Constraining halo occupation properties of X-ray AGNs using clustering of Chandra sources in the Bootes survey region

We present one of the most precise measurement to date of the spatial clustering of X-ray selected AGNs using a sample derived from the Chandra X-ray Observatory survey in the Bootes field. The real-space two-point correlation function over a redshift interval from z=0.17 to z~3 is well described by the power law, xi(r)=(r/r0)^-gamma, for comoving separations r<~20h^-1 Mpc. We find gamma=1.84+-0.12 and r0 consistent with no redshift trend within the sample (varying between r0=5.5+-0.6 h^-1 Mpc for =0.37 and r0=6.9+-1.0 h^-1 Mpc for =1.28). Further, we are able to measure the projections of the two-point correlation function both on the sky plane and in the line of sight. We use these measurements to show that the Chandra/Bootes AGNs are predominantly located at the centers of dark matter halos with the circular velocity Vmax>320 km/s or M_200 > 4.1e12 h^-1 Msun, and tend to avoid satellite galaxies in halos of this or higher mass. The halo occupation properties inferred from the clustering properties of Chandra/Bootes AGNs --- the mass scale of the parent dark matter halos, the lack of significant redshift evolution of the clustering length, and the low satellite fraction --- are broadly consistent with the Hopkins et al. scenario of quasar activity triggered by mergers of similarly-sized galaxies.Comment: Accepted to ApJ. The revision matches the accepted version. The most significant changes include the recalculation of uncertainties using mock catalogs and explicit comparison with the AGN HOD studies based on projected correlation function, w(rp

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CO80 89. Estudio multicéntrico español de la capacidad predictiva de las escalas de riesgo CHADS2 y CHA2DS2vasc en el accidente cerebrovascular tras cirugía coronaria aislada

ObjetivosValidar las escalas de riesgo CHADS2 y CHA2DS-2VASC como modelos predictivos de desarrollo de accidente cerebrovascular (ACV) en cirugía coronaria aislada (CCA).Material y métodosPacientes consecutivos sometidos a CCA en 16 hospitales españoles. Excluidos casos con igual o más de una variable/s incompleta/s. Puntuaciones CHADS2 y CHA2DS2VASC computadas para todos los pacientes, considerándose variable de resultado la aparición de ACV (ataque isquémico transitorio [AIT]/ictus) perioperatorio precoz (primer mes postoperatorio y/o alta hospitalaria). Análisis uni y multivariante. La capacidad discriminativa fue cuantificada por el cálculo del área bajo la curva ROC (AUC).ResultadosVeinte mil novecientos ochenta pacientes incluidos, 282 desarrollaron ACV postoperatorio (1,34%). La incidencia de ACV fue superior en pacientes con insuficiencia cardíaca congestiva (ICC) y/o fracción de eyección inferior al 40% (4,10 vs 0,83%), diabéticos (1,70 vs 1,11%), hipertensos (1,60 vs 0,98%), ACV previo (2,72 vs 1,26%) y a enfermedad arterial periférica (EAP) (3,04 vs 1,04%; p < 0,05). En el análisis multivariante, ICCC (odds ratio [OR]: 4,06), ACV previo (OR: 1,48), EAP (OR: 1,49) constituyeron factores de riesgo independientes para el desarrollo de ACV postoperatorio (p < 0,05). El AUC para CHADS2 fue 0,666, y para CHA2DS2VASc 0,655 (p < 0,0001). La distribución de las tasas de ACV postoperatorio según las puntuaciones de las anteriores escalas se recoge en la figura 1 (p < 0,0001). Figura 1Tasas de ACV postoperatorio en pacientes sometidos a CCA según puntuaciones de las escalas CHADS2 (gris) y CHA2DS2VASC (negro).ConclusionesLas escalas de riesgo CHADS2 y CHA2DS-2VASC pueden resultar útiles en la práctica clínica para estratificar el riesgo de desarrollo de ACV postoperatorio en pacientes sometidos a CCA

