arXiv subjects

Efrem Maconi

Publications and source records attributed to Efrem Maconi.

4 recordsLinked to original sources

arXiv2026

The fading hierarchy of Galactic open clusters

Galactic open clusters provide a record of both hierarchical star formation and the subsequent dynamical evolution of the Milky Way disk. We use the two-point correlation function to characterize the spatial and kinematic clustering of open clusters in the solar neighborhood, considering their three-dimensional (3D) distributions and their projections onto the Galactic plane, as well as subsamples divided by age, mass, and survey volume. We quantify the clustering through fractal dimensions and characteristic correlation scales. We find that the youngest clusters have fractal dimensions comparable to those measured in the interstellar medium, suggesting that they retain part of the hierarchical structure of their natal molecular clouds. The clustering strength then decreases systematically with age and becomes weak on a characteristic timescale of order 100 Myr. This evolution is scale dependent: the excess correlation at tens of parsecs fades more rapidly than the weaker correlation at hundreds of parsecs. By contrast, we find only a weak dependence of the clustering properties on cluster mass and volume. Using the same cluster sample, we derive an empirical mapping between projected and 3D fractal dimensions, providing an observational calibration for comparing the Milky Way with studies of external galaxies, where only projected measurements are available. The open-cluster population exhibits characteristic spatial and kinematic clustering scales of approximately 370 pc and 11 km/s, respectively. These results support a picture in which young open clusters inherit a spatial hierarchy from star formation and progressively lose their spatial correlations through subsequent evolution.

astro-ph.GA↗

arXiv2026

The Nearby Star Formation and Supernova Histories Reconstructed from Young Star Clusters

We reconstruct the recent star formation and core-collapse supernova (ccSN) histories of the Solar Neighborhood from the past trajectories of young star clusters. Using a \textit{Gaia}-based cluster sample with newly derived ages, masses, and bulk 3D velocities, we integrate orbits backward in an assumed axisymmetric Galactic potential and combine the trajectories with IMF sampling and stellar lifetimes to infer ccSN times and locations over the past 50 Myr. The result is an all-sky, 3D, time-resolved map of nearby ccSN activity for comparison with high-resolution 3D views of the local interstellar medium. The 0--15 Myr map shows strong enhancements toward Orion, Vela, Sco--Cen, and Cepheus, many within present-day cavities and shells. At earlier times, the dominant enhancements trace the Collinder 135, Messier 6, and Alpha Persei cluster families, showing how the remnants of massive star-forming complexes have shaped the recent local feedback history. We recover a bursty star formation history followed by a delayed, smoother ccSN history. Over the last 40 Myr, the mean star formation and ccSN rates are $823~M_\odot~\mathrm{Myr}^{-1}$ and $7.7~\mathrm{Myr}^{-1}$, respectively, corresponding to a Milky Way rate of $0.55\pm0.03~\mathrm{century}^{-1}$. Present-day OB-star catalogs yield rates ranging from agreement with the cluster reconstruction to several times higher. Because the catalogs overlap weakly and require different corrections, we do not rescale the ccSN map. Our reconstruction provides an empirical framework for connecting the recent history of massive-star feedback to the 3D structure and life cycle of gas in the nearby Milky Way.

astro-ph.GA↗

arXiv2026

Shaping the diffuse X-ray sky: Structure, Variability and Visibility

The Local Bubble (LB) is a hot, low-density cavity in the solar neighborhood, inside which the Solar System is currently located. The X-ray emission from such bubbles is strongly governed by the gas density, temperature, and the effects of line-of-sight column density. Yet the physical processes that control the formation and evolution of this emission remain incompletely understood. We analyze a LB analogue identified within a magnetohydrodynamical simulation to investigate the key physical factors that shape its X-ray properties. In post-processing, we examine the spatial distribution, variability, and observational constraints of the X-ray emission. Our study reveals three main results: (1) Shortly after a supernova (SN), the bulk of the X-ray emission arises from a small fraction of the bubble's volume, concentrated in hot regions around recent SN sites. Approximately 95% of the X-ray luminosity originates from less than 1% of the total bubble volume. During quiescent phases without recent SNe, the emission morphology changes substantially, with X-ray-bright regions becoming more volume-filling. (2) Column density effects strongly modulate the observable X-ray signal. Gas with column densities exceeding $N_\mathrm{H} \gtrsim 10^{20} \,\mathrm{cm}^{-2}$ efficiently absorbs soft X-ray photons, limiting the depth to which observations can probe. This absorption causes a significant fraction of the sky to be obscured from external soft X-rays. Differences between active and quiescent phases further influence how much of the total bubble emission is visible from within. (3) The X-ray flux shows pronounced temporal variability on Myr timescales, with SN events producing rapid, transient luminosity enhancements, followed by steep declines due to adiabatic cooling. The total flux varies by several orders of magnitude, with SN-driven peaks fading within $10^5$ years.

astro-ph.HE↗

arXiv2025

Modeling Local Bubble analogs II: Synthetic Faraday rotation maps

Faraday rotation describes the change of the linear polarization angle of radiation passing through a magnetized plasma and it is quantified by the rotation measure (RM), which is related to the line-of-sight (LOS) magnetic field component and the thermal electron density traversed by light along its path toward the observer. However, it is challenging to disentangle the signal from different LOS portions and separate the contribution from the local ISM. This is particularly relevant since the Sun is located within the Local Bubble (LB), a low-density and hot cavity formed by past SN events, making it essential to investigate how this environment may influence the observed RM values. The present study investigates the imprint of the local environment on the synthetic RM signal, as measured by an observer within a LB-like cavity. The RM derived from diffuse polarized synchrotron radiation produced by CR electrons at decimeter wavelengths is also analyzed. We produce synthetic RM maps for an observer placed inside a LB candidate, selected from a MHD simulation that resembles the properties of the ISM in the Solar vicinity. Using the capabilities of the radiative transfer code POLARIS, we study the imprint of the cavity walls on the RM signal. As the MHD simulation does not account for CR diffusion, we develop a CR toy-model to study the Faraday rotation of the diffuse polarized synchrotron radiation. We find that (i) the imprint of local structures, such as the walls of the LB candidate and the edges of other supernovae blown cavities, is of fundamental importance for interpreting the global Faraday sky; (ii) the LB has a non negligible contribution to the sinusoidal patterns of RM as a function of Galactic longitude seen in observations; and (iii) the RM signal from diffuse synchrotron emission shows a strong correspondence with the RM signal generated by the LB candidate walls.

astro-ph.GA↗