107 research outputs found
The XMM Cluster Survey: Evidence for energy injection at high redshift from evolution of the X-ray luminosity-temperature relation
We measure the evolution of the X-ray luminosity-temperature (L_X-T) relation
since z~1.5 using a sample of 211 serendipitously detected galaxy clusters with
spectroscopic redshifts drawn from the XMM Cluster Survey first data release
(XCS-DR1). This is the first study spanning this redshift range using a single,
large, homogeneous cluster sample. Using an orthogonal regression technique, we
find no evidence for evolution in the slope or intrinsic scatter of the
relation since z~1.5, finding both to be consistent with previous measurements
at z~0.1. However, the normalisation is seen to evolve negatively with respect
to the self-similar expectation: we find E(z)^{-1} L_X = 10^{44.67 +/- 0.09}
(T/5)^{3.04 +/- 0.16} (1+z)^{-1.5 +/- 0.5}, which is within 2 sigma of the zero
evolution case. We see milder, but still negative, evolution with respect to
self-similar when using a bisector regression technique. We compare our results
to numerical simulations, where we fit simulated cluster samples using the same
methods used on the XCS data. Our data favour models in which the majority of
the excess entropy required to explain the slope of the L_X-T relation is
injected at high redshift. Simulations in which AGN feedback is implemented
using prescriptions from current semi-analytic galaxy formation models predict
positive evolution of the normalisation, and differ from our data at more than
5 sigma. This suggests that more efficient feedback at high redshift may be
needed in these models.Comment: Accepted for publication in MNRAS; 12 pages, 6 figures; added
references to match published versio
Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM)
Abstract. There is a temporal correlation between the peak activity of the North
Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum
(PETM), suggesting that the NAIP may have initiated and/or prolonged this
extreme warming event. However, corroborating a causal relationship is
hampered by a scarcity of expanded sedimentary records that contain both
climatic and volcanic proxies. One locality hosting such a record is the island of Fur in Denmark, where an expanded pre- to post-PETM succession containing
hundreds of NAIP ash layers is exceptionally well preserved. We compiled a
range of environmental proxies, including mercury (Hg) anomalies,
paleotemperature proxies, and lithium (Li) and osmium (Os) isotopes, to
trace NAIP activity, hydrological changes, weathering, and seawater
connectivity across this interval. Volcanic proxies suggest that NAIP
activity was elevated before the PETM and appears to have peaked during the
body of the δ13C excursion but decreased considerably during
the PETM recovery. This suggests that the acme in NAIP activity, dominated
by flood basalt volcanism and thermogenic degassing from contact
metamorphism, was likely confined to just ∼ 200 kyr (ca. 56.0–55.8 Ma). The hundreds of thick (> 1 cm) basaltic ashes in the post-PETM strata
likely represent a change from effusive to explosive activity, rather than
an increase in NAIP activity. Detrital δ7Li values and clay
abundances suggest that volcanic ash production increased the basaltic reactive
surface area, likely enhancing silicate weathering and atmospheric carbon
sequestration in the early Eocene. Signals in lipid biomarkers and Os
isotopes, traditionally used to trace paleotemperature and weathering
changes, are used here to track seaway connectivity. These proxies indicate
that the North Sea was rapidly cut off from the North Atlantic in under 12 kyr during the PETM recovery due to NAIP thermal uplift. Our findings
reinforce the hypothesis that the emplacement of the NAIP had a profound and
complex impact on Paleocene–Eocene climate, both directly through volcanic
and thermogenic degassing and indirectly by driving regional uplift and
changing seaway connectivity
The XMM Cluster Survey: testing chameleon gravity using the profiles of clusters
The chameleon gravity model postulates the existence of a scalar field that couples with matter to mediate a fifth force. If it exists, this fifth force would influence the hot X-ray emitting gas filling the potential wells of galaxy clusters. However, it would not influence the clusters weak lensing signal. Therefore, by comparing X-ray and weak lensing profiles, one can place upper limits on the strength of a fifth force. This technique has been attempted before using a single, nearby cluster (Coma, z = 0.02). Here we apply the technique to the stacked profiles of 58 clusters at higher redshifts (0.1 < z < 1.2), including 12 new to the literature, using X-ray data from the XMM Cluster Survey and weak lensing data from the Canada-France-Hawaii-Telescope Lensing Survey. Using a multiparameter Markov chain Monte Carlo analysis, we constrain the two chameleon gravity parameters (beta and phi∞). Our fits are consistent with general relativity, not requiring a fifth force. In the special case of f(R) gravity (where beta = &surd;{1/6}), we set an upper limit on the background field amplitude today of |fR0| < 6 × 10-5 (95 per cent CL). This is one of the strongest constraints to date on |fR0| on cosmological scales. We hope to improve this constraint in future by extending the study to hundreds of clusters using data from the Dark Energy Survey
The XMM Cluster Survey: The interplay between the brightest cluster galaxy and the intra-cluster medium via AGN feedback
Using a sample of 123 X-ray clusters and groups drawn from the XMM-Cluster
Survey first data release, we investigate the interplay between the brightest
cluster galaxy (BCG), its black hole, and the intra-cluster/group medium (ICM).
