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Chris Smith

Publications and source records attributed to Chris Smith.

27 records · Page 2Linked to original sources
arXiv2013

The UM, a fully--compressible, non--hydrostatic, deep atmosphere GCM, applied to hot Jupiters

We are adapting the Global Circulation Model (GCM) of the UK Met Office, the so--called Unified Model (UM), for the study of hot Jupiters. In this work we demonstrate the successful adaptation of the most sophisticated dynamical core, the component of the GCM which solves the equations of motion for the atmosphere, available within the UM, ENDGame (Even Newer Dynamics for General atmospheric modelling of the environment). Within the same numerical scheme ENDGame supports solution to the dynamical equations under varying degrees of simplification. We present results from a simple, shallow (in atmospheric domain) hot Jupiter model (SHJ), and a more realistic (with a deeper atmosphere) HD 209458b test case. For both test cases we find that the large--scale, time--averaged (over the 1200 days prescribed test period), dynamical state of the atmosphere is relatively insensitive to the level of simplification of the dynamical equations. However, problems exist when attempting to reproduce the results for these test cases derived from other models. For the SHJ case the lower (and upper) boundary intersects the dominant dynamical features of the atmosphere meaning the results are heavily dependent on the boundary conditions. For the HD 209458b test case, when using the more complete dynamical models, the atmosphere is still clearly evolving after 1200 days, and in a transient state. Solving the complete (deep atmosphere and non--hydrostatic) dynamical equations allows exchange between the vertical and horizontal momentum of the atmosphere, via Coriolis and metric terms. Subsequently, interaction between the upper atmosphere and the deeper more slowly evolving (radiatively inactive) atmosphere significantly alters the results, and acts over timescales longer than 1200 days.

astro-ph.EP↗
arXiv2013

Using the UM dynamical cores to reproduce idealised 3D flows

We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held-Suarez test, a simplified model of Earth (including a stratosphere), and a hypothetical tidally locked Earth. Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics.

astro-ph.EP↗
arXiv2013

Choirs, HI Galaxy Groups: Catalogue and Detection of Star-forming Dwarf Group Members

Hα observations centred on galaxies selected from the HI Parkes All Sky Survey (HIPASS, Barnes et al. 2001) typically show one and sometimes two star-forming galaxies within the approximately 15-arcminute beam of the Parkes 64-m HI detections. In our Survey of Ionization in Neutral Gas Galaxies (SINGG, Meurer et al. 2006) we found fifteen cases of HIPASS sources containing four or more emission line galaxies (ELGs). We name these fields Choir groups. In the most extreme case we found a field with at least nine ELGs. In this paper we present a catalogue of Choir group members in the context of the wider SINGG sample. The dwarf galaxies in the Choir groups would not be individually detectable in HIPASS at the observed distances if they were isolated, but are detected in SINGG narrow-band imaging due to their membership of groups with sufficiently large total HI mass. The ELGs in these groups are similar to the wider SINGG sample in terms of size, Hα equivalent width, and surface brightness. Eight of these groups have two large spiral galaxies with several dwarf galaxies and may be thought of as morphological analogues of the Local Group. However, on average our groups are not significantly HI-deficient, suggesting that they are at an early stage of assembly, and more like the M81 group. The Choir groups are very compact at typically only 190 kpc in projected distance between the two brightest members. They are very similar to SINGG fields in terms of star formation efficiency (the ratio of star formation rate to HI mass; SFE), showing an increasing trend in SFE with stellar mass.

astro-ph.CO↗
arXiv2010

First Results from the NOAO Survey of the Outer Limits of the Magellanic Clouds

[abridged] We describe the first results from the NOAO Outer Limits Survey. The survey consists of deep images of 55 0.6x0.6 degree fields at distances up to 20 degrees from the LMC/SMC, and 10 controls. The fields probe the outer structure of the Clouds, the Magellanic Stream, the Leading Arm, and the wake of the new LMC orbit. Images were taken in 5 filters on the CTIO Blanco 4-m and Mosaic2 camera, with calibration at the CTIO 0.9-m. The CRI images reach depths below the oldest LMC/SMC main sequence (MS) turnoffs, yielding probes of structure combined with ability to measure stellar ages and metallicities. M and DDO51 images allow for discrimination of LMC and SMC giant stars from foreground dwarfs, allowing us to use giants as additional probes. From photometry of 8 fields at radii of 7-19 degrees N of the LMC bar, we find MS stars associated with the LMC to 16 degrees from the LMC center, while the much rarer giants can only be convincingly detected out to 11 degrees. In one control field, we see the signature of the Milky Way globular cluster NGC 1851. The CMDs show that while at 7-degree radius LMC populations as young as 500 Myr are present, at radii more than 11 degrees only the underlying old metal-poor population remains, demonstrating the existence of a population gradient. Even at extreme distances, the dominant age is much less than "globular Cluster age." MS star counts follow an exponential decline with a scale length of 1.15 kpc, essentially the same scale length as gleaned for the inner LMC disk from prior studies. While we cannot rule out tidal structure elsewhere, detection of ordered structure to 12 disk scale lengths is unprecedented, and adds to the puzzle of the LMC's interaction history. Our results do not rule out the possible existence of an LMC stellar halo, which may only dominate the disk at yet larger radii.

