Reproducing the assembly of massive galaxies within the hierarchical cosmogony

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 micron-selected galaxies (such as number counts, redshift distributions and luminosity functions) by combining MORGANA with the spectrophotometric model GRASIL. We find that it is possible to reproduce the K- and 850 micron-band datasets at the same time and with a standard Salpeter IMF, and ascribe this success to our improved modeling of cooling in DM halos. We then predict that massively star-forming discs are common at z~2 and dominate the star-formation rate, but most of them merge with other galaxies within ~100 Myr. Our preferred model produces an overabundance of bright galaxies at z<1; this overabundance might be connected to the build-up of the diffuse stellar component in galaxy clusters, as suggested by Monaco et al. (2006), but a naive implementation of the mechanism suggested in that paper does not produce a sufficient slow-down of the evolution of these objects. Moreover, our model over-predicts the number of 10^{10}-10^{11} M_sun galaxies at z~1; this is a common behavior of theoretical models as shown by Fontana et al. (2006). 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.Comment: 14 pages; 11 figures; accepted for publication by MNRA

Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth vs. Resolution

We present a study of the trade-off between depth and resolution using a large number of U-band imaging observations in the GOODS-North field (Giavalisco et al. 2004) from the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT). Having acquired over 30 hours of data (315 images with 5-6 mins exposures), we generated multiple image mosaics, starting with the best atmospheric seeing images (FWHM $\lesssim$0.8"), which constitute $\sim$10% of the total data set. For subsequent mosaics, we added in data with larger seeing values until the final, deepest mosaic included all images with FWHM $\lesssim$1.8" ($\sim$94% of the total data set). From the mosaics, we made object catalogs to compare the optimal-resolution, yet shallower image to the lower-resolution but deeper image. We show that the number counts for both images are $\sim$90% complete to $U_{AB}$ $\lesssim26$. Fainter than $U_{AB}$$\sim$ 27, the object counts from the optimal-resolution image start to drop-off dramatically (90% between $U_{AB}$ = 27 and 28 mag), while the deepest image with better surface-brightness sensitivity ($\mu^{AB}_{U}$$\lesssim$ 32 mag arcsec$^{-2}$) show a more gradual drop (10% between $U_{AB}$ $\simeq$ 27 and 28 mag). For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. Finally, we find - for 220 brighter galaxies with $U_{AB}$$\lesssim$ 24 mag - only marginal differences in total flux between the optimal-resolution and lower-resolution light-profiles to $\mu^{AB}_{U}$$\lesssim$ 32 mag arcsec$^{-2}$. In only 10% of the cases are the total-flux differences larger than 0.5 mag. This helps constrain how much flux can be missed from galaxy outskirts, which is important for studies of the Extragalactic Background Light.Comment: 24 pages, 14 figures, submitted to PASP, comments welcom

A mass threshold in the number density of passive galaxies at z∼\sim2

The process that quenched star formation in galaxies at intermediate and high redshift is still the subject of considerable debate. One way to investigate this puzzling issue is to study the number density of quiescent galaxies at z~2, and its dependence on mass. Here we present the results of a new study based on very deep Ks-band imaging (with the HAWK-I instrument on the VLT) of two HST CANDELS fields (the UKIDSS Ultra-deep survey (UDS) field and GOODS-South). The new HAWK-I data (taken as part of the HUGS VLT Large Program) reach detection limits of Ks>26 (AB mag). We select a sample of passively-evolving galaxies in the redshift range 1.4<z<2.5. Thanks to the depth and large area coverage of our imaging, we have been able to extend the selection of quiescent galaxies a magnitude fainter than previous analyses. Through extensive simulations we demonstrate, for the first time, that the observed turn-over in the number of quiescent galaxies at K>22 is real. This has enabled us to establish unambiguously that the number counts of quiescent galaxies at z~2 flatten and slightly decline at magnitudes fainter than Ks~22(AB mag.). We show that this trend corresponds to a stellar mass threshold $M_*10^{10.8}\,{\rm M_{\odot}}$ below which the mechanism that halts the star formation in high-redshift galaxies seems to be inefficient. Finally we compare the observed pBzK number counts with those of quiescent galaxies extracted from four different semi-analytic models. We find that none of the models provides a statistically acceptable description of the number density of quiescent galaxies at these redshifts. We conclude that the mass function of quiescent galaxies as a function of redshift continues to present a key and demanding challenge for proposed models of galaxy formation and evolution.Comment: Accepted for publication on Astronomy and Astrophysic

