Naylor, David

Permanent URI for this collection

https://opus.uleth.ca/handle/10133/3634

Browse

Browsing Naylor, David by Title

Now showing 1 - 11 of 11
  • Thumbnail Image
    Item
    Calibration of Herschel SPIRE FTS observations at different spectral resolutions
    (Oxford University Press, 2017) Marchili, N.; Hopwood, R.; Fulton, T.; Polehampton, E. T.; Valtchanov, I.; Zaretski, J.; Naylor, David A.; Griffin, M. J.; Imhof, P.; Lim, T.; Lu, N.; Makiwa, G.; Pearson, C.; Spencer, Locke Dean
    The SPIRE Fourier Transform Spectrometer on-board the Herschel Space Observatory had two standard spectral resolution modes for science observations: high resolution (HR) and low resolution (LR), which could also be performed in sequence (H+LR). A comparison of the HR and LR resolution spectra taken in this sequential mode revealed a systematic discrepancy in the continuum level. Analysing the data at different stages during standard pipeline processing demonstrates that the telescope and instrument emission affect HR and H+LR observations in a systematically different way. The origin of this difference is found to lie in the variation of both the telescope and instrument response functions, while it is triggered by fast variation of the instrument temperatures. As it is not possible to trace the evolution of the response functions using housekeeping data from the instrument subsystems, the calibration cannot be corrected analytically. Therefore, an empirical correction for LR spectra has been developed, which removes the systematic noise introduced by the variation of the response functions.
  • Thumbnail Image
    Item
    Calibration of the Herschel SPIRE Fourier Transform Spectrometer
    (Oxford University Press, 2014) Swinyard, B. M.; Polehampton, E. T.; Hopwood, R.; Valtchanov, I.; Lu, N.; Fulton, T.; Benielli, D.; Imhof, P.; Marchili, N.; Baluteau, J.-P.; Bendo, G. J.; Ferlet, M.; Griffin, M. J.; Lim, T. L.; Makiwa, G.; Naylor, David A.; Orton, G. S.; Papageorgiou, A.; Pearson, C. P.; Schulz, B.; Sidher, S. D.; Spencer, Locke Dean; van der Wiel, M. H. D.; Wu, R.
    The Herschel Spectral and Photometric REceiver (SPIRE) instrument consists of an imaging photometric camera and an imaging Fourier Transform Spectrometer (FTS), both operating over a frequency range of∼450–1550GHz. In this paper, we briefly review the FTS design, operation, and data reduction, and describe in detail the approach taken to relative calibration (removal of instrument signatures) and absolute calibration against standard astronomical sources. The calibration scheme assumes a spatially extended source and uses the Herschel telescopeasprimarycalibrator.Conversionfromextendedtopoint-sourcecalibrationiscarried out using observations of the planet Uranus. The model of the telescope emission is shown to beaccuratetowithin6percent andrepeatable tobetterthan0.06percent and,bycomparison with models of Mars and Neptune, the Uranus model is shown to be accurate to within 3 per cent. Multiple observations of a number of point-like sources show that the repeatability of the calibration is better than 1 per cent, if the effects of the satellite absolute pointing error (APE) are corrected. The satellite APE leads to a decrement in the derived flux, which can be up to∼10 per cent (1 σ) at the high-frequency end of the SPIRE range in the first part of the mission, and∼4 per cent after Herschel operational day 1011. The lower frequency range of the SPIRE band is unaffected by this pointing error due to the larger beam size. Overall, for well-pointed, point-like sources, the absolute flux calibration is better than 6 per cent, and for extended sources where mapping is required it is better than 7 per cent.
  • Thumbnail Image
    Item
    Correcting the extended-source calibration for the Herschel SPIRE Fourier-transform spectrometer
    (Oxford University Press, 2017) Valtchanov, I.; Hopwood, R.; Bendo, G.; Benson, Christopher S.; Conversi, L.; Fulton, T.; Griffin, M. J.; Joubaud, T.; Lim, T.; Lu, N.; Marchili, N.; Makiwa, G.; Meyer, R. A.; Naylor, David A.; North, C.; Papageorgiou, A.; Pearson, C.; Polehampton, E. T.; Scott, Jeremy P.; Schulz, B.; Spencer, Locke Dean; van der Wiel, M. H. D.; Wu, R.
