Browsing by Author "D'Amato, Q."

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    Discovery of a galaxy overdensity around a powerful, heavily obscured FRII radio galaxy at z=1.7: star formation promoted by large-scale AGN feedback?
    (2019) Gilli, R.; Mignoli, M.; Peca, A.; Nanni, R.; Prandoni, I.; Liuzzo, E.; D'Amato, Q.; Brusa, M.; Calura, F.; Caminha, G. B.; Chiaberge, M.; Comastri, A.; Cucciati, O.; Cusano, F.; Grandi, P.; Decarli, R.; Lanzuisi, G.; Mannucci, F.; Pinna, E.; Tozzi, P.; Vanzella, E.; Vignali, C.; Vito, F.; Balmaverde, B.; Citro, A.; Cappelluti, N.; Zamorani, G.; Norman, C.
    We report the discovery of a galaxy overdensity around a Compton-thick Fanaroff-Riley type II (FRII) radio galaxy at z = 1:7 in the deep multiband survey around the z = 6.3 quasi-stellar object (QSO) SDSS J1030 +0524. Based on a 6 h VLT/MUSE and on a 4 h LBT/LUCI observation, we identify at least eight galaxy members in this structure with spectroscopic redshift z = 1 .687 1 .699, including the FRII galaxy at z = 1.699. Most members are distributed within 400 kpc from the FRII core. Nonetheless, the whole structure is likely much more extended, as one of the members was serendipitously found at similar to 800 kpc projected separation. The classic radio structure of the FRII itself extends for similar to 600 kpc across the sky. Most of the identified overdensity members are blue, compact galaxies that are actively forming stars at rates of similar to 8-60 M-circle dot yr(-1). For the brightest of them, a half-light radius of 2 .2 similar to 0 .8 kpc at 8000A rest-frame was determined based on adaptive optics-assisted observations with LBT/SOUL in the Ks band. We do not observe any strong galaxy morphological segregation or concentration around the FRII core. This suggests that the structure is far from being virialized and likely constitutes the progenitor of a local massive galaxy group or cluster caught in its main assembly phase. Based on a 500 ks Chandra ACIS-I observation, we found that the FRII nucleus hosts a luminous QSO (L2-10 keV = 1 .3 similar to 10(44) erg s(-1), intrinsic and rest-frame) that is obscured by Compton-thick absorption (N-H = 1.5 +/- 0 .6 x 10(24) cm(-2)). Under standard bolometric corrections, the total measured radiative power (L-rad similar to 4 x 10(45) erg s(-1)) is similar to the jet kinetic power that we estimated from radio observations at 150MHz (P-kin = 6.3 x 10(45) erg s(-1)), in agreement with what is observed in powerful jetted AGN. Our Chandra observation is the deepest so far for a distant FRII within a galaxy overdensity. It revealed significant di ffuse X-ray emission within the region that is covered by the overdensity. In particular, X-ray emission extending for similar to 240 kpc is found around the eastern lobe of the FRII. Four out of the six MUSE star-forming galaxies in the overdensity are distributed in an arc-like shape at the edge of this di ffuse X-ray emission. These objects are concentrated within 200 kpc in the plane of the sky and within 450 kpc in radial separation. Three of them are even more concentrated and fall within 60 kpc in both transverse and radial distance. The probability of observing four out of the six z = 1.7 sources by chance at the edge of the di ffuse emission is negligible. In addition, these four galaxies have the highest specific star formation rates of the MUSE galaxies in the overdensity and lie above the main sequence of field galaxies of equal stellar mass at z = 1.7. We propose that the di ffuse X-rays originate from an expanding bubble of gas that is shock heated by the FRII jet, and that star formation is promoted by the compression of the cold interstellar medium of the galaxies around the bubble, which may be remarkable evidence of positive AGN feedback on cosmological scales.
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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.