Browsing by Subject "POINT-SOURCE CATALOG"

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  • Smolcic, V.; Miettinen, O.; Tomicic, N.; Zamorani, G.; Finoguenov, A.; Lemaux, B. C.; Aravena, M.; Capak, P.; Chiang, Y. -K.; Civano, F.; Delvecchio, I.; Ilbert, O.; Jurlin, N.; Karim, A.; Laigle, C.; Le Fevre, O.; Marchesi, S.; McCracken, H. J.; Riechers, D. A.; Salvato, M.; Schinnerer, E.; Tasca, L.; Toft, S. (2017)
    We investigate the environment of 23 submillimetre galaxies (SMGs) drawn from a signal-to-noise (S/N)-limited sample of SMGs originally discovered in the James Clerk Maxwell Telescope (JCMT)/AzTEC 1.1 mm continuum survey of a Cosmic Evolution Survey (COSMOS) subfield and then followed up with the Submillimetre Array and Plateau de Bure Interferometer at 890 mu m and 1.3 mm, respectively. These SMGs already have well-defined multiwavelength counterparts and redshifts. We also analyse the environments of four COSMOS SMGs spectroscopically confirmed to lie at redshifts z(spec) > 4 : 5, and one at z(spec) = 2 : 49 resulting in a total SMG sample size of 28. We search for overdensities using the COSMOS photometric redshifts based on over 30 UV-NIR photometric measurements including the new UltraVISTA data release 2 and Spitzer/SPLASH data, and reaching an accuracy of sigma(Delta z/(1+z)) = (1 + z) = 0 : 0067 (0 : 0155) at z <3 : 5 (> 3.5). To identify overdensities we apply the Voronoi tessellation analysis, and estimate the redshift-space overdensity estimator delta(g) as a function of distance from the SMG and/or overdensity centre. We test and validate our approach via simulations, X-ray detected groups or clusters, and spectroscopic verifications using VUDS and zCOSMOS catalogues which show that even with photometric redshifts in the COSMOS field we can e ffi ciently retrieve overdensities out to z approximate to 5. Our results yield that 11 out of 23 (48%) JCMT/AzTEC 1.1 mm SMGs occupy overdense environments. Considering the entire JCMT/AzTEC 1.1 mm S = N >= 4 sample and taking the expected fraction of spurious detections into account, this means that 35-61% of the SMGs in the S/N-limited sample occupy overdense environments. We perform an X-ray stacking analysis in the 0.5-2 keV band using a 32 '' aperture and our SMG positions, and find statistically significant detections. For our z <2 subsample we find an average flux of (4.0 +/- 0.8) x 10(-16) erg s(-1) cm(-2) and a corresponding total mass of M-200 = 2.8 x 10(13) M-circle dot. The z > 2 subsample yields an average flux of (1.3 +/- 0.5) x 10(-16) erg s(-1) cm(-2) and a corresponding total mass of M-200 = 2 x 10(13) M-circle dot. Our results suggest a higher occurrence of SMGs occupying overdense environments at z >= 3 than at z <3. This may be understood if highly star-forming galaxies can only be formed in the highest peaks of the density field tracing the most massive dark matter haloes at early cosmic epochs, while at later times cosmic structure may have matured su ffi ciently that more modest overdensities correspond to su ffi ciently massive haloes to form SMGs.
  • Wang, Tao; Elbaz, David; Daddi, Emanuele; Finoguenov, Alexis; Liu, Daizhong; Schreiber, Corentin; Martin, Sergio; Strazzullo, Veronica; Valentino, Francesco; van der Burg, Remco; Zanella, Anita; Ciesla, Laure; Gobat, Raphael; Le Brun, Amandine; Pannella, Maurilio; Sargent, Mark; Shu, Xinwen; Tan, Qinghua; Cappelluti, Nico; Li, Yanxia (2016)
    We report the discovery of a remarkable concentration of massive galaxies with extended X-ray emission at z(spec) = 2.506, which contains 11 massive (M-* greater than or similar to 10(11) M-circle dot) galaxies in the central 80 kpc region (11.6 sigma overdensity). We have spectroscopically confirmed 17 member galaxies with 11 from CO and the remaining ones from Ha. The X-ray luminosity, stellar mass content, and velocity dispersion all point to a collapsed, cluster-sized dark matter halo with mass M-200c = 10(13.9 +/- 0.2) M-circle dot, making it the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive galaxies classified as quiescent. The star formation rate (SFR) in the 80 kpc core reaches similar to 3400 M-circle dot yr(-1) with a. gas depletion time of similar to 200 Myr, suggesting that we caught this cluster in rapid build-up of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst fraction (similar to 25%, compared to 3%-5% in the field). The presence of both a collapsed, cluster-sized halo and a predominant population of massive SFGs suggests that this structure could represent an important transition phase between protoclusters and mature clusters. It provides evidence that the main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster, providing new insights into massive cluster formation at early epochs. The large integrated stellar mass at such high redshift challenges our understanding of massive cluster formation.
