arXiv subjects

Frank C. van den Bosch

Publications and source records attributed to Frank C. van den Bosch.

At least 199 records · Page 11Linked to original sources

arXiv2004

The Abundance and Radial Distribution of Satellite Galaxies

Using detailed mock galaxy redshift surveys (MGRSs) we investigate the abundance and radial distribution of satellite galaxies. The mock surveys are constructed using the conditional luminosity function (CLF), and are compared against data from the 2dFGRS. We use Monte Carlo Markov Chains to explore the full posterior distribution of the CLF parameter space, and show that the average relation between light and mass is tightly constrained. The radial number density distribution of satellite galaxies in the 2dFGRS reveals a pronounced absence of satellites at small projected separations from their host galaxies. This is (at least partially) due to the overlap and merging of galaxy images in the APM catalogue. Because of the resulting close-pair incompleteness we are unfortunately unable to put meaningful constraints on the radial distribution of satellite galaxies. Marginalizing over the full CLF parameter space, we show that in a LCDM concordance cosmology the observed abundances of host and satellite galaxies in the 2dFGRS indicate a power spectrum normalization of sigma_8=0.7. The same cosmology but with sigma_8=0.9 is unable to simultanously match the abundances of host and satellite galaxies. This confirms our previous conclusions based on the pairwise peculiar velocity dispersions and the group multipliticy function.

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arXiv2004

The Three-point Correlation Function of Galaxies: Comparing Halo Occupation Models with Observations

We present models for the three-point correlation function (3PCF) of both dark matter and galaxies. We show that models based on the halo model can reasonably match the dark matter 3PCF obtained from high-resolution $N$-body simulations. On small scales ($r\la 0.5\mpch$) the 3PCF is sensitive to details regarding the density distributions of dark matter haloes. On larger scales ($r \ga 2.0\mpch$) the results are very sensitive to the abundance of the few most prominant haloes. Using the conditional luminosity function, we also construct models for the 3PCF of galaxies, which we test against large mock galaxy samples. The bias of the galaxy distrubution with respect to the dark matter, and the finite number of galaxies that can be hosted by individual haloes, significantly reduce the normalized three-point correlation function with respect to that of dark matter. Contrary to the 3PCF of the dark matter, the galaxy 3PCF is much less sensitive to details regarding the spatial number density distribution of galaxies in individual haloes or to the abundance of the few most massive systems. Finally, we show that our model based on the conditional luminosity function is in good agreement with results obtained from the 2-degree Field Galaxy Redshift Survey. In particular, the model nicely reproduces the observational finding that the 3PCF for early-type galaxies is slightly higher than that of late-type galaxies, and that there is no significant dependence of the 3PCF on galaxy luminosity.

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arXiv2004

Probing Dark Matter Haloes with Satellite Kinematics

Using detailed mock galaxy redshift surveys we investigate to what extent the kinematics of large samples of satellites galaxies extracted from flux-limited surveys can be used to constrain halo masses. Previous host-satellite selection criteria yield relatively large fractions of interlopers and with a velocity distribution that, contrary to what has typically been assumed, differs strongly from uniform. A new adaptive selection criterion is proposed which yields much larger host-satellite samples and with strongly reduced interloper fractions. We show that satellite weighting, which occurs naturally when stacking many host-satellite pairs, introduces a bias towards higher velocity dispersions compared to the true, host-averaged mean. A further bias, in the same direction, is introduced when using flux-limited, rather than volume-limited surveys. We apply our adaptive selection criterion to the 2dFGRS and obtain a sample of 12613 satellite galaxies and 8004 host galaxies. The satellite kinematics are in excellent agreement with predictions based on the conditional luminosity function (CLF), providing independent, dynamical confirmation of the average mass-to-light ratios predicted by the CLF formalism.

