Search

We present the discovery and preliminary characterisation of two high-redshift gravitationally lensed quasar systems in Gaia Data Release 2 (DR2). Candidates with multiple close-separation Gaia detections and quasar-like colours in WISE , Pan-STARRS, and DES are selected for follow-up spectroscopy with the New Technology Telescope. We confirm DES J215028.71−465251.3 as a |$z$| = 4.130 ± 0.006 asymmetric, doubly imaged lensed quasar system and model the lensing mass distribution as a singular isothermal sphere. The system has an Einstein radius of 1.202 ± 0.005 arcsec and a predicted time delay of ∼122.0 d between the quasar images, assuming a lensing galaxy redshift of |$z$| = 0.5, making this a priority system for future optical monitoring. We confirm PS J042913.17+142840.9 as a |$z$| = 3.866 ± 0.003 four-image quasar system in a cusp configuration, lensed by two foreground galaxies. The system is well modelled using a singular isothermal ellipsoid for the primary lens and a singular isothermal sphere for the secondary lens with Einstein radii 0.704 ± 0.006 and 0.241 ± 0.030 arcsec, respectively. A maximum predicted time delay of 9.6 d is calculated, assuming lensing galaxy redshifts of |$z$| = 1.0. Furthermore, PS J042913.17+142840.9 exhibits a large flux ratio anomaly, up to a factor of 2.66 ± 0.37 in i band, that varies across optical and near-infrared wavelengths. We discuss LSST and its implications for future high-redshift lens searches and outline an extension to the search using supervised machine learning techniques. [ABSTRACT FROM AUTHOR]

We present two catalogues of active galactic nucleus (AGN) candidates selected from the latest data of two all-sky surveys – Data Release 2 of the Gaia mission and the unWISE catalogue of the Wide-field Infrared Survey Explorer (WISE). We train a random forest classifier to predict the probability of each source in the Gaia –unWISE joint sample being an AGN, P RF, based on Gaia astrometric and photometric measurements and unWISE photometry. The two catalogues, which we designate C75 and R85, are constructed by applying different P RF threshold cuts to achieve an overall completeness of 75 per cent (≈90 per cent at Gaia G ≤ 20 mag) and reliability of 85 per cent, respectively. The C75 (R85) catalogue contains 2734 464 (2182 193) AGN candidates across the effective 36 000 deg2 sky, of which ≈0.91 (0.52) million are new discoveries. Photometric redshifts of the AGN candidates are derived by a random forest regressor using Gaia and WISE magnitudes and colours. The estimated overall photometric redshift accuracy is 0.11. Cross-matching the AGN candidates with a sample of known bright cluster galaxies, we identify a high-probability strongly lensed AGN candidate system, SDSS J1326+4806, with a large image separation of 21 |${^{\prime\prime}_{.}}$| 06. All the AGN candidates in our catalogues will have ∼5-yr long light curves from Gaia by the end of the mission, and thus will be a great resource for AGN variability studies. Our AGN catalogues will also be helpful in AGN target selections for future spectroscopic surveys, especially those in the Southern hemisphere. The C75 catalogue can be downloaded at https://www.ast.cam.ac.uk/~ypshu/AGN_Catalogues.html. [ABSTRACT FROM AUTHOR]

We report the discovery and spectroscopic confirmation of 22 new gravitationally lensed quasars found using Gaia data release 2. The selection was made using several techniques: multiple Gaia detections around objects in quasar candidate catalogues, modelling of unWISE coadd pixels using Gaia astrometry, and Gaia detections offset from photometric and spectroscopic galaxies. Spectra of 33 candidates were obtained with the William Herschel Telescope, 22 of which are lensed quasars, two highly probably lensed quasars, five nearly identical quasar pairs, one inconclusive system, and three contaminants. Of the three confirmed quadruply imaged systems, J2145+6345 is a 2.1 arcsec separation quad with four bright images (G  = 16.86, 17.26, 18.34, 18.56), making it ideal for time delay monitoring. Analysing this new sample alongside known lenses in the Pan-STARRS footprint, and comparing to expected numbers of lenses, we show that, as expected, we are biased towards systems with bright lensing galaxies and low source redshifts. We discuss possible techniques to remove this bias from future searches. A | b | > 20 complete sample of lensed quasars detected by Gaia and with image separations above 1 arcsec will provide a valuable statistical sample of around 350 systems. Currently only 96 known lenses satisfy these criteria, yet promisingly, our unWISE modelling technique is able to recover all of these with simple WISE- Gaia colour cuts that remove ∼80 per cent of previously followed-up contaminants. Finally, we provide an online data base of known lenses, quasar pairs, and contaminant systems. [ABSTRACT FROM AUTHOR]

