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Before about 500 million years ago, most probably our planet experienced temporary snowball conditions, with continental and sea ices covering a large fraction of its surface. This points to a potential bistability of Earth's climate that can have at least two different (statistical) equilibrium states for the same external forcing (i.e. solar radiation). Here, we explore the probability of finding bistable climates in Earth-like exoplanets and consider the properties of planetary climates obtained by varying the semimajor orbital axis (thus, received stellar radiation), eccentricity and obliquity, and atmospheric pressure. To this goal, we use the Earth-like planet surface temperature model (ESTM), an extension of one-dimensional Energy Balance Models developed to provide a numerically efficient climate estimator for parameter sensitivity studies and long climatic simulations. After verifying that the ESTM is able to reproduce Earth climate bistability, we identify the range of parameter space where climate bistability is detected. An intriguing result of this work is that the planetary conditions that support climate bistability are remarkably similar to those required for the sustenance of complex, multicellular life on the planetary surface. The interpretation of this result deserves further investigation, given its relevance for the potential distribution of life in exoplanetary systems. [ABSTRACT FROM AUTHOR]

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 K- and 850-μm-selected galaxies (such as number counts, redshift distributions and luminosity functions) by combiningmorgana with the spectrophotometric modelgrasil. We find that it is possible to reproduce the K- and 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 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 ; 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 galaxies at ; 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. [ABSTRACT FROM AUTHOR]

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 µm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). The final map in each band was constructed by the co-addition of four independent rasters, registered using bright sources securely detected in all rasters, with the absolute astrometry being defined by a radio source detected at both 6.7 and 15 µm. We sought detections of bright sources in a circular region of radius 2.5 arcmin at the centre of each map, in a manner that simulations indicated would produce highly reliable and complete source catalogues using simple selection criteria. Merging source lists in the two bands yielded a catalogue of 35 distinct sources, which we calibrated photometrically using photospheric models of late-type stars detected in our data. We present extragalactic source count results in both bands, and discuss the constraints that they impose on models of galaxy evolution, given the volume of space sampled by this galaxy population. [ABSTRACT FROM AUTHOR]

We present results from a deep mid-infrared survey of the Hubble Deep Field South (HDF-S) region performed at 6.7 and 15 µm with the ISOCAM instrument on board the Infrared Space Observatory (ISO). We find reliable optical/near-infrared associations for 32 of the 35 sources detected in this field by Oliver et al. (Paper I): eight of them are identified as stars, one is definitely an active galactic nucleus (AGN), a second seems likely to be an AGN too, while the remaining 22 appear to be normal spiral or starburst galaxies. Using model spectral energy distributions (SEDs) of similar galaxies, we compare methods for estimating the star formation rates (SFRs) in these objects, finding that an estimator based on integrated (3-1000 µm) infrared luminosity reproduces the model SFRs best. Applying this estimator to model fits to the SEDs of our 22 spiral and starburst galaxies, we find that they are forming stars at rates of ∼ 1-100M...yr[sup -l], with a median value of ∼40M...yr[sup -1], assuming an Einstein-de Sitter universe with a Hubble constant of 50 km s[sup -1] Mpc[sup -1], and star formation taking place according to a Salpeter initial mass function (IMF) across the mass range 0.1-100M.... We split the redshift range 0.0 ≤ z ≤ 0.6 into two equal-volume bins to compute raw estimates of the star formation rate density, ...[sub *], contributed by these sources, assuming the same cosmology and IMF as above and computing errors based on estimated uncertainties in the SFRs of individual galaxies. We compare these results with other estimates of ...[sub *] made with the same assumptions, showing them to be consistent with the results of Flores et al. from their ISO survey of the CFRS 1415+52 field. However, the relatively small volume of our survey means that our ...[sub *] estimates suffer from a large sampling variance, implying that our results, by themselves, do not place tight constraints on the global mean star formation rate density. [ABSTRACT FROM AUTHOR]