    We describe an update to the Herschel-Spectral and Photometric Imaging Receiver (SPIRE) Fourier-transform spectrometer (FTS) calibration for extended sources, which incorporates a correction for the frequency-dependent far-field feedhorn efficiency, ηff. This significant correction affects all FTS extended-source calibrated spectra in sparse or mapping mode, regardless of the spectral resolution. Line fluxes and continuum levels are underestimated by factors of 1.3–2 in the spectrometer long wavelength band (447–1018 GHz; 671–294 µm) and 1.4–1.5 in the spectrometer short wavelength band (944–1568 GHz; 318–191 µm). The correctionwasimplementedintheFTSpipelineversion14.1andhasalsobeendescribedinthe SPIRE Handbook since 2017 February. Studies based on extended-source calibrated spectra produced prior to this pipeline version should be critically reconsidered using the current products available in the Herschel Science Archive. Once the extended-source calibrated spectra are corrected for ηff, the synthetic photometry and the broad-band intensities from SPIRE photometer maps agree within 2–4percent – similar levels to the comparison of point-source calibrated spectra and photometry from point-source calibrated maps. The two calibration schemes for the FTS are now self-consistent: the conversion between the corrected extended-source and point-source calibrated spectra can be achieved with the beam solid angle and a gain correction that accounts for the diffraction loss.
  • Thumbnail Image
    Item
    The data processing pipeline for the Herschel SPIRE Fourier Transform Spectrometer
    (Oxford University Press, 2016) Fulton, T.; Naylor, David A.; Polehampton, E. T.; Valtchanov, I.; Hopwood, R.; Lu, N.; Baluteau, J.-P.; Mainetti, G.; Pearson, C.; Papageorgiou, A.; Guest, S.; Zhang, L.; Imhof, P.; Swinyard, B. M.; Griffin, M. J.; Lim, T. L.
    We present the data processing pipeline to generate calibrated data products from the Spectral and Photometric Imaging Receiver (SPIRE) imaging Fourier Transform Spectrometer on the Herschel Space Observatory. The pipeline processes telemetry from SPIRE observations and produces calibrated spectra for all resolution modes. The spectrometer pipeline shares some elements with the SPIRE photometer pipeline, including the conversion of telemetry packets into data timelines and calculation of bolometer voltages. We present the following fundamental processing steps unique to the spectrometer: temporal and spatial interpolation of the scan mechanism and detector data to create interferograms; Fourier transformation; apodization; and creation of a data cube. We also describe the corrections for various instrumental effects including first- and second-level glitch identification and removal, correction of the effects due to emission from the Herschel telescope and from within the spectrometer instrument, interferogram baseline correction, temporal and spatial phase correction, non-linear response of the bolometers, and variation of instrument performance across the focal plane arrays. Astronomical calibration is based on combinations of observations of standard astronomical sources and regions of space known to contain minimal emission.
  • Thumbnail Image
    Item
    Far-infrared/submillimetre properties of pre-stellar cores L1521E, L1521F and L1689B as revealed by the Herschel SPIRE instrument - I. Central positions
    (Oxford University Press, 2016) Makiwa, G.; Naylor, David A.; van der Wiel, M. H. D.; Ward-Thompson, D.; Kirk, J. M.; Eyres, S.; Abergel, A.; Köhler, M.