The Mid-Infrared Properties of X-ray Sources

We combine the results of the Spitzer IRAC Shallow Survey and the Chandra XBootes Survey of the 8.5 square degrees Bootes field of the NOAO Deep Wide- Field Survey to produce the largest comparison of mid-IR and X-ray sources to date. The comparison is limited to sources with X-ray fluxes >8x10-15 erg cm-2s-1 in the 0.5-7.0 keV range and mid-IR sources with 3.6 um fluxes brighter than 18.4 mag (12.3 uJy). In this most sensitive IRAC band, 85% of the 3086 X-ray sources have mid-IR counterparts at an 80% confidence level based on a Bayesian matching technique. Only 2.5% of the sample have no IRAC counterpart at all based on visual inspection. Even for a smaller but a significantly deeper Chandra survey in the same field, the IRAC Shallow Survey recovers most of the X-ray sources. A majority (65%) of the Chandra sources detected in all four IRAC bands occupy a well-defined region of IRAC [3.6] - [4.5] vs [5.8] - [8.0] color-color space. These X-ray sources are likely infrared luminous, unobscured type I AGN with little mid-infrared flux contributed by the AGN host galaxy. Of the remaining Chandra sources, most are lower luminosity type I and type II AGN whose mid-IR emission is dominated by the host galaxy, while approximately 5% are either Galactic stars or very local galaxies.Comment: Accepted for publication in Ap

AEGIS-X: The Chandra Deep Survey of the Extended Groth Strip

We present the AEGIS-X survey, a series of deep Chandra ACIS-I observations of the Extended Groth Strip. The survey comprises pointings at 8 separate positions, each with nominal exposure 200ks, covering a total area of approximately 0.67 deg2 in a strip of length 2 degrees. We describe in detail an updated version of our data reduction and point source detection algorithms used to analyze these data. A total of 1325 band-merged sources have been found to a Poisson probability limit of 4e-6, with limiting fluxes of 5.3e-17 erg/cm2/s in the soft (0.5-2 keV) band and 3.8e-16 erg/cm2/s in the hard (2-10 keV) band. We present simulations verifying the validity of our source detection procedure and showing a very small, <1.5%, contamination rate from spurious sources. Optical/NIR counterparts have been identified from the DEEP2, CFHTLS, and Spitzer/IRAC surveys of the same region. Using a likelihood ratio method, we find optical counterparts for 76% of our sources, complete to R(AB)=24.1, and, of the 66% of the sources that have IRAC coverage, 94% have a counterpart to a limit of 0.9 microJy at 3.6 microns (m(AB)=23.8). After accounting for (small) positional offsets in the 8 Chandra fields, the astrometric accuracy of the Chandra positions is found to be 0.8 arcsec RMS, however this number depends both on the off-axis angle and the number of detected counts for a given source. All the data products described in this paper are made available via a public website.Comment: 17 pages, 9 figures. Accepted for publication in ApJS. Data products are available at http://astro.imperial.ac.uk/research/aegis

Resolving the Galactic X-ray background

We use Chandra deep observations of the Galactic Center (GC) region to improve the constraints on the unresolved fraction of the Galactic X-ray background (also known as the Galactic ridge X-ray emission). We emphasize the importance of correcting the measured source counts at low fluxes for bias associated with Poisson noise. We find that at distances of 2'-4' from Sgr A* at least ~40% of the total X-ray emission in the energy band 4-8 keV originates from point sources with luminosities L(2-10 keV)> 10^{31} erg/sec. From a comparison of the source number-flux function in the GC region with the known luminosity function of faint X-ray sources in the Solar vicinity, we infer that Chandra has already resolved a large fraction of the cumulative contribution of cataclysmic variables to the total X-ray flux from the GC region. This comparison further indicates that most of the yet unresolved ~60% of the X-ray flux from the GC region is likely produced by weak cataclysmic variables and coronally active stars with L(2-10 keV)<10^{31} erg/sec. We conclude that the bulk of the Galactic X-ray background is produced by discrete sources.Comment: Submitted to A&