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In recent observations of extremely metal-poor low-mass starburst galaxies, almost solar Fe/O ratios are reported, despite N/O ratios consistent with the low metallicity. We investigate if the peculiar Fe/O ratios can be a distinctive signature of an early enrichment produced by very massive objects dying as Pair-Instability Supernovae (PISN). We run chemical evolution models with yields that account for the contribution by PISN. We use both the recent non-rotating stellar yields from Goswami et al. 2021, and new yields from rotating very massive stars calculated on purpose in this work. We also search for the best initial mass function (IMF) that is able to reproduce the observations. We can reproduce the observations by adopting a bi-modal IMF and by including an initial burst of rotating very massive stars. Only with a burst of very massive stars can we reproduce the almost solar Fe/O ratios at the estimated young ages. We also confirm that rotation is absolutely needed to concomitantly reproduce the observed N/O ratios. These results stress the importance of very massive stars in galactic chemical evolution studies and strongly support a top-heavy initial mass function in the very early evolutionary stages of metal poor starburst galaxies., Comment: 12 pages, 6 figures, accepted for publication in A&A

Nowadays, Machine Learning techniques offer fast and efficient solutions for classification problems that would require intensive computational resources via traditional methods. We examine the use of a supervised Random Forest to classify stars in simulated galaxy clusters after subtracting the member galaxies. These dynamically different components are interpreted as the individual properties of the stars in the Brightest Cluster Galaxy (BCG) and IntraCluster Light (ICL). We employ matched stellar catalogues (built from the different dynamical properties of BCG and ICL) of 29 simulated clusters from the DIANOGA set to train and test the classifier. The input features are cluster mass, normalized particle cluster-centric distance, and rest-frame velocity. The model is found to correctly identify most of the stars, while the larger errors are exhibited at the BCG outskirt, where the differences between the physical properties of the two components are less obvious. We investigate the robustness of the classifier to numerical resolution, redshift dependence (up to $z=1$), and included astrophysical models. We claim that our classifier provides consistent results in simulations for $z<1$, at different resolution levels and with significantly different subgrid models. The phase-space structure is examined to assess whether the general properties of the stellar components are recovered: (i) the transition radius between BCG-dominated and ICL-dominated region is identified at $0.04$ \r200; (ii) the BCG outskirt ($> 0.1$ \r200) is significantly affected by uncertainties in the classification process. In conclusion, this work suggests the importance of employing Machine Learning to speed up a computationally expensive classification in simulations., Comment: 19 pages, accepted to MNRAS

Using the DIANOGA hydrodynamical zoom-in simulation set of galaxy clusters, we analyze the dynamics traced by stars belonging to the Brightest Cluster Galaxies (BCGs) and their surrounding diffuse component, forming the intracluster light (ICL), and compare it to the dynamics traced by dark matter and galaxies identified in the simulations. We compute scaling relations between the BCG and cluster velocity dispersions and their corresponding masses (i.e. $M_\mathrm{BCG}^{\star}$- $\sigma_\mathrm{BCG}^{\star}$, $M_{200}$- $\sigma_{200}$, $M_\mathrm{BCG}^{\star}$- $M_{200}$, $\sigma_\mathrm{BCG}^{\star}$- $\sigma_{200}$), we find in general a good agreement with observational results. Our simulations also predict $\sigma_\mathrm{BCG}^{\star}$- $\sigma_{200}$ relation to not change significantly up to redshift $z=1$, in line with a relatively slow accretion of the BCG stellar mass at late times. We analyze the main features of the velocity dispersion profiles, as traced by stars, dark matter, and galaxies. As a result, we discuss that observed stellar velocity dispersion profiles in the inner cluster regions are in excellent agreement with simulations. We also report that the slopes of the BCG velocity dispersion profile from simulations agree with what is measured in observations, confirming the existence of a robust correlation between the stellar velocity dispersion slope and the cluster velocity dispersion (thus, cluster mass) when the former is computed within $0.1 R_{500}$. Our results demonstrate that simulations can correctly describe the dynamics of BCGs and their surrounding stellar envelope, as determined by the past star-formation and assembly histories of the most massive galaxies of the Universe., Comment: 16 pages, 14 figures

We studied the star formation rate (SFR) in cosmological hydrodynamical simulations of galaxy (proto-)clusters in the redshift range $0

We have fit the far-ultraviolet (FUV) to sub-millimeter (850 micron) spectral energy distributions (SEDs) of the 61 galaxies from the "Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel" (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multi-wavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple "recipes" for stellar mass (Mstar), star-formation rate (SFR), dust mass (Mdust), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime, in particular between 25 and 70 micron where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard "recipes" for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a "standard" constant stellar mass-to-light ratio overestimates Mstar relative to the SED fitting, and we provide new SED-based formulations for estimating Mstar from WISE W1 (3.4 micron) luminosities and colors. From a Principal Component Analysis of Mstar, SFR, Mdust, and O/H, we reproduce previous scaling relations among Mstar, SFR, and O/H, and find that Mdust can be predicted to within roughly 0.3 dex using only Mstar and SFR., Comment: 42 pages, 23 figures, 8 tables, 2 appendices: updated to v2, A&A, accepted

We analyze the stellar growth of Brightest Cluster Galaxies (BCGs) produced by cosmological zoom-in hydrodynamical simulations of the formation of massive galaxy clusters. The evolution of the stellar mass content is studied considering different apertures, and tracking backwards either the main progenitor of the $z=0$ BCG or that of the cluster hosting the BCG at $z=0$. Both methods lead to similar results up to $z \simeq 1.5$. The simulated BCGs masses at $z=0$ are in agreement with recent observations. In the redshift interval from $z=1$ to $z=0$ we find growth factors 1.3, 1.6 and 3.6 for stellar masses within 30kpc, 50kpc and 10% of $R_{500}$ respectively. The first two factors, and in general the mass evolution in this redshift range, are in agreement with most recent observations. The last larger factor is similar to the growth factor obtained by a semi-analytical model (SAM). Half of the star particles that end up in the inner 50 kpc was typically formed by redshift $\sim$ 3.7, while the assembly of half of the BCGs stellar mass occurs on average at lower redshifts $\sim 1.5$. This assembly redshift correlates with the mass attained by the cluster at high $z \gtrsim 1.3$, due to the broader range of the progenitor clusters at high-$z$. The assembly redshift of BCGs decreases with increasing apertures. Our results are compatible with the {\it inside-out} scenario. Simulated BCGs could lack intense enough star formation (SF) at high redshift, while possibly exhibit an excess of residual SF at low redshift., Comment: 13 pages, 10 figures, Accepted by MNRAS 2018 June 17

A far-infrared observatory such as the {\it SPace Infrared telescope for Cosmology and Astrophysics} ({\it SPICA}), with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last $\sim10$ Gyr of the Universe ($z=1.5-2$), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionized gas. We quantify the detectability of galaxy-scale massive molecular and ionized outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths., Comment: This paper belongs to the SPICA Special Issue on PASA. Accepted for publication in PASA

