Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 70 )

2019 ( 634 )

2018 ( 727 )

2017 ( 756 )

Custom range...

Search Results: 1 - 10 of 486377 matches for " R. S. Brusa "
All listed articles are free for downloading (OA Articles)
Page 1 /486377
Display every page Item
Is there any evidence that ionised outflows quench star formation in type 1 quasars at z<1?
B. Balmaverde,A. Marconi,M. Brusa,S. Carniani,G. Cresci,E. Lusso,R. Maiolino,F. Mannucci,T. Nagao
Physics , 2015,
Abstract: The aim of this paper is to test the basic model of negative AGN feedback. According to this model, once the central black hole accretes at the Eddington limit and reaches a certain critical mass, AGN driven outflows blow out gas, suppressing star formation in the host galaxy and self-regulating black hole growth. We consider a sample of 224 quasars selected from the SDSS at z<1 observed in the infrared band by Herschel. We evaluate the star formation rate in relation to several outflow signatures traced by the [OIII]4959,5007 and [OII]3726,3729 emission lines in about half of the sample with high quality spectra. Most of the quasars show asymmetric and broad wings in [OIII], which we interpret as outflow signatures. We separate the quasars in two groups, ``weakly'' and ``strongly'' outflowing, using three different criteria. When we compare the mean star formation rate in five redshift bins in the two groups, we find that the SFRs are comparable or slightly larger in the strongly outflowing quasars. We estimate the stellar mass from SED fitting and the quasars are distributed along the star formation main sequence, although with a large scatter. The scatter from this relation is uncorrelated with respect to the kinematic properties of the outflow. Moreover, for quasars dominated in the infrared by starburst or by AGN emission, we do not find any correlation between the star formation rate and the velocity of the outflow, a trend previously reported in the literature for pure starburst galaxies. We conclude that the basic AGN negative feedback scenario seems not to agree with our results. Although we use a large sample of quasars, we did not find any evidence that the star formation rate is suppressed in the presence of AGN driven outflows on large scale. A possibility is that feedback is effective over much longer timescales than those of single episodes of quasar activity.
Demography of obscured and unobscured AGN: prospects for a Wide Field X-ray Telescope
R. Gilli,P. Tozzi,P. Rosati,M. Paolillo,S. Borgani,M. Brusa,A. Comastri,E. Lusso,F. Marulli,C. Vignali
Physics , 2010,
Abstract: We discuss some of the main open issues in the evolution of Active Galactic Nuclei which can be solved by the sensitive, wide area surveys to be performed by the proposed Wide Field X-ray Telescope mission.
On the nature of X-ray Bright Optically Normal galaxies
A. Comastri,M. Brusa,P. Ciliegi,M. Mignoli,F. Fiore,R. Maiolino,P. Severgnini,A. Baldi,S. Molendi,C. Vignali,F. La Franca,G. Matt,G. C. Perola
Physics , 2002,
Abstract: Multiwavelength observations of the hard X-ray selected sources by Chandra and XMM-Newton surveys have significantly improved our knowledge of the objects responsible of the hard X-ray background. A surprising finding is the discovery of a population of optically dull, X-ray bright galaxies emerging at 2-10 keV fluxes of the order of 10^{-14} erg cm^{-2} s^{-1}. We present preliminary results of multiwavelength observations of a few objects serendipitously discovered in the field of XMM-Newton and Chandra observations and intensively studied at longer wavelengths.
The primordial environment of super massive black holes: large scale galaxy overdensities around $z\sim6$ QSOs with LBT
L. Morselli,M. Mignoli,R. Gilli,C. Vignali,A. Comastri,E. Sani,N. Cappelluti,G. Zamorani,M. Brusa,S. Gallozzi,E. Vanzella
Physics , 2014, DOI: 10.1051/0004-6361/201423853
Abstract: We investigated the presence of galaxy overdensities around four $z\sim6$ QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep $r$-, $i$- and $z$- band imaging obtained with the wide-field ($\sim23'\times25'$) Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted color-color selections within the $i-z$ vs $r-z$ plane to identify samples of $i$-band dropouts at the QSO redshift and measure their relative abundance and spatial distribution in the four LBC fields, each covering $\sim8\times8$ physical Mpc at $z\sim6$. The same selection criteria were then applied to $z$-band selected sources in the $\sim$1 deg$^2$ Subaru-XMM Newton Deep Survey to derive the expected number of dropouts over a blank LBC-sized field ($\sim$0.14 deg$^2$). The four observed QSO fields host a number of candidates larger than what is expected in a blank field. By defining as $i$-band dropouts objects with $z_{AB}<25$, $i-z>1.4$ and undetected in the $r$-band, we found 16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg$^2$ blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, 2.5$\sigma$, respectively. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg$^2$ each, we find that high-z QSOs reside in overdense environments at the $3.7\sigma$ level. This is the first direct and unambiguous measurement of the large scale structures around $z\sim6$ QSOs. [shortened]
