arXiv subjects

Lewis McCallum

Publications and source records attributed to Lewis McCallum.

11 recordsLinked to original sources

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

Milky Way Atlas: A radial-velocity-resolved, three-dimensional map of H I within 1.25 kpc

We present a velocity-resolved three-dimensional map of local atomic hydrogen (HI) within 1.25 kpc of the Sun, tackling the challenge of converting emission from position-position-velocity space into true 3D structure. Our method combines the HI4PI full-sky survey with the Edenhofer et al. (2024) 3D dust map in the framework of Information Field Theory, enabling a joint reconstruction of the local HI density, radial velocity field, and effective line width while also separating emission arising inside the mapped local volume from more distant Galactic HI. The inference is driven by morphological matching between dust and HI structures together with kinematic coherence in 3D space. Synthetic data tests show that the method recovers the local density and velocity structure, even in the presence of substantial contamination from distant emission. The resulting map reveals a smoother, more diffuse local HI distribution than the dust, a declining HI-to-dust ratio toward high dust column densities consistent with the atomic-to-molecular transition, and a velocity field that captures both large-scale Galactic rotation and local non-circular velocities. Independent comparisons with maser and young stellar cluster velocities agree with the recovered kinematics. This HI map provides a new three-dimensional, kinematically resolved view of the nearby atomic interstellar medium and a foundation for localising other velocity-resolved Galactic emission in physical space.

astro-ph.GA↗

arXiv2026

The radial component of the local Galactic magnetic field in 3D

We present a distance-resolved reconstruction of the local line-of-sight Galactic magnetic field, $B_{||}$, by combining a 3D electron density ($n_{e}$) map derived from dust map-informed simulations and a full-sky map of Faraday rotation measure (RM). The forward model evaluates RM on the same 3D grid as the $n_{e}$ map and compares to the Galactic Faraday rotation sky. We infer $B_{||}$ with a Gaussian-process prior whose power spectrum is inferred from the data using geometric variational inference. The result is a local (within 1.25 kpc where $|b|>5^{\circ}$) map of $B_{||}$ with uncertainties. The reconstructed RM sky reproduces prominent features of Faraday rotation sky, with a root mean square average strength of $B_{||}$ of $1.63\pm 0.16$ $\mu$G. In face-on views, the magnetic field exhibits coherent patches with alternating sign and hints of kpc-scale modulations, but with significant structure seen on scales of order 100 pc. The $B_{||}$ field is seen to exhibit a 3D power spectrum with an average slope of $-2.73 \pm 0.19$. We validate our $B_{||}$ reconstruction with Galactic pulsars. Predicted RMs (computed by integrating $n_{e}B_{||}$ to each pulsar's distance) correlates with observed RMs, and predicted dispersion measures (DMs) from the $n_{e}$ map also correlate with measured DMs, albeit with significant scatter.

astro-ph.GA↗

arXiv2025

WASP-12, shrouded in mystery or just cold gas?

Observations of the planet-hosting star WASP-12 show a distinctive depression in the \ion{Mg}{ii} and \ion{Ca}{ii} resonance lines. This has been interpreted as a marker of atmospheric loss from the close-in hot Jupiter WASP-12b and the resulting formation of a gas torus around the star. In this paper we quantify the \ion{Mg}{ii} absorption from this torus, compared to that provided by the stellar wind, the stellar astrosphere and the ISM. To do this we piece together the full density profile of \ion{Mg}{ii} from WASP-12 to an observer on Earth using a combination of hydrodynamical simulations and observations. We find that the bulk of the gas along the line of sight is contained within a dense torus close to WASP-12. However, the temperatures in this torus are sufficient to promote Mg into a doubly (\ion{Mg}{iii}) or higher ionized state. As a result, the singly ionized fraction (\ion{Mg}{ii}) is low. We find that most of the \ion{Mg}{ii} is not in the torus but in the ISM. Despite this, the total column density of \ion{Mg}{ii} is two orders of magnitude lower than required to explain observations of the system. To resolve this discrepancy, we note that the torus gas is at a temperature where it will cool efficiently. We speculate that the onset of the cooling instability will cause the torus to fragment, forming cold clumps with a higher fraction of \ion{Mg}{ii}, capable of explaining the observed absorption.