The physical processes driving the chemical evolution of galaxies in the last $\sim 11\, \rm{Gyr}$ cannot be understood without directly probing the dust-obscured phase of star-forming galaxies and active galactic nuclei. This phase, hidden to optical tracers, represents the bulk of star formation and black hole accretion activity in galaxies at $1 < z < 3$. Spectroscopic observations with a cryogenic infrared (IR) observatory like SPICA will be sensitive enough to peer through the dust-obscured regions of galaxies and access the rest-frame mid- to far-IR range in galaxies at high-$z$. This wavelength range contains a unique suite of spectral lines and dust features that serve as proxies for the abundances of heavy elements and the dust composition, providing tracers with a feeble response to both extinction and temperature. In this work, we investigate how SPICA observations could be exploited to understand key aspects in the chemical evolution of galaxies: the assembly of nearby galaxies based on the spatial distribution of heavy element abundances, the global content of metals in galaxies reaching the knee of the luminosity function up to $z \sim 3$, and the dust composition of galaxies at high-$z$. Possible synergies with facilities available in the late 2020s are also discussed., Comment: In press. This paper belongs to the "SPICA Special Issue" on PASA

By means of the updated PARSEC database of evolutionary tracks of massive stars, we compute the integrated stellar light, the ionizing photon budget and the supernova rates of young simple stellar populations (SSPs), for different metallicities and IMF upper mass limits. Using CLOUDY we compute and include in the SSP spectra the neb- ular emission contribution. We also revisit the thermal and non-thermal radio emission contribution from young stars. Using GRASIL we can thus predict the panchromatic spectrum and the main recombination lines of any type of star-forming galaxy, including the effects of dust absorption and re-emission. We check the new models against the spectral energy distributions (SEDs) of selected well-observed nearby galaxies. From the best-fit models we obtain a consistent set of star formation rate (SFR) calibrations at wavelengths ranging from ultraviolet (UV) to radio. We also provide analytical calibrations that take into account the dependence on metallcity and IMF upper mass limit of the SSPs. We show that the latter limit can be well constrained by combining information from the observed far infrared, 24 {\mu}m, 33 GHz and H{\alpha} luminosities. Another interesting property derived from the fits is that, while in a normal galaxy the attenuation in the lines is significantly higher than that in the nearby continuum, in individual star bursting regions they are similar, supporting the notion that this effect is due to an age selective extinction. Since in these conditions the Balmer decrement method may not be accurate, we provide relations to estimate the attenuation from the observed 24 {\mu}m or 33 GHz fluxes. These relations can be useful for the analysis of young high redshift galaxies., Comment: 25 pages, 15 figures

The distribution of metals in the intracluster medium (ICM) of galaxy clusters provides valuable information on their formation and evolution, on the connection with the cosmic star formation and on the effects of different gas processes. By analyzing a sample of simulated galaxy clusters, we study the chemical enrichment of the ICM, its evolution, and its relation with the physical processes included in the simulation and with the thermal properties of the core. These simulations, consisting of re-simulations of 29 Lagrangian regions performed with an upgraded version of the SPH GADGET-3 code, have been run including two different sets of baryonic physics: one accounts for radiative cooling, star formation, metal enrichment and supernova (SN) feedback, and the other one further includes the effects of feedback from active galactic nuclei (AGN). In agreement with observations, we find an anti-correlation between entropy and metallicity in cluster cores, and similar radial distributions of heavy-element abundances and abundance ratios out to large cluster-centric distances (~R180). In the outskirts, namely outside of ~0.2R180, we find a remarkably homogeneous metallicity distribution, with almost flat profiles of the elements produced by either SNIa or SNII. We investigated the origin of this phenomenon and discovered that it is due to the widespread displacement of metal-rich gas by early (z>2-3) AGN powerful bursts, acting on small high-redshift haloes. Our results also indicate that the intrinsic metallicity of the hot gas for this sample is on average consistent with no evolution between z=2 and z=0, across the entire radial range., Comment: 18 pages; submitted to MNRAS

We analyze the radial pressure profiles, the ICM clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the TreePM-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, AGN and/or stellar feedback. Our results are analyzed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z=1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster center and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping ($\sqrt C_{\rho}\sim 1.2$ at $R_{200}$) in good agreement with recent observational estimates. The simulated $Y_{SZ}-M$ scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters., Comment: 22 pages, 14 figures, 2 tables. Submitted to MNRAS

We analyse cosmological hydrodynamical simulations of galaxy clusters to study the X-ray scaling relations between total masses and observable quantities such as X-ray luminosity, gas mass, X-ray temperature, and $Y_{X}$. Three sets of simulations are performed with an improved version of the smoothed particle hydrodynamics GADGET-3 code. These consider the following: non-radiative gas, star formation and stellar feedback, and the addition of feedback by active galactic nuclei (AGN). We select clusters with $M_{500} > 10^{14} M_{\odot} E(z)^{-1}$, mimicking the typical selection of Sunyaev-Zeldovich samples. This permits to have a mass range large enough to enable robust fitting of the relations even at $z \sim 2$. The results of the analysis show a general agreement with observations. The values of the slope of the mass-gas mass and mass-temperature relations at $z=2$ are 10 per cent lower with respect to $z=0$ due to the applied mass selection, in the former case, and to the effect of early merger in the latter. We investigate the impact of the slope variation on the study of the evolution of the normalization. We conclude that cosmological studies through scaling relations should be limited to the redshift range $z=0-1$, where we find that the slope, the scatter, and the covariance matrix of the relations are stable. The scaling between mass and $Y_X$ is confirmed to be the most robust relation, being almost independent of the gas physics. At higher redshifts, the scaling relations are sensitive to the inclusion of AGNs which influences low-mass systems. The detailed study of these objects will be crucial to evaluate the AGN effect on the ICM., Comment: 24 pages, 11 figures, 5 tables, replaced to match accepted version

In this paper we investigate the level of hydrostatic equilibrium (HE) in the intra-cluster medium of simulated galaxy clusters, extracted from state-of-the-art cosmological hydrodynamical simulations performed with the Smoothed-Particle-Hydrodynamic code GADGET-3. These simulations include several physical processes, among which stellar and AGN feedback, and have been performed with an improved version of the code that allows for a better description of hydrodynamical instabilities and gas mixing processes. Evaluating the radial balance between the gravitational and hydrodynamical forces, via the gas accelerations generated, we effectively examine the level of HE in every object of the sample, its dependence on the radial distance from the center and on the classification of the cluster in terms of either cool-coreness or dynamical state. We find an average deviation of 10-20% out to the virial radius, with no evident distinction between cool-core and non-cool-core clusters. Instead, we observe a clear separation between regular and disturbed systems, with a more significant deviation from HE for the disturbed objects. The investigation of the bias between the hydrostatic estimate and the total gravitating mass indicates that, on average, this traces very well the deviation from HE, even though individual cases show a more complex picture. Typically, in the radial ranges where mass bias and deviation from HE are substantially different, the gas is characterized by a significant amount of random motions (>~30 per cent), relative to thermal ones. As a general result, the HE-deviation and mass bias, at given interesting distance from the cluster center, are not very sensitive to the temperature inhomogeneities in the gas., Comment: 14 pages, 13 figures, 1 table; submitted

