Two phase galaxy formation: The Evolutionary Properties of Galaxies

We use our model for the formation and evolution of galaxies within a two-phase galaxy formation scenario, showing that the high-redshift domain typically supports the growth of spheroidal systems, whereas at low redshifts the predominant baryonic growth mechanism is quiescent and may therefore support the growth of a disc structure. Under this framework we investigate the evolving galaxy population by comparing key observations at both low and high-redshifts, finding generally good agreement. By analysing the evolutionary properties of this model, we are able to recreate several features of the evolving galaxy population with redshift, naturally reproducing number counts of massive star-forming galaxies at high redshifts, along with the galaxy scaling relations, star formation rate density and evolution of the stellar mass function. Building upon these encouraging agreements, we make model predictions that can be tested by future observations. In particular, we present the expected evolution to z=2 of the super-massive black hole mass function, and we show that the gas fraction in galaxies should decrease with increasing redshift in a mass, with more and more evolution going to higher and higher masses. Also, the characteristic transition mass from disc to bulge dominated system should decrease with increasing redshift.Comment: 15 pages, 11 figures. Version polished for publication in MNRA

The essential signature of a massive starburst in a distant galaxy

Observations of carbon monoxide (CO) emission in high redshift (z>2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus (AGN) powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the AGN, or from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds; gas densities are n(H2)>105 cm-3 in the cores. Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations is at a much lower density. In galaxies in the local Universe, the HCN(J=1-0) line is an effective tracer of the high-density molecular gas. Here we report observations of HCN emission in the early Universe from the infrared luminous 'Cloverleaf' quasar (at a redshift z=2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst that contributes, together with the AGN it harbors, to its high infrared luminosity.Comment: PDF pape

Modelling the radio to X-ray SED of galaxies

We present our model to interpret the SED of galaxies. The model for the UV to sub-mm SED is already well established (Silva et al 1998). We remind here its main features and show some applications. Recently we have extended the model to the radio range (Bressan et al 2001), and we have started to include the X-ray emission from the stellar component.Comment: 4 pages, to be published in "The link between stars and cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico, by Kluwer, eds. M. Chavez, A. Bressan, A. Buzzoni, and D. Mayy

Evolution and role of mergers in the BCG-cluster alignment. A view from cosmological hydrosimulations

Contradictory results have been reported on the time evolution of the alignment between clusters and their brightest cluster galaxy (BCG). We study this topic by analysing cosmological hydrosimulations of 24 massive clusters with M-200 vertical bar z=0 greater than or similar to 10(15) M-circle dot, plus 5 less massive with 1 x 10(14) less than or similar to M-200 vertical bar z=0 less than or similar to 7 x 10(14) M (circle dot), which have already proven to produce realistic BCG masses. We compute the BCG alignment with both the distribution of cluster galaxies and the dark matter (DM) halo. At redshift z = 0, the major axes of the simulated BCGs and their host cluster galaxy distributions are aligned on average within 20 degrees. The BCG alignment with the DM halo is even tighter. The alignment persists up to z less than or similar to 2 with no evident evolution. This result continues, although with a weaker signal, when considering the projected alignment. The cluster alignment with the surrounding distribution of matter (3R(200)) is already in place at z similar to 4 with a typical angle of 35., before the BCG-cluster alignment develops. The BCG turns out to be also aligned with the same matter distribution, albeit always to a lesser extent. These results taken together might imply that the BCG-cluster alignment occurs in an outside-in fashion. Depending on their frequency and geometry, mergers can promote, destroy or weaken the alignments. Clusters that do not experience recent majormergers are typically more relaxed and aligned with their BCG. In turn, accretions closer to the cluster elongation axis tend to improve the alignment as opposed to accretions closer to the cluster minor axis

On Semiclassical Limits of String States

We explore the relation between classical and quantum states in both open and closed (super)strings discussing the relevance of coherent states as a semiclassical approximation. For the closed string sector a gauge-fixing of the residual world-sheet rigid translation symmetry of the light-cone gauge is needed for the construction to be possible. The circular target-space loop example is worked out explicitly.Comment: 12 page