We report the discovery, spectroscopic confirmation, and preliminary characterization of 24 gravitationally lensed quasars identified using Gaia observations. Candidates were selected in the Pan-STARRS footprint with quasar-like WISE colours or as photometric quasars from Sloan Digital Sky Survey (SDSS), requiring either multiple detections in Gaia or a single Gaia detection near a morphological galaxy. The Pan-STARRS grizY images were modelled for the most promising candidates and 60 candidate systems were followed up with the William Herschel Telescope. 13 of the lenses were discovered as Gaia multiples and 10 as single Gaia detections near galaxies. We also discover 1 lens identified through a quasar emission line in an SDSS galaxy spectrum. The lenses have median image separation 2.13 arcsec and the source redshifts range from 1.06 to 3.36. 4 systems are quadruply imaged and 20 are doubly imaged. Deep CFHT data reveal an Einstein ring in one double system. We also report 12 quasar pairs, 10 of which have components at the same redshift and require further follow-up to rule out the lensing hypothesis. We compare the properties of these lenses and other known lenses recovered by our search method to a complete sample of simulated lenses to show the lenses we are missing are mainly those with small separations and higher source redshifts. The initial Gaia data release only catalogues all images of ∼30 per cent of known bright lensed quasars, however the improved completeness of Gaia data release 2 will help find all bright lensed quasars on the sky. [ABSTRACT FROM AUTHOR]

Gaia's exceptional resolution (FWHM ~ 0.1 arcsec) allows identification and cataloguing of the multiple images of gravitationally lensed quasars. We investigate a sample of 49 known lensed quasars in the Sloan Digital Sky Survey (SDSS) footprint, with image separations less than 2 arcsec, and find that eight are detected with multiple components in the first Gaia data release. In the case of the 41 single Gaia detections, we generally are able to distinguish these lensed quasars from single quasars when comparing Gaia flux and position measurements to those of Pan-STARRS and SDSS. This is because the multiple images of these lensed quasars are typically blended in ground-based imaging and therefore the total flux and a flux-weighted centroid are measured, which can differ significantly from the fluxes and centroids of the individual components detected by Gaia. We compare the fluxes through an empirical fit of Pan-STARRS griz photometry to the wide optical Gaia bandpass values using a sample of isolated quasars. The positional offsets are calculated from a recalibrated astrometric SDSS catalogue. Applying flux and centroid difference criteria to spectroscopically confirmed quasars, we discover four new sub-arcsecond-separation lensed quasar candidates which have two distinct components of similar colour in archival Canada-France-Hawaii Telescope or Hyper Suprime Cam data. Our method based on single Gaia detections can be used to identify the ~1400 lensed quasars with image separation above 0.5 arcsec, expected to have only one image bright enough to be detected by Gaia. [ABSTRACT FROM AUTHOR]

We present a search for metal absorption line systems at the highest redshifts to date using a deep (30 h) Very Large Telescope/X-Shooter spectrum of the z = 7.084 quasi-stellar object (QSO) ULAS J1120+0641. We detect seven intervening systems at z > 5.5, with the highest redshift system being a C IV absorber at z = 6.51. We find tentative evidence that the mass density of C IV remains flat or declines with redshift at z < 6, while the number density of C II systems remains relatively flat over 5 < z < 7. These trends are broadly consistent with models of chemical enrichment by star formation-driven winds that include a softening of the ultraviolet background towards higher redshifts. We find a larger number of weak (Wrest < 0.3 Å) Mg II systems over 5.9 < z < 7.0 than predicted by a power-law fit to the number density of stronger systems. This is consistent with trends in the number density of weak Mg II systems at z ≲ 2.5, and suggests that the mechanisms that create these absorbers are already in place at z ~ 7. Finally, we investigate the associated narrow Si IV, C IV and N V absorbers located near the QSO redshift, and find that at least one component shows evidence of partial covering of the continuum source. [ABSTRACT FROM AUTHOR]

We present the discovery of a z = 0.65 low-ionization broad absorption line (LoBAL) quasar in a post-starburst galaxy in data from the Dark Energy Survey (DES) and spectroscopy from the Australian Dark Energy Survey (OzDES). LoBAL quasars are a minority of all BALs, and rarer still is that this object also exhibits broad Fe II (an FeLoBAL) and Balmer absorption. This is the first BAL quasar that has signatures of recently truncated star formation, which we estimate ended about 40 Myr ago. The characteristic signatures of an FeLoBAL require high column densities, which could be explained by the emergence of a young quasar from an early, dust-enshrouded phase, or by clouds compressed by a blast wave. The age of the starburst component is comparable to estimates of the lifetime of quasars, so if we assume the quasar activity is related to the truncation of the star formation, this object is better explained by the blast wave scenario. [ABSTRACT FROM AUTHOR]

