Search

Recently, Carnall et al. discovered two bright high redshift quasars using the combination of the VST ATLAS and WISE surveys. The technique involved using the 3-D colour plane i-z:z-W1:W1-W2 with the WISE W1 (3.4 micron) and W2 (4.5 micron) bands taking the place of the usual NIR J band to help decrease stellar dwarf contamination. Here we report on our continued search for 5.76 quasars, VST-ATLAS J158.6938-14.4211 at z=6.07 and J332.8017-32.1036 at z=6.32 with magnitudes of z_AB=19.4 and 19.7 mag respectively. J158.6938-14.4211 was confirmed by Keck LRIS observations and J332.8017-32.1036 was confirmed by ESO NTT EFOSC-2 observations. Here we present VLT X-shooter Visible and NIR spectra for the four ATLAS quasars. We have further independently rediscovered two z>5.7 quasars previously found by the VIKING/KiDS and PanSTARRS surveys. This means that in ATLAS we have now discovered a total of six quasars in our target 5.7

We present ALMA detections of the [CII] 158 micron emission line and the underlying far-infrared continuum of three quasars at 6.6~6 quasar hosts correlate with the quasar's bolometric luminosity. In one quasar, the [CII] line is significantly redshifted by ~1700 km/s with respect to the MgII broad emission line. Comparing to values in the literature, we find that, on average, the MgII is blueshifted by 480 km/s (with a standard deviation of 630 km/s) with respect to the host galaxy redshift, i.e. one of our quasars is an extreme outlier. Through modeling we can rule out a flat rotation curve for our brightest [CII] emitter. Finally, we find that the ratio of black hole mass to host galaxy (dynamical) mass is higher by a factor 3-4 (with significant scatter) than local relations., Comment: 16 pages, 12 figures. Accepted for publication in ApJ

We present the results of our first year of quasar search in the on-going ESO public Kilo Degree Survey (KiDS) and VISTA Kilo-Degree Infrared Galaxy (VIKING) surveys. These surveys are among the deeper wide-field surveys that can be used to uncovered large numbers of z~6 quasars. This allows us to probe a more common population of z~6 quasars that is fainter than the well-studied quasars from the main Sloan Digital Sky Survey. From this first set of combined survey catalogues covering ~250 deg^2 we selected point sources down to Z_AB=22 that had a very red i-Z (i-Z>2.2) colour. After follow-up imaging and spectroscopy, we discovered four new quasars in the redshift range 5.8

We present the discovery of two z > 6 quasars, selected as i band dropouts in the VST ATLAS survey. Our first quasar has redshift, z = 6.31 \pm 0.03, z band magnitude, z_AB = 19.63 \pm 0.08 and rest frame 1450A absolute magnitude, M_1450 = -27.8 \pm 0.2, making it the joint second most luminous quasar known at z > 6. The second quasar has z = 6.02 \pm 0.03, z_AB = 19.54 \pm 0.08 and M_1450 = -27.0 \pm 0.1. We also recover a z = 5.86 quasar discovered by Venemans et al. (2015, in prep.). To select our quasars we use a new 3D colour space, combining the ATLAS optical colours with mid-infra-red data from the Wide-field Infrared Survey Explorer (WISE). We use i_AB - z_AB colour to exclude main sequence stars, galaxies and lower redshift quasars, W1 - W2 to exclude L dwarfs and z_AB - W2 to exclude T dwarfs. A restrictive set of colour cuts returns only our three high redshift quasars and no contaminants, albeit with a sample completeness of ~50%. We discuss how our 3D colour space can be used to reject the majority of contaminants from samples of bright 5.7 < z < 6.3 quasars, replacing follow-up near-infra-red photometry, whilst retaining high completeness., Comment: 5 pages, 2 figures, submitted to MNRAS letters

