Establishing an analogue population for the most distant galaxies

Lyman break analogues (LBAs) are local galaxies selected to match a more distant (usually z~3) galaxy population in luminosity, UV-spectral slope and physical characteristics, and so provide an accessible laboratory for exploring their properties. However, as the Lyman break technique is extended to higher redshifts, it has become clear that the Lyman break galaxies (LBGs) at z~3 are more massive, luminous, redder, more extended and at higher metallicities than their z~5 counterparts. Thus extrapolations from the existing LBA samples (which match z=3 properties) have limited value for characterising z>5 galaxies, or inferring properties unobservable at high redshift. We present a new pilot sample of twenty-one compact star forming galaxies in the local (0.05<z<0.25) Universe, which are tuned to match the luminosities and star formation volume densities observed in z>~5 LBGs. Analysis of optical emission line indices suggests that these sources have typical metallicities of a few tenths Solar (again, consistent with the distant population). We also present radio continuum observations of a subset of this sample (13 sources) and determine that their radio fluxes are consistent with those inferred from the ultraviolet, precluding the presence of a heavily obscured AGN or significant dusty star formation.Comment: 13 pages, MNRAS accepte

Applications of Stellar Population Synthesis in the Distant Universe

Comparison with artificial galaxy models is essential for translating the incomplete and low signal-to-noise data we can obtain on astrophysical stellar populations to physical interpretations which describe their composition, physical properties, histories and internal conditions. In particular, this is true for distant galaxies, whose unresolved light embeds clues to their formation and evolution as well as their impact on their wider environs. Stellar population synthesis models are now used as the foundation of analysis at all redshifts, but are not without their problems. Here we review the use of stellar population synthesis models, with a focus on applications in the distant Universe.Comment: 32 page review, published in Galaxies special issue, "Star Formation in the UV", ed. Jorick Vin

Magnetorheological landing gear: 1. A design methodology

Aircraft landing gears are subjected to a wide range of excitation conditions, which result in conflicting damping requirements. A novel solution to this problem is to implement semi-active damping using magnetorheological (MR) fluids. This paper presents a design methodology that enables an MR landing gear to be optimized, both in terms of its damping and magnetic circuit performance, whilst adhering to stringent packaging constraints. Such constraints are vital in landing gear, if MR technology is to be considered as feasible in commercial applications. The design approach focuses on the impact or landing phase of an aircraft's flight, where large variations in sink speed, angle of attack and aircraft mass makes an MR device potentially very attractive. In this study, an equivalent MR model of an existing aircraft landing gear is developed. This includes a dynamic model of an MR shock strut, which accounts for the effects of fluid compressibility. This is important in impulsive loading applications such as landing gear, as fluid compression will reduce device controllability. Using the model, numerical impact simulations are performed to illustrate the performance of the optimized MR shock strut, and hence the effectiveness of the proposed design methodology. Part 2 of this contribution focuses on experimental validation

High-redshift galaxies and low-mass stars

The sensitivity available to near-infrared surveys has recently allowed us to probe the galaxy population at z ≈ 7 and beyond. The existing Hubble Wide Field Camera 3 (WFC3) and Visible and Infrared Survey Telescope for Astronomy (VISTA) Infrared Camera (VIRCam) instruments allow deep surveys to be undertaken well beyond 1 μm – a capability that will be further extended with the launch and commissioning of the James Webb Space Telescope (JWST). As new regions of parameter space in both colour and depth are probed, new challenges for distant galaxy surveys are identified. In this paper, we present an analysis of the colours of L- and T-dwarf stars in widely used photometric systems. We also consider the implications of the newly identified Y-dwarf population – stars that are still cooler and less massive than T-dwarfs for both the photometric selection and spectroscopic follow-up of faint and distant galaxies. We highlight the dangers of working in the low-signal-to-noise regime, and the potential contamination of existing and future samples. We find that Hubble/WFC3 and VISTA/VIRCam Y-drop selections targeting galaxies at z ∼ 7.5 are vulnerable to contamination from T- and Y-class stars. Future observations using JWST, targeting the z ∼ 7 galaxy population, are also likely to prove difficult without deep medium-band observations. We demonstrate that single emission line detections in typical low-signal-to-noise spectroscopic observations may also be suspect, due to the unusual spectral characteristics of the cool dwarf star population

