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Register a new userThe UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
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The UKIRT Infrared Deep Sky Survey is a set of five surveys of complementary combinations of area, depth, and Galactic latitude, which began in 2005 May. The surveys use the UKIRT Wide Field Camera (WFCAM), which has a solid angle of 0.21deg^2. Here we introduce and characterise the ZYJHK photometric system of the camera, which covers the wavelength range 0.83-2.37 microns. We synthesise response functions for the five passbands, and compute colours in the WFCAM, SDSS and 2MASS bands, for brown dwarfs, stars, galaxies and quasars of different types. We provide a recipe for others to compute colours from their own spectra. Calculations are presented in the Vega system, and the computed offsets to the AB system are provided, as well as colour equations between WFCAM filters and the SDSS and 2MASS passbands. We highlight the opportunities presented by the new Y filter at 0.97-1.07 microns for surveys for hypothetical Y dwarfs (brown dwarfs cooler than T), and for quasars of very--high redshift, z>6.4.
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In this paper we describe the photometric calibration of data taken with the near-infrared Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). The broadband ZYJHK data are directly calibrated from 2MASS point sources which are abundant in every WFCAM pointing. We perform an analysis of spatial systematics in the photometric calibration, both inter- and intra-detector and show that these are present at up to the 5 per cent level in WFCAM. Although the causes of these systematics are not yet fully understood, a method for their removal is developed and tested. Following application of the correction procedure the photometric calibration of WFCAM is found to be accurate to approximately 1.5 per cent for the JHK bands and 2 per cent for the ZY bands, meeting the survey requirements. We investigate the transformations between the 2MASS and WFCAM systems and find that the Z and Y calibration is sensitive to the effects of interstellar reddening for large values of E(B-V), but that the JHK filters remain largely unaffected. We measure a small correction to the WFCAM Y-band photometry required to place WFCAM on a Vega system, and investigate WFCAM measurements of published standard stars from the list of UKIRT faint standards. Finally we present empirically determined throughput measurements for WFCAM.
UKIDSS is the next generation near-infrared sky survey. The survey will commence in early 2004, and over 7 years will collect 100 times as many photons as 2MASS. UKIDSS will use the UKIRT Wide Field Camera to survey 7500 square degrees of the northern sky, extending over both high and low Galactic latitudes, in JHK to K=18.5 (over three magnitudes deeper than 2MASS). UKIDSS will be the true near-infrared counterpart to the Sloan survey, and will produce as well a panoramic clear atlas of the Galactic plane. In fact UKIDSS is made up of five surveys and includes two deep extra-Galactic elements, one covering 35 square degrees to K=21, and the other reaching K=23 over 0.77 square degrees. This paper provides the details of the five UKIDSS surveys and describes the main science goals.
The First Data Release (DR1) of the UKIRT Infrared Deep Sky Survey (UKIDSS) took place on 2006 July 21. UKIDSS is a set of five large near-infrared surveys, covering a complementary range of areas, depths, and Galactic latitudes. DR1 is the first large release of survey-quality data from UKIDSS and includes 320 sq degs of multicolour data to (Vega) K=18, complete (depending on the survey) in three to five bands from the set ZYJHK, together with 4 sq degs of deep JK data to an average depth K=21. In addition the release includes a similar quantity of data with incomplete filter coverage. In JHK, in regions of low extinction, the photometric uniformity of the calibration is better than 0.02 mag. in each band. The accuracy of the calibration in ZY remains to be quantified, and the same is true of JHK in regions of high extinction. The median image FWHM across the dataset is 0.82 arcsec. We describe changes since the Early Data Release in the implementation, pipeline and calibration, quality control, and archive procedures. We provide maps of the areas surveyed, and summarise the contents of each of the five surveys in terms of filters, areas, and depths. DR1 marks completion of 7 per cent of the UKIDSS 7-year goals.
The UKIRT Infrared Deep Sky Survey (UKIDSS) is a set of five large near-infrared surveys, covering a complementary range of areas, depths, and Galactic latitudes. The UKIDSS Second Data Release (DR2) includes the First Data Release (DR1), with minor improvements, plus new data for the LAS, GPS, GCS, and DXS, from observations made over 2006 May through July (when the UDS was unobservable). DR2 was staged in two parts. The first part excluded the GPS, and took place on 2007 March 1. The GPS was released on 2007 April 12. DR2 includes 282 sq. degs of multicolour data to (Vega) K=18, complete in the full YJHK set for the LAS, 57 sq. degs in the ZYJHK set for the GCS, and 236 sq. degs in the JHK set for the GPS. DR2 includes nearly 7 sq. degs of deep JK data (DXS, UDS) to an average depth K=21. In addition the release includes a comparable quantity of data where coverage of the filter set for any survey is incomplete. We document changes that have occurred since DR1 to the pipeline, calibration, and archive procedures. The two most noteworthy changes are presentation of the data in a single database (compared to two previously), and provision of additional error flags for detected sources, flagging potentially spurious artifacts, corrupted data and suspected cross-talk sources. We summarise the contents of each of the surveys in terms of filters, areas, and depths.
Optical and near-infrared (NIR) spectra are presented for ULAS J131911.29+095951.4 (hereafter ULAS J1319+0950), a new redshift z = 6.127 +/- 0.004 quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared Deep Sky Survey (UKIDSS). The source has Y_Vega = 19.10 +/- 0.03, corresponding to M_1450,AB = -27.12, which is comparable to the absolute magnitudes of the z ~= 6 quasars discovered in the SDSS. ULAS J1319+0950 was, in fact, registered by SDSS as a faint source with z_AB = 20.1 +/- 0.1, just below the signal--to--noise ratio limit of the SDSS high-redshift quasar survey. The faint z-band magnitude is a consequence of the weak Ly alpha/N V emission line, which has a rest-frame equivalent width of only ~20 A and provides only a small boost to the z-band flux. Nevertheless, there is no evidence from this UKIDSS-based search for a significant population of high-redshift quasars with weak emission lines. The Ly alpha optical depth to ULAS J1319+0950 is consistent with that measured towards similarly distant SDSS quasars, implying that results from optical- and NIR-selected quasars may be combined. Also presented is a new NIR-spectrum of the previously discovered UKIDSS quasar ULAS J020332.38+001229.2, which reveals the object to be a broad absorption line quasar. The new spectrum shows that the emission line previously identified as Ly alpha is actually N V, leading to a revised redshift of z = 5.72, rather than z = 5.86 as previously estimated.
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