The dusty SF history of high-z galaxies, modelling tools and future prospects

We summarize recent advances in the determination of the cosmic history of star formation and other properties of high-z galaxies, and the relevance of this information in our understanding of the formation of structures. We emphasize the importance of dust reprocessing in the high--z universe, as demonstrated in particular by IR and sub-mm data. This demand a panchromatic approach to observations and suitable modelling tools. We spend also some words on expectations from future instruments

The Formation and Evolution of the First Massive Black Holes

The first massive astrophysical black holes likely formed at high redshifts (z>10) at the centers of low mass (~10^6 Msun) dark matter concentrations. These black holes grow by mergers and gas accretion, evolve into the population of bright quasars observed at lower redshifts, and eventually leave the supermassive black hole remnants that are ubiquitous at the centers of galaxies in the nearby universe. The astrophysical processes responsible for the formation of the earliest seed black holes are poorly understood. The purpose of this review is threefold: (1) to describe theoretical expectations for the formation and growth of the earliest black holes within the general paradigm of hierarchical cold dark matter cosmologies, (2) to summarize several relevant recent observations that have implications for the formation of the earliest black holes, and (3) to look into the future and assess the power of forthcoming observations to probe the physics of the first active galactic nuclei.Comment: 39 pages, review for "Supermassive Black Holes in the Distant Universe", Ed. A. J. Barger, Kluwer Academic Publisher

Influence of GB virus C on IFN-γ and IL-2 production and CD38 expression in T lymphocytes from chronically HIV-infected and HIV-HCV-co-infected patients

This study was designed to assess the effect of GB virus (GBV)-C on the immune response to human immunodeficiency virus (HIV) in chronically HIV-infected and HIV- hepatitis C virus (HCV)-co-infected patients undergoing antiretroviral therapy. A cohort of 159 HIV-seropositive patients, of whom 52 were HCV-co-infected, was included. Epidemiological data were collected and virological and immunological markers, including the production of interferon gamma (IFN-γ) and interleukin (IL)-2 by CD4, CD8 and Tγδ cells and the expression of the activation marker, CD38, were assessed. A total of 65 patients (40.8%) presented markers of GBV-C infection. The presence of GBV-C did not influence HIV and HCV replication or TCD4 and TCD8 cell counts. Immune responses, defined by IFN-γ and IL-2 production and CD38 expression did not differ among the groups. Our results suggest that neither GBV-C viremia nor the presence of E2 antibodies influence HIV and HCV viral replication or CD4 T cell counts in chronically infected patients. Furthermore, GBV-C did not influence cytokine production or CD38-driven immune activation among these patients. Although our results do not exclude a protective effect of GBV-C in early HIV disease, they demonstrate that this effect may not be present in chronically infected patients, who represent the majority of patients in outpatient clinics.Universidade Federal de São Paulo (UNIFESP) Laboratório de Virologia e Imunologia Disciplina de InfectologiaFleury Medicina DiagnósticaUNIFESP, Laboratório de Virologia e Imunologia Disciplina de InfectologiaSciEL

THICK TORI AROUND ACTIVE GALACTIC NUCLEI - A COMPARISON OF MODEL PREDICTIONS WITH OBSERVATIONS OF THE INFRARED CONTINUUM AND SILICATE FEATURES

The continuum expected from active galactic nuclei (AGN) surrounded by thick tori is compared to the data available for a sample of optically selected Seyfert 1 galaxies. The optical and near-IR nuclear fluxes have previously been derived for these objects, and hence the spectral energy distributions (SEDs) of their active nuclei can be analysed. We perform detailed calculations of the 0.1 to 1000 mum SEDs for AGN surrounded by dust tori with different opening angles. The dust mixture is mimicked by using three silicate and three graphite grains of different sizes. The radiative transfer equation for a cloud having azimuthal symmetry and containing a mixture of dust grains is solved by means of a numerical code that takes absorption, emission and scattering into account. We discuss the optimization of the free parameters by comparing the spectra predicted by the code to available data. The general absence of the silicate emission feature at about 10 mum in the spectra of broad-line AGN and the general presence of the 10-mum silicate absorption feature in narrow-line AGN are addressed. The ensuing constraints are discussed. We show that models of thick tori extending up to a few hundred parsecs in which physical processes such as shocks significantly reduce the silicate grain abundance within the first few tens of parsecs are fully consistent with available broad-band data and high-resolution IR spectra of Seyfert 1 and 2 nuclei