astro-ph.GA↗
arXiv2006

Photometric Calibration of the DES

The Dark Energy Survey (DES) is a 5000 sq deg griz imaging survey to be conducted using a proposed 3 sq deg (2.2deg-diameter) wide-field mosaic camera on the CTIO Blanco 4m telescope. The primary scientific goal of the DES is to constrain dark energy cosmological parameters via four complementary methods: galaxy cluster counting, weak lensing, galaxy angular correlations, and Type Ia supernovae, supported by precision photometric redshifts. Here we present the photometric calibration plans for the DES, including a discussion of standard stars and field-to-field calibrations.

astro-ph↗
arXiv2005

Supernova Cosmology and the ESSENCE project

The proper usage of Type Ia supernovae (SNe Ia) as distance indicators has revolutionized cosmology, and added a new dominant component to the energy density of the Universe, dark energy. Following the discovery and confirmation era, the currently ongoing SNe Ia surveys aim to determine the properties of the dark energy. ESSENCE is a five year ground-based supernova survey aimed at finding and characterizing 200 SNe Ia in the redshift domain z=[0.2-0.8]. The goal of the project is to put constraints on the equation of state parameter, w, of the dark energy with an accuracy of <10%. This paper presents these ongoing efforts in the context of the current developments in observational cosmology.

astro-ph↗
arXiv2002

Chandra Observations of the QSO Pair Q2345+007: Binary Quasar or Massive Dark Lens?

The components of the wide (7.3") separation quasar pair Q2345+007A,B (z=2.15) have the most strikingly similar optical spectra seen to date (Steidel & Sargent 1991) yet no detected lensing mass, making this system the best candidate known for a massive (1e14 Msun) dark matter lens system. Here we present results from a 65ksec Chandra observation designed to investigate whether it is a binary quasar or a gravitational lens. We find no X-ray evidence for a lensing cluster to a (0.5-2keV) flux limit of 2e-15 cgs, which is consistent with lensing only for a reduced baryon fraction. Using the Chandra X-ray observations of the quasars themselves, together with new and published optical measurements, we use the observed emission properties of the quasars for further tests between the lens and binary hypotheses. Assuming similar line-of-sight absorption to the images, we find that their X-ray continuum slopes are inconsistent (Gamma_A=2.30 and Gamma_B=0.83) as are their X-ray to optical flux ratios. The probability that B suffers absorption sufficient to account for these spectral differences is negligible. We present new optical evidence that the flux ratio of the pair is variable, so the time-delay in a lens scenario could cause some of the discrepancies. However, adequately large variations in overall spectral energy distribution are rare in individual QSOs. All new evidence here weighs strongly toward the binary interpretation. Q2345+007 thus may represent the highest redshift example known of interaction-triggered but as-yet unmerged luminous AGN.

astro-ph↗
arXiv1999

The Luminous Type Ic SN 1992ar at z=0.145

We present spectroscopic and photometric observations of SN1992ar, the more distant SN in the Calan/Tololo Survey. We compare its spectrum with those of nearby Type Ia and Ic SNe and conclude that the latter type is a better match to SN 1992ar. Using K-corrections based on the spectra of well observed Type Ic and Ia SNe we compute different possible rest frame light curves of SN 1992ar and compare them with those of representative SNe of each type observed in the nearby universe. From the photometry and the spectra, we are able to conclude that SN 1992ar cannot be matched by any known example of a Type Ia SN. Even though the data set collected is fairly complete (one spectrum and 10 photometric points), it is not possible to decide whether SN 1992ar was a fast Type Ic SN, like SN 1994I, or a slow one, like SN 1983V. The absolute V magnitudes at maximum implied by each of these possibilities are -19.2 and -20.2, respectively. The latter would make SN 1992ar one of the brightest SNe on record. SN 1992ar, hence, illustrates the problem of contamination faced by the high z Type Ia SNe samples whose luminosity distances are used to determine the cosmological parameters of the Universe. We present observational criteria to distinguish the two SN types when the SiII 6355 line is redshifted out of the sensitivity range of typical CCD detectors, and discuss the effect that these luminous Type Ic SNe would have on the measured cosmological parameters, if not removed from the High-z Type Ia SN samples.

astro-ph↗