Determining the relative evolutionary stages of very young massive star formation regions

We have recently completed an observing program with the Australia Telescope Compact Array towards massive star formation regions traced by 6.7 GHz methanol maser emission. We found the molecular cores could be separated into groups based on their association with/without methanol maser and 24 GHz continuum emission. Analysis of the molecular and ionised gas properties suggested the cores within the groups may be at different evolutionary stages. In this contribution we derive the column densities and temperatures of the cores from the NH3 emission and investigate if this can be used as an indicator of the relative evolutionary stages of cores in the sample. The majority of cores are well fit using single-temperature large velocity gradient models, and exhibit a range of temperatures from ~10 K to >200 K. Under the simple but reasonable assumption that molecular gas in the cores will heat up and become less quiescent with age due to feedback from the powering source(s), the molecular gas kinetic temperature combined with information of the core kinematics seems a promising probe of relative core age in the earliest evolutionary stages of massive star formation

Star formation rates on global and cloud scales within the Galactic Centre

The environment within the inner few hundred parsecs of the Milky Way, known as the "Central Molecular Zone" (CMZ), harbours densities and pressures orders of magnitude higher than the Galactic Disc; akin to that at the peak of cosmic star formation (Kruijssen & Longmore 2013). Previous studies have shown that current theoretical star-formation models under-predict the observed level of star-formation (SF) in the CMZ by an order of magnitude given the large reservoir of dense gas it contains. Here we explore potential reasons for this apparent dearth of star formation activity

Star formation rates and efficiencies in the Galactic Centre

The inner few hundred parsecs of the Milky Way harbours gas densities, pressures, velocity dispersions, an interstellar radiation field and a cosmic ray ionisation rate orders of magnitude higher than the disc; akin to the environment found in star-forming galaxies at high-redshift. Previous studies have shown that this region is forming stars at a rate per unit mass of dense gas which is at least an order of magnitude lower than in the disc, potentially violating theoretical predictions. We show that all observational star formation rate diagnostics - both direct counting of young stellar objects and integrated light measurements - are in agreement within a factor two, hence the low star formation rate is not the result of the systematic uncertainties that affect any one method. As these methods trace the star formation over different timescales, from $0.1 - 5$ Myr, we conclude that the star formation rate has been constant to within a factor of a few within this time period. We investigate the progression of star formation within gravitationally bound clouds on $\sim$ parsec scales and find $1 - 4$ per cent of the cloud masses are converted into stars per free-fall time, consistent with a subset of the considered "volumetric" star formation models. However, discriminating between these models is obstructed by the current uncertainties on the input observables and, most importantly and urgently, by their dependence on ill-constrained free parameters. The lack of empirical constraints on these parameters therefore represents a key challenge in the further verification or falsification of current star formation theories

Which feedback mechanisms dominate in the high-pressure environment of the Central Molecular Zone?

Supernovae (SNe) dominate the energy and momentum budget of stellar feedback, but the efficiency with which they couple to the interstellar medium (ISM) depends strongly on how effectively early, pre-SN feedback clears dense gas from star-forming regions. There are observational constraints on the magnitudes and timescales of early stellar feedback in low ISM pressure environments, yet no such constraints exist for more cosmologically typical high ISM pressure environments. In this paper, we determine the mechanisms dominating the expansion of HII regions as a function of size-scale and evolutionary time within the high-pressure (P/k_\rm{B}~$10^{7-8}$K cm$^{-3}$) environment in the inner 100pc of the Milky Way. We calculate the thermal pressure from the warm ionised (P_\rm{HII}; 10$^{4}$K) gas, direct radiation pressure (P_\rm{dir}), and dust processed radiation pressure (P_\rm{IR}). We find that (1) P_\rm{dir} dominates the expansion on small scales and at early times (0.01-0.1pc; $0.1$pc; $>1$Myr); (3) during the first ~1Myr of growth, but not thereafter, either $P_{\rm IR}$ or stellar wind pressure likely make a comparable contribution. Despite the high confining pressure of the environment, natal star-forming gas is efficiently cleared to radii of several pc within ~2Myr, i.e. before the first SNe explode. This `pre-processing' means that subsequent SNe will explode into low density gas, so their energy and momentum will efficiently couple to the ISM. We find the HII regions expand to a radius of 3pc, at which point they have internal pressures equal with the surrounding external pressure. A comparison with HII regions in lower pressure environments shows that the maximum size of all HII regions is set by pressure equilibrium with the ambient ISM

