Search for: All records

Abstract We present a population study of Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 6 observations of the 100 most gravitationally unstable dense cores in Aquila using a simple mass versus size analysis. We identify 66 continuum sources from ALMA 12 m observations at 106 GHz and through comparisons with known protostellar catalogs; two of these detected dense cores appear to be completely starless, without any accompanying/nearby protostar detections. Additionally, we find nine other starless ALMA 12 m detections within protostellar cores that have fragmented into a mixture of starless and protostellar substructures. We test the turbulent core collapse model by conducting synthetic observations of turbulent magnetohydrodynamical simulations of collapsing starless cores in order to predict how many starless cores should be detected given their central density and density profile. The simulations predict at least one (1.19) detection, consistent with our two detections of ALMA 12 m emission within completely starless cores. We also use a combination of ALMA Compact Array Cycle 4 observations and the Herschel Gould Belt Survey data to analyze how mass is distributed on three distinct spatial scales, in order to understand how turbulence shapes the evolution of substructure development as dense cores collapse to form new star systems. We find an increase in multiplicity at the smallest scales when the parent larger-scale structure also has a higher degree of fragmentation. 

Abstract Star formation occurs within dense regions of giant molecular clouds (GMCs); however, exactly how gas collects and evolves to form individual stars and what role dense cores play remains unclear. We use the Lagrangian cell information in the STARFORGE simulation suite to track star-forming gas in three GMCs with varying magnetic field strengths. We find that once a protostar forms, the lifetime of the unaccreted gas correlates with the final stellar mass, where low-mass stars (M_* < 0.5M_⊙) accrete for 0.5–0.6 Myr from a relatively local reservoir of gas and high-mass stars (M_* > 2M_⊙) accrete over 3.3–4.7 Myr from a much larger volume. Although the protostellar accretion time increases weakly with magnetic field strength, the accreting gas radii, velocity dispersions, virial parameters, and magnetic energy ratios are largely insensitive to the global cloud properties. At the time of protostar formation, the unaccreted gas exhibits linewidth-size and mass-size relations characteristic of turbulently regulated, isothermal dense cores, followingσ_v ∝ R^1.0−1.1andM ∝ R^0.47−0.55, respectively. Low- and intermediate-mass stars undergo relatively continuous accretion, and their accretion histories are well-fit by isothermal sphere, turbulent core, or competitive accretion models, where no one model fits all masses. However, many high-mass stars experience intermittent accretion, and their accretion histories are not well-fit by any of these models. While the distribution of accreting gas is more extended than typically defined dense cores, the physical properties and structure of the star-forming gas resemble those of observed cores and are largely regulated by turbulence and feedback. 

Abstract We present the first systematic study of explosive dispersal outflows (EDOs) as potential sources of high-energy emission in the Milky Way. EDOs are energetic outflows produced during dynamical interactions in young, massive star-forming regions, and their physical conditions make them promising environments for cosmic-ray acceleration. Using 16 yr of 0.2–500 GeV Fermi-Large Area Telescope observations, we study theγ-ray properties of seven EDOs. Three EDOs, DR21, G34.26+0.15, and G5.89−0.39, show spatially coincident GeV emission, while the remaining systems yield nondetections. Among the sample, DR21 stands out as the brightest candidate, with a detection significance ≥40σ. Its spectrum is well described by a power law with an exponential cutoff, and the integrated luminosity in the 0.1–500 GeV band isL_γ ≃ 2 × 10³⁵erg s⁻¹. When compared with the outflow’s estimated kinetic energy, the inferred cosmic-ray acceleration efficiency is ≤15%, consistent with values for shocks in dense molecular environments. The energetics and morphology support an association between the DR21 molecular outflow and the observedγ-rays. Our results demonstrate that EDOs span a wide range ofγ-ray luminosities and efficiencies, suggesting they may contribute to the Galactic cosmic-ray budget. This motivates searches for additional EDOs and improved multiwavelength characterization of their environments. 

Abstract Most stars form in multiple systems, with profound implications in numerous astronomical phenomena intrinsically linked to multiplicity. However, our knowledge about the process of how multiple stellar systems form is incomplete and biased toward nearby molecular clouds forming only low-mass stars, which are unrepresentative of the stellar population in the Galaxy. Most stars form within dense cores in clusters alongside high-mass stars (>8M_⊙), as the Sun likely did. Here we report deep Atacama Large Millimeter/submillimeter Array (ALMA) 1.33 mm dust continuum observations at ∼160 au spatial resolution, revealing 72 low-mass multiple systems embedded in 23 high-mass cluster-forming regions, as part of the Digging into the Interior of Hot Cores with ALMA survey. We find that the companion separation distribution presents a distinct peak at ∼1200 au, in contrast to the one at ∼4000 au observed in nearby low-mass regions. The shorter fragmentation scale can be explained by considering the higher pressure exerted by the surrounding medium, which is higher than the one in low-mass regions, due to the larger turbulence and densities involved. Because the peak of the companion separation distribution occurs at much larger scales than the expected disk sizes, we argue that the observed fragmentation is produced by turbulent core fragmentation. Contrary to predictions, the multiplicity fraction remains constant as the stellar density increases. We propose that in the extremely dense environments where high-mass stars form, dynamical interactions play an important role in disrupting weakly bound systems.