317 research outputs found
Reconstruction of the two-dimensional gravitational potential of galaxy clusters from X-ray and Sunyaev-Zel'dovich measurements
The mass of galaxy clusters is not a direct observable, nonetheless it is
commonly used to probe cosmological models. Based on the combination of all
main cluster observables, that is, the X-ray emission, the thermal
Sunyaev-Zel'dovich (SZ) signal, the velocity dispersion of the cluster
galaxies, and gravitational lensing, the gravitational potential of galaxy
clusters can be jointly reconstructed. We derive the two main ingredients
required for this joint reconstruction: the potentials individually
reconstructed from the observables and their covariance matrices, which act as
a weight in the joint reconstruction. We show here the method to derive these
quantities. The result of the joint reconstruction applied to a real cluster
will be discussed in a forthcoming paper. We apply the Richardson-Lucy
deprojection algorithm to data on a two-dimensional (2D) grid. We first test
the 2D deprojection algorithm on a -profile. Assuming hydrostatic
equilibrium, we further reconstruct the gravitational potential of a simulated
galaxy cluster based on synthetic SZ and X-ray data. We then reconstruct the
projected gravitational potential of the massive and dynamically active cluster
Abell 2142, based on the X-ray observations collected with XMM-Newton and the
SZ observations from the Planck satellite. Finally, we compute the covariance
matrix of the projected reconstructed potential of the cluster Abell 2142 based
on the X-ray measurements collected with XMM-Newton. The gravitational
potentials of the simulated cluster recovered from synthetic X-ray and SZ data
are consistent, even though the potential reconstructed from X-rays shows
larger deviations from the true potential. Regarding Abell 2142, the projected
gravitational cluster potentials recovered from SZ and X-ray data reproduce
well the projected potential inferred from gravitational-lensing observations.
(abridged)Comment: accepted for publication in the journal A&
The distinct stellar-to-halo mass relations of satellite and central galaxies: Insights from the IllustrisTNG simulations
We study the stellar-to-halo mass relation (SHMR) for central and satellite galaxies with total dynamical masses above 1010.5 M⊙ using the suite of cosmological magnetohydrodynamical simulations IllustrisTNG. In particular, we quantify environmental effects on satellite populations from TNG50, TNG100, and TNG300 located within the virial radius of group- and clusterlike hosts with total masses of 1012-15.2 M⊙. At fixed stellar mass, the satellite SHMR exhibits a distinct shift towards lower dynamical mass compared to the SHMR of centrals. Conversely, at fixed dynamical mass, satellite galaxies appear to have larger stellar-to-total mass fractions than centrals by up to a factor of a few. The systematic deviation from the central SHMR is larger for satellites in more massive hosts, at smaller cluster-centric distances, with earlier infall times, and that inhabits higher local density environments; moreover, it is in place already at early times (z 2). Systematic environmental effects might contribute to the perceived galaxy-to-galaxy variation in the measured SHMR when galaxies cannot be separated into satellites and centrals. The SHMR of satellites exhibits a larger scatter than centrals (by up to ∼0.8 dex), over the whole range of dynamical mass. The shift of the satellite SHMR results mostly from tidal stripping of their dark matter, which affects satellites in an outside-in fashion: The departure of the satellite SHMR from the centrals' relation diminishes for measurements of dynamical mass in progressively smaller apertures. Finally, we provide a family of fitting functions for the SHMR predicted by IllustrisTNG
Constructing Impactful Machine Learning Research for Astronomy: Best Practices for Researchers and Reviewers
Machine learning has rapidly become a tool of choice for the astronomical
community. It is being applied across a wide range of wavelengths and problems,
from the classification of transients to neural network emulators of
cosmological simulations, and is shifting paradigms about how we generate and
report scientific results. At the same time, this class of method comes with
its own set of best practices, challenges, and drawbacks, which, at present,
are often reported on incompletely in the astrophysical literature. With this
paper, we aim to provide a primer to the astronomical community, including
authors, reviewers, and editors, on how to implement machine learning models
and report their results in a way that ensures the accuracy of the results,
reproducibility of the findings, and usefulness of the method.Comment: 14 pages, 3 figures; submitted to the Bulletin of the American
Astronomical Societ
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Duality and distance formulas in spaces defined by means of oscillation
For the classical space of functions with bounded mean oscillation, it is well known that VMO∗∗=BMOVMO∗∗=BMO and there are many characterizations of the distance from a function f in BMOBMO to VMOVMO. When considering the Bloch space, results in the same vein are available with respect to the little Bloch space. In this paper such duality results and distance formulas are obtained by pure functional analysis. Applications include general Möbius invariant spaces such as QK-spaces, weighted spaces, Lipschitz–Hölder spaces and rectangular BMOBMO of several variables