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arXiv2004

The Dependence of the Galaxy Luminosity Function on Large-Scale Environment

A basic assumption in current halo occupation model is that the properties of a galaxy depend only on the mass of its dark matter halo. An important consequence of this is that the segregation of the galaxy population by large-scale environment is entirely due to the environmental dependence of the halo population. In this paper we use such a model to predict how the galaxy luminosity function depends on large-scale environment. The latter is represented by the density contrast (delta) averaged over a spherical volume of radius R=8Mpc/h. The model predicts that the Schechter function is a good approximation to the luminosity functions of galaxies brighter than ~10^9 h^{-2}L_sun (b_j-band) in virtually all environments. The characteristic luminosity, L^{\star}, increases moderately with δ. The faint-end slope, α, on the other hand, is quite independent of $δ$. However, when splitting the galaxy population into early and late types, it is found that for late-types αis virtually constant, whereas for early-types αincreases from ~-0.3 in underdense regions (δ~-0.5) to ~-0.8 in highly overdense regions with δ~ 10. The luminosity function at L_{b_j}<10^9 h^{-2} L_sun is significantly steeper than the extrapolation of the Schechter function that fits the brighter galaxies. This steepening is more significant for early-types and in low-density environments. The model also predicts that the luminosity density and mass density are closely correlated. The relation between the two is monotonic but highly non-linear. This suggests that one can use the luminosity density, averaged over a large volume, to rank the mass density. This, in turn, allows the environmental effects predicted here to be tested by observations.

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arXiv2004

Populating Dark Matter Haloes with Galaxies: Comparing the 2dFGRS with Mock Galaxy Redshift Surveys

In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N-body simulations of the standard LCDM cosmogony with Omega_m=0.3 and sigma_8=0.9. Stacking simulation boxes of 100 Mpc/h and 300 Mpc/h with 512^3 CDM particles each we construct Mock Galaxy Redshift Surveys out to a redshift of z=0.2. We use these mock surveys to investigate various clustering statistics. The projected correlation functions for galaxies with different luminosities and types match the observations well on scales larger than about 3 Mpc/h. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Furthermore, the model predicts pairwise velocity dispersions (PVD) that are about 400 km/s too high at projected pair separations of ~1 Mpc/h. A strong velocity bias in massive haloes can reduce the predicted PVD to the observed level, but does not help to resolve the over-prediction of clustering power on small scales. Consistent results can be obtained within the standard LCDM model only when the mass-to-light ratio of clusters is almost twice the observed value. Alternatively, a LCDM model with sigma_8=0.75 can also reproduce the observational results.

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arXiv2003

Linking Early and Late Type Galaxies to their Dark Matter Haloes

(Abridged) Using data from the 2dFGRS we compute the conditional luminosity functions (CLFs) of early- and late-type galaxies. These functions give the average number of galaxies with luminosity L that reside in a halo of mass M, and are a powerful statistical tool to link the distribution of galaxies to that of dark matter haloes. We find that the average mass-to-light ratios of dark matter haloes have a minimum of about 100 Msun/Lsun around a halo mass of about 3x10^{11} Msun. In addition, haloes with M < 10^{10} Msun are virtually devoid of galaxies, while clusters have b_J band mass-to-light ratios in the range 500-1000 Msun/Lsun. Finally, the fact that early-type galaxies are more strongly clustered than late-type galaxies requires that the fraction of late-type galaxies is a strongly declining function of halo mass. We also compute two-point correlation functions as function of both luminosity and galaxy type, and find a weak (strong) luminosity dependence for the late (early) type galaxies. Finally we compare our CLFs with predictions from several semi-analytical models for galaxy formation. As long as these models accurately fit the 2dFGRS luminosity function the agreement with our predictions is remarkably good. This indicates that we have recovered a statistical description of how galaxies populate dark matter haloes which fits nicely within the standard framework for galaxy formation.

