1,232 research outputs found
Using local communities to establish geographical boundaries for case studies
Aim: To discuss using local communities to establish geographical boundaries in a case study approach.
Background: Case study is widely used in the social sciences to explore complex phenomena within a real-life setting. Applying case boundaries is vital to ensure cases are easily identifiable and similar enough to be treated as instances of the same phenomenon. Discussion: Post codes can be used to define geographical boundaries. A broad range of statistical data is collected from these populations including demographic information, which can assist in identifying communities that have issues or characteristics which may benefit from further research. Data collection from communities allows researchers to access appropriate populations. Conclusion: Using local communities to identify case boundaries helps to provide a clear periphery to the case, and generate local solutions to local problems. Implications for research/practice: Researchers using this approach benefit from being able to immerse themselves in the local community. This close engagement helps to ensure local community engagement with research projects and findings
Globally optimal 3D image reconstruction and segmentation via energy minimisation techniques
This paper provides an overview of a number of techniques developed within our group to perform 3D reconstruction and image segmentation based of the application of energy minimisation concepts. We begin with classical snake techniques and show how similar energy minimisation concepts can be extended to derive globally optimal segmentation methods. Then we discuss more recent work based on geodesic active contours that can lead to globally optimal segmentations and reconstructions in 2D. Finally we extend the work to 3D by introducing continuous flow globally minimal surfaces. Several applications are discussed to show the wide applicability and suitability of these techniques to several difficult image analysis problems
Non-Nuclear Hyper/Ultraluminous X-Ray Sources in the Starbursting Cartwheel Ring Galaxy
We report the Chandra/ACIS-S detection of more than 20 ultraluminous X-ray
sources (ULXs, L_{0.5-10 keV} >~ 3 x 10^{39} ergs/sec) in the Cartwheel
collisional ring galaxy system, of which over a dozen are located in the outer
active star-forming ring. A remarkable hyperluminous X-ray source (HLX,
L_{0.5-10 keV} >~ 10^{41} ergs/sec assuming isotropic radiation), which
dominates the X-ray emission from the Cartwheel ring, is located in the same
segment of the ring as most ULXs. These powerful H/ULXs appear to be coincident
with giant HII region complexes, young star clusters, and radio and
mid-infrared hot-spots: all strong indicators of recent massive star formation.
The X-ray spectra show that H/ULXs have similar properties as those of the {\it
most luminous} ULXs found in the nearest starbursts and galaxy mergers such as
the Antennae galaxies and M82. The close association between the X-ray sources
and the starbursting ring strongly suggests that the H/ULXs are intimately
associated with the production and rapid evolution of short-lived massive
stars. The observations represent the most extreme X-ray luminosities
discovered to date associated with star-forming regions--rivaling the X-ray
luminosities usually associated with active galactic nuclei.Comment: ApJ Letters, accepted (scheduled for the Oct. 20 issue). Full
resolution paper in a single .ps.gz file available at:
http://spider.ipac.caltech.edu/staff/gao/Papers/cartw.ps.g
Spatially Resolved Spitzer-IRS Spectroscopy of the Central Region of M82
We present high spatial resolution (~ 35 parsec) 5-38 um spectra of the
central region of M82, taken with the Spitzer Infrared Spectrograph. From these
spectra we determined the fluxes and equivalent widths of key diagnostic
features, such as the [NeII]12.8um, [NeIII]15.5um, and H_2 S(1)17.03um lines,
and the broad mid-IR polycyclic aromatic hydrocarbon (PAH) emission features in
six representative regions and analysed the spatial distribution of these lines
and their ratios across the central region. We find a good correlation of the
dust extinction with the CO 1-0 emission. The PAH emission follows closely the
ionization structure along the galactic disk. The observed variations of the
diagnostic PAH ratios across M82 can be explained by extinction effects, within
