ArcAdiA

Spectroscopy identifications of Spitzer sources in the SWIRE/XMM-Newton/ELAIS-S1 field : a large fraction of active galactic nuclei with high F(24 mu m)/F(R) ratio

Wed, 30 Sep 2009 22:00:00 GMT

Spectroscopy identifications of Spitzer sources in the SWIRE/XMM-Newton/ELAIS-S1 field : a large fraction of active galactic nuclei with high F(24 mu m)/F(R) ratio Sacchi, Nicola; La Franca, Fabio; Feruglio, Chiara; Fiore, Fabrizio; Puccetti, Simonetta; Cocchia, Filomena; Berta, Stefano; Brusa, Marcella; Cimatti, Andrea; Comastri, Andrea; Franceschini, Alberto; Gruppioni, Carlotta; Maiolino, Roberto; Matute, Israel; Polletta, Maria; Pozzetti, Lucia; Pozzi, Francesca; Vignali, Cristian; Zamorani, Giovanni; Oliver, Seb; Rowan-Robinson, Michael; Smith, Gene; Lonsdale, Colin J. 2009-10-01 Astrophysical Journal 703 1778-1790 We present a catalog of optical spectroscopic identifications of sources detected by Spitzer at 3.6 or 24 mu m down to similar to 10 and similar to 280 mu Jy, respectively, in the SWIRE/XMM-Newton/ELAIS-S1 field and classified via line width analysis and diagnostic diagrams. A total of 1376 sources down to R similar to 24.2 mag have been identified (1362 detected at 3.6 mu m, 419 at 24 mu m, and 405 at both) by low-resolution optical spectroscopy carried out with FORS2, VIMOS, and EFOSC2 at the Very Large Telescope and 3.6 m ESO telescope. The spectroscopic campaigns have been carried out over the central 0.6deg(2) area of ELAIS-S1 which, in particular, has also been observed byXMM-Newton and Chandra. We find the first direct optical spectroscopic evidence that the fraction of active galactic nuclei (AGNs; mostlyAGN2) increases with increasing F(24 mu m)/F(R) ratio, reaching values of 70(+/- 20)% in the range 316 < F(24 mu m)/F(R) < 1000. We present an Infrared Array Camera - Multiband Imaging Photometer color - color diagram able to separate AGN1 from obscured AGN2 candidates. After having corrected for the spectroscopic incompleteness of our sample, the result is that the AGN fraction at F(24 mu m) similar to 0.8 mJy is similar to 22(+/- 7)% and decreases slowly to similar to 19(+/- 5)% down to F(24 mu m) similar to 0.3 mJy.

The contribution of AGN and star-forming galaxies to the mid-infrared as revealed by their spectral energy distributions (vol 684, pg 136, 2008)

Sun, 09 Aug 2009 22:00:00 GMT

The contribution of AGN and star-forming galaxies to the mid-infrared as revealed by their spectral energy distributions (vol 684, pg 136, 2008) Gruppioni, Carlotta; Pozzi, Francesca; Polletta, Maria; Zamorani, Giovanni; La Franca, Fabio; Sacchi, Nicola; Comastri, Andrea; Pozzetti, Lucia; Vignali, Cristian; Lonsdale, Colin J.; Rowan-Robinson, Michael; Surace, Jason; Shupe, David; Fang, Fan; Matute, Israel; Berta, Stefano 2009-08-10 Astrophysical Journal 701 850-855 Erratum

The HELLAS2XMM survey - XII. The infrared/submillimetre view of anX-ray selected type 2 quasar at z approximate to 2

