Cameren Swiggum

Recent 3D dust maps of the local Milky Way are revolutionizing our understanding of the Sun’s Galactic neighborhood, providing much needed insight into the large-scale organization of the interstellar medium. Focusing on the largest scales in Gaia -based 3D dust maps, we find a pattern of seven highly elongated, mostly parallel structures in the local ∼5 kpc ² , five of which were previously unknown. These structures show pitch angles of 33.5 ± 4.0 ^◦ and masses ranging from 10 ⁵ to 10 ⁶ M _⊙ . We refer to these structures as superclouds. Nearly all known star-forming regions in the solar neighborhood lie within the superclouds, primarily along their central axes, supporting the idea that they act as gas reservoirs for the formation of giant molecular clouds. All but one of the seven superclouds show an underlying undulation, indicating that this is not a property unique to the Radcliffe Wave. We find that while the superclouds have linear masses that vary by about a factor of 4, their volume densities only vary by about 10%. This suggests that superclouds self-regulate their physical sizes and internal structure to maintain pressure equilibrium with their environment. These findings establish a new framework for understanding how large-scale Galactic structures shape the conditions for star formation in the solar vicinity, and likely in galaxies like the Milky Way.

We present a nonparametric reconstruction of the three-dimensional velocity field of the Scorpius-Centaurus OB association (Sco-Cen). Using Gaia DR3 astrometry and radial velocities, we inferred the velocity field using information field theory on a 70 × 70 × 50 grid at a 3 pc resolution. Our model suggests the existence of a primary stellar velocity field with a secondary field that accounts for an additional young kinematic component in Upper Scorpius and Lupus. We find clear tracers of a feedback-driven expansion of the association, while Galactic rotation appears to play a subordinate role. The results confirm the existence of cluster chains and reveal coherent large-scale expansion with characteristic speeds of 1–2 km s ⁻¹ and local maxima of about 10 km s ⁻¹ . Power spectra indicate an excess of small-scale structure and slopes shallower than Kolmogorov, consistent with energy injection from stellar feedback. Maps of the divergence reveal net positive values, implying an approximate dispersal timescale of 10–15 Myr. A comparison with molecular gas in Lupus and Ophiuchus shows broadly consistent patterns but systematic velocity offsets of several km s ⁻¹ , suggesting partial decoupling for optically visible young stars and gas. The framework presented provides a physically motivated description of the Sco-Cen velocity field and a basis for quantifying the dynamical state and feedback history of OB associations in the local Galaxy.

Recent measurements of cosmogenic ¹⁰Be in deep-ocean ferromanganese crusts from the central and northern Pacific have revealed an anomalous concentration between 11.5 and 9.0 Myr ago, peaking at 10.1 Myr. One possible explanation is a nearby supernova (SN) event. Motivated by this and by the proximity of the Solar System to the Orion star-forming region during that period, we estimated the probability that at least one SN occurred between the onset and peak of the anomaly. Using an open cluster catalog based on Gaia DR3, we traced back the orbits of 2725 clusters and the Sun over the past 20 Myr and computed the expected number of SN events. We found 19 clusters with a probability greater than 1% each of producing at least one SN within 100 pc of the Sun in the time interval 11.5–10.1 Myr ago. The total cumulative probability exceeds zero at 35 pc from the Sun and increases rapidly with distance, reaching 68% near 100 pc. Two young clusters dominate the SN probability: ASCC 20 contributes most within 70 pc, while OCSN 61 becomes more significant beyond that distance. Our results support the possibility of an SN origin for the ¹⁰Be anomaly and highlight the importance of additional ¹⁰Be records from independent terrestrial archives to determine whether the anomaly is of astrophysical or terrestrial origin.

Moving groups in the solar neighborhood are ensembles of commoving stars, likely originating due to forces from spiral arms, the Galactic bar, or external perturbations. Their comovement with young clusters indicates recent star formation within these moving groups, but a lack of precise 3D position and velocity measurements has obscured this connection. Using backward orbit integrations of 509 clusters within 1 kpc–based on Gaia DR3 and supplemented with APOGEE-2 and GALAH DR3 radial velocities–we traced their evolution over the past 100 Myr. We find that most clusters separate into three spatial groups that each trace one of the Pleiades, Coma Berenices, and Sirius moving groups. The same trend is not seen for the Hyades moving group. The young clusters of the Alpha Persei, Messier 6, and Collinder 135 families of clusters, previously found to have formed in three massive star-forming complexes, commove with either the Pleiades (Alpha Persei and Messier 6) or the Coma Berenices (Collinder 135). Our results provide a sharper view of how large-scale Galactic dynamics have shaped recent, nearby star formation.