  • Allevato, V.; Civano, F.; Finoguenov, A.; Marchesi, S.; Shankar, F.; Zamorani, G.; Hasinger, G.; Salvato, M.; Miyaji, T.; Gilli, R.; Cappelluti, N.; Brusa, M.; Suh, H.; Lanzuisi, G.; Trakhtenbrot, B.; Griffiths, R.; Vignali, C.; Schawinski, K.; Karim, A. (2016)
    We present the measurement of the projected and redshift-space two-point correlation function (2pcf) of the new catalog of Chandra COSMOS-Legacy active galactic nucleus (AGN) at 2.9 similar to 10(46) erg s(-1)) using the generalized clustering estimator based on phot-z probability distribution functions in addition to any available spec-z. We model the projected 2pcf, estimated using pi(max) = 200 h(-1) Mpc with the two-halo term and we derive a bias at z similar to 3.4 equal to b. =. 6.6(+0.60) -(0.55), which corresponds to a typical mass of the hosting halos of log M-h. =. 12.83(+0.12) -(0.11) h(-1)M circle dot. A similar bias is derived using the redshift-space 2pcf, modeled including the typical phot-z error sigma(z). =. 0.052 of our sample at z >= 2.9. Once we integrate the projected 2pcf up to pi(max). =. 200 h(-1) Mpc, the bias of XMM and Chandra COSMOS at z =. 2.8 used in Allevato et al. is consistent with our results at higher redshifts. The results suggest only a slight increase of the bias factor of COSMOS AGNs at z greater than or similar to 3 with the typical hosting halo mass of moderate-luminosity AGNs almost constant with redshift and equal to log M-h = 12.92(+0.-13) (0.18) at z - 2.8 and log M-h - 12.83(+0.11) (-0.12) at z similar to 3.4, respectively. The observed redshift evolution of the bias of COSMOS AGNs implies that moderate-luminosity AGNs. still inhabit group-sized halos at z greater than or similar to 3, but slightly less massive than observed in different independent studies using X-ray AGNs. at z less than or similar to 2.
  • Cappelluti, Nico; Li, Yanxia; Ricarte, Angelo; Agarwal, Bhaskar; Allevato, Viola; Ananna, Tonima Tasnim; Ajello, Marco; Civano, Francesca; Comastri, Andrea; Elvis, Martin; Finoguenov, Alexis; Gilli, Roberto; Hasinger, Guenther; Marchesi, Stefano; Natarajan, Priyamvada; Pacucci, Fabio; Treister, E.; Urry, C. Megan (2017)
    Using Chandra observations in the 2.15 deg(2) COSMOS-legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT similar to 0.27 and 0.07 keV and an extragalactic power law with a photon spectral index Gamma = 1.45 +/- 0.02. The 1 keV normalization of the extragalactic component is 10.91 +/- 0.16 keV cm(-2) s(-1) sr(-1) keV(-1). Removing all X-ray-detected sources, the remaining unresolved CXB is best fit by a power law with normalization 4.18 +/- 0.26 keV cm(-2) s(-1) sr(-1) keV(-1) and photon spectral index Gamma = 1.57 +/- 0.10. Removing faint galaxies down to i(AB) similar to 27-28 leaves a hard spectrum with Gamma similar to 1.25 and a 1 keV normalization of similar to 1.37 keV cm(-2) s(-1) sr(-1) keV(-1). This means that similar to 91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute similar to 8%-9% of the total CXB show marginal evidence of being harder and possibly more obscured than resolved sources. Another similar to 1% of the CXB can be attributed to still undetected star-forming galaxies and absorbed active galactic nuclei. According to these limits, we investigate a scenario where early black holes totally account for non-source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the z similar to 6 accreted mass density, such a population of black holes must grow in Compton-thick envelopes with N-H > 1.6 x 10(25) cm(-2) and form in extremely low-metallicity environments (Z(circle dot)) similar to 10(-3).
