Extragalactic Source Counts in the Spitzer 24-micron Band: What Do We Expect From ISOCAM 15-micron Data and Models?

The comparison between the new Spitzer data at 24 micron and the previous ISOCAM data at 15 micron is a key tool to understand galaxy properties and evolution in the infrared and to interpret the observed number counts, since the combination of Spitzer with the ISO cosmological surveys provides for the first time the direct view of the Universe in the Infrared up to z~2. We present the prediction in the Spitzer 24-micron band of a phenomenological model for galaxy evolution derived from the 15-micron data. Without any ``a posteriori'' update, the model predictions seem to agree well with the recently published 24-micron extragalactic source counts, suggesting that the peak in the 24-micron counts is dominated by ``starburst'' galaxies like those detected by ISOCAM at 15 micron, but at higher redshifts (1 < z < 2 instead of 0.5 < z < 1.5).Comment: 8 pages: 4 pages of main text + 5 postscript figures, use aastex. Accepted for publication in ApJL. Replaced with the proof version (added missing references and corrected a few sentences

The star formation rate cookbook at 1 < z < 3: Extinction-corrected relations for UV & [OII]{\lambda}3727 luminosities

We use a spectroscopic sample of 286 star-forming galaxies (SFGs) at 1<z<3 from the GMASS survey to study different star formation rate (SFR) estimators. Infrared (IR) data are used to derive empirical calibrations to correct ultraviolet (UV) and [OII]{\lambda}3727 luminosities for dust extinction and dust-corrected estimates of SFR. In the selection procedure we fully exploit the available spectroscopic information. On the basis of three continuum indices, we are able to identify and exclude from the sample galaxies in which old stellar populations might bring a non-negligible contribution to IR luminosity (LIR) and continuum reddening. Using Spitzer-MIPS and Herschel-PACS data we derive LIR for two-thirds of our sample. The LIR/LUV ratio is used as a probe of effective attenuation (AIRX) to search for correlations with continuum and spectroscopic features. The relation between AIRX and UV continuum slope ({\beta}) was tested for our sample and found to be broadly consistent with the literature results at the same redshift, though with a larger dispersion with respect to UV-selected samples. We find a correlation between the rest-frame equivalent width (EW) of the [OII]{\lambda}3727 line and {\beta}, which is the main result of this work. We therefore propose the [OII]{\lambda}3727 line EW as a dust attenuation probe and calibrate it through AIRX, though the assumption of a reddening curve is still needed to derive the actual attenuation towards the [OII]{\lambda}3727 line. We tested the issue of differential attenuation towards stellar continuum and nebular emission: our results are in line with the traditional prescription of extra attenuation towards nebular lines. A set of relations is provided that allows the recovery of the total unattenuated SFR from UV and [OII]{\lambda}3727 luminosities. (Abridged)Comment: Accepted for publication in A&A; 20 pages, 19 figures, 5 table

Vitiligo: What’s old, what’s new

Vitiligo is an acquired pigmentary disorder afflicting 0.5-2% of the world population for both sexes and all races with a capricious and unpredictable course. It has a complex etiology and varies in its manifestation, progression and response to treatment. Even if the precise aetiology and pathobiology of the disease are complex and still debated, recent evidence supports that vitiligo is a T CD8+ cell-mediated autoimmune disease triggered by oxidative stress. To date no clinical, biological and histological criteria allow us to establish the prognosis with certainty. The choice of the best therapy for adult and childhood vitiligo is based on various factors, such as the patient’s age, psychological condition and expectations, distribution and extension of skin lesions, type of vitiligo (stable or not) and availability and cost of therapeutic options. Since vitiligo has a deep psychological impact on patients and their quality of life, treating the disease is very important. As dermatologists, we have important goals in the treatment of vitiligo patients: stabilization of the disease progression, repigmentation of the lesions and especially the persistence of the aforementioned repigmentation. Although several medical and surgical therapeutic options have been proposed, no definite cure has yet been developed and the long-term persistence of repigmentation is unpredictable. We review the different therapeutic options with particular attention on the recurrence rate

