James Michael De Buizer

We present results from Karl G. Jansky Very Large Array radio-continuum observations of 12 intermediate-mass (IM) protostars, as part of the SOFIA Massive Star Formation Survey. Using these observations, we studied their morphology, multiplicity, and radio spectral energy distributions (SEDs). Across our target regions, we resolve multiple compact sources and report eight new detections, four of which are entirely new and four that have counterparts at other wavelengths, but are detected here for the first time at radio frequencies. Based on radio morphologies and spectral indices, we assess the nature of the detected sources, highlighting seven that display jetlike structures and spectral indices consistent with ionized jets. Combining our results with the SOMA Radio I and II results, we expand the overall sample to 29 protostars, covering a bolometric luminosity range from L _bol ∼ 10 ² to 10 ⁶ L _⊙ . These sources help define a potential evolutionary sequence in the radio versus bolometric luminosity diagram. IM protostars have radio luminosities that are lower than expected from a simple power-law extrapolation from low-mass protostars. However, this result is consistent with theoretical expectations from protostellar evolution models, which show low levels of photoionization and reduced shock ionization emission due to expanded stellar radii during this phase. Overall our expanded SOMA Radio sample provides new constraints on theoretical models of massive protostellar evolution, especially the connection to ionized gas structures.

In this eighth paper of the Stratospheric Observatory For Infrared Astronomy-FORCAST series on Milky Way GH ii regions, we present an analysis of the massive star-forming complex W43 Main. We compared our 11–37 μ m maps with multiwavelength observations from the near-infrared to radio, and investigated the physical nature of compact sources and dust substructures. We applied spectral energy distribution fitting to constrain properties of the compact infrared objects, and examined the evolutionary states of the extended subregions. We identified 20 compact infrared objects, 16 (80%) of which we classify as massive young stellar object candidates (MYSOs) or candidate MYSOs. W43 Main resides at the junction of the Scutum spiral arm and the Galactic Bar, a location where enhanced turbulence is anticipated and has been proposed as a potential influence on star formation activity. Nevertheless, our analysis shows that its Lyman continuum photon production rate, the mass of its most massive MYSO, and its MYSO density are all consistent with the survey-wide median values. We therefore conclude that, despite W43 Main’s unique Galactic environment, its present star formation activity appears broadly consistent with that of an average Galactic GH ii region.

In this eighth paper of the SOFIA-FORCAST series on Milky Way GHII regions, we present an analysis of the massive star-forming complex W43 Main. We compared our 11 - 37 micron maps with multi-wavelength observations from the near-infrared to radio, and investigated the physical nature of compact sources and dust substructures. We applied SED fitting to constrain properties of the compact infrared objects, and examined the evolutionary states of the extended subregions. We identified 20 compact infrared objects, 16 (80%) of which we classify as massive young stellar objects (MYSOs) or candidate MYSOs. W43 Main resides at the junction of the Scutum spiral arm and the Galactic Bar, a location where enhanced turbulence is anticipated and has been proposed as a potential influence on star-formation activity. Nevertheless, our analysis shows that its Lyman continuum photon production rate, the mass of its most massive MYSO, and its MYSO density are all consistent with the survey-wide median values. We therefore conclude that, despite W43 Main's unique Galactic environment, its present star formation activity appears broadly consistent with that of an average Galactic GHII region.

We present centimeter continuum observations of seven high-luminosity massive protostars and their surrounding sources in regions with multiple targets, as part of the SOFIA Massive (SOMA) Star Formation Survey. With data from the Very Large Array and the Australia Telescope Compact Array, we analyze the spectral index, morphology, and multiplicity of the detected radio sources. The high-sensitivity, high-resolution observations allow us to resolve many sources; 65% of the reported sources are resolved at least within the synthesized beam. We report 15 new detections, 13 of which are entirely new, and 2 have counterparts at other wavelengths but are detected here for the first time at radio frequencies. We use the observations to build radio spectral energy distributions to calculate spectral indices. With radio morphologies and the spectral indices, we give assessments on the nature of the sources, highlighting six sources that display a radio jetlike morphology and a spectral index consistent with ionized jets. Combining with the SOMA Radio I sample, we present the radio–bolometric luminosity relation, especially probing the regime from L _bol ∼ 10 ⁴ to 10 ⁶ L _⊙ . Here, we find a steep rise in radio luminosity, which is expected by models that transition from shock ionization to photoionization.

We present ∼8–40 μm SOFIA-FORCAST images of seven regions of “clustered” star formation as part of the SOFIA Massive Star Formation Survey. We identify a total of 34 protostar candidates and build their spectral energy distributions (SEDs). We fit these SEDs with a grid of radiative transfer models based on the turbulent core accretion (TCA) theory to derive key protostellar properties, including initial core mass, M _c , clump environment mass surface density, Σ_cl, and current protostellar mass, m _*. We also carry out empirical graybody (GB) estimation of Σ_cl, which allows a case of restricted SED fitting within the TCA model grid. We also release version 2.0 of the open-source Python package sedcreator, which is designed to automate the aperture photometry and SED building and fitting process for sources in clustered environments, where flux contamination from close neighbors typically complicates the process. Using these updated methods, SED fitting yields values of M _c ∼ 30–200 M _⊙, Σ_cl,SED ∼ 0.1–3 g cm⁻², and m _* ∼ 4–50 M _⊙. The GB fitting yields smaller values of Σ_cl,GB ≲ 1 g cm⁻². From these results, we do not find evidence for a critical Σ_cl needed to form massive (≳8 M _⊙) stars. However, we do find tentative evidence for a dearth of the most massive (m _* ≳ 30 M _⊙) protostars in the clustered regions, suggesting a potential impact of environment on the stellar initial mass function.

