The stellar metallicity distribution of disc galaxies and bulges in cosmological simulations

By means of high-resolution cosmological hydrodynamical simulations of Milky Way-like disc galaxies, we conduct an analysis of the associated stellar metallicity distribution functions (MDFs). After undertaking a kinematic decomposition of each simulation into spheroid and disc sub-components, we compare the predicted MDFs to those observed in the solar neighbourhood and the Galactic bulge. The effects of the star formation density threshold are visible in the star formation histories, which show a modulation in their behaviour driven by the threshold. The derived MDFs show median metallicities lower by 0.2-0.3 dex than the MDF observed locally in the disc and in the Galactic bulge. Possible reasons for this apparent discrepancy include the use of low stellar yields and/or centrally-concentrated star formation. The dispersions are larger than the one of the observed MDF; this could be due to simulated discs being kinematically hotter relative to the Milky Way. The fraction of low metallicity stars is largely overestimated, visible from the more negatively skewed MDF with respect to the observational sample. For our fiducial Milky Way analog, we study the metallicity distribution of the stars born "in situ" relative to those formed via accretion (from disrupted satellites), and demonstrate that this low-metallicity tail to the MDF is populated primarily by accreted stars. Enhanced supernova and stellar radiation energy feedback to the surrounding interstellar media of these pre-disrupted satellites is suggested as an important regulator of the MDF skewness.Comment: 20 pages, 14 figures, MNRAS, accepte

The cold gas content of bulgeless dwarf galaxies

We present an analysis of the neutral hydrogen (H i) properties of a fully cosmological hydrodynamical dwarf galaxy, run with varying simulation parameters. As reported by Governato et al., the high-resolution, high star formation density threshold version of this galaxy is the first simulation to result in the successful reproduction of a (dwarf) spiral galaxy without any associated stellar bulge. We have set out to compare in detail the H i distribution and kinematics of this simulated bulgeless disc with what is observed in a sample of nearby dwarfs. To do so, we extracted the radial gas density profiles, velocity dispersion (e.g. velocity ellipsoid and turbulence) and the power spectrum of structure within the cold interstellar medium (ISM) from the simulations. The highest resolution dwarf, when using a high-density star formation threshold comparable to densities of giant molecular clouds, possesses bulk characteristics consistent with those observed in nature, though the cold gas is not as radially extended as that observed in nearby dwarfs, resulting in somewhat excessive surface densities. The lines-of-sight velocity dispersion radial profiles have values that are in good agreement with the observed dwarf galaxies, but due to the fact that only the streaming velocities of particles are tracked, a correction to include the thermal velocities can lead to profiles that are quite flat. The ISM power spectra of the simulations appear to possess more power on smaller spatial scales than that of the Small Magellanic Cloud. We conclude that unavoidable limitations remain due to the unresolved physics of star formation and feedback within parsec-scale molecular cloud

Gas Accretion and Galactic Chemical Evolution: Theory and Observations

This chapter reviews how galactic inflows influence galaxy metallicity. The goal is to discuss predictions from theoretical models, but particular emphasis is placed on the insights that result from using models to interpret observations. Even as the classical G-dwarf problem endures in the latest round of observational confirmation, a rich and tantalizing new phenomenology of relationships between $M_*$, $Z$, SFR, and gas fraction is emerging both in observations and in theoretical models. A consensus interpretation is emerging in which star-forming galaxies do most of their growing in a quiescent way that balances gas inflows and gas processing, and metal dilution with enrichment. Models that explicitly invoke this idea via equilibrium conditions can be used to infer inflow rates from observations, while models that do not assume equilibrium growth tend to recover it self-consistently. Mergers are an overall subdominant mechanism for delivering fresh gas to galaxies, but they trigger radial flows of previously-accreted gas that flatten radial gas-phase metallicity gradients and temporarily suppress central metallicities. Radial gradients are generically expected to be steep at early times and then flattened by mergers and enriched inflows of recycled gas at late times. However, further theoretical work is required in order to understand how to interpret observations. Likewise, more observational work is needed in order to understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springer. 29 pages, 2 figure

Radiative Efficiency and Content of Extragalactic Radio Sources: Toward a Universal Scaling Relation Between Jet Power and Radio Power