Multicolor observations of the Hubble Deep Field South

We present a deep multicolor (UBVIJsHKs) catalog of galaxies in the HDF-S, based on observations obtained with the HST WFPC2 in 1998 and VLT-ISAAC in 1999. The photometric procedures were tuned to derive a catalog optimized for the estimation of photometric redshifts. In particular we adopted a ``conservative'' detection threshold which resulted in a list of 1611 objects. The behavior of the observed source counts is in general agreement with the result of Casertano et al. (2000) in the HDF-S and Williams et al. (1996) in the HDF-N, while the corresponding counts in the HDF-N provided by Fernandez-Soto et al. (1999) are systematically lower by a factor 1.5 beyond I_AB=26. After correcting for the incompleteness of the source counts, the object surface density at I_AB<27.5 is estimated to be 220 per square arcmin, providing an estimate of the Extragalactic Background Light in the I band consistent with the work of Madau & Pozzetti(2000). The comparison between the median V-I color in the HDF-North and South shows a significant difference around I_AB~26, possibly due to the presence of large scale structure at z~1 in the HDF-N. High-z galaxy candidates (90 U dropout and 17 B dropout) were selected by means of color diagrams, down to a magnitude I_AB=27, with a surface density of (21+-1) and (3.9+-0.9) per square arcmin, respectively. 11 EROs (with (I-K)_AB>2.7) were selected down to K_AB=24, plus 3 objects whose upper limit to the Ks flux is still compatible with the selection criterion. The corresponding surface density of EROs is (2.5+-0.8) per sq.arcmin ((3.2+-0.9) per sq.arcmin if we include the three Ks upper limits). They show a remarkably non-uniform spatial distribution and are classified with roughly equal fractions in the categories of elliptical and starburst galaxies.Comment: 36 pages Latex, with 12 PostScript figures. Accepted for publication in Astronomical Journa

On the Evolution of the Star Formation Rate Function of Massive Galaxies. Constraints at 0.4<z<1.8 from the GOODS-MUSIC Catalogue

[abridged] We study the evolution of the Star Formation Rate Function (SFRF) of massive galaxies over the 0.4<z<1.8 redshift range and its implications for our understanding of the physical processes responsible for galaxy evolution. We use multiwavelength observations included in the GOODS-MUSIC catalogue, which provides a suitable coverage of the spectral region from 0.3 to 24 micron and either spectroscopic or photometric redshifts for each object. Individual SFRs have been obtained by combining UV and 24 micron observations, when the latter were available. For all other sources an "SED fitting" SFR estimate has been considered. We then define a stellar mass limited sample, complete in the Mstar>1.e10 Msun range and determine the SFRF using the 1/Vmax algorithm. We define simulated galaxy catalogues based on three different semi-analytical models of galaxy formation and evolution. We show that the theoretical SFRFs are well described by a double power law functional form and its redshift evolution is approximated with high accuracy by a pure evolution of the typical SFR. We find good agreement between model predictions and the high-SFR end of the SFRF, when the observational errors on the SFR are taken into account. However, the observational SFRF is characterised by a double peaked structure, which is absent in its theoretical counterparts. At z>1.0 the observed SFRF shows a relevant density evolution, which is not reproduced by SAMs, due to the well known overprediction of intermediate mass galaxies at z~2. The agreement at the low-SFR end is poor: all models overpredict the space density of SFR~1 Msun/yr and no model reproduces the double peaked shape of the observational SFRF. If confirmed by deeper IR observations, this discrepancy will provide a key constraint on theoretical modelling of star formation and stellar feedback.Comment: 12 pages, 4 figures and 3 table. Accepted for publication by MNRAS - updated reference

The Asiago-ESO/RASS QSO Survey. III. Clustering analysis and its theoretical interpretation

This is the third paper of a series describing the Asiago-ESO/RASS QSO survey (AERQS), a project aimed at the construction of an all-sky statistically well-defined sample of relatively bright QSOs (B<15) at z<0.3. We present here the clustering analysis of the full spectroscopically identified database (392 AGN). The clustering signal at 0.02<z<0.22 is detected at a 3-4 sigma level and its amplitude is measured to be r_0=8.6\pm 2.0 h^{-1} Mpc (in a LambdaCDM model). The comparison with other classes of objects shows that low-redshift QSOs are clustered in a similar way to Radio Galaxies, EROs and early-type galaxies in general, although with a marginally smaller amplitude. The comparison with recent results from the 2QZ shows that the correlation function of QSOs is constant in redshift or marginally increasing toward low redshift. We discuss this behavior with physically motivated models, deriving interesting constraints on the typical mass of the dark matter halos hosting QSOs, M_DMH= 10^{12.7} h^{-1} M_sun (10^{12.0}-10^{13.5}h^{-1} M_sun at 1 sigma confidence level). Finally, we use the clustering data to infer the physical properties of local AGN, obtaining M_BH=2 10^8 h^{-1} M_sun (10^7-3 10^9 h^{-1} M_sun) for the mass of the active black holes, tau_{AGN}= 8 10^6 yr (2 10^{6}-5 10^{7} yr) for their life-time and eta = 0.14 for their efficiency (always for a LambdaCDM model).Comment: 37 pages, Astronomical Journal in press. Changes to match the referee comment

Escape Fraction of Ionizing Radiation from Starburst Galaxies at High Redshifts

Recent data indicates that the cosmic UV emissivity decreased with decreasing redshift z near the end of reionization. Lacking evidence for very massive early stars, this could signal a decline with time in the mass-averaged escape fraction of ionizing radiation from galaxies at z > 6. We calculate the evolution of ionization fronts in dark matter halos which host gas in hydrostatic equilibrium at its cooling temperature floor (T~10^4 K for atomic hydrogen). We find a high escape fraction only for the lowest mass halos (with M 10^-3. Since the low-mass galaxy population is depleted by radiative feedback, we find that indeed decreases with time during reionization.Comment: 9 pages, submitted to MNRA

The dusty environment of Quasars. Far-IR properties of Optical Quasars

We present the ISO far-IR photometry of a complete sub-sample of optically selected bright quasars belonging to two complete surveys selected through multicolour (U,B,V,R,I) techniques. The ISOPHOT camera on board of the ISO Satellite was used to target these quasars at wavelengths of 7.3, 11.5, 60, 100 and 160 micron. Almost two thirds of the objects were detected at least in one ISOPHOT band. The detection rate is independent of the source redshift, very likely due to the negative K-correction of the far-IR thermal emission. More than a half of the optically selected QSOs show significant emission between 4 and 100 micron in the quasar rest-frame. These fluxes have a very likely thermal origin, although in a few objects an additional contribution from a non-thermal component is plausible in the long wavelength bands. In a colour-colour diagram these objects span a wide range of properties from AGN-dominated to ULIRG-like. The far-IR composite spectrum of the quasar population presents a broad far-IR bump between 10 and 30 micron and a sharp drop at wavelengths greater than 100 micron in the quasar restframe. The amount of energy emitted in the far-IR, is on average a few times larger than that emitted in the blue and the ratio L(FIR)/L(B) increases with the bolometric luminosity. Objects with fainter blue magnitudes have larger ratios between the far-IR (wavelengths > 60 micron) fluxes and the blue band flux, which is attributed to extinction by dust around the central source. No relation between the blue absolute magnitude and the dust colour temperature is seen, suggesting that the dominant source of FIR energy could be linked to a concurrent starburst rather than to gravitational energy produced by the central engine.Comment: Astronomical Journal, in pres

Il Cispio e le sue adiacenze in età antica. Storia urbana e analisi topografica di un settore dell'Esquilino

La ricerca è stata avviata col fine di analizzare la topografia storica di uno dei settori della città antica meno conosciuti: il Cispio. Ci si è così proposti di restituire la storia urbana di una delle aree di Roma che, a causa di una marginalità evidente all’interno delle fonti letterarie risulta tra le più neglette negli studi contemporanei. A livello metodologico si è operato distinguendo tre differenti livelli: analitico, sintetico e interpretativo. Nella struttura della ricerca si è imposta una qualche ridondanza nella organizzazione e nell’analisi delle fonti disponibili, interrogandole sulle diverse tematiche affrontate e riarticolandole secondo prospettive interpretative differenti. La natura stessa del dossier non ha consentito, infatti, una narrazione continua e cronologicamente ordinata, a cui si è così rinunciato. La raccolta dei dati ha mirato a ricostruire ogni ritrovamento occorso lungo la superficie del Cispio, confluito poi nella carta archeologica, che costituisce la parte catalogica di questo lavoro. Ad un livello successivo, quello di sintesi, si è scelto di esaminare ogni tematica topografica sotto una duplice prospettiva quella delle fonti archeologiche e quella delle fonti scritte, cercando in questo modo sia di distinguere il più possibile la lettura dall’interpretazione, sia di valorizzare un dossier di sua natura poco “parlante”. Sono state così affrontate problematiche quali la toponomastica e la topografia, le suddivisioni dello spazio urbano, la viabilità e gli spazi pubblici e i luoghi di culto nell’ambito delle fonti scritte. Per quelle archeologiche, invece, si sono esaminate le dinamiche dello sviluppo pre-urbano, il tessuto insediativo, la viabilità e, seppur brevemente, l’analisi dei reperti mobili. Un apposito spazio, inoltre, è stato dedicato alla complessa problematica della localizzazione del tempio di Giunone Lucina sul Cispio, di fatto il solo edificio che le fonti antiche situano con certezza sul mons. La proposta di localizzazione, ottenuta tramite l’analisi integrata del dossier archeologico con quello letterario ed epigrafico, si è giovata in gran parte della ricerca archivistica sopramenzionata. Si è tentato comunque, per quanto possibile, di restituire un quadro e un areale accettabile per la localizzazione del luogo di culto, e successivamente indagare le distinte possibilità, avanzando una proposta specifica. Infine, ad un ultimo livello più interpretativo si sono analizzate le problematiche di storia urbana dell’area. In questo senso, proprio a causa della limitatezza delle fonti letterarie disponibili il lavoro si è giovato del dossier epigrafico per approfondire il paesaggio religioso e la storia sociale del quartiere. Sulla prima tematica, sostanzialmente limitata alla festività dei Matronalia ci si è proposti di chiarire la ritualità connessa alla celebrazione delle feste in onore della dea, al suo contesto storico ed alle vicende connesse alla fondazione del tempio, tra le più dibattute nella storia degli studi. Sulla storia sociale del quartiere è stata indagata e verificata la presenza di specifiche forme di sociabilità connessa alla eventuale caratterizzazione “professionale” di alcune aree del Cispio. Contestualmente si è cercato di comprendere e ricostruire la presenza di memorie di famiglie nella toponomastica, ed infine, di tracciare un quadro degli abitanti del quartiere, provando a riconoscerne le abitazioni e analizzando i caratteri specifici del popolamento. L’obiettivo finale è stato quello di colmare un vuoto nella storia urbana della città antica, cercando di comprendere l’area nella sua integrità e il complesso sistema di fonti ad essa associate