Reality and Myths of AGN Feedback

Feedback from active galactic nuclei (AGN) remains controversial despite its wide acceptance as necessary to regulate massive galaxy growth. A dedicated workshop was held on 16-20 October 2017 at the Lorentz Center in Leiden to distinguish between the reality and myths of AGN feedback from the observational side. Here, we summarize briefly all the sessions and outcome of the stimulating workshop. More details on the outcome of the discussions are provided in a series of articles.Comment: Author's version of Nature Astronomy Meeting Report. View-only version of full text publicly available at this link: http://rdcu.be/HUT

Minocycline differentially modulates human spatial memory systems

Microglia play a critical role in many processes fundamental to learning and memory in health and are implicated in Alzheimer’s pathogenesis. Minocycline, a centrally-penetrant tetracycline antibiotic, inhibits microglial activation and enhances long-term potentiation, synaptic plasticity, neurogenesis and hippocampal-dependent spatial memory in rodents, leading to clinical trials in human neurodegenerative diseases. However, the effects of minocycline on human memory have not previously been investigated. Utilising a double-blind, randomised crossover study design, we recruited 20 healthy male participants (mean 24.6 ± 5.0 years) who were each tested in two experimental sessions: once after 3 days of Minocycline 150 mg (twice daily), and once 3 days of placebo (identical administration). During each session, all completed an fMRI task designed to tap boundary- and landmark-based navigation (thought to rely on hippocampal and striatal learning mechanisms respectively). Given the rodent literature, we hypothesised that minocycline would selectively modulate hippocampal learning. In line with this, minocycline biased use of boundary- compared to landmark-based information (t980 = 3.140, p = 0.002). However, though this marginally improved performance for boundary-based objects (t980 = 1.972, p = 0.049), it was outweighed by impaired landmark-based navigation (t980 = 6.374, p < 0.001) resulting in an overall performance decrease (t980 = 3.295, p = 0.001). Furthermore, against expectations, minocycline significantly reduced activity during memory encoding in the right caudate (t977 = 2.992, p = 0.003) and five other cortical regions, with no significant effect in the hippocampus. In summary, minocycline impaired human spatial memory performance, likely through disruption of striatal processing resulting in greater biasing towards reliance on boundary-based navigation

National Eclipse Weather Experiment use and evaluation of a citizen science tool for schools outreach

The National Eclipse Weather Experiment (NEWEx) was a citizen science project for atmospheric data collection from the partial solar eclipse of 20th March 2015. Its role as a tool for schools’ outreach is discussed here, in seeking to bridge the gap between self-identification with the role of a scientist and engagement with science, technology, engineering and maths (STEM) subjects. (The science data generated has had other uses beyond this, explored elsewhere.) We describe the design of webforms for weather data collection, and the use of several external partners for the dissemination of the project nationwide. We estimate that up to 3500 pupils and teachers took part in this experiment, through the 127 schools’ postcodes identified in the data submission. Further analysis revealed that 43.3% of the schools were primary schools and 35.4% secondary. 96.3% of participants reported themselves as “captivated” or “inspired” by NEWEx. We also found that 60% of schools who took part in the experiment lie within the highest quintiles of engagement with higher education, which emphasises the need for the scientific community to be creative when using citizen science to target minority audiences

A Connection between Obscuration and Star Formation in Luminous Quasars

We present a measurement of the star formation properties of a uniform sample of mid-IR selected, unobscured and obscured quasars (QSO1s and QSO2s) in the Bo\ otes survey region. We use an spectral energy distribution (SED) analysis for photometric data spanning optical to far-IR wavelengths to decompose AGN and host galaxy components. We find that when compared to a matched sample of QSO1s, the QSO2s have higher far-IR detection fractions, far-IR fluxes and infrared star formation luminosities (LSFIR) by a factor of ∼2. Correspondingly, we show that the AGN obscured fraction rises from 0.3 to 0.7 between 4−40×1011L⊙. We also find evidence associating the absorption in the X-ray emission with the presence of far-IR emitting dust. Overall, these results are consistent with galaxy evolution models in which quasar obscurations can be associated with a dust-enshrouded starburst galaxie

Identifying robust response options to manage environmental change using an ecosystem approach:a stress-testing case study for the UK

