We present models of photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included with particular care. A chemical evolution code follows the star formation rate, the gas fraction and the metallicity, basic ingredients for the stellar population synthesis. The latter is performed with a grid of integrated spectra of simple stellar populations (SSP) of different ages and metallicities, in which the effects of dusty envelopes around asymptotic giant branch (AGB) stars are included. The residual fraction of gas in the galaxy is divided into two phases: the star forming molecular clouds and the diffuse medium. The relative amount is a model parameter. The molecular gas is sub-divided into clouds of given mass and radius: it is supposed that each SSP is born within the cloud and progressively escapes it. The emitted spectrum of the star forming molecular clouds is computed with a radiative transfer code. The diffuse dust emission (cirrus) is derived by describing the galaxy as an axially symmetric system, in which the local dust emissivity is consistently calculated as a function of the local field intensity due to the stellar component. Effects of very small grains, subject to temperature fluctuations, as well as polycyclic aromatic hydrocarbons (PAH) are included.The model is compared and calibrated with available data of normal and starburst galaxies in the local universe, in particular new broad-band and spectroscopic ISO observations. It will be a powerful tool to investigate the star formation, the initial mass function (IMF), supernovae rate (SNR) in nearby starbursts and normal galaxies, as well as to predict the evolution of luminosity functions of different types of galaxies at wavelengths covering four decades.

We estimate the contribution of AGNs and of their host galaxies to the infrared background. We use the luminosity function and evolution of AGNs recently determined by the hard X-ray surveys, and new Spectral Energy Distributions connecting the X-ray and the infrared emission, divided in intervals of absorption. These two ingredients allow us to determine the contribution of AGNs to the infrared background by using mostly observed quantities, with only minor assumptions. We obtain that AGN emission contributes little to the infrared background ($<$5% over most of the infrared bands), implying that the latter is dominated by star formation. However, AGN host galaxies may contribute significantly to the infrared background, and more specifically 10--20% in the 1--20$\mu$m range and $\sim$5% at $\lambda<60\mu m$. We also give the contribution of AGNs and of their host galaxies to the source number counts in various infrared bands, focusing on those which will be observed with Spitzer. We also report a significant discrepancy between the expected contribution of AGN hosts to the submm background and bright submm number counts with the observational constraints. We discuss the causes and implications of this discrepancy and the possible effects on the Spitzer far-IR bands.Comment: to appear in MNRAS, replaced with accepted version, paper shortened, results unchange

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In order to gain insight into the physical mechanisms leading to the formation of stars and their assembly in galaxies, we compare the predictions of the MOdel for the Rise of GAlaxies aNd Active nuclei (MORGANA) to the properties of Kand 850-μm-selected galaxies (such as number counts, redshift distributions and luminosity functions) by combining MORGANA with the spectrophotometric model GRASIL. We find that it is possible to reproduce the Kand 850-μm-band data sets at the same time and with a standard Salpeter initial mass function, and ascribe this success to our improved modelling of cooling in DM haloes. We then predict that massively star-forming discs are common at z ∼ 2 and dominate the star formation rate, but most of them merge with other galaxies within ∼100 Myr. Our preferred model produces an overabundance of bright galaxies at z < 1; this overabundance might be connected to the build-up of the diffuse stellar component in galaxy clusters, as suggested by Monaco et al., but a naive implementation of the mechanism suggested in that paper does not produce a sufficient slowdown of the evolution of these objects. Moreover, our model overpredicts the number of 10 10 -10 11 M galaxies at z ∼ 1; this is a common behaviour of theoretical models as shown by Fontana et al.. These findings show that, while the overall build-up of the stellar mass is correctly reproduced by galaxy formation models, the 'downsizing' trend of galaxies is not fully reproduced yet. This hints to some missing feedback mechanism in order to reproduce at the same time the formation of both the massive and the small galaxies.

We have investigated the properties of a complete K-band selected sample of 35 elliptical and S0 galaxies brighter than K = 20 m .15 in the Hubble Deep Field, as representative of the field galaxy population. This sample has been derived from deep K-band image by the KPNO-IRIM camera, by applying a rigorous morphological classification scheme based on quantitative analyses of the surface brightness profiles. The completeness of the sample is proven by a careful evaluation of all biasing effects inherent in the automated selection procedure. Fifteen objects have spectroscopic redshifts, while for the remaining twenty a photometric redshift is estimated from a seven-colour broad-band spectrum (including 4 HST and 3 near-IR bands). This dataset, based on public archives from HST and from deep observations at Kitt-Peak and Hawaii, is unique as for the morphological information, and for the photometric -2and spectroscopic coverage. The broad-band spectra of the sample galaxies, together with a few basic assumptions about the IMF and the stellar evolutionary paths, allow us to date their dominant stellar populations. The majority of bright early-type galaxies in this field are found at redshifts z ∼ < 1.3 to display colors indicative of a fairly wide range of ages (typically 1.5 to 3 Gyrs). Because of the different cosmological timescales, the star-formation history depends to some extent on the assumed value for the cosmological deceleration parameter: we find that the major episodes of star-formation building up typical M ⋆ galaxies have taken place during a wide redshift interval 1 < z < 4 for q 0 =0.5, which becomes 1 < z < 3 for q 0 =0.15. There seems to be a tendency for lower-mass (M < 5 10 10 M ⊙ ) systems to have their bulk of SF protracted to lower redshifts. Our estimated galactic masses, for a Salpeter IMF, are found in the range from a few ∼ 10 9 M ⊙ to a few 10 11 M ⊙ already at z ≃ 1. So the bright end of the E/S0 population is mostly in place by that cosmic epoch, with space densities, masses and luminosities consistent with those of the local field E/S0 population. We argue that the strong decrease of the comoving mass density of early-type galaxies found by some authors already by z ≃ 1 might be due to improper color classification, since these objects are usually found to display blue young populations mixed with old red stars. Instead, what distinguishes the present sample is a remarkable absence of objects at z > 1.3, which should be detectable during the luminous star-formation phase expected to happen at these redshifts. Obvious solutions are a) that the merging events triggering the SF imply strongly perturbed morphologies which prevent selecting them by our morphological classification filter, or b) that a dust-polluted ISM obscures the (either continuous or episodic) events of star-formation, after which gas consumption (or a galactic wind) cleans up the galaxy. We conclude that the likely solution is a combination thereof, i.e. a set of dust-enshrouded merging-driven starbursts occurring duri...