We present the discovery and preliminary characterization of a gravitationally lensed quasar with a source redshift zs = 2.74 and image separation of 2.9 arcsec lensed by a foreground zl = 0.40 elliptical galaxy. Since optical observations of gravitationally lensed quasars show the lens system as a superposition of multiple point sources and a foreground lensing galaxy, we have developed a morphology-independent multi-wavelength approach to the photometric selection of lensed quasar candidates based on Gaussian Mixture Models (GMM) supervised machine learning. Using this technique and gi multicolour photometric observations from the Dark Energy Survey (DES), near-IR JK photometry from the VISTA Hemisphere Survey (VHS) and WISE mid-IR photometry, we have identified a candidate system with two catalogue components with iAB = 18.61 and iAB = 20.44 comprising an elliptical galaxy and two blue point sources. Spectroscopic follow-up with NTT and the use of an archival AAT spectrum show that the point sources can be identified as a lensed quasar with an emission line redshift of z = 2.739 ± 0.003 and a foreground early-type galaxy with z = 0.400 ± 0.002. We model the system as a single isothermal ellipsoid and find the Einstein radius θE ~ 1.47 arcsec, enclosed mass Menc ~ 4 x 1011 Mʘ and a time delay of ~52 d. The relatively wide separation, month scale time delay duration and high redshift make this an ideal system for constraining the expansion rate beyond a redshift of 1. [ABSTRACT FROM AUTHOR]

We use near-infrared integral field unit spectroscopy to search for Hα emission associated with star formation in a sample of 28 heavily reddened (E(B - V) ≃ 0.5-1.9), hyperluminous (log(Lbol/erg s-1) ≃ 47-48) broad-line quasars at z ≃ 1.4-2.7. 16 of the 28 quasars show evidence for star formation with an average extinction-corrected star formation rate (SFR) of 320 ± 70 M๏ yr-1. A stacked spectrum of the detections shows weak [NII], consistent with star formation as the origin of the narrow Hα emission. The star-forming regions are spatially unresolved in 11 of the 16 detections and constrained to lie within ~6 kpc of the quasar emission. In the five resolved detections we find the star-forming regions are extended on scales of ~8 kpc around the quasar emission. The prevalence of high SFRs is consistent with the identification of the heavily reddened quasar population as representing a transitional phase from apparent 'starburst galaxies' to optically luminous quasars. Upper limits are determined for 10 quasars in which star formation is undetected. In two of the quasars the SFR is constrained to be relatively modest, <50 M๏ yr-1, but significantly higher levels of star formation could be present in the other eight quasars. The combination of the 16 strong star formation detections and the eight high SFR limits means that high levels of star formation may be present in the majority of the sample. Higher spatial resolution data, of multiple emission lines, will allow us to better understand the interplay between star formation and active galactic nucleus activity in these transitioning quasars. [ABSTRACT FROM AUTHOR]

As part of the Australian spectroscopic dark energy survey (OzDES) we are carrying out a large-scale reverberation mapping study of ≥500 quasars over five years in the 30 deg2 area of the Dark Energy Survey (DES) supernova fields. These quasars have redshifts ranging up to 4 and have apparent AB magnitudes between 16.8 mag < r < 22.5 mag. The aim of the survey is to measure time lags between fluctuations in the quasar continuum and broad emission-line fluxes of individual objects in order to measure black hole masses for a broad range of active galactic nuclei (AGN) and constrain the radius–luminosity (R–L) relationship. Here we investigate the expected efficiency of the OzDES reverberation mapping campaign and its possible extensions. We expect to recover lags for ∼35–45 per cent of the quasars. AGN with shorter lags and greater variability are more likely to yield a lag measurement, and objects with lags ≲6 months or ∼1 yr are expected to be recovered the most accurately. The baseline OzDES reverberation mapping campaign is predicted to produce an unbiased measurement of the R–L relationship parameters for H β, Mg II λ2798, and C iv λ1549. Extending the baseline survey by either increasing the spectroscopic cadence, extending the survey season, or improving the emission-line flux measurement accuracy will significantly improve the R–L parameter constraints for all broad emission lines. [ABSTRACT FROM AUTHOR]