It appears that for groups and clusters with a BCG likely to host significant
AGN feedback, gas cooling dominates in those with Tx > 2 keV while AGN feedback
dominates below. This may be understood through the sub-unity exponent found in
the scaling relation we derive between the BCG mass and cluster mass over the
halo mass range 10^13 < M500 < 10^15Msol and the lack of correlation between
radio luminosity and cluster mass, such that BCG AGN in groups can have
relatively more energetic influence on the ICM. The Lx - Tx relation for
systems with the most massive BCGs, or those with BCGs co-located with the peak
of the ICM emission, is steeper than that for those with the least massive and
most offset, which instead follows self-similarity. This is evidence that a
combination of central gas cooling and powerful, well fuelled AGN causes the
departure of the ICM from pure gravitational heating, with the steepened
relation crossing self-similarity at Tx = 2 keV. Importantly, regardless of
their black hole mass, BCGs are more likely to host radio-loud AGN if they are
in a massive cluster (Tx > 2 keV) and again co-located with an effective fuel
supply of dense, cooling gas. This demonstrates that the most massive black
holes appear to know more about their host cluster than they do about their
host galaxy. The results lead us to propose a physically motivated, empirical
definition of 'cluster' and 'group', delineated at 2 keV.Comment: Accepted for publication in MNRAS - replaced to match corrected proo
Comprehensive analysis of cancer-associated somatic mutations in class I HLA genes
Detection of somatic mutations in human leukocyte antigen (HLA) genes using whole-exome sequencing (WES) is hampered by the high polymorphism of the HLA loci, which prevents alignment of sequencing reads to the human reference genome. We describe a computational pipeline that enables accurate inference of germline alleles of class I HLA-A, B and C genes and subsequent detection of mutations in these genes using the inferred alleles as a reference. Analysis of WES data from 7,930 pairs of tumor and healthy tissue from the same patient revealed 298 nonsilent HLA mutations in tumors from 266 patients. These 298 mutations are enriched for likely functional mutations, including putative loss-of-function events. Recurrence of mutations suggested that these \u27hotspot\u27 sites were positively selected. Cancers with recurrent somatic HLA mutations were associated with upregulation of signatures of cytolytic activity characteristic of tumor infiltration by effector lymphocytes, supporting immune evasion by altered HLA function as a contributory mechanism in cancer
Phase 2 Study of the Safety and Tolerability of Maraviroc-Containing Regimens to Prevent HIV Infection in Men Who Have Sex With Men (HPTN 069/ACTG A5305)
Maraviroc (MVC) is a candidate for human immunodeficiency virus (HIV) pre-exposure prophylaxis
The XMM Cluster Survey: evolution of the velocity dispersion–temperature relation over half a Hubble time
We measure the evolution of the velocity dispersion–temperature (σv–TX) relation up to z = 1 using a sample of 38 galaxy clusters drawn from the XMM Cluster Survey. This work improves upon previous studies by the use of a homogeneous cluster sample and in terms of the number of high-redshift clusters included. We present here new redshift and velocity dispersion measurements for 12 z > 0.5 clusters observed with the Gemini Multi Object
Spectographs instruments on the Gemini telescopes. Using an orthogonal regression method,we find that the slope of the relation is steeper than that expected if clusters were self-similar, and that the evolution of the normalization is slightly negative, but not significantly different from zero (σv ∝T0.86±0.14E(z)−0.37±0.33). We verify our results by applying our methods to cosmological hydrodynamical simulations. The lack of evolution seen in our data is consistent with simulations that include both feedback and radiative cooling
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