Wed, 31 Dec 2008 23:00:00 GMT

The HELLAS2XMM survey - XII. The infrared/submillimetre view of anX-ray selected type 2 quasar at z approximate to 2 Vignali, Cristian; Pozzi, Francesca; Fritz, Jacopo; Comastri, Andrea; Gruppioni, Carlotta; Bellocchi, Enrica; Fiore, Fabrizio; Brusa, Marcella; Maiolino, Roberto; Mignoli, Marco; La Franca, Fabio; Pozzetti, Lucia; Zamorani, Giovanni; Merloni, Andrea 2009 MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 395 2189-2195 We present multiwavelength observations (from optical to submillimetre,including Spitzer and Submillimetre Common-User Bolometer Array) ofH2XMMJ003357.2-120038 (also GD158_19), an X-ray selected, luminousnarrow-line (type 2) quasar at z = 1.957 selected from the HELLAS2XMMsurvey. Its broad-band properties can be reasonably well modelledassuming three components: a stellar component to account for theoptical and near-infrared (IR) emission; an active galactic nucleus(AGN) component (i.e. dust heated by an accreting active nucleus),dominant in the mid-IR, with an optical depth at 9.7 mu m along theline of sight ( close to the equatorial plane of the obscuring matter)of tau(9.7) = 1 and a full covering angle of the reprocessing matter(torus) of 140 degrees and a far-IR starburst component (i.e. dustheated by star formation) to reproduce the wide bump observed longwardof 70 mu m.The derived star formation rate is approximate to 1500M(circle dot)yr(-1). The overall modelling indicates that GD158_19 is ahigh-redshift X-ray luminous, obscured quasar with coeval powerful AGNactivity and intense star formation. It is probably caught before theprocess of expelling the obscuring gas has started, thus quenching thestar formation.

Mid-infrared spectroscopy of infrared-luminous galaxies at z similar to 0.5-3

Wed, 22 Apr 2009 22:00:00 GMT

Mid-infrared spectroscopy of infrared-luminous galaxies at z similar to 0.5-3 Hernan-Caballero, Antonio; Perez-Fournon, Ismael; Hatziminaoglou, Evanthia; Afonso-Luis, Alejandro; Rowan-Robinson, Michael; Rigopoulou, Dimitra; Farrah, Duncan; Lonsdale, Colin J.; Babbedge, Thomas; Clements, Dave; Serjeant, Stephen; Pozzi, Francesca; Vaccari, Mattia; Montenegro-Montes, Francisco Miguel; Valtchanov, Ivan; Gonzalez-Solares, Eduardo; Oliver, Seb; Shupe, David; Gruppioni, Carlotta; Vila-Vilaró, Baltazar; Lari, Carlo; La Franca, Fabio 2009-04-23 Monthly Notices of the Royal Astronomical Society 395 1695-1722 We present results on low-resolution mid-infrared (MIR) spectra of 70IR-luminous galaxies obtained with the infrared spectrograph (IRS)onboard Spitzer. We selected sources from the European Large AreaInfrared Survey with S-15 > 0.8 mJy and photometric or spectroscopic z> 1. About half of the samples are quasi-stellar objects (QSOs) in theoptical, while the remaining sources are galaxies, comprising bothobscured active galactic nuclei (AGN) and starbursts. Redshifts wereobtained from optical spectroscopy, photometric redshifts and the IRSspectra. The later turn out to be reliable for obscured and/orstar-forming sources, thus becoming an ideal complement to opticalspectroscopy for redshift estimation. We estimate monochromatic luminosities at several rest-framewavelengths, equivalent widths and luminosities for the polycyclicaromatic hydrocarbon (PAH) features, and strength of the silicatefeature in individual spectra. We also estimate integrated 8-1000 mu mIR luminosities via spectral energy distribution fitting to MIR andfar-IR (FIR) photometry from the Spitzer Wide-Area InfraredExtragalactic survey and the MIR spectrum. Based on these measurements,we classify the spectra using well-known IR diagnostics, as well as anew one that we propose, into three types of source: those dominated byan unobscured AGN, mostly corresponding to optical quasars (QSOs),those dominated by an obscured AGN and starburst-dominated sources.Starbursts concentrate at z similar to 0.6-1.0 favoured by the shift ofthe 7.7-mu m PAH band into the selection 15-mu m band, while AGN spreadover the 0.5 < z < 3.1 range.Star formation rates (SFR) are estimated for individual sources fromthe luminosity of the PAH features. An estimate of the average PAHluminosity in QSOs and obscured AGN is obtained from the compositespectrum of all sources with reliable redshifts. The estimated mean SFRin the QSOs is 50-100M(circle dot) yr(-1), but the implied FIRluminosity is 3-10 times lower than that obtained from stackinganalysis of the FIR photometry, suggesting destruction of the PAHcarriers by energetic photons from the AGN. The SFR estimated inobscured AGN is two to three times higher than in QSOs of similar MIRluminosity. This discrepancy might not be due to luminosity effects orselection bias alone, but could instead indicate a connection betweenobscuration and star formation. However, the observed correlationbetween silicate absorption and the slope of the NIR to MIR spectrum iscompatible with the obscuration of the AGN emission in these sourcesbeing produced in a dust torus.