The IRAS Vela Shell (IVS) is a structure of enhanced far-IR (FIR) emission located toward the Gum Nebula, a prominent region of Hα 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 × 1 0 4 M ⊙ and, incorporating previous studies on shell expansion, a momentum of 6 . 0 − 3.4 + 4.7 × 1 0 5 M ⊙ km s − 1 . We find a spatial correlation between the morphology of the dust-traced IVS and the Gum Nebula’s Hα emission when projected onto the sky. We quantify contributions of feedback from stellar winds, an expanding H ii region, and supernovae to the IVS formation, finding that stellar winds are subdominant. Our momentum analysis shows that both an H ii 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 γ2 Velorum and ζ Puppis are currently within the IVS, producing enough ionizing luminosity to form an H ii region of comparable size. Alternatively, if the IVS’ momentum is primarily driven by supernovae, one to two events would be required. We also identify several young massive clusters that could have hosted supernovae within the past 3 Myr.

We present a reconstruction of the line-of-sight motions of the local interstellar medium (ISM) based on the combination of a model of the three-dimensional dust density distribution within 1.25 kpc from the Sun and the H I and CO line emission within Galactic latitudes |b| ≤ 5°. We used the histogram of oriented gradient (HOG) method, a computer vision technique for evaluating the morphological correlation between images, to match the plane-of-the-sky dust distribution across distances with the atomic and molecular line emission. We identified a significant correlation between the 3D dust model and the line emission. We employed this correlation to assign line-of-sight velocities to the dust across density channels and produce a face-on map of the local ISM radial motions with respect to the local standard of rest (LSR). We find that most of the material in the 3D dust model follows the large-scale pattern of Galactic rotation; however, we also report local departures from the rotation pattern with standard deviations of 10.8 and 6.6 km s⁻¹ for the H I and CO line emission, respectively. The mean kinetic energy densities corresponding to these streaming motions are around 0.11 and 0.04 eV/cm³ from either gas tracer. Assuming homogeneity and isotropy in the velocity field, these values are within a factor of a few of the total kinetic energy density. These kinetic energy values are roughly comparable to other energy densities, thus confirming the near-equipartition in the local ISM. Yet, we identify energy and momentum overdensities of around a factor of ten concentrated in the Radcliffe Wave, the Split, and other local density structures. Although we do not find evidence of the local spiral arm’s impact on these energy overdensities, their distribution suggests the influence of large-scale effects that, in addition to supernova feedback, shape the energy distribution and dynamics in the solar neighborhood.

Context. As the Solar System orbits the Milky Way, it encounters various Galactic environments, including dense regions of the interstellar medium (ISM). These encounters can compress the heliosphere, exposing parts of the Solar System to the ISM, while also increasing the influx of interstellar dust into the Solar System and Earth’s atmosphere. The discovery of new Galactic structures, such as the Radcliffe wave, raises the question of whether the Sun has encountered any of them. Aims. The present study investigates the potential passage of the Solar System through the Radcliffe wave gas structure over the past 30 million years (Myr). Methods. We used a sample of 56 high-quality, young (≤30 Myr) open clusters associated with a region of interest of the Radcliffe wave to trace its motion back and investigate a potential crossing with the Solar System’s past orbit. Results. We find that the Solar System’s trajectory intersected the Radcliffe wave in the Orion region. We have constrained the timing of this event to between 18.2 and 11.5 Myr ago, with the closest approach occurring between 14.8 and 12.4 Myr ago. Notably, this period coincides with the Middle Miocene climate transition on Earth, providing an interdisciplinary link with paleoclimatology. The potential impact of the crossing of the Radcliffe wave on the climate on Earth is estimated. This crossing could also lead to anomalies in radionuclide abundances, which is an important research topic in the field of geology and nuclear astrophysics.