We present results obtained from a set of cosmological hydrodynamic simulations of galaxy clusters, aimed at comparing predictions with observational data on the diversity between cool-core (CC) and non-cool-core (NCC) clusters. Our simulations include the effects of stellar and AGN feedback and are based on an improved version of the smoothed particle hydrodynamics code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical instabilities by including a suitable artificial thermal diffusion. In this Letter, we focus our analysis on the entropy profiles, the primary diagnostic we used to classify the degree of cool-coreness of clusters, and on the iron profiles. In keeping with observations, our simulated clusters display a variety of behaviors in entropy profiles: they range from steadily decreasing profiles at small radii, characteristic of cool-core systems, to nearly flat core isentropic profiles, characteristic of non-cool-core systems. Using observational criteria to distinguish between the two classes of objects, we find that they occur in similar proportions in both simulations and in observations. Furthermore, we also find that simulated cool-core clusters have profiles of iron abundance that are steeper than those of NCC clusters, which is also in agreement with observational results. We show that the capability of our simulations to generate a realistic cool-core structure in the cluster population is due to AGN feedback and artificial thermal diffusion: their combined action allows us to naturally distribute the energy extracted from super-massive black holes and to compensate for the radiative losses of low-entropy gas with short cooling time residing in the cluster core., Comment: 6 pages, 4 figures, accepted in ApJL, v2 contains some modifications on the text (results unchanged)

We present a backward approach for the interpretation of the evolution of the near-infrared and the far-infrared luminosity functions across the redshift range 02 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e. that the bulk of proto-spheroids can be modelled by means of a single model which describes the evolution of galaxies at the break of the present-day early type K-band LF., Comment: Accepted for publication in ApJ; 26 pages; 13 figures

Using cosmological galaxy simulations from the MaGICC project, we study the evolution of the stellar masses, star formation rates and gas phase abundances of star forming galaxies. We derive the stellar masses and star formation rates using observational relations based on spectral energy distributions by applying the new radiative transfer code GRASIL-3D to our simulated galaxies. The simulations match well the evolution of the stellar mass-halo mass relation, have a star forming main sequence that maintains a constant slope out to redshift z $\sim$ 2, and populate projections of the stellar mass - star formation - metallicity plane, similar to observed star forming disc galaxies. We discuss small differences between these projections in observational data and in simulations, and the possible causes for the discrepancies. The light-weighted stellar masses are in good agreement with the simulation values, the differences between the two varying between 0.06 dex and 0.20 dex. We also find a good agreement between the star formation rate tracer and the true (time-averaged) simulation star formation rates. Regardless if we use mass- or light-weighted quantities, our simulations indicate that bursty star formation cycles can account for the scatter in the star forming main sequence., Comment: 12 pages, 8 figures, submitted to MNRAS

We introduce a new model for the spectral energy distribution of galaxies, GRASIL-3D, which includes a careful modelling of the dust component of the interstellar medium. GRASIL-3D is an entirely new model based on the formalism of an existing and widely applied spectrophotometric model, GRASIL, but specifically designed to be interfaced with galaxies with any arbitrarily given geometry, such as galaxies calculated by theoretical hydrodynamical galaxy formation codes. GRASIL-3D is designed to separately treat radiative transfer in molecular clouds and in the diffuse cirrus component. The code has a general applicability to the outputs of simulated galaxies, either from Lagrangian or Eulerian hydrodynamic codes. As an application, the new model has been interfaced to the P-DEVA and GASOLINE smoothed-particle hydrodynamic codes, and has been used to calculate the spectral energy distribution for a variety of simulated galaxies from UV to sub-millimeter wavelengths, whose comparison with observational data gives encouraging results. In addition, GRASIL-3D allows 2D images of such galaxies to be obtained, at several angles and in different bands., Comment: 24 pages, 13 Figures and 6 Tables. Accepted in MNRAS

We present an analysis of the properties of the ICM in an extended set of cosmological hydrodynamical simulations of galaxy clusters and groups performed with the TreePM+SPH GADGET-3 code. Besides a set of non-radiative simulations, we carried out two sets of simulations including radiative cooling, star formation, metal enrichment and feedback from supernovae, one of which also accounts for the effect of feedback from AGN resulting from gas accretion onto super-massive black holes. These simulations are analysed with the aim of studying the relative role played by SN and AGN feedback on the general properties of the diffuse hot baryons in galaxy clusters and groups: scaling relations, temperature, entropy and pressure radial profiles, and ICM chemical enrichment. We find that simulations including AGN feedback produce scaling relations that are in good agreement with X-ray observations at all mass scales. However, our simulations are not able to account for the observed diversity between CC and NCC clusters: unlike for observations, we find that temperature and entropy profiles of relaxed and unrelaxed clusters are quite similar and resemble more the observed behaviour of NCC clusters. As for the pattern of metal enrichment, we find that an enhanced level of iron abundance is produced by AGN feedback with respect to the case of purely SN feedback. As a result, while simulations including AGN produce values of iron abundance in groups in agreement with observations, they over-enrich the ICM in massive clusters. The efficiency of AGN feedback in displacing enriched gas from halos into the inter-galactic medium at high redshift also creates a widespread enrichment in the outskirts of clusters and produces profiles of iron abundance whose slope is in better agreement with observations., Comment: 23 pages, 14 figures, 1 table, accepted for publication in MNRAS

[Abridged] In this paper, we carry out a detailed analysis of the performance of two different methods to identify the diffuse stellar light in cosmological hydrodynamical simulations of galaxy clusters. One method is based on a dynamical analysis of the stellar component. The second method is closer to techniques commonly employed in observational studies. Both the dynamical method and the method based on the surface brightness limit criterion are applied to the same set of hydrodynamical simulations for a large sample about 80 galaxy clusters. We find significant differences between the ICL and DSC fractions computed with the two corresponding methods, which amounts to about a factor of two for the AGN simulations, and a factor of four for the CSF set. We also find that the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of 1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters, thus in excess of what found from observational analysis. We identify the average surface brightness limits that yields the ICL fraction from the SBL method close to the DSC fraction from the dynamical method. These surface brightness limits turn out to be brighter in the CSF than in the AGN simulations. This is consistent with the finding that AGN feedback makes BCGs to be less massive and with shallower density profiles than in the CSF simulations. The BCG stellar component, as identified by both methods, are slightly older and more metal-rich than the stars in the diffuse component., Comment: 18 Pages, 15 figures. Matches to MNRAS published version

We empirically test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.06 - 0.46 with both Ha detection (from 20k zCOSMOS survey) and new far-IR Herschel data (100 and 160 {\mu}m). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B - V) and LIR that allows to estimate extinction values for each galaxy even if the Ha emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 {\mu}m the SED that is best fitting our data. We compare SFR(Ha) with the SFR(LIR). We find a very good agreement between the two SFR estimates, with a slope of m = 1.01 \pm 0.03 in the SFR(LIR) vs SFR(Ha) diagram, a normalization constant of a = -0.08 \pm 0.03 and a dispersion of sigma = 0.28 dex.We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)-SFR(Ha) relation, such as the redshift, the mass, the SSFR or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by approx. 0.6 dex from metal-poor to metal-rich galaxies (8.1 < log(O/H) + 12 < 9.2). This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fit slope becomes much steeper (m = 1.62 \pm 0.43), but it is still consistent with 1 at the 1.5 sigma level, because of the reduced statistics of this sub-sample., Comment: 13 pages, 11 figures, accepted for publication in MNRAS

