Avon Huxor

University of Exeter, Computer science, Faculty Member

Cardiff Metropolitan University, Computing and Information Systems, Faculty Member

University of Bristol, School for Policy Studies, Faculty Member

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I am an experienced researcher, having worked in both astrophysics and artificial intelligence.

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Papers by Avon Huxor

Deaths of people with intellectual disabilities: Analysis of deaths in England from <scp>COVID</scp> ‐19 and other causes

Mental Handicap Research, Jul 16, 2021

BackgroundPeople with intellectual disabilities experience significant health inequities. The aim... more BackgroundPeople with intellectual disabilities experience significant health inequities. The aim of this report is to understand the circumstances leading to death from COVID‐19 in people with intellectual disabilities.MethodLocal areas in England prioritised reviewing 200 deaths of adults with intellectual disabilities. Of these, approximately 80% were required to be deaths from suspected or confirmed COVID‐19 as this was the focus of the study; the remainder from other causes. All deaths occurred between 2 March2020 and 9 June 2020.ResultsPeople with intellectual disabilities differed from the general population in their symptoms of COVID‐19 and age at death. The overall quality of care was rated similar to other deaths of people with intellectual disabilities. Concerns were raised relating to recognising acute deterioration and do not attempt cardio‐pulmonary resuscitation decisions.ConclusionsService improvements are indicated in the ways in which people with intellectual disabilities encounter COVID‐19 and experience the disease.

THE <i>HST</i> /ACS COMA CLUSTER SURVEY. II. DATA DESCRIPTION AND SOURCE CATALOGS

Astrophysical Journal Supplement Series, Oct 27, 2010

The Coma cluster, Abell 1656, was the target of an HST-ACS Treasury program designed for deep ima... more The Coma cluster, Abell 1656, was the target of an HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in early 2007, the partially completed survey still covers ∼50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (∼1.75 Mpc or 1 •) with a total coverage area of 274 arcmin 2. The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the southwest region of the cluster. In this paper, we present reprocessed images and SExtractor source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SExtractor Kron magnitudes based only on the measured source flux and its half-light radius. We have performed photometry for ∼73,000 unique objects; approximately one-half of our detections are brighter than the 10σ point-source detection limit at F814W = 25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5%-10% of all source detections, which consist of a large population of unresolved compact sources (primarily globular clusters but also ultra-compact dwarf galaxies) and a wide variety of extended galaxies from a cD galaxy to dwarf low surface brightness galaxies. The red sequence of Coma member galaxies has a color-magnitude relation with a constant slope and dispersion over 9 mag HAMMER ET AL. Vol. 191 (−21 < M F814W < −13). The initial data release for the HST-ACS Coma Treasury program was made available to the public in 2008 August. The images and catalogs described in this study relate to our second data release.

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Tracing the Tidal Streams of the Sagittarius dSph with Long-Period Variable Carbon Stars

The AIMSS Project – III. The stellar populations of compact stellar systems

Carolina Digital Repository (University of North Carolina at Chapel Hill), 2016

Over the last decade and a half a growing zoo of compact stellar systems (CSSs) have been found w... more Over the last decade and a half a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between those displayed by classical globular clusters (GCs) and those of true galaxies. This has led to significant debate about their exact nature. An important, and until now, underutilized discriminant in this debate is provided by in the stellar population properties. Here we present the single stellar population equivalent ages, metallicities, and [α/Fe] of 29 CSSs, based on new spectroscopy from 8-10m class telescopes. With the sample compiled from the AIMSS project and a search for CSSs in the Sloan Digital Sky Survey (Huxor et al.) we sample CSSs ranging from GCs with sizes of merely a few parsec to compact ellipticals (cEs) larger than M32. Together with a literature compilation of comparison samples, this provides a panoramic view of the stellar population characteristics of early-type systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the cEs depart from the mass-metallicity relation of massive early-type galaxies, which continuously forms a sequence with dwarf galaxies. At lower mass, we find a transition in the ultracompact dwarf (UCD) metallicity distribution at a few times 10 7 M , which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in UCDs and cEs are only paralleled by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as an indication that they were more massive at an earlier time and underwent tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS escape velocities.

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Kinematic analysis of the M31 halo globular clusters

Memorie della Societa Astronomica Italiana, 2015

The Newly-Discovered Outer Halo Globular Cluster System of M31

Variable Carbon Stars as Tracers of the Sgr

TilePix

In this paper we present TilePix, an ongoing project to design and build a visual interface to ma... more In this paper we present TilePix, an ongoing project to design and build a visual interface to massive, astronomical, imaging databases. We focus on the motivation, design rationale and early decisions taken to design the interface. We address the problem that arises when astronomical image data is reduced to metadata by automated tools, losing much of the basic information. TilePix

The Hubble Space Telescope advanced camera for surveys coma cluster survey. I. Survey objectives and design

The Astrophysical Journal, 2008

ABSTRACT

SAGITTARIUS II, DRACO II AND LAEVENS 3: THREE NEW MILKY WAY SATELLITES DISCOVERED IN THE PAN-STARRS 1 3<i>π</i>SURVEY

The Astrophysical Journal, Oct 27, 2015

We present the discovery of three new Milky Way satellites from our search for compact stellar ov... more We present the discovery of three new Milky Way satellites from our search for compact stellar overdensities in the photometric catalog of the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS 1, or PS1) 3π survey. The first satellite, Laevens 3, is located at a heliocentric distance of d = 67 ± 3 kpc. With a total magnitude of M V = −4.4 ± 0.3 and a half-light radius r h = 7 ± 2 pc, its properties resemble those of outer halo globular clusters. The second system, Draco II/Laevens 4 (Dra II), is a closer and fainter satellite (d ∼ 20 kpc, M V = −2.9 ± 0.8), whose uncertain size (r h = 19 +8 −6 pc) renders its classification difficult without kinematic information; it could either be a faint and extended globular cluster or a faint and compact dwarf galaxy. The third satellite, Sagittarius II/Laevens 5 (Sgr II), has an ambiguous nature as it is either the most compact dwarf galaxy or the most extended globular cluster in its luminosity range (r h = 37 +9 −8 pc and M V = −5.2 ± 0.4). At a heliocentric distance of 67 ± 5 kpc, this satellite lies intriguingly close to the expected location of the trailing arm of the Sagittarius stellar stream behind the Sagittarius dwarf spheroidal galaxy (Sgr dSph). If confirmed through spectroscopic follow up, this connection would locate this part of the trailing arm of the Sagittarius stellar stream that has so far gone undetected. It would further suggest that Sgr II was brought into the Milky Way halo as a satellite of the Sgr dSph.

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Tracing the Tidal Streams of the Sagittarius dSph with Long-Period Variable Carbon Stars

VizieR Online Data Catalog: HST/ACS Coma cluster survey. II. (Hammer+, 2010)

This data release contains catalogs for the ACS Images in F475W and F814W bands of 25 fields in t... more

SDSS J122958.84+000138.0: A compact, optically red galaxy

Monthly Notices of the Royal Astronomical Society, 2016

We report a new compact galaxy, SDSS J122958.84+138.0 (SDSS J1229+0001), which has unique morphol... more We report a new compact galaxy, SDSS J122958.84+138.0 (SDSS J1229+0001), which has unique morphological and stellar population properties that are rare in observations of the nearby Universe. SDSS J1229+0001 has an r-band absolute magnitude (M r) and halflight radius (R h) of −17.75 mag and 520 pc, respectively. Located in a fairly low-density environment, morphologically it is akin to a typical early-type galaxy as it has a smooth appearance and red colour. However, interestingly, it possesses centrally concentrated starforming activity with a significant amount of dust. We present an analysis of its structural and stellar population properties using archival images and VLT/FORS2 spectroscopy. An analysis of the UKIDSS H-band image shows that the observed light distribution is better fitted with a two-component Sérsic function with inner and outer component effective radii of 190 and 330 pc, respectively. The overall half-light radius measured in the H band is much smaller compared to optical, i.e. 290 pc. We prepared a spectral energy distribution from optical to far-infrared and interpret it to derive the star-formation rate, dust mass and stellar mass. We find that SDSS J1229+0001 has dust mass M dust = 5.1 × 10 5 M with a dust-to-stellar mass ratio log(M dust /M *) = −3.5. While the observed stellar population properties are-to some extent-like those of a typical S0 galaxy, a unified view from stellar population and structural properties may suggest that SDSS J1229+0001 is a smoking gun example of a compact early-type galaxy in formation.

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VizieR Online Data Catalog: JHKs photometry of LPVs in M33 (Cioni+, 2008)

yCat, Jun 1, 2008

Accretion in action: phase space coherence of stellar debris and globular clusters in Andromeda's South-West Cloud⋆

Monthly Notices of the Royal Astronomical Society: Letters, Sep 24, 2014

A central tenet of the current cosmological paradigm is that galaxies grow over time through the ... more A central tenet of the current cosmological paradigm is that galaxies grow over time through the accretion of smaller systems. Here, we present new kinematic measurements near the centre of one of the densest pronounced substructures, the SouthWest Cloud, in the outer halo of our nearest giant neighbour, the Andromeda galaxy. These observations reveal that the kinematic properties of this region of the SouthWest Cloud are consistent with those of PA-8, a globular cluster previously shown to be co-spatial with the stellar substructure. In this sense, the situation is reminiscent of the handful of globular clusters that sit near the heart of the Sagittarius dwarf galaxy, a system that is currently being accreted into the Milky Way, confirming that accretion deposits not only stars but also globular clusters into the haloes of large galaxies.

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Metallicity and Mean Age Across M,33

Springer eBooks, 2008

New wide-field near-infrared (NIR) imaging observations of M33 were obtained from UKIRT. These sh... more New wide-field near-infrared (NIR) imaging observations of M33 were obtained from UKIRT. These show a large population of intermediate-age stars considerably improving on previous NIR data. The spatial distribution of super giant stars, carbon-rich (C-rich or C stars) and oxygen-rich (O-rich or M stars) asymptotic giant branch (AGB) stars distinguished from the NIR colour-magnitude diagram (CMD) have been studied as well as the C/M ratio. The K s magnitude distribution has been interpreted using theoretical models to derive the mean age and the mean metallicity across M33.

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A Bird's Eye View of M31 and Its Satellite Galaxies

A panoramic survey of M31&#39;s outer regions using the Isaac Newton Telescope Wide Field Cam... more A panoramic survey of M31&#39;s outer regions using the Isaac Newton Telescope Wide Field Camera has revealed a substantial and surprising amount of stellar substructure in the halo of this spiral galaxy, some of which can be used to probe the dark matter distribution of the halo. In particular, a giant stellar stream is observed to extend over a radial

Newly discovered globular clusters in NGC 147 and NGC 185 from PAndAS

Monthly Notices of the Royal Astronomical Society, Sep 16, 2013

Using data from the Pan-Andromeda Archaeological Survey (PAndAS), we have discovered four new glo... more Using data from the Pan-Andromeda Archaeological Survey (PAndAS), we have discovered four new globular clusters (GCs) associated with the M31 dwarf elliptical (dE) satellites NGC 147 and NGC 185. Three of these are associated with NGC 147 and one with NGC 185. All lie beyond the main optical boundaries of the galaxies and are the most remote clusters yet known in these systems. Radial velocities derived from low-resolution spectra are used to argue that the GCs are bound to the dwarfs and are not part of the M31 halo population. Combining PAndAS with United Kingdom Infrared Telescope (UKIRT)/WFCAM (Wide-Field Camera) data, we present the first homogeneous optical and near-IR photometry for the entire GC systems of these dEs. Colour-colour plots and published colour-metallicity relations are employed to constrain GC ages and metallicities. It is demonstrated that the clusters are in general metal poor ([Fe/H] < −1.25 dex), while the ages are more difficult to constrain. The mean (V − I) 0 colours of the two GC systems are very similar to those of the GC systems of dEs in the Virgo and Fornax clusters, as well as the extended halo GC population in M31. The new clusters bring the GC-specific frequency (S N) to ∼9 in NGC 147 and ∼5 in NGC 185, consistent with values found for dEs of similar luminosity residing in a range of environments.

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Major substructure in the M31 outer halo: the South-West Cloud★

Monthly Notices of the Royal Astronomical Society, Dec 3, 2013

We undertake the first detailed analysis of the stellar population and spatial properties of a di... more We undertake the first detailed analysis of the stellar population and spatial properties of a diffuse substructure in the outer halo of M31. The SouthWest Cloud lies at a projected distance of ∼100 kpc from the centre of M31 and extends for at least ∼50 kpc in projection. We use Pan-Andromeda Archaeological Survey photometry of red giant branch stars to determine a distance to the SouthWest Cloud of 793 +45 −45 kpc. The metallicity of the cloud is found to be [Fe/H] = −1.3 ± 0.1. This is consistent with the coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities determined using an independent technique of [Fe/H] = −1.35 ± 0.15. We measure a brightness for the Cloud of M V = −12.1 mag; this is ∼75 per cent of the luminosity implied by the luminosity-metallicity relation. Under the assumption that the SouthWest Cloud is the visible remnant of an accreted dwarf satellite, this suggests that the progenitor object was amongst M31's brightest dwarf galaxies prior to disruption.

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