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Eelco van Kampen

Publications and source records attributed to Eelco van Kampen.

At least 55 records · Page 3Linked to original sources
arXiv2008

The STAGES view of red spirals and dusty red galaxies: Mass-dependent quenching of star-formation in cluster infall

We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ~0.17 using restframe near-UV-optical SEDs, 24 micron IR data and HST morphologies from the STAGES dataset. The cluster sample is based on COMBO-17 redshifts with an rms precision of sigma_cz~2000 km/sec. We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only 4x lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M*/Msol=[10,11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific SFR of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M*/Msol<10, such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note, that edge-on spirals play a minor role; despite being dust-reddened they form only a small fraction of spirals independent of environment.

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arXiv2008

STAGES: the Space Telescope A901/2 Galaxy Evolution Survey

We present an overview of the Space Telescope A901/2 Galaxy Evolution Survey (STAGES). STAGES is a multiwavelength project designed to probe physical drivers of galaxy evolution across a wide range of environments and luminosity. A complex multi-cluster system at z~0.165 has been the subject of an 80-orbit F606W HST/ACS mosaic covering the full 0.5x0.5 (~5x5 Mpc^2) span of the supercluster. Extensive multiwavelength observations with XMM-Newton, GALEX, Spitzer, 2dF, GMRT, and the 17-band COMBO-17 photometric redshift survey complement the HST imaging. Our survey goals include simultaneously linking galaxy morphology with other observables such as age, star-formation rate, nuclear activity, and stellar mass. In addition, with the multiwavelength dataset and new high resolution mass maps from gravitational lensing, we are able to disentangle the large-scale structure of the system. By examining all aspects of environment we will be able to evaluate the relative importance of the dark matter halos, the local galaxy density, and the hot X-ray gas in driving galaxy transformation. This paper describes the HST imaging, data reduction, and creation of a master catalogue. We perform Sersic fitting on the HST images and conduct associated simulations to quantify completeness. In addition, we present the COMBO-17 photometric redshift catalogue and estimates of stellar masses and star-formation rates for this field. We define galaxy and cluster sample selection criteria which will be the basis for forthcoming science analyses, and present a compilation of notable objects in the field. Finally, we describe the further multiwavelength observations and announce public access to the data and catalogues.

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arXiv2008

The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey

We present a high resolution dark matter reconstruction of the z=0.165 Abell 901/902 supercluster from a weak lensing analysis of the HST STAGES survey. We detect the four main structures of the supercluster at high significance, resolving substructure within and between the clusters. We find that the distribution of dark matter is well traced by the cluster galaxies, with the brightest cluster galaxies marking out the strongest peaks in the dark matter distribution. We also find a significant extension of the dark matter distribution of Abell 901a in the direction of an infalling X-ray group Abell 901alpha. We present mass, mass-to-light and mass-to-stellar mass ratio measurements of the structures and substructures that we detect. We find no evidence for variation of the mass-to-light and mass-to-stellar mass ratio between the different clusters. We compare our space-based lensing analysis with an earlier ground-based lensing analysis of the supercluster to demonstrate the importance of space-based imaging for future weak lensing dark matter 'observations'.

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arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) -- VI. 350 micron mapping of submillimetre galaxies

A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 microns has been carried out to map the regions around several 850 micron-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared luminosities and hence star-formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350 micron flux densities for 24 850 micron sources, seven of which are detected at >2.5-sigma within a 10 arcsec search radius of the 850 micron positions. When results from the literature are included the total number of 350 micron flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-infrared (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich (Mdust~9x10^8 Msun), luminous (Lfir~2x10^12 Lsun), star-forming galaxies with intrinsic dust temperatures of ~35 K and star-formation rates of ~400 Msun/yr. We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350 micron source counts, N350(>25mJy)~200-500 deg^-2.