We present an analysis of the energetics and particle content of the lobes of 24 radio galaxies at the cores of cooling clusters. The radio lobes in these systems have created visible cavities in the surrounding hot, X-ray-emitting gas, which allow direct measurement of the mechanical jet power of radio sources over six decades of radio luminosity, independently of the radio properties themselves. Using these measurements, we examine the ratio between radio power and total jet power (the radiative efficiency). We find that jet (cavity) power increases with radio synchrotron power approximately as P_jet ~ (L_radio)^beta, where 0.35 < beta < 0.70 depending on the bandpass of measurement and state of the source. However, the scatter about these relations caused by variations in radiative efficiency spans more than four orders of magnitude. After accounting for variations in synchrotron break frequency (age), the scatter is reduced by ~ 50%, yielding the most accurate scaling relation available between the lobe bolometric radio power and the jet (cavity) power. We place limits on the magnetic field strengths and particle content of the radio lobes using a variety of X-ray constraints. We find that the lobe magnetic field strengths vary between a few to several tens of microgauss depending on the age and dynamical state of the lobes. If the cavities are maintained in pressure balance with their surroundings and are supported by internal fields and particles in equipartition, the ratio of energy in electrons to heavy particles (k) must vary widely from approximately unity to 4000, consistent with heavy (hadronic) jets.Comment: 20 pages, 11 figures. Accepted for publication in Ap

Meeting the needs of young adults with life‐limiting conditions: A UK survey of current provision and future challenges for hospices

Aim To seek views of UK children's and adult hospices on the availability and challenges of providing services for young adults with life‐limiting conditions. Background Internationally there are a growing number of young adults with life‐limiting conditions and/or complex needs which are degenerative, progressive and diverse and involve complex life‐long symptom, medication management as well as palliative care. There are 55,721 young adults, aged 18‐40 in England, which continues to increase. The hospice sector is experiencing demands to extend services for this population despite concerns about the appropriateness of adult hospices and their nursing staff to provide care for the complex and unfamiliar conditions of this patient group. Evidence is needed of hospices’ views and the main challenges faced providing services for young adults. Design Descriptive cross‐sectional survey. Methods Children and adult hospices completed an online survey exploring service provision and their views of respite care for young adults with life‐limiting conditions from 18 years old and onward. Data were collected between October 2015‐February 2016. Findings Respondents (N=76 hospices) reported that children's hospices predominantly provided short breaks and end‐of‐life care; adult hospices provided mainly symptom management, end‐of‐life care and day services. Main challenges were: a lack of existing adult respite services; lack of funding and capacity; lack of a skilled workforce in adult hospices; and the need for better integrated service provision. Conclusion Examples of good collaborative working were reported. With an increasing population of young adults and pressure on families, it is vital that services work together to find sustainable solutions to the challenges

Thin disc, Thick Disc and Halo in a Simulated Galaxy

Within a cosmological hydrodynamical simulation, we form a disc galaxy with sub- components which can be assigned to a thin stellar disc, thick disk, and a low mass stellar halo via a chemical decomposition. The thin and thick disc populations so selected are distinct in their ages, kinematics, and metallicities. Thin disc stars are young (<6.6 Gyr), possess low velocity dispersion ({\sigma}U,V,W = 41, 31, 25 km/s), high [Fe/H], and low [O/Fe]. The thick disc stars are old (6.6<age<9.8 Gyrs), lag the thin disc by \sim21 km/s, possess higher velocity dispersion ({\sigma}U,V,W = 49, 44, 35 km/s), relatively low [Fe/H] and high [O/Fe]. The halo component comprises less than 4% of stars in the "solar annulus" of the simulation, has low metallicity, a velocity ellipsoid defined by ({\sigma}U,V,W = 62, 46, 45 km/s) and is formed primarily in-situ during an early merger epoch. Gas-rich mergers during this epoch play a major role in fuelling the formation of the old disc stars (the thick disc). This is consistent with studies which show that cold accretion is the main source of a disc galaxy's baryons. Our simulation initially forms a relatively short (scalelength \sim1.7 kpc at z=1) and kinematically hot disc, primarily from gas accreted during the galaxy's merger epoch. Far from being a competing formation scenario, migration is crucial for reconciling the short, hot, discs which form at high redshift in {\Lambda}CDM, with the properties of the thick disc at z=0. The thick disc, as defined by its abundances maintains its relatively short scale-length at z = 0 (2.31 kpc) compared with the total disc scale-length of 2.73 kpc. The inside-out nature of disc growth is imprinted the evolution of abundances such that the metal poor {\alpha}-young population has a larger scale-length (4.07 kpc) than the more chemically evolved metal rich {\alpha}-young population (2.74 kpc).Comment: Submitted to MNRAS. This version after helpful referee comments. Comments welcome to [email protected]

