A. J. Adamson

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 WFCAM Science Archive

We describe the WFCAM Science Archive, which is the primary point of access for users of data from the wide-field infrared camera WFCAM on the United Kingdom Infrared Telescope (UKIRT), especially science catalogue products from the UKIRT Infrared Deep Sky Survey. We describe the database design with emphasis on those aspects of the system that enable users to fully exploit the survey data sets in a variety of different ways. We give details of the database-driven curation applications that take data from the standard nightly pipeline-processed and calibrated files for the production of science-ready survey data sets. We describe the fundamentals of querying relational databases with a set of astronomy usage examples, and illustrate the results.

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

Parallaxes and physical properties of 11 mid-to-late T dwarfs

Aims. We present parallaxes of 11 mid-to-late T dwarfs observed in the UKIRT Infrared Deep Sky Survey. We use these results to test the reliability of model predictions in magnitude‐color space, determine a magnitude-spectral type calibration, and, estimate a bolometric luminosity and effective temperature range for the targets. Methods. We used observations from the UKIRT WFCAM instrument pipeline processed at the Cambridge Astronomical Survey Unit. The parallaxes and proper motions of the sample were calculated using standard procedures. The bolometric luminosity was estimated using near- and mid-infrared observations with two different methods. The corresponding effective temperature ranges were found adopting a large age-radius range. Results. We show the models are unable to predict the colors of the latest T dwarfs indicating the incompleteness of model opacities for NH3 ,C H4 and H2 as the temperature declines. We report the effective temperature ranges obtained.

A glimpse of the end of the dark ages: the gamma-ray burst of 23 April 2009 at redshift 8.3

Long-duration gamma-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-alpha emitting galaxy. Here we report that GRB 090423 lies at a redshift of z approximately 8.2, implying that massive stars were being produced and dying as GRBs approximately 630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.It is thought that the first generations of massive stars in the Universe were an important, and quite possibly dominant, source of the ultra-violet radiation that reionized the hydrogen gas in the intergalactic medium (IGM); a state in which it has remained to the present day. Measurements of cosmic microwave background anisotropies suggest that this phase-change largely took place in the redshift range z=10.8 +/- 1.4, while observations of quasars and Lyman-alpha galaxies have shown that the process was essentially completed by z=6. However, the detailed history of reionization, and characteristics of the stars and proto-galaxies that drove it, remain unknown. Further progress in understanding requires direct observations of the sources of ultra-violet radiation in the era of reionization, and mapping the evolution of the neutral hydrogen fraction through time. The detection of galaxies at such redshifts is highly challenging, due to their intrinsic faintness and high luminosity distance, whilst bright quasars appear to be rare beyond z~7. Here we report the discovery of a gamma-ray burst, GRB 090423, at redshift z=8.26 -0.08 +0.07. This is well beyond the redshift of the most distant spectroscopically confirmed galaxy (z=6.96) and quasar (z=6.43). It establishes that massive stars were being produced, and dying as GRBs, ~625 million years after the Big Bang. In addition, the accurate position of the burst pinpoints the location of the most distant galaxy known to date. Larger samples of GRBs beyond z~7 will constrain the evolving rate of star formation in the early universe, while rapid spectroscopy of their afterglows will allow direct exploration of the progress of reionization with cosmic time.Long-duration γ-ray bursts (GRBs) are thought to result from the explosions of certain massive stars, and some are bright enough that they should be observable out to redshifts of z > 20 using current technology. Hitherto, the highest redshift measured for any object was z = 6.96, for a Lyman-α emitting galaxy. Here we report that GRB 090423 lies at a redshift of z ≈ 8.2, implying that massive stars were being produced and dying as GRBs ∼630 Myr after the Big Bang. The burst also pinpoints the location of its host galaxy.

Infrared and visual interstellar absorption features towards heavily reddened field stars

We present measurements of the 3.4-μm hydrocarbon dust absorption feature, and four visual diffuse interstellar bands, for 12 highly reddened [9.0 < A(V) < 15.8], early-type stars identified from the Stephenson catalogue, covering a range of Galactic longitude. The hydrocarbon feature is detected in 11 sightlines with optical depths of up to 0.05, and corresponding column densities are derived. The feature is weaker per unit A(V) than previously reported, further underlining earlier observations of its enhancement in the Galactic Centre. A comparison of the 3.4-μm feature substructure indicates organic material similar to that seen in earlier diffuse medium studies, suggesting a uniform formation history across the Galactic disc. The profile is well matched by both meteoritic material and several laboratory-prepared analogues. The diffuse interstellar bands (DIBs) measured were λλ6177, 6203, 6284 and 6614; no strong correlations were detected, either between these bands themselves or between the DIBs and the 3.4-μm feature, although λλ6284 and 6614 appear to vary together. If the carriers of the DIBs are organic and molecular in nature and have cosmic carbon abundance requirements similar to those of the C-H stretch, these results imply that there is little direct carbon exchange between them and the aliphatic dust component. Measurements of the extinction to these objects suggest luminosity anomalies similar to that already seen in Cyg OB2 no 12.

The distance to the cool T9 brown dwarf ULAS J003402.77-005206.7

Aims. We demonstrate the feasibility ofdetermining parallaxes for nearby objects withthe WideField Camera on the United Kingdom Infrared Telescope (UKIRT) using the UKIRT Infrared Deep Sky Survey as a first epoch. We determine physical parameters for ULAS J003402.77-005206.7, one of the coolest brown dwarfs currently known, using atmospheric and evolutionary models with the distance found here. Methods. Observations over the period 10/2005 to 07/2009 were pipeline processed at the Cambridge Astronomical Survey Unit and combined to produce a parallax and proper motion using standard procedures. Results. We determined π = 79.6 ±3. 8m as,μα = −20.0 ±3. 7m as/yr and μδ = −363.8 ±4. 3m as/yr for ULAS J003402.77-005206.7. Conclusions. We have made a direct parallax determination for one of the coolest objects outside of the solar system. The distance is consistent with a relatively young, 1−2 Gyr, low mass, 13−20 MJ, cool, 550−600 K, brown dwarf. We present a measurement of the radial velocity that is consistent with an age between 0.5 and 4.0 Gyr.