1,721,076 research outputs found
Testing the rotation versus merger scenario in the galaxy cluster Abell 2107
Full text linkWe search for global rotation of the intracluster medium in the galaxy cluster Abell 2107, where previous studies have detected rotational motion in the member galaxies with a high-significance level. By fitting the centroid of the iron Kα line complex at 6.7–6.9 keV rest frame in Chandra ACIS-I spectra, we identify the possible rotation axis with the line that maximizes the difference between the emission-weighted spectroscopic redshift measured in the two halves defined by the line itself. Then, we measure the emission-weighted redshift in linear regions parallel to the preferred rotation axis, and find a significant gradient as a function of the projected distance from the rotation axis, compatible with a rotation pattern with maximum tangential velocity vmax = 1380 ± 600 km s−1 at a radius λ0 ∼ 160 kpc. This result, if interpreted in the framework of hydrostatic equilibrium, as suggested by the regular morphology of Abell 2107, would imply a large mass correction of the order of ∆M = (6 ± 4) × 1013 M☉ at ∼160 kpc, which is incompatible with the cluster morphology itself. A more conservative interpretation may be provided by an unnoticed off-centre, head-on collision between two comparable haloes. Our analysis confirms the peculiar dynamical nature of the otherwise regular cluster Abell 2107, but is not able to resolve the rotation versus merger scenario, a science case that can be addressed by the next-generation X-ray facilities carrying X-ray bolometers on board
The nature of hot gas in galaxy clusters: exploring the chemical and dynamical properties of the intracluster medium
Full text linkIn this Thesis I focus on the chemical enrichment of galaxy clusters by tracing the evolution of iron in the intracluster medium (ICM) through high-angular resolution X-ray observations from the Chandra X-ray Observatory. The detailed search and modelization of the emission lines of iron also allow me to perform dynamical studies of the ICM by measuring its velocity through the accurate position of the line centroid in X-ray spectra extracted from different regions. Eventually, the chemical, thermodynamical and dynamical properties of the ICM investigated in this work can be put together in a unique framework in the context of the cosmological evolution of galaxy clusters
Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China
No full textDing, Cong, Liu, Ang, Yu, Xun-Lin, Zhang, Chun-Ping (2021): Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China. Phytotaxa 511 (1): 51-64, DOI: 10.11646/phytotaxa.511.1.4, URL: http://dx.doi.org/10.11646/phytotaxa.511.1.
On the origin of central abundance drops in the intracluster medium of galaxy groups and clusters
Full text linkA central drop of ICM Fe abundance has been observed in several cool-core clusters. It has been proposed that this abundance drop may be due, at least partially, to the depletion of Fe into dust grains in the central, high-density regions. According to this scenario, noble gas elements such as Ar and Ne are not expected to be depleted into dust, and therefore should not show any drop, but follow the general increase of metal abundance towards the centre. In this work, we test this scenario by measuring with Chandra data the radial profiles of Ar and Ne in a sample of 12 groups and clusters where a central drop in Fe abundance has been detected. We confirm the presence of the Fe drop in 10 out of 12 clusters at more than 2σ c.l., and 4 Ar drops with similar significance. We also find 4 Ne drops, with the caveat that Ne abundance measurement from CCD spectra suffers from systematics not completely under control. Our results are consistent with an abundance drop common to the three elements. When comparing the profiles, we find that, on average, the abundance profiles of Ar and Ne are significantly higher than Fe and steeper towards the centre, while they all gradually become consistent with solar composition at r ≥ 0.05r 500 . We also check that Si and S profiles are mostly consistent with Fe. This result confirms a scenario in which some fraction of Fe is depleted into dust grains in the inner regions, although the global central abundance drop is mostly due to mechanical processes, like the displacement of metal-rich ICM from the very centre to larger radii by AGN-driven feedback. Finally, we report the detection of an Fe drop in the cluster MACSJ1423.8+2404 at z = 0.543, showing that this feature appears early on in cool-core clusters
Comparison of team effectiveness between globally distributed and locally distributed engineering project teams
No full textFIGURE 3 in Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China
No full textFIGURE 3. The Bayesian phylogenetic tree from atpB-rbcL sequence data with BI posterior probability/MP bootstrap support values (>0.5 or 50%) shown above and below the corresponding branches. * indicates the new species.Published as part of Ding, Cong, Liu, Ang, Yu, Xun-Lin & Zhang, Chun-Ping, 2021, Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China, pp. 51-64 in Phytotaxa 511 (1) on page 57, DOI: 10.11646/phytotaxa.511.1.4, http://zenodo.org/record/542649
FIGURE 2. The Bayesian phylogenetic tree from trnL-F in Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China
No full textFIGURE 2. The Bayesian phylogenetic tree from trnL-F sequence data with BI posterior probability/MP bootstrap support values (>0.5 or 50%) shown above and below the corresponding branches. * indicates the new species.Published as part of Ding, Cong, Liu, Ang, Yu, Xun-Lin & Zhang, Chun-Ping, 2021, Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China, pp. 51-64 in Phytotaxa 511 (1) on page 56, DOI: 10.11646/phytotaxa.511.1.4, http://zenodo.org/record/542649
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
FIGURE 5. Primulina cataractarum X.L in Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China
No full textFIGURE 5. Primulina cataractarum X.L.Yu & A.Liu. A. Plant B. Flower side view. C. Front view of flower. D. Opened corolla showing stamens and staminodes. E. Stamens. F. Stigma. G. Pistil. H. Bracts and bractlet. I. Calyx. J. Capsule. (Drawn by Jing Tian).Published as part of Ding, Cong, Liu, Ang, Yu, Xun-Lin & Zhang, Chun-Ping, 2021, Primulina cataractarum sp. nov. (Gesneriaceae) from limestone landform in Southern Hunan, China, pp. 51-64 in Phytotaxa 511 (1) on page 60, DOI: 10.11646/phytotaxa.511.1.4, http://zenodo.org/record/542649
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