Radio Observations of GRB Host Galaxies

We present 5.5 and 9.0 GHz observations of a sample of seventeen GRB host galaxies at 0.5<z<1.4, using the radio continuum to explore their star formation properties in the context of the small but growing sample of galaxies with similar observations. Four sources are detected, one of those (GRB 100418A) likely due to lingering afterglow emission. We suggest that the previously-reported radio afterglow of GRB 100621A may instead be due to host galaxy flux. We see no strong evidence for redshift evolution in the typical star formation rate of GRB hosts, but note that the fraction of `dark' bursts with detections is higher than would be expected given constraints on the more typical long GRB population. We also determine the average radio-derived star formation rates of core collapse supernovae at comparable redshift, and show that these are still well below the limits obtained for GRB hosts, and show evidence for a rise in typical star formation rate with redshift in supernova hosts.Comment: 15 pages, MNRAS accepte

Core-collapse supernovae ages and metallicities from emission-line diagnostics of nearby stellar populations

Massive stars are the main objects that illuminate H II regions and they evolve quickly to end their lives in core-collapse supernovae (CCSNe). Thus it is important to investigate the association between CCSNe and H II regions. In this paper, we present emission line diagnostics of the stellar populations around nearby CCSNe, that include their host H II regions, from the PMAS/PPAK Integral-field Supernova hosts COmpilation (PISCO). We then use BPASS stellar population models to determine the age, metallicity and gas parameters for H II regions associated with CCSNe, contrasting models that consider either single star evolution alone or incorporate interacting binaries. We find binary-star models, that allow for ionizing photon loss, provide a more realistic fit to the observed CCSN hosts with metallicities that are closer to those derived from the oxygen abundance in O3N2. We also find that type II and type Ibc SNe arise from progenitor stars of similar age, mostly from 7 to 45 Myr, which corresponds to stars with masses < 20 solar mass . However these two types SNe have little preference in their host environment metallicity measured by oxygen abundance or in progenitor initial mass. We note however that at lower metallicities supernovae are more likely to be of type II.Comment: 22 pages, 19 Figures, 6 Tables. Accepted by MNRAS. Comments welcom

The detection of FIR emission from high redshift star-forming galaxies in the ECDF-S

ABRIDGED: We have used the LABOCA Survey of the ECDF-S (LESS) to investigate rest-frame FIR emission from typical SF systems (LBGs) at redshift 3, 4, and 5. We initially concentrate on LBGs at z~3 and select three subsamples on stellar mass, extinction corrected SF and rest-frame UV-magnitude. We produce composite 870micron images of the typical source in our subsamples, obtaining ~4sigma detections and suggesting a correlation between FIR luminosity and stellar mass. We apply a similar procedure to our full samples at z~3, 4, 4.5 and 5 and do not obtain detections - consistent with a simple scaling between FIR luminosity and stellar mass. In order to constrain the FIR SED of these systems we explore their emission at multiple wavelengths spanning the peak of dust emission at z~3 using the Herschel SPIRE observations of the field. We obtain detections at multiple wavelengths for both our stellar mass and UV-magnitude selected samples, and find a best-fit SED with T_dust in the ~33-41K range. We calculate L_FIR, obscured SFRs and M_dust, and find that a significant fraction of SF in these systems is obscured. Interestingly, our extinction corrected SFR sample does not display the large FIR fluxes predicted from its red UV-spectral slope. This suggests that the method of assuming an intrinsic UV-slope and correcting for dust attenuation may be invalid for this sample - and that these are not in fact the most actively SF systems. All of our z~3 samples fall on the `main sequence' of SF galaxies at z~3 and our detected subsamples are likely to represent the high obscuration end of LBGs at their epoch. We compare the FIR properties of our subsamples with various other populations, finding that our stellar mass selected sample shows similar FIR characteristics to SMGs at the same epoch and therefore potentially represents the low L_FIR end of the high redshift FIR luminosity function.Comment: 18 pages, 10 figure, MNRAS accepted, corrected typos, acknowledgements adde

Non-linear identification of a squeeze-film damper

Described is an experimental study to identify the damping laws associated with a squeeze-film vibration damper. This is achieved by using a non-linear filtering algorithm to process displacement responses of the damper ring to synchronous excitation and thus to estimate the parameters in an nth-power velocity model. The experimental facility is described in detail and a representative selection of results is included. The identified models are validated through the prediction of damper-ring orbits and comparison with observed responses