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Can galactic magnetic fields diffuse into the voids?
No full textInternational audienceCosmic voids are magnetized at the level of at least G on Mpc scales, as implied by blazar observations. We show that an electrically conducting plasma is present in the voids, and that, because of the plasma, \emph{diffusion} into the voids of galactic fields generated by a mean-field dynamo is far too slow to explain the present-day void magnetization. Indeed, we show that even in the presence of turbulence in the voids, dynamo-generated galactic fields diffuse out to a galactocentric radius of only 200-400 kpc. Therefore, it is challenging to meet the required volume filling-factor of the void magnetic field. We conclude that a primordial origin remains the most natural explanation to the space-filling weak fields in voids
The multimessenger view of Pulsar Timing Array black holes with the Horizon-AGN simulation
No full textInternational audienceWe use the Horizon-AGN cosmological simulation to study the properties of supermassive black hole binaries (MBHBs) contributing most to the gravitational wave background (GWB) signal expected in the pulsar timing array (PTA) band. We develop a pipeline to generate realistic populations of MBHBs, allowing us to estimate both the characteristic strain and GWB time series observable by PTA experiments. We identify potential continuous wave (CW) candidates standing above the background noise, using toy PTA sensitivities representing the current EPTA and future SKA. We estimate the probability of detecting at least one CW with signal-to-noise ratio to be () for EPTA (SKA)-like sensitivities, assuming a 10-year baseline. We find the GWB to be dominated by hundreds to thousands of binaries at redshifts in the range , with chirp masses of , hosted mainly in quiescent massive galaxies residing in halos of mass . CW candidates have larger masses, lower redshifts and are found in even more massive halos, typical of galaxy groups and clusters. The majority of these systems would appear as AGN rather than quasars, because of their low Eddington ratios. Nevertheless, CW candidates with can still outshine their hosts, particularly in radio and X-ray bands, suggesting them as the most promising route for identification. Our findings imply that optical and near-infrared searches based on light curve variability are challenging and biased toward more luminous systems. Finally, we highlight important caveats in the common method used to compare PTA observations with theoretical models. We find that GWB spectral inferences used by PTAs could be biased toward shallower slopes and higher amplitudes at , thereby reducing the apparent tension between astrophysical expectations and PTA observations
Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4
No full textInternational audienceRecent James Webb Space Telescope (JWST) observations have revealed a population of sources with a compact morphology and a `v-shaped' continuum, namely blue at rest-frame A and red at longer wavelengths. The nature of these sources, called `little red dots' (LRDs), is still debated, since it is unclear if they host active galactic nuclei (AGN) and their number seems to drastically drop at z<4. We utilise the 63 covered by the quick Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and to lower z than what has been possible with JWST to have a broader view of the evolution of this peculiar galaxy population. The selection is done by fitting the available photometric data (Euclid, Spitzer/IRAC, and ground-based griz data) with two power laws, to retrieve the rest-frame optical and UV slopes consistently over a large redshift range (i.e, z<7.6). We exclude extended objects and possible line emitters, and perform a visual inspection to remove imaging artefacts. The final selection includes 3341 LRD candidates from z=0.33 to z=3.6, with 29 detected in IRAC. Their rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high-z down to z=1.5-2.5 and decreases at even lower z. Less evolution is apparent focusing on the subsample of more robust LRD candidates having IRAC detections, which is affected by low statistics and limited by the IRAC resolution. The comparison with previous quasar UV luminosity functions shows that LRDs are not the dominant AGN population at z<4. Follow-up studies of these LRD candidates are key to confirm their nature, probe their physical properties and check for their compatibility with JWST sources, since the different spatial resolution and wavelength coverage of Euclid and JWST could select different samples of compact sources
The Online Data Filter for the KM3NeT Neutrino Telescopes
No full textInternational audienceThe KM3NeT research infrastructure comprises two neutrino telescopes located in the deep waters of the Mediterranean Sea, namely ORCA and ARCA. KM3NeT/ORCA is designed for the measurement of neutrino properties and KM3NeT/ARCA for the detection of high\nobreakdashes-energy neutrinos from the cosmos. Neutrinos are indirectly detected using three\nobreakdashes-dimensional arrays of photo\nobreakdashes-sensors which detect the Cherenkov light that is produced when relativistic charged particles emerge from a neutrino interaction. The analogue pulses from the photo\nobreakdashes-sensors are digitised offshore and all digital data are sent to a station on shore where they are processed in real time using a farm of commodity servers and custom software. In this paper, the design and performance of the software that is used to filter the data are presented. The performance of the data filter is evaluated in terms of its purity, capacity and efficiency. The purity is measured by a comparison of the event rate caused by muons produced by cosmic ray interactions in the Earth's atmosphere with the event rate caused by the background from decays of radioactive elements in the sea water and bioluminescence. The capacity is measured by the minimal number of servers that is needed to sustain the rate of incoming data. The efficiency is measured by the effective volumes of the sensor arrays
