Almus T. Kenter

XBOOTES: AN X-RAY SURVEY OF THE NDWFS BOOTES FIELD. II. THE X-RAY SOURCE CATALOG

We present results from a Chandra survey of the 9 deg 2 Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). This XBootes survey consists of 126 separate contiguous ACIS-I observations each of approximately 5000 s in duration. These unique Chandra observations allow us to search for large-scale structure and to calculate X-raysource statistics overawide,contiguousfieldofviewwitharcsecondangularresolutionanduniformcoverage. Opticalspectroscopicfollow-upobservationsandtherichNDWFSdatasetwillallowustoidentifyandclassifythese X-ray‐selected sources. Using wavelet decomposition, we detect 4642 point sources with n � 2 counts. In order to keep our detections � 99% reliable, we limit our list to sources with n � 4 counts. For a 5000 s observation and assuming a canonical unabsorbed active galactic nucleus (AGN) type X-ray spectrum, a 4 count on-axis source correspondsto afluxof4:7 ;10 � 15 ergscm � 2 s � 1 inthe soft (0.5‐2keV) band, 1:5 ; 10 � 14 ergscm � 2 s � 1 in thehard (2‐7 keV) band, and 7:8 ; 10 � 15 ergs cm � 2 s � 1 in the full (0.5‐7 keV) band. The full 0.5‐7 keV band n � 4 count list has 3293 point sources. In addition to the point sources, 43 extended sources have been detected, consistent with the depth of these observations and the number counts of clusters. We present here the X-ray catalog for the XBootes survey, including source positions, X-ray fluxes, hardness ratios, and their uncertainties. We calculate and present the differential number of sources per flux density interval, N(S), for the point sources. In the soft (0.5‐2 keV) band, N(S) is well fitted by a broken power law with slope of 2:60 þ0:11 � 0:12 at bright fluxes and 1:74 þ0:28 � 0:22 for faint fluxes. The hard source N(S) is well described by a single power law with an index of � 2:93 þ0:09 � 0:09.

The Chandra XBoötes survey. III. Optical and near-infrared counterparts

The XBootes Survey is a 5 ks Chandra survey of the Bootes Field of the NOAO Deep Wide-Field Survey (NDWFS). This survey is unique in that it is the largest (9.3 deg2) contiguous region imaged in X-ray with complementary deep optical and near-infrared (near-IR) observations. We present a catalog of the optical counterparts to the 3213 X-ray point sources detected in the XBootes survey. Using a Bayesian identification scheme, we successfully identified optical counterparts for 98% of the X-ray point sources. The optical colors suggest that the optically detected galaxies are a combination of z 10). These objects are likely high-redshift and/or dust-obscured AGNs. These sources have generally harder X-ray spectra than sources with 0.1 < fX/fo < 10. Of the 73 X-ray sources with no optical counterpart in the NDWFS catalog, 47 are truly optically blank down to R ~ 25.5 (the average 50% completeness limit of the NDWFS R-band catalogs). These sources are also likely to be high-redshift and/or dust-obscured AGNs.

A CHANDRA HIGH-RESOLUTION X-RAY IMAGE OF CENTAURUS A

We present first results from a Chandra X-Ray Observatory observation of the radio galaxy Centaurus A with the High-Resolution Camera. All previously reported major sources of X-ray emission including the bright nucleus, the jet, individual point sources, and diffuse emission are resolved or detected. The spatial resolution of this observation is better than 1&arcsec; in the center of the field of view and allows us to resolve X-ray features of this galaxy not previously seen. In particular, we resolve individual knots of emission in the inner jet and diffuse emission between the knots. All of the knots are diffuse at the 1&arcsec; level, and several exhibit complex spatial structure. We find the nucleus to be extended by a few tenths of an arcsecond. Our image also suggests the presence of an X-ray counterjet. Weak X-ray emission from the southwest radio lobe is also seen, and we detect 63 pointlike galactic sources (probably X-ray binaries and supernova remnants) above a luminosity limit of approximately 1.7x1037 ergs s-1.

CONSTRAINING HALO OCCUPATION PROPERTIES OF X-RAY ACTIVE GALACTIC NUCLEI USING CLUSTERING OF CHANDRA SOURCES IN THE BOÖTES SURVEY REGION

We present one of the most precise measurements to date of the spatial clustering of X-ray-selected active galactic nuclei (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, ξ(r) = (r/r 0)–γ, for comoving separations r 20 h –1 Mpc. We find γ = 1.84 ± 0.12 and r 0 consistent with no redshift trend within the sample (varying between r 0 = 5.5 ± 0.6 h –1 Mpc for z = 0.37 and r 0 = 6.9 ± 1.0 h –1 Mpc for z = 1.28). Furthermore, 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 circular velocity v max > 320 km s–1 or M 180 > 4.1 × 1012 h –1 M ☉, 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.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 Boötes field. The real-space twopoint correlation function over a redshift interval from z = 0.17 to z ∼ 3 is well described by the power law, ξ(r) = (r/r0), for comoving separations r . 20 h−1 Mpc. We find γ = 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 〈z〉 = 0.37 and r0 = 6.9 ± 1.0 h−1 Mpc for 〈z〉 = 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/Boötes AGNs are predominantly located at the centers of dark matter halos with the circular velocity vmax > 320 km s−1 or M180 > 4.1 × 1012 h−1 M , and tend to avoid satellite galaxies in halos of this or higher mass. The halo occupation properties inferred from the clustering properties of Chandra/Boötes 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. (2006) scenario of quasar activity triggered by mergers of similarly-sized galaxies.