    Dust grains play a key role in the physics of star-forming regions, even though they constitute only ∼1 per cent of the mass of the interstellar medium. The derivation of accurate dust parameters such as temperature (Td), emissivity spectral index (β) and column density requires broad-band continuum observations at far-infrared wavelengths. We present Herschel-Spectral and Photometric Imaging Receiver Array (SPIRE) Fourier Transform Spectrometer (FTS) measurements of three starless cores: L1521E, L1521F and L1689B, covering wavelengths between 194 and 671 µm. This paper is the first to use our recently updated SPIRE-FTS intensity calibration, yielding a direct match with SPIRE photometer measurements of extended sources. In addition, we carefully assess the validity of calibration schemes depending on-source extent and on the strength of background emission. The broad-band far-infrared spectra for all three sources peak near 250 µm. Our observations therefore provide much tighter constraints on the spectral energy distribution (SED) shape than measurements that do not probe the SED peak. The spectra are fitted using modified blackbody functions, allowing both Td and β to vary as free parameters.This yields Td of9.8±0.2,15.6±0.5and10.9±0.2K and corresponding β of 2.6∓0.9, 0.8∓0.1 and 2.4∓0.8 for L1521E, L1521F and L1689B, respectively.Thederivedcoremassesare1.0±0.1,0.10±0.01and0.49±0.05M ,respectively. The core mass/Jeans mass ratios for L1521E and L1689B exceed unity indicating that they are unstable to gravitational collapse, and thus pre-stellar cores. By comparison, the elevated temperature and gravitational stability of L1521F support previous arguments that this source is more evolved and likely a protostar.
  • Thumbnail Image
    Item
    Physical structure of the photodissociation regions in NGC 7023: observations of gas and dust emission with Herschel*
    (EDP Sciences, 2014) Kohler, M.; Habart, E.; Arab, H.; Bernard-Salas, J.; Ayasso, H.; Abergel, A.; Zavagno, A.; Polehampton, E.; van der Wiel, M.H.D.; Naylor, David A.; Makiwa, Gibion; Dassas, K.; Joblin, C.; Pilleri, P.; Berne, O.; Fuente, A.; Gerin, M.; Goicoechea, J.R.; Teyssier, D.
    Context. The determination of the physical conditions in molecular clouds is a key step towards our understanding of their formation and evolution of associated star formation. We investigate the density, temperature, and column density of both dust and gas in the photodissociation regions (PDRs) located at the interface between the atomic and cold molecular gas of the NGC 7023 reflection nebula. We study how young stars a ect the gas and dust in their environment. Aims. Several Herschel Space Telescope programs provide a wealth of spatial and spectral information of dust and gas in the heart of PDRs. We focus our study on Spectral and Photometric Image Receiver (SPIRE) Fourier-Transform Spectrometer (FTS) fully sampled maps that allow us for the first time to study the bulk of cool/warm dust and warm molecular gas (CO) together. In particular, we investigate if these populations spatially coincide, if and how the medium is structured, and if strong density and temperature gradients occur, within the limits of the spatial resolution obtained with Herschel. Methods. The SPIRE FTS fully sampled maps at di erent wavelengths are analysed towards the northwest (NW) and the east (E) PDRs in NGC 7023. We study the spatial and spectral energy distribution of a wealth of intermediate rotational 12CO 4 Ju 13 and 13CO 5 Ju 10 lines. A radiative transfer code is used to assess the gas kinetic temperature, density, and column density at di erent positions in the cloud. The dust continuum emission including Spitzer, the Photoconductor Array Camera and Spectrometer (PACS), and SPIRE photometric and the Institute for Radio Astronomy in the Millimeter Range (IRAM) telescope data is also analysed. Using a single modified black body and a radiative transfer model, we derive the dust temperature, density, and column density. Results. The cloud is highly inhomogeneous, containing several irradiated dense structures. Excited 12CO and 13CO lines and warm dust grains localised at the edge of the dense structures reveal high column densities of warm/cool dense matter. Both tracers give a good agreement in the local density, column density, and physical extent, leading to the conclusion that they trace the same regions. The derived density profiles show a steep gradient at the cloud edge reaching a maximum gas density of 10^5 -10^6 cm^-3 in the PDR NGC 7023 NW and 10^4 -10^5 cm^-3 in the PDR NGC 7023 E and a subsequent decrease inside the cloud. Close to the PDR edges, the dust temperature (30 K and 20 K for the NW and E PDRs, respectively) is lower than the gas temperature derived from CO lines (65-130 K and 45-55 K, respectively). Further inside the cloud, the dust and gas temperatures are similar. The derived thermal pressure is about 10 times higher in NGC 7023NWthan in NGC 7023 E. Comparing the physical conditions to the positions of known young stellar object candidates in NGC 7023 NW, we find that protostars seem to be spatially correlated with the dense structures. Conclusions. Our approach combining both dust and gas delivers strong constraints on the physical conditions of the PDRs. We find dense and warm molecular gas of high column density in the PDRs.