Contrasting Diversity Patterns of Crenarchaeal, Bacterial and Fungal Soil Communities in an Alpine Landscape
International audienceBackground: The advent of molecular techniques in microbial ecology has aroused interest in gaining an understanding about the spatial distribution of regional pools of soil microbes and the main drivers responsible of these spatial patterns. Here, we assessed the distribution of crenarcheal, bacterial and fungal communities in an alpine landscape displaying high turnover in plant species over short distances. Our aim is to determine the relative contribution of plant species composition, environmental conditions, and geographic isolation on microbial community distribution. Methodology/Principal Findings: Eleven types of habitats that best represent the landscape heterogeneity were investigated. Crenarchaeal, bacterial and fungal communities were described by means of Single Strand Conformation Polymorphism. Relationships between microbial beta diversity patterns were examined by using Bray-Curtis dissimilarities and Principal Coordinate Analyses. Distance-based redundancy analyses and variation partitioning were used to estimate the relative contributions of different drivers on microbial beta diversity. Microbial communities tended to be habitat- specific and did not display significant spatial autocorrelation. Microbial beta diversity correlated with soil pH. Fungal beta- diversity was mainly related to soil organic matter. Though the effect of plant species composition was significant for all microbial groups, it was much stronger for Fungi. In contrast, geographic distances did not have any effect on microbial beta diversity. Conclusions/Significance: Microbial communities exhibit non-random spatial patterns of diversity in alpine landscapes. Crenarcheal, bacterial and fungal community turnover is high and associated with plant species composition through different set of soil variables, but is not caused by geographical isolation
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
The Impact of Insulin Pump Therapy on Glycemic Profiles in Patients with Type 2 Diabetes: Data from the OpT2mise Study
Background: The OpT2mise randomized trial was designed to compare the effects of continuous subcutaneous insulin infusion (CSII) and multiple daily injections (MDI) on glucose profiles in patients with type 2 diabetes. Research Design and Methods: Patients with glycated hemoglobin (HbA1c) levels of ≥8% (64 mmol/mol) and ≤12% (108 mmol/mol) despite insulin doses of 0.7-1.8 U/kg/day via MDI were randomized to CSII (n=168) or continued MDI (n=163). Changes in glucose profiles were evaluated using continuous glucose monitoring data collected over 6-day periods before and 6 months after randomization. Results: After 6 months, reductions in HbA1c levels were significantly greater with CSII (-1.1±1.2% [-12.0±13.1 mmol/mol]) than with MDI (-0.4±1.1% [-4.4±12.0 mmol/mol]) (P<0.001). Similarly, compared with patients receiving MDI, those receiving CSII showed significantly greater reductions in 24-h mean sensor glucose (SG) (treatment difference, -17.1 mg/dL; P=0.0023), less exposure to SG >180 mg/dL (-12.4%; P=0.0004) and SG >250 mg/dL (-5.5%; P=0.0153), and more time in the SG range of 70-180 mg/dL (12.3%; P=0.0002), with no differences in exposure to SG<70 mg/dL or in glucose variability. Changes in postprandial (4-h) glucose area under the curve >180 mg/dL were significantly greater with CSII than with MDI after breakfast (-775.9±1,441.2 mg/dL/min vs. -160.7±1,074.1 mg/dL/min; P=0.0015) and after dinner (-731.4±1,580.7 mg/dL/min vs. -71.1±1,083.5 mg/dL/min; P=0.0014). Conclusions: In patients with suboptimally controlled type 2 diabetes, CSII significantly improves selected glucometrics, compared with MDI, without increasing the risk of hypoglycemia
Cold streams in early massive hot haloes as the main mode of galaxy formation
The massive galaxies in the young universe, ten billion years ago, formed
stars at surprising intensities. Although this is commonly attributed to
violent mergers, the properties of many of these galaxies are incompatible with
such events, showing gas-rich, clumpy, extended rotating disks not dominated by
spheroids (Genzel et al. 2006, 2008). Cosmological simulations and clustering
theory are used to explore how these galaxies acquired their gas. Here we
report that they are stream-fed galaxies, formed from steady, narrow, cold gas
streams that penetrate the shock-heated media of massive dark matter haloes
(Dekel & Birnboim 2006; Keres et al. 2005). A comparison with the observed
abundance of star-forming galaxies implies that most of the input gas must
rapidly convert to stars. One-third of the stream mass is in gas clumps leading
to mergers of mass ratio greater than 1:10, and the rest is in smoother flows.
With a merger duy cycle of 0.1, three-quarters of the galaxies forming stars at
a given rate are fed by smooth streams. The rarer, submillimetre galaxies that
form stars even more intensely are largely merger-induced starbursts. Unlike
destructive mergers, the streams are likely to keep the rotating disk
configuration intact, although turbulent and broken into giant star-forming
clumps that merge into a central spheroid (Noguchi 1999; Genzel et al. 2008,
Elmegreen, Bournaud & Elmegreen 2008, Dekel, Sari & Ceverino 2009). This
stream-driven scenario for the formation of disks and spheroids is an
alternative to the merger picture.Comment: Improved version, 25 pages, 13 figures, Letter to Nature with
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