systematic uncertainties. The 16-18um PAH complex is very prominent, and its
equivalent width is enhanced outwards from the galactic plane. We interpret
this as a consequence of the variation of the UV radiation field. The EWs of
the 11.3um PAH feature and the H_2 S(1) line correlate closely, and we conclude
that shocks in the outflow regions have no measurable influence on the H_2
emission. The [NeIII]/[NeII] ratio is on average low at ~0.18, and shows little
variations across the plane, indicating that the dominant stellar population is
evolved (5 - 6 Myr) and well distributed. There is a slight increase of the
ratio with distance from the galactic plane of M82 which we attribute to a
decrease in gas density. Our observations indicate that the star formation rate
has decreased significantly in the last 5 Myr. The quantities of dust and
molecular gas in the central area of the galaxy argue against starvation and
for negative feedback processes, observable through the strong extra-planar
outflows.Comment: 15 pages, 12 figures, 3 tables, ApJ, emulateap
The Role of a Hot Gas Environment on the Evolution of Galaxies
Most spiral galaxies are found in galaxy groups with low velocity
dispersions; most E/S0 galaxies are found in galaxy groups with relatively high
velocity dispersions. The mass of the hot gas we can observe in the E/S0 groups
via their thermal X-ray emission is, on average, as much as the baryonic mass
of the galaxies in these groups. By comparison, galaxy clusters have as much or
more hot gas than stellar mass. Hot gas in S-rich groups, however, is of low
enough temperature for its X-ray emission to suffer heavy absorption due to
Galactic HI and related observational effects, and hence is hard to detect. We
postulate that such lower temperature hot gas does exist in low velocity
dispersion, S-rich groups, and explore the consequences of this assumption. For
a wide range of metallicity and density, hot gas in S-rich groups can cool in
far less than a Hubble time. If such gas exists and can cool, especially when
interacting with HI in existing galaxies, then it can help link together a
number of disparate observations, both Galactic and extragalactic, that are
otherwise difficult to understand.Comment: 16 pages with one figure. ApJ Letters, in pres
2D Spectroscopy of Candidate Polar-Ring Galaxies: I. The Pair of Galaxies UGC 5600/09
Observations of the pair of galaxies VV 330 with the SCORPIO multimode
instrument on the 6-m Special Astrophysical Observatory telescope are
presented. Large-scale velocity fields of the ionized gas in H-alfa and
brightness distributions in continuum and H-alfa have been constructed for both
galaxies with the help of a scanning Fabry Perot interferometer. Long-slit
spectroscopy is used to study the stellar kinematics. Analysis of the data
obtained has revealed a complex structure in each of the pair components. Three
kinematic subsystems have been identified in UGC 5600: a stellar disk, an inner
gas ring turned with respect to the disk through ~80degrees, and an outer gas
disk. The stellar and outer gas disks are noncoplanar. Possible scenarios for
the formation of the observed multicomponent kinematic galactic structure are
considered, including the case where the large-scale velocity field of the gas
is represented by the kinematic model of a disk with a warp. The velocity field
in the second galaxy of the pair, UGC 5609, is more regular. A joint analysis
of the data on the photometric structure and the velocity field has shown that
this is probably a late-type spiral galaxy whose shape is distorted by the
gravitational interaction, possibly, with UGC 5600.Comment: 18 pages, 6 figure
A blind HI survey of the M81 group
Results are presented of the first blind HI survey of the M81 group of
galaxies. The data were taken as part of the HI Jodrell All Sky Survey
(HIJASS). The survey reveals several new aspects to the complex morphology of
the HI distribution in the group. All four of the known dwarf irregular (dIrr)
galaxies close to M81 can be unambiguously seen in the HIJASS data. Each forms
part of the complex tidal structure in the area. We suggest that at least three
of these galaxies may have formed recently from the tidal debris in which they
are embedded. The structure connecting M81 to NGC2976 is revealed as a single
tidal bridge of mass approx. 2.1 x 10^8 Msol and projected spatial extent
approx. 80 kpc. Two `spurs' of HI projecting from the M81 complex to lower
declinations are traced over a considerably larger spatial and velocity extent