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arXiv2003

Towards Cosmological Concordance on Galactic Scales

We use the observed abundance and clustering of galaxies from the 2dFGRS to determine the matter density Omega_m and the linear amplitude of mass fluctuations sigma_8. We use a method based on the conditional luminosity function, which allows straightforward computation of the luminosity dependent bias of galaxies. In addition, it allows the inclusion of constraints on the redshift space distortion parameter beta=Omega_m^{0.6}/b, and yields average mass-to-light ratios as function of halo mass. Using only the luminosity function and the correlation lengths as function of luminosity we obtain constraints on Omega_m and sigma_8 that are in good agreement with COBE. Using additional constraints on the mass-to-light ratios of clusters and on the value of beta as determined from the 2dFGRS yields Omega_m = (0.27 +/- 0.06) and sigma_8 = (0.77 +/- 0.06). Adding further constraints from current CMB data, we obtain Omega_m = (0.25 +/- 0.04) and sigma_8 = (0.78 +/- 0.06). Thus, we find strong indications that both Omega_m and sigma_8 are significantly lower than their ``standard'' concordance values of 0.3 and 0.9, respectively. Finally, we show that the cosmologies favored here predict dark matter haloes that are significantly less centrally concentrated than for the standard LCDM concordance model. This may solve both the problem with the rotation curves of dwarf and LSB galaxies, as well as the problem of simultaneously matching the galaxy luminosity function and the Tully-Fisher zero-point. (Abridged)

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arXiv2003

The Angular Momentum of Gas in Proto-Galaxies: II -- The Impact of Preheating

We examine the effect of preheating of the intergalactic medium on galaxy formation using cosmological hydrodynamical simulations. By performing simulations both with and without a simple model for preheating, we analyse and compare the angular momentum distributions of the dark matter and the baryons. Preheating unbinds baryons from their dark matter haloes, yielding a baryonic mass fraction that declines with decreasing halo mass. In addition, the spin parameter of the gas is reduced with respect to the case without preheating, while the misalignment between the angular momentum directions of the gas and dark matter increases strongly. The angular momentum distributions of individual haloes reveal that preheating decreases (increases) the mass fraction with low (negative) specific angular momentum. We discuss the implications of these findings for the formation of disk galaxies in a preheated intergalactic medium, and compare our results to the predictions of Maller & Dekel (2002), who propose an alternative interpretation for the origin of the angular momentum of (proto)-galaxies.

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arXiv2002

New Problems for the Formation of Disk Galaxies

The standard picture for the formation of disk galaxies has come to face a number of problems related to angular momentum. Numerical simulations produce disks that are too small, and analytical models predict too much low angular momentum compared to observations. In addition, angular momentum distributions of proto-galaxies in numerical simulations reveal large mass fractions with negative specific angular momentum, which implies that the gas cannot conserve its detailed distribution of specific angular momentum when cooling to form the disk. This crumples one of the main pillars of our standard picture, and indicates that a new spin on the angular momentum acquisition of disk galaxies may be required.

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arXiv2002

Constraining Galaxy Formation and Cosmology with the Conditional Luminosity Function of Galaxies

We use the conditional luminosity function (CLF), which gives the number of galaxies with luminosities in the range [L, L+dL] that reside in a halo of mass M, to link the distribution of galaxies to that of dark matter haloes. We seek the CLF that reproduces the galaxy luminosity function and the luminosity dependence of the galaxy clustering strength and test the models by comparing the resulting mass-to-light ratios (M/L) with constraints from the Tully-Fisher (TF) relation. We obtain a number of stringent constraints on both galaxy formation and cosmology. In particular, this method can break the degeneracy between Omega_0 and the power-spectrum normalization sigma_8, inherent in current weak-lensing and cluster-abundance studies. For flat LCDM cosmogonies with sigma_8 normalized by recent weak lensing observations, the best results are obtained for Omega_0~0.3; Omega_0 < 0.2 leads to too large galaxy correlation lengths, while Omega_0 > 0.4 gives too high M/L. The best-fit model for the LCDM concordance cosmology (Omega_0=0.3) predicts M/L that are slightly too high. We discuss a number of possible effects that might remedy this problem, including small modification of cosmological parameters, warm in stead of cold dark matter, systematic errors in current observational data, and the existence of dark galaxies. Finally we use the CLF to predict several statistics about the distribution of galaxy light in the local Universe.

