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$_{\rm FIR}$ 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$_2$ 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