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Ivison R.J.,Astronomy Technology Center | Ivison R.J.,University of Edinburgh | Papadopoulos P.P.,Argelander Institute For Astronomie | Smail I.,Durham University | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We report the results of a pilot study with the Expanded Very Large Array (EVLA) of 12CO J= 1-0 emission from four submillimetre-selected galaxies at z= 2.2-2.5, each with an existing detection of 12CO J= 3-2, one of which comprises two distinct spatial components. Using the EVLA's most compact configuration, we detect strong, broad [medians: 990kms-1 full width at zero intensity; 540kms-1 full width at half-maximum (FWHM)]J= 1-0 line emission from all of our targets - coincident in position and velocity with their J= 3-2 emission. The median linewidth ratio, σ1-0/σ3-2= 1.15 ± 0.06, suggests that the J= 1-0 is more spatially extended than the J= 3-2 emission, a situation confirmed by our maps which reveal velocity structure in several cases and typical sizes of ∼16kpc FWHM. The median brightness temperature (Tb) ratio is r3-2/1-0= 0.55 ± 0.05, consistent with local galaxies with LIR > 1011L⊙, noting that our value may be biased high because of the J= 3-2 based sample selection. Naively, this suggests gas masses roughly two times higher than estimates made using higher J transitions of CO, with the discrepancy due entirely to the difference in assumed Tb ratio. We also estimate molecular gas masses using the 12CO J= 1-0 line and the observed global Tb ratios, assuming standard underlying Tb ratios for the non-star-forming and star-forming gas phases as well as a limiting star formation efficiency for the latter in all systems, i.e. without calling upon XCO (≡α). Using this new method, we find a median molecular gas mass of (2.5 ± 0.8) × 1010M⊙, with a plausible range stretching up to three times higher. Even larger masses cannot be ruled out, but are not favoured by dynamical constraints: the median dynamical mass within R∼ 7kpc for our sample is (2.3 ± 1.4) × 1011M⊙ or ∼6 times more massive than UV-selected galaxies at this epoch. We examine the Schmidt-Kennicutt (S-K) relation for all the distant galaxy populations for which CO J= 1-0 or J= 2-1 data are available, finding small systematic differences between galaxy populations. These have previously been interpreted as evidence for different modes of star formation, but we argue that these differences are to be expected, given the still considerable uncertainties, certainly when considering the probable excitation biases due to the molecular lines used, and the possibility of sustained S-K offsets during the evolution of individual gas-rich systems. Finally, we discuss the morass of degeneracies surrounding molecular gas mass estimates, the possibilities for breaking them, and the future prospects for imaging and studying cold, quiescent molecular gas at high redshifts. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Sobral D.,Leiden University | Smail I.,Durham University | Best P.N.,Institute for Astronomy | Geach J.E.,McGill University | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

This paper presents new deep and wide narrow-band surveys undertaken with United Kingdom Infrared Telescope (UKIRT), Subaru and the Very Large Telescope (VLT), a unique combined effort to select large, robust samples of Hα star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyr) in a uniform manner over ~2 deg2 in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch Hα surveys reach a matched 3σ flux limit of ≈3M yr-1 out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow us to greatly overcome cosmic variance and assemble by far the largest samples of Hα emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Hα emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the Hα luminosity function and its evolution. The faint-end slope of the Hα luminosity function is found to be α = -1.60 ± 0.08 over z = 0-2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L * Hα, evolves significantly as log L * Hα(z) = 0.45z + log L * z=0. This is the first time Hα has been used to trace star formation activity with a single homogeneous survey at z = 0.4-2.23. Overall, the evolution seen with Hα is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as far-infrared and ultraviolet, jointly pointing towards the bulk of the evolution in the last 11 Gyr being driven by a statistically similar star-forming population across cosmic time, but with a strong luminosity increase from z ~ 0 to ~2.2. Our uniform analysis allows us to derive the Hα star formation history (SFRH) of the Universe, showing a clear rise up to z ~ 2.2, for which the simple parametrization log10ρSFR = -2.1(1 + z)-1 is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalization of the Hα SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Hα SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last ~11 Gyr is responsible for producing ~95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past ~11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Morrison G.E.,University of Hawaii at Manoa | Morrison G.E.,Canada France Hawaii Telescope Corporation | Owen F.N.,U.S. National Radio Astronomy Observatory | Dickinson M.,National Optical Astronomy Observatory | And 3 more authors.
Astrophysical Journal, Supplement Series | Year: 2010

