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Search Results: 1 - 10 of 539414 matches for " A. V. Macciò "
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Cold dark matter haloes in the Planck era: evolution of structural parameters for Einasto and NFW profiles
Aaron A. Dutton,Andrea V. Macciò
Physics , 2014, DOI: 10.1093/mnras/stu742
Abstract: We present the evolution of the structure of relaxed cold dark matter haloes in the cosmology from the Planck satellite. Our simulations cover 5 decades in halo mass, from dwarf galaxies to galaxy clusters. Due to the increased matter density and power spectrum normalization the concentration mass relation in the Planck cosmology has a 20 percent higher normalization at redshift z=0 compared to WMAP cosmology. We confirm that CDM haloes are better described by the Einasto profile; for example, at scales near galaxy half-light radii CDM haloes have significantly steeper density profiles than implied by NFW fits. There is a scatter of 0.2 dex in the Einasto shape parameter at fixed halo mass, adding further to the diversity of CDM halo profiles. The evolution of the concentration mass relation in our simulations is not reproduced by any of the analytic models in the literature. We thus provide a simple fitting formula that accurately describes the evolution between redshifts z=5 to z=0 for both NFW and Einasto fits. Finally, the observed concentrations and halo masses of spiral galaxies, groups and clusters of galaxies at low redshifts are in good agreement with our simulations, suggesting only mild halo response to galaxy formation on these scales.
Evidence for Early Filamentary Accretion from the Andromeda Galaxy's Thin Plane of Satellites
Tobias Buck,Andrea V. Macciò,Aaron A. Dutton
Physics , 2015, DOI: 10.1088/0004-637X/809/1/49
Abstract: Recently it has been shown that a large fraction of the dwarf satellite galaxies orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended and kinematically coherent planar structure. The presence of such a structure seems to challenge the current Cold Dark Matter paradigm of structure formation, which predicts a more uniform distribution of satellites around central objects. We show that it is possible to obtain a thin, extended, rotating plane of satellites resembling the one in Andromeda in cosmological collisionless simulations based on the Cold Dark Matter model. Our new high resolution simulations show a correlation between the formation time of the dark matter halo and the thickness of the plane of satellites. Our simulations have a high incidence of satellite planes as thin, extended, and as rich as the one in Andromeda and with a very coherent kinematic structure when we select high concentration/early forming halos. By tracking the formation of the satellites in the plane we show that they have been mainly accreted onto the main object along thin dark matter filaments at high redshift. Our results show that the presence of a thin, extended, rotating plane of satellites is not a challenge for the Cold Dark Matter paradigm, but actually supports one of the predictions of this paradigm related to the presence of filaments of dark matter around galaxies at high redshift.
The Star Formation and AGN luminosity relation: Predictions from a semi-analytical model
Thales A. Gutcke,Nikos Fanidakis,Andrea V. Macciò,Cedric Lacey
Physics , 2015, DOI: 10.1093/mnras/stv1205
Abstract: In a Universe where AGN feedback regulates star formation in massive galaxies, a strong correlation between these two quantities is expected. If the gas causing star formation is also responsible for feeding the central black hole, then a positive correlation is expected. If powerful AGNs are responsible for the star formation quenching, then a negative correlation is expected. Observations so far have mainly found a mild correlation or no correlation at all (i.e. a flat relation between star formation rate (SFR) and AGN luminosity), raising questions about the whole paradigm of "AGN feedback". In this paper, we report the predictions of the GALFORM semi-analytical model, which has a very strong coupling between AGN activity and quenching of star formation. The predicted SFR-AGN luminosity correlation appears negative in the low AGN luminosity regime, where AGN feedback acts, but becomes strongly positive in the regime of the brightest AGN. Our predictions reproduce reasonably well recent observations by Rosario et al., yet there is some discrepancy in the normalisation of the correlation at low luminosities and high redshifts. Though this regime could be strongly influenced by observational biases, we argue that the disagreement could be ascribed to the fact that GALFORM neglects AGN variability effects. Interestingly, the galaxies that dominate the regime where the observations imply a weak correlation are massive early-type galaxies that are subject to AGN feedback. Nevertheless, these galaxies retain high enough molecular hydrogen contents to maintain relatively high star formation rates and strong infrared emission.
