11,791,650 research outputs found
A Stochastic Theory of the Hierarchical Clustering. II. Halo Progenitor Mass Function and Large-scale Bias
No full textWe generalize the stochastic theory of hierarchical clustering presented in Paper I by Lapi & Danese to derive the (conditional) halo progenitor mass function and the related large-scale bias. Specifically, we present a stochastic differential equation that describes fluctuations in the mass growth of progenitor halos of given descendant mass and redshift, as driven by a multiplicative Gaussian white noise involving the power spectrum and the spherical collapse threshold of density perturbations. We demonstrate that, as cosmic time passes, the noise yields an average drift of the progenitors toward larger masses, which quantitatively renders the expectation from the standard extended Press and Schechter (EPS) theory. We solve the Fokker-Planck equation associated with the stochastic dynamics, and obtain as an exact, stationary solution, the EPS progenitor mass function. Then we introduce a modification of the stochastic equation in terms of a mass-dependent collapse threshold modulating the noise, and solve analytically the associated Fokker-Planck equation for the progenitor mass function. The latter is found to be in excellent agreement with the outcomes of N-body simulations; even more remarkably, this is achieved with the same shape of the collapse threshold used in Paper I to reproduce the halo mass function. Finally, we exploit the above results to compute the large-scale halo bias, and find it in pleasing agreement with the N-body outcomes. All in all, the present paper illustrates that the stochastic theory of hierarchical clustering introduced in Paper I can describe effectively not only halos' abundance, but also their progenitor distribution and their correlation with the large-scale environment across cosmic times
Editorial [Hot Topic: Ulcerative Colitis: A Cinderella Story (Guest Editor: Silvio Danese)]
No full textSocrate a Copenaghen. Søren Kierkegaard e la Guldalder danese
No full textIl ruolo di S. Kierkegaard nel contesto della Guldalder danese e la peculiarità del suo linguaggio filosofico nel panorama scandinavo
Toward a tomographic analysis of the cross-correlation between planck cmb lensing and h-atlas galaxies
No full textINAF PRIN; ASI/INAF [2014-024-R.0]; INFN-INDARK initiative; Spanish MINECOBianchini, F., Lapi, A., Calabrese, M., Bielewicz, P., Gonzalez-Nuevo, J., Baccigalupi, C., Danese, L., Zotti, G.D., Bourne, N., Cooray, A., Dunne, L., Eales, S., Valiante, E
Statistics of dark matter halos in the excursion set peak framework
No full textWe derive approximated, yet very accurate analytical expressions for the abundance and clustering properties of dark matter halos in the excursion set peak framework; the latter relies on the standard excursion set approach, but also includes the effects of a realistic filtering of the density field, a mass-dependent threshold for collapse, and the prescription from peak theory that halos tend to form around density maxima. We find that our approximations work excellently for diverse power spectra, collapse thresholds and density filters. Moreover, when adopting a cold dark matter power spectra, a tophat filtering and a mass-dependent collapse threshold (supplemented with conceivable scatter), our approximated halo mass function and halo bias represent very well the outcomes of cosmological N-body simulations
Digitalizzazione – uno studio dei fattori propulsivi del diritto amministrativo danese
No full textL’A. affronta la problematica della digitalizzazione della pubblica amministrazione danese, esponendo i principi alla base dello sviluppo del diritto amministrativo danese: buona amministrazione, responsabilità e accountability; quindi, esamina le tendenze del diritto digitale dell’Unione Europea e le forme di protezione dei dati, della sicurezza informatica, dell’informazione e dell’A.I.The Author addresses the issue of the digitalisation of Danish public administration, exposing the principles underlying the development of Danish administrative law: good administration, responsibility and accountability. The author also examines trends in European Union digital law and types of data protection, cybersecurity, information, and artificial intelligence (A.I.)
Mass function of dormant black holes and the evolution of active galactic nuclei
No full textUnder the assumption that accretion on to massive black holes (BHs) powers active galactic nuclei (AGNs), the mass function (MF) of the BHs responsible for their past activity is estimated. For this, we take into account not only the activity related to the optically selected AGNs, but also that required to produce the hard X-ray background (HXRB), The MF of the massive dark objects (MDOs) in nearby quiescent galaxies is computed by means of the most recent results on their demography. The two mass functions match well under the assumption that the activity is concentrated in a single significant burst with lambda = L/L-Edd being a weakly increasing function of luminosity. This behaviour may be indicative of some level of recurrence and/or of accretion rates insufficient to maintain the Eddington rates in low-luminosity/low-redshift objects. Our results support the scenario in which the early phase of intense nuclear activity occurred mainly in early-type galaxies (E/S0) during the relatively short period in which they still had an abundant interstellar medium. Only recently, with the decline of the quasi-stellar object (QSO) luminosities, did the activity in late-type galaxies (Sa/Sab) become statistically significant
Correction to: Inflammatory bowel disease position statement of the Italian Society of Colorectal Surgery (SICCR): Crohn's disease (Techniques in Coloproctology, (2020), 24, 5, (421-448), 10.1007/s10151-020-02183-z)
No full textThe affiliation of the author Silvio Danese has been incorrectly published in the original publication
A Stochastic Theory of the Hierarchical Clustering. I. Halo Mass Function
No full textWe present a new theory for the hierarchical clustering of dark matter (DM) halos, based on stochastic differential equations, that constitutes a change of perspective with respect to existing frameworks (e.g., the excursion set approach); this work is specifically focused on the halo mass function. First, we present a stochastic differential equation that describes fluctuations in the mass growth of DM halos, as driven by a multiplicative white (Gaussian) noise dependent on the spherical collapse threshold and on the power spectrum of DM perturbations. We demonstrate that such a noise yields an average drift of the halo population toward larger masses, that quantitatively renders the standard hierarchical clustering. Then, we solve the Fokker–Planck equation associated to the stochastic dynamics, and obtain the Press & Schechter mass function as a (stationary) solution. Moreover, generalizing our treatment to a mass-dependent collapse threshold, we obtain an exact analytic solution capable of fitting remarkably well the N-body mass function over a wide range in mass and redshift. All in all, the new perspective offered by the theory presented here can contribute to a better understanding of the gravitational dynamics leading to the formation, evolution, and statistics of DM halos across cosmic times
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