We present the analysis of Spitzer-IRS spectra of four early-type galaxies, NGC 1297, NGC 5044, NGC 6868, and NGC 7079, all classified as LINERs in the optical bands. Their IRS spectra present the full series of H2 rotational emission lines in the range 5--38 microns, atomic lines, and prominent PAH features. We investigate the nature and origin of the PAH emission, characterized by unusually low 6 -- 9/11.3 microns inter-band ratios. After the subtraction of a passive early type galaxy template, we find that the 7 -- 9 microns spectral region requires dust features not normally present in star forming galaxies. Each spectrum is then analyzed with the aim of identifying their components and origin. In contrast to normal star forming galaxies, where cationic PAH emission prevails, our 6--14 microns spectra seem to be dominated by large and neutral PAH emission, responsible for the low 6 -- 9/11.3 microns ratios, plus two broad dust emission features peaking at 8.2 microns and 12 microns. Theses broad components, observed until now mainly in evolved carbon stars and usually attributed to pristine material, contribute approximately 30-50% of the total PAH flux in the 6--14 microns region. We propose that the PAH molecules in our ETGs arise from fresh carbonaceous material which is continuously released by a population of carbon stars, formed in a rejuvenation episode which occurred within the last few Gyr. The analysis of the MIR spectra allows us to infer that, in order to maintain the peculiar size and charge distributions biased to large and neutral PAHs, this material must be shocked, and excited by the weak UV interstellar radiation field of our ETG., Comment: ApJ accepted

The spectral energy distribution of galaxies is a complex function of the star formation history and geometrical arrangement of stars and gas in galaxies. The computation of the radiative transfer of stellar radiation through the dust distribution is time-consuming. This aspect becomes unacceptable in particular when dealing with the predictions by semi-analytical galaxy formation models populating cosmological volumes, to be then compared with multi-wavelength surveys. Mainly for this aim, we have implemented an artificial neural network algorithm into the spectro-photometric and radiative transfer code GRASIL in order to compute the spectral energy distribution of galaxies in a short computing time. This allows to avoid the adoption of empirical templates that may have nothing to do with the mock galaxies output by models. The ANN has been implemented to compute the dust emission spectrum (the bottleneck of the computation), and separately for the star-forming molecular clouds and the diffuse dust (due to their different properties and dependencies). We have defined the input neurons effectively determining their emission, which means this implementation has a general applicability and is not linked to a particular galaxy formation model. We have trained the net for the disc and spherical geometries, and tested its performance to reproduce the SED of disc and starburst galaxies, as well as for a semi-analytical model for spheroidal galaxies. We have checked that for this model both the SEDs and the galaxy counts in the Herschel bands obtained with the ANN approximation are almost superimposed to the same quantities obtained with the full GRASIL. We conclude that this method appears robust and advantageous, and will present the application to a more complex SAM in another paper., Comment: 16 pages, 14 figures, MNRAS, Accepted 2010 August 22

We use deep observations taken with the Photodetector Array Camera and Spectrometer (PACS), on board the Herschel satellite as part of the PACS evolutionary probe (PEP) guaranteed project along with submm ground-based observations to measure the dust mass of a sample of high-z submillimeter galaxies (SMGs). We investigate their dust content relative to their stellar and gas masses, and compare them with local star-forming galaxies. High-z SMGs are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to local spiral galaxies (by a factor of 30) and also compared to local ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that the large masses of gas typically hosted in SMGs have already been highly enriched with metals and dust. Indeed, for those SMGs whose gas mass is measured, we infer dust-to-gas ratios similar or higher than local spirals and ULIRGs. However, similarly to other strongly star-forming galaxies in the local Universe and at high-z, SMGs are characterized by gas metalicities lower (by a factor of a few) than local spirals, as inferred from their optical nebular lines, which are generally ascribed to infall of metal-poor gas. This is in contrast with the large dust content inferred from the far-IR and submm data. In short, the metalicity inferred from the dust mass is much higher (by more than an order of magnitude) than that inferred from the optical nebular lines. We discuss the possible explanations of this discrepancy and the possible implications for the investigation of the metalicity evolution at high-z., Comment: Accepted for publication in Astronomy & Astrophysics Letters. One reference updated

We study in detail the mid-infrared Spitzer-IRS spectrum of M 87 in the range 5 to 20 micron. Thanks to the high sensitivity of our Spitzer-IRS spectra we can disentangle the stellar and nuclear components of this active galaxy. To this end we have properly subtracted from the M 87 spectrum, the contribution of the underlying stellar continuum, derived from passive Virgo galaxies in our sample. The residual is a clear power-law, without any additional thermal component, with a zero point consistent with that obtained by high spatial resolution, ground based observations. The residual is independent of the adopted passive template. This indicates that the 10 micron silicate emission shown in spectra of M 87 can be entirely accounted for by the underlying old stellar population, leaving little room for a possible torus contribution. The MIR power-law has a slope alpha ~ 0.77-0.82 (S$_\nu\propto\nu^{-\alpha}$), consistent with optically thin synchrotron emission., Comment: 5 pages, 4 figures, accepted for publication in ApJ main journal

We use a model for the evolution of galaxies in the far-IR based on the LambdaCDM cosmology to make detailed predictions for upcoming cosmological surveys with the Herschel Space Observatory. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy SEDs including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al. (2005), assumes two different IMFs: a normal solar neighbourhood IMF for quiescent star formation in disks, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF appears necessary to explain the number counts and redshifts of faint sub-mm galaxies. In this paper, we present predictions for galaxy luminosity functions, number counts and redshift distributions in the Herschel imaging bands. We find that source confusion will be a serious problem in the deepest planned surveys. We also show predictions for physical properties such as star formation rates and stellar, gas and halo masses, together with fluxes at other wavelengths (from the far-UV to the radio) relevant for multi-wavelength follow-up observations. We investigate what fraction of the total IR emission from dust and of the high-mass star formation over the history of the Universe should be resolved by planned surveys with Herschel, and find a fraction ~30-50%, depending on confusion. Finally, we show that galaxies in Herschel surveys should be significantly clustered., Comment: 28 pages, 22 figures, 2 tables. Accepted for publication in MNRAS. Minor changes in response to referee, including new figure comparing to BLAST number counts

We investigate the atomic (HI) and molecular (H_2) Hydrogen content of normal galaxies by combining observational studies linking galaxy stellar and gas budgets to their host dark matter (DM) properties, with a physically grounded galaxy formation model. This enables us to analyse empirical relationships between the virial, stellar, and gaseous masses of galaxies and explore their physical origins. Utilising a semi-analytic model (SAM) to study the evolution of baryonic material within evolving DM halos, we study the effects of baryonic infall and various star formation and feedback mechanisms on the properties of formed galaxies using the most up-to-date physical recipes. We find that in order to significantly improve agreement with observations of low-mass galaxies we must suppress the infall of baryonic material and exploit a two-phase interstellar medium (ISM), where the ratio of HI to H_2 is determined by the galactic disk structure. Modifying the standard Schmidt-Kennicutt star formation law, which acts upon the total cold gas in galaxy discs and includes a critical density threshold, and employing a star formation law which correlates with the H_2 gas mass results in a lower overall star formation rate. This in turn, allows us to simultaneously reproduce stellar, HI and H_2 mass functions of normal galaxies., Comment: 16 pages, 12 figures, 1 table. Moderate revision to match version accepted for publication in MNRAS