InGaAs spin light emitting diodes measured in the Faraday and oblique Hanle geometries

InGaAs quantum well light emitting diodes (LED) with spin-injecting, epitaxial Fe contacts were fabricated using an in situ wafer transfer process where the semiconductor wafer was transferred under ultrahigh vacuum (UHV) conditions to a metals growth chamber to achieve a high quality interface between the two materials. The spin LED devices were measured optically with applied magnetic fields in either the Faraday or the oblique Hanle geometries in two experimental set-ups. Optical polarizations efficiencies of 4.5% in the Faraday geometry and 1.5% in the Hanle geometry are shown to be equivalent. The polarization efficiency of the electroluminescence is seen to decay as the temperature increases although the spin lifetime remains constant due to the influence of the D'yakonov–Perel' spin scattering mechanism in the quantum well.RM would like to acknowledge support from the EPSRC.This is the final version of the article. It first appeared from the Institute of Physics via https://doi.org/10.1088/0022-3727/49/16/16510

Magnetotransport in p-type Ge quantum well narrow wire arrays

We report magnetotransport measurements of a SiGe heterostructure containing a 20 nm p-Ge quantum well with a mobility of 800 000 cm2 V−1 s−1. By dry etching arrays of wires with widths between 1.0 μm and 3.0 μm, we were able to measure the lateral depletion thickness, built-in potential, and the phase coherence length of the quantum well. Fourier analysis does not show any Rashba related spin-splitting despite clearly defined Shubnikov-de Haas oscillations being observed up to a filling factor of ν = 22. Exchange-enhanced spin-splitting is observed for filling factors below ν = 9. An analysis of boundary scattering effects indicates lateral depletion of the hole gas by 0.5 ± 0.1 μm from the etched germanium surface. The built-in potential is found to be 0.25 ± 0.04 V, presenting an energy barrier for lateral transport greater than the hole confinement energy. A large phase coherence length of 3.5 ± 0.5 μm is obtained in these wires at 1.7 K.This work was supported by the EPSRC funded “Spintronic device physics in Si/Ge heterostructures” EP/J003263/1 and EP/J003638/1 projects and a Platform Grant No. EP/J001074/1.This is the author accepted manuscript. The final version is available from AIP via http://dx.doi.org/10.1063/1.4919053

Investigating the structure and fragmentation of a highly filamentary IRDC

We present 3.7 arcsec (~0.05 pc) resolution 3.2 mm dust continuum observations from the IRAM PdBI, with the aim of studying the structure and fragmentation of the filamentary Infrared Dark Cloud G035.39-00.33. The continuum emission is segmented into a series of 13 quasi-regularly spaced (~0.18pc) cores, following the major axis of the IRDC. We compare the spatial distribution of the cores with that predicted by theoretical work describing the fragmentation of hydrodynamic fluid cylinders, finding a significant (factor of ~8) discrepancy between the two. Our observations are consistent with the picture emerging from kinematic studies of molecular clouds suggesting that the cores are harboured within a complex network of independent sub-filaments. This result emphasises the importance of considering the underlying physical structure, and potentially, dynamically important magnetic fields, in any fragmentation analysis. The identified cores exhibit a range in (peak) beam-averaged column density ($3.6{\rm x}10^{23}{\rm cm}^{-2}<N_{H,c}<8.0{\rm x}10^{23}{\rm cm}^{-2}$), mass ($8.1M_{\odot}<M_{c}<26.1M_{\odot}$), and number density ($6.1{\rm x}10^{5}{\rm cm}^{-3}<n_{H, c, eq}<14.7{\rm x}10^{5}{\rm cm}^{-3}$). Two of these cores, dark in the mid-infrared, centrally-concentrated, monolithic (with no traceable substructure at our PdBI resolution), and with estimated masses of the order ~20-25$M_{\odot}$, are good candidates for the progenitors of intermediate-to-high-mass stars. Virial parameters span a range $0.2<\alpha_{\rm vir}<1.3$. Without additional support, possibly from dynamically important magnetic fields with strengths of the order 230$\mu$G<B<670$\mu$G, the cores are susceptible to gravitational collapse. These results may imply a multi-layered fragmentation process, which incorporates the formation of sub-filaments, embedded cores, and the possibility of further fragmentation