We describe deep, new, wide-field radio continuum observations of the Great Observatories Origins Deep Survey-North field. The resulting map has a synthesized beam size of ∼1.7 and an rms noise level of ∼3.9 μJy beam -1 near its center and ∼8 μJy beam -1 at 15′ from phase center. We have cataloged 1230 discrete radio emitters, within a 40′ × 40′ region, above a 5σ detection threshold of ∼20 μJy at the field center. New techniques, pioneered by Owen & Morrison, have enabled us to achieve a dynamic range of 6800:1 in a field that has significantly strong confusing sources. We compare the 1.4 GHz (20 cm) source counts with those from other published radio surveys. Our differential counts are nearly Euclidean below 100 μJy with a median source diameter of ∼1.2. This adds to the evidence presented by Owen & Morrison that the natural confusion limit may lie near 1 μJy. If the Euclidean slope of the counts continues down to the natural confusion limit as an extrapolation of our log N-log S, this indicates that the cutoff must be fairly sharp below 1 μJy else the cosmic microwave background temperature would increase above 2.7 K at 1.4 GHz. © 2010. The American Astronomical Society. All rights reserved.

Thi W.-F.,University of Edinburgh | Woitke P.,Astronomy Technology Center | Kamp I.,NOVA Kapteyn Astronomical Institute
Monthly Notices of the Royal Astronomical Society | Year: 2010

The origin of Earth oceans is controversial. Earth could have acquired its water either from hydrated silicates (wet Earth scenario) or from comets (dry Earth scenario). [HDO]/[H2O] ratios are used to discriminate between the scenarios. High [HDO]/[H2O] ratios are found in Earth oceans. These high ratios are often attributed to the release of deuterium enriched cometary water ice, which was formed at low gas and dust temperatures. Observations do not show high [HDO]/[H2O] in interstellar ices. We investigate the possible formation of high [HDO]/[H2O] ratios in dense (nH > 106 cm-3) and warm gas (T= 100-1000 K) by gas-phase photochemistry in the absence of grain surface chemistry. We derive analytical solutions, taking into account the major neutral-neutral reactions for gases at T > 100 K. The chemical network is dominated by photodissociation and neutral-neutral reactions. Despite the high gas temperature, deuterium fractionation occurs because of the difference in activation energy between deuteration enrichment and the back reactions. The analytical solutions were confirmed by the time-dependent chemical results in a 10-3 M⊙ disc around a typical T Tauri star using the photochemical code ProDiMo. The ProDiMo code includes frequency-dependent 2D dust-continuum radiative transfer, detailed non-local thermodynamic equilibrium gas heating and cooling and hydrostatic calculation of the disc structure. Both analytical and time-dependent models predict high [HDO]/[H2O] ratios in the terrestrial planet-forming region (<3 au) of circumstellar discs. Therefore, the [HDO]/[H2O] ratio may not be an unique criterion to discriminate between the different origins of water on the Earth. © 2009 The Authors. Journal compilation © 2009 RAS.

Kamp I.,NOVA Kapteyn Astronomical Institute | Tilling I.,Astronomy Technology Center | Woitke P.,Astronomy Technology Center | Thi W.-F.,Institute for Astronomy | Hogerheijde M.,Leiden University
Astronomy and Astrophysics | Year: 2010

