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Abstract The most direct method of measuring the star formation rate is with young stellar objects (YSOs), but this requires high-resolution observations and high-quality models. Using the latest YSO radiation transfer and stellar evolution models, we have developed a population synthesis code that generates model YSO populations that can be observed by JWST. We combine these model populations with principal component analysis (PCA) and maximum likelihood fitting to create a complete framework for predicting the ages and masses of YSO populations. We dub this combination of population synthesis and PCA as PxP, and show that it is effective at predicting masses and ages with self-fitting tests. We apply PxP to Spitzer Space Telescope–identified YSOs in N44 and find a mass of (1.1 ± 0.1) × 10⁴ M_⊙and an age of $0.74_{-0.03}^{+0.06}$  Myr, consistent with previous work. Next, we identify 112 YSO candidates in the archival JWST observations of NGC 604. Applying PxP to this newly identified population we find a mass of (2.2 ± 0.2) × 10⁴ M_⊙and an age of 0.62 ± 0.01 Myr. This first look at this framework demonstrates its effectiveness with a specific set of models and leaves clear opportunities for future exploration. PxP allows us to directly determine the recent (<3 Myr) star formation history, giving an unprecedented look at the effect of the large-scale environment on individual star formation. 

Abstract The construction of an accurate 3D model of the Milky Way center is necessary to understand inflow processes that drive its overall evolution and to compare our Galactic nucleus to other galaxies’ nuclei. A main point of contention is the line-of-sight location of sources observed toward the central 10 pc of the Galaxy, including recent star formation (the Sgr A East supernova remnant and Sgr A HIIregions) and copious gas (the 50 and 20 km s⁻¹molecular clouds, the circumnuclear disk, and the Sgr A West ionized “minispiral” that encircles the central supermassive black hole, Sgr A*). Some models place all of these structures within a radius of 5 pc from Sgr A*, while others place the 20 and 50 km s⁻¹clouds at a distance of at least 30−50 pc away from Sgr A* along the line of sight. We present new radio and millimeter observations of the molecular gas toward the central ∼10 pc, from which we have constructed an alternative 3D model that is consistent with both prior radio observations and orbital gas kinematics. Our model places the 20 km s⁻¹cloud, 50 km s⁻¹cloud, and Sgr A East more than 10 pc in front of Sgr A*. While this model does not conclusively rule out a connection between the 50 and 20 km s⁻¹clouds and the circumnuclear disk, we argue that prior evidence for these connections is tenuous, especially given the complex spatial and kinematic overlap of structures along the line of sight. 

Abstract We present observations of the W51A region, including the massive protoclusters W51-E and W51-IRS2, with JWST in 10 NIRCam and 5 MIRI filters. In this work, we highlight the most novel features apparent in these images and compare them with other multiwavelength images. The broad view of the NIRCam/MIRI images of the W51A region shows that areas dominated by warm dust and ionized gas are distinct from those dominated by polycyclic aromatic hydrocarbons. The high angular resolution of the JWST images resolves dust filaments in high contrast, revealing geometrically converging features feeding W51-E and a cavity around W51-IRS2. This picture adds support to the hypothesis that feedback from W51-IRS2 is suppressing further gas infall onto the protocluster, while by contrast, gas is still accreting onto W51-E. Comparing the NIRCam and MIRI images to Atacama Large Millimeter/submillimeter Array (ALMA) data, we find 24 sources detected by both JWST and ALMA, accounting for only ∼10% of the ALMA sources; the rest are too embedded or too cool to be detected by JWST. A knot of [Feii] and H₂emission north of W51-IRS2, previously detected in ground-based images, reveals peculiarly bright and compact peaks detected in all JWST bands. The knot is likely the most energetic example of a protostellar jet driven by a massive star impacting dense interstellar medium. The new images provide a complementary view to the previous long-wavelength perspective on this 4 × 8 pc area of one of the most active star-forming regions in our Galaxy, revealing new mysteries to be further explored. 

