X-UDS: The Chandra Legacy Survey of the UKIDSS Ultra Deep Survey Field

Abstract

We present the X-UDS survey, a set of wide and deep Chandra observations of the Subaru-XMM Deep/UKIDSS Ultra Deep Survey (SXDS/UDS) field. The survey consists of 25 observations that cover a total area of 0.33 deg 2 . The observations are combined to provide a nominal depth of ∼600 ksec in the central 100 arcmin 2 region of the field that has been imaged with Hubble/WFC3 by the CANDELS survey and ∼200 ksec in the remainder of the field. In this paper, we outline the survey's scientific goals, describe our observing strategy, and detail our data reduction and point source detection algorithms. Our analysis has resulted in a total of 868 band-merged point sources detected with a false-positive Poisson probability of < 1 × 10 −4 . In addition, we present the results of an X-ray spectral analysis and provide best-fitting neutral hydrogen column densities, N H , as well as a sample of 51 Compton-thick active galactic nucleus candidates. Using this sample, we find the intrinsic Compton-thick fraction to be 30-35% over a wide range in redshift (z = 0.1 − 3), suggesting the obscured fraction does not evolve very strongly with epoch. However, if we assume that the Compton-thick fraction is dependent on luminosity, as is seen for Compton-thin sources, then our results are consistent with a rise in the obscured fraction out to z ∼ 3. Finally, an examination of the host morphologies of our Compton-thick candidates shows a high fraction of morphological disturbances, in agreement with our previous results. All data products described in this paper are made available via a public website.

The role of galaxy mass on AGN emission: a view from the VANDELS survey

“…Also, we remind that the lower number of associations found in this work as compared to that of Kocevski et al (2018) derives from the fact that we only looked for counterparts within VANDELS, without enlarging our search to all catalogues available in the literature. At variance with §3.1, we could not check for how many of the counterparts provided by Kocevski et al (2018) coincide with those found in the present work, since the Kocevski et al (2018) catalogues only include redshift information without listing their coordinates. Figure 4 illustrates the distribution of unobscured X-ray luminosities for all the Kocevski et al (2018) sources with a VANDELS identification.…”

“…Relatively deep X-ray observations of the UDS field are presented by the recent work of Kocevski et al (2018) who provide a catalogue of 864 sources observed down to a depth of ∼ 600 Ks in the central 100 arcmin 2 and to ∼ 200 Ks in the remainder of the field. As it is possible to appreciate from Table 4, of these 864 sources 628 fall within the VAN-DELS area, 414 have a VANDELS counterpart obtained as in §3.1, and 97 also possess a spectroscopic redshift determination.…”

“…Also in this case, we stress that we use spectroscopic redshifts whenever possible and photometric redshifts otherwise. As it was for the CDFS, in the few cases when the redshifts provided by Kocevski et al (2018) did not agree with those from VANDELS, we have re-calculated the Xray luminosities of the sources to the values of VANDELS redshifts, starting from the original LX and assuming an average spectral slope of 0.8. Also, we remind that the lower number of associations found in this work as compared to that of Kocevski et al (2018) derives from the fact that we only looked for counterparts within VANDELS, without enlarging our search to all catalogues available in the literature.…”

“…As it was for the CDFS, in the few cases when the redshifts provided by Kocevski et al (2018) did not agree with those from VANDELS, we have re-calculated the Xray luminosities of the sources to the values of VANDELS redshifts, starting from the original LX and assuming an average spectral slope of 0.8. Also, we remind that the lower number of associations found in this work as compared to that of Kocevski et al (2018) derives from the fact that we only looked for counterparts within VANDELS, without enlarging our search to all catalogues available in the literature. At variance with §3.1, we could not check for how many of the counterparts provided by Kocevski et al (2018) coincide with those found in the present work, since the Kocevski et al (2018) catalogues only include redshift information without listing their coordinates.…”

Extended Hα over compact far-infrared continuum in dusty submillimeter galaxies

“…C.-C. Chen et al: Extended Hα over compact far-infrared continuum in dusty submillimeter galaxies (a) The AGN classification in X-ray is based on catalog matching; ALESS SMGs are matched to the Chandra 7 Ms catalog and classified as AGN based on the criteria set in Luo et al (2017). The AS2UDS SMGs are matched to the Chandra X-UDS catalog (Kocevski et al 2018) with a simple luminosity cut of L 2−10kev > 3 × 10 42 erg s −1 , which is one of the criteria used in Luo et al (2017). The steep slope in mid-infrared has suggested that ALESS75.1 is an IR AGN Stanley et al 2018 (Table 1) with a size of 25×25 kpc and a color stretch from zero to 99.5% of the peak.…”