than by previous surveys. The dwarf elliptical (dE) galaxies BK5N and Kar 64
lie at the spatial extremity of one of these features and appear to be
associated with it. We suggest that these may be the remnants of dIrrs which
has been stripped of gas and transmuted into dEs by close gravitational
encounters with NGC3077. The nucleated dE galaxy Kar 61 is unambiguously
detected in HI for the first time and has an HI mass of approx.10^8 Msol,
further confirming it as a dE/dIrr transitional object. HIJASS has revealed one
new possible group member, HIJASS J1021+6842. This object contains approx. 2 x
10^7 Msol of HI and lies approx.105arcmin from IC2574. It has no optical
counterpart on the Digital Sky Survey.Comment: To be published in Astrophysical Journal Letters 9 pages, including 3
figure
Strong Far-IR Cooling Lines, Peculiar CO Kinematics and Possible Star Formation Suppression in Hickson Compact Group 57
We present [C II] and [O I] observations from Herschel and CO(1-0) maps from
the Combined Array for{\dag} Research in Millimeter Astronomy (CARMA) of the
Hickson Compact Group HCG 57, focusing on the galaxies HCG 57a and HCG 57d. HCG
57a has been previously shown to contain enhanced quantities of warm molecular
hydrogen consistent with shock and/or turbulent heating. Our observations show
that HCG 57d has strong [C II] emission compared to L and weak
CO(1-0), while in HCG 57a, both the [C II] and CO(1-0) are strong. HCG 57a lies
at the upper end of the normal distribution of [C II]/CO and [C II]/FIR ratios,
and its far-IR cooling supports a low density warm diffuse gas that falls close
to the boundary of acceptable PDR models. However, the power radiated in the [C
II] and warm H emission have similar magnitudes, as seen in other
shock-dominated systems and predicted by recent models. We suggest that
shock-heating of the [C II] is a viable alternative to photoelectric heating in
violently disturbed diffuse gas. The existence of shocks is also consistent
with peculiar CO kinematics in the galaxy, indicating highly non-circular
motions are present. These kinematically disturbed CO regions also show
evidence of suppressed star formation, falling a factor of 10-30 below normal
galaxies on the Kennicutt-Schmidt relation. We suggest that the peculiar
properties of both galaxies are consistent with a highly dissipative off-center
collisional encounter between HCG 57d and 57a, creating ring-like morphologies
in both systems. Highly dissipative gas-on-gas collisions may be more common in
dense groups because of the likelihood of repeated multiple encounters. The
possibility of shock-induced SF suppression may explain why a subset of these
HCG galaxies have been found previously to fall in the mid-infrared green
valley.Comment: ApJ accepted, 16 pages, 12 figures, 3 table
Mid-Infrared Spectral Diagnostics of Luminous Infrared Galaxies
We present a statistical analysis of the mid-infrared (MIR) spectra of 248
luminous infrared (IR) galaxies (LIRGs) which comprise the Great Observatories
All-sky LIRG Survey (GOALS) observed with the Infrared Spectrograph (IRS)
on-board the Spitzer Space Telescope. The GOALS sample enables a direct
measurement of the relative contributions of star-formation and active galactic
nuclei (AGN) to the total IR emission from a large sample of local LIRGs. The
AGN contribution to the MIR emission (f-AGN) is estimated by employing several
diagnostics based on the properties of the [NeV], [OIV] and [NeII] fine
structure gas emission lines, the 6.2 microns PAH and the shape of the MIR
continuum. We find that 18% of all LIRGs contain an AGN and that in 10% of all
sources the AGN contributes more than 50% of the total IR luminosity. Summing
up the total IR luminosity contributed by AGN in all our sources suggests that
AGN supply ~12% of the total energy emitted by LIRGs. The average spectrum of
sources with an AGN looks similar to the average spectrum of sources without an
AGN, but it has lower PAH emission and a flatter MIR continuum. AGN dominated
LIRGs have higher IR luminosities, warmer MIR colors and are found in
interacting systems more often than pure starbursts LIRGs. However we find no
linear correlations between these properties and f-AGN. We used the IRAC colors
of LIRGs to confirm that finding AGN on the basis of their MIR colors may miss
~40% of AGN dominated (U)LIRGsComment: accepted for publication in ApJ, 34 pages, 12 figure
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