Abstract We present a study of core fragmentation in the W51-E and W51-IRS2 protoclusters in the W51 high-mass star-forming region. The identification of core fragmentation is achieved by the spatial correspondence of cores and compact sources, which are detected in the short- (low-resolution) and the long-baseline (high-resolution) continuum images from the Atacama Large Millimeter/submillimeter Array (ALMA) in Bands 3 (3 mm) and 6 (1.3 mm), respectively. We characterize the compact sources found in the long-baseline images, and conclude that the compact sources are pre-/protostellar objects (PPOs) that are either prestellar dust cores or dust disks or envelopes around protostars. The observed trend of core fragmentation in W51 is that (i) massive cores host more PPOs, (ii) bright PPOs are preferentially formed in massive cores, and (iii) equipartition of flux between PPOs is uncommon. The thermal Jeans masses of the parent cores are insufficient to explain the masses of their fragments, and this trend is more prominent for high-mass cores. We also find that unfragmented cores are large, less massive, and less dense than fragmented cores. 

Abstract The Galactic center (GC) is an extreme region of the Milky Way that is host to a complex set of thermal and nonthermal structures. In particular, the GC contains high-density gas and dust that is collectively referred to as the Central Molecular Zone (CMZ). In this work, we study a subset of HNCO filaments identified in Band 3 Atacama Large Millimeter/submillimeter Array (ALMA) observations of the GC obtained by the ALMA CMZ Exploration Survey that are comparable to high-density filaments identified in the Galactic disk. We compare the orientation of the magnetic field derived from 214μm Stratospheric Observatory for Infrared Astronomy and 850μm James Clerk Maxwell Telescope observations with the filament orientation to determine which mechanisms dominate the formation of these filaments. We observe a large range of magnetic orientations in our observed filaments indicating the complex environments the filaments are located in. We also compare the observational results to synthetic datasets created using an MHD model of the GC. Our analysis reveals that the dominant mechanisms local to the HNCO filaments vary throughout the GC with some filaments being dominated by supersonic turbulence and others by subsonic turbulence. The comparison to synthetic observations indicates that the observed filaments are in magnetically dominated environments that could be supporting these filaments against collapse. Our results on the CMZ filaments are also compared to results obtained on similar filaments located in the Galactic disk, and we find that the filaments studied here are possible CMZ analogs to the dense filamentary “bones” observed previously in the Galactic disk. 

Abstract We present an overview of the final data release (DR2) from the Green Bank Ammonia Survey (GAS). GAS is a large program at the Green Bank Telescope to map all Gould Belt star-forming regions withA_V ≳ 7 mag visible from the Northern Hemisphere in emission from NH₃and other key molecular tracers. This final release includes the data for all the regions observed: Heiles Cloud 2 and B18 in Taurus; Barnard 1, Barnard 1-E, IC 348, NGC 1333, L1448, L1451, and Per7/34 in Perseus; L1688 and L1689 in Ophiuchus; Orion A (North and South) and Orion B in Orion; Cepheus; B59 in Pipe; Corona Australis East and West; IC 5146; and Serpens Aquila and MWC297 in Serpens. Similar to what was presented in GAS DR1, we find that the NH₃emission and dust continuum emission from Herschel correspond closely. We find that the NH₃emission is generally extended beyond the typical 0.1 pc length scales of dense cores, and we find that the transition between coherent core and turbulent cloud is a common result. This shows that the regions of coherence are common throughout different star-forming regions, with a substantial fraction of the high column density regions displaying subsonic nonthermal velocity dispersions. We produce maps of the gas kinematics, temperature, and NH₃column densities through forward modeling of the hyperfine structure of the NH₃(1,1) and (2,2) lines. We show that the NH₃velocity dispersion,σ_v, and gas kinetic temperature,T_K, vary systematically between the regions included in this release, with an increase in both the mean value and spread ofσ_vandT_Kwith increasing star formation activity. The data presented in this paper are publicly available via doi:10.11570/24.0091. 

Abstract Measuring properties of young stellar objects (YSOs) is necessary for probing the pre-main-sequence evolution of stars. As YSOs exhibit complex geometry, measurement generally entails comparing observed radiation to template populations of radiative-transfer model YSO spectral energy distributions (SEDs). Due to uncertainty on the precise mechanics of star formation, the properties inferred for YSOs using these models often depend strongly on the assumed accretion history. We develop a framework for predicting observable properties of YSOs that is agnostic to the underlying accretion history, enabling comparison between theories. This framework links a set of radiative-transfer SEDs with protostellar evolutionary tracks to create models of evolving YSOs. Unlike previous works, we directly relate evolution models to observables through theoretical physical parameters rather than through intermediate, observationally derived analogs. We make flux predictions for YSOs corresponding to stars with birth masses from 0.2 to 50M_⊙during their accretion phase following isothermal-sphere, turbulent-core, and competitive accretion histories, showing that these histories may be observationally distinguished by examining the 100μm and 3 mm fluxes of a YSO. We discuss the impact of dust models and parameter ranges on the output of radiative-transfer simulations through a comparison to another SED model grid. We quantify the degree of confusion between YSO Stages and Classes across a wide range of physical scenarios; for each, we calculate confusion matrices that enable inference of the number of objects of a given Stage from an observed population. Finally, we critically examine the physical significance of various literature Stage and Class definitions. 