We present a new population of z > 2 dust-reddened, type 1 quasars with 0.5 ≲ E(B − V) ≲ 1.5, selected using near-infrared (NIR) imaging data from the UKIDSS-LAS (Large Area Survey), ESO-VHS (European Southern Obseratory-VISTA Hemisphere Survey) and WISE surveys. NIR spectra obtained using the Very Large Telescope for 24 new objects bring our total sample of spectroscopically confirmed hyperluminous (>1013 L⊙), high-redshift dusty quasars to 38. There is no evidence for reddened quasars having significantly different Hα equivalent widths relative to unobscured quasars. The average black hole masses (∼109–1010 M⊙) and bolometric luminosities (∼1047 erg s−1) are comparable to the most luminous unobscured quasars at the same redshift, but with a tail extending to very high luminosities of ∼1048 erg s−1. 66 per cent of the reddened quasars are detected at >3σ at 22 μm by WISE. The average 6-μm rest-frame luminosity is log10(L6 μm/ erg s−1) = 47.1 ± 0.4, making the objects among the mid-infrared brightest active galactic nuclei (AGN) currently known. The extinction-corrected space density estimate now extends over three magnitudes (−30 < Mi < −27) and demonstrates that the reddened quasar luminosity function is significantly flatter than that of the unobscured quasar population at z = 2–3. At the brightest magnitudes, Mi ≲ −29, the space density of our dust-reddened population exceeds that of unobscured quasars. A model where the probability that a quasar becomes dust reddened increases at high luminosity is consistent with the observations and such a dependence could be explained by an increase in luminosity and extinction during AGN-fuelling phases. The properties of our obscured type 1 quasars are distinct from the heavily obscured, Compton-thick AGN that have been identified at much fainter luminosities and we conclude that they likely correspond to a brief evolutionary phase in massive galaxy formation. [ABSTRACT FROM AUTHOR]

We present optical and near-infrared imaging of the field of the z = 7.0842 quasar ULAS J112001.48+064124.3 taken with the Hubble Space Telescope. We use these data to search for galaxies that may be physically associated with the quasar, using the Lyman break technique, and find three such objects, although the detection of one in Spitzer Space Telescope imaging strongly suggests it lies at z ∼ 2. This is consistent with the field luminosity function and indicates that there is no excess of >L★ galaxies within 1 Mpc of the quasar. A detection of the quasar shortwards of the Lyα line is consistent with the previously observed evolution of the intergalactic medium at z > 5.5. [ABSTRACT FROM PUBLISHER]

ABSTRACT We present a new sample of purely near-infrared-selected KVega < 16.5 [ KAB < 18.4] extremely red [( J − K)Vega > 2.5] quasar candidates at z ∼ 2 from ≃900 deg2 of data in the UKIDSS Large Area Survey (LAS). Five of these are spectroscopically confirmed to be heavily reddened type 1 active galactic nuclei (AGN) with broad emission lines bringing our total sample of reddened quasars from the UKIDSS-LAS to 12 at z = 1.4-2.7. At these redshifts, Hα (6563 Å) is in the K band. However, the mean Hα equivalent width of the reddened quasars is only 10 per cent larger than that of the optically selected population and cannot explain the extreme colours. Instead, dust extinction of A V ∼ 2-6 mag is required to reproduce the continuum colours of our sources. This is comparable to the dust extinctions seen in submillimetre galaxies at similar redshifts. We argue that the AGN are likely being observed in a relatively short-lived breakout phase when they are expelling gas and dust following a massive starburst, subsequently turning into UV-luminous quasars. Some of our quasars show direct evidence for strong outflows ( v ∼ 800-1000 km s−1) affecting the Hα line consistent with this scenario. We predict that a larger fraction of reddened quasar hosts are likely to be submillimetre bright compared to the UV-luminous quasar population. We use our sample to place new constraints on the fraction of obscured type 1 AGN likely to be missed in optical surveys. Taken at face value our findings suggest that the obscured fraction depends on quasar luminosity. The space density of obscured quasars is approximately five times that inferred for UV-bright quasars from the Sloan Digital Sky Survey (SDSS) luminosity function at M i < −30 but seems to drop at lower luminosities even accounting for various sources of incompleteness in our sample. We find that at M i ∼ −28 for example, this fraction is unlikely to be larger than ∼20 per cent although these fractions are highly uncertain at present due to the small size of our sample. A deeper K-band survey for highly obscured quasars is clearly needed to test this hypothesis fully and is now becoming possible with new sensitive all-sky infrared surveys such as the VISTA Hemisphere Survey and the Wide Infrared Survey Explorer ( WISE) All Sky Survey. [ABSTRACT FROM AUTHOR]

ABSTRACT High-redshift quasars (HZQs) with redshifts of z ≳ 6 are so rare that any photometrically selected sample of sources with HZQ-like colours is likely to be dominated by Galactic stars and brown dwarfs scattered from the stellar locus. It is impractical to re-observe all such candidates, so an alternative approach was developed in which Bayesian model comparison techniques are used to calculate the probability that a candidate is a HZQ, Pq, by combining models of the quasar and star populations with the photometric measurements of the object. This method was motivated specifically by the large number of HZQ candidates identified by cross-matching the UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) to the Sloan Digital Sky Survey (SDSS): in the covered by the LAS in the UKIDSS Eighth Data Release (DR8) there are ∼9 × 103 real astronomical point sources with the measured colours of the target quasars, of which only ∼10 are expected to be HZQs. Applying Bayesian model comparison to the sample reveals that most sources with HZQ-like colours have Pq≲ 0.1 and can be confidently rejected without the need for any further observations. In the case of the UKIDSS DR8 LAS, there were just 107 candidates with Pq≥ 0.1; these objects were prioritized for re-observation by ranking according to Pq (and their likely redshift, which was also inferred from the photometric data). Most candidates were rejected after one or two (moderate-depth) photometric measurements by recalculating Pq using the new data. That left 12 confirmed HZQs, six of which were previously identified in the SDSS and six of which were new UKIDSS discoveries. The high efficiency of this Bayesian selection method suggests that it could usefully be extended to other HZQ surveys (e.g. searches by the Panoramic Survey Telescope And Rapid Response System, Pan-STARRS, or the Visible and Infrared Survey Telescope for Astronomy, VISTA) as well as to other searches for rare objects. [ABSTRACT FROM AUTHOR]