AXAF High-Resolution Camera (HRC): calibration and recalibration at XRCF and beyond

The high resolution camera (HRC) is a microchannel plate based imaging detector for the Advanced X-Ray Astrophysics Facility (AXAF) that will be placed in a high earth orbit scheduled for launch in August, 1998. An end-to-end calibration of the HRC and the AXAF high resolution mirror assembly (HRMA) was carried out at the Marshall Space Flight Centers X-Ray Calibration Facility (XRCF). This activity was followed by several modifications to the HRC to improve its performance, and a series of flat field calibrations. In this paper, and the following companion papers, we discuss the calibration plans, sequences, and results of these tests. At the time of this conference, the HRC has been fully flight qualified and is being integrated into the science instrument module (SIM) in preparation for integration into the AXAF spacecraft.

In-flight performance of the Chandra high-resolution camera

The High Resolution Camera (HRC) is one of the two focal plane instruments on NASAs Chandra X-ray Observatory which was successfully launched July 23, 1999. The Chandra Observatory will perform high resolution spectroscopy and imaging in the X-ray band of 0.1 to 10 keV. The HRC instrument consists of two detectors, the HRC-I for imaging and the HRC-S for spectroscopy. In this paper we present an overview of the in-flight performance of the High Resolution Camera and discuss some of the initial scientific results.

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 deg2 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 >8 × 10−15 ergs cm−2 s−1 in the 0.5-7.0 keV range and mid-IR sources with 3.6 μm fluxes brighter than 18.4 mag (12.3 μJy). 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] versus [5.8] − [8.0] color-color space. These X-ray sources are likely infrared-luminous, unobscured type I AGNs 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 AGNs whose mid-IR emission is dominated by the host galaxy, while approximately 5% are either Galactic stars or very local galaxies.

Description and performance of the low-energy transmission grating spectrometer on board Chandra

The Chandra spacecraft has been launched successfully on July 23, 1999. The payload consists of a high resolution X- ray telescope, two imaging detector systems in the focal plane and two transmission gratings. Each one of the two gratings can be put in the beam behind the telescope and the grating spectrometers are optimized for high and low energy, respectively. The Low Energy Transmission Grating Spectrometer consists of three parts: the high-resolution telescope, the transmission grating array and the detector, to read-out the spectral image.

Tracing the nuclear accretion history of the red galaxy population

We investigate the evolution of the hard X-ray luminosity of the red galaxy population using a large sample of 3316 red galaxies selected over a wide range in redshift (0.3 < z < 0.9) from a 1.4 deg2 region in the Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). The red galaxies are early-type, bulge-dominated galaxies and are selected to have the same evolution-corrected, absolute R-band magnitude distribution as a function of redshift to ensure that we are tracing the evolution in the X-ray properties of a comparable optical population. Using a stacking analysis of 5 ks Chandra/ACIS observations within this field to study the X-ray emission from these red galaxies in three redshift bins, we find that the mean X-ray luminosity increases as a function of redshift. The large mean X-ray luminosity and the hardness of the mean X-ray spectrum suggest that the X-ray emission is largely dominated by active galactic nuclei (AGNs) rather than stellar sources. The hardness ratio can be reproduced by either an absorbed (NH ≈ 2 × 1022 cm-2) Γ = 1.7 power-law source, consistent with that of a population of moderately obscured Seyfert-like AGNs, or an unabsorbed Γ = 0.7 source, suggesting a radiatively inefficient accretion flow (e.g., an advection-dominated accretion flow). We also find that the emission from this sample of red galaxies constitutes at least 5% of the hard X-ray background. These results suggest a global decline in the mean AGN activity of normal early-type galaxies from z ~ 1 to the present, which indicates that we are witnessing the tailing off of the accretion activity onto supermassive black holes in early-type galaxies since the quasar epoch.

A New Technique for Determining the Number of X-Ray Sources per Flux Density Interval

We present a technique for determining the number of X-ray sources per flux density interval, the log N-log S relationship, that is mathematically analogous to spectral fitting. This technique is ideal for X-ray source counts obtained using the Chandra X-ray Observatory since the telescope and the focal plane instruments have been well modeled. This technique is of general applicability. In this paper, we apply it to a wavelet source-detect analysis of a Chandra Advanced CCD Imaging Spectrometer (ACIS-I) mosaic image of a 1.35 deg2 survey of the Lockman Hole. We verify the technique via Monte Carlo simulations.