Yago Ascasibar

The local environment of a Type Ia supernova (SN Ia) traces the local stellar-population age (a statistical proxy for the progenitor age), star formation, dust, and chemical enrichment that can influence both its light-curve properties and its standardized luminosity. We assembled a homogeneous explosion-site dataset to test how near-ultraviolet (UV) imaging combined with optical integral-field spectroscopy improves the characterization of SN Ia environments and their connection to SN Ia observables. We analyzed 340 low-redshift SN Ia explosion sites observed with HST/WFC3 in F275W together with their matched VLT/MUSE spectroscopy. For each site, we measured local photometry and extracted a 1 kpc-aperture spectrum. We then modeled the stellar continuum with STARLIGHT in a joint UV+optical fit, derived local stellar and gas-phase properties, and fit the SN light curves with sncosmo /SALT3-NIR. We find that UV emission is detected at 235 of the 337 sites with valid HST imaging. The UV- and H α -based star-formation-rate surface densities are strongly correlated, with the UV estimates systematically higher by about 0.5 dex. Including the UV constraint in the STARLIGHT fit shifts local luminosity-weighted ages toward older values by a median of +0.20 dex for UV detections and +0.45 dex for UV nondetections, showing that UV data help break age-dust-metallicity degeneracies and substantially alter and tighten the inferred local stellar-population ages within the adopted modeling framework. Consistently, F275W− r is found to be very strongly correlated with the joint-fit stellar age. Within the 169-SN Ia calibration sample, the joint stellar age, the H α specific star-formation rate (sSFR), and the UV sSFR all correlate strongly with the SALT3 stretch parameter, x ₁ , with significances above 6.8 σ . After standardization, the residual Hubble-residual trends are weaker: the strongest trend is found for the local mass-weighted age, while the UV and H α sSFRs show residual offsets of comparable sign and amplitudes of order ∼0.05 mag. None of the environmental dependencies of the Hubble residual exceeds 3 σ . The results point to a dominant empirical association between light-curve stretch and a covariant young-stellar-population axis, largely absorbed by the standard light-curve corrections, while any residual luminosity dependence on the local environment is weaker and more subtle. If confirmed with larger samples, these residual trends may still become relevant for the younger SN Ia populations expected at higher redshift. Therefore, they should be tested in cosmology analyses with forthcoming Roman and JWST SN samples.

The star-forming main sequence (SFMS) is a tight relation observed between stellar masses and star formation rates (SFR) in a population of galaxies. This relation is observed at different redshifts, in various morphological, and environmental domains, and is key to understanding the underlying relations between a galaxy budget of cold gas and its stellar content. Euclid Quick Data Release 1 (Q1) gives us the opportunity to investigate this fundamental relation in galaxy formation and evolution. We complement the Euclid release with public IRAC observations of the Euclid Deep Fields, improving the quality of recovered photometric redshifts, stellar masses, and SFRs, as is shown both with simulations and a comparison with available spectroscopic redshifts. From Q1 data alone, we recover more than ∼30 k galaxies with log ₁₀ ( M _* / M _⊙ ) > 11, giving a precise constraint of the SFMS at the high-mass end. We investigated the SFMS, in a redshift interval between 0.2 and 3.0, comparing our results with the existing literature and fitting them with a parameterisation taking into account the presence of a bending of the relation at the high-mass end, depending on the bending mass, M ₀ . We find good agreement with previous results in terms of M ₀ values, and an increasing trend for the relation scatter at higher stellar masses. We also investigate the distribution of physical (e.g. dust absorption, A _V , and formation age) and morphological properties (e.g., Sérsic index and radius) in the SFR–stellar mass plane, and their relation with the SFMS. These results highlight the potential of Euclid in studying the fundamental scaling relations that regulate galaxy formation and evolution in anticipation of the forthcoming Data Release 1.

Context . In the current era of multi-wavelength and multi-messenger astronomy, international organisations are actively working on the definition of new standards for the publication of astronomical data, and substantial effort is being devoted to making them available through public archives. Aims . We present a set of tools that allow user-friendly access and the basic scientific analysis of observations in the Hierarchical Progressive Survey (HiPS) format, and we use them to gauge the quality of representative skymaps at ultraviolet, optical, and infrared wavelengths. Methods . We apply a fully automatic procedure to derive aperture photometry in ten different bands for the 323 nearby galaxies in the Herschel Reference Sample (HRS), and compare its results with the rigorous analyses involving specialised knowledge and human intervention carried out by the HRS team. Results . Our experiment shows that nine of the ten skymaps considered preserve the original quality of the data, and the photometric fluxes returned by our pipeline are consistent with the HRS measurements within a few percent. In the case of Herschel PACS maps at 100 μm, we uncovered a systematic error that we ascribe to an inconsistent combination of data products with different spatial resolutions. For the remaining skymaps, the estimated statistical uncertainties provide a realistic indication of the differences with respect to the HRS catalogue. Conclusions . In principle, the currently available HiPS skymaps in the Flexible Image Transport System (FITS) format allow one to carry out broadband photometric analyses with an accuracy of the order of a few percent, but some level of human intervention is still required. In addition to assessing data quality, we also propose a series of recommendations to realise the full potential of the HiPS format for the scientific analysis of large astronomical datasets.