An accurate method to measure the abundance of high-redshift galaxies involves the observation of absorbers along the line of sight towards a background quasar. Here, we present abundance measurements of 13 z≥ 3 sub-damped Lyman α (sub-DLA) systems (quasar absorbers with H i column density in the range 19 < log N(H i) < 20.3 cm−2) based on high-resolution observations with the VLT UVES spectrograph. These observations more than double the amount of metallicity information for sub-DLAs available at z > 3. These new data, combined with other sub-DLA measurements from the literature, confirm the stronger evolution of metallicity with redshift for sub-DLAs than for the classical damped Lyman α absorbers. In addition, these observations are used to compute for the first time, using photoionization modelling in a sample of sub-DLAs, the fraction of gas that is ionized. Based on these results, we calculate that sub-DLAs contribute no more than 6 per cent of the expected amount of metals at z∼ 2.5. We therefore conclude that, even if sub-DLAs are found to be more metal-rich than classical DLAs, their contribution is insufficient to solve the so-called ‘missing-metals’ problem. [ABSTRACT FROM AUTHOR]

Absorbers seen in the spectrum of background quasars are a unique tool with which to select H i-rich galaxies at all redshifts. In turns, these galaxies allow us to determine the cosmological evolution of the H i gas , which is a possible indicator of gas consumption as star formation proceeds. The damped Lyman α (Lyα) systems (DLAs with ), in particular, are believed to contain a large fraction of the H i gas but there are also indications that lower column-density systems, called ‘sub-damped Lyα’ systems, play a role at high redshift. Here we present the discovery of high-redshift sub-DLAs based on quasar spectra observed with the Ultraviolet–Visual Echelle Spectrograph (UVES) on the Very Large Telescope (VLT). This sample is composed of 21 new sub-DLAs which, together with another 10 systems from previous European Southern Observatory archive studies, make up a homogeneous sample. The redshift evolution of the number density of several classes of absorbers is derived and shows that all systems seem to be evolving in the redshift range from z= 5 to . These results are further used to estimate the redshift evolution of the characteristic radius of these classes of absorbers, assuming a Holmberg relation and one unique underlying parent population. DLAs are found to have , while sub-DLAs have . The redshift evolution of the column density distribution, f(N,z), down to is also presented. A departure from a power law due to a flattening of f(N,z) in the sub-DLA regime is present in the data. f(N,z) is further used to determine the H i gas mass contained in sub-DLAs at z > 2. The complete sample shows that sub-DLAs are important at all redshifts from z= 5 to z= 2. Finally, the possibility that sub-DLAs are less affected by the effects of dust obscuration than classical DLAs is discussed. [ABSTRACT FROM AUTHOR]

We analyse near-infraredHubble Space Telescope(HST)/Near-Infrared Camera and Multi-Object SpectrometerF110W(J) andF160W(H) band photometry of a sample of 27i′-drop candidategalaxies in the central region of theHST/Advanced Camera for SurveysUltra Deep Field. The infrared colours of the 20 objects not affected by near neighbours are consistent with a high-redshift interpretation. This suggests that the low-redshift contamination of thisi′-drop sample is smaller than that observed at brighter magnitudes, where values of 10–40 per cent have been reported. TheJ– Hcolours are consistent with a slope flat in, as would be expected for an unreddened starburst. However, there is evidence for a marginally bluer spectral slope, which is perhaps indicative of an extremely young starburst (∼10 Myr old) or a top heavy initial mass function and little dust. The low levels of contamination, median photometric redshift ofand blue spectral slope, inferred using the near-infrared data, support the validity of the assumptions in our earlier work in estimating the star formation rates, and that the majority of thei-drop candidates galaxies lie at. [ABSTRACT FROM AUTHOR]

