Dynamics of avian species and functional diversity in secondary tropical forests

Deforestation for agriculture in the tropics, followed by abandonment, has resulted in large areas of secondary forest. Some authors have suggested that this secondary regrowth could help prevent mass extinction in the tropics by providing habitat for forest species. However, there is little generalised understanding of the biodiversity value of secondary forest. To address this knowledge gap, we conducted an analysis of avian responses to secondary forest succession, comparing data from 44 tropical secondary forest sites with nearby primary forest sites and investigating both species and functional diversity based metrics. Total species richness in secondary forests was 12% lower than in primary forests and was not related to secondary forest age. In contrast, forest specialist species richness increased with time since disturbance, reaching 99% of primary forest values after 100 years. In terms of functional diversity, functional dispersion (FDis) and functional divergence (FDiv) were similar in primary and secondary forests. However, functional evenness (FEve) was 5% higher in secondary than in primary forests. The standardized effect size of functional diversity (sesFD) was higher in young secondary forests than primary forests and declined with time since disturbance. Overall, these results suggest that secondary tropical forests can support provision of ecosystem services but that these services may be less stable in young forests. Therefore, secondary tropical forests, particularly older regrowth, have biodiversity value and can support important ecosystem functions. These secondary forests should be protected from further disturbance but preserving primary forest is vital for supporting overall and forest specialist species richness

Group finding in the stellar halo using M-giants in 2MASS: An extended view of the Pisces Overdensity?

A density based hierarchical group-finding algorithm is used to identify stellar halo structures in a catalog of M-giants from the Two Micron All Sky Survey (2MASS). The intrinsic brightness of M-giant stars means that this catalog probes deep into the halo where substructures are expected to be abundant and easy to detect. Our analysis reveals 16 structures at high Galactic latitude (greater than 15 degree), of which 10 have been previously identified. Among the six new structures two could plausibly be due to masks applied to the data, one is associated with a strong extinction region and one is probably a part of the Monoceros ring. Another one originates at low latitudes, suggesting some contamination from disk stars, but also shows protrusions extending to high latitudes, implying that it could be a real feature in the stellar halo. The last remaining structure is free from the defects discussed above and hence is very likely a satellite remnant. Although the extinction in the direction of the structure is very low, the structure does match a low temperature feature in the dust maps. While this casts some doubt on its origin, the low temperature feature could plausibly be due to real dust in the structure itself. The angular position and distance of this structure encompass the Pisces overdensity traced by RR Lyraes in Stripe 82 of the Sloan Digital Sky Survey (SDSS). However, the 2MASS M-giants indicate that the structure is much more extended than what is visible with the SDSS, with the point of peak density lying just outside Stripe 82. The morphology of the structure is more like a cloud than a stream and reminiscent of that seen in simulations of satellites disrupting along highly eccentric orbits.Comment: Accepted for publication in Ap

Carbon pools recover more quickly than plant biodiversity in tropical secondary forests.

Although increasing efforts are being made to restore tropical forests, little information is available regarding the time scales required for carbon and plant biodiversity to recover to the values associated with undisturbed forests. To address this knowledge gap, we carried out a meta-analysis comparing data from more than 600 secondary tropical forest sites with nearby undisturbed reference forests. Above-ground biomass approached equivalence to reference values within 80 years since last disturbance, whereas below-ground biomass took longer to recover. Soil carbon content showed little relationship with time since disturbance. Tree species richness recovered after about 50 years. By contrast, epiphyte richness did not reach equivalence to undisturbed forests. The proportion of undisturbed forest trees and epiphyte species found in secondary forests was low and changed little over time. Our results indicate that carbon pools and biodiversity show different recovery rates under passive, secondary succession and that colonization by undisturbed forest plant species is slow. Initiatives such as the Convention on Biological Diversity and REDD+ should therefore encourage active management to help to achieve their aims of restoring both carbon and biodiversity in tropical forests

