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Magnetised turbulent plasmas as high-energy particle accelerators
No full textInternational audienceThis proceedings paper reports on the theoretical modelling of particle acceleration in magnetised turbulent plasmas. It briefly reviews some recent findings obtained from fully kinetic numerical simulations of large-amplitude, semi to fully relativistic turbulence. The paper then argues that these findings can be understood within the framework of a ``generalised Fermi'' picture of stochastic acceleration, which it summarises. The dominant contributions to acceleration appear to arise from particle interactions with sharp, dynamic bends of the magnetic field lines and regions of velocity compression. Interestingly, the acceleration rate is spatially inhomogeneous and its probability distribution follows a broken power law extending up to large values. This makes relativistic, large-amplitude turbulence an extreme particle accelerator. Some implications for particle transport and the shape of the particle energy spectrum in the presence of radiative losses and over long timescales are also discussed
Cleaning Galactic foregrounds with spatially varying spectral dependence from CMB observations with \texttt{fgbuster}
No full textInternational audienceIn the context of maximum-likelihood parametric component separation for next-generation full-sky CMB polarization experiments, we study the impact of fitting different spectral parameters of Galactic foregrounds in distinct subsets of pixels on the sky, with the goal of optimizing the search for primordial B modes. Using both simulations and analytical arguments, we highlight how the post-component separation uncertainty and systematic foreground residuals in the cleaned CMB power spectrum depend on spatial variations in the spectral parameters. We show that allowing spectral parameters to vary across subsets of the sky pixels is essential to achieve competitive S/N on the reconstructed CMB after component separation while keeping residual foreground bias under control. Although several strategies exist to define pixel subsets for the spectral parameters, each with its advantages and limitations, we show using current foreground simulations in the context of next-generation space-borne missions that there are satisfactory configurations in which both statistical and systematic residuals become negligible. The exact magnitude of these residuals, however, depends on the mission's specific characteristics, especially its frequency coverage and sensitivity. We also show that the post-component separation statistical uncertainty is only weakly dependent on the properties of the foregrounds and propose a semi-analytical framework to estimate it. On the contrary, the systematic foreground residuals highly depend on both the properties of the foregrounds and the chosen spatial resolution of the spectral parameters
Precise boron abundance in a sample of metal-poor stars from far-ultraviolet lines
No full textInternational audienceContext. The light elements beryllium (Be; Z = 4) and boron (B; Z = 5) are mainly produced by spallation reactions between cosmic rays and carbon (C; Z = 6), nitrogen (N; Z = 7), and oxygen (O; Z = 8) nuclei. Only traces of Be or B would have been produced in the Big Bang, but there could be a contribution from the ν-process in type II supernovae. Their abundances at very low metallicities have been debated in the literature, with the aim of understanding their origin. Aims. Our aim is to derive the boron abundance in a sample of metal-poor stars based for the first time on observations with the STIS spectrograph on board the Hubble Space Telescope, using clean B lines measured in space ultraviolet. Methods. We identified a measurable line of B i at 2089.6 Å. In our sample of metal-poor warm stars, this line is practically free from blending lines, and for this reason the precision of the presently derived boron abundances is unprecedented. Results. We find that in the interval -2.6 < [Fe/H] < -1.0, the slope of the relation A(B) versus [Fe/H] is significantly larger than 1, and thus steeper than that obtained with Be abundances. As a consequence, we find in this interval of metallicity a B/Be ratio that slightly increases with [Fe/H]. Since at [Fe/H] = -1 the abundance of B is already close to the solar abundance, there should be a break in the B enrichment at a metallicity of about [Fe/H] = -1.</div
Euclid preparation. Predicting star-forming galaxy scaling relations with the spectral stacking code SpectraPyle
No full textInternational audienceWe introduce SpectraPyle, a versatile spectral stacking pipeline developed for the Euclid mission's NISP spectroscopic surveys, aimed at extracting faint emission lines and spectral features from large galaxy samples in the Wide and Deep Surveys. Designed for computational efficiency and flexible configuration, SpectraPyle supports the processing of extensive datasets critical to Euclid's non-cosmological science goals. We validate the pipeline using simulated spectra processed to match Euclid's expected final data quality. Stacking enables robust recovery of key emission lines, including Halpha, Hbeta, [O III], and [N II], below individual detection limits. However, the measurement of galaxy properties such as star formation rate, dust attenuation, and gas-phase metallicity are biased at stellar mass below log10(M*/Msol) ~ 9 due to the flux-limited nature of Euclid spectroscopic samples, which cannot be overcome by stacking. The SFR-stellar mass relation of the parent sample is recovered reliably only in the Deep survey for log10(M*/Msol) > 10, whereas the metallicity-mass relation is recovered more accurately over a wider mass range. These limitations are caused by the increased fraction of redshift measurement errors at lower masses and fluxes. We examine the impact of residual redshift contaminants that arises from misidentified emission lines and noise spikes, on stacked spectra. Even after stringent quality selections, low-level contamination (< 6%) has minimal impact on line fluxes due to the systematically weaker emission of contaminants. Percentile-based analysis of stacked spectra provides a sensitive diagnostic for detecting contamination via coherent spurious features at characteristic wavelengths. While our simulations include most instrumental effects, real Euclid data will require further refinement of contamination mitigation strategies