SPRITZ is sparkling: Simulated CO and [C II] luminosities

Aims. We present a new prediction for the luminosity functions (LFs) of the [C II] line at 158 mu M, of the CO lines from J = 0 to J = 24, and of the molecular gas mass density up to z = 10, using the Spectro-Photometric Realisations of Infrared-selected Targets at all-z (SPRITz) simulation.Methods. We update the state-of-the-art phenomenological simulation SPRITZ to include both the CO (J &lt;= 24) and the [C II] line luminosities. This has been performed using different empirical and theoretical relations to convert the total infrared luminosity (or star formation rate, SFR) to the [C II] or CO luminosity. The resulting line LFs were compared for validation with a large set of observations available in the literature. We then used the derived CO and [C II] line luminosities to estimate the molecular gas mass density and compare it with available observations.Results. The CO and [C II] LFs presented here are in good agreement with all the available observations. In particular, the best results for [C II] are obtained deriving the [C II] luminosity directly from the SFR, but considering a dependence of this relation on the gas metallicity. For all the CO LFs, the estimates favoured by the data are derived considering different relations, depending on the ionisation mechanism dominating each galaxy, namely star formation or active galactic nuclei, and, moreover, by deriving the J &gt;= 4 CO lines directly from the [C II] luminosity. However, further data are necessary to fully distinguish between models. Finally, the best agreements with observations of the molecular gas mass density are derived by converting the [C II] luminosity to H-2 mass, using a [C II]-to-H-2 conversion similar to 130 M-circle dot/L-circle dot. All the line LFs, useful for planning and interpreting future observations, are made publicly available

Simulating the infrared sky with a S PRITZ

Aims. Current hydrodynamical and semi-empirical simulations of galaxy formation and evolution have difficulties in reproducing the number densities of infrared-detected galaxies. Therefore, a phenomenological simulation tool that is new and versatile is necessary to reproduce current and predict future observations at infrared (IR) wavelengths. Methods. In this work we generate simulated catalogues starting from the Herschel IR luminosity functions of different galaxy populations to consider different populations of galaxies and active galactic nuclei (AGN) in a consistent way. We associated a spectral energy distribution and physical properties, such as stellar mass, star formation rate, and AGN contribution, with each simulated galaxy using a broad set of empirical relations. We compared the resulting simulated galaxies, extracted up to z = 10, with a broad set of observational relations. Results. Spectro-Photometric Realisations of IR-Selected Targets at all-z (SPRITZ) simulations allow us to obtain, in a fully consistent way, simulated observations for a broad set of current and future facilities with photometric capabilities as well as low-resolution IR spectroscopy, such as the James Webb Space Telescope (JWST) or the Origin Space Telescope (OST). The derived simulated catalogue contains galaxies and AGN that by construction reproduce the observed IR galaxy number density, but this catalogue also agrees with the observed number counts from UV to far-IR wavelengths, the observed stellar mass function, the star formation rate versus stellar mass plane, and the luminosity function from the radio to X-ray wavelengths. The proposed simulation is therefore ideal to make predictions for current and future facilities, in particular, but not limited to, those operating at IR wavelengths

Simulating the infrared sky with a Spritz

Current hydrodynamical and semi-empirical simulations of galaxy formation and evolution have difficulties in reproducing the number densities of IR-detected galaxies. Therefore, a versatile, phenomenological new simulation tool is necessary to reproduce current and predict future observations at IR wavelengths. In this work we generate simulated catalogues starting from the Herschel infrared luminosity functions of different galaxy populations, in order to consider in a consistent way different populations of galaxies and active galactic nuclei. We associated a spectral energy distribution and physical properties, such as stellar mass, star-formation-rate and AGN contribution, to each simulated galaxy using a broad set of empirical relations. We compare the resulting simulated galaxies, extracted up to z$=$10, with a broad set of observational relations. The Spectro-Photometric Realisations of Infrared-selected Targets at all-z (SPRITZ) simulation will allow us to obtain in a fully consistent way simulated observations for a broad set of current and future facilities with photometric capabilities as well as low-resolution IR spectroscopy, like the James Webb Space Telescope (JWST) or the Origin Space Telescope (OST). The derived simulated catalogue contains galaxies and active galactic nuclei that by construction reproduce the observed IR galaxy number density, but it is also in agreement with the observed number counts from UV to far-IR wavelengths, the observed stellar mass function, the star-formation-rate vs. stellar mass plane and the luminosity function from the radio to the X-ray. The proposed simulation is therefore ideal to make predictions for current and future facilities, in particular, but not limited to, those operating at IR wavelengths. The SPRITZ simulation will be publicly available.Comment: Accepted for publication in A&A, 32 pages, 30 figure