Weak localization and weak antilocalization in doped germanium epilayers

The magnetoresistance of 50 nm thick epilayers of doped germanium is measured at a range of temperatures down to 1.6 K. Both n- and p-type devices show quantum corrections to the conductivity in an applied magnetic field, with n-type devices displaying weak localization and p-type devices showing weak antilocalization. From fits to these data using the Hikami-Larkin-Nagaoka model, the phase coherence length of each device is extracted, as well as the spin diffusion length of the p-type device. We obtain phase coherence lengths as large as 325 nm in the highly doped n-type device, presenting possible applications in quantum technologies. The decay of the phase coherence length with temperature is found to obey the same power law of lφ∝Tc, where c=-0.68±0.03, for each device, in spite of the clear differences in the nature of the conduction. In the p-type device, the measured spin diffusion length does not change over the range of temperatures for which weak antilocalization can be observed. The presence of a spin-orbit interaction manifested as weak antilocalization in the p-type epilayer suggests that these structures could be developed for use in spintronic devices such as the spin-FET, where significant spin lifetimes would be important for efficient device operation.This work was supported by the EPSRC funded “Spintronic device physics in Si/Ge heterostructures” EP/J003263/1 and EP/J003638/1 projects and a Platform Grant No. EP/J001074/1

Using young massive star clusters to understand star formation and feedback in high-redshift-like environments

The formation environment of stars in massive stellar clusters is similar to the environment of stars forming in galaxies at a redshift of 1 - 3, at the peak star formation rate density of the Universe. As massive clusters are still forming at the present day at a fraction of the distance to high-redshift galaxies they offer an opportunity to understand the processes controlling star formation and feedback in conditions similar to those in which most stars in the Universe formed. Here we describe a system of massive clusters and their progenitor gas clouds in the centre of the Milky Way, and outline how detailed observations of this system may be able to: (i) help answer some of the fundamental open questions in star formation and (ii) quantify how stellar feedback couples to the surrounding interstellar medium in this high-pressure, high-redshift analogue environment

Use of low-dose oral theophylline as an adjunct to inhaled corticosteroids in preventing exacerbations of chronic obstructive pulmonary disease: study protocol for a randomised controlled trial.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) is associated with high morbidity, mortality, and health-care costs. An incomplete response to the anti-inflammatory effects of inhaled corticosteroids is present in COPD. Preclinical work indicates that 'low dose' theophylline improves steroid responsiveness. The Theophylline With Inhaled Corticosteroids (TWICS) trial investigates whether the addition of 'low dose' theophylline to inhaled corticosteroids has clinical and cost-effective benefits in COPD. METHOD/DESIGN: TWICS is a randomised double-blind placebo-controlled trial conducted in primary and secondary care sites in the UK. The inclusion criteria are the following: an established predominant respiratory diagnosis of COPD (post-bronchodilator forced expiratory volume in first second/forced vital capacity [FEV1/FVC] of less than 0.7), age of at least 40 years, smoking history of at least 10 pack-years, current inhaled corticosteroid use, and history of at least two exacerbations requiring treatment with antibiotics or oral corticosteroids in the previous year. A computerised randomisation system will stratify 1424 participants by region and recruitment setting (primary and secondary) and then randomly assign with equal probability to intervention or control arms. Participants will receive either 'low dose' theophylline (Uniphyllin MR 200 mg tablets) or placebo for 52 weeks. Dosing is based on pharmacokinetic modelling to achieve a steady-state serum theophylline of 1-5 mg/l. A dose of theophylline MR 200 mg once daily (or placebo once daily) will be taken by participants who do not smoke or participants who smoke but have an ideal body weight (IBW) of not more than 60 kg. A dose of theophylline MR 200 mg twice daily (or placebo twice daily) will be taken by participants who smoke and have an IBW of more than 60 kg. Participants will be reviewed at recruitment and after 6 and 12 months. The primary outcome is the total number of participant-reported COPD exacerbations requiring oral corticosteroids or antibiotics during the 52-week treatment period. DISCUSSION: The demonstration that 'low dose' theophylline increases the efficacy of inhaled corticosteroids in COPD by reducing the incidence of exacerbations is relevant not only to patients and clinicians but also to health-care providers, both in the UK and globally. TRIAL REGISTRATION: Current Controlled Trials ISRCTN27066620 was registered on Sept. 19, 2013, and the first subject was randomly assigned on Feb. 6, 2014