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1. Multi-scale Physical Properties of NGC 6334 as Revealed by Local Relative Orientations between Magnetic Fields, Density Gradients, Velocity Gradients, and Gravity

   https://doi.org/10.3847/1538-4357/acb540  

   Liu, Junhao ; Zhang, Qizhou ; Koch, Patrick M. ; Liu, Hauyu Baobab ; Li, Zhi-Yun ; Li, Shanghuo ; Girart, Josep Miquel ; Chen, Huei-Ru Vivien ; Ching, Tao-Chung ; Ho, Paul T. ; et al ( March 2023 , The Astrophysical Journal)

   We present ALMA dust polarization and molecular line observations toward four clumps (I(N), I, IV, and V) in the massive star-forming region NGC 6334. In conjunction with large-scale dust polarization and molecular line data from JCMT, Planck, and NANTEN2, we make a synergistic analysis of relative orientations between magnetic fields (θ_B), column density gradients (θ_NG), local gravity (θ_LG), and velocity gradients (θ_VG) to investigate the multi-scale (from ∼30 to 0.003 pc) physical properties in NGC 6334. We find that the relative orientation betweenθ_Bandθ_NGchanges from statistically more perpendicular to parallel as column density ($N_{{\mathrm{H}}_2}$) increases, which is a signature of trans-to-sub-Alfvénic turbulence at complex/cloud scales as revealed by previous numerical studies. Becauseθ_NGandθ_LGare preferentially aligned within the NGC 6334 cloud, we suggest that the more parallel alignment betweenθ_Bandθ_NGat higher$N_{{\mathrm{H}}_2}$is because the magnetic field line is dragged by gravity. At even higher$N_{{\mathrm{H}}_2}$, the angle betweenθ_Bandθ_NGorθ_LGtransits back to having no preferred orientation, or statistically slightly more perpendicular, suggesting that the magnetic field structure is impacted by star formation activities. A statistically more perpendicular alignment is found betweenθ_Bandθ_VGthroughout our studied$N_{{\mathrm{H}}_2}$range, which indicates a trans-to-sub-Alfvénic state at small scales as well, and this signifies that magnetic field has an important role in the star formation process in NGC 6334. The normalized mass-to-flux ratio derived from the polarization-intensity gradient (KTH) method increases with$N_{{\mathrm{H}}_2}$, but the KTH method may fail at high$N_{{\mathrm{H}}_2}$due to the impact of star formation feedback.

    

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2. Hidden Gems on a Ring: Infant Massive Clusters and Their Formation Timeline Unveiled by ALMA, HST, and JWST in NGC 3351

   https://doi.org/10.3847/1538-4357/ad3de6  

   Sun_孙, Jiayi 嘉懿 ; He_何, Hao 浩 ; Batschkun, Kyle ; Levy, Rebecca C ; Emig, Kimberly ; Rodríguez, M Jimena ; Hassani, