Examinando por Autor "Gavignaud, I."
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Ítem A study on the multicolour evolution of red-sequence galaxy populations: Insights from hydrodynamical simulations and semi-analytical models(Astronomy and Astrophysics, 2015-09) Romeo, A.D.; Kang, Xi; Contini, E.; Sommer-Larsen, J.; Fassbender, R.; Napolitano, N.R.; Antonuccio-Delogu, V.; Gavignaud, I.Context. By means of our own cosmological-hydrodynamical simulation (SIM) and semi-analytical model (SAM), we studied galaxy population properties in clusters and groups, spanning over ten different bands from the ultraviolet to the near-infrared (NIR), and their evolution since redshift z = 2. Aims. We compare our results in terms of red/blue galaxy fractions and of the luminous-to-faint ratio (LFR) on the red sequence (RS) with recent observational data reaching beyond z = 1.5. Methods. Different selection criteria were tested to retrieve the galaxies that effectively belong to the RS: either by their quiescence degree measured from their specific star formation rate (sSFR; the so-called "dead sequence"), or by their position in a colour-colour plane, which is also a function of sSFR. In both cases, the colour cut and the lower limit magnitude thresholds were let to evolve with redshift so that they would follow the natural shift of the characteristic luminosity in the luminosity function (LF). Results. We find that the Butcher-Oemler effect is wavelength-dependent, with the fraction of blue galaxies increasing more steeply in optical-optical than in NIR-optical colours. Moreover, a steep trend in the blue fraction can only be reproduced when an optically fixed luminosity-selected sample is chosen, while the trend flattens when selecting samples by stellar mass or by an evolving magnitude limit. We also find that the RS-LFR behaviour, highly debated in the literature, is strongly dependent on the galaxy selection function: in particular, the very mild evolution that is recovered when using a mass-selected galaxy sample agrees with values reported for some of the highest redshift-confirmed (proto)clusters. For differences that are attributable to environments, we find that normal groups and (to a lesser extent) cluster outskirts present the highest values of both the star-forming fraction and LFR at low z, while fossil groups and cluster cores have the lowest values: this separation among groups begins after z ~ 0.5, while at earlier epochs all groups share similar star-forming properties. Conclusions. Our results support a picture where star formation is still active in SIM galaxies at redshift 2, in contrast with SAM galaxies, which have formed earlier and are already quiescent in cluster cores at that epoch. Over the whole interval considered, we also find that the more massive RS galaxies from the mass-selected sample grow their stellar mass at a higher rate than less massive ones. On the other hand, no dearth of red dwarfs is reported at z 1 from either model. © 2015 ESO.Ítem BAT AGN Spectroscopic Survey – XIX. Type 1 versus type 2 AGN dichotomy from the point of view of ionized outflows(Oxford University Press, 2019-11) Rojas, A.F; Sani, E.; Gavignaud, I.; Ricci, C.; Lamperti, I.; Koss, M.; Trakhtenbrot, B.; Schawinski, K.; K., Oh.; Bauer, F. E.; Bischetti, M.; Boissay-Malaquin, R.; Bongiorno, A.; Harrison, F.; Kakkad, A.D; Masetti, N.; Ricci, F.; Shimizu, T.; Stalevski, M.; Stern, D.; Vietri, G.We present a detailed study of ionized outflows in a large sample of ∼650 hard X-raydetected active galactic neuclei (AGNs). Using optical spectroscopy from the BAT AGN Spectroscopic Survey (BASS), we are able to reveal the faint wings of the [OIII] emission lines associated with outflows covering, for the first time, an unexplored range of low AGN bolometric luminosity at low redshift (z ∼0.05).We test if and how the incidence and velocity of ionized outflow is related to AGN physical parameters: black hole mass (MBH), gas column density (NH), Eddington ratio (λEdd), [O III], X-ray, and bolometric luminosities. We find a higher occurrence of ionized outflows in type 1.9 (55 per cent) and type 1 AGNs (46 per cent) with respect to type 2 AGNs (24 per cent). While outflows in type 2 AGNs are evenly balanced between blue and red velocity offsets with respect to the [OIII] narrow component, they are almost exclusively blueshifted in type 1 and type 1.9 AGNs. We observe a significant dependence between the outflow occurrence and accretion rate, which becomes relevant at high Eddington ratios [log(λEdd) −1.7]. We interpret such behaviour in the framework of covering factor-Eddington ratio dependence. We do not find strong trends of the outflow maximum velocity with AGN physical parameters, as an increase with bolometric luminosity can be only identified when including samples of AGNs at high luminosity and high redshift taken from literature.Ítem Optical atmospheric extinction over Cerro Paranal(2010) Patat, F.; Moehler, S.; O’Brien, K.; Pompei, E.; Bensby, T.; Carraro, G.; de Ugarte Postigo, A.; Fox, A.; Gavignaud, I.; James, G.; Korhonen, H.; Ledoux, C.; Randall, S.; Sana, H.; Smoker, J.; Stefl, S.; Szeifert, T.Aims. The present study was conducted to determine the optical extinction curve for Cerro Paranal under typical clear-sky observing conditions, with the purpose of providing the community with a function to be used to correct the observed spectra, with an accuracy of 0.01 mag airmass1. Additionally, this work was meant to analyze the variability of the various components, to derive the main atmospheric parameters, and to set a term of reference for future studies, especially in view of the construction of the Extremely Large Telescope on the nearby Cerro Armazones. Methods. The extinction curve of Paranal was obtained through low-resolution spectroscopy of 8 spectrophotometric standard stars observed with FORS1 mounted at the 8.2 m Very Large Telescope, covering a spectral range 3300–8000 Å. A total of 600 spectra were collected on more than 40 nights distributed over six months, from October 2008 to March 2009. The average extinction curve was derived using a global fit algorithm, which allowed us to simultaneously combine all the available data. The main atmospheric parameters were retrieved using the LBLRTM radiative transfer code, which was also utilised to study the impact of variability of the main molecular bands of O2, O3, and H2O, and to estimate their column densities. Results. In general, the extinction curve of Paranal appears to conform to those derived for other astronomical sites in the Atacama desert, like La Silla and Cerro Tololo. However, a systematic deficit with respect to the extinction curve derived for Cerro Tololo before the El Chich´on eruption is detected below 4000 Å.We attribute this downturn to a non standard aerosol composition, probably revealing the presence of volcanic pollutants above the Atacama desert. An analysis of all spectroscopic extinction curves obtained since 1974 shows that the aerosol composition has been evolving during the last 35 years. The persistence of traces of non meteorologic haze suggests the e ect of volcanic eruptions, like those of El Chich´on and Pinatubo, lasts several decades. The usage of the standard CTIO and La Silla extinction curves implemented in IRAF and MIDAS produce systematic over/under-estimates of the absolute flux.Ítem Seeking for the leading actor on the cosmic stage: Galaxies versus supermassive black holes(Hindawi Limited, 2012) Bongiorno, A.; Shankar, F.; Civano, F.; Gavignaud, I.; Georgakakis, A.A major development in extragalactic astrophysics in recent years has been the realization that active galactic nuclei (AGN), which signpost accretion events onto supermassive black holes (SMBHs) [1, 2], may play a fundamental role in the formation and evolution of galaxies. Understanding the physics that drive the growth of SMBH across cosmic time is therefore important for having a complete picture of galaxy formation. The two processes of galaxy and BH evolution can no longer be regarded as separate, as was the case until about 10 years ago, but need to be studied in conjunction.Ítem The cosmic growth of the active black hole population at 1 < z < 2 in zCOSMOS, VVDS and SDSS(Oxford University Press, 2015-03) Schulze, A.; Bongiorno, A.; Gavignaud, I.; Schramm, M.; Silverman, J.; Merloni, A.; Zamorani, G.; Hirschmann, M.; Mainieri, V.; Wisotzki, L.; Shankar, F.; Fiore, F.; Koekemoer, A.M.; Temporin, G.We present a census of the active black hole population at 1 < z < 2, by constructing the bivariate distribution function of black hole mass and Eddington ratio, employing a maximum likelihood fitting technique. The study of the active black hole mass function (BHMF) and the Eddington ratio distribution function (ERDF) allows us to clearly disentangle the active galactic nuclei (AGN) downsizing phenomenon, present in the AGN luminosity function, into its physical processes of black hole mass downsizing and accretion rate evolution. We are utilizing type-1 AGN samples from three optical surveys (VVDS, zCOSMOS and SDSS), that cover a wide range of 3 dex in luminosity over our redshift interval of interest. We investigate the cosmic evolution of the AGN population as a function of AGN luminosity, black hole mass and accretion rate. Compared to z = 0, we find a distinct change in the shape of the BHMF and the ERDF, consistent with downsizing in black hole mass. The active fraction or duty cycle of type-1 AGN at z ~ 1.5 is almost flat as a function of black hole mass, while it shows a strong decrease with increasing mass at z = 0. We are witnessing a phase of intense black hole growth, which is largely driven by the onset of AGN activity in massive SMBHs (supermassive black holes) towards z = 2. We finally compare our results to numerical simulations and semiempirical models and while we find reasonable agreement over certain parameter ranges, we highlight the need to refine these models in order to match our observations. © 2015 The Authors.Ítem The nature of 50 Palermo Swift -BAT hard X-ray objects through optical spectroscopy(EDP Sciences, 2017-06) Rojas, A.F.; Masetti, N.; Minniti, D.; Jiménez-Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V.A.; Bassani, L.; Bazzano, A.; Bird, A.J.; Galaz, G.l.; Gavignaud, I.; Landi, R.; Malizia, A.; Morelli, L.; Palazzi, E.; Patiño-Álvarez, V.; Stephen, J.B.; Ubertini, P.We present the nature of 50 hard X-ray emitting objects unveiled through an optical spectroscopy campaign performed at seven telescopes in the northern and southern hemispheres. These objects were detected with the Burst Alert Telescope (BAT) instrument onboard the Swift satellite and listed as of unidentified nature in the 54-month Palermo BAT catalogue. In detail, 45 sources in our sample are identified as active galactic nuclei of which, 27 are classified as type 1 (with broad and narrow emission lines) and 18 are classified as type 2 (with only narrow emission lines). Among the broad-line emission objects, one is a type 1 high-redshift quasi-stellar object, and among the narrow-line emission objects, one is a starburst galaxy, one is a X-ray bright optically normal galaxy, and one is a low ionization nuclear emission line region. We report 30 new redshift measurements, 13 confirmations and 2 more accurate redshift values. The remaining five objects are galactic sources: three are Cataclismic Variables, one is a X-ray Binary probably with a low mass secondary star, and one is an active star.