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arXiv2007

The SCUBA HAlf Degree Extragalactic Survey (SHADES) - IV: Radio-mm-FIR photometric redshifts

We present the redshift distribution of the SHADES galaxy population based on the rest-frame radio-mm-FIR colours of 120 robustly detected 850um sources in the Lockman Hole East (LH) and Subaru XMM-Newton Deep Field (SXDF). The redshift distribution derived from the full SED information is shown to be narrower than that determined from the radio-submm spectral index, as more photometric bands contribute to a higher redshift accuracy. The redshift distribution of sources derived from at least two photometric bands peaks at z ~ 2.4 and has a near-Gaussian distribution, with 50 per cent (interquartile range) of sources at z=1.8-3.1. We find a statistically-significant difference between the measured redshift distributions in the two fields; the SXDF peaking at a slightly lower redshift (median z ~ 2.2) than the LH (median z ~ 2.7), which we attribute to the noise-properties of the radio observations. We demonstrate however that there could also be field-to-field variations that are consistent with the measured differences in the redshift distributions, and hence, that the incomplete area observed by SHADES with SCUBA, despite being the largest sub-mm survey to date, may still be too small to fully characterize the bright sub-mm galaxy population. Finally we present a brief comparison with the predicted, or assumed, redshift distributions of sub-mm galaxy formation and evolution models, and we derive the contribution of these SHADES sources and the general sub-mm galaxy population to the star formation-rate density at different epochs.

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arXiv2005

The extragalactic sub-mm population: predictions for the SCUBA Half-Degree Extragalactic Survey (SHADES)

We present predictions for the angular correlation function and redshift distribution for SHADES, the SCUBA HAlf-Degree Extragalactic Survey, which will yield a sample of around 300 sub-mm sources in the 850 micron waveband in two separate fields. Complete and unbiased photometric redshift information on these sub-mm sources will be derived by combining the SCUBA data with i) deep radio imaging already obtained with the VLA, ii) guaranteed-time Spitzer data at mid-infrared wavelengths, and iii) far-infrared maps to be produced by BLAST, the Balloon-borne Large-Aperture Sub-millimeter Telescope. Predictions for the redshift distribution and clustering properties of the final anticipated SHADES sample have been computed for a wide variety of models, each constrained to fit the observed number counts. Since we are dealing with around 150 sources per field, we use the sky-averaged angular correlation function to produce a more robust fit of a power-law shape w(theta)=(theta/A)^{-delta} to the model data. Comparing the predicted distributions of redshift and of the clustering amplitude A and slope delta, we find that models can be constrained from the combined SHADES data with the expected photometric redshift information.

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arXiv2000

The survival of subhaloes in galaxies and galaxy clusters

This paper discusses physical and numerical disruption processes acting on subhaloes in galaxy haloes and in galaxy cluster haloes, and compare the effects of these processes on the subhalo abundance within both types of haloes. N-body simulations with a resolution high enough not to suffer from overmerging (subhalo disruption due to numerical processes) show a high abundance of subhaloes in both galaxies and in galaxy clusters. However, observations seem to show a high subhalo abundance in galaxy clusters only. Thus, it appears that too many subhaloes survive in simulated galaxy haloes. There are five main causes for this apparent galaxy subhalo problem. The most radical one is a change to a cosmology in which structure formation is not hierarchical below the galaxy halo mass scale. If this is unacceptable, four causes remain, of which the most important one appears to be that dynamical friction is not properly simulated yet, not even for the highest resolution simulations to date, resulting in an 'undermerging' problem. The other causes are (numerical) overmerging, differences in the timing of halo formation and merging in hierarchical structure formation, and significant differences is mass-to-light ratios. The net effect of these four causes is that galaxies have a relatively low abundance of subhaloes, i.e. dwarfs, while at the same time a large number of field dwarf galaxies can exist which are dark enough to be missed observationally.

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arXiv2000

Modelling galaxy clustering at high redshift

Most phenomenological galaxy formation models show a discrepancy between the predicted Tully-Fisher relation and the luminosity function. We show that this is mainly due to overmerging of galaxy haloes, which is inherent in both the Press-Schechter formalism and dissipationless N-body simulations. This overmerging problem be circumvented by including a specific galaxy halo formation recipe into an otherwise standard N-body code. Resolving the overmerging also allows us to include models for chemical evolution and starbursts, which improves the match to observational data and renders the modelling more realistic. We use high-redshift clustering data to try and distinguish models which predict similar results at low redshifts for different sets of parameters.

