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Register a new userMeasuring Dark Matter Flows in Merging Clusters of Galaxies
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Added by
J. A. Rubino-Martin
Publication date
2004
fields
Physics
and research's language is
English
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The Rees-Sciama effect produced in mergers of galaxy clusters is discussed, and an analytical approximation to compute this effect from numerical simulations is given. Using this approximation and a novel toy model describing the physics of the merger, we characterize the spatial properties and symmetries of the Rees-Sciama signal. Based on these properties, we propose a method to extract the physical parameters of the merger, which relies on the computation of the quadrupole moment of the observed brightness distribution on the sky. The relationships between the quadrupole coefficients and the physical parameters of the merger (physical separation, projection angle on the sky and angular momentum) are discussed. Finally, we propose a method to co-add coherently the RS signals from a sample of cluster mergers, in order to achieve an statistical detection of the effect for those cases where individual signals are masked by the kinetic SZ effect, the primordial CMB components, and by observational noise.
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The study of cluster populations as tracer of galaxy evolution is now quite possible with 8 m class telescopes and modern instrumentation. The cluster population can be used as a good tracer of the star forming episodes undergone by the merging system. We present two young galaxies mergers NGC3256 and NGC4038, and the studies about the young cluster population on those system. We found that the clusters ages are agree with the mergers age and their metallicities are consistent with them being the progenitors of the old metal rich globulars in ellipticals.
We compute the evolution of the space-dependent mass distribution of galaxies in clusters due to binary aggregations by solving a space-dependent Smoluchowski equation. We derive the distribution of intergalactic distance for different ranges of mass (and of corresponding magnitude). We compare the results with the observed distributions, and find that the different degrees of luminosity segregation observed in clusters are well accounted for by our merging model. In addition, the presence of luminosity segregation is related to dynamical effects which also show up in different but connected observables, such as galaxy velocity profiles decreasing toward the center and X-ray measured beta-parameters smaller than 1. We predict both luminosity segregation and the observables above (being a product of binary aggregations) to be inversely correlated with the core radius and with the galaxy velocity dispersion; we discuss how the whole set of predictions compares with up-to-date observations.
We describe the first results from two observational projects aimed at measuring the amount and spatial distribution of dark matter in distant early-type galaxies (E/S0s) and clusters of galaxies. At the galaxy scale, the Lenses Structure and Dynamics (LSD) Survey is gathering kinematic data for distant (up to $zsim1$) E/S0s that are gravitational lenses. A joint lensing and dynamical analysis constrains the fraction of dark matter within the Einstein radius, the mass-to-light ratio of the stellar component, and the total slope of the mass density profile. These properties and their evolution with redshift are briefly discussed in terms of the formation and evolution of E/S0 galaxies and measurement of the Hubble Constant from gravitational time delay systems. At the cluster scale -- after careful removal of the stellar component with a joint lensing and dynamical analysis -- systems with giant radial arcs can be used to measure precisely the inner slope of the dark matter halo. An HST search for radial arcs and the analysis of a first sample are briefly discussed in terms of the universal dark matter halos predicted by CDM simulations.
Theoretical models for the expected merger rates of intermediate-mass black holes (IMBHs) are vital for planned gravitational-wave detection experiments such as the Laser Interferometer Space Antenna (LISA). Using collisionless $N$-body simulations of dwarf galaxy (DG) mergers, we examine how the orbital decay of IMBHs and the efficiency of IMBH binary formation depend on the central dark matter (DM) density profile of the merging DGs. Specifically, we explore various asymptotic inner slopes $gamma$ of the DGs DM density distribution, ranging from steep cusps ($gamma=1$) to shallower density profiles ($gamma<1$), motivated by well-known baryonic-feedback effects as well as by DM models that differ from cold DM at the scales of DGs. We find that the inner DM slope is crucial for the formation (or lack thereof) of an IMBH binary; only mergers between DGs with cuspy DM profiles ($gamma=1$) are favourable to forming a hard IMBH binary, whereas when $gamma<1$ the IMBHs stall at a separation of 50-100 pc. Consequently, the rate of LISA signals from IMBH coalescence will be determined by the fraction of DGs with a cuspy DM profile. Conversely, the LISA event rates at IMBH mass scales offer in principle a novel way to place constraints on the inner structure of DM halos in DGs and address the core-cusp controversy. We also show that, with spatial resolutions of $sim$0.1 kpc, as often adopted in cosmological simulations, all IMBHs stall, independent of $gamma$. This suggests caution in employing cosmological simulations of galaxy formation to study BH dynamics in DGs.
Large galaxies may contain an atmosphere of hot interstellar X-ray gas, and the temperature and radial density profile of this gas can be used to measure the total mass of the galaxy contained within a given radius r. We use this technique for 102 early-type galaxies (ETGs) with stellar masses M_* > 10^10 M_Sun, to evaluate the mass fraction of dark matter (DM) within the fiducial radius r = 5 r_e, denoted f_5 = f_{DM}(5r_e). On average, these systems have a median f_5 = 0.8 - 0.9 with a typical galaxy-to-galaxy scatter +-0.15. Comparisons with mass estimates made through the alternative techniques of satellite dynamics (e.g. velocity distributions of globular clusters, planetary nebulae, satellite dwarfs) as well as strong lensing show encouraging consistency over the same range of stellar mass. We find that many of the disk galaxies (S0/SA0/SB0) have a significantly higher mean $f_5$ than do the pure ellipticals, by Delta f_5 = 0.1. We suggest that this higher level may be a consequence of sparse stellar haloes and quieter histories with fewer major episodes of feedback or mergers. Comparisons are made with the Magneticum Pathfinder suite of simulations for both normal and centrally dominant Brightest Cluster galaxies. Though the observed data exhibit somewhat larger scatter at a given galaxy mass than do the simulations, the mean level of DM mass fraction for all classes of galaxies is in good first-order agreement with the simulations. Lastly, we find that the group galaxies with stellar masses near M_* ~ 10^11 M_Sun have relatively more outliers at low $f_5$ than in other mass ranges, possibly the result of especially effective AGN feedback in that mass range leading to expansion of their dark matter halos.
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