We introduce a new technique based on artificial neural networks which allows us to make accurate predictions for the spectral energy distributions (SEDs) of large samples of galaxies, at wavelengths ranging from the far-ultra-violet to the sub-millimetre and radio. The neural net is trained to reproduce the SEDs predicted by a hybrid code comprised of the GALFORM semi-analytical model of galaxy formation, which predicts the full star formation and galaxy merger histories, and the GRASIL spectro-photometric code, which carries out a self-consistent calculation of the SED, including absorption and emission of radiation by dust. Using a small number of galaxy properties predicted by GALFORM, the method reproduces the luminosities of galaxies in the majority of cases to within 10% of those computed directly using GRASIL. The method performs best in the sub-mm and reasonably well in the mid-infrared and the far-ultra-violet. The luminosity error introduced by the method has negligible impact on predicted statistical distributions, such as luminosity functions or colour distributions of galaxies. We use the neural net to predict the overlap between galaxies selected in the rest-frame UV and in the observer-frame sub-mm at z=2. We find that around half of the galaxies with a 850um flux above 5 mJy should have optical magnitudes brighter than R_AB < 25 mag. However, only 1% of the galaxies selected in the rest-frame UV down to R_AB < 25 mag should have 850um fluxes brighter than 5 mJy. Our technique will allow the generation of wide-angle mock catalogues of galaxies selected at rest-frame UV or mid- and far-infrared wavelengths., Comment: 24 pages, 18 figures. Submitted to MNRAS

We propose and test a scenario for the assembly and evolution of luminous matter in galaxies which substantially differs from that adopted by other semianalytic models. As for the dark matter (DM), we follow the detailed evolution of halos within the canonical LCDM cosmology using standard Montecarlo methods. However, when overlaying prescriptions for baryon evolution, we take into account an effect pointed out in the past few years by a number of studies mostly based on intensive N-body simulations, namely that typical halo growth occurs in two phases: an early, fast collapse phase featuring several major merger events, followed by a late, quiescent accretion onto the halo outskirts. We propose that the two modes of halo growth drive two distinct modes for the evolution of baryonic matter, favoring the development of the spheroidal and disc components of galaxies, respectively. We test this idea using the semianalytic technique. Our galaxy formation model envisages an early coevolution of spheroids and the central supermassive black holes, already tested in our previous works, followed by a relatively quiescent growth of discs around the preformed spheroids. In this exploratory study, we couple our model to the spectrophotometric code GRASIL, and compare our results on several properties of the local galaxy population with observations, Finding an encouraging agreement., Comment: 16 pages, 21 figures, MNRAS Accepted 23/04/2009

We fit the near-infrared to radio spectral energy distributions of a sample of 30 luminous and ultra-luminous infrared galaxies with models that include both starburst and AGN components. The aim of the work was to determine important physical parameters for this kind of objects such as the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and the AGN fraction. We found that although about half of our sample have best-fit models that include an AGN component, only 30 % have an AGN which accounts for more than 10 % of the infrared luminosity whereas all have an energetically dominant starburst. Our models also determine the mass of dense molecular gas. Assuming that this mass is that traced by the HCN molecule, we reproduce the observed linear relation between HCN luminosity and infrared luminosity found by Gao and Solomon (2004). However, our derived conversion factor between HCN luminosity and the mass of dense molecular gas is a factor of 2 smaller than that assumed by these authors. Finally, we find that the star formation efficiency falls as the starburst ages., Comment: 6 pages, 4 figures, Proceedings of "A Long Walk Through Astronomy: A Celebration of Luis Carrasco's 60th Birthday", Huatulco, Mexico, October 2008, ed. E. Recillas, L. Aguilar, A. Luna, and J.R. Valdes; RevMexAA (Serie de Conferencias)

We present photometric evolution models of galaxies, in which, in addition to the stellar component, the effects of an evolving dusty interstellar medium have been included with particular care. Starting from the work of Calura, Pipino & Matteucci (2008), in which chemical evolution models have been used to study the evolution of both the gas and dust components of the interstellar medium in the solar neighbourhood, elliptical and irregular galaxies, it has been possible to combine these models with a spectrophotometric stellar code that includes dust reprocessing (GRASIL) (Silva et al. 1998) to analyse the evolution of the spectral energy distributions (SED) of these galaxies. We test our models against observed SEDs both in the local universe and at high redshift and use them to predict how the percentage of reprocessed starlight evolves for each type of galaxy. The importance of following the dust evolution is investigated by comparing our results with those obtained by adopting simple assumptions to treat this component., Comment: 25 pages, 25 figures. Accepted for publication in MNRAS

We use 16 micron, Spitzer-IRS, blue peakup photometry of 50 early-type galaxies in the Coma cluster to define the mid-infrared colour-magnitude relation. We compare with recent simple stellar population models that include the mid-infrared emission from the extended, dusty envelopes of evolved stars. The Ks-[16] colour in these models is very sensitive to the relative population of dusty Asymptotic Giant Branch (AGB) stars. We find that the passively evolving early-type galaxies define a sequence of approximately constant age (~10 Gyr) with varying metallicity. Several galaxies that lie on the optical/near-infrared colour-magnitude relation do not lie on the mid-infrared relation. This illustrates the sensitivity of the Ks-[16] colour to age. The fact that a colour-magnitude relation is seen in the mid-infrared underlines the extremely passive nature of the majority (68%) of early-type galaxies in the Coma cluster. The corollary of this is that 32% of the early-type galaxies in our sample are not `passive', insofar as they are either significantly younger than 10 Gyr or they have had some rejuvenation episode within the last few Gyr., Comment: 11 pages, 8 figures. Accepted for publication in MNRAS. This replacement has mainly cosmetic textual changes but the model in figure 6 has been modified

In a previous work, three bright MIR/radio sources were discovered in the nuclear region of NGC1365. We here confirm that these sources are young and massive ``embedded'' clusters, and derive their parameters, such as extinction, age and mass. Using ISAAC and VISIR at the VLT we obtained NIR and MIR maps and LR spectra. The dataset is first interpreted by comparing the observations with images and spectra of the close-by young cluster R136 in the LMC and then by using model predictions for both the nebular emission lines and the spectral energy distribution of the sources. We produce maps of the region containing the three sources in the R, J, Ks, L' bands and at 12.8micro. We also provide spectra in K, L and N. The spectral energy distribution of the three sources rises with wavelength. Emission lines from ionised hydrogen and molecular hydrogen are detected, as well as PAH emission. Conspicuous [NeII]12.8 line is also present, while neither the [ArIII] 8.9 nor the [SIV] 10.4 lines are detected. This provides a stringent constraint on the age of the sources: they are relatively evolved young clusters (6-8 Myr). Owing to their ionising photon rates and ages, they must be extremely massive clusters (around 10^7 solar masses). Their MIR spectral energy distribution suggests the presence of two components: (1) an optically thin component, with a continuum comparable to that of R136, and (2) an optically thick component which might be related to subsequent or on-going episodes of star formation. These sources are good candidates for evolving according to a bi-modal hydrodynamical regime, in which matter is trapped at the centre of a compact and massive cluster., Comment: A&A accepted, 23 pages, 22 figures and 1 table