  • Marchesi, S.; Civano, F.; Salvato, M.; Shankar, F.; Comastri, A.; Elvis, M.; Lanzuisi, G.; Trakhtenbrot, B.; Vignali, C.; Zamorani, G.; Allevato, V.; Brusa, M.; Fiore, F.; Gilli, R.; Griffiths, R.; Hasinger, G.; Miyaji, T.; Schawinski, K.; Treister, E.; Urry, C. M. (2016)
    We present the largest high-redshift (3 <z <6.85) sample of X-ray-selected active galactic nuclei (AGNs) on a contiguous field, using sources detected in the Chandra COSMOS-Legacy survey. The sample contains 174 sources, 87 with spectroscopic redshift and the other 87 with photometric redshift (z(phot)). In this work, we treat z(phot) as a probability-weighted sum of contributions, adding to our sample the contribution of sources with zphot. <3 but zphot probability distribution > 0 at z > 3. We compute the number counts in the observed 0.5-2 keV band, finding a decline in the number of sources at z > 3 and constraining phenomenological models of the X-ray background. We compute the AGN space density at z. > 3 in two different luminosity bins. At higher luminosities (logL(2-10 keV) > 44.1 erg s(-1)), the space density declines exponentially, dropping by a factor of similar to 20 from z similar to 3 to z similar to 6. The observed decline is similar to 80% steeper at lower luminosities (43.55 erg s(-1) <logL(2-10 keV) <44.1 erg s(-1)) from z similar to 3 to z similar to 4.5. We study the space density evolution dividing our sample into optically classified Type 1 and Type 2 AGNs. At logL (2-10 keV) > 44.1 erg s(-1), unobscured and obscured objects may have different evolution with redshift, with the obscured component being three times higher at z similar to 5. Finally, we compare our space density with predictions of quasar activation merger models, whose calibration is based on optically luminous AGNs. These models significantly overpredict the number of expected AGNs at logL (2-10 keV) > 44.1 erg s(-1) with respect to our data.
  • Suh, Hyewon; Civano, Francesca; Hasinger, Guenther; Lusso, Elisabeta; Lanzuisi, Giorgio; Marchesi, Stefano; Trakhtenbrot, Benny; Allevato, Viola; Cappelluti, Nico; Capak, Peter L.; Elvis, Martin; Griffiths, Richard E.; Laigle, Clotilde; Lira, Paulina; Riguccini, Laurie; Rosario, David J.; Salvato, Mara; Schawinski, Kevin; Vignali, Cristian (2017)
    We investigate the star formation properties of a large sample of similar to 2300 X-ray-selected Type 2 Active Galactic Nuclei (AGNs) host galaxies out to z similar to 3 in the Chandra COSMOS Legacy Survey in order to understand the connection between the star formation and nuclear activity. Making use of the existing multi-wavelength photometric data available in the COSMOS field, we perform a multi-component modeling from far-infrared to near-ultraviolet using a nuclear dust torus model, a stellar population model and a starburst model of the spectral energy distributions (SEDs). Through detailed analyses of SEDs, we derive the stellar masses and the star formation rates (SFRs) of Type 2 AGN host galaxies. The stellar mass of our sample is in the range of 9 <logM(stellar)/M-circle dot <12 with uncertainties of similar to 0.19 dex. We find that Type 2 AGN host galaxies have, on average, similar SFRs compared to the normal star-forming galaxies with similar M-stellar and redshift ranges, suggesting no significant evidence for enhancement or quenching of star formation. This could be interpreted in a scenario, where the relative massive galaxies have already experienced substantial growth at higher redshift (z > 3), and grow slowly through secular fueling processes hosting moderate-luminosity AGNs.