Lee Clewley

X-ray groups and clusters of galaxies in the Subaru-XMM Deep Field

We present the results of a search for galaxy clusters in the Subaru–XMM Deep Field (SXDF). We reach a depth for a total cluster flux in the 0.5–2 keV band of 2 × 10^(−15) erg cm^(−2) s^(−1) over one of the widest XMM–Newton contiguous raster surveys, covering an area of 1.3 deg^2. Cluster candidates are identified through a wavelet detection of extended X-ray emission. The red-sequence technique allows us to identify 57 cluster candidates. We report on the progress with the cluster spectroscopic follow-up and derive their properties based on the X-ray luminosity and cluster scaling relations. In addition, three sources are identified as X-ray counterparts of radio lobes, and in three further sources, an X-ray counterpart of the radio lobes provides a significant fraction of the total flux of the source. In the area covered by near-infrared data, our identification success rate achieves 86 per cent. We detect a number of radio galaxies within our groups, and for a luminosity-limited sample of radio galaxies we compute halo occupation statistics using a marked cluster mass function. We compare the cluster detection statistics in the SXDF with that in the literature and provide the modelling using the concordance cosmology combined with current knowledge of the X-ray cluster properties. The joint cluster log(N) − log(S) is overpredicted by the model, and an agreement can be achieved through a reduction of the concordance σ_8 value by 5 per cent. Having considered the dn/dz and the X-ray luminosity function of clusters, we conclude that to pin down the origin of disagreement a much wider (50 deg^2) survey is needed.

The cosmic evolution of low-luminosity radio sources from the Sloan Digital Sky Survey Data Release 1

In this paper we constrain the evolution in the comoving space density for low-luminosity (typically FRI) radio sources as a function of cosmic epoch by matching deep radio surveys (WENSS, FIRST and NVSS) with the Sloan Digital Sky Survey (SDSS). This results in 1014 matched radio sources covering an effective area of 0.217 sr, 686 with L(325 MHz) < 10^25 W/Hz/sr, which is an order of magnitude larger than any previous study at these luminosities. Using the non-parametric V/Vmax test we show that low-luminosity radio sources evolve differently to their more powerful, predominantly FRII, counterparts. Indeed, we find that the lower luminosity population is consistent with a constant comoving space density with redshift, as opposed to the strong positive evolution for the more powerful sources.

Galaxy clusters at 0.6 < z < 1.4 in the UKIDSS Ultra Deep Survey Early Data Release

We present the first cluster catalogue extracted from the UKIRT Infrared Deep Sky Survey Early Data Release. The catalogue is created using UKIDSS Ultra Deep Survey infrared J and K data combined with 3.6 µm and 4.5 µm Spitzer bands and optical BV Rizimaging from the Subaru Telescope over 0.5 square degrees in the Subaru XMM-Newton Deep Field. We have created a new cluster-detection algorithm, based on the Friends-Of-Friends and Voronoi Tessellation methods, which utilises probability distribution functions derived from a photometric redshift analysis. We employ mock catalogues to understand the selection effects and contamination associated with the algorithm. The cluster catalogue contains 13 clusters at redshifts 0.61 6 z 6 1.39 with luminosities 10L ∗ � Ltot � 50L ∗ , corresponding to masses 5 × 10 13 M⊙ � Mcluster � 3 × 10 14 M⊙ for M/M ⊙ L/L⊙ = 75h. The measured sky surface density of � 10 deg −2 for high-redshift (z = 0.5 1.5), massive (> 10 14 M⊙) clusters is precisely in line with theoretical predictions presented by Kneissl et al. (2001).

The discovery of a massive supercluster at z=0.9 in the UKIDSS Deep eXtragalactic Survey

We analyse the first publicly released deep field of the UK Infrared Deep Sky Survey (UKIDSS) Deep eXtragalactic Survey to identify candidate galaxy overdensities at z similar to 1 across similar to 1 deg(2) in the ELAIS-N1 field. Using I - K, J - K and K - 3.6 mu m colours, we identify and spectroscopically follow up five candidate structures with Gemini/Gemini Multi-Object Spectrograph and confirm that they are all true overdensities with between five and 19 members each. Surprisingly, all five structures lie in a narrow redshift range at z = 0.89 +/- 0.01, although they are spread across 30 Mpc on the sky. We also find a more distant overdensity at z = 1.09 in one of the spectroscopic survey regions. These five overdense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogues from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift.