We determine the abundance ofi′-band dropouts in the recently releasedHST/ACSHubble Ultra-Deep Field(UDF). Because the majority of these sources are likely to begalaxies whose flux decrement between the F775Wi′-band and F850LPz′-band arises from Lyman-α absorption, the number of detected candidates provides a valuable upper limit to the unextincted star formation rate at this redshift. We demonstrate that the increased depth of UDF enables us to reach anlimiting magnitude of(equivalent toat, orfor theU-drop population), permitting us to address earlier ambiguities arising from the unobserved form of the luminosity function. We identify 54 galaxies (and only one star) atwithover the deepest 11-arcmin2 portion of the UDF. The characteristic luminosityis consistent with values observed at. The faint end slopeis less well constrained, but is consistent with only modest evolution. The main change appears to be in the number density. Specifically, and regardless of possible contamination from cool stars and lower-redshift sources, the UDF data support our previous result that the star formation rate atwas approximately six timeslessthan at. This declining comoving star formation rate[atatfor a Salpeter initial mass function (IMF)] poses an interesting challenge for models which suggest thatstar-forming galaxies atreionized the Universe. The short-fall in ionizing photons might be alleviated by galaxies fainter than our limit, or a radically different IMF. Alternatively, the bulk of reionization might have occurred at. [ABSTRACT FROM AUTHOR]

Damped Lyman α systems (DLAs), with , observed in the spectra of quasars have allowed us to quantify the chemical content of the Universe over cosmological scales. Such studies can be extended to lower column densities, in the sub-DLA range , which are systems believed to contain a large fraction of the neutral hydrogen at . In this paper, we use a homogeneous sample of sub-DLAs from the European Southern Oberservatory (ESO) Ultraviolet–Visual Echelle Spectrograph (UVES) archives presented in Paper I, to determine observationally for the first time the shape of the column density distribution, f( N), down to . The results are in good agreement with the predictions from Péroux et al. We also present the kinematic and clustering properties of this survey of sub-DLAs, which appear to be marginally different from the DLAs. We compare low- and high-ionization transition widths and find that the properties of the sub-DLAs span roughly the parameter space of DLAs. We also find hints of an increase of metallicity in systems with larger velocity widths in the metal lines, although the statistical significance of this result is low. Then we analyse the chemical content of this sample in conjunction with a compilation of abundances from 72 DLAs taken from the literature. As previously reported, the individual metallicities traced by [Fe/H] of these systems evolve mildly with redshift. Moreover, we analyse the H i column-density-weighted mean abundance, which is believed to be an indicator of the metallicity of the Universe. Although the number statistics is limited in the current sample, the results suggest a slightly stronger evolution of this quantity in the sub-DLA range. The effect is predominant at and most of the evolution observed lies in this redshift range. Observational arguments support the hypothesis that the evolution we probe in the sub-DLA range is not due to their lower dust content. Therefore, these systems might be associated with a different class of objects, which better trace the overall chemical evolution of the Universe. Finally, we present abundance ratios of [Si/Fe], [O/Fe], [C/Fe] and [Al/Fe] for sub-DLAs in conjunction with DLA measurements from the literature. The elemental ratios in sub-DLAs are comparable with those from DLAs. It is difficult to decipher whether the observed values are the effect of nucleosynthesis or are due to differential dust depletion. The metallicities are compared with two different sets of models of galaxy evolution in order to provide constraints on the morphology of quasar absorbers. [ABSTRACT FROM AUTHOR]

We determine the space density of UV-luminous starburst galaxies at z ≈ 6 using deep HST ACS SDSS-i' (F775W) and SDSS-z' (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i' - z') > 1.5 to a depth of z'[sub AB] = 25.6 (an 8σ detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ≈15 h[sup -2, sub 70] M⊙ yr[sup -1] at z = 5.9, equivalent to L[sup *] for the Lymanbreak population at z = 3-4 (Ω[sub Λ] = 0.7, Ω[sub M] = 0.3). We are sensitive to star-forming galaxies at 5.6 ... z ... 7.0 with an effective comoving volume of ≈1.8 × 10[sup 5] h[sup -3, sub 70] Mpc³ after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L[sup *] galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 ± 2.7) × 10[sup -4] h[sub 70] M⊙ yr[sup -1] Mpc[sup -3] at z ∼ 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z ∼ 6 the star formation density at the bright end is a factor of ∼6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z = 3-4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred. [ABSTRACT FROM AUTHOR]

ABSTRACT We present results of the first systematic search for submillimetre (submm) continuum emission from z∼ 2 , radio-quiet, optically-luminous (M[sub B] < -27.5) quasars, using the SCUBA array camera on the James Clerk Maxwell Telescope (JCMT). We have observed a homogeneous sample of 57 quasars in the redshift range 1.5 < z < 3.0 – the epoch during which the comoving density of luminous active galactic nuclei (AGN) peaks – to make a systematic comparison with an equivalent sample at high redshift ( z > 4 ; Paper I). The target sensitivity of the survey, 3σ= 10 mJy at 850 μm, was chosen to enable efficient identification of bright submm sources, suitable for detailed follow-up. Nine targets are detected with 3σ significance or greater, with fluxes in the range 7–17 mJy. Although the detection rate above 10 mJy is lower than that of the z > 4 survey, the weighted mean flux of the undetected sources, 1.9 ± 0.4 mJy , is similar to that at z > 4 (2.0 ± 0.6 mJy) . The statistical significance of trends is analysed, and it is found that: (i) within the limited optical luminosity range studied, there is no strong evidence for a correlation between submm and optical luminosity; (ii) there is a suggestion of a variation of submm detectability with redshift, but that this is consistent with the K-correction of a characteristic far-infrared spectrum. [ABSTRACT FROM AUTHOR]