The Plane Truth: Andromeda analog thin Planes of Satellites are not kinematical coherent structures
Tobias Buck,Aaron A. Dutton,Andrea V. Macciò
Physics , 2015,
Abstract: A large fraction of the dwarf satellite galaxies orbiting the Andromeda galaxy are surprisingly aligned in a thin, extended and seemingly kinematically coherent planar structure. Such a structure is not easily found in simulations based on the Cold Dark Matter model. Using 21 high resolution cosmological simulations based on this model we analyze in detail the kinematical structure of planes of satellites resembling the one observed around Andromeda when co-rotation is characterized by the line-of-sight velocity. At the same time, when co-rotation is inferred by the angular momenta of the satellites, the planes are in excellent agreement with the plane around the Milky Way. Furthermore, we find such planes to be common in our simulations. Investigation of the kinematics of the satellites in the plane reveals that the number of co-rotating satellites varies by 2 to 5 out of ~12 depending on the viewing angle. These variations are consistent with that obtained from a sample with random velocities. Using instead the clustering of angular momentum vectors of the satellites in the plane results in a better measure of kinematic coherence. Thus we conclude that the line-of-sight velocity as a proxy for the kinematical coherence of the plane is not a robust measure. Detailed analysis of the kinematics of our planes shows that the planes consist of ~30% chance aligned satellites. Tracking the satellites in the plane back in time reveals that the plane is a transient feature and not kinematically coherent as would appear at first sight.
The effect of Warm Dark Matter on galaxy properties: constraints from the stellar mass function and the Tully-Fisher relation
Xi Kang,Andrea V. Macciò,Aaron A. Dutton
Physics , 2012, DOI: 10.1088/0004-637X/767/1/22
Abstract: In this paper we combine high resolution N-body simulations with a semi analytical model of galaxy formation to study the effects of a possible Warm Dark Matter (WDM) component on the observable properties of galaxies. We compare three WDM models with a dark matter mass of 0.5, 0.75 and 2.0 keV, with the standard Cold Dark Matter case. For a fixed set of parameters describing the baryonic physics the WDM models predict less galaxies at low (stellar) masses, as expected due to the suppression of power on small scales, while no substantial difference is found at the high mass end. However these differences in the stellar mass function, vanish when different set of parameters are used to describe the (largely unknown) galaxy formation processes. We show that is possible to break this degeneracy between DM properties and the parameterization of baryonic physics by combining observations on the stellar mass function with the Tully-Fisher relation (the relation between stellar mass and the rotation velocity at large galactic radii as probed by resolved HI rotation curves). WDM models with a too warm candidate (m<0.75 keV) cannot simultaneously reproduce the stellar mass function and the Tully-Fisher relation. We conclude that accurate measurements of the galaxy stellar mass function and the link between galaxies and dark matter haloes down to the very low-mass end can give very tight constraints on the nature of DM candidates.
3D simulations of the early stages of AGN jets: geometry, thermodynamics and backflow
S. Cielo,V. Antonuccio-Delogu,A. V. Macciò,A. D. Romeo,J. Silk
Physics , 2013, DOI: 10.1093/mnras/stu161
Abstract: We investigate the interplay between jets from Active Galactic Nuclei (AGNs) and the surrounding InterStellar Medium (ISM) through full 3D, high resolution, Adaptive Mesh Refinement simulations performed with the FLASH code. We follow the jet- ISM system for several Myr in its transition from an early, compact source to an extended one including a large cocoon. During the jet evolution, we identify three major evolutionary stages and we find that, contrary to the prediction of popular theoretical models, none of the simulations shows a self-similar behavior. We also follow the evolution of the energy budget, and find that the fraction of input power deposited into the ISM (the AGN coupling constant) is of order of a few percent during the first few Myr. This is in broad agreement with galaxy formation models employing AGN feedback. However, we find that in these early stages, this energy is deposited only in a small fraction (< 1%) of the total ISM volume. Finally we demonstrate the relevance of backflows arising within the extended cocoon generated by a relativistic AGN jet within the ISM of its host galaxy, previously proposed as a mechanism for self-regulating the gas accretion onto the central object. These backflows tend later to be destabilized by the 3D dynamics, rather than by hydrodynamic (Kelvin- Helmholtz) instabilities. Yet, in the first few hundred thousand years, backflows may create a central accretion region of significant extent, and convey there as much as a few millions of solar masses.