We present initial results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z>3 by means of deep near-IR spectroscopy. Gas metallicities are measured, for an initial sample of nine star forming galaxies at z~3.5, by means of optical nebular lines redshifted into the near-IR. Stellar masses are accurately determined by using Spitzer-IRAC data, which sample the rest-frame near-IR stellar light in these distant galaxies. When compared with previous surveys, the mass-metallicity relation inferred at z~3.5 shows an evolution much stronger than observed at lower redshifts. The evolution is prominent even in massive galaxies, indicating that z~3 is an epoch of major action in terms of star formation and metal enrichment also for massive systems. There are also indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.5 is difficult to reconcile with the predictions of some hierarchical evolutionary models. Such discrepancies suggest that at z>3 galaxies are assembled mostly with relatively un-evolved sub-units, i.e. small galaxies with low star formation efficiency. The bulk of the star formation and metallicity evolution probably occurs once small galaxies are already assembled into bigger systems., Comment: 19 pages, 11 figures, A&A in press, replaced with accepted version

Motivated by the recent observational and theoretical evidence that long Gamma-Ray Bursts (GRBs) are likely associated with low metallicity, rapidly rotating massive stars, we examine the cosmological star formation rate (SFR) below a critical metallicity Z_crit Z_sun/10 - Z_sun/5, to estimate the event rate of high-redshift long GRB progenitors. To this purpose, we exploit a galaxy formation scenario already successfully tested on a wealth of observational data on (proto)spheroids, Lyman break galaxies, Lyman alpha emitters, submm galaxies, quasars, and local early-type galaxies. We find that the predicted rate of long GRBs amounts to about 300 events/yr/sr, of which about 30 per cent occur at z>~6. Correspondingly, the GRB number counts well agree with the bright SWIFT data, without the need for an intrinsic luminosity evolution. Moreover, the above framework enables us to predict properties of the GRB host galaxies. Most GRBs are associated with low mass galaxy halos M_H<~10^11 M_sun, and effectively trace the formation of small galaxies in such halos. The hosts are young, with age smaller than 5*10^7 yr, gas rich, but poorly extincted (A_V<~0.1) because of their chemical immaturity; this also implies high specific SFR and quite extreme alpha-enhancement. Only the minority of hosts residing in large halos with M_H>~10^12 M_sun have larger extinction (A_V~0.7-1), SFRs exceeding 100 M_sun/yr and can be detected at submm wavelengths. Most of the hosts have UV magnitudes in the range -20 <~M_1350<~ -16, and Lyman alpha luminosity in the range 2*10^40 <~L_Lya<~2*10^42 erg/s. GRB hosts are thus tracing the faint end of the luminosity function of Lyman break galaxies and Lyman alpha emitters., Comment: 11 pages, 8 figures, uses mn2e.cls. Minor changes. In press on MNRAS

We present preliminary results of an ESO-VLT large programme (AMAZE) aimed at determining the evolution of the mass-metallicity relation at z~3 by means of deep near-IR spectroscopy. Gas metallicities and stellar masses are measured for an initial sample of nine star forming galaxies at z~3.3. When compared with previous surveys, the mass-metallicity relation inferred at z~3.3 shows an evolution significantly stronger than observed at lower redshifts. There are also some indications that the metallicity evolution of low mass galaxies is stronger relative to high mass systems, an effect which can be considered as the chemical version of the galaxy downsizing. The mass-metallicity relation observed at z~3.3 is difficult to reconcile with the predictions of some hierarchical evolutionary models. We shortly discuss the possible implications of such discrepancies., Comment: 6 pages, 4 figures, to appear in the proceedings of "A Century of Cosmology: Past, Present and Future" (Venezia, August 2007)

We fit the near-infrared to radio spectral energy distributions of 30 luminous and ultra-luminous infrared galaxies with pure starburst models or models that include both starburst and AGN components to determine important physical parameters for this population of objects. In particular we constrain the optical depth towards the luminosity source, the star formation rate, the star formation efficiency and the AGN fraction. We find that although about half of our sample have best-fit models that include an AGN component, only 30% have an AGN which accounts for more than 10% of the infrared luminosity, whereas all have an energetically dominant starburst. Our derived AGN fractions are generally in good agreement other measurements based in the mid-infrared line ratios measured by Spitzer IRS, but lower than those derived from PAH equivalent widths or the mid-infrared spectral slope. Our models determine the mass of dense molecular gas via the extinction required to reproduce the SED. Assuming that this mass is that traced by HCN, we reproduce the observed linear relation between HCN and infrared luminosities found by Gao & Solomon. We also find that the star formation efficiency, defined as the current star formation rate per unit of dense molecular gas mass, is enhanced in the ULIRGs phase. If the evolution of ULIRGs includes a phase in which an AGN contributes an important fraction to the infrared luminosity, this phase should last an order of magnitude less time than the starburst phase. Because the mass of dense molecular gas which we derive is consistent with observations of the HCN molecule,it should be possible to estimate the mass of dense, star-forming molecular gas in such objects when molecular line data are not available., Comment: Re-submitted to A&A

We have studied the submillimetre (submm) properties of the following classes of near-infrared (NIR)-selected massive galaxies at high redshifts: BzK-selected star-forming galaxies (BzKs); distant red galaxies (DRGs); and extremely red objects (EROs). We used the SCUBA HAlf Degree Extragalactic Survey (SHADES), the largest uniform submm survey to date. Partial overlap of SIRIUS/NIR images and SHADES in SXDF has allowed us to identify 4 submm-bright NIR-selected galaxies, which are detected in the mid-infrared, 24 micron, and the radio, 1.4 GHz. We find that all of our submm-bright NIR-selected galaxies satisfy the BzK selection criteria, except for one galaxy whose B-z and z-K colours are however close to the BzK colour boundary. Two of the submm-bright NIR-selected galaxies satisfy all of the selection criteria we considered, i.e. they belong to the BzK-DRG-ERO overlapping population, or `extremely red' BzKs. Although these extremely red BzKs are rare (0.25 arcmin^{-2}), up to 20 % of this population could be submm galaxies. This fraction is significantly higher than that found for other galaxy populations studied here. Via a stacking analysis, we have detected the 850 micron flux of submm-faint BzKs and EROs in our SCUBA maps. While the contribution of z~2 BzKs to the submm background is about 10--15 % and similar to that from EROs typically at z~1, BzKs have a higher fraction (~30 %) of submm flux in resolved sources compared with EROs and submm sources as a whole. From the SED fitting analysis for both submm-bright and submm-faint BzKs, we found no clear signature that submm-bright BzKs are experiencing a specifically luminous evolutionary phase, compared with submm-faint BzKs. An alternative explanation might be that submm-bright BzKs are more massive than submm-faint ones., Comment: 20 pages, 11 figures, accepted for publication in MNRAS