  • Thumbnail Image
    Item
    Signatures of warm carbon monoxide in protoplanetary discs observed with Herschel SPIRE
    (Oxford University Press, 2014) van der Wiel, M. H. D.; Naylor, David A.; Kamp, I.; Ménard, F.; Thi, W.-F.; Woitke, P.; Olofsson, G.; Pontoppidan, K. M.; Di Francesco, J.; Glauser, A. M.; Greaves, J. S.; Ivison, R. J.
    Molecular gas constitutes the dominant mass component of protoplanetary discs. To date, these sources have not been studied comprehensively at the longest far-infrared and shortest submillimetre wavelengths. This paper presents Herschel SPIRE FTS spectroscopic observations towards 18 protoplanetary discs, covering the entire 450–1540GHz (666–195 μm) range at ν/ ν ≈ 400–1300. The spectra reveal clear detections of the dust continuum and, in six targets, a significant amount of spectral line emission primarily attributable to 12CO rotational lines. Other targets exhibit little to no detectable spectral lines. Low signal-to-noise detections also include signatures from 13CO, [CI] and HCN. For completeness, we present upper limits of non-detected lines in all targets, including low-energy transitions of H2O and CH+ molecules. The 10 12CO lines that fall within the SPIRE FTS bands trace energy levels of ∼50–500K. Combined with lower and higher energy lines from the literature, we compare the CO rotational line energy distribution with detailed physical–chemical models, for sources where these are available and published. Our 13CO line detections in the disc around Herbig Be star HD 100546 exceed, by factors of ∼10–30, the values predicted by a model that matches a wealth of other observational constraints, including the SPIRE 12COladder. To explain the observed 12CO/13COratio, it may be necessary to consider the combined effects of optical depth and isotope selective (photo)chemical processes. Considering the full sample of 18 objects, we find that the strongest line emission is observed in discs around Herbig Ae/Be stars, although not all show line emission. In addition, two of the six T Tauri objects exhibit detectable 12CO lines in the SPIRE range.
  • Thumbnail Image
    Item
    Spatial variation of the cooling lines in the Orion Bar from Hersehel/PACS
    (EDP Sciences, 2012) Bernard-Salas, J.; Habart, E.; Arab, H.; Abergel, A.; Dartois, E.; Martin, P.; Bontemps, S.; Joblin, C.; White, G. J.; Bernard, J.-P.; Naylor, David A.