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arXiv2002

The Angular Momentum of Gas in Proto-Galaxies I. Implications for the Formation of Disk Galaxies

We use non-radiative N-body/SPH simulations of structure formation in a LCDM cosmology to compare the angular momentum distributions of dark matter and gas in a large sample of halos. We show that the two components have identical spin parameter distributions and that their angular momentum distributions within individual halos are very similar, all in excellent agreement with standard assumptions. Despite these similarities, however, we find that the angular momentum vectors of the gas and dark matter are poorly aligned, with a median misalignment angle of about 30 degrees, which might have important implications for spin correlation statistics used in weak lensing studies. We present distributions for the component of the angular momentum that is aligned with the total angular momentum of each halo, and find that for between 5 and 50 percent of the mass this component is negative. This disagrees with the `Universal' angular momentum distribution suggested by Bullock et al. (2001), for which the mass fraction with negative specific angular momentum is zero. We discuss the implications of our results for the formation of disk galaxies. Since galactic disks generally do not contain counter-rotating stars or gas, disk formation cannot occur under detailed conservation of specific angular momentum. We suggest that the material with negative specific angular momentum combines with positive angular momentum material to build a bulge component, and show that in such a scenario the remaining material can form a disk with a density distribution that is very close to exponential.

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arXiv2002

Galaxy Cores as Relics of Black Hole Mergers

We investigate the hypothesis that the cores of elliptical galaxies and bulges are created from the binding energy liberated by the coalescence of supermassive binary black holes during galaxy mergers. Assuming that the central density profiles of galaxies were initially steep power laws, we define the ``mass deficit'' as the mass in stars that had to be removed from the nucleus in order to produce the observed core. We use nonparametric deprojection to compute the mass deficit in a sample of 35 early-type galaxies with high-resolution imaging data. We find that the mass deficit correlates well with the mass of the nuclear black hole, consistent with the predictions of merger models. We argue that core sizes in halos of non-interacting dark matter particles should be comparable to those observed in the stars.

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arXiv2002

The Origin of the Correlation between the Spin Parameter and the Baryon Fraction of Galactic Disks

The puzzling correlation between the spin parameter lambda of galactic disks and the disk-to-halo mass fraction fdisk is investigated. We show that such a correlation arises naturally from uncertainties in determining the virial masses of dark matter halos. This result leads to the conclusion that the halo properties derived from fits to observed rotation curves are still very uncertain which might explain part of the disagreements between cosmological models and observations. We analyse lambda and fdisk as function of the adopted halo virial mass. Reasonable halo concentrations require fdisk=0.01-0.07 which is significantly smaller than the universal baryon fraction. Most of the available gas either never settled into the galactic disks or was ejected subsequently. In both cases it is not very surprising that the specific angular momentum distribution of galactic disks does not agree with the cosmological predictions which neglect these effects.

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arXiv2002

Measuring the Virial Masses of Disk Galaxies

I present detailed models for the formation of disk galaxies, and investigate which observables are best suited as virial mass estimators. Contrary to naive expectations, the luminosities and circular velocities of disk galaxies are extremely poor indicators of total virial mass. Instead, I show that the product of disk scale length and rotation velocity squared yields a much more robust estimate. Finally, I show how this estimator may be used to put limits on the efficiencies of cooling and feedback during the process of galaxy formation.

