| Frank C. van den Bosch |
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 I'm leading an independent research group in the Theory Division of the Galaxies and Cosmology Department at the Max-Planck-Institute for Astronomy (MPIA) in Heidelberg. Our research focusses on various theoretical aspects of cosmology, large scale structure, and galaxy formation. In particular, we have ongoing projects to study the structure and formation of dark matter haloes, the formation of disk galaxies, the galaxy occupation statistics of dark matter haloes, galaxy-galaxy lensing, preheating of the IGM by pancake formation, and on the bias of galaxies and dark matter haloes. For more details please consult the research page.
 ... NEWS ..... NEWS ..... NEWS ..... NEWS ..... NEWS ... We investigate the correlation of star formation quenching with internal galaxy properties and large scale environment (halo mass) in empirical data and theoretical models. For central galaxies, we find that the fractions of ``red'' and ``passive'' galaxies in the observational group catalogs are a strong function of halo mass at fixed stellar mass, and a weak function of stellar mass at fixed halo mass. For satellite galaxies, a nearly equally strong dependence on halo mass and stellar mass is seen. A comparison with five different semi-analytic models shows that models with AGN feedback can reproduce the trends of central galaxies, but not for satellite galaxies, which are too red/passivein the models. This satellite overquenching problem is caused by the too-rapid stripping of the satellites' hot gas halos, which leads to rapid strangulation of star formation. Using our SDSS group catalogue, we compare the sizes, concentrations, colour gradients and surface brightness profiles of central and satellite galaxies as fixed stellar mass. We find that at fixed stellar mass, late type satellite galaxies have smaller radii and larger concentrations than late type central galaxies. No such differences are found for early-type galaxies. Late-type satellite galaxies have a lower surface brightness and redder colours than late-type central galaxies. All these differences between satellite and central galaxies can be explained by a simple fading model, in which the star formation in the disk decreases over timescales of 2-3 Gyr after a galaxy becomes a satellite. We use the conditional stellar mass functions of satellite galaxies obtained from our SDSS galaxy group catalogue together with models of the subhalo mass functions to explore the fraction and fate of stars stripped from satellites in galaxy groups and clusters of different masses. The majority of the stripped stars in massive halos are predicted to end up as intra-cluster stars, and the predicted amounts of the intra-cluster component as a function halo mass are in good agreement with direct observational constraints. Using our SDSS galaxy group catalogue, we investigate the luminosity and stellar mass functions for different populations of galaxies and for groups themselves. We also determine the conditional stellar mass function, which describes the stellar distribution of galaxies in halos of a given mass. We use the observed stellar mass function of central galaxies to constrain the stellar mass - halo mass relation for low mass halos, and obtain that M_* \propto M_{halo}^{4.9} We use the abundance and clustering properties of galaxies in the SDSS in order to constrain the conditional luminosity function (CLF), which describes the link between galaxies and dark matter haloes. The resulting CLF model is then used to predict the galaxy-galaxy lensing signal. We show that the predicted lensing signal is in agreement with the data for a cosmology with Omega_m=0.238 and sigma_8=0.734, but not for a cosmology with Omega_m=0.3 and sigma_8=0.9. We use a large galaxy group catalogue to predict the galaxy-galaxy lensing signal, which we compare to data from the SDSS. In agreement with our CLF study we only find a good match to the data if we assume a cosmology with relatively low Omega_m and sigma_8. Using the method outlined in Paper I we determine both the mean and the scatter of the mass-luminosity relation of central galaxies in the SDSS. We find that the scatter in halo masses for centrals of a given luminosity increases with increasing luminosity, and discuss the implications for the amount of stochasticity in galaxy formation. We present a new method that uses satellite kinematics to constrain both the mean and the scatter of the mass-luminosity relation of central galaxies. Using a large SDSS galaxy group catalogue, we study the dependence of galaxy activity on stellar mass, halo mass, and group hierarchy (centrals vs. satellites). We split our galaxy sample in star-forming galaxies, galaxies with optical AGN activity and radio sources. Among others, we find a smooth transition in halo mass as the activity of central galaxies changes from star formation to optical AGN activity to radio emission. Using a large suite of numerical simulations, we study the concentrations of dark matter haloes as function of halo mass and cosmology. Our simulations cover 5 order of magnitude in halo mass, and three different cosmological models. We present a new model to compute the average concentration as function of halo mass which accuretely fits our simulation results. We also compare our simulation results to constraints from various observational techniques. We study the dependence of the colors and concentrations of satellite galaxies on their stellar mass, their halo mass, and their halo-centric distance. We find that the properties of satellite galaxies are almost entirely determined by their stellar mass, with no significant environment