This study examines the mid-infrared properties of Giant H ii (GH ii) regions in the Milky Way’s Central Molecular Zone (CMZ)—Sgr B1, Sgr B2, and Sgr C—using SOFIA-FORCAST imaging at 25 and 37 μm. It compares these mid-infrared data with previous multiwavelength observations to explore their present star formation activity and global properties. The study identifies 77 massive young stellar object (MYSO) candidates in and around the three regions. Sgr B2 appears to host the youngest MYSOs and have much higher extinction than the other regions, containing several radio sources not detected in the mid-infrared even at 37 μm. Meanwhile, cm radio continuum regions of Sgr B1 shows remarkable correspondence to its mid-infrared emission. Sgr C has fewer confirmed MYSOs, and it seems to have a higher fraction of low-mass young stellar objects and contamination from more evolved interloper/foreground stars. Derived MYSO densities are consistent with GH ii regions elsewhere in the Galactic plane, though the CMZ GH ii regions appear to have less prolific present star formation overall. Unlike Sgr B2, the cm continuum emission in Sgr B1 and Sgr C GH ii regions appears to be absent cold dust and molecular gas, suggesting environmental differences, possibly driven by turbulence and rapid dynamical changes near the Galactic center. Furthermore, unlike typical GH ii regions, Sgr B1 and Sgr C are significantly ionized by evolved interloper stars, which likely did not form within these regions. In these ways, Sgr B1 and Sgr C deviate from classical GH ii region behavior, thus potentially representing a new category of GH ii region or challenging their classification as GH ii regions.

This study examines the mid-infrared properties of Giant HII (GHII) regions in the Milky Way's Central Molecular Zone (CMZ) -- Sgr B1, Sgr B2, and Sgr C -- using SOFIA-FORCAST imaging at 25 and 37 microns. It compares these mid-infrared data with previous multi-wavelength observations to explore their present star formation activity and global properties. The study identifies 77 massive young stellar object (MYSO) candidates in and around the three regions. Sgr B2 appears to host the youngest MYSOs and have much higher extinction than the other regions, containing several radio sources not detected in the mid-infrared even at 37 microns. Meanwhile, cm radio continuum regions of Sgr B1 shows remarkable correspondence to its mid-infrared emission. Sgr C has fewer confirmed MYSOs, and seems to have a higher fraction of low-mass young stellar objects and contamination from more evolved interloper/foreground stars. Derived MYSO densities are consistent with GHII regions elsewhere in the Galactic plane, though the CMZ GHII regions appear to have less prolific present star formation overall. Unlike Sgr B2, the cm continuum emission in Sgr B1 and Sgr C GHII regions appears to be absent cold dust and molecular gas, suggesting environmental differences, possibly driven by turbulence and rapid dynamical changes near the Galactic Center. Furthermore, unlike typical GHII regions, Sgr B1 and Sgr C are significantly ionized by evolved interloper stars, which likely did not form within these regions. In these ways, Sgr B1 and Sgr C deviate from classical GHII region behavior, thus potentially representing a new category of GHII region or challenging their classification as GHII regions.

JWST/NIRCam obtained high angular resolution (0.05–0.1 arcsec), deep near-infrared 1–5 |$\mu$|m imaging of Supernova (SN) 1987A taken 35 yr after the explosion. In the NIRCam images, we identify: (1) faint H₂ crescents, which are emissions located between the ejecta and the equatorial ring, (2) a bar, which is a substructure of the ejecta, and (3) the bright 3–5 |$\mu$|m continuum emission exterior to the equatorial ring. The emission of the remnant in the NIRCam 1–2.3 |$\mu$|m images is mostly due to line emission, which is mostly emitted in the ejecta and in the hotspots within the equatorial ring. In contrast, the NIRCam 3–5 |$\mu$|m images are dominated by continuum emission. In the ejecta, the continuum is due to dust, obscuring the centre of the ejecta. In contrast, in the ring and exterior to the ring, synchrotron emission contributes a substantial fraction to the continuum. Dust emission contributes to the continuum at outer spots and diffuse emission exterior to the ring, but little within the ring. This shows that dust cooling and destruction time-scales are shorter than the synchrotron cooling time-scale, and the time-scale of hydrogen recombination in the ring is even longer than the synchrotron cooling time-scale. With the advent of high sensitivity and high angular resolution images provided by JWST/NIRCam, our observations of SN 1987A demonstrate that NIRCam opens up a window to study particle-acceleration and shock physics in unprecedented details, probed by near-infrared synchrotron emission, building a precise picture of how an SN evolves.