International School for Advanced Studies

About: International School for Advanced Studies is a education organization based out in Trieste, Friuli-Venezia Giulia, Italy. It is known for research contribution in the topics: Galaxy & Dark matter. The organization has 3751 authors who have published 13433 publications receiving 588454 citations. The organization is also known as: SISSA & Scuola Internazionale Superiore di Studi Avanzati.

The Coevolution of Supermassive Black Holes and Massive Galaxies at High Redshift

Abstract: We exploit the recent, wide samples of far-infrared (FIR) selected galaxies followed up in X-rays and of X-ray/optically selected active galactic nuclei (AGNs) followed up in the FIR band, along with the classic data on AGNs and stellar luminosity functions at high redshift z gsim 1.5, to probe different stages in the coevolution of supermassive black holes (BHs) and host galaxies. The results of our analysis indicate the following scenario: (1) the star formation in the host galaxy proceeds within a heavily dust-enshrouded medium at an almost constant rate over a timescale lesssim 0.5-1 Gyr and then abruptly declines due to quasar feedback, over the same timescale; (2) part of the interstellar medium loses angular momentum, reaches the circum-nuclear regions at a rate proportional to the star formation, and is temporarily stored in a massive reservoir/proto-torus wherefrom it can be promptly accreted; (3) the BH grows by accretion in a self-regulated regime with radiative power that can slightly exceed the Eddington limit L/L Edd lesssim 4, particularly at the highest redshifts; (4) for massive BHs, the ensuing energy feedback at its maximum exceeds the stellar one and removes the interstellar gas, thus stopping the star formation and the fueling of the reservoir; (5) afterward, if the latter has retained enough gas, a phase of supply-limited accretion follows, exponentially declining with a timescale of about two e-folding times. We also discuss how the detailed properties and the specific evolution of the reservoir can be investigated via coordinated, high-resolution observations of star-forming, strongly lensed galaxies in the (sub-)mm band with ALMA and in the X-ray band with Chandra and the next-generation X-ray instruments.

The contribution of primordial binaries to the blue straggler population in 47 tucanae

Abstract: The recent observation (Ferraro et al. 2003b) of the blue str aggler population in 47 Tucanae gives the first detailed characterization of their spatial distribution i n the cluster over its entire volume. Relative to the light distribution, blue stragglers appear to be overabundant in the core and at large radii. The observed surface density profile shows a central peak, a zone of avoidance and a rise bey ond twenty core radii. In light of these findings we explored the evolution of blue stragglers mimicking their dynamics in a multi-mass King model for 47 Tucanae. We find that the observed spatial distribution can not be expl ained within a purely collisional scenario in which blue stragglers are generated exclusively in the core throu gh direct mergers. An excellent fit is obtained if we require that a sizable fraction of blue stragglers is generate d in the peripheral regions of the cluster inside primordial binaries that evolve in isolation experiencing mass-trans fer. Subject headings: stars: blue stragglers - binaries: general - globular clust ers: individual (47 Tuc)

Dwarf spheroidal galaxy kinematics and spiral galaxy scaling laws

Abstract: Kinematic surveys of the dwarf spheroidal (dSph) satellites of the Milky Way are revealing tantalising hints about the structure of dark matter (DM) haloes at the low-mass end of the galaxy luminosity function. At the bright end, modelling of spiral galaxies has shown that their rotation curves are consistent with the hypothesis of a Universal Rotation Curve whose shape is supported by a cored dark matter halo. In this paper, we investigate whether the internal kinematics of the Milky Way dSphs are consistent with the particular cored DM distributions which reproduce the properties of spiral gal axies. Although the DM densities in dSphs are typically almost two orders of magnitude higher than those found in (larger) disk systems, we find consistency between dSph kinematics an d Burkert DM haloes whose core radii r0 and central densitiesρ0 lie on the extrapolation of the scaling law seen in spiral galaxies: log ρ0≃α log r0 + const with 0.9< α< 1.1. We similarly find that the dSph data are consistent with the relation betweenρ0 and baryon scale length seen in spiral galaxies. While the origin of these scaling relations is unclear, the fi nding that a single DM halo profile is consistent with kinematic data in galaxies of widely varying size, luminosity and Hubble Type is important for our understanding of observed galaxies and must be accounted for in models of galaxy formation.

Covariant and gauge-independent perfect-fluid Robertson-Walker perturbations.

Abstract: In the preceding paper, covariant and gauge-invariant quantities were defined that characterize density inhomogeneities in an almost-uniform model universe in a transparent way. In this paper second-order propagation equations are derived for these quantities in the case of a general perfect fluid,'' and their properties examined. We do not use a harmonic decomposition in our definitions, but when such a decomposition is applied, our results are compatible with those obtained by Bardeen in his harmonically based gauge-invariant analysis. Our second-order equation enables a unified and transparent derivation of a series of results in the literature, without any ambiguity from choice of any particular gauge.