Using Bayesian Inference to Distinguish Neutrino Flavor Conversion Scenarios via a Prospective Supernova Neutrino Signal
No full textInternational audienceThe upcoming galactic core-collapse supernova is expected to produce a considerable number of neutrino events within terrestrial detectors. By using Bayesian inference techniques, we address the feasibility of distinguishing among various neutrino flavor conversion scenarios in the supernova environment, using such a neutrino signal. In addition to the conventional MSW, we explore several more sophisticated flavor conversion scenarios, such as spectral swapping, fast flavor conversions, flavor equipartition caused by non-standard neutrino interactions, magnetically-induced flavor equilibration, and flavor equilibrium resulting from slow flavor conversions. Our analysis demonstrates that with a sufficiently large number of neutrino events during the supernova accretion phase (exceeding several hundreds), there exists a good probability of distinguishing among feasible neutrino flavor conversion scenarios in the supernova environment
The next generation Virgo cluster survey-infrared (NGVS-IR). i. a new near-ultraviolet, optical, and near-infrared globular cluster selection tool
No full textInternational audienceThe NGVS-IR project (Next Generation Virgo Cluster Survey-Infrared) is a contiguous, near-infrared imaging survey of the Virgo cluster of galaxies. It complements the optical wide-field survey of Virgo (NGVS). In its current state, NGVS-IR consists of K-s-band imaging of 4 deg(2) centered on M87 and J- and K-s-band imaging of similar to 16 deg(2) covering the region between M49 and M87. We present observations of the central 4 deg(2) centered on Virgo's core region. The data were acquired with WIRCam on the Canada-France-Hawaii Telescope, and the total integration time was 41 hr distributed over 34 contiguous tiles. A survey-specific strategy was designed to account for extended galaxies while still measuring accurate sky brightness within the survey area. The average 5s limiting magnitude is K-s = 24.4 AB mag, and the 50% completeness limit is K-s = 23.75 AB mag for point-source detections, when using only images with better than 0.” 7 seeing (median seeing 0.” 54). Star clusters are marginally resolved in these image stacks, and Virgo galaxies with mu(Ks) similar or equal to 24.4 AB mag arcsec(-2) are detected. Combining the K-s data with optical and ultraviolet data, we build the uiK(s) color-color diagram, which allows a very clean color-based selection of globular clusters in Virgo. This diagnostic plot will provide reliable globular cluster candidates for spectroscopic follow-up campaigns, needed to continue the exploration of Virgo's photometric and kinematic substructures, and will help the design of future searches for globular clusters in extragalactic systems. We show that the new uiK(s) diagram displays significantly clearer substructure in the distribution of stars, globular clusters, and galaxies than the gzK(s) diagram-the NGVS + NGVS-IR equivalent of the BzK diagram that is widely used in cosmological surveys. Equipped with this powerful new tool, future NGVS-IR investigations based on the uiK(s) diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies
Hyperbolicity in scalar-Gauss-Bonnet gravity: a gauge invariant study for spherical evolution
No full textInternational audienceWe study spherical evolution in scalar-Gauss-Bonnet gravity with additional Ricci coupling and use the gauge-invariant approach of Ref.~\cite{Reall:2021voz} to track well-posedness. Our results show that loss of hyperbolicity when it occurs, is due to the behaviour of physical degrees of freedom. They provide further support to the idea that this behaviour can be tamed by additional interactions of scalar. We also point out a limitation of this gauge-invariant approach: the fact that field redefinitions can change the character of the evolution equations
The nested morphology of disk winds from young stars revealed by JWST/NIRSpec observations
No full textInternational audienceRadially extended disk winds could be the key to unlocking how protoplanetary disks accrete and how planets form and migrate. A distinctive characteristic is their nested morphology of velocity and chemistry. Here we report James Webb Space Telescope near-infrared spectrograph spectro-imaging of four young stars with edge-on disks, three of which have already dispersed their natal envelopes. For each source, a fast collimated jet traced by [Fe II] is nested inside a hollow cavity within wider lower-velocity H2. In one case, a hollow structure is also seen in CO ro-vibrational (v = 1 → 0) emission but with a wider opening angle than the H2, and both of those are nested inside an Atacama Large Millimeter Array CO (J = 2 → 1) cone with an even wider opening angle. This nested morphology, even for sources with no envelope, strongly supports theoretical predictions for wind-driven accretion and underscores the need for theoretical work to assess the role of winds in the formation and evolution of planetary systems
Unraveling the Nature of HAWC J1844-034 with Fermi-LAT Data Analysis and Multi-wavelength modelling
No full textInternational audienceThe extended ultra-high-energy gamma-ray source HAWC J1844-034 is closely associated with two other sources, HAWC J1843-032 and HWC J1846-025. Moreover, other gamma-ray observatories like H.E.S.S., LHAASO, and Tibet AS have detected ultra-high-energy gamma-ray sources whose spatial positions coincide with the position of HAWC J1844-034. The ultra-high-energy gamma-ray data from several observatories help analyse the spectral features of this source in detail at TeV energies. Of the four pulsars near HAWC J1844-034, PSR J1844-0346 is closest to it and possibly supplies the cosmic-ray leptons to power this source. We have analysed the Fermi-LAT data to explore this source's morphology and identify its spectral feature in the Fermi-LAT energy band. After removing the contribution of the pulsar to the gamma-ray spectral energy distribution by pulsar phased analysis, we have obtained upper limits on the photon flux and identified the GeV counterpart PS J1844.2-0342 in the Fermi-LAT energy band with more than 5 significance, which may be a pulsar wind nebula. Finally, the multi-wavelength spectral energy distribution has been modelled, assuming HAWC J1844-034 is a pulsar wind nebula