X-ray bright optically quiet galaxies: the case of P3
A. Comastri,M. Brusa,P. Ciliegi,M. Mignoli,C. Vignali,P. Severgnini,R. Maiolino,F. Fiore,F. La Franca,G. Matt,G. C. Perola,A. Baldi,S. Molendi
Physics , 2001,
Abstract: Recent X-ray surveys have clearly demonstrated that a population of optically dull, X-ray bright galaxies is emerging at X-ray fluxes of the order of 10-14 erg cm-2 s-1. The nature of these objects is still unknown. We present the results of multiwavelength observations of what can be considered the best studied example: the Chandra source CXOUJ031238.9-765134 optically identified by Fiore et al. (2000) with an apparently normal galaxy at z=0.159 and called ``Fiore P3''.
Optical identification of sources from the HELLAS2XMM survey
F. Fiore,G. Matt,F. La Franca,G. C. Perola,M. Brusa,A. Comastri,M. Mignoli,P. Ciliegi,P. Severgnini,R. Maiolino,A. Baldi,S. Molendi,C. Vignali
Physics , 2001,
Abstract: We present preliminary results on the optical identifications of sources from the High Energy Large Area Survey performed with XMM-Newton (HELLAS2XMM). This survey covers about 3 square degrees of sky down to a 2-10 keV flux of 7 x 10^-15 erg cm-2 s-1 (Baldi & Molendi these proceedings, Baldi et al. 2001). The survey good sensitivity over a large area allows us to confirm and extend previous Chandra results about a population of X-ray luminous but optically dull galaxies emerging at 2-10 keV fluxes of about 10-14 erg cm-2 s-1. Although the statistics are still rather poor, it appears that at these X-ray fluxes the fraction of these galaxies is similar or even higher than that of narrow line AGN.
The most obscured AGN in the COSMOS field
G. Lanzuisi,M. Perna,I. Delvecchio,S. Berta,M. Brusa,N. Cappelluti,A. Comastri,R. Gilli,C. Gruppioni,M. Mignoli,F. Pozzi,G. Vietri,C. Vignali,G. Zamorani
Physics , 2015,
Abstract: Highly obscured active galactic nuclei (AGN) are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black hole accretion rate density. Furthermore, Compton-thick (CT) absorbers (NH>10^24 cm^-2) suppress even the hard X-ray (2-10 keV) AGN nuclear emission, and therefore the column density distribution above 10^24 cm^-2 is largely unknown. We present the identification and multi-wavelength properties of a heavily obscured (NH>~10^25 cm^-2), intrinsically luminous (L(2-10keV)>10^44 erg s^-1) AGN at z=0.353 in the COSMOS field. Several independent indicators, such as the shape of the X-ray spectrum, the decomposition of the spectral energy distribution and X-ray/[NeV] and X-ray/6{\mu}m luminosity ratios, agree on the fact that the nuclear emission must be suppressed by a 10^25 cm^-2 column density. The host galaxy properties show that this highly obscured AGN is hosted in a massive star-forming galaxy, showing a barred morphology, which is known to correlate with the presence of CT absorbers. Finally, asymmetric and blueshifted components in several optical high-ionization emission lines indicate the presence of a galactic outflow, possibly driven by the intense AGN activity (L(Bol)/L(Edd) = 0.3-0.5). Such highly obscured, highly accreting AGN are intrinsically very rare at low redshift, whereas they are expected to be much more common at the peak of the star formation and BH accretion history, at z~2-3. We demonstrate that a fully multi-wavelength approach can recover a sizable sample of such peculiar sources in large and deep surveys such as COSMOS.
The XMM-Newton deep survey in the Chandra Deep Field South. III. Point source catalogue and number counts in the hard X-rays
P. Ranalli,A. Comastri,C. Vignali,F. J. Carrera,N. Cappelluti,R. Gilli,S. Puccetti,W. N. Brandt,H. Brunner,M. Brusa,I. Georgantopoulos,K. Iwasawa,V. Mainieri
Physics , 2013, DOI: 10.1051/0004-6361/201321211
