Riding the wake of a merging galaxy cluster

Using WHT OASIS integral field unit observations, we report the discovery of a thin plume of ionised gas extending from the brightest cluster galaxy in Abell 2146 to the sub-cluster X-ray cool core which is offset from the BCG by ~37 kpc. The plume is greater than 15 kpc long and less than 3 kpc wide. This plume is unique in that the cluster it is situated in is currently undergoing a major galaxy cluster merger. The brightest cluster galaxy is unusually located behind the X-ray shock front and in the wake of the ram pressure stripped X-ray cool core and evidence for recent disruption to the BCG is observed. We examine the gas and stellar morphology, the gas kinematics of the BCG and their relation to the X-ray gas. We propose that a causal link between the ionised gas plume and the offset X-ray cool core provides the simplest explanation for the formation of the plume. An interaction or merger between the BCG and another cluster galaxy is probably the cause of the offset.Comment: 14 pages, 18 figures, accepted for publication in MNRA

Identifying the role of environmental drivers in organic carbon export from a forested peat catchment

Carbon export in streams draining peat catchments represents a potential loss of carbon from long-term stores to downstream aquatic systems and ultimately, through mineralisation, to the atmosphere. There is now a large body of evidence that dissolved organic carbon (DOC) export has increased significantly in recent decades at many sites, although there is still debate about the drivers of this increase. In this study, DOC export and particulate organic carbon (POC) export were quantified from a forested peatland catchment in the west of Ireland over two years at a fine temporal resolution. The principle drivers of change in stream DOC and POC concentrations were investigated using a general additive modelling (GAM) approach. The study period included drought conditions in the early summer of 2010 and clearfelling of some commercial forestry in early 2011. The results indicated that annual loads of 9.5 t DOC km2 year− 1 and 6.2 t POC km2 year− 1 were exported from the catchment in 2010. This combined annual load of 15.7 t C km2 year− 1 would represent between 0.01% and 0.02% of typical estimates for peat soil carbon storage in the region. Soil temperature, river discharge and drought explained 59.7% the deviance in DOC concentrations, while soil temperature, river discharge, and rainfall were the significant drivers of variation in POC concentrations, explaining 58.3% of deviance. Although clearfelling was not a significant factor in either model, large spikes in POC export occurred in 2011 after the first forestry clearance. The results illustrate the complexity of the interactions between climate and land management in driving stream water carbon export. They also highlight the sensitivity of peatland carbon stores to changes in temperature and precipitation, which are projected to be more extreme and variable under future climate scenarios.Marine Institute, Dundalk Institute of Technolog

Black hole candidate XTE J1752-223: Swift observations of canonical states during outburst

We present Swift broadband observations of the recently discovered black hole candidate, X-ray transient, XTE J1752-223, obtained over the period of outburst from October 2009 to June 2010. From Swift-UVOT data we confirm the presence of an optical counterpart which displays variability correlated, in the soft state, to the X-ray emission observed by Swift-XRT. The optical counterpart also displays hysteretical behaviour between the states not normally observed in the optical bands, suggesting a possible contribution from a synchrotron emitting jet to the optical emission in the rising hard state. We offer a purely phenomenological treatment of the spectra as an indication of the canonical spectral state of the source during different periods of the outburst. We find that the high energy hardness-intensity diagrams over two separate bands follows the canonical behavior, confirming the spectral states. Our XRT timing analysis shows that in the hard state there is significant variability below 10Hz which is more pronounced at low energies, while during the soft state the level of variability is consistent with being minimal. These properties of XTE J1752-223 support its candidacy as a black hole in the Galactic centre region.Comment: 8 pages, 8 figures; MNRAS in pres