As a constraint for new starburst/AGN models of IRAS bright galaxies we determine the radio spectra of 31 luminous and ultraluminous IRAS galaxies (LIRGs/ULIRGs). We construct the radio spectra using both new and archival data. From our sample of radio spectra we find that very few have a straight power-law slope. Although some sources show a flattening of the radio spectral slope at high frequencies the average spectrum shows a steepening of the radio spectrum from 1.4 to 22.5 GHz. This is unexpected because in sources with high rates of star formation we expect flat spectrum, free-free emission to make a significant contribution to the radio flux at higher radio frequencies. Despite this trend the radio spectral indices between 8.4 and 22.5 GHz are flatter for sources with higher values of the FIR-radio flux density ratio q, when this is calculated at 8.4 GHz. Therefore, sources that are deficient in radio emission relative to FIR emission (presumably younger sources) have a larger thermal component to their radio emission. However, we find no correlation between the radio spectral index between 1.4 and 4.8 GHz and q at 8.4 GHz. Because the low frequency spectral index is affected by free-free absorption, and this is a function of source size for a given mass of ionized gas, this is evidence that the ionized gas in ULIRGs shows a range of densities. The youngest LIRGs and ULIRGs are characterized by a larger contribution to their high-frequency radio spectra from free-free emission. However, the youngest sources are not those that have the greatest free-free absorption at low radio frequencies. The sources in which the effects of free-free absorption are strongest are instead the most compact sources. Although these have the warmest FIR colours, they are not necessarily the youngest sources., Comment: 16 pages. Submitted to A&A Re-submitted, with aesthetic improvements to the text and figures

We present predictions for the evolution of the galaxy luminosity function, number counts and redshift distributions in the IR based on the Lambda-CDM cosmological model. We use the combined GALFORM semi-analytical galaxy formation model and GRASIL spectrophotometric code to compute galaxy SEDs including the reprocessing of radiation by dust. The model, which is the same as that in Baugh et al (2005), assumes two different IMFs: a normal solar neighbourhood IMF for quiescent star formation in disks, and a very top-heavy IMF in starbursts triggered by galaxy mergers. We have shown previously that the top-heavy IMF seems to be necessary to explain the number counts of faint sub-mm galaxies. We compare the model with observational data from the SPITZER Space Telescope, with the model parameters fixed at values chosen before SPITZER data became available. We find that the model matches the observed evolution in the IR remarkably well over the whole range of wavelengths probed by SPITZER. In particular, the SPITZER data show that there is strong evolution in the mid-IR galaxy luminosity function over the redshift range z ~ 0-2, and this is reproduced by our model without requiring any adjustment of parameters. On the other hand, a model with a normal IMF in starbursts predicts far too little evolution in the mid-IR luminosity function, and is therefore excluded., Comment: LaTeX, 26 pages, 19 figures. Accepted for publication in MNRAS. Minor changes from original version in response to referee's report

We present a quantitative analysis of the astrophysical and cosmological information that can be extracted from the many important wide-area, shallow surveys that will be carried out in the next few years. Our calculations combine the predictions of the physical model by Granato et al. (2004) for the formation and evolution of spheroidal galaxies with up-to-date phenomenological models for the evolution of starburst and normal late-type galaxies and of radio sources. We compute the expected number counts and the redshift distributions of these source populations separately and then focus on proto-spheroidal galaxies. For the latter objects we predict the counts and redshift distributions of strongly lensed sources at 250, 350, 500, and 850 micron, the angular correlation function of sources detected in the surveys considered, the angular power spectra due to clustering of sources below the detection limit in Herschel and Planck surveys. An optimal survey for selecting strongly lensed proto-spheroidal galaxies is described, and it is shown how they can be easily distinguished from the other source populations. We also discuss the detectability of the imprints of the 1-halo and 2-halo regimes on angular correlation functions and clustering power spectra, as well as the constraints on cosmological parameters that can be obtained from the determinations of these quantities. The novel data relevant to derive the first sub-millimeter estimates of the local luminosity functions of starburst and late-type galaxies, and the constraints on the properties of rare source populations, such as blazars, are also briefly described., Comment: 16 pages, 10 figures. Accepted for publication on MNRAS

The mid infrared emission of early type galaxies traces the presence of intermediate age stellar populations as well as even tiny amounts of ongoing star formation. Here we discuss high S/N Spitzer IRS spectra of a sample of Virgo early type galaxies, with particular reference to NGC 4435. We show that, by combining mid infrared spectroscopic observations with existing broad band fluxes, it is possible to obtain a very clean picture of the nuclear activity in this galaxy., Comment: 4 pages; proceedings of IAU Symposium No. 241, "Stellar Populations as Building Blocks of Galaxies", editors A. Vazdekis and R. Peletier

We are performing a systematic study of the properties of early-type galaxies in the mid infrared spectral region with the Spitzer Space Telescope. We present here high S/N Spitzer IRS spectra of 17 Virgo early-type galaxies. Thirteen objects of the sample (76%) show a pronounced broad feature (above 10 microns) which is spatially extended and likely of stellar origin. We argue that this feature is (mostly) due to silicate emission from circumstellar envelopes of asymptotic giant branch (AGB) stars. The remaining 4 objects, namely NGC 4486, NGC 4636, NGC 4550 and NGC 4435, are characterized by various levels and type of activity., Comment: Comments: 8 pages, to appear in the Proceedings of the Conf. "From Stars to Galaxies: Building the Pieces to Build Up the Universe", Vallenari et al. eds., ASP Conf. Series

We analyse the attenuation properties of a sample of UV selected galaxies, with the use of the spectrophotometric model Grasil. In particular, we focus on the relation between dust attenuation and the reddening in the UV spectral region. We show that a realistic modelling of geometrical distribution of dust and of the different population of stars can explain the UV reddening of normal spiral galaxies also with a standard Milky Way dust. Our results clearly underline that it is fundamental to take into account that younger stars suffer a higher attenuation than older stars (the age-dependent extinction) because stars are born in more-than-average dusty environments. In this work we also find that the concentration of young stars on the galactic plane of spirals has a relevant impact on the expected UV colours, impact that has not been explored before this paper. Finally, we discuss the role of IMF in shaping the relation between UV reddening and dust attenuation, and we show that a Kroupa IMF is more consistent with observed data than the classical Salpeter IMF., Comment: 10 pages, accepted for publication on MNRAS

We explore the onset of star formation in the early Universe, exploiting the observations of high-redshift Lyman-break galaxies (LBGs) and Lyman alpha emitters (LAEs), in the framework of the galaxy formation scenario elaborated by Granato et al. (2004) already successfully tested against the wealth of data on later evolutionary stages. Complementing the model with a simple, physically plausible, recipe for the evolution of dust attenuation in metal poor galaxies we reproduce the luminosity functions (LFs) of LBGs and of LAEs at different redshifts. This recipe yields a much faster increase with galactic age of attenuation in more massive galaxies, endowed with higher star formation rates. These objects have therefore shorter lifetimes in the LAE and LBG phases, and are more easily detected in the dusty submillimeter bright phase. The short UV bright lifetimes of massive objects strongly mitigate the effect of the fast increase of the massive halo density with decreasing redshift, thus accounting for the weaker evolution of the LBG LF, compared to that of the halo mass function, and the even weaker evolution between z~6 and z~3 of the LAE LF. LAEs are on the average expected to be younger, with lower stellar masses, and associated to less massive halos than LBGs. Finally, we show that the intergalactic medium can be completely reionized at redshift z~6-7 by massive stars shining in protogalactic spheroids with halo masses from a few 10^10 to a few 10^11 M_sun, showing up as faint LBGs with magnitude in the range -17