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arXiv2000

Overmerging in N-body simulations

The aim of this paper is to clarify the notion and cause of overmerging in N-body simulations, and to present analytical estimates for its timescale. Overmerging is the disruption of subhaloes within embedding haloes due to {\it numerical} problems connected with the discreteness of N-body dynamics. It is shown that the process responsible for overmerging is particle-subhalo two-body heating. Various solutions to the overmerging problem are discussed

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arXiv1999

Overmerging and M/L ratios in phenomenological galaxy formation models

We show that the discrepancy between the Tully-Fisher relation and the luminosity function predicted by most phenomenological galaxy formation models is mainly due to overmerging of galaxy haloes. We have circumvented this overmerging problem, which is inherent in both the Press-Schechter formalism and dissipationless N-body simulations, by including a specific galaxy halo formation recipe into an otherwise standard N-body code. This numerical technique provides the merger trees which, together with simplified gas dynamics and star formation physics, constitute our implementation of a phenomenological galaxy formation model. Resolving the overmerging problem provides us with the means to match both the I-band Tully-Fisher relation and the B and K band luminosity functions within an EdS sCDM structure formation scenario. It also allows us to include models for chemical evolution and starbursts, which improves the match to observational data and renders the modelling more realistic. We show that the inclusion of chemical evolution into the modelling requires a significant fraction of stars to be formed in short bursts triggered by merging events.

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arXiv1999

Galaxy formation in dissipationless N-body models

We present a method of including galaxy formation in dissipationless N-body simulations. Galaxies that form during the evolution are identified at several epochs and replaced by single massive soft particles. This allows one to produce two-component models containing galaxies and a background dark matter distribution. We applied this technique to obtain two sets of models: one for field galaxies and one for galaxy clusters. We tested the method for the standard CDM scenario for structure formation in the universe. A direct comparison of the simulated galaxy distribution to the observed one sets the amplitude of the initial density fluctuation spectrum, and thus the present time in the simulations. The rates of formation and merging compare very well to simulations that include hydrodynamics, and are compatible with observations. We also discuss the cluster luminosity function.

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arXiv1998

Cluster mass estimation from lens magnification

The surface mass density of a cluster of galaxies, and thus its total mass, can be estimated from its lens magnification. The magnification can be determined from the variation in number counts of its background galaxies. In the weak lensing approximation the surface mass density is a linear function of the magnification. However, most observational data is concentrated in the central parts of clusters, so one needs to go beyond the weak lensing approximation, and consider the lens shear as well, which is unknown from the variation in number counts alone. We studied the lensing properties of a catalogue of numerical cluster models in order to find the best possible approximation for the shear which still allows straightforward determination of the surface mass density. We show that by using such an approximation one can fairly well reconstruct the surface mass distribution from the magnification alone. It is demonstrated that the mass estimated using the weak lens magnification approximation is usually at least twice the true mass. We illustrate our technique on existing data, and show that the resulting masses compare well to other estimates.

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arXiv1998

The Mass-Temperature Relation for Clusters of Galaxies

A tight mass-temperature relation, M(r)/r ~ T_X, is expected in most cosmological models if clusters of galaxies are homologous and the intracluster gas is in global equilibrium with the dark matter. We here calibrate this relation using 8 clusters with well-defined global temperatures measured with ASCA and masses inferred from weak and strong gravitational lensing. The surface lensing masses are deprojected in accordance with N-body simulations and analytic results. The data are well-fit by the mass-temperature relation and are consistent with the empirical normalisation found by Evrard et al. (1996) using gasdynamic simulations. Thus, there is no discrepancy between lensing and X-ray derived masses using this approach. The dispersion around the relation is 27 per cent, entirely dominated by observational errors. The next generation of X-ray telescopes combined with wide-field HST imaging could provide a sensitive test of the normalisation and intrinsic scatter of the relation resulting in a powerful and expedient way of measuring masses of clusters of galaxies. In addition, as M(r)/r (as derived from lensing) is dependent on the cosmological model at high redshift, the relation represents a new tool for determination of cosmological parameters, notably the cosmological constant Lambda.