Abstract We present 7–180 μm photometry of a sample of hyperluminous infrared galaxies (HyLIGs) obtained with the photometer and camera mounted on the Infrared Space Observatory. We have used radiative transfer models of obscured starbursts and dusty torii to model their spectral energy distributions (SEDs). We find that IRAS F00235+1024, IRAS F14218+3845 and IRAS F15307+3252 require a combination of starburst and active galactic nuclei (AGN) components to explain their mid- to far-infrared (FIR) emission, while for TXS 0052+471 a dust torus AGN model alone is sufficient. For IRAS F00235+1024 and IRAS F14218+3845 the starburst component is the predominant contributor, whereas for IRAS F15307+3252 the dust torus component dominates. The implied star formation rates (SFRs) for these three sources estimated from their infrared luminosities are yr[sup -1]h[sub 50][sup -2] and are amongst the highest SFRs estimated to date. We also demonstrate that the well-known radio–FIR correlation extends into both higher radio and infrared power than previously investigated. The relation for HyLIGs has a mean q value of 1.94. The results of this study imply that better sampling of the infrared spectral energy distributions of HyLIGs may reveal that both AGN and starburst components are required to explain all the emission from the near-infrared to the submillimetre. [ABSTRACT FROM AUTHOR]

We present the first detection of a gravitational depletion signal at near-infrared wavelengths, based on deep panoramic images of the cluster Abell 2219 (z=0.22) taken with the Cambridge Infrared Survey Instrument (CIRSI) at the prime focus of the 4.2-m William Herschel Telescope. Infrared studies of gravitational depletion offer a number of advantages over similar techniques applied at optical wavelengths, and can provide reliable total masses for intermediate-redshift clusters. Using the maximum-likelihood technique developed by Schneider, King & Erben, we detect the gravitational depletion at the 3σ confidence level. By modelling the mass distribution as a singular isothermal sphere and ignoring the uncertainty in the unlensed number counts, we find an Einstein radius of [equation] (66 per cent confidence limit). This corresponds to a projected velocity dispersion of σ[sub v]∼800 km s[sup -1], in agreement with constraints from strongly lensed features. For a Navarro, Frenk & White mass model, the radial dependence observed indicates a best-fitting halo scalelength of 125h[sup -1] kpc. We investigate the uncertainties arising from the observed fluctuations in the unlensed number counts, and show that clustering is the dominant source of error. We extend the maximum-likelihood method to include the effect of incompleteness, and discuss the prospects of further systematic studies of lensing in the near-infrared band. [ABSTRACT FROM AUTHOR]

We present sensitive 850-μm SCUBA photometry of a statistically complete sample of six of the most luminous (MB<−27.5; νL(1450 Å)≳1013 L⊙), z>4 radio-quiet quasars, reaching noise levels (1σ∼1.5 mJy) comparable with the deep blank sky surveys. These observations probe the rest-frame far-infrared region (∼150 μm), at luminosity levels for thermal sources comparable with those that IRAS permitted for low redshift quasars. One quasar (BR2237-0607; z=4.55) is detected at 850 μm with a flux of 5.0±1.1 mJy (4.5σ), whilst a second (BR0019-1522; z=4.52) has a detection at the 2σ level. When combined with our previous millimetre measurements of z>4 quasars, we find that there is a large range (5–10) in far-infrared (FIR) luminosity (LFIR) at fixed UV luminosity, and that the typical quasar has a LFIR and mass of cool (50 K) dust similar to that of the archetyepal low redshift (z=0.018) ultraluminous IRAS galaxy (ULIRG) Arp220 [LFIR∼5×1012 L⊙; Md(cool)∼108 M⊙]. If one assumes a fiducial FIR luminosity of 5×1012 L⊙ for for all quasars with MB<- 23, we find that ≳15 per cent of the sources in the SCUBA deep surveys could be classical broad-lined radio-quiet active galactic nuclei (AGN). Thus if one considers the observed ratio of Seyfert II to Seyfert I galaxies at low redshift and any contribution from totally optically obscured AGN, a significant fraction of the SCUBA source population will harbour AGN and hence the inferred star formation rates from submm fluxes may be overestimated if the active nuclei are bolometrically dominant or the initial mass function (IMF) is top heavy. [ABSTRACT FROM AUTHOR]

Describes the selection of candidate radio-loud quasars obtained by cross matching positions from the low-frequency 7C survey. Emergence of fast plate-measuring machines; Use of the Cambridge Low Frequency Synthesis Telescope; Causes of incompleteness in the resulting sample of radio quasars.