Distant field blue horizontal branch stars and the mass of the Galaxy – I. Classification of halo A-type stars

This is the first in a series of three papers presenting a new calculation of the mass of the Galaxy based on radial velocities and distances measured for a sample of some 100 faint 16 30 kpc with measured radial velocities by a factor of 5. Faint A-type stars in the Galactic halo have been identified from ubjr photometry in six UK Schmidt fields. These samples include field BHB stars as well as less luminous stars of main-sequence surface gravity, which are predominantly field blue stragglers. We obtain accurate charge-coupled device photometry and spectra to classify these stars. This paper describes our methods for separating out clean samples of BHB stars in a way that is efficient in terms of telescope time required. We use the high signal-to-noise (S/N) ratio spectra of A-type stars of Kinman, Suntzeff & Kraft (published in 1994), and their definitive spectrophotometric A classifications, to assess the reliability of two methods, and to quantify the S/N ratio requirements. First we revisit, refine and extend the hydrogen linewidth versus colour relation as a classifier (here called the D 0 . 1 5 -colour method). The second method is new and compares the shapes of the Balmer lines. With this method (here called the scale-width-shape method) there is no need for colours or spectrophotometry. Using the equivalent width of the Ca II K line as an additional filter we find we can reproduce Kinman, Suntzeff & Krafts A classifications with both methods. In a sample of stars with strong Balmer lines, equivalent width Hy > 13 A [equivalent to the colour range 0 ≤ (B - V) 0 ≤ 0.2], halo BHB stars can be separated from halo blue stragglers reliably. For the spectroscopy (i.e. both classification methods) the minimum required continuum S/N ratio is 15 A - 1 . For the D 0 . 1 5 -colour method (B - V) 0 colours accurate to 0.03 mag are needed.

A reliable cluster detection technique using photometric redshifts: introducing the 2TecX algorithm

We present a new cluster detection algorithm designed for finding high-redshift clusters using optical/infrared imaging data. The algorithm has two main characteristics. First, it utilizes each galaxys full redshift probability function, instead of an estimate of the photometric redshift based on the peak of the probability function and an associated Gaussian error. Second, it identifies cluster candidates through cross-checking the results of two substantially different selection techniques (the name 2TecX representing the cross-check of the two techniques). These are adaptations of the Voronoi Tesselations and Friends-Of-Friends methods. Monte Carlo simulations of mock catalogues show that cross-checking the cluster candidates found by the two techniques significantly reduces the detection of spurious sources. Furthermore, we examine the selection effects and relative strengths and weaknesses of either method. The simulations also allow us to fine-tune the algorithms parameters, and define completeness and mass limit as a function of redshift. We demonstrate that the algorithm isolates high-redshift clusters at a high level of efficiency and low contamination.

Spectroscopic follow-up of a cluster candidate at z= 1.45

We have obtained deep optical spectroscopic data of the highest-redshift cluster candidate (z ∼ 1.4, CVB13) selected by Van Breukelen et al. in a photometric optical/infrared catalogue of the Subaru XMM‐Newton Deep Field. The data, which comprise 104 targeted galaxies, were taken with the DEep Imaging Multi-Object Spectrograph on the Keck 2 telescope and yielded 31 secure redshifts in the range 1.25 < z < 1.54 within a 7 × 4-arcmin 2 field centred on CVB13. Instead of one massive cluster at z = 1.4, we find evidence for three projected structures at z = 1.40, 1.45 and 1.48. The most statistically robust of these structures, at z = 1.454, has

Spectroscopic follow-up of a cluster candidate at z = 1.45

We have obtained deep optical spectroscopic data of the highest-redshift cluster candidate (z ∼ 1.4, CVB13) selected by Van Breukelen et al. in a photometric optical/infrared catalogue of the Subaru XMM‐Newton Deep Field. The data, which comprise 104 targeted galaxies, were taken with the DEep Imaging Multi-Object Spectrograph on the Keck 2 telescope and yielded 31 secure redshifts in the range 1.25 < z < 1.54 within a 7 × 4-arcmin 2 field centred on CVB13. Instead of one massive cluster at z = 1.4, we find evidence for three projected structures at z = 1.40, 1.45 and 1.48. The most statistically robust of these structures, at z = 1.454, has