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arXiv1997

Cluster mass estimation from lens magnification

The mass of a cluster of galaxies can be estimated from its lens magnification, which can be determined from the variation in number counts of background galaxies. In order to derive the mass one needs to make assumptions for the lens shear, which is unknown from the variation in number counts alone. Furthermore, one needs to go beyond the weak lensing (linear) approximation as most of the observational data is concentrated in the central parts of clusters, where the lensing is strong. By studying the lensing properties of a complete catalogue of galaxy cluster models, one can find reasonable approximations about the lens shear as a function of the lens convergence. We show that using these approximations one can fairly well reconstruct the surface mass distribution from the magnification alone.

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arXiv1997

Properties of galaxy clusters in N-body simulations: Intrinsic properties

We study the influence of the various parameters of scenarios of large-scale structure formation on properties of galaxy clusters, and investigate which cluster properties are most sensitive to these parameters. We present a set of large N-body simulations and derive the intrinsic properties of galaxy clusters in these simulations, which represent a volume of $256^3 h^{-3}$ Mpc^3. The cosmological scenarios studied differ in either the shape of the power spectrum of initial fluctuations, its normalization, the density parameter $Ω_{0}$, or the Hubble parameter $H_{0}$. Between each of the simulations, only one parameter is set differently, so that we can study the influence of that parameter on the cluster properties. The cluster properties that are studied are the mass, line-of-sight velocity dispersion, peculiar velocity, intrinsic shape, and orientation with respect to its surroundings. $σ_{8}$ has a large impact on the cluster properties. The latter, viz. the cluster number density, mass, line-of-sight velocity dispersion and peculiar velocity, are also determined by $Ω_{0}$, though somewhat less. Other parameters, such as $H_{0}$, the tilt of the initial fluctuation spectrum, and the exact shape of this spectrum, are generally less important. Unlike the other cluster properties studied, the peculiar velocity is found to depend on all parameters of the formation scenario. Using scaling relations between the average properties of the cluster sample and the parameters of the formation scenario, one may try and interpolate between the scenarios studied here in order to find the parameters of the scenario that is most consistent with the data.

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arXiv1997

A catalogue of galaxy cluster models

We present a technique to construct a fair sample of simulated galaxy clusters, and build such a sample for a specific cosmological structure formation scenario. Conventionally one extracts such a sample from a single low-resolution large-scale simulation. Here we simulate the clusters individually at high resolution. We construct a model catalogue selected on expected final cluster mass. Such a catalogue will not have a well-defined richness limit, because the relation between richness and mass is fairly broad. However, by applying the appropriate completeness corrections, the results for the mass-selected catalogue can be compared with observations for richness-selected cluster catalogues. We build a model cluster catalogue for the Omega_0=1 CDM scenario that is designed to mimic the ENACS sample of rich Abell clusters. We use the distribution of richness, corrected for incompleteness, to fix the present epoch. We find sigma_8=0.4-0.5, which is consistent with other determinations. The catalogue is 70 per cent complete for a richness larger than 50, but we do have a complete subsample for a richness limit of 75. As a first test we compare the cumulative distribution of line-of-sight velocity dispersions to those found for several observational samples, and find that they match best for a value of around 0.4 for sigma_8. This means that we find consistent values for sigma_8 for the CDM Omega_0=1 scenario on cluster scales.

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arXiv1996

Distribution functions for clusters of galaxies from N-body simulations

We present the results of an attempt to adapt the distribution function formalism to characterize large-scale structures like clusters of galaxies that form in a cosmological N-body simulation. While galaxy clusters are systems that are not strictly in equilibrium, we show that their evolution can nevertheless be studied using a physically motivated extension of the language of equilibrium stellar dynamics. Restricting our analysis to the virialized region, a prescription to limit the accessible phase-space is presented, which permits the construction of both the isotropic and the anisotropic distribution functions $f(E)$ and $f(E,L)$. The method is applied to models extracted from a catalogue of simulated clusters. Clusters evolved in open and flat background cosmologies are followed during the course of their evolution, and are found to transit through a sequence of what we define as `quasi-equilibrium' states. An interesting feature is that the computed $f(E)$ is well fit by an exponential form. We conclude that the dynamical evolution of a cluster, undergoing relaxation punctuated by interactions and violent mergers with consequent energy-exchange, can be studied both in a qualitative and quantitative fashion by following the time evolution of $f(E)$.

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