenological model for understanding the origins and evolution of galaxy morphologies from a phenomenological perspective. The model includes an observationally motivated prescription for star formation in galaxy disks, as well as a merger-driven starburst mode of star formation. We consider the formation of bulges and ellipticals both in mergers and by global instabilities in disks. We use our model to investigate the fundamental properties of disk galaxies and the effects of surface-brightness limits on large galaxy surveys.

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arXiv2002

Lens magnification by CL0024+1654 in the U and R band

[ABRIDGED] We estimate the total mass distribution of the galaxy cluster CL0024+1654 from the measured source depletion due to lens magnification in the R band. Within a radius of 0.54Mpc/h, a total projected mass of (8.1+/-3.2)*10^14 M_sol/h (EdS) is measured, which corresponds to a mass- to-light ratio of M/L(B)=470+/-180. We compute the luminosity function of CL0024+1654 in order to estimate contamination of the background source counts from cluster galaxies. Three different magnification-based reconstruction methods are employed using both local and non-local techniques. We have modified the standard single power-law slope number count theory to incorporate a break and applied this to our observations. Fitting analytical magnification profiles of different cluster models to the observed number counts, we find that the cluster is best described either by a NFW model with scale radius r_s=334+/-191 kpc/h and normalisation kappa_s=0.23+/-0.08 or a power-law profile with slope xi=0.61+/-0.11, central surface mass density kappa_0=1.52+/-0.20 and assuming a core radius of r_core=35 kpc/h. The NFW model predicts that the cumulative projected mass contained within a radius R scales as M( 0.15 up to U_AB<=26.4 with 95% confidence.

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arXiv2001

Properties of galaxy halos in Clusters and Voids

We use the results of a high resolution N-body simulation to investigate the role of the environment on the formation and evolution of galaxy-sized halos. Starting from a set of constrained initial conditions, we have produced a final configuration hosting a double cluster in one octant and a large void extending over two octants of the simulation box. We present results for two statistics: the relationship between 1-D velocity dispersion and mass and the probability distribution of the spin parameter $P(λ)$. The \svm relationship is well reproduced by the Truncated Isothermal Sphere (TIS) model introduced by Shapiro et al. (1999), although the slope is different from the original prediction. A series of \svm relationships for different values of the anisotropy parameter $β$, obtained using the theoretical predictions by Lokas and Mamon (2001) for NFW density profiles are found to be only marginally consistent with the data. Using some properties of the equilibrium TIS models, we construct subsamples of {\em fiducial} equilibrium TIS halos from each of the three subregions, and we study their properties. For these halos, we do find an environmental dependence of their properties, in particular of the spin parameter distribution $P(λ)$. We study in more detail the TIS model, and we find new relationships between the truncation radius and other structural parameters. No gravitationally bound halo is found having a radius larger than the critical value for gravithermal instability for TIS halos (\rt $\ge 34.2 r_{0}$, where $r_{0}$ is the core radius of the TIS solution). We do however find a dependence of this relationship on the environment, like for the $P(λ)$ statistics. These facts hint at a possible rôle of tidal fields at determining the statistical properties of halos.

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arXiv2000

Depletion of background galaxies due to the cluster lens CL0024+1654: U and R band observations

We have obtained U and R band observations of the depletion of background galaxies due to the gravitational lensing of the galaxy cluster CL0024+1654 (z=0.39). The radial depletion curves show a significant depletion in both bands within a radius of 40''-70'' from the cluster center. This is the first time depletion is detected in the U band. This gives independent evidence for a break in the slope of the U band luminosity function at faint magnitudes. The radially averaged R band depletion curve is broader and deeper than in the U band. The differences can be attributed to the wavelength dependence of the slope of the luminosity function and to the different redshift distribution of the objects probed in the two bands. We estimate the Einstein radius of a singular isothermal sphere lens model using maximum likelihood analysis. Adopting a slope of the number counts of 0.2 and using the background density found beyond 150'' from the cluster center we find an Einstein radius of 17''+/-3'' and 25''+/-3'' in the U and R band, respectively. When combined with the redshift of the single background galaxy at z=1.675 seen as four giant arcs around 30'' from the cluster center, these values indicate a median redshift in the range 0.7 to 1.1 for the U_AB > 24 mag and R_AB > 24 mag populations.

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arXiv1998

Gravitational Lens Magnification and the Mass of Abell 1689

We present the first application of lens magnification to measure the absolute mass of a galaxy cluster; Abell 1689. The absolute mass of a galaxy cluster can be measured by the gravitational lens magnification of a background galaxy population by the cluster potential. The lensing signal is complicated by the variation in number counts due to galaxy clustering and shot-noise, and by additional uncertainties in relating magnification to mass in the strong lensing regime. Clustering and shot-noise can be dealt with using maximum likelihood methods. Local approximations can then be used to estimate the mass from magnification. Alternatively if the lens is axially symmetric we show that the amplification equation can be solved nonlocally for the surface mass density and the tangential shear. In this paper we present the first maps of the total mass distribution in Abell 1689, measured from the deficit of lensed red galaxies behind the cluster. Although noisier, these reproduce the main features of mass maps made using the shear distortion of background galaxies but have the correct normalisation, finally breaking the ``sheet-mass'' degeneracy that has plagued lensing methods based on shear. We derive the cluster mass profile in the inner 4' (0.48 Mpc/h). These show a profile with a near isothermal surface mass density κ= (0.5+/-0.1)(θ/1')^{-1} out to a radius of 2.4' (0.28Mpc/h), followed by a sudden drop into noise. We find that the projected mass interior to 0.24 h^{-1}$Mpc is M(<0.24 Mpc/h)=(0.50+/- 0.09) \times 10^{15} Msol/h. We compare our results with masses estimated from X-ray temperatures and line-of-sight velocity dispersions, as well as weak shear and lensing arclets and find all are in fair agreement for Abell 1698.

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arXiv1994

The Shapes of Galaxy Clusters

We have reanalyzed a data set of 99 low redshift ($ z < 0.1 $) Abell clusters and determined their shapes. For this, three different measures are used. We use Monte-Carlo simulations to investigate the errors in the methods. The corrected distribution of cluster ellipticities shows a peak at $ ε\sim 0.4 $ and extends to $ ε\sim 0.8 $. The results are self-consistent, i.e., with the corrected distribution over projected cluster shapes we can reconstruct the observed distribution and the observed relation between the number of galaxies in a cluster and its ellipticity. It is shown that the richer clusters are intrinsically more nearly spherical than the poorer ones. The corrected distribution of cluster shapes is more consistent with a prolate population than with an oblate population. We compare the corrected true distribution of (projected) ellipticities with predictions from N-body simulations. For this, we use a catalogue of 75 N-body simulated clusters (van Kampen 1994) which assume a CDM spectrum with $ Ω= 1.0 $. The simulations include a recipe for galaxy formation and merging. 'Observing' these simulated clusters produces an ellipticity distribution that extends to much higher $ ε$ and that has too few nearly spherical clusters. Preliminary results of simulations of the formation of clusters in an $ Ω= 0.2 $ universe suggest that, on average, clusters are more nearly spherical in this case.

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