The TW Hydrae Association (TWA) is a young local association (YLA) about 50 pc from the Sun, offering a unique opportunity to study star and planet formation processes in detail. We characterized TWA’s location, kinematics, and age, investigating its origin within the Scorpius-Centaurus (Sco-Cen) OB association. Using Gaia DR3 astrometric data and precise ground-based radial velocities, we identified substructures within TWA, tentatively dividing them into TWA-a and TWA-b. Sco-Cen’s massive cluster σ Cen (15 Myr, 1805 members) may have influenced TWA’s formation. The alignment of σ Cen, TWA-a, and TWA-b in 3D positions, velocities, and ages resembles patterns in regions such as Corona Australis, suggesting that TWA is part of a cluster chain from sequential star formation induced by massive stars in Sco-Cen. TWA’s elongation in the opposite direction to that produced by Galactic differential rotation indicates its shape is still influenced by its formation processes and will dissipate in less than 50 Myr due to Galactic forces. These findings unveil the nature of YLAs and low-mass clusters in a new light. We propose that clusters such as ϵ Chamaeleontis, η Chamaeleontis, and TWA were forged by stellar feedback from massive stars in Sco-Cen, while others–such as β Pictoris, Carina, Columba, and Tucana-Horologium–are older and formed differently. Remarkably, all these YLAs and Sco-Cen are part of the α Persei cluster family, a vast kiloparsec-scale star formation event active over the past 60 Myr. This suggests that YLAs are the smallest stellar structures emerging from major star formation episodes and should be common in the Milky Way. Crucially, their formation in regions with intense stellar feedback may have influenced planet formation in these systems.

High-velocity outflows are ubiquitous in compact, massive (M _* ∼ 10¹¹ M _⊙), z ∼ 0.5 galaxies with extreme star formation surface densities (Σ_SFR ∼ 2000 M _⊙ yr⁻¹ kpc⁻²). We have previously detected and characterized these outflows using Mg ii absorption lines. To probe their full extent, we present Keck/KCWI integral field spectroscopy of the [O ii] and Mg ii emission nebulae surrounding all of the 12 galaxies in this study. We find that [O ii] is more effective than Mg ii in tracing low surface brightness, extended emission in these galaxies. The [O ii] nebulae are spatially extended beyond the stars, with radial extent R ₉₀ between 10 and 40 kpc. The nebulae exhibit nongravitational motions, indicating galactic outflows with maximum blueshifted velocities ranging from −335 to −1920 km s⁻¹. The outflow kinematics correlate with the bursty star formation histories of these galaxies. Galaxies with the most recent bursts of star formation (within the last σ ≳ 400 km s⁻¹), while the oldest bursts have the lowest-velocity outflows. Many galaxies exhibit both high-velocity cores and more extended, slower-moving gas indicative of multiple outflow episodes. The slower, larger outflows occurred earlier and have decelerated as they propagate into the circumgalactic medium and mix on timescales ≳50 Myr.

Efforts to unveil the structure of the local interstellar medium and its recent star-formation history have spanned the past 70 years (refs. ^1,2,3,4,5,6). Recent studies using precise data from space astrometry missions have revealed nearby, newly formed star clusters with connected origins^{7,8,9,10,11,12}. Nonetheless, mapping young clusters across the entire sky back to their natal regions has been hindered by a lack of clusters with precise radial-velocity data. Here we show that 155 out of 272 (57%) high-quality young clusters^13,14 within 1 kiloparsec of the Sun arise from three distinct spatial volumes. This conclusion is based on the analysis of data from the third Gaia release¹⁵ and other large-scale spectroscopic surveys. At present, dispersed throughout the solar neighbourhood, their past positions more than 30 million years ago reveal that these families of clusters each formed in one of three compact, massive star-forming complexes. One of these families includes all of the young clusters near the Sun—the Taurus and Scorpius–Centaurus star-forming complexes^16,17. We estimate that more than 200 supernovae were produced from these families and argue that these clustered supernovae produced both the Local Bubble¹⁸ and the largest nearby supershell GSH 238+00+09 (ref. ¹⁹), both of which are clearly visible in modern three-dimensional dust maps^20,21,22.