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arXiv2001

The Impact of Cooling and Feedback on Disc Galaxies

We present detailed, analytical models for the formation of disc galaxies to investigate the impact that cooling and feedback have on their structural properties. In particular, we investigate which observables extracted directly from the models are best suited as virial mass estimators, and to what extent they allow the recovery of the model input parameters regarding the feedback and cooling efficiencies. Contrary to naive expectations, the luminosities and circular velocities of disc galaxies are extremely poor indicators of total virial mass. Instead, we show that the product of disc scale length and rotation velocity squared yields a much more robust estimate. We show that feedback can cause a narrow correlation between galaxy mass fraction and halo spin parameter, similar to that found recently by van den Bosch, Burkert and Swaters from an analysis of dwarf galaxy rotation curves. Finally we investigate the impact that cooling and feedback have on the colors, metallicities, star formation histories and Tully-Fisher relation of disc galaxies.

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arXiv2001

The Universal Mass Accretion History of CDM Haloes

We use the extended Press-Schechter formalism to investigate the rate at which cold dark matter haloes accrete mass. We discuss the shortcomings of previous methods that have been used to compute the mass accretion histories of dark matter haloes, and present an improved method based on the N-branch merger tree algorithm of Somerville & Kolatt. We show that this method no longer suffers from inconsistencies in halo formation times, and compare its predictions with high resolution N-body simulations. Although the overall agreement is reasonable, there are slight inconsistencies which are most easily interpreted as a reflection of ellipsoidal collapse (as opposed to spherical collapse assumed in the Press-Schechter formalism). We show that the average mass accretion histories follow a simple, universal profile, and we present a recipe for computing the two scale-parameters which is applicable to a wide range of halo masses and cosmologies. Together with the universal profiles for the density and angular momentum distributions of CDM haloes, these universal mass accretion histories provide a simple but accurate framework for modeling the structure and formation of dark matter haloes. In particular, they can be used as a backbone for modeling various aspects of galaxy formation where one is not interested in the detailed effects of merging. As an example we use the universal mass accretion history to compute the rate at which haloes accrete mass, which we compare to the cosmic star formation history of the Universe.

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arXiv2001

The Origin of the Density Distribution of Disk Galaxies: A New Problem for the Standard Model of Disk Formation

We present new models for the formation of disk galaxies that improve upon previous models by following the detailed accretion and cooling of the baryonic mass, and by using realistic distributions of specific angular momentum. Under the assumption of detailed angular momentum conservation the disks that form have density distributions that are more centrally concentrated than an exponential. We examine the influence of star formation, bulge formation, and feedback on the outcome of the surface brightness distributions of the stars. Whereas the models are succesful in reproducing high surface brightness disks, they fail to produce exponential disks of low surface brightness. In addition, the models predict truncation radii in the gas that occur at too high surface density. This signals a new problem for the standard model of disk formation: if the baryonic component of the protogalaxies out of which disk galaxies form have the same angular momentum distribution as the dark matter, disks are too compact.

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arXiv2001

The Angular Momentum Content of Dwarf Galaxies: New Challenges for the Theory of Galaxy Formation

We compute the specific angular momentum distributions of a sample of low mass disk galaxies observed by Swaters. We compare these distributions to those of dark matter haloes obtained by Bullock et al. from high resolution N-body simulations of structure formation in a LCDM Universe. We find that although the disk mass fractions are significantly smaller than the Universal baryon fraction, the total specific angular momenta of the disks are in good agreement with those of dark matter haloes. This suggests that disks form out of only a small fraction of the available baryons, but yet manage to draw most of the available angular momentum. In addition we find that the angular momentum distributions of disks are clearly distinct from those of the dark matter; disks lack predominantly both low and high specific angular momentum. Understanding these findings in terms of a coherent picture for disk formation is challenging. Cooling, feedback and stripping, which are the main mechanisms to explain the small disk mass fractions found, seem unable to simultaneously explain the disk's angular momentum distribution. In fact, it seems that the baryons that make up the disks must have been born out of angular momentum distributions that are clearly distinct from those of LCDM haloes. Therefore, understanding the angular momentum content of disk galaxies remains an important challenge for our picture of galaxy formation.

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