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Astrometric exomoon detection by means of optical interferometry
No full textContext. With no conclusive detection to date, the search for exomoons, satellites of planets orbiting other stars, remains a formidable challenge. Detecting these objects, compiling a population-level sample and constraining their occurrence will inform planet and moon formation models and shed light on moon habitability.
Aims. Here, we demonstrate the possibility of a moon search based on astrometric time series data, repeated measurements of the position of a given planet relative to its host star. The perturbing influence of an orbiting moon induces a potentially detectable planetary reflex motion.
Methods. Based on an analytical description of the astrometric signal amplitude, we placed the expected signatures of putative moons around real exoplanets into context with our current and future astrometric measurement precision. Modelling the orbital perturbation as a function of time, we then simulated the detection process given different target system configurations, instrumental measurement precisions and numbers of observational epochs to obtain the first astrometric exomoon sensitivity curves.
Results. The astrometric technique already allows for the detection and characterisation of favourable moons around giant exoplanets and brown dwarfs. Since the detection sensitivity of this method is mainly governed by the achievable astrometric precision, long-baseline interferometry lends itself ideally to this pursuit. We find that, on the basis of 12 epochs obtained with VLTI/GRAVITY, it is already today possible to infer at a confidence of 5 σ the presence of a 0.14 MJup satellite at a separation of 0.39 AU around AF Lep b. Future facilities offering better precision will refine our sensitivity in both moon mass and separation from the host planet by several orders of magnitude.
Conclusions. The astrometric method of exomoon detection, especially when applied to interferometric observations, provides a promising avenue towards making the detection of these elusive worlds a reality and efficiently building a sample of confirmed objects. With a future facility that achieves an astrometric precision of 1 μas, probing for Earth-like moons within the habitable zone of a given star will become a realistic proposition
Probing the millisecond pulsar origin of the
No full textThe gigaelectronvolt γ-ray excess observed towards the Galactic centre remains unexplained. While dark matter annihilation has long been considered a leading explanation, an alternative scenario involving a large population of millisecond pulsars remains viable. Testing this hypothesis with electromagnetic observations is difficult, as pulsar searches in the bulge are strongly affected by interstellar scattering, high sky temperature, and source confusion. We investigate whether gravitational-wave observations with the Laser Interferometer Space Antenna (LISA) could provide an independent probe of the millisecond pulsar binary population in the Galactic bulge in the future. We constructed synthetic populations of detached millisecond pulsar–white dwarf binaries under two illustrative formation scenarios: an accreted scenario, in which systems are deposited by disrupted globular clusters, and an in situ scenario, in which binaries form through isolated binary evolution. In both cases, only 10−5–10−4 of the underlying bulge population is detectable by LISA. Still, even a few detections would imply tens to hundreds of thousands of unseen systems. Accreted binaries are expected to have lower chirp masses (∼0.4 M⊙), while in situ binaries produce more massive companions (∼0.9 M⊙), though part of this contrast reflects our modelling assumptions. LISA will measure binary frequencies with high precision, but chirp masses can only be determined for the most massive or highest-frequency systems. Thus, identifying millisecond-pulsar binaries among the far more numerous double white dwarfs will be challenging, as their gravitational-wave signals alone are indistinguishable. However, coordinated follow-up with the Square Kilometre Array of LISA-selected targets could directly test the millisecond-pulsar explanation of the γ-ray excess
Intrinsic alignments of galaxies in multiple projections
No full textThe intrinsic alignments of galaxies can be measured and modelled to gain cosmological information and further improve our understanding of the interactions between galaxies, as well as to mitigate their effects on gravitational weak lensing studies. Hydrodynamical simulations are often used to constrain priors or calibrate models. Therefore, obtaining the maximum amount of information possible from these simulations is imperative. In this work, we combined the information of shapes projected over two or three axes (x, y, z), for intrinsic alignment signals (), showing a consistent gain in signal-to-noise ratio (S/N) for all cases studied using TNG300-1. The gain in S/N is found to be higher for the addition of the second projection than for the third, and it is also higher for shapes calculated using the reduced inertia tensor, rather than the simple one. The two shape samples studied, n★ > 300 and log(M★ h/M⊙) > 10.5, where the latter has a much higher signal amplitude, show similar gains in S/N when more projections are added. We also modelled the correlation functions with the non-linear alignment model for scales greater than 6 Mpc/h. The S/N gains on the non-linear alignment amplitude, AIA, and galaxy bias, bg, are higher than those seen for the full measurements, indicating potential advantages for future works, particularly on larger scales with an increased uncertainty on the alignment signals. Using multiple projection axes increases the overall S/N, enabling a more efficient use of numerically expensive hydrodynamical simulations
Evolution and mass dependence of UV-to-near-IR color gradients up to
No full textAims. We present the redshift evolution of radial color gradients (in rest-frame U − V and V − J) for galaxies in the range 0.5 < z < 2.5 and investigate their origin and the dependence on stellar mass.