    Context. The energetics in photo-dissociation regions (PDRs) are mainly regulated by the balance between the heating from the photo-electric effect acting on dust grains, and the cooling via the copious emission of photons in far-infrared lines. The Orion Bar is a luminous and nearby PDR, which presents to the observer an ideal edge-on orientation in which to study this energy balance. Spatially resolved studies of such a nearby system are essential as they enable us to characterise the physical processes that control the energetics of the regions and can serve as templates for distant systems where these processes cannot be disentangled. Aims. We characterise the emission of the far-infrared fine-structure lines of [Cii](158 μm),[Oi](63and145 μm),and[Nii](122 μm) that trace the gas local conditions, via spatially resolved observations of the Orion Bar. The observed distribution and variation of the lines are discussed in relation to the underlying geometry and linked to the energetics associated with the Trapezium stars. Methods. Herschel/PACS observations are used to map the spatial distribution of these fine-structure lines across the Bar, with a spatial resolution between 4 and 11 and covering a total square area of about 120 ×105 . The spatial profile of the emission lines are modelled using the radiative transfer code Cloudy. Results. TheHerschel observations reveal in unprecedented detail the morphology of the Bar.The spatial distribution of the [Cii] line coincides with that of the [Oi] lines. The [Nii] line peaks closer to the ionising star than the other three lines, but with a small region of overlap. We can distinguish several knots of enhanced emission within the Bar indicating the presence of an in homogenous and structured medium. The emission profiles cannot be reproduced by a single PDR, clearly indicating that, besides the Bar, there is a significant contribution from additional PDR(s)over the area studied. The combination of both the [Nii] and [Oi] 145 μm lines can be used to estimate the [Cii] emission and distinguish between it sionised or neutral origin. We have calculated how much[Cii] emission comes from the neutral and ionised region, and find that at least ∼82% originates from the photo-dissocciation region. Together, the [Cii] 158 μm and [Oi] 63 and 145 μm lines account for∼90% of the power emitted by the main cooling lines in the Bar (including CO, H2, etc.), with [Oi] 63μm alone accounting for 72% of the total.
  • Thumbnail Image
    Item
    Star formation relations and co spectral line energy distributions across the J-ladder and redshift
    (American Astronomical Society, 2014) Greve, T. R.; Leonidaki, I.; Xilouris, E.M.; Weiss, A.; Zhang, Z.-Y.; van der Werf, P.; Aalto, S.; Armus, L.; Diaz-Santos, T.; Evans, A.S.; Fischer, J.; Gao, Y.; Gonzalez-Alfonso, E.; Harris, A.; Henkel, C.; Mekjerink, R.; Naylor, David A.; Smith, H.A.; Spaans, M.; Stacey, G.J.; Veilleux, S.; Walter, F.
    We present FIR[50-300 um]-CO luminosity relations (i.e., log Lfir = a log L’co + B) for the full CO rotational ladder from J = 1 – 0 up to J = 13 -12 for a sample of 62 local (z <= 0.1) (Ultra) Luminous Infrared Galaxies (LIRGs; lIR[8-1000um > 10^11 Lo) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 (sub)-millimeter selected dusty star forming galaxies from the literature with robust CO observations, and sufficiently well-sampled FIR/sub-millimeter spectral energy distributions (SEDs) so that accurate FIR luminosities can be deduced. The addition of luminous starbursts at high redshifts enlarge the range of the FIR-CO luminosity relations towards the high-IR-luminosity end while also significantly increasing the small amount of mid-J/high-J CO line data (J = 5 – 4 and higher) that was available prior to Herschel. The new data-set (both in terms of IR luminosity and J-ladder) reveals linear FIR-CO luminosity relations (i.e., a ~= 1) for J = 1 – 0 up to J = 5 – 4, with a nearly constant normalization (B ~ 2). In the simplest physical scenario this is expected from the (also) linear FIR-(molecular line) relations recently found for the dense gas tracer lines (HCN and CS), as long as the dense gas mass fraction does not vary strongly within our (merger/starburst)-dominated sample. However from J = 6 – 5 and up to the J = 13 – 12 transition we find an increasingly sub-linear slope (~ 100K) and dense (> 104 cm-3) gas component whose thermal state is unlikely to be maintained by star formation powered far-UV radiation fields (and thus is no longer directly tied to the star formation rate). We suggest that mechanical heating (e.g., supernova driven turbulence and shocks), and not cosmic rays, is the most likely source of energy for this component. The global CO spectral line energy distributions (SLEDs), which remain highly excited from J = 6 – 5 up to J = 13 – 12, are found to be a generic feature of the (U)LIRGs in our sample, and further support of the presence of this gas component.
