1,721,198 research outputs found
ISOPHOT 95 μm observations in the Lockman Hole. The catalogue and an assessment of the source counts
No full textResolving the FIR/SMM Cosmic Background and thus Studying the High-Redshift Universe from Concordia Station
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Revisiting the infrared spectra of active galactic nuclei with a new torus emission model
No full textWe describe improved modelling of the emission by dust in a toroidal-like structure heated by a central illuminating source within active galactic nuclei (AGNs). We have chosen a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type 1 AGNs. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type 1 and type 2) sources using archival optical and infrared data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-infrared luminosity is found to be higher in type 1 sources, with all the type 2 requiring a substantial contribution from a circumnuclear starburst. Our results appear in agreement with the AGN unified scheme, because the distributions of key parameters of the torus models turn out to be compatible for type 1 and type 2 AGNs. Further support to the unification concept comes from comparison with medium-resolution infrared spectra of type 1 AGNs by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 μm, which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGNs characterized by high equatorial optical depths (AV~= 100), moderate sizes (Rmax < 100 pc) and very high covering factors (f~= 80 per cent) on average
The HerMES Local Luminosity Function
No full textWe exploit the Herschel Extragalactic Multi-Tiered Survey (HerMES) dataset along with ancillary multi-wavelength photometry and spectroscopy from the Spitzer Data Fusion to provide the most accurate determination to date of the local (0.02 < z < 0.5) Far-Infrared Luminosity and Star Formation Rate Function. We present and compare our results with model predictions as well as other multi-wavelength estimates of the local star formation rate density
The extragalactic background light revisited and the cosmic photon-photon opacity
Full text linkContext. In addition to its relevant astrophysical and cosmological significance, the extragalactic background light (EBL) is a fundamental source of opacity for cosmic high energy photons, as well as a limitation for the propagation of high-energy particles in the Universe.
Aims. We review our previously published determinations of the EBL photon density in the Universe and its evolution with cosmic time, in the light of recent surveys of IR sources at long wavelengths.
Methods. We exploit deep survey observations by the Herschel Space Observatory and the Spitzer telescope, matched to optical and near-IR photometric and spectroscopic data, to re-estimate number counts and luminosity functions longwards of a few microns, and the contribution of resolved sources to the EBL.
Results. These new data indicate slightly lower photon densities in the mid- and far-infrared and sub-millimeter compared to previous determinations. This implies slightly lower cosmic opacity for photon-photon interactions.
Conclusions. The new data do not modify previously published EBL modeling in the UV-optical and near-IR up to several microns, while reducing the photon density at longer wavelengths. This improved model of the EBL alleviates some tension that had emerged in the interpretation of the highest-energy TeV observations of local blazars, reducing the case for new physics beyond the standard model (like violations of the Lorenz Invariance, LIV, at the highest particle energies), or for exotic astrophysics, that had sometimes been called for to explain it. Applications of this improved EBL model on current data are considered, as well as perspectives for future instrumentation, the Cherenkov Telescope Array (CTA) in particular
GECO: Galaxy Evolution COde - A new semi-analytical model of galaxy formation
No full textAims. We present a new semi-analytical model of galaxy formation, GECO (Galaxy Evolution COde), designed to improve our understanding of when and how the processes of both star formation and galaxy assembly took place, by comparison with a wide variety of data about galaxy mass-function evolution and star-formation histories.
Methods. Our model is structured into a Monte Carlo algorithm based on the extended Press-Schechter theory, to represent the merging hierarchy of dark matter halos, and a set of analytic algorithms to treat the baryonic physics, including classical recipes for gas cooling, star-formation timescales, galaxy mergers, and supernova (SN) feedback. In addition to the galaxies, the parallel growth of BHs is followed in time, and their feedback on the hosting galaxies is modelled. We set the model free parameters by matching data on local stellar mass functions and the relation between galaxy bulge and black-hole mass at
z = 0.
Results. Based on these local boundary conditions, we investigate how data on the high-redshift universe constrain our understanding of the physical processes driving the evolution, focusing in particular on the assembly of stellar mass and the star-formation history of galaxies. Since both processes are currently strongly constrained by cosmological near- and far-IR surveys with the Spitzer Space Telescope, the basic physics of the
Λ CDM hierarchical clustering concept of galaxy formation can be effectively tested by us by comparison with the most reliable set of observables using a minimal number of free parameters.
Conclusions. Our investigation shows that when the timescales of star formation and mass assembly are studied as a function of dark matter halo mass and a given galaxy stellar mass, the “downsizing” fashion of star formation appears to be a natural outcome of the model, being reproduced even in the absence of the AGN feedback. In contrast, the stellar mass assembly history turns out to follow a more standard hierarchical pattern that is progressive with cosmic time, the more massive systems being assembled at later times mainly through dissipationless mergers
Local Benchmarks of Infrared Galaxy Evolution : the SWIRE-SDSS Database, Far-Infrared Local Luminosity Functions and Virtual Observatory Tools
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