Methods. We selected ≈10 200 galaxies with stellar masses M★ > 109.5 M⊙ from publicly available JWST/NIRCam-selected catalogs. Using 2D Sérsic profile fits to account for point spread function broadening, we performed a spatially resolved spectral energy distribution fitting on HST and JWST/NIRCam photometry to retrieve accurate rest-frame U − V and V − J color gradients within 2 Re, F444W.
Results. The generally negative V − J color gradients of star-forming galaxies strongly depend on mass and redshift. For massive star-forming galaxies (M★ > 1010.5 M⊙) at z > 1.5, the V − J colors are ≈0.5 mag redder within the effective radius than outside on average. At all redshifts and throughout the entire stellar mass range, the V − J gradients strongly correlate with global attenuation (AV), which suggests that they predominantly trace dust attenuation gradients. Edge-on galaxies are redder and have stronger gradients at all z, although the correlation weakens at higher z. The U − V and V − J color gradients in the quiescent galaxy population, in contrast, are weakly negative (from ≈ − 0.1 to ≈ − 0.2 mag) but significant, and they depend little or not at all on stellar mass, redshift, or axis ratio. The implication is that quiescent galaxies must be largely transparent, with low AV, and their color gradients are mostly attributable to stellar population gradients
Catching the 2021
No full textThe γ-ray–loud blazar TXS 2013+370, a powerful multiwavelength emitter at z = 0.859, underwent an exceptional gigaelectron volt outburst in late 2020 to early 2021. In this work, we present full polarization VLBI imaging at 22, 43, and 86 GHz (11 February 2021) together with contemporaneous single-dish monitoring (OVRO 15 GHz; SMA 226 GHz) and Fermi–LAT light curves to localize the high-energy dissipation site and probe the magnetic field of the inner jet. The images enabled us to study the jet structure and field topology on sub-parsec scales, revealing a compact near-core knot at r ≃ 40 − 60 μas along with the gigaelectron volt (GeV) flare and a flat core-dominated spectrum (α ≳ −0.5). The core has strong linear polarization and exhibits a ∼50° electric vector polarization angle rotation at 86 GHz. The pixel-based and integrated fits we employed yielded a high, uniform rotation measure, RM = (7.8 ± 0.2)×104 rad m−2, consistent with an external Faraday screen. Performing a cross-correlation of Fermi–LAT and 15 GHz light curves revealed a highly significant peak, with the γ rays leading by Δt = (102 ± 12) d. Adopting βapp = 4.2 ± 0.5 and θ = 4.1° ±0.2° implies a de-projected separation of Δrγ − 15 = (2.71 ± 0.47) pc and locates the GeV emission between the jet apex and ∼0.42 pc (in the 1σ range) downstream. Our results do not pinpoint the emission site; rather, they support two valid scenarios. The γ-ray production occurs within the broad-line region (∼0.07 pc), where external-Compton scatters optical/UV photons to γ-rays, and beyond the broad-line region, reaching ∼0.42 pc (1σ) within the inner parsecs, where external-Compton scattering of dusty-torus infrared photons dominates. Both scenarios are compatible in the allowed range of emission distances, while opacity-driven core shifts modulate the observed radio–γ delay without requiring large relocations of the dissipation zone
J-PLUS: Reconstructing the Milky Way disc's star formation history with 12-filter photometry
No full textContext. Wide-field, multi-filter photometric surveys enable the reconstruction of the Milky Way’s star formation history (SFH) on Galactic scales and provide complementary insights into disc assembly. The 12-filter system of the Javalambre Photometric Local Universe Survey (J-PLUS) is particularly suitable, as its colours trace stellar chemical abundances and help mitigate the age-metallicity degeneracy in colour-magnitude diagram fitting.
Aims. We aim to recover the SFH of the Milky Way disc and separate its chemically distinct components by combining J-PLUS DR3 photometry with Gaia astrometry. We also intend to test the potential of isochrone fitting to estimate ages and metallicities for individual stars as proxies for disc evolutionary trends.
Methods. We fitted magnitudes and parallaxes of 1.38 × 106 stars using a Bayesian multiple-isochrone technique. The bright region of the colour-absolute-magnitude diagram (Mr ≤ 4.2 mag) constrains stellar ages, while the faint region provides an empirical metallicity prior that mitigates the age-metallicity degeneracy. Both PARSEC and BaSTI isochrones, in solar-scaled and α-enhanced versions, were adopted.
Results. The recovered SFH shows two sequences: an α-enhanced population forming rapidly between 12.5 and 8 Gyr ago, enriching from [M/H]~ −0.6 to 0.1 dex; and a solar-scaled sequence emerging ∼8 Gyr ago, dominating after ∼7 Gyr with slower enrichment and reaching solar metallicity by 3 Gyr. Metal-rich ([M/H] > 0) stars are confined to |zGC| ≲ 1 kpc, whereas metal-poor ([M/H] < -0.5) stars reach |zGC| ~ 2 kpc.
