Tide gauge data are used to estimate trends in global sea level for the period from 1955 to 2007. Linear trends over 15-yr segments are computed for each tide gauge record, averaged over latitude ...bands, and combined to form an area-weighted global mean trend. The uncertainty of the global trend is specified as a sampling error plus a random vertical land motion component, but land motion corrections do not change the results. The average global sea level trend for the time segments centered on 1962–90 is 1.5 ± 0.5 mm yr−1(standard error), in agreement with previous estimates of late twentieth-century sea level rise. After 1990, the global trend increases to the most recent rate of 3.2 ± 0.4 mm yr−1, matching estimates obtained from satellite altimetry. The acceleration is distinct from decadal variations in global sea level that have been reported in previous studies. Increased rates in the tropical and southern oceans primarily account for the acceleration. The timing of the global acceleration corresponds to similar sea level trend changes associated with upper ocean heat content and ice melt.
Wave setup over a Pacific Island fringing reef Vetter, O.; Becker, J. M.; Merrifield, M. A. ...
Journal of Geophysical Research,
December 2010, Letnik:
115, Številka:
C12
Journal Article
Recenzirano
Odprti dostop
Measurements obtained across a shore‐attached, fringing reef on the southeast coast of the island of Guam are examined to determine the relationship between incident waves and wave‐driven setup ...during storm and nonstorm conditions. Wave setup on the reef flat correlates well (r > 0.95) and scales near the shore as approximately 35% of the incident root mean square wave height in 8 m water depth. Waves generated by tropical storm Man‐Yi result in a 1.3 m setup during the peak of the storm. Predictions based on traditional setup theory (steady state, inviscid cross‐shore momentum and depth‐limited wave breaking) and an idealized model of localized wave breaking at the fore reef are in agreement with the observations. The reef flat setup is used to estimate a similarity parameter at breaking that is in agreement with observations from a steeply sloping sandy beach. A weak (∼10%) increase in setup is observed across the reef flat during wave events. The inclusion of bottom stress in the cross‐shore momentum balance may account for a portion of this signal, but this assessment is inconclusive as the reef flat currents in some cases are in the wrong direction to account for the increase. An independent check of fringing reef setup dynamics is carried out for measurements at the neighboring island of Saipan with good agreement.
ABSTRACT In order to examine where, how and why the quenching of star formation begins in the outskirts of galaxy clusters, we investigate the de-projected radial distribution of a large sample of ...quenched and star-forming galaxies (SFGs) out to 30R500 around clusters. We identify the SFG sample using radio continuum emission from the Low-Frequency Array Two-metre Sky Survey. We find that the SFG fraction starts to decrease from the field fraction as far out as 10R500, well outside the virial radius of the clusters. We investigate how the SFG fraction depends on both large-scale and local environments, using radial distance from a cluster to characterise the former, and distance from fifth nearest neighbour for the latter. The fraction of SFGs in high-density local environments is consistently lower than that found in low-density local environments, indicating that galaxies’ immediate surroundings have a significant impact on star formation. However, for high-mass galaxies – and low mass galaxies to a lesser extent – high-density local environments appear to act as a protective barrier for those SFGs that survived this pre-processing, shielding them from the external quenching mechanisms of the cluster outskirts. For those galaxies that are not in a dense local environment, the global environment causes the fraction of SFGs to decrease toward the cluster centre in a manner that is independent of galaxy mass. Thus, the fraction of SFGs depends on quite a complex interplay between the galaxies’ mass, their local environment, and their more global cluster-centric distance.
We study the dynamics of faint stellar substructures around the Umbrella Galaxy, NGC 4651, which hosts a dramatic system of streams and shells formed through the tidal disruption of a nucleated dwarf ...elliptical galaxy. We elucidate the basic characteristics of the system (colours, luminosities, stellar masses) using multiband Subaru/Suprime-Cam images. The implied stellar mass ratio of the ongoing merger event is ∼1:50. We identify candidate kinematic tracers (globular clusters, planetary nebulae, H ii regions) and follow up a subset with Keck/DEIMOS (DEep Imaging Multi-object Spectrograph) spectroscopy to obtain velocities. We find that 15 of the tracers are likely associated with halo substructures, including the probable stream progenitor nucleus. These objects delineate a kinematically cold feature in position–velocity phase space. We model the stream using single test particle orbits, plus a rescaled pre-existing N-body simulation. We infer a very eccentric orbit with a period of ∼0.35 Gyr and turning points at ∼2–4 and ∼40 kpc, implying a recent passage of the satellite through the disc, which may have provoked the visible disturbances in the host galaxy. This work confirms that the kinematics of low surface brightness substructures can be recovered and modelled using discrete tracers – a breakthrough that opens up a fresh avenue for unravelling the detailed physics of minor merging.