The Redshift Evolution of LCDM Halo Parameters: Concentration, Spin, and Shape
J. C. Mu?oz-Cuartas,A. V. Macciò,S. Gottl?ber,A. A. Dutton
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17704.x
Abstract: We present a detailed study of the redshift evolution of dark matter halo structural parameters in a LambdaCDM cosmology. We study the mass and redshift dependence of the concentration, shape and spin parameter in Nbody simulations spanning masses from 10^{10} Msun/h to 10^{15} Msun/h and redshifts from 0 to 2. We present a series of fitting formulas that accurately describe the time evolution of the concentration-mass relation since z=2. Using arguments based on the spherical collapse model we study the behaviour of the scale length of the density profile during the assembly history of haloes, obtaining physical insights on the origin of the observed time evolution of the concentration mass relation. We also investigate the evolution with redshift of dark matter halo shape and its dependence on mass. Within the studied redshift range the relation between halo shape and mass can be well fitted by a power law. Finally we show that although for z=0 the spin parameter is practically mass independent, at increasing redshift it shows a increasing correlation with mass.
The response of dark matter haloes to elliptical galaxy formation: a new test for quenching scenarios
Aaron A. Dutton,Andrea V. Macciò,Gregory S. Stinson,Thales A. Gutcke,Camilla Penzo,Tobias Buck
Physics , 2015, DOI: 10.1093/mnras/stv1755
Abstract: We use cosmological hydrodynamical zoom-in simulations with the SPH code gasoline of four haloes of mass M_{200} \sim 10^{13}\Msun to study the response of the dark matter to elliptical galaxy formation. Our simulations include metallicity dependent gas cooling, star formation, and feedback from massive stars and supernovae, but not active galactic nuclei (AGN). At z=2 the progenitor galaxies have stellar to halo mass ratios consistent with halo abundance matching, assuming a Salpeter initial mass function. However by z=0 the standard runs suffer from the well known overcooling problem, overpredicting the stellar masses by a factor of > 4. To mimic a suppressive halo quenching scenario, in our forced quenching (FQ) simulations, cooling and star formation are switched off at z=2. The resulting z=0 galaxies have stellar masses, sizes and circular velocities close to what is observed. Relative to the control simulations, the dark matter haloes in the FQ simulations have contracted, with central dark matter density slopes d\log\rho/d\log r \sim -1.5, showing that dry merging alone is unable to fully reverse the contraction that occurs at z>2. Simulations in the literature with AGN feedback however, have found expansion or no net change in the dark matter halo. Thus the response of the dark matter halo to galaxy formation may provide a new test to distinguish between ejective and suppressive quenching mechanisms.
Non-linear weak lensing forecasts
Luciano Casarini,Giuseppe La Vacca,Luca Amendola,Silvio A. Bonometto,Andrea V. Macciò
Physics , 2011, DOI: 10.1088/1475-7516/2011/03/026
Abstract: We investigate the impact of non-linear corrections on dark energy parameter estimation from weak lensing probes. We find that using halofit expressions, suited to LCDM models, implies substantial discrepancies with respect to results directly obtained from N-body simulations, when w(z)\neq-1. Discrepancies appear strong when using models with w'(z=0)>0, as fiducial models; they are however significant even in the neighborhood of LCDM, where neglecting the degrees of freedom associated with the DE state equation can lead to a misestimate of the matter density parameter \Omega_m.
The Distribution of Satellites Around Central Galaxies in a Cosmological Hydrodynamical Simulation
Xuce Dong,Weipeng Lin,Xi Kang,Yang O. Wang,Aaron A. Dutton,Andrea V. Macciò
Physics , 2014, DOI: 10.1088/2041-8205/791/2/L33
Abstract: Observations have shown that the spatial distribution of satellite galaxies is not random, but rather is aligned with the major axes of central galaxies (CGs). The strength of the alignment is dependent on the properties of both the satellites and centrals. Theoretical studies using dissipationless N-body simulations are limited by their inability to directly predict the shape of CGs. Using hydrodynamical simulations including gas cooling, star formation, and feedback, we carry out a study of galaxy alignment and its dependence on the galaxy properties predicted directly from the simulations.We found that the observed alignment signal is well produced, as is the color dependence: red satellites and red centrals both show stronger alignments than their blue counterparts. The reason for the stronger alignment of red satellites is that most of them stay in the inner region of the dark matter halo where the shape of the CG better traces the dark matter distribution. The dependence of alignment on the color of CGs arises from the halo mass dependence, since the alignment between the shape of the central stellar component and the inner halo increases with halo mass. We also find that the alignment of satellites is most strongly dependent on their metallicity, suggesting that the metallicity of satellites, rather than color, is a better tracer of galaxy alignment on small scales. This could be tested in future observational studies.
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