dependence. This has important implications for the physical processes responsible for transforming satellite galaxies. We present a new method to reconstruct the cosmic density field from the distribution of dark matter haloes extracted from a large galaxy group catalogue. We demonstrate that our method works remarkably well using haloes (groups) with masses down to 10^12 Msun, even in redshift space. We discuss a number of potentially powerful applications. Using semi-analytical models for galaxy formation, and data from the SDSSS we constrain the efficiency with which satellite galaxies are stripped of hot gas, and tidally disrupted by the potential of their host halo. Using a set of halo stars extracted from the SDSS as kinematic tracers, we derive new constraints on the mass of the Milky Way's dark matter halo. Our results indicate a halo virial mass of M$_{\rm vir}=1.1\pm 0.2 \times 10^{12}$M$_\odot$. This implies that nearly 40% of the baryons within the virial radius of the Milky Way's dark matter halo reside in the stellar components of our Galaxy. Using N-Body simulations we study the mass loss rates of dark matter subhaloes, and interpret the mass function of subhaloes at redshift zero in terms of the evolution of the mass function of systems accreted by the main halo progenitor. Using the cross-correlation between galaxy groups and galaxies in the SDSS we determine how the bias of dark matter halos depends on halo mass and on the color of its galaxy population. We find that the mass dependence is in excellent agreement with predictions for a LCDM cosmology, and that red groups are more strongly clustered than blue groups of the same mass. We discuss how this relates to the assembly bias of dark matter haloes. Using a large SDSS galaxy group catalogue we study the occupation statistics or dark matter haloes. In particular, we determine the conditional luminosity function, halo occupation numbers, gap statistics in both luminosity and stellar mass, and satellites fractions, all for both red and blue galaxies. Using a large SDSS galaxy group catalogue we study the importance of satellite for the build-up of the red sequence of present day galaxies. We do this by comparing the properties of central and satellite galaxies that are matched in stellar mass. Using a large SDSS galaxy group catalogue we study the three-dimensional and projected shapes of dark matter haloes. We find that the halo shape has a strong dependence on the halo mass. While the haloes of low-mass groups are nearly spherical, those of massive groups tend to be prolate. We investigate the incidence of major mergers creating massive galaxies in present-day groups and clusters. This results in, among others, the largest sample of dry mergers currently available. We present the global structural parameters for a large sample of 1300 spiral galaxies and explore the joint distribution of luminosity, rotation velocity, and disk size. We present a new galaxy group catalogue constructed from the SDSS data release 4 Using a large numerical simulation we investigate various spatial and kinematic alignments between dark matter haloes probing scales out to 6 virial radii. Using a semi-analytical model for galaxy formation, combined with a large N-body simulation we investigate the origin of the dichotomy of early-type galaxies. Using a sample of 847 early-type galaxies selected from the SDSS DR4 we study the disky fraction as function of luminosity and halo mass. Using a large galaxy group catalogue constructed from the SDSS DR4 we investigate three types of galaxy alignments, and discuss their implications for weak lensing measurements. We investigate the luminosity and color dependence of galaxy clustering in the SDSS using measurements of the two-point auto and cross correlation functions. We also use these to test for the importance of non-linearity and stochasticity. Using large N-body simulations which we populate with galaxies following a semi-analytical model for galaxy formation, we study the alignment between the orientation of central galaxies and the distribution of satellite galaxies. We use the Conditional Luminosity Function and data from the 2dFGRS to constrain the average relation between light and mass in the Universe. Using a suite of N-body simulations, we study the concentrations, spin parameters and shapes of dark matter haloes covering a wide range in halo masses. We also study their environment dependence and discuss the implications for interpreting LSB rotation curves. We demonstrate how galaxy groups can be used to split the population of galaxies in centrals and satellites. Galaxy-galaxy lensing measurements of these two separate populations is shown to yield accurate constraints on the masses and density profiles of dark matter haloes and sub-haloes. Using a galaxy group catalogue extracted from the SDSS we analyze the fraction of blue galaxies as function of halo mass and luminosity. A comparison with semi-analytical models for galaxy formation provides valuable new insights into the physics of star formation truncation We show that the phenomenon of `downsizing' is not `anti-hierachical', but in fact has its natural roots in the bottom-up clustering process of dark-matter haloes For a brief summary you can also check our poster on this topic. We present a new model for disk formation. Contrary to common ideas, we suggest that disks formation involves low spin parameters and halo expansion, rather than contraction Using galaxy groups selected from the SDSS we show that the distribution of satellite galaxies is aligned with the major axis of the central galaxy; this is contrary to the old Holmberg effect |
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