D. Mortlock

The UKIRT infrared deep sky survey (UKIDSS)

Final published version including significant revisions. Twenty four pages, fourteen figures. Original version April 2006; final version published in MNRAS August 2007

A luminous quasar at a redshift of z = 7.085

The intergalactic medium was not completely reionized until approximately a billion years after the Big Bang, as revealed by observations of quasars with redshifts of less than 6.5. It has been difficult to probe to higher redshifts, however, because quasars have historically been identified in optical surveys, which are insensitive to sources at redshifts exceeding 6.5. Here we report observations of a quasar (ULAS J112001.48+064124.3) at a redshift of 7.085, which is 0.77 billion years after the Big Bang. ULAS J1120+0641 has a luminosity of 6.3 × 1013L⊙ and hosts a black hole with a mass of 2 × 109M⊙ (where L⊙ and M⊙ are the luminosity and mass of the Sun). The measured radius of the ionized near zone around ULAS J1120+0641 is 1.9 megaparsecs, a factor of three smaller than is typical for quasars at redshifts between 6.0 and 6.4. The near-zone transmission profile is consistent with a Lyα damping wing, suggesting that the neutral fraction of the intergalactic medium in front of ULAS J1120+0641 exceeded 0.1.

The UKIRT Infrared Deep Sky Survey Early Data Release

This paper defines the UKIRT Infrared Deep Sky Survey (UKIDSS) Early Data Release (EDR). UKIDSS is a set of five large near-infrared surveys being undertaken with the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). The programme began in 2005 May and has an expected duration of 7 yr. Each survey uses some or all of the broad-band filter complement ZY JHK. The EDR is the first public release of data to the European Southern Observatory (ESO) community. All worldwide releases occur after a delay of 18 months from the ESO release. The EDR provides a small sample data set, ∼50 deg(2) (about 1 per cent of the whole of UKIDSS), that is a lower limit to the expected quality of future survey data releases. In addition, an EDR+ data set contains all EDR data plus extra data of similar quality, but for areas not observed in all of the required filters (amounting to ∼220 deg(2)). The first large data release, DR1, will occur in mid-2006. We provide details of the observational implementation, the data reduction, the astrometric and photometric calibration and the quality control procedures. We summarize the data coverage and quality (seeing, ellipticity, photometricity, depth) for each survey and give a brief guide to accessing the images and catalogues from the WFCAM Science Archive.

The United Kingdom Infrared Telescope Infrared Deep Sky Survey First Data Release

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 deg of multicolour data to (Vega) K = 18, complete (depending on the survey) in three to five bands from the set ZYJHK, together with 4 deg 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 0.02mag. 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. 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.

A very cool brown dwarf in UKIDSS DR1

We report the discovery of a very cool brown dwarf, ULAS J003402.77−005206.7 (ULAS J0034−00), identified in the UKIRT Infrared Deep Sky Survey First Data Release. We provide optical, near-infrared, and mid-infrared photometry of the source, and two near-infrared spectra. Comparing the spectral energy distribution of ULAS J0034−00 to that of the T8 brown dwarf 2MASS J04151954−0935066 (2MASS J0415−09), the latest type and coolest well-studied brown dwarf to date, with effective temperature Teff ∼ 750 K, we find evidence that ULAS J0034−00 is significantly cooler. First, the measured values of the near-infrared absorption spectral indices imply a later classification, of T8.5. Secondly, the H − [4.49] colour provides an empirical estimate of the effective temperature of 540 < Teff < 660 K (± 2σ range). Thirdly, the J- and H-band peaks are somewhat narrower in ULAS J0034−00, and detailed comparison against spectral models calibrated to 2MASS J0415−09 yields an estimated temperature lower by 60 <� T eff < 120 K relative to 2MASS J0415−09 i.e. 630 < Teff < 690 K (± 2σ ), and lower gravity or higher metallicity according to the degenerate combination −0.5 <� (log g − 2[m/H]) < −0.25 (± 2σ ). Combining these estimates, and considering systematics, it is likely the temperature lies in the range 600 < Teff < 700 K. Measurement of the parallax will allow an additional check of the inferred low temperature. Despite the low inferred Teff we find no evidence for strong absorption by NH3 over the wavelength range 1.51‐1.56 μm. Evolutionary models imply that the mass and age are in the ranges 15‐36 MJup and 0.5‐8 Gyr, respectively. The measured proper motion, of 0.37 ± 0.07 arcsec yr −1 , combined with the photometrically