Aims. In this paper, we explore the diagnostic power of the far-IR fine-structure lines of [Oi] 63.2 μm, 145.5 μm, [Cii] 157.7 μm, as well as the radio and sub-mm lines of CO J=1-0, 2{-}1 and 3{-}2 in application to disks around Herbig Ae stars. We aim at understanding where the lines originate from, how the line formation process is affected by density, temperature and chemical abundance in the disk, and to what extent non-LTE effects are important. The ultimate aim is to provide a robust way to determine the gas mass of protoplanetary disks from line observations. Methods. We use the recently developed disk code ProDiMo to calculate the physico-chemical structure of protoplanetary disks and apply the Monte-Carlo line radiative transfer code Ratran to predict observable line profiles and fluxes. We consider a series of Herbig Ae type disk models ranging from 10-6 Ṁ to 2.2 × 10-2 Ṁ (between 0.5 and 700 AU) to discuss the dependency of the line fluxes and ratios on disk mass for otherwise fixed disk parameters. This paper prepares for a more thorough multi-parameter analysis related to the Herschel open time key program Gasps. Results. We find the [Cii] 157.7 μm line to originate in LTE from the surface layers of the disk, where. The total emission is dominated by surface area and hence depends strongly on disk outer radius. The [Oi] lines can be very bright (>10 -16 W/m-2) and form in slightly deeper and closer regions under non-LTE conditions. For low-mass models, the [Oi] lines come preferentially from the central regions of the disk, and the peak separation widens. The high-excitation [Oi] 145.5 μm line, which has a larger critical density, decreases more rapidly with disk mass than the 63.2 μm line. Therefore, the [Oi] 63.2 μm/145.5 μm ratio is a promising disk mass indicator, especially as it is independent of disk outer radius for R rm out}>200 AU. CO is abundant only in deeper layers AV ga 0.05. For too low disk masses (Mrm disk}\!\la\!10 -4Ṁ) the dust starts to become transparent, and CO is almost completely photo-dissociated. For masses larger than that the lines are an excellent independent tracer of disk outer radius and can break the outer radius degeneracy in the [Oi] 63.2 μm/[C ii]157.7 μm line ratio. Conclusions. The far-IR fine-structure lines of [Cii] and [Oi] observable with Herschel provide a promising tool to measure the disk gas mass, although they are mainly generated in the atomic surface layers. In spatially unresolved observations, none of these lines carry much information about the inner, possibly hot regions <30 AU. © ESO, 2010.

Born A.J.,Astronomy Technology Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

This paper considers the development and progression of the VISTA telescope, from conception to the point where it is now being operated by the scientific community (end user). It analyses and evaluates the value of effective project management and systems engineering practices with practical examples. The practical application of systems engineering is addressed throughout the requirement capture and management, design, manufacture, assembly, and installation, integration, verification and acceptance phases, highlighting the value gained by appropriate application of step-by-step procedures and tools. The special emphasis given to the importance of effective systems engineering during on-site installation, verification and validation will be illustrated. Project management aspects are covered from tendering and procurement through contractor management processes to final integration and commissioning, with great emphasis placed on the importance of a "win-win" approach and the benefits of effective, constructive customer/contractor liaison. Consideration is given to the details and practicalities of day-to-day site management, safety, housekeeping, and the management and support of site personnel and services. Recommendations are made to improve the effectiveness of UK ATC system engineering and project management so that future projects can benefit from the lessons learned on VISTA. © 2010 Copyright SPIE - The International Society for Optical Engineering.

Dunlop J.S.,University of Edinburgh | Mclure R.J.,University of Edinburgh | Robertson B.E.,California Institute of Technology | Ellis R.S.,California Institute of Technology | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

Following the discovery of the first significant samples of galaxies at z > 6.5 with Wide Field Camera 3/Infra-Red (WFC3/IR) on board Hubble Space Telescope (HST), it has been claimed that the faintest high-redshift galaxies display extremely blue ultraviolet (UV) continuum slopes, with a UV power-law index β≃-3 (where f λ∝λ β). Such slopes are bluer than previously reported for any other galaxy population, and are most readily explained theoretically by extinction-free, young and very low metallicity stellar populations with a high ionizing photon escape fraction. Here we undertake a critical study of the evidence for such extreme values of β, combining three new WFC3/IR-selected samples of galaxies spanning nearly two decades in UV luminosity over the redshift range z≃ 4.5-8. We explore the impact of inclusion/exclusion of less robust high-redshift candidates and use the varying depths of the samples to explore the effects of noise and selection bias at a given UV luminosity. Simple data-consistency arguments suggest that artificially blue average values of β can result when the analysis is extended into the deepest ≃0.5 mag bin of these WFC3/IR-selected galaxy samples, regardless of the actual luminosity or redshift range probed. By confining attention to robust high-redshift galaxy candidates, with at least one 8σ detection in the WFC3/IR imaging, we find that the average value of β is consistent with 〈β〉=-2.05 ± 0.10 over the redshift range z= 5-7 and the UV absolute magnitude range -22 < M UV, AB < - 18, and that 〈β〉 shows no significant trend with either redshift or M UV. We create and analyse a set of simple end-to-end simulations based on the WFC3/IR+ACS Hubble Ultra Deep Field (HUDF) and Early Release Science data sets which demonstrate that a bias towards artificially low/blue average values of β is indeed 'expected' when the UV slope analysis is extended towards the source detection threshold, and conclude that there is as yet no clear evidence for UV slopes significantly bluer than β≃-2, the typical value displayed by the bluest star-forming galaxies at more modest redshifts. A robust measurement of 〈β〉 for the faintest galaxies at z≃ 7 (and indeed z≃ 8) remains a key observational goal, as it provides a fundamental test for high escape fractions from a potentially abundant source of re-ionizing photons. This goal is achievable with HST, but requires still deeper WFC3/IR imaging in the HUDF. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Wells M.,Astronomy Technology Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2016