Stealth Galaxies in the Halo of the Milky Way

We predict that there is a population of low-luminosity dwarf galaxies orbiting within the halo of the Milky Way that have surface brightnesses low enough to have escaped detection in star-count surveys. The overall count of stealth galaxies is sensitive to the presence (or lack) of a low-mass threshold in galaxy formation. These systems have luminosities and stellar velocity dispersions that are similar to those of known ultrafaint dwarf galaxies but they have more extended stellar distributions (half light radii greater than about 100 pc) because they inhabit dark subhalos that are slightly less massive than their higher surface brightness counterparts. As a result, the typical peak surface brightness is fainter than 30 mag per square arcsec. One implication is that the inferred common mass scale for Milky Way dwarfs may be an artifact of selection bias. If there is no sharp threshold in galaxy formation at low halo mass, then ultrafaint galaxies like Segue 1 represent the high-mass, early forming tail of a much larger population of objects that could number in the hundreds and have typical peak circular velocities of about 8 km/s and masses within 300 pc of about 5 million solar masses. Alternatively, if we impose a low-mass threshold in galaxy formation in order to explain the unexpectedly high densities of the ultrafaint dwarfs, then we expect only a handful of stealth galaxies in the halo of the Milky Way. A complete census of these objects will require deeper sky surveys, 30m-class follow-up telescopes, and more refined methods to identify extended, self-bound groupings of stars in the halo.Comment: 12 pages, 7 figures, accepted by ApJ. Several crucial references added and the discussion has been expanded. Conclusions are unchanged

On the assembly of the Milky Way dwarf satellites and their common mass scale

We use a particle tagging technique to dynamically populate the N-body Via Lactea II high-resolution simulation with stars. The method is calibrated using the observed luminosity function of Milky Way satellites and the concentration of their stellar populations, and self-consistently follows the accretion and disruption of progenitor dwarfs and the build-up of the stellar halo in a cosmological "live host". Simple prescriptions for assigning stellar populations to collisionless particles are able to reproduce many properties of the observed Milky Way halo and its surviving dwarf satellites, like velocity dispersions, sizes, brightness profiles, metallicities, and spatial distribution. Our model predicts the existence of approximately 1,850 subhalos harboring "extremely faint" satellites (with mass-to-light ratios >5,000) lying beyond the Sloan Digital Sky Survey detection threshold. Of these, about 20 are "first galaxies", i.e. satellites that formed a stellar mass above 10 Msun before redshift 9. The ten most luminous satellites (L> 1e6 Lsun) in the simulation are hosted by subhalos with peak circular velocities today in the range V_max=10-40 km/s that have shed between 80% and 99% of their dark mass after being accreted at redshifts 1.7< z <4.6. The satellite maximum circular velocity and stellar line-of-sight velocity dispersion today follow the relation V_max=2.2 sigma_los. We apply a standard mass estimation algorithm based on Jeans modelling of the line-of-sight velocity dispersion profiles to the simulated dwarf spheroidals, and test the accuracy of this technique. The inner (within 300 pc) mass-luminosity relation for currently detectable satellites is nearly flat in our model, in qualitative agreement with the "common mass scale" found in Milky Way dwarfs. We do, however, predict a weak, but significant positive correlation for these objects: M_300 ~L^{0.088 \pm 0.024}.Comment: 14 pages, 9 figures, accepted for publication in The Astrophysical Journa

Local Group Dwarf Spheroidals: Correlated Deviations from the Baryonic Tully-Fisher Relation

Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption in the sense that fainter, more elliptical, and tidally more susceptible dwarfs deviate farther from the BTFR. These correlations disfavor stochastic processes and suggest a role for tidal effects. We identify a test to distinguish between the {\Lambda}CDM and MOND based on the orbits of the dwarf satellites of the Milky Way and how stars are lost from them.Comment: 16 pages, 7 figures. Submitted to ApJ. Revised in response to referee repor

International Mindedness in Practice: The Evidence from International Baccalaureate Schools