The VLT Survey Telescope (VST) ATLAS is an optical ugriz survey aiming to cover ~4700deg^2 of the Southern sky to similar depths as the Sloan Digital Sky Survey (SDSS). From reduced images and object catalogues provided by the Cambridge Astronomical Surveys Unit we first find that the median seeing ranges from 0.8 arcsec FWHM in i to 1.0 arcsec in u, significantly better than the 1.2-1.5 arcsec seeing for SDSS. The 5 sigma magnitude limit for stellar sources is r_AB=22.7 and in all bands these limits are at least as faint as SDSS. SDSS and ATLAS are more equivalent for galaxy photometry except in the z band where ATLAS has significantly higher throughput. We have improved the original ESO magnitude zeropoints by comparing m<16 star magnitudes with APASS in gri, also extrapolating into u and z, resulting in zeropoints accurate to ~+-0.02 mag. We finally compare star and galaxy number counts in a 250deg^2 area with SDSS and other count data and find good agreement. ATLAS data products can be retrieved from the ESO Science Archive, while support for survey science analyses is provided by the OmegaCAM Science Archive (OSA), operated by the Wide-Field Astronomy Unit in Edinburgh., Comment: 13 pages, 23 figures, submitted to MNRAS

Studying quasars at the highest redshifts can constrain models of galaxy and black hole formation, and it also probes the intergalactic medium in the early universe. Optical surveys have to date discovered more than 60 quasars up to z~6.4, a limit set by the use of the z-band and CCD detectors. Only one z>6.4 quasar has been discovered, namely the z=7.08 quasar ULAS J1120+0641, using near-infrared imaging. Here we report the discovery of three new z>6.4 quasars in 332 square degrees of the Visible and Infrared Survey Telescope for Astronomy Kilo-degree Infrared Galaxy (VIKING) survey, thus extending the number from 1 to 4. The newly discovered quasars have redshifts of z=6.60, 6.75, and 6.89. The absolute magnitudes are between -26.0 and -25.5, 0.6-1.1 mag fainter than ULAS J1120+0641. Near-infrared spectroscopy revealed the MgII emission line in all three objects. The quasars are powered by black holes with masses of ~(1-2)x10^9 M_sun. In our probed redshift range of 6.4410^9 M_sun) > 1.1x10^(-9) Mpc^(-3). The discovery of three quasars in our survey area is consistent with the z=6 quasar luminosity function when extrapolated to z~7. We do not find evidence for a steeper decline in the space density of quasars with increasing redshift from z=6 to z=7., Comment: 14 pages, 9 figures. Published in ApJ

The European Southern Observatory's (ESO) Visible and Infrared Survey Telescope for Astronomy (VISTA) is a 4-m class survey telescope for wide-field near-infrared imaging. VISTA is currently running a suite of six public surveys, which will shortly deliver their first Europe wide public data releases to ESO. The VISTA Kilo-degree Infrared Galaxy Survey (VIKING) forms a natural intermediate between current wide shallow, and deeper more concentrated surveys, by targeting two patches totalling 1500 sq.deg in the northern and southern hemispheres with measured 5-sigma limiting depths of Z ~ 22.4, Y ~ 21.4, J ~ 20.9, H ~ 19.9 and Ks ~19.3 (Vega). This architecture forms an ideal working parameter space for the discovery of a significant sample of 6.5 <= z <= 7.5 quasars. In the first data release priority has been placed on small areas encompassing a number of fields well sampled at many wavelengths, thereby optimising science gains and synergy whilst ensuring a timely release of the first products. For rare object searches e.g. high-z quasars, this policy is not ideal since photometric selection strategies generally evolve considerably with the acquisition of data. Without a reasonably representative data set sampling many directions on the sky it is not clear how a rare object search can be conducted in a highly complete and efficient manner. In this paper, we alleviate this problem by supplementing initial data with a realistic model of the spatial, luminosity and colour distributions of sources known to heavily contaminate photometric quasar selection spaces, namely dwarf stars of spectral type M, L and T. We use this model along with a subset of available data to investigate contamination of quasar selection space by cool stars and galaxies and lay down a set of benchmark selection constraints that limit contamination to reasonable levels whilst maintaining high completeness..., Comment: 16 pages, 14 figures