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1. The Disk Population in a Distant Massive Protocluster

   https://doi.org/10.3847/1538-4357/ac9b54  

   Cheng, Yu ; Tan, Jonathan C. ; Tobin, John J. ; Fedriani, Rubén ; Andersen, Morten ; Wang, Junfeng ( November 2022 , The Astrophysical Journal)

   The unprecedented angular resolution and sensitivity of the Atacama Large Millimeter/submillimeter Array make it possible to unveil disk populations in distant (>2 kpc), embedded young cluster environments. We have conducted an observation toward the central region of the massive protocluster G286.21+0.16 at 1.3 mm. With a spatial resolution of 23 mas and a sensitivity of 15μJy beam⁻¹, we detect a total of 38 protostellar disks. These disks have dust masses ranging from about 53 to 1825M_⊕, assuming a dust temperature of 20 K. This sample is not closely associated with previously identified dense cores, as would be expected for disks around Class 0 protostars. Thus, we expect our sample, being flux-limited, to be mainly composed of Class I/flat-spectrum source disks, since these are typically more massive than Class II disks. Furthermore, we find that the distributions of disk masses and radii are statistically indistinguishable from those of the Class I/flat-spectrum objects in the Orion molecular cloud, indicating that similar processes are operating in G286.21+0.16 to regulate disk formation and evolution. The cluster center appears to host a massive protostellar system composed of three sources within 1200 au, including a potential binary with 600 au projected separation. Relative to thismore »center, there is no evidence for widespread mass segregation in the disk population. We do find a tentative trend of increasing disk radius versus distance from the cluster center, which may point to the influence of dynamical interactions being stronger in the central regions.

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2. Dust Temperature Uncertainties Hamper the Inference of Dust and Molecular Gas Masses from the Dust Continuum Emission of Quiescent High-redshift Galaxies

   https://doi.org/10.3847/2041-8213/ac951d  

   Cochrane, R. K. ; Hayward, C. C. ; Anglés-Alcázar, D. ( November 2022 , The Astrophysical Journal Letters)

   Single flux density measurements at observed-frame submillimeter and millimeter wavelengths are commonly used to probe dust and gas masses in galaxies. In this Letter, we explore the robustness of this method to infer dust mass, focusing on quiescent galaxies, using a series of controlled experiments on four massive halos from the Feedback in Realistic Environments project. Our starting point is four star-forming central galaxies at seven redshifts betweenz= 1.5 andz= 4.5. We generate modified quiescent galaxies that have been quenched for 100 Myr, 500 Myr, or 1 Gyr prior to each of the studied redshifts by reassigning stellar ages. We derive spectral energy distributions for each fiducial and modified galaxy using radiative transfer. We demonstrate that the dust mass inferred is highly dependent on the assumed dust temperature,T_dust, which is often unconstrained observationally. Motivated by recent work on quiescent galaxies that assumedT_dust∼ 25 K, we show that the ratio between dust mass and 1.3 mm flux density can be higher than inferred by up to an order of magnitude, due to the considerably lower dust temperatures seen in non-star-forming galaxies. This can lead to an underestimation of dust mass (and, when submillimeter flux density is used as a proxymore »for molecular gas content and gas mass). This underestimation is most severe at higher redshifts, where the observed-frame 1.3 mm flux density probes rest-frame wavelengths far from the Rayleigh–Jeans regime, and hence depends superlinearly on dust temperature. We fit relations between ratios of rest-frame far-infrared flux densities and mass-weighted dust temperature that can be used to constrain dust temperatures from observations and hence derive more reliable dust and molecular gas masses.

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3. VLA and NOEMA Views of Bok Globule CB 17: The Starless Nature of a Proposed First Hydrostatic Core Candidate

   https://doi.org/10.3847/1538-4357/ac3083  

   Spear, Stephanie ; José Maureira, María ; Arce, Héctor G. ; Pineda, Jaime E. ; Dunham, Michael ; Caselli, Paola ; Segura-Cox, Dominique ( December 2021 , The Astrophysical Journal)