Twinkle is a small satellite mission to observe the atmospheres of exoplanets in the visible to near infrared. This paper describes the design of the infrared (1.3 to 4.5 micron) spectrometer which works at the diffraction limit of the 450mm diameter telescope and at a resolving power of 300 (1.3-2.4 microns) and, in order to achieve the required SNR, R=30 for 2.4-4.5 microns. The planetary spectrum is obtained by taking differences between the spectra of star + planet at different phases of the planet's orbit so there is an emphasis of spectral and radiometric stability. The design incorporates a number of features to enhance this stability - compact all aluminium structure and mirror substrates to reduce alignment offsets when cooled to the operating temperature of ∼100K - pupil imaging in the across dispersion direction to minimise changes due to sub-pixel variations in sensitivity and reduce the number of illuminated pixels for background measurements. © 2016 SPIE.

Cullen F.,University of Edinburgh | Cirasuolo M.,University of Edinburgh | Cirasuolo M.,Astronomy Technology Center | McLure R.J.,University of Edinburgh | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present new accurate measurements of the mass, metallicity and star-formation rate of a statistically significant sample of 93 galaxies at z ≳ 2 using near-infrared spectroscopy taken as part of the 3D-Hubble Space Telescope survey.We derive a mass-metallicity relation (MZR) for our sample with metallicities based on the oxygen and Hβ nebular emission lines. We find the MZR derived from our data to have the same trend as previous determinations in the range 0 < z < 3 with metallicity decreasing with stellar mass. However, we find that our MZR is offset from a previous determination at z ≳ 2 which used metallicities derived from the [NII]/Hα ratio. Incorporating star formation rate information, we find that our galaxies are also offset from the fundamental metallicity relation (FMR) by ~0.3 dex. Using the Baldwin- Phillips-Terlevich (BPT) diagram we argue that, if the physical conditions of star-forming regions evolve with redshift, metallicity indicators based on [N II] and Hα, calibrated in the local Universe, may not be consistent with the ones based on oxygen lines and Hβ. Our results thus suggest that the evolution of the FMR previously reported at z ~ 2-3 may be an artefact of the differential evolution in metallicity indicators and caution against using locally calibrated empirical metallicity relations at high redshift, which do not account for evolution in the physical conditions of star-forming regions. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Varricatt W.P.,Joint Astronomy Center | Davis C.J.,Joint Astronomy Center | Ramsay S.,European Southern Observatory | Todd S.P.,Astronomy Technology Center
Monthly Notices of the Royal Astronomical Society | Year: 2010

We have carried out a near-infrared imaging survey of luminous young stellar outflow candidates using the United Kingdom Infrared Telescope. Observations were obtained through the broad-band K (2.2 μm) and narrow-band filters at the wavelengths of H2 v = 1-0 S(1) (2.1218 μm) and Brγ (2.166 μm) lines. 50 regions were imaged with a field of view of 2.2 × 2.2 arcmin2. Several young embedded clusters are unveiled in our near-infrared images. 76 per cent of the objects exhibit H2 emission and 50 per cent or more of the objects exhibit aligned H2 emission features suggesting collimated outflows, many of which are new detections. These observations suggest that disc accretion is probably the leading mechanism in the formation of stars, at least up to late O spectral types. The young stellar objects (YSOs) responsible for many of these outflows are positively identified in our images based on their locations with respect to the outflow lobes, Two-Micron All-Sky Survey colours and association with Midcourse Space Experiment, Infrared Astronomical Satellite, millimetre and radio sources. The close association of molecular outflows detected in CO with the H2 emission features produced by shock excitation by jets from the YSOs suggests that the outflows from these objects are jet-driven. Towards strong radio emitting sources, H2 jets were either not detected or were weak when detected, implying that most of the accretion happens in the pre-ultracompact (pre-UC) H ii phase; accretion and outflows are probably weak when the YSO has advanced to its UC H ii stage. © 2010 The Authors. Journal compilation © 2010 RAS.

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