We report on submillimetre (submm) observations of three high-redshift quasars made using the SCUBA camera on the James Clerk Maxwell Telescope (JCMT). Only one of the sample was detected (>10σ significance) at 850 . It was also detected at significance), one of the few quasars at for which this has been the case. In combination with existing millimetric data, the 850- and 450-μm detections allow us to place limits on the temperature of the submm-emitting dust. The dust temperature is of no trivial importance given the high redshift of the source, since a cold temperature would signify a large mass of dust to be synthesized in the little time available (as an extreme upper limit in only 0.9 Gyr since ). We find, however, that the combined millimetre and submm data for the source cannot simply be characterized using the single-temperature greybody fit that has been used at lower redshifts. We discuss the results of the observing and modelling, and speculate as to the origin of the deviations. [ABSTRACT FROM AUTHOR]

Presents submillimeter (submm) continuum observations of a sample of some of the highest redshift quasars currently known, made with the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. Consistency of the submm spectral indices measured for two the sources with thermal reradiation from dust, rather from synchrotron emission; Sensitive upper limits; Galaxy extinction and dust.

We report the discovery of a luminous z = 5.78 star-forming galaxy in the Chandra Deep Field South. This galaxy was selected as an 'i-drop' from the GOODS public survey imaging with the Hubble Space Telescope/Advanced Camera for Surveys (object 3 in the work of Stanway, Bunker & McMahon 2003). The large colour of (I' - z')[SUBAB] = 1.6 indicated a spectral break consistent with the Lyman a forest absorption shortward of Lyman a at z &ap; 6. The galaxy is very compact (marginally resolved with ACS with a half-light radius of 0.08 arcsec, so r[SUBhl] < 0.5 h[SUP-1,SUB70] kpc). We have obtained a deep (5.5 h) spectrum of this z'[SUBAB] = 24.7 galaxy with the DEIMOS optical spectrograph on the Keck Telescope, and here we report the discovery of a single emission line centred on 8245 Å detected at 20σ with a flux of f &ap; 2 × 10[SUP-17] erg cm[SUP-2]s[SUP-1]. The line is clearly resolved with detectable structure at our resolution of better than 55 km s[SUP-1], and the only plausible interpretation consistent with the ACS photometry is that we are seeing Lyman a emission from a z = 5.78 galaxy. This is the highest redshift galaxy to be discovered and studied using HST data. The velocity width (Δν[SUBFWHM] = 260 km s[SUP-1]) and rest-frame equivalent width (W[SUPLyα,SUBrest] = 20 Å) indicate that this line is most probably powered by star formation, as an AGN would typically have larger values. The starburst interpretation is supported by our non-detection of the high-ionization N v λ 1240-Å emission line, and the absence of this source from the deep Chandra X-ray images. The star formation rate inferred from the rest-frame UV continuum is 34 h[SUP-2,SUB70] M[SUB&Odot; yr[SUP-1] (Ω[SUBM] = 0.3, Ω[SUB∇] = 0.7). This is the most luminous starburst known at z > 5. Our spectroscopic redshift for this object confirms the validity of the I' -drop technique of Stanway et al. to select star-forming... [ABSTRACT FROM AUTHOR]

We combine photometric observations of high-redshift (z > 4) quasars, obtained at submillimetre to millimetre wavelengths, to obtain a mean far-infrared (rest-frame) spectral energy distribution (SED) of the thermal emission from dust, parametrized by a single temperature (T) and power-law emissivity index (β). The best-fitting values are T = 41 ± 5 K and β = 1.95 ± 0.3. Our method exploits the redshift spread of this set of quasars, which allows us to sample the SED at a larger number of rest wavelengths than is possible for a single object: the wavelength range extends down to ∼60 ±m, and therefore samples the turnover in the greybody curve for these temperatures. This parametrization is of use to any studies that extrapolate from a flux at a single wavelength, for example to infer dust masses and far-infrared luminosities. We interpret the cool, submillimetre component as arising from dust heated by star formation in the host galaxy of the quasar, although we do not exclude the presence of dust heated directly by the active galactic nucleus (AGN). Applying the mean SED to the data, we derive consistent star formation rates ∼1000 M⊙ yr[sup -1] and dust masses ∼10[sup 9]M˙, and investigate a simple scheme of AGN and host galaxy co-evolution to account for these quantities. The time-scale for formation of the host galaxy is 0.5-1 Gyr, and the luminous quasar phase occurs towards the end of this period, just before the reservoir of cold gas is depleted. Given the youth of the Universe at z = 4 (1.6 Gyr), the coexistence of a massive black hole and a luminous starburst at high redshifts is a powerful constraint on models of quasar host galaxy formation. [ABSTRACT FROM AUTHOR]