   Abstract We use 3 mm continuum NOrthern Extended Millimeter Array and NH 3 Very Large Array observations toward the First Hydrostatic Core (FHSC) candidate CB 17 MMS in order to reveal the dust structure and gas properties to 600–1100 au scales and to constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise ratio of 9. The gas traced by NH 3 exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius ∼1800 au and a central density of ∼6 × 10 5 cm −3 . Virial and density structure analysis reveals the core is marginally bound ( α vir = 0.73). The region is entirely consistent with that of a young starless core, hence ruling out CB 17 MMS as an FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the position–velocity diagram and an off-center region with high velocity dispersion, caused by two distinct velocity peaks. These features could be due to interactions withmore »the nearby outflow, which appears to deflect due to the dense gas near the NH 3 column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of similar radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1000 au scales are determined by large-scale dense cloud motions, and may be preserved throughout the early stages of star formation.« less
4. Dust masses of young disks: constraining the initial solid reservoir for planet formation

   https://doi.org/10.1051/0004-6361/202037851  

   Tychoniec, Łukasz ; Manara, Carlo F. ; Rosotti, Giovanni P. ; van Dishoeck, Ewine F. ; Cridland, Alexander J. ; Hsieh, Tien-Hao ; Murillo, Nadia M. ; Segura-Cox, Dominique ; van Terwisga, Sierk E. ; Tobin, John J. ( August 2020 , Astronomy & Astrophysics)

   Context. Recent years have seen building evidence that planet formation starts early, in the first ~0.5 Myr. Studying the dust masses available in young disks enables us to understand the origin of planetary systems given that mature disks are lacking the solid material necessary to reproduce the observed exoplanetary systems, especially the massive ones. Aims. We aim to determine if disks in the embedded stage of star formation contain enough dust to explain the solid content of the most massive exoplanets. Methods. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (1.1–1.3 mm) continuum observations of embedded disks in the Perseus star-forming region together with Very Large Array (VLA) Ka -band (9 mm) data to provide a robust estimate of dust disk masses from the flux densities measured in the image plane. Results. We find a strong linear correlation between the ALMA and VLA fluxes, demonstrating that emission at both wavelengths is dominated by dust emission. For a subsample of optically thin sources, we find a median spectral index of 2.5 from which we derive the dust opacity index β = 0.5, suggesting significant dust growth. Comparison with ALMA surveys of Orion shows that the Class I dust disk massmore »distribution between the two regions is similar, but that the Class 0 disks are more massive in Perseus than those in Orion. Using the DIANA opacity model including large grains, with a dust opacity value of κ 9 mm = 0.28 cm 2 g −1 , the median dust masses of the embedded disks in Perseus are 158 M ⊕ for Class 0 and 52 M ⊕ for Class I from the VLA fluxes. The lower limits on the median masses from ALMA fluxes are 47 M ⊕ and 12 M ⊕ for Class 0 and Class I, respectively, obtained using the maximum dust opacity value κ 1.3 mm = 2.3 cm 2 g −1 . The dust masses of young Class 0 and I disks are larger by at least a factor of ten and three, respectively, compared with dust masses inferred for Class II disks in Lupus and other regions. Conclusions. The dust masses of Class 0 and I disks in Perseus derived from the VLA data are high enough to produce the observed exoplanet systems with efficiencies acceptable by planet formation models: the solid content in observed giant exoplanets can be explained if planet formation starts in Class 0 phase with an efficiency of ~15%. A higher efficiency of ~30% is necessary if the planet formation is set to start in Class I disks.« less
5. Pre-main-sequence Brackett Emitters in the APOGEE DR17 Catalog: Line Strengths and Physical Properties of Accretion Columns

   https://doi.org/10.3847/1538-4357/aca324  

   Campbell, Hunter ; Khilfeh, Elliott ; Covey, Kevin R. ; Kounkel, Marina ; Ballantyne, Richard ; Corey, Sabrina ; Román-Zúñiga, Carlos G. ; Hernández, Jesús ; Martínez, Ezequiel Manzo ; Ramírez, Karla Peña ; et al ( December 2022 , The Astrophysical Journal)

   Very young (t≲ 10 Myr) stars possess strong magnetic fields that channel ionized gas from the interiors of their circumstellar disks to the surface of the star. Upon impacting the stellar surface, the shocked gas recombines and emits hydrogen spectral lines. To characterize the density and temperature of the gas within these accretion streams, we measure equivalent widths of Brackett (Br) 11–20 emission lines detected in 1101 APOGEE spectra of 326 likely pre-main-sequence accretors. For sources with multiple observations, we measure median epoch-to-epoch line strength variations of 10% in Br11 and 20% in Br20. We also fit the measured line ratios to predictions of radiative transfer models by Kwan & Fischer. We find characteristic best-fit electron densities ofn_e= 10¹¹–10¹²cm⁻³, and excitation temperatures that are inversely correlated with electron density (fromT∼ 5000 K forn_e∼ 10¹²cm⁻³toT∼ 12,500 K atn_e∼ 10¹¹cm⁻³). These physical parameters are in good agreement with predictions from modeling of accretion streams that account for the hydrodynamics and radiative transfer within the accretion stream. We also present a supplementary catalog of line measurements from 9733 spectra of 4255 Brackett emission-line sources in the APOGEE Data Release 17 data set.