It has recently been shown that galaxy formation models within the Λ cold dark matter cosmology predict that, compared to the observed population, small galaxies (with stellar masses <1011 M⊙) form too early, are too passive since z∼ 3 and host too old stellar populations at z= 0. We then expect an overproduction of small galaxies at z≳ 4 that should be visible as an excess of faint Lyman‐break galaxies. To check whether this excess is present, we use the morgana galaxy formation model and grasil spectrophotometric + radiative transfer code to generate mock catalogues of deep fields observed with Hubble Space Telescope Advanced Camera for Surveys. We add observational noise and the effect of Lyman α emission, and perform colour–colour selections to identify Lyman‐break galaxies. The resulting mock candidates have plausible properties that closely resemble those of observed galaxies. We are able to reproduce the evolution of the bright tail of the luminosity function of Lyman‐break galaxies (with a possible underestimate of the number of the brightest i‐dropouts), but uncertainties and degeneracies in dust absorption parameters do not allow to give strong constraints to the model. Besides, our model shows a clear excess with respect to observations of faint Lyman‐break galaxies, especially of z850∼ 27V‐dropouts at z∼ 5. We quantify the properties of these ‘excess’ galaxies and discuss the implications: these galaxies are hosted in dark matter haloes with circular velocities in excess of 100 km s−1, and their suppression may require a deep rethinking of stellar feedback processes taking place in galaxy formation.

As a contribution to the study of the habitability of extrasolar planets, we implemented a 1-D Energy Balance Model (EBM), the simplest seasonal model of planetary climate, with new prescriptions for most physical quantities. Here we apply our EBM to investigate the surface habitability of planets with an Earth-like atmospheric composition but different levels of surface pressure. The habitability, defined as the mean fraction of the planet's surface on which liquid water could exist, is estimated from the pressure-dependent liquid water temperature range, taking into account seasonal and latitudinal variations of surface temperature. By running several thousands of EBM simulations we generated a map of the habitable zone (HZ) in the plane of the orbital semi-major axis, a, and surface pressure, p, for planets in circular orbits around a Sun-like star. As pressure increases, the HZ becomes broader, with an increase of 0.25 AU in its radial extent from p=1/3 bar to p=3 bar. At low pressure, the habitability is low and varies with a; at high pressure, the habitability is high and relatively constant inside the HZ. We interpret these results in terms of the pressure dependence of the greenhouse effect, the efficiency of horizontal heat transport, and the extent of the liquid water temperature range. Within the limits discussed in the paper, the results can be extended to planets in eccentric orbits around non-solar type stars. The main characteristics of the pressure-dependent HZ are modestly affected by variations of planetary properties, particularly at high pressure.

We present the redshift distribution of the Submillimetre Common‐User Bolometer Array (SCUBA) Half Degree Survey (SHADES) galaxy population based on the rest‐frame radio–mm–far‐infrared (FIR) colours of 120 robustly detected 850 μm sources in the Lockman Hole East (LH) and Subaru XMM–Newton Deep Field (SXDF). The redshift distribution derived from the full spectral energy distribution (SED) information is shown to be narrower than that determined from the radio–sub‐mm spectral index, as more photometric bands contribute to a higher redshift accuracy. The redshift distribution of sources derived from at least two photometric bands peaks at z≈ 2.4 and has a near‐Gaussian distribution, with 50 per cent (interquartile range) of sources at z= 1.8–3.1. We find a statistically significant difference between the measured redshift distributions in the two fields; the SXDF peaking at a slightly lower redshift (median z≈ 2.2) than the LH (median z≈ 2.7), which we attribute to the noise properties of the radio observations. We demonstrate, however, that there could also be field‐to‐field variations that are consistent with the measured differences in the redshift distributions and, hence, that the incomplete area observed by SHADES with SCUBA, despite being the largest sub‐mm survey to date, may still be too small to fully characterize the bright sub‐mm galaxy population. Finally, we present a brief comparison with the predicted, or assumed, redshift distributions of sub‐mm galaxy formation and evolution models, and we derive the contribution of these SHADES sources and the general sub‐mm galaxy population to the star formation rate density at different epochs.