astro-ph.EP↗

arXiv2025

SDSO1 is a Shocked Ghost Planetary Nebula in Front of M 31

We present new, deep narrowband imagery and discuss the nature of SDSO 1, the large [O III]-emitting nebula centered 1.5 degrees SE of M 31. We find strong evidence to support the hypothesis that SDSO 1 is unrelated to M 31 and is instead a faded, giant (D = 20 pc), ghost planetary nebula (GPN) expelled by the symbiotic WD binary star EG Andromedae. The associated 45-pc long turbulent tail, seen in projection in front of M 31, yields an estimated age of 400 kyr. The initial hypersonic velocity of 91 km/s drives a strong bow shock into the local interstellar medium and a reverse shock into the GPN. The SDSO 1 GPN has reached the terminal phase in its evolution where its outward expansion and forward motion have been decelerated greatly by ram pressure and the [O III] emission arises primarily from the reverse shock. We establish the shock-powered GPN phase as a new phase of planetary nebula (PN) evolution, and identify 24 candidate GPNe by their large size and shock-tail morphology. This includes several giant halos of younger PNe, possibly expelled by now degenerate binary companions. The interaction of an old, fast-moving GPN with the ISM generates shocks that remain visible long after the photoionized PN shell has faded below the limit of detectability.

astro-ph.GA↗

arXiv2025

A three-dimensional, multi-wavelength view and time-dependent analysis of the Milky Way's local ionized gas

This work is the continuation of a series attempting to characterize the local warm ionized medium through both static and time dependent simulations. We build upon our three dimensional, observationally-derived simulation of the local photoionized interstellar medium - based on static photoionization simulations constrained by 3D dust maps - to include metals required to predict collisionally excited optical and infrared emission lines, providing the first all-sky prediction of a series of lines including [SII] 6716$\mathring{A}$, [NII] 6584$\mathring{A}$ and [OIII] 5007$\mathring{A}$. While these predictions only include O-star photoionization under ionization equilibrium, we also carry out a suite of radiation-hydrodynamics simulations including time-dependent metal ionization and the effects of supernova feedback to highlight missing features in our predicted skies. We use the simulations to estimate the very local (1 $\rm kpc^{2}$) Galactic star formation rate, finding a rate of 370 $\rm M_{\odot}~Myr^{-1}~kpc^{-2}$ provides the best match between the observationally-derived and ab-initio simulations. This is approximately a factor of four lower than previous estimates for the star formation rate required to support an observed layer of high-altitude diffuse ionized gas, possibly suggesting a `bursty' star formation history in the region surrounding the Sun. We also investigate the effects of O-star environments on their ability to ionize large volumes of diffuse ionized gas, and find it is likely ionized by a small number of luminous O-stars located in regions where the leakage of their Lyman continuum photons can produce the vast volumes of ionized gas observed in the midplane and at high galactic altitudes.

astro-ph.GA↗

arXiv2025

Origin of the IRAS Vela Shell: New Insights from 3D Dust Mapping

The IRAS Vela Shell (IVS) is a structure of enhanced FIR emission located towards the Gum Nebula, a prominent region of $\rm H\alpha$ emission in the local Milky Way shaped by various galactic stellar feedback over the past several million years. We constrain the 3D spatial geometry of the IVS using a parsec-resolution 3D dust map and contextualize it within the broader Gum Nebula. Our analysis reveals a dense, bowl-like IVS structure below the Galactic plane, with a more diffuse component above. We obtain a total shell mass of $5.1_{-2.4}^{+2.4}\times 10^{4}\;\rm M_{\odot}$ and, incorporating previous studies on shell expansion, a momentum of $6.0_{-3.4}^{+4.7}\times 10^{5}\;\rm M_{\odot}\;km\; s^{-1}$. We find a spatial correlation between the morphology of the dust-traced IVS and the Gum Nebula's $\rm H\alpha$ emission when projected onto the sky. We quantify contributions of feedback from stellar winds, an expanding HII region, and supernovae to the IVS formation, finding that stellar winds are subdominant. Our momentum analysis shows that both an HII region and supernova feedback could drive the shell's expansion. Using astrometric constraints from Gaia and Hipparcos, we trace back nearby feedback sources and find that the massive stars $\gamma2$ Velorum and $\zeta$ Puppis are currently within the IVS, producing enough ionizing luminosity to form an HII region of comparable size. Alternatively, if the IVS' momentum is primarily driven by supernovae, $1-2$ events would be required. We also identify several young massive clusters that could have hosted supernovae within the past 3 Myr.