A diverse range of response options was evaluated in terms of their utility for sustaining ecosystem services in the UK. Robustness of response options was investigated by applying a ‘stress-testing’ method which evaluated expected performance against combined scenarios of socioeconomic and climate change. Based upon stakeholder feedback, a reference scenario representing current trends in climate and socioeconomic drivers (‘business-as-usual’) was used as a dynamic baseline against which to compare results of other scenarios. The robustness of response options was evaluated by their utility in different environmental and social contexts as represented by the scenarios, and linked to their adaptability to adjust to changing conditions. Key findings demonstrate that adaptability becomes increasingly valuable as the magnitude and rate of future change diverges from current trends. Stress-testing also revealed that individual responses in isolation are unlikely to be robust meaning there are advantages from integrating cohesive combinations (bundles) of response options to maximise their individual strengths and compensate for weaknesses. This identifies a role for both top-down and bottom-up responses, including regulation, spatial targeting, incentives and partnership initiatives, and their use in combination through integrated assessment and planning consistent with the adoption of an Ecosystem Approach. Stress-testing approaches can have an important role in future-proofing policy appraisals but important knowledge gaps remain, especially for cultural and supporting ecosystem services. Finally, barriers and enablers to the implementation of more integrated long-term adaptive responses were identified drawing on the ‘4 Is’ (Institutions, Information, Incentives, Identity) conceptual framework. This highlighted the crucial but usually understated role of identity in promoting ownership and uptake of responses

Saturation of intersubband transitions in p-doped GaAs/AlGaAs quantum wells

Optical saturation experiments have been performed on hh1-hh2 intersubband transitions in two samples of p-doped GaAs/AlGaAs quantum wells. The transitions had energies of 183 and 160 meV and the measured population relaxation times were 2±1.5 and 0.3±0.1 ps, respectively. Modeling of the quantum wells with a 6×6 k·p method shows that intersubband scattering by LO phonons can account for these relaxation times. The valence bandstructure is typically more complicated than the conduction bandstructure in a quantum well but these measurements show that LO phonons are the dominant intersubband scattering mechanism in both cases

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr – Part 2: A new reconstruction of the interplanetary magnetic field

We present a new reconstruction of the interplanetary magnetic field (IMF, B) for 1846–2012 with a full analysis of errors, based on the homogeneously constructed IDV(1d)composite of geomagnetic activity presented in Part 1 (Lockwood et al., 2013a). Analysis of the dependence of the commonly used geomagnetic indices on solar wind parameters is presented which helps explain why annual means of interdiurnal range data, such as the new composite, depend only on the IMF with only a very weak influence of the solar wind flow speed. The best results are obtained using a polynomial (rather than a linear) fit of the form B = χ · (IDV(1d) − β)α with best-fit coefficients χ = 3.469, β = 1.393 nT, and α = 0.420. The results are contrasted with the reconstruction of the IMF since 1835 by Svalgaard and Cliver (2010)

High-Energy X-ray Imaging of the Pulsar Wind Nebula MSH~15-52: Constraints on Particle Acceleration and Transport

We present the first images of the pulsar wind nebula (PWN) MSH 15-52 in the hard X-ray band (>8 keV), as measured with the Nuclear Spectroscopic Telescope Array (NuSTAR). Overall, the morphology of the PWN as measured by NuSTAR in the 3-7 keV band is similar to that seen in Chandra high-resolution imaging. However, the spatial extent decreases with energy, which we attribute to synchrotron energy losses as the particles move away from the shock. The hard-band maps show a relative deficit of counts in the northern region towards the RCW 89 thermal remnant, with significant asymmetry. We find that the integrated PWN spectra measured with NuSTAR and Chandra suggest that there is a spectral break at 6 keV which may be explained by a break in the synchrotron-emitting electron distribution at ~200 TeV and/or imperfect cross calibration. We also measure spatially resolved spectra, showing that the spectrum of the PWN softens away from the central pulsar B1509-58, and that there exists a roughly sinusoidal variation of spectral hardness in the azimuthal direction. We discuss the results using particle flow models. We find non-monotonic structure in the variation with distance of spectral hardness within 50" of the pulsar moving in the jet direction, which may imply particle and magnetic-field compression by magnetic hoop stress as previously suggested for this source. We also present 2-D maps of spectral parameters and find an interesting shell-like structure in the NH map. We discuss possible origins of the shell-like structure and their implications.Comment: 15 pages, 9 figures, accepted for publication in Ap

Double Neutron Star Systems and Natal Neutron Star Kicks

We study the four double neutron star systems found in the Galactic disk in terms of the orbital characteristics of their immediate progenitors and the natal kicks imparted to neutron stars. Analysis of the effect of the second supernova explosion on the orbital dynamics, combined with recent results from simulations of rapid accretion onto neutron stars lead us to conclude that the observed systems could not have been formed had the explosion been symmetric. Their formation becomes possible if kicks are imparted to the radio-pulsar companions at birth. We identify the constraints imposed on the immediate progenitors of the observed double neutron stars and calculate the ranges within which their binary characteristics (orbital separations and masses of the exploding stars) are restricted. We also study the dependence of these limits on the magnitude of the kick velocity and the time elapsed since the second explosion. For each of the double neutron stars, we derive a minimum kick magnitude required for their formation, and for the two systems in close orbits we find it to exceed 200km/s. Lower limits are also set to the center-of-mass velocities of double neutron stars, and we find them to be consistent with the current proper motion observations.Comment: 25 pages, 6 figs (9 parts), 4 tables, AASTeX, Accepted in Ap