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.

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.

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.