This paper is the first in a series in which we perform an extensive comparison of various galaxy-based cluster mass estimation techniques that utilize the positions, velocities and colours of ...galaxies. Our primary aim is to test the performance of these cluster mass estimation techniques on a diverse set of models that will increase in complexity. We begin by providing participating methods with data from a simple model that delivers idealized clusters, enabling us to quantify the underlying scatter intrinsic to these mass estimation techniques. The mock catalogue is based on a Halo Occupation Distribution (HOD) model that assumes spherical Navarro, Frenk and White (NFW) haloes truncated at R
200, with no substructure nor colour segregation, and with isotropic, isothermal Maxwellian velocities. We find that, above 1014M⊙, recovered cluster masses are correlated with the true underlying cluster mass with an intrinsic scatter of typically a factor of 2. Below 1014M⊙, the scatter rises as the number of member galaxies drops and rapidly approaches an order of magnitude. We find that richness-based methods deliver the lowest scatter, but it is not clear whether such accuracy may simply be the result of using an over-simplistic model to populate the galaxies in their haloes. Even when given the true cluster membership, large scatter is observed for the majority non-richness-based approaches, suggesting that mass reconstruction with a low number of dynamical tracers is inherently problematic.
We present new planetary nebulae (PNe) positions, radial velocities and magnitudes for six early-type galaxies obtained with the Planetary Nebulae Spectrograph (PNS), along with derived ...two-dimensional velocity and velocity dispersion fields, and the α parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for three galaxies in the sample, obtained with the FOcal Reducer and low dispersion Spectrograph (FORS2) at the Very Large Telescope (VLT).
We extend this study to include additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, including previous PNS studies, in order to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar absorption-line kinematics to typically several and up to 8 effective radii.
The combination of photometry, absorption-line and PNe kinematics shows (i) a good agreement between the PNe number density distribution and the stellar surface brightness in the region where the two data sets overlap; (ii) a good agreement between PNe and absorption-line kinematics; (iii) that the mean rms velocity profiles fall into two groups, with part of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles; (iv) a larger variety of velocity dispersion radial profiles; (v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotator galaxies; (vi) that outer haloes are characterized by more complex radial profiles of the specific angular momentum-related λR parameter than observed within 1 R
e; (vii) that many objects are more rotationally dominated at large radii than in their central parts and (viii) that the halo kinematics are correlated with other galaxy properties, such as total B band and X-ray luminosity, isophotal shape, total stellar mass, V/σ and α parameter, with a clear separation between fast and slow rotators.
Wave‐driven extreme water levels are examined for coastlines protected by fringing reefs using field observations obtained in the Republic of the Marshall Islands. The 2% exceedence water level near ...the shoreline due to waves is estimated empirically for the study sites from breaking wave height at the outer reef and by combining separate contributions from setup, sea and swell, and infragravity waves, which are estimated based on breaking wave height and water level over the reef flat. Although each component exhibits a tidal dependence, they sum to yield a 2% exceedence level that does not. A hindcast based on the breaking wave height parameterization is used to assess factors leading to flooding at Roi‐Namur caused by an energetic swell event during December 2008. Extreme water levels similar to December 2008 are projected to increase significantly with rising sea level as more wave and tide events combine to exceed inundation threshold levels.
Key PointsWaves are a major contributor to extreme sea levels at island shorelinesFringing reefs exert a strong control on extreme wave‐driven water levelsExtreme water levels at atolls will increase significantly with sea level rise
ABSTRACT In this work, we use 8 years of deep near-infrared imaging to select and study a new set of 601 active galaxies identified through long-term near-infrared (NIR) variability in the UKIDSS ...Ultra Deep Survey (UDS). These objects are compared to 710 X-ray bright Active Galactic Nuclei (AGN) detected by the Chandra X-ray observatory. We show that infrared variability and X-ray emission select distinct sets of active galaxies, finding only a 37 per cent overlap of galaxies detected by both techniques and confirming NIR-variable AGN to be typically X-ray quiet. Examining the mass functions of the active galaxies shows that NIR variability detects AGN activity in galaxies over a significantly wider range of host stellar mass compared to X-ray detection. For example, at z ∼ 1, variable AGN are identified among approximately 1 per cent of galaxies in a roughly flat distribution above the stellar mass completeness limit ($\gt 10^{9}\rm \, {\rm M}_{\odot }$), while X-ray detection primarily identifies AGN in galaxies of higher mass ($\gt 10^{10}\rm \, {\rm M}_{\odot }$). We conclude that long-term near-infrared variability provides an important new tool for obtaining more complete samples of AGN in deep survey fields.
This paper is the second in a series in which we perform an extensive comparison of various galaxy-based cluster mass estimation techniques that utilize the positions, velocities and colours of ...galaxies. Our aim is to quantify the scatter, systematic bias and completeness of cluster masses derived from a diverse set of 25 galaxy-based methods using two contrasting mock galaxy catalogues based on a sophisticated halo occupation model and a semi-analytic model. Analysing 968 clusters, we find a wide range in the rms errors in log M
200c delivered by the different methods (0.18–1.08 dex, i.e. a factor of ∼1.5–12), with abundance-matching and richness methods providing the best results, irrespective of the input model assumptions. In addition, certain methods produce a significant number of catastrophic cases where the mass is under- or overestimated by a factor greater than 10. Given the steeply falling high-mass end of the cluster mass function, we recommend that richness- or abundance-matching-based methods are used in conjunction with these methods as a sanity check for studies selecting high-mass clusters. We see a stronger correlation of the recovered to input number of galaxies for both catalogues in comparison with the group/cluster mass, however, this does not guarantee that the correct member galaxies are being selected. We do not observe significantly higher scatter for either mock galaxy catalogues. Our results have implications for cosmological analyses that utilize the masses, richnesses, or abundances of clusters, which have different uncertainties when different methods are used.
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