MeerKAT discovers mystery clouds

An international team led by astronomers Gyula Józsa, Michelle Cluver, and Thomas Jarrett has utilized the South African MeerKAT telescope to discover a mysterious chain of hydrogen gas clouds the size of a massive galaxy. Indeed, the accumulation of so much elemental hydrogen without associated stellar components is the largest yet discovered. Appearing at the …

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How baryons affect halos and large-scale structure: a unified picture from the Simba simulation

Using the state-of-the-art suite of hydrodynamic simulations Simba, as well as its dark-matter-only counterpart, we study the impact of the presence of baryons and of different stellar/AGN feedback mechanisms on large-scale structure, halo density profiles, and on the abundance of different baryonic phases within halos and in the intergalactic medium (IGM). The unified picture that …

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Cosmological constraints on Newton’s gravitational constant

We study the variation of the gravitational Newton’s constant on cosmological scales in scalar-tensor theories of gravity. We focus on the simplest models of scalar-tensor theories with a coupling to the Ricci scalar of the form F(σ)=N2pl+ξσ2, such as extended Jordan-Brans-Dicke (Npl=0), or a non-minimally coupled scalar field with Npl=Mpl, which permits the gravitational constant to vary …

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Measurements of the diffuse Galactic synchrotron spectral index and curvature from MeerKLASS pilot data

21cm intensity mapping experiments are bringing an influx of high spectral resolution observational data in the ∼100 MHz −1 GHz regime. We use pilot 971−1075 MHz data from MeerKAT in single-dish mode, recently used to test the calibration and data reduction scheme of the upcoming MeerKLASS survey, to probe the spectral index of diffuse synchrotron emission below 1 GHz within 145∘<α<180∘, −1∘<δ<8∘. Through …

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Inferring halo masses with Graph Neural Networks

Understanding the halo-galaxy connection is fundamental in order to improve our knowledge on the nature and properties of dark matter. In this work we build a model that infers the mass of a halo given the positions, velocities, stellar masses, and radii of the galaxies it hosts. In order to capture information from correlations among …

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High Molecular-Gas to Dust Mass Ratios Predicted in Most Quiescent Galaxies

Observations of cold molecular gas reservoirs are critical for understanding the shutdown of star formation in massive galaxies. While dust continuum is an efficient and affordable tracer, this method relies upon the assumption of a “normal” molecular-gas to dust mass ratio, δGDR, typically of order one hundred. Recent null detections of quiescent galaxies in deep dust …

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Large MeerKAT data release reveals beautiful new cosmic puzzles

An international team led by a young South African researcher has just announced a comprehensive overview paper for the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). The paper to be published in the Astronomy & Astrophysicsjournal presents some exciting, novel results, and is accompanied by the public release of a huge trove of curated data now available …

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Superhorizon perturbations: A possible explanation of the Hubble–Lemaître Tension and the Large Scale Anisotropy of the Universe

Current cosmological observations point to a serious discrepancy between the observed Hubble parameter obtained using direct and cosmic microwave background radiation (CMBR) measurements. Besides this, the so called Hubble–Lemaître tension, we also find considerable evidence in diverse cosmological observables that indicate violation of the cosmological principle. In this paper, we suggest that both these discrepancies …

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Real-time detection of anomalies in large-scale transient surveys

New time-domain surveys, such as the Rubin Observatory Legacy Survey of Space and Time (LSST), will observe millions of transient alerts each night, making standard approaches of visually identifying new and interesting transients infeasible. We present two novel methods of automatically detecting anomalous transient light curves in real-time. Both methods are based on the simple …

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