Talk the talk, walk the walk: Defining Critical Race Theory in research

Over the last decade there has been a noticeable growth in published works citing Critical Race Theory (CRT). This has led to a growth in interest in the UK of practical research projects utilising CRT as their framework. It is clear that research on 'race' is an emerging topic of study. What is less visible is a debate on how CRT is positioned in relation to methodic practice, substantive theory and epistemological underpinnings. The efficacy of categories of data gathering tools, both traditional and non-traditional is a discussion point here to explore the complexities underpinning decisions to advocate a CRT framework. Notwithstanding intersectional issues, a CRT methodology is recognisable by how philosophical, political and ethical questions are established and maintained in relation to racialised problematics. This paper examines these tensions in establishing CRT methodologies and explores some of the essential criteria for researchers to consider in utilising a CRT framework. © 2012 Copyright Taylor and Francis Group, LLC

Anti-cancer effects and mechanism of actions of aspirin analogues in the treatment of glioma cancer

INTRODUCTION: In the past 25 years only modest advancements in glioma treatment have been made, with patient prognosis and median survival time following diagnosis only increasing from 3 to 7 months. A substantial body of clinical and preclinical evidence has suggested a role for aspirin in the treatment of cancer with multiple mechanisms of action proposed including COX 2 inhibition, down regulation of EGFR expression, and NF-κB signaling affecting Bcl-2 expression. However, with serious side effects such as stroke and gastrointestinal bleeding, aspirin analogues with improved potency and side effect profiles are being developed. METHOD: Effects on cell viability following 24 hr incubation of four aspirin derivatives (PN508, 517, 526 and 529) were compared to cisplatin, aspirin and di-aspirin in four glioma cell lines (U87 MG, SVG P12, GOS – 3, and 1321N1), using the PrestoBlue assay, establishing IC50 and examining the time course of drug effects. RESULTS: All compounds were found to decrease cell viability in a concentration and time dependant manner. Significantly, the analogue PN517 (IC50 2mM) showed approximately a twofold increase in potency when compared to aspirin (3.7mM) and cisplatin (4.3mM) in U87 cells, with similar increased potency in SVG P12 cells. Other analogues demonstrated similar potency to aspirin and cisplatin. CONCLUSION: These results support the further development and characterization of novel NSAID derivatives for the treatment of glioma

International validation of a urinary biomarker panel for identification of active lupus nephritis in children.

Conventional markers of juvenile-onset systemic lupus erythematosus (JSLE) disease activity fail to adequately identify lupus nephritis (LN). While individual novel urine biomarkers are good at detecting LN flares, biomarker panels may improve diagnostic accuracy. The aim of this study was to assess the performance of a biomarker panel to identify active LN in two international JSLE cohorts.Novel urinary biomarkers, namely vascular cell adhesion molecule-1 (VCAM-1), monocyte chemoattractant protein 1 (MCP-1), lipocalin-like prostaglandin D synthase (LPGDS), transferrin (TF), ceruloplasmin, alpha-1-acid glycoprotein (AGP) and neutrophil gelatinase-associated lipocalin (NGAL), were quantified in a cross-sectional study that included participants of the UK JSLE Cohort Study (Cohort 1) and validated within the Einstein Lupus Cohort (Cohort 2). Binary logistic regression modelling and receiver operating characteristic curve analysis [area under the curve (AUC)] were used to identify and assess combinations of biomarkers for diagnostic accuracy.A total of 91 JSLE patients were recruited across both cohorts, of whom 31 (34 %) had active LN and 60 (66 %) had no LN. Urinary AGP, ceruloplasmin, VCAM-1, MCP-1 and LPGDS levels were significantly higher in those patients with active LN than in non-LN patients [all corrected p values (p c) < 0.05] across both cohorts. Urinary TF also differed between patient groups in Cohort 2 (p c = 0.001). Within Cohort 1, the optimal biomarker panel included AGP, ceruloplasmin, LPGDS and TF (AUC 0.920 for active LN identification). These results were validated in Cohort 2, with the same markers resulting in the optimal urine biomarker panel (AUC 0.991).In two international JSLE cohorts, urinary AGP, ceruloplasmin, LPGDS and TF demonstrate an 'excellent' ability for accurately identifying active LN in children