  • Thumbnail Image
    Item
    Systematic characterization of the Herschel SPIRE Fourier Transform Spectrometer
    (Oxford University Press, 2015) Hopwood, R.; Polehampton, E. T.; Valtchanov, I.; Swinyard, B. M.; Fulton, T.; Lu, N.; Marchili, N.; van der Wiel, M. H. D.; Benielli, D.; Imhof, P.; Baluteau, J.-P.; Pearson, C.; Clements, D. L.; Griffin, M. J.; Lim, T. L.; Makiwa, G.; Naylor, David A.; Noble, G.; Puga, E.; Spencer, Locke Dean
    A systematic programme of calibration observations was carried out to monitor the performance of the Spectral and Photometric Imaging REceiver (SPIRE) Fourier Transform Spectrometer (FTS) instrument on board the Herschel Space Observatory. Observations of planets (including the prime point-source calibrator, Uranus), asteroids, line sources, dark sky and cross-calibration sources were made in order to monitor repeatability and sensitivity, and to improve FTS calibration. We present a complete analysis of the full set of calibration observations and use them to assess the performance of the FTS. Particular care is taken to understand and separate out the effect of pointing uncertainties, including the position of the internal beam steering mirror for sparse observations in the early part of the mission. The repeatability of spectral-line centre positions is <5kms−1, for lines with signal-to-noise ratios>40, corresponding to <0.5–2.0 percent of a resolution element. For spectral-lineflux,the repeatability is better than 6percent, which improves to 1–2percent for spectra corrected for pointing offsets. The continuum repeatability is 4.4percent for the SPIRE Long Wavelength spectrometer (SLW) band and 13.6percent for the SPIRE Short Wavelength spectrometer (SSW) band, which reduces to ∼1percent once the data have been corrected for pointing offsets. Observations of dark sky were used to assess the sensitivity and the systematic offset in the continuum, both of which were found to be consistent across the FTS-detector arrays. Theaveragepoint-sourcecalibratedsensitivityforthecentredetectorsis0.20and0.21Jy[1σ; 1h],forSLWandSSW.Theaveragecontinuumoffsetis0.40JyfortheSLWbandand0.28Jy for the SSW band.
  • Thumbnail Image
    Item
    Three-dimensional distribution of hydrogen fluoride gas toward NGC 6334 I and I(N)
    (EDP Sciences, 2016) van der Wiel, M. H. D.; Naylor, David A.; Makiwa, Gibion; Satt, M.; Abergel, A.
    Context. The HF molecule has been proposed as a sensitive tracer of diffuse interstellar gas, while at higher densities its abundance could be influenced heavily by freeze-out onto dust grains. Aims. We investigate the spatial distribution of a collection of absorbing gas clouds, some associated with the dense, massive star-forming core NGC6334I, and others with diffuse foreground clouds elsewhere along the line of sight. For the former category, we aim to study the dynamical properties of the clouds in order to assess their potential to feed the accreting protostellar cores. Methods. We use far-infrared spectral imaging from the Herschel SPIRE iFTS to construct a map of HF absorption at 243 µm in a 60 ×30 .5 region surrounding NGC6334 I and I(N). Results.The combination of new mapping that is fully sampled spatially, but is spectrally unresolved with a previous, single-pointing, spectrally resolved HF signature yields a three-dimensional picture of absorbing gas clouds in the direction of NGC6334. Toward core I, the HF equivalent width matches that of the spectrally resolved observation. At angular separations &2000 from core I, the HF absorption becomes weaker, which is consistent with three of the seven components being associated with this dense star-forming envelope. Of the remaining four components, two disappear beyond∼10 distance from the NGC6334 filament, suggesting that these clouds are spatially associated with the star-forming complex. Our data also implies a lack of gas-phase HF in the envelope of core I(N). Using a simple description of adsorption onto and desorption from dust grain surfaces, we show that the overall lower temperature of the envelope of source I(N) is consistent with freeze-out of HF, while it remains in the gas phase in source I. Conclusions. We use the HF molecule as a tracer of column density in diffuse gas(nH ≈102–103 cm−3),and find that it may uniquely trace a relatively low-density portion of the gas reservoir available for star formation that otherwise escapes detection. At higher densities prevailing in protostellar envelopes (&104 cm−3), we find evidence of HF depletion from the gas phase under sufficiently cold conditions.