Euclid Quick Data Release (Q1). First detections from the galaxy cluster workflow
No full textInternational audienceThe first survey data release by the Euclid mission covers approximately in the Euclid Deep Fields to the same depth as the Euclid Wide Survey. This paper showcases, for the first time, the performance of cluster finders on Euclid data and presents examples of validated clusters in the Quick Release 1 (Q1) imaging data. We identify clusters using two algorithms (AMICO and PZWav) implemented in the Euclid cluster-detection pipeline. We explore the internal consistency of detections from the two codes, and cross-match detections with known clusters from other surveys using external multi-wavelength and spectroscopic data sets. This enables assessment of the Euclid photometric redshift accuracy and also of systematics such as mis-centring between the optical cluster centre and centres based on X-ray and/or Sunyaev--Zeldovich observations. We report 426 joint PZWav and AMICO-detected clusters with high signal-to-noise ratios over the full Q1 area in the redshift range . The chosen redshift and signal-to-noise thresholds are motivated by the photometric quality of the early Euclid data. We provide richness estimates for each of the Euclid-detected clusters and show its correlation with various external cluster mass proxies. Out of the full sample, 77 systems are potentially new to the literature. Overall, the Q1 cluster catalogue demonstrates a successful validation of the workflow ahead of the Euclid Data Release 1, based on the consistency of internal and external properties of Euclid-detected clusters
Growth Index in the CDM model
No full textInternational audienceTo better distinguish the nature of and tensions, it is necessary to separate the effects of expansion and the growth of structure. The growth index was identified as the single parameter that characterizes the growth of density fluctuations independently of the effects of cosmic expansion. Analyses performed with various cosmological datasets indicate that the growth index has to be larger than its theoretically predicted value in the CDM model. Cosmological models based on gravity theories have scale-dependent growth indices, whose values are even more at odds with the growth rate data. In this work, we evaluate the growth index in the CDM model both theoretically and numerically. Although based on gravity theory, we show through several analyses with different combinations of datasets that the growth index and growth rate in the CDM model behave similarly to the CDM and the CDM models. When faced with cosmological data, we also demonstrate that the CDM model fits better than the CDM and the CDM models
Search for Magnetic Monopoles with the Complete ANTARES Dataset
No full textInternational audienceThis study presents a novel search for magnetic monopoles using data collected over a 14 year period (2008-2022) by the ANTARES neutrino telescope. The interaction of magnetic monopoles with matter was modeled according to Kazama, Yang, and Goldhaber cross-section. Upper limits on the flux of magnetic monopoles are obtained for velocities both above and below the Cherenkov threshold. No events consistent with the passage of magnetic monopoles were detected, enabling the setting of an upper flux limit for relativistic magnetic monopoles of the order of
Generalised non-linear electrodynamics: classical picture and effective mass generation
No full textInternational audienceAbstract Starting from a generic Lagrangian, we discuss the number of propagating degrees of freedom in the framework of generalised non-linear electrodynamics when a photon-background split is applied. We start by stating results obtained in a previous paper, before modifying the action to an equivalent form. Within this new formulation, we highlight the presence of an effective mass and consider the mechanical reduction of the model to ensure the positivity of said mass. We then study the constraint algebra of the model and show that we shift from a model with two first-class to two second-class constraints, which implies the propagation of an additional degree of freedom. We also show that the Hamiltonian is bound from below and thus does not suffer from Ostrogradski-type instabilities. We conclude by deriving the propagator for the model, and discussing the potential link between the nature of this additional polarisation and the mechanism behind the effective mass generation in this class of models
High sensitivity and accuracy with a large area cold atom gyroscope
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Scattering angle at 3PM in scalar-tensor theories using the PM-EFT formalism
No full textInternational audienceIn this work, we derive the conservative dynamics of non-spinning binaries in the massless scalar-tensor theories using the post-Minkowskian Effective Field Theory (EFT) approach. Our main result is an analytic expression of the scattering angle, computed up to third Post-Minkowskian order via two-loop Feynman diagrams. Our results are in perfect agreement with previous literature, in particular within the post-Newtonian limit