We present a sub-grid model for star formation in galaxy simulations, incorporating molecular hydrogen (H ₂ ) production via dust grain condensation and its destruction through star formation and photodissociation. Implemented within the magnetohydrodynamical code AREPO , our model tracks the non-equilibrium mass fractions of molecular, ionised, and atomic hydrogen, as well as a stellar component, by solving a system of differential equations governing mass exchange between these phases. Star formation is treated with a variable rate dependent on the local H ₂ abundance, which itself varies in a complex way with key quantities such as gas density and metallicity. Testing the model in a cosmological simulation of a Milky Way-mass galaxy, we obtain a well-defined spiral structure at z =0, including a gas disc twice the size of the stellar one, alongside a realistic star formation history. Our results show a broad range of star formation efficiencies per free-fall time, from as low as 0.001% at high redshift to values between 0.1% and 10% for ages ≳ 3−4 Gyr. These findings align well with observational estimates and simulations of a turbulent interstellar medium. Notably, our model reproduces a star formation rate versus molecular hydrogen surface densities relation akin to the molecular Kennicutt-Schmidt law. Furthermore, we find that the star formation efficiency varies with density and metallicity, providing an alternative to fixed-efficiency assumptions and enabling comparisons with more detailed star formation models. Comparing different star formation prescriptions, we find that in models that link star formation to H ₂ , star formation onset is ∼ 500 Myr later than those relying solely on total or cold gas density.

Stellar population synthesis is a crucial methodology in astrophysics, enabling the interpretation of the integrated light of galaxies and stellar clusters. By combining empirical and/or theoretical libraries of the spectral energy distributions emitted by simple stellar populations (SSPs) with star formation history (SFH) and chemical evolution models, population synthesis can help estimate essential properties of galaxies, such as total stellar mass, star formation rate, massweighted age, metallicity, and so on. PST is a Python library that offers a comprehensive and flexible framework for stellar population synthesis. Its main goal is to easily and efficiently compute composite spectra using different galaxy evolution models and SSP libraries. It also incorporates additional effects such as cosmic redshift, dust extinction and attenuation, and computes several observable quantities derived from the spectra, including broadband photometric fluxes and equivalent widths.

Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical or instrumental backgrounds. We provide an updated assessment of the sensitivity of the Cherenkov Telescope Array (CTA) to such signals, based on observations of the Galactic centre region as well as of selected dwarf spheroidal galaxies. We find that current limits and detection prospects for dark matter masses above 300 GeV will be significantly improved, by up to an order of magnitude in the multi-TeV range. This demonstrates that CTA will set a new standard for gamma-ray astronomy also in this respect, as the world's largest and most sensitive high-energy gamma-ray observatory, in particular due to its exquisite energy resolution at TeV energies and the adopted observational strategy focussing on regions with large dark matter densities. Throughout our analysis, we use up-to-date instrument response functions, and we thoroughly model the effect of instrumental systematic uncertainties in our statistical treatment. We further present results for other potential signatures with sharp spectral features, e.g. box-shaped spectra, that would likewise very clearly point to a particle dark matter origin.

We study the origin of the positron excess observed in the local cosmic-ray spectrum at high energies, and relate it to the cosmic rays and gamma-ray emission across the entire Galaxy. In particular, we explore the hypothesis of a single, dominant source accountable for primary electron-positron pairs. Since we are agnostic about the physical nature of the underlying source population, we consider four models that are representative of young pulsars, old stars (as a tracer of millisecond pulsars), and annihilating dark matter particles. In the dark matter hypothesis, we consider both a cored and a cuspy model for the halo in the Milky Way. Then, we compare the associated gamma-ray sky maps with Fermi-LAT data. We find that the emission arising from pulsar wind nebulae is fairly concentrated near the mid plane, and therefore additional cosmic-ray sources must be invoked to explain the emission at the center of the Galaxy. If the local positron excess were mainly due to millisecond pulsars, inverse Compton scattering by the particles injected would naturally account for a non-negligible fraction of the central gamma-ray emission. The same process would lead to a tension for a standard NFW dark matter profile, exceeding the gamma-ray data by almost a factor of 2 in some regions of the Galaxy. Although the results for an isothermal, cored profile are in agreement with these data, the cross section needed in both cases is around 2 orders of magnitude above the thermal cross-section, disfavouring the dark matter interpretation.

Context. The first hydrostatic core (FHSC) phase is a brief stage in the protostellar evolution that is difficult to detect. Its chemical composition determine that of later evolutionary stages. Numerical simulations are the tool of choice to study these objects. Aims. Our goal is to characterize the chemical evolution of gas and dust during the formation of the FHSC. Moreover, we are interested in analyzing, for the first time with 3D magnetohydrodynamic (MHD) simulations, the role of grain growth in its chemistry. Methods. We postprocessed 2 × 10⁵ tracer particles from a RAMSES non-ideal MHD simulation using the codes NAUTILUS and SHARK to follow the chemistry and grain growth throughout the simulation. Results. Gas-phase abundances of most of the C, O, N, and S reservoirs in the hot corino at the end of the simulation match the ice-phase abundances from the prestellar phase. Interstellar complex organic molecules such as methyl formate, acetaldehyde, and formamide are formed during the warm-up process. Grain size in the hot corino (n_H > 10¹¹ cm⁻³) increases forty-fold during the last 30 kyr, with negligible effects on its chemical composition. At moderate densities (10¹⁰ < n_H < 10¹¹ cm⁻³) and cool temperatures 15 < T < 50 K, increasing grain sizes delay molecular depletion. At low densities (n_H ~ 10⁷ cm⁻³), grains do not grow significantly. To assess the need to perform chemo-MHD calculations, we compared our results with a two-step model that reproduces well the abundances of C and O reservoirs, but not the N and S reservoirs. Conclusions. The chemical composition of the FHSC is heavily determined by that of the parent prestellar core. Chemo-MHD computations are needed for an accurate prediction of the abundances of the main N and S elemental reservoirs. The impact of grain growth in moderately dense areas delaying depletion permits the use of abundance ratios as grain growth proxies.