The ~800 optically unseen (R>25.5) 24mum-selected sources in the complete Spitzer First Look Survey sample (Fadda et al. 2006) with F[24mum]>0.35 mJy are found to be very strongly clustered. If, as indicated by several lines of circumstantial evidence, they are ultraluminous far-IR galaxies at z ~ [1.6-2.7], the amplitude of their spatial correlation function is very high. The associated comoving clustering length is estimated to be r_0=14.0_{-2.4}^{+2.1} Mpc, value which puts these sources amongst the most strongly clustered populations of our known universe. Their 8mum-24mum colours suggest that the AGN contribution dominates above F[24mum] ~ 0.8 mJy, consistent with earlier analyses. The properties of these objects (number counts, redshift distribution, clustering amplitude) are fully consistent with those of proto-spheroidal galaxies in the process of forming most of their stars and of growing their active nucleus, as described by the Granato et al. (2004) model. In particular, the inferred space density of such galaxies at z ~ 2 is much higher than what expected from most semi-analytic models. Matches of the observed projected correlation function w(\theta) with models derived within the so-called Halo Occupation Scenario show that these sources have to be hosted by haloes more massive than ~10^{13.4} M_\odot. This value is significantly higher than that for the typical galactic haloes hosting massive elliptical galaxies, suggesting a duration of the starburst phase of massive high-redshift dusty galaxies of T_B ~ 0.5 Gyr., Comment: 14 pages, 10 figures, minor revisions, to appear on MNRAS

We present new HI observations of the nearby dwarf galaxy NGC 3741. This galaxy has an extremely extended HI disk, which allows us to trace the rotation curve out to unprecedented distances in terms of the optical disk: we reach 42 B-band exponential scale lengths or about 7 kpc. The HI disk is strongly warped, but the warp is very symmetric. The distribution and kinematics are accurately derived by building model data cubes, which closely reproduce the observations. In order to account for the observed features in the data cube, radial motions of the order of 5-13 km/s are needed. They are consistent with an inner bar of several hundreds of pc and accretion of material in the outer regions. The observed rotation curve was decomposed into its stellar, gaseous and dark components. The Burkert dark halo (with a central constant density core) provides very good fits. The dark halo density distribution predicted by the LambdaCDM theory fails to fit the data, unless NGC 3741 is a 2.5-sigma exception to the predicted relation between concentration parameter and virial mass and has at the same time a high value of the virial mass (though poorly constrained) of 10$^{11}$ solar masses. Noticeably, MOND seems to be consistent with the observed rotation curve. Scaling up the contribution of the gaseous disk also gives a good fit., Comment: Accepted for publication in MNRAS; 16 pages, 19 figures. Version with full resolution figures available at http://www.phys.unm.edu/~ggentile/paper.ps

We present a population synthesis study of NGC4435, an early-type Virgo galaxy interacting with NGC4438. We combine new spectroscopic observations obtained with the Spitzer Space Telescope IRS instrument with IRAC archival data and broad band data from the literature. The IRS spectrum shows prominent PAH features, low ionization emission lines and H_2 rotational lines arising from the dusty circumnuclear disk characterizing this galaxy. The central SED, from X-ray to radio, is well fitted by a model of an exponential burst superimposed on an old simple stellar population. From the lack of high excitation nebular lines, the [NeIII]15.5/[NeII]12.8 ratio, the temperature of molecular hydrogen, and the fit to the full X-ray to radio SED we argue that the present activity of the galaxy is driven by star formation alone. The AGN contribution to the ionizing flux is constrained to be less than 2%. The age of the burst is found to be around 190 Myr and it is fully consistent with the notion that the star formation process has been triggered by the interaction with NGC4438. The mass involved in the rejuvenation episode turns out to be less than 1.5% of the stellar galaxy mass sampled in a 5" central aperture. This is enough to render NGC4435 closely similar to a typical interacting early-type galaxy with inverted CaII[H+K] lines that will later turn into a typical cluster E+A galaxy and enforces the notion that these objects are the result of a recent rejuvenation episode rather than a genuine delayed formation., Comment: 12 pages, accepted for publication on ApJ

We present the maps, source catalogue and number counts of the largest, most complete and unbiased extragalactic submillimetre survey ever undertaken: the 850-micron SCUBA HAlf Degree Extragalactic Survey (SHADES). Using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT), SHADES mapped two separate regions of sky: the Subaru/XMM-Newton Deep Field (SXDF) and the Lockman Hole East (LH). These SCUBA maps cover 720 square arcmin with an RMS noise level of about 2 mJy and have uncovered >100 submillimetre galaxies. In order to ensure the utmost robustness of the resulting source catalogue, data reduction was independently carried out by four sub-groups drawn within the SHADES team, providing an unprecedented degree of reliability with respect to other SCUBA catalogues available from the literature. Individual source lists from the four groups were combined to produce a robust 120-object SHADES catalogue; an invaluable resource for follow-up campaigns aiming to study the properties of a complete and consistent sample of submillimetre galaxies. We present differential and integral source number counts of submillimetre galaxies and find that the differential counts are better fit with a broken power-law or a Schechter function than with a single power-law; the SHADES data alone significantly show that a break is required at several mJy, although the precise position of the break is not well constrained. We also find that an 850-micron survey complete down to 2 mJy would resolve 20-30 per cent of the Far-IR background into point sources. [abridged], Comment: 36 pages including 21 figures and 8 tables. Accepted for publication in MNRAS. Plain-text source catalogue available on the SHADES website http://www.roe.ac.uk/ifa/shades

We have obtained high S/N Spitzer IRS spectra of 17 Virgo early-type galaxies that lie on the colour-magnitude relation of passively evolving galaxies in the cluster. To flux calibrate these extended sources we have devised a new procedure that allows us to obtain the intrinsic spectral energy distribution and to disentangle resolved and unresolved emission within the same object. Thirteen objects of the sample (76%) show a pronounced broad silicate feature (above 10micron) which is spatially extended and likely of stellar origin, in agreement with model predictions. The other 4 objects (24%) are characterized by different levels of activity. In NGC 4486 (M87) the line emission and the broad silicate emission are evidently unresolved and, given also the typical shape of the continuum, they likely originate in the nuclear torus. NGC 4636 show emission lines superimposed to extended silicate emission (i.e. likely of stellar origin, pushing the percentage of galaxies with silicate emission to 82%). Finally NGC 4550 and NGC 4435 are characterized by PAH and line emission, arising from a central unresolved region., Comment: To appear in the proceedings of "The Spitzer Science Center 2005 Conference: Infrared Diagnostics of Galaxy Evolution", held in Pasadena, November 2005

We show that our previously proposed anti-hierarchical baryon collapse scenario for the joint evolution of black holes and host galaxies predicts quasar luminosity functions at redshifts 1.51.5, the population of Extremely Red Objects, and the properties of local ellipticals., Comment: 15 pages, 8 figures, uses REVTeX 4 + emulateapj.cls and apjfonts.sty. Version revised following referee's comments. Accepted on ApJ