Conclusions. Simultaneous fitting of solar-scaled and α-enhanced isochrones reveals distinct formation epochs for the thin and thick discs. J-PLUS multi-filter photometry, combined with Gaia parallaxes, effectively mitigates age-metallicity degeneracies and enables detailed mapping of the Milky Way’s temporal and chemical evolution
CHILLING: Continuum Halos in LVHIS Local Irregular Nearby Galaxies
No full textContext. Dwarf galaxies, due to their shallow gravitational potentials, provide critical environments for studying feedback mechanisms from star formation and its impacts on dwarf galaxy evolution. In particular, radio continuum (RC) observations offer valuable insights into cosmic ray dynamics, which play a significant role in shaping these processes.
Aims. This study investigates the detectability and spectral characteristics of RC emission in a sample of 15 dwarf galaxies (11 gas-rich, star-forming dwarfs and four blue compact dwarfs) spanning a broad range of stellar masses and star formation histories.
Methods. Using multi-band RC data (L/S-, C-, and X-band) from the Australia Telescope Compact Array, we analyse the physical conditions responsible for RC emission and explore the dominant emission mechanisms within these systems.
Results. RC emission is detected in 11 out of the 15 galaxies. Our results indicate that RC emission correlates strongly with star formation rate, far-infrared, and stellar mass, while dynamic parameters such as H
Microquasar remnants as hidden PeVatrons
No full textThe Large High Altitude Air Shower Observatory (LHAASO) has revealed numerous ultrahigh-energy gamma-ray sources of unknown origin. We propose that a fraction of them can be explained by microquasar remnants, i.e., binary systems where mass transfer has ceased and the central engine is quenched. Cosmic rays injected during the active phase of a microquasar may remain confined within its cocoon and subsequently interact with nearby molecular clouds, producing bright gamma-ray emission through pp collisions. Remnants of former super-Eddington systems can act as dark PeVatrons, releasing particles up to ∼10 PeV that illuminate surrounding clouds producing gamma rays reaching hundreds of tera-electron volts. This scenario provides a natural explanation for several unidentified Galactic LHAASO sources
JWST spectroscopic confirmation of the Cosmic Gems arc at
No full textWe present JWST/NIRSpec integral field spectroscopy of the Cosmic Gems arc, strongly magnified by the galaxy cluster SPT-CL J0615−5746. Six-hour integration using NIRSpec prism spectroscopy (resolution R ≃ 30 − 300), covering the spectral range 0.8 − 5.3 μm, reveals a pronounced Lyα-continuum break at λ ≃ 1.3 μm, as well as weak optical Hβ and [O II
Magnetic fields in the Shapley Supercluster core with POSSUM: Challenging model predictions
No full textContext. Faraday rotation measure (RM) grids provide a sensitive means to trace magnetized plasma across a wide range of cosmic environments.
Aims. We study the RM signal from the Shapley Supercluster core (SSC) in order to constrain the magnetic field properties of its gas. The SSC region consists of two galaxy clusters, A3558 and A3562, and two galaxy groups between them, at z ≃ 0.048.
Methods. We combined RM Grid data with thermal Sunyaev-Zeldovich effect data, obtained from the POlarisation Sky Survey of the Universe’s Magnetism (POSSUM) pilot survey, and Planck, respectively. To robustly determine the gas density, its magnetic field properties, and their correlation |B| ∝ neη, we studied the RM scatter in the SSC region (RM) and its behavior as a function of distance to the nearest cluster and/or group (dnrst). We compared observational results with semi-analytic Gaussian random field models and more realistic cosmological magnetohydrodynamical (MHD) simulations.
Results. With a sky-density of 36 RMs/deg2, we detect an excess RM scatter of 30.5 ± 4.6 rad/m2 in the SSC region. When we compare with models, we find an average magnetic field strength of ∼1−3 μG (in the groups and clusters). The RM(dnrst) profile, derived from data ranging from ∼0.3−1.8 r500 for all objects, is systematically flatter than expected compared to the models, with η < 0.5 being favored. Despite this discrepancy, we find that cosmological MHD simulations matched to the SSC structure most closely align with scenarios where the magnetic field is amplified by the turbulent velocity (vturb) in the intercluster regions Bℱ ∝ ne1/2vturb on scales dnrst ≲ 0.8.
Conclusions. The dense RM grid and precision provided by POSSUM allows us to probe magnetized gas in the SSC clusters and groups on scales within and beyond their r500. Flatter-than-expected RM scatter profiles reveal a significant challenge in reconciling observations with even the most realistic predictions from cosmological MHD simulations in the outskirts of interacting clusters