Ultraviolet Spectroscopy of Asteroid (4) Vesta

We report a comprehensive review of the UV-visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift Gamma-ray Burst Observatory with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm are derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope as measured between 240 and 320 nm in the ultraviolet displays a sharp minimum near a sub-Earth longitude of 20^{\circ}, and maximum in the eastern hemisphere. This is consistent with the longitudinal distribution of the spectral slope in the visible wavelength. The photometric uncertainty in the ultraviolet is ~20%, and in the visible wavelengths it is better than 10%. The amplitude of Vesta's rotational lightcurves is ~10% throughout the range of wavelengths we observed, but is smaller at 950 nm (~6%) near the 1-\mum band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/near-infrared lightcurves with respect to sub-Earth longitude. Vesta's average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible, and near-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies a lack of global space weathering on Vesta, as previously inferred from visible-near-infrared data.Comment: 44 pages, 5 figures, 1 tabl

The interplay between extrinsic and intrinsic factors in determining migration decisions in brown trout (Salmo trutta): An experimental study

Many species are capable of facultative migration, but the relative roles of extrinsic versus intrinsic factors in generating diverse migratory tactics remain unclear. Here we explore the proximate drivers of facultative migration in brown trout in an experimental laboratory setting. The effects of reduced food, as a putative environmental cue, were examined in two populations: one that exhibits high rates of anadromy (sea-migration) in nature, and one that does not exhibit anadromy in nature. Juveniles derived from wild-caught parents were reared for two years under four environmental treatments: low food in years 1 and 2 (Low-Low); high food in years 1 and 2 (High-High), low food in year 1 and high in year 2 (Low-High), and vice versa (High-Low). Food restriction had a significant effect on migratory tactics, with the frequency of smolts (juveniles choosing migration) highest in the Low-Low treatment in both populations. No individuals became smolts in the High-High treatment, and intermediate smolting rates were observed in the Low-High and High-Low treatments. Higher overall smolting rates in the naturally anadromous population suggested an inherited component to anadromy/migration decisions, but both populations showed variability in migratory tactics. Importantly, some fish from the naturally non-anadromous population became smolts in the experiment, implying the capacity for migration was lying ‘dormant’, but they exhibited lower hypo-osmoregulatory function than smolts from the naturally anadromous population. Tactic frequencies in the naturally anadromous population were more affected by food in the 2nd year, while food in the 1st year appeared more important for the naturally non-anadromous population. Migratory tactics were also related to sex, but underpinned in both sexes by growth in key periods, size and energetic state. Collectively these results reveal how migration decisions are shaped by a complex interplay between extrinsic and intrinsic factors, informing our ability to predict how facultatively migratory populations will respond to environmental change

A multi-proxy palaeolimnological study to reconstruct the evolution of a coastal brackish lake (Lough Furnace, Ireland) during the late Holocene

Peer-reviewed. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Palaeogeography, Palaeoclimatology, Palaeoecology, Vol 383-384, August 2013, Pages 1-15. To access the final edited and published work see doi: http://dx.doi.org/10.1016/j.palaeo.2013.04.016This study examines the evolution of Lough Furnace, a coastal brackish lake in the west of Ireland, using high-resolution sensors in the water column and palaeolimnological examination of the sediment archive. Palaeoenvironmental reconstructions suggest that meromixis formed as a result of sea level rise prior to ca. 4000 cal. yr BP. Increased seawater inflow has progressively led to permanent water stratification, which caused the onset of anoxia, making the monimolimnion a harsh environment for biological life. Diatom floristic interpretations suggest a progressive upcore increase in salinity, which is paralleled by a reduction in cladocera remains. Diagenetic processes have not altered the sediment organic matter signature. Organic matter mainly derives from freshwater DOC and appears to be linked to the presence of peat bogs in the catchment as confirmed by the C/N ratio. Upcore variations in the C/N ratio with a ca. 800-year periodicity have been interpreted as the result of alternating dry and wet climatic phases during the late Holocene, which appear synchronous with the NAO and long-term solar cycles. The current hydrology is largely controlled by freshwater inflow, which determines permanent meromictic conditions. Overturns are rare, requiring a specific combination of factors such as exceptionally dry and warm summers followed by cool autumns. According to the climate projections for the next century in Ireland, permanent meromictic conditions will probably continue