astro-ph.GA↗

arXiv2025

The H$\alpha$ sky in three dimensions

We combine parallax distances to nearby O stars with parsec-scale resolution three-dimensional dust maps of the local region of the Milky Way (within 1.25 kpc of the Sun) to simulate the transfer of Lyman continuum photons through the interstellar medium. Assuming a fixed gas-to-dust ratio, we determine the density of ionized gas, electron temperature, and H$\alpha$ emissivity throughout the local Milky Way. There is good morphological agreement between the predicted and observed H$\alpha$ all-sky map of the Wisconsin H$\alpha$ Mapper. We find that our simulation underproduces the observed H$\alpha$ emission while overestimating the sizes of HII regions, and we discuss ways in which agreement between simulations and observations may be improved. Of the total ionizing luminosity of $5.84 \times 10^{50}~{\rm photons~s^{-1}}$, 15% is absorbed by dust, 64% ionizes "classical'' HII regions, 11% ionizes the diffuse warm ionized medium, and 10% escapes the simulation volume. We find that 18% of the high altitude ($|b| > 30^{\circ}$) H$\alpha$ arises from dust-scattered rather than direct emission. These initial results provide an impressive validation of the three-dimensional dust maps and O-star parallaxes, opening a new frontier for studying the ionized ISM's structure and energetics in three dimensions.

astro-ph.GA↗

arXiv2024

Time-dependent metal ionization and the persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies

We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from midplane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low density gas result in persistent large volumes of ions with high ionization potentials, such as O III and Ne III. In particular, the vertically extended layers of Ne III in our time-dependent simulations result in [Ne III] 15$\mu$m/[Ne II] 12$\mu$m emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low density gas at high altitudes.

astro-ph.GA↗

arXiv2024

JWST MIRI and NIRCam observations of NGC 891 and its circumgalactic medium

We present new JWST observations of the nearby, prototypical edge-on, spiral galaxy NGC 891. The northern half of the disk was observed with NIRCam in its F150W and F277W filters. Absorption is clearly visible in the mid-plane of the F150W image, along with vertical dusty plumes that closely resemble the ones seen in the optical. A $\sim 10 \times 3~{\rm kpc}^2$ area of the lower circumgalactic medium (CGM) was mapped with MIRI F770W at 12 pc scales. Thanks to the sensitivity and resolution of JWST, we detect dust emission out to $\sim 4$ kpc from the disk, in the form of filaments, arcs, and super-bubbles. Some of these filaments can be traced back to regions with recent star formation activity, suggesting that feedback-driven galactic winds play an important role in regulating baryonic cycling. The presence of dust at these altitudes raises questions about the transport mechanisms at play and suggests that small dust grains are able to survive for several tens of million years after having been ejected by galactic winds in the disk-halo interface. We lay out several scenarios that could explain this emission: dust grains may be shielded in the outer layers of cool dense clouds expelled from the galaxy disk, and/or the emission comes from the mixing layers around these cool clumps where material from the hot gas is able to cool down and mix with these cool cloudlets. This first set of data and upcoming spectroscopy will be very helpful to understand the survival of dust grains in energetic environments, and their contribution to recycling baryonic material in the mid-plane of galaxies.

astro-ph.GA↗

arXiv2024

The persistence of high altitude non-equilibrium diffuse ionized gas in simulations of star forming galaxies

Widespread, high altitude, diffuse ionized gas with scale heights of around a kiloparsec is observed in the Milky Way and other star forming galaxies. Numerical radiation-magnetohydrodynamic simulations of a supernova-driven turbulent interstellar medium show that gas can be driven to high altitudes above the galactic midplane, but the degree of ionization is often less than inferred from observations. For computational expediency, ionizing radiation from massive stars is often included as a post-processing step assuming ionization equilibrium. We extend our simulations of a Milky Way-like interstellar medium to include the combined effect of supernovae and photoionization feedback from midplane OB stars and a population of hot evolved low mass stars. The diffuse ionized gas has densities below 0.1 ${\rm cm^{-3}}$, so recombination timescales can exceed millions of years. Our simulations now follow the time-dependent ionization and recombination of low density gas. The long recombination timescales result in diffuse ionized gas that persists at large altitudes long after the deaths of massive stars that produce the vast majority of the ionized gas. The diffuse ionized gas does not exhibit the large variability inherent in simulations that adopt ionization equilibrium. The vertical distribution of neutral and ionized gas is close to what is observed in the Milky Way. The volume filling factor of ionized gas increases with altitude resulting in the scale height of free electrons being larger than that inferred from H$α$ emission, thus reconciling the observations of ionized gas made in H$α$ and from pulsar dispersion measurements.

astro-ph.GA↗