Eddington accreting black holes in the epoch of reionization

The evolution of the luminosity function (LF) of active galactic nuclei (AGNs) at redshift z ≳ 5 represents a key constraint to understand their contribution to the ionizing photon budget necessary to trigger the last phase transition in the Universe, i.e. the epoch of reionization. Recent searches for bright high-z AGNs suggest that the space densities of this population at z > 4 have to be revised upwards, and spark new questions about their evolutionary paths. Gas accretion is the key physical mechanism to understand both the distribution of luminous sources and the growth of central supermassive black holes (SMBHs). In this work, we model the high-z AGN-LF assuming that high-z luminous AGNs shine at their Eddington limit: We derive the expected evolution as a function of the ‘duty cycle’ (fdc), i.e. the fraction of lifetime that a given SMBH spends accreting at the Eddington rate. Our results show that intermediate values (fdc ≃ 0.1) predict the best agreement with the ionizing background and photoionization rate, but do not provide enough ionizing photons to account for the observed evolution of the hydrogen neutral fraction. Smaller values (fdc≲ 0.05) are required for AGNs to be the dominant population responsible for hydrogen reionization in the early Universe. We then show that this low-fdc evolution can be reconciled with the current constraints on helium reionization, although it implies a relatively large number of inactive SMBHs at z ≳ 5, in tension with SMBH growth models based on heavy seeding

Counting individual galaxies from deep 24-μm Spitzer surveys

We address the question of how to deal with confusion-limited surveys in the mid-infrared (MIR) domain by using information from shorter-wavelength observations over the same sky regions. Such information, once applied to apparently extended MIR sources, which are indeed ‘blends’ of two or more different sources, allow us to disentangle the single counterparts and to split the measured flux density into different components. We present the application of this method to the 24-μm Spitzer archival data in the Great Observatories Origins Deep Survey ELAIS-N1 (GOODS EN1) test field, where apparently extended, ‘blended’ sources constitute about 20 per cent of a reliable sample of 983 sources detected above the 5σ threshold down to 40 μJy. As a shorter-wavelength data set, we have considered the public Infrared Array Camera (IRAC) images and catalogues of the same field. We show that the 24-μm sample is almost unbiased down to ~40 μJy and the careful application of the deblending procedure does not require any statistical completeness correction (at least at the flux level considered). This is probed by direct comparison of our results with results in the literature that analysed the same data set through extensive Monte Carlo simulations. The extrapolation of the source counts down to fainter fluxes suggests that our 24-μm sample is able to resolve ~62 per cent of the cosmic background down to a flux level of 38 μJy

An Eddington ratio-driven origin for the LX- M∗relation in quiescent and star-forming active galaxies

A mild correlation exists in active galaxies between the mean black hole accretion, as traced by the mean X-ray luminosity and the host galaxy stellar mass M∗, characterised by a normalization steadily decreasing with cosmic time and lower in more quiescent galaxies. We create comprehensive semi-empirical mock catalogues of active black holes to pin down which parameters control the shape and evolution of the - M∗ relation of X-ray-detected active galaxies. We find that the normalization of the - M∗ relation is largely independent of the fraction of active galaxies (the duty cycle), but strongly dependent on the mean Eddington ratio, when adopting a constant underlying MBH - M∗ relation as suggested by observational studies. The data point to a decreasing mean Eddington ratio with cosmic time and with galaxy stellar mass at fixed redshift. Our data can be reproduced by black holes and galaxies evolving on similar MBH - M∗ relations but progressively decreasing their average Eddington ratios, mean X-ray luminosities, and specific star formation rates, when moving from the starburst to the quiescent phase. Models consistent with the observed - M∗ relation and independent measurements of the mean Eddington ratios are characterised by MBH - M∗ relations lower than those derived from dynamically measured local black holes. Our results point to the - M∗ relation as a powerful diagnostic to: (1) probe black hole-galaxy scaling relations and the level of accretion on to black holes; (2) efficiently break the degeneracies between duty cycles and accretion rates in cosmological models of black holes