Abstract We present near-infraredJHK_sand narrowband H₂(1–0) photometric observations of the W51A region, obtained with GTC EMIR, aiming to characterize its young stellar population, and provide mass estimates for individual cluster members and the protoclusters. Our observations reveal over 3000 new sources, out of which 88 are located in the protoclusters, W51 IRS2 and W51 Main. The average extinction (A_V), measured from theJ–Hcolor, of sources is 19A_Vin W51 IRS2 and 14A_Vin W51 Main. We document 17 new instances of H₂emission in the region by utilizing observations from the H₂(1–0) narrowband filter. Despite limited completeness, we estimated masses for each cluster member and estimated the total cluster mass to be in the range of 900–4700M_⊙for W51 IRS2 and 500–2700M_⊙for W51 Main, using an assumed age range of 1–3 Myr. We measured the initial mass function (IMF) in the proto-clusters assuming a range of ages from 1–3 Myr and found that the IMF slopes for both protoclusters are consistent with the Salpeter IMF in the mass rangeM ≳ 8M_⊙within 1σ–2σ. 

Abstract We present high-resolution Karl G. Jansky Very Large Array observations of the 22 GHz H₂O maser line in the extended Sagittarius B2 cloud. We detect 499 H₂O masers across the observed velocities between −39 and 172 km s⁻¹. To investigate the nature of the masers, we analyze their spatial distribution and crossmatch with catalogs of HIIregions and protostellar cores. 62% of masers are associated with protostellar cores and 32% with HIIregions. The nature of the remaining 6% of sources was not established but is likely associated with protostellar cores. Based on the spatial extent of the groups of masers, we classify them as either outflow-associated or young stellar object (YSO)–associated. We identify 144 unique sites of maser emission: 23 are associated with HIIregions and 94 with protostellar cores, of which 33 are associated with protostellar outflows and 18 with YSOs. The outflow-associated H₂O maser emission is confined to within <2000 au of the central continuum source, despite shocked SiO emission extending over tens of thousands of astronomical units. The YSO-associated masers show a lack of detections at 5 < V_rel < 30 km s⁻¹, which we suggest may be due to maser self-absorption. We show how H₂O masers trace the large-scale material flow in Sgr B2 North, also seen in SiO and millimeter continuum emission. Finally, we find that protostellar cores with associated H₂O masers tend to have brighter 3 mm continuum emission on average, although there is no strong correlation between maser brightness and continuum flux. 

Abstract The Milky Way’s Central Molecular Zone (CMZ) is the largest concentration of dense molecular gas in the Galaxy, the structure of which is shaped by the complex interplay between Galactic-scale dynamics and extreme physical conditions. Understanding the 3D geometry of this gas is crucial, as it determines the locations of star formation and subsequent feedback. We present a catalog of clouds in the CMZ using Herschel data. Using archival data from the APEX and MOPRA CMZ surveys, we measure averaged kinematic properties of the clouds at 1 and 3 mm. We use archival ATCA data of the H₂CO (1_1,0–1_1,1) 4.8 GHz line to search for absorption towards the clouds, and 4.85 GHz Green Bank Telescope (GBT)C-band data to measure the radio continuum emission. We measure the absorption against the continuum to provide new constraints for the line-of-sight positions of the clouds relative to the Galactic Center, and find a highly asymmetric distribution, with most clouds residing in front of the Galactic Center. The results are compared with different orbital models, and we introduce a revised toy model of a vertically oscillating closed elliptical orbit. We find that most models describe the position–position–velocity structure of the gas reasonably well, but find significant inconsistencies in all cases regarding the near versus far placement of individual clouds. Our results highlight that the CMZ is likely more complex than can be captured by these simple geometric models, along with the need for new data to provide further constraints on the true 3D structure of the CMZ.