Exploring the substellar temperature regime down to ∼550 K

We report the discovery of three very late T dwarfs in the UKIRT Infrared Deep Sky Survey (UKIDSS) Third Data Release: ULAS J101721.40+011817.9 (ULAS1017), ULAS J123828.51+095351.3 (ULAS1238) and ULAS J133553.45+113005.2 (ULAS1335). We detail optical and near-infrared photometry for all three sources, and mid-infrared photometry for ULAS1335. We use near-infrared spectra of each source to assign spectral types T8p (ULAS1017), T8.5 (ULAS1238) and T9 (ULAS1335) to these objects. ULAS1017 is classed as a peculiar T8 (T8p) due to appearing as a T8 dwarf in the J-band, whilst exhibiting H and K-band flux ratios consistent with a T6 classification. Through comparison to BT-Settl model spectra we estimate that ULAS1017 has 750K T8 dwarfs to the rest of the T dwarf sequence, the suggestion of the Y0 spectral class for these objects is premature. Comparison of model spectra with that of ULAS1335 suggest a temperature below 600K, possibly combined with low-gravity and/or high-metallicity. We find ULAS1335 to be extremely red in near to mid-infrared colours, with H [4.49] = 4.34 ± 0.04 . This is the reddest near to mid-infrared colour yet observed for a T dwarf. The near to mid-infrared spectral energy distribution of ULAS1335 further supports Teff < 600K, and we estimate Teff � 550 600K for ULAS1335. We estimate that ULAS1335 has an age of 0.6–5.3 Gyr, a mass of 15–31 MJ and lies at a distance of 8–12 pc.

A high-significance detection of non-Gaussianity in the Wilkinson Microwave Anisotropy Probe 1-yr data using directional spherical wavelets

A directional spherical wavelet analysis is performed to examine the Gaussianity of the Wilkinson Microwave Anisotropy Probe (WMAP) 1-yr data. Such an analysis is facilitated by the introduction of a fast directional continuous spherical wavelet transform. The directional nature of the analysis allows us to probe orientated structure in the data. Significant deviations from Gaussianity are detected in the skewness and kurtosis of spherical elliptical Mexican hat and real Morlet wavelet coefficients for both the WMAP and Tegmark, de Oliveira-Costa & Hamilton foreground-removed maps. The previous non-Gaussianity detection made by Vielva et al. using the spherical symmetric Mexican hat wavelet is confirmed, although their detection at the 99.9 per cent significance level is only made at the 95.3 per cent significance level using our most conservative statistical test. Furthermore, deviations from Gaussianity in the skewness of spherical real Morlet wavelet coefficients on a wavelet scale of 550 arcmin (corresponding to an effective global size on the sky of ∼26° and an internal size of ∼3°) at an azimuthal orientation of 72°, are made at the 98.3 per cent significance level, using the same conservative method. The wavelet analysis inherently allows us to localize on the sky those regions that introduce skewness and those that introduce kurtosis. Preliminary noise analysis indicates that these detected deviation regions are not atypical and have average noise dispersion. Further analysis is required to ascertain whether these detected regions correspond to secondary or instrumental effects, or whether in fact the non-Gaussianity detected is due to intrinsic primordial fluctuations in the cosmic microwave background.

Reconstruction of total solar irradiance 1974-2009

Context. The study of variations in total solar irradiance (TSI) is important for understanding how the Sun affects the Earth’s climate. Aims. Full-disk continuum images and magnetograms are now available for three full solar cycles. We investigate how modelled TSI compares with direct observations by building a consistent modelled TSI dataset. The model, based only on changes in the photospheric magnetic flux can then be tested on rotational, cyclical and secular timescales. Methods. We use Kitt Peak and SoHO/MDI continuum images and magnetograms in the SATIRE-S model to reconstruct TSI over cycles 21–23. To maximise independence from TSI composites, SORCE/TIM TSI data are used to fix the one free parameter of the model. We compare and combine the separate data sources for the model to estimate an uncertainty on the reconstruction and prevent any additional free parameters entering the model. Results. The reconstruction supports the PMOD composite as being the best historical record of TSI observations, although on timescales of the solar rotation the IRMB composite provides somewhat better agreement. Further to this, the model is able to account for 92% of TSI variations from 1978 to 2009 in the PMOD composite and over 96% during cycle 23. The reconstruction also displays an inter-cycle, secular decline of 0.20 +0.12 −0.09 Wm −2 between cycle 23 minima, in agreement with the PMOD composite.

Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between �24–93pc), identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations), and find that one of these new T dwarfs may be metal poor, three may have low surface gravity, and one may have high surface gravity. The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y J with decreasing effective temperature, and some interesting colour changes in J H and z J (deserving further investigation) beyond T8. The LAS T dwarf sample from the first and second main data releases show good evidence for a consistent level of completion to J=19. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17±4 >T4 dwarfs in the J 619 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent α between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the α � 1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.

Eight new T4.5–T7.5 dwarfs discovered in the UKIDSS Large Area Survey Data Release 1

The definitive version is available at www.blackwell-synergy.com Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.12023.x