Browsing by Author "Circosta, C."

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    Dust and gas content of high-redshift galaxies hosting obscured AGN in the Chandra Deep Field-South
    (2020) D'Amato, Q.; Gilli, R.; Vignali, C.; Massardi, M.; Pozzi, F.; Zamorani, G.; Circosta, C.; Vito, F.; Fritz, J.; Cresci, G.; Casasola, V.; Calura, F.; Feltre, A.; Manieri, V.; Rigopoulou, D.; Tozzi, P.; Norman, C.
    Context. Obscured active galactic nuclei (AGN) represent a significant fraction of the entire AGN population, especially at high redshift (similar to 70% at z=3-5). They are often characterized by the presence of large gas and dust reservoirs that are thought to sustain and possibly obscure vigorous star formation processes that make these objects shine at FIR and submillimeter wavelengths. Studying the physical properties of obscured AGN and their host galaxies is crucial to shedding light on the early stages of a massive system lifetime.Aims. We aim to investigate the contribution of the interstellar medium (ISM) to the obscuration of quasars in a sample of distant highly star forming galaxies and to unveil their morphological and kinematics properties.Methods. We exploit Atacama Large Millimeter/submillimeter Array Cycle 4 observations of the continuum (similar to 2.1 mm) and high-J CO emission of a sample of six X-ray selected, FIR detected galaxies hosting an obscured AGN at z(spec)> 2.5 in the 7 Ms Chandra Deep Field-South. We measured the masses and sizes of the dust and molecular gas by fitting the images, visibilities, and spectra, and we derived the gas density and column density on the basis of a uniform sphere geometry. Finally, we compared the measured column densities with those derived from the Chandra X-ray spectra.Results. We detected both the continuum and line emission for three sources for which we measured both the flux density and size. For the undetected sources, we derived an upper limit on the flux density from the root mean square of the images. We found that the detected galaxies are rich in gas and dust (molecular gas mass in the range < 0.5-2.7x10(10) M- for alpha (CO)=0.8 and up to similar to 2x10(11) M-circle dot for alpha (CO)=6.5, and dust mass < 0.9-4.9x10(8) M-) and generally compact (gas major axis 2.1-3.0 kpc, dust major axis 1.4-2.7 kpc). The column densities associated with the ISM are on the order of 10(23-24) cm(-2), which is comparable with those derived from the X-ray spectra. For the detected sources we also derived dynamical masses in the range 0.8-3.7x10(10) M-circle dot.Conclusions. We conclude that the ISM of high redshift galaxies can substantially contribute to nuclear obscuration up to the Compton-thick (> 10(24) cm(-2)) regime. In addition, we found that all the detected sources show a velocity gradient reminding one rotating system, even though two of them show peculiar features in their morphology that can be associated with a chaotic, possibly merging, structure.
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    The WISSH quasars project : IX. Cold gas content and environment of luminous QSOs at z ∼2.4-4.7
    (2021) Bischetti, M.; Feruglio, C.; Piconcelli, E.; Duras, F.; Perez-Torres, M.; Herrero, R.; Venturi, Giacomo; Carniani, S.; Bruni, G.; Gavignaud, I.; Testa, V.; Bongiorno, A.; Brusa, M.; Circosta, C.; Cresci, G.; D'Odorico, V.; Maiolino, R.; Marconi, A.; Mingozzi, M.; Pappalardo, C.; Perna, M.; Traianou, E.; Travascio, A.; Vietri, G.; Zappacosta, L.; Fiore, F.
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    X-ray emission of z > 2.5 active galactic nuclei can be obscured by their host galaxies
    (2019) Circosta, C.; Vignali, C.; Gilli, R.; Feltre, A.; Vito, F.; Calura, F.; Mainieri, V; Massardi, M.; Norman, C.
    We present a multiwavelength study of seven active galactic nuclei (AGN) at spectroscopic redshift >2.5 in the 7 Ms Chandra Deep Field South that were selected for their good far-infrared (FIR) and submillimeter (submm) detections. Our aim is to investigate the possibility that the obscuration observed in the X-rays can be produced by the interstellar medium (ISM) of the host galaxy. Based on the 7 Ms Chandra spectra, we measured obscuring column densities N-H,N- X in excess of 7 x 10(22) cm(-2) and intrinsic X-ray luminosities L-X > 10(44) erg s(-1) for our targets, as well as equivalent widths for the Fe K alpha emission line EWrest greater than or similar to 0.5-1 keV. We built the UV-to-FIR spectral energy distributions (SEDs) by using broadband photometry from the CANDELS and Herschel catalogs. By means of an SED decomposition technique, we derived stellar masses (M-* similar to 10(11) M-circle dot), IR luminosities (L-IR > 10(12) L-circle dot), star formation rates (SFR similar to 190-1680 M-circle dot yr(-1)) and AGN bolometric luminosities (L-bol similar to 10(46) erg s(-1)) for our sample. We used an empirically calibrated relation between gas masses and FIR/submm luminosities and derived M-gas similar to 0.8-5.4 x 10(10) M-circle dot. High-resolution (0.3-0.7 '') ALMA data (when available, CANDELS data otherwise) were used to estimate the galaxy size and hence the volume enclosing most of the ISM under simple geometrical assumptions. These measurements were then combined to derive the column density associated with the ISM of the host, which is on the order of N-H,N- ISM similar to 10(23-24) cm(-2). The comparison between the ISM column densities and those measured from the X-ray spectral analysis shows that they are similar. This suggests that at least at high redshift, significant absorption on kiloparsec scales by the dense ISM in the host likely adds to or substitutes that produced by circumnuclear gas on parsec scales (i.e., the torus of unified models). The lack of unobscured AGN among our ISM-rich targets supports this scenario.