Cosmic Star Formation: a simple model of the SFRD(z)

We investigate the evolution of the cosmic star formation rate density (SFRD) from redshift z=20 to z=0 and compare it with the observational one by Madau and Dickinson derived from recent compilations of UV and IR data. The theoretical SFRD(z) and its evolution are obtained using a simple model which folds together the star formation histories of prototype galaxies designed to represent real objects of different morphological type along the Hubble sequence and the hierarchical growing of structures under the action of gravity from small perturbations to large scale objects in \Lambda-CDM cosmogony, i.e. the number density of dark matter halos N(M,z). Although the overall model is very simple and easy to set up, it provides results that well mimic those obtained from large scale N-body simulations of great complexity. The simplicity of our approach allows us to test different assumptions for the star formation law in galaxies, the effects of energy feedback from stars to interstellar gas and the efficiency of galactic winds, and also the effect of N(M,z). The result of our analysis is that in the framework of the hierarchical assembly of galaxies the so-called time-delayed star formation under plain assumptions mainly for the energy feedback and galactic winds can reproduce the observational SFRD(z).Comment: ApJ (accepted for publication

Sarcoma risk and dioxin emissions from incinerators and industrial plants: a population-based case-control study (Italy)

This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

On the Origin of the Fundamental Plane and Faber-Jackson Relations: Implications for the Star Formation Problem

We provide an explanation of the properties of the fundamental plane (FP) relation and its observed projections for a sample of nearby early-type galaxies (ETGs) in terms of a fine-tuning between the time-averaged star formation rate and their structural and dynamical characteristics. Their total V luminosity is linked with and the central velocity dispersion σ through the relation {log}(L)=0.48(+/- 0.06){log}( )+1.00 (+/- 0.13){log}(σ )+7.81(+/- 0.26), with an rms = 0.215 (R = 0.64 and P-16). This fine-tuning permits us to obtain the FP in terms of two distinct “virtual planes” in the {log}({R}e){--}{log}(e> ){--}{log}(σ ) space. The first one (the virial plane; VP) represents the total galaxy mass derived from the scalar virial theorem and the mass-to-light ratio M/L, while the second plane comes from the relation L={L}0\prime {σ }-2, where {L}0\prime is a parameter connected with . This is a mathematically convenient way for expressing the independence of the galaxy light from the virial equilibrium. Each galaxy in the {log}({R}e){--}{log}(e> ){--}{log}(σ ) space is identified by the intersection of these two planes. A posteriori, we show that the properties of the FP (tilt and scatter) and the zone of exclusion visible in the FP projections are consequences of this fine-tuning. The link between the FP properties and the SFR of galaxies provides a new view of the star formation phenomenon. The star formation history of an unperturbed galaxy seems to be driven by the initial conditions in the protogalaxies and is regulated across cosmic epochs by the variation of the main galaxy parameters (mass, luminosity, structural shape, and velocity dispersion)

Pre-main-sequence stars in the stellar association N 11 in the Large Magellanic Cloud: clustering properties

AbstractMagellanic Clouds are of extreme importance to study the star-formation process in low-metallicity environments. Here, we discuss the clustering properties of the pre-main-sequence candidates and young embedded stellar objects in N 11, located in the Large Magellanic Cloud. Deep archival HST/ACS photometry is used to derive color–magnitude diagrams of the associations in N 11 and of the foreground field population. These data are complemented by archival infrared Spitzer data which allow detection of young embedded stellar objects. The spatial distribution of the pre-main-sequence candidates and young embedded stellar objects is discussed. The degree of clustering is derived using the minimal-spanning-tree method. No significant difference is found in clustering degree of young blue main-sequence stars and faint pre-main-sequence candidates, suggesting that they might be part of the same formation process.</jats:p

The coloured areas indicate the LHUs studied; (small box: Italy, Veneto Region, province of Venice)

<p><b>Copyright information:</b></p><p>Taken from "Sarcoma risk and dioxin emissions from incinerators and industrial plants: a population-based case-control study (Italy)"</p><p>http://www.ehjournal.net/content/6/1/19</p><p>Environmental Health 2007;6():19-19.</p><p>Published online 16 Jul 2007</p><p>PMCID:PMC1948886.</p><p></p

Trend by year of the emission levels of the incinerators and industrial plants (I-TEQ gr/s)

<p><b>Copyright information:</b></p><p>Taken from "Sarcoma risk and dioxin emissions from incinerators and industrial plants: a population-based case-control study (Italy)"</p><p>http://www.ehjournal.net/content/6/1/19</p><p>Environmental Health 2007;6():19-19.</p><p>Published online 16 Jul 2007</p><p>PMCID:PMC1948886.</p><p></p