International Mindedness is an overarching construct related to multilingualism, intercultural understanding and global engagement (Hill, 2012). The concept is central to the International Baccalaureate (IB) and sits at the heart of its education policies and programmes. The aim of this research study was to examine systematically how schools offering International Baccalaureate programmes (so-called IB World Schools) conceptualise, develop, assess and evaluate International Mindedness (IM), and to understand related challenges and problems, with a view to improving practice in schools. Nine case study schools, identified as being strongly engaged with IM, were selected for in-depth scrutiny of their practice and thinking related to IM. Conclusions from this study will also inform on-going debate on other similar global initiatives.</p

Heated Disc Stars in the Stellar Halo

Minor accretion events with mass ratio M_sat : M_host ~ 1:10 are common in the context of LCDM cosmology. We use high-resolution simulations of Galaxy-analogue systems to show that these mergers can dynamically eject disk stars into a diffuse light component that resembles a stellar halo both spatially and kinematically. For a variety of orbital configurations, we find that ~3-5e8 M_sun of primary stellar disk material is ejected to a distance larger than 5 kpc above the galactic plane. This ejected contribution is similar to the mass contributed by the tidal disruption of the satellite galaxy itself, though it is less extended. If we restrict our analysis to the approximate solar neighborhood in the disk plane, we find that ~1% of the initial disk stars in that region would be classified kinematically as halo stars. Our results suggest that the inner parts of galactic stellar halos contain ancient disk stars and that these stars may have been liberated in the very same events that delivered material to the outer stellar halo.Comment: 9 pages, 5 figures; MNRAS accepte

Orbiting Circum-galactic Gas as a Signature of Cosmological Accretion

We use cosmological SPH simulations to study the kinematic signatures of cool gas accretion onto a pair of well-resolved galaxy halos. Cold-flow streams and gas-rich mergers produce a circum-galactic component of cool gas that generally orbits with high angular momentum about the galaxy halo before falling in to build the disk. This signature of cosmological accretion should be observable using background-object absorption line studies as features that are offset from the galaxy's systemic velocity by ~100 km/s. Accreted gas typically co-rotates with the central disk in the form of a warped, extended cold flow disk, such that the observed velocity offset is in the same direction as galaxy rotation, appearing in sight lines that avoid the galactic poles. This prediction provides a means to observationally distinguish accreted gas from outflow gas: the accreted gas will show large one-sided velocity offsets in absorption line studies while radial/bi-conical outflows will not (except possibly in special polar projections). This rotation signature has already been seen in studies of intermediate redshift galaxy-absorber pairs; we suggest that these observations may be among the first to provide indirect observational evidence for cold accretion onto galactic halos. Cold mode halo gas typically has ~3-5 times more specific angular momentum than the dark matter. The associated cold mode disk configurations are likely related to extended HI/XUV disks seen around galaxies in the local universe. The fraction of galaxies with extended cold flow disks and associated offset absorption-line gas should decrease around bright galaxies at low redshift, as cold mode accretion dies out.Comment: 15 pages, 9 figures, edited to match published version. Includes expanded discussion, with primary results unchange

Qudit surface codes and gauge theory with finite cyclic groups

Surface codes describe quantum memory stored as a global property of interacting spins on a surface. The state space is fixed by a complete set of quasi-local stabilizer operators and the code dimension depends on the first homology group of the surface complex. These code states can be actively stabilized by measurements or, alternatively, can be prepared by cooling to the ground subspace of a quasi-local spin Hamiltonian. In the case of spin-1/2 (qubit) lattices, such ground states have been proposed as topologically protected memory for qubits. We extend these constructions to lattices or more generally cell complexes with qudits, either of prime level or of level $d^\ell$ for $d$ prime and $\ell \geq 0$, and therefore under tensor decomposition, to arbitrary finite levels. The Hamiltonian describes an exact $\mathbb{Z}_d\cong\mathbb{Z}/d\mathbb{Z}$ gauge theory whose excitations correspond to abelian anyons. We provide protocols for qudit storage and retrieval and propose an interferometric verification of topological order by measuring quasi-particle statistics.Comment: 26 pages, 5 figure