Abstract: (abridged) The XMM-Newton survey in the Chandra Deep Field South (XMM-CDFS) aims at detecting and studying the spectral properties of a significant number of obscured and Compton-thick AGN. The large effective area of XMMin the 2--10 and 5--10 keV bands, coupled with a 3.45 Ms nominal exposure time, allows us to build clean samples in both bands, and makes the XMM-CDFS the deepest XMM survey currently published in the 5--10 keV band. The large multi-wavelength and spectroscopic coverage of the CDFS area allows for an immediate and abundant scientific return. We present the data reduction of the XMM-CDFS observations, the method for source detection in the 2--10 and 5--10keV bands, and the resulting catalogues. A number of 339 and 137 sources are listed in the above bands with flux limits of 6.6e-16 and 9.5e-16 erg/s/cm^2, respectively. The flux limits at 50% of the maximum sky coverage are 1.8e-15 and 4.0e-15 erg/s/cm^2, respectively. The catalogues have been cross-correlated with the Chandra ones: 315 and 130 identifications have been found with a likelihood-ratio method, respectively. A number of 15 new sources, previously undetected by Chandra, is found; 5 of them lie in the 4 Ms area. Redshifts, either spectroscopic or photometric, are available for ~92% of the sources. The number counts in both bands are presented and compared to other works. The survey coverage has been calculated with the help of two extensive sets of simulations, one set per band. The simulations have been produced with a newly-developed simulator, written with the aim of the most careful reproduction of the background spatial properties. We present a detailed decomposition of the XMM background into its components: cosmic, particle, and residual soft protons.
Detailed Shape and Evolutionary Behavior of the X-ray Luminosity Function of Active Galactic Nuclei
T. Miyaji,G. Hasinger,M. Salvato,M. Brusa,N. Cappelluti,F. Civano,S. Puccetti,M. Elvis,H. Brunner,S. Fotopoulou,Y. Ueda,R. E. Griffiths,A. M. Koekemoer,M. Akiyama,A. Comastri,R. Gilli,G. Lanzuisi,A. Merloni,C. Vignali
Physics , 2015, DOI: 10.1088/0004-637X/804/2/104
Abstract: We construct the rest-frame 2--10 keV intrinsic X-ray luminosity function of Active Galactic Nuclei (AGNs) from a combination of X-ray surveys from the all-sky Swift BAT survey to the Chandra Deep Field-South. We use ~3200 AGNs in our analysis, which covers six orders of magnitude in flux. The inclusion of the XMM and Chandra COSMOS data has allowed us to investigate the detailed behavior of the XLF and evolution. In deriving our XLF, we take into account realistic AGN spectrum templates, absorption corrections, and probability density distributions in photometric redshift. We present an analytical expression for the overall behavior of the XLF in terms of the luminosity-dependent density evolution, smoothed two power-law expressions in 11 redshift shells, three-segment power-law expression of the number density evolution in four luminosity classes, and binned XLF. We observe a sudden flattening of the low luminosity end slope of the XLF slope at z>~0.6. Detailed structures of the AGN downsizing have been also revealed, where the number density curves have two clear breaks at all luminosity classes above log LX>43. The two break structure is suggestive of two-phase AGN evolution, consisting of major merger triggering and secular processes.
The XMM deep survey in the CDFS IV. Candidate Compton-thick AGN
I. Georgantopoulos,A. Comastri,C. Vignali,P. Ranalli,E. Rovilos,K. Iwasawa,R. Gilli,N. Cappelluti,F. Carrera,J. Fritz,M. Brusa,D. Elbaz,R. J. Mullaney,N. Castello-Mor,X. Barcons,P. Tozzi,I. Balestra,S. Falocco
Physics , 2013,
Abstract: The Chandra Deep Field is the region of the sky with the highest concentration of X-ray data available: 4Ms of Chandra and 3Ms of XMM data, allowing excellent quality spectra to be extracted even for faint sources. We take advantage of this in order to compile a sample of heavily obscured Active Galactic Nuclei (AGN) using X-ray spectroscopy. We select our sample among the 176 brightest XMM sources, searching for either a) flat X-ray spectra (Photon index<1.4 at the 90% confidence level) suggestive of a reflection dominated continuum or b) an absorption turn-over suggestive of a column density higher than ~10^{24} cm-2. We find a sample of nine candidate heavily obscured sources satisfying the above criteria. Four of these show statistically significant FeKalpha lines with large equivalent widths (three out of four have EW consistent with 1 keV) suggesting that these are the most secure Compton-thick AGN candidates. Two of these sources are transmission dominated while the other two are most probably reflection dominated Compton-thick AGN. Although this sample of four sources is by no means statistically complete, it represents the best example of Compton-thick sources found at moderate-to-high redshift with three sources at z=1.2-1.5 and one source at z=3.7. Using Spitzer and Herschel observations, we estimate with good accuracy the X-ray to mid-IR (12 micron) luminosity ratio of our sources. These are well below the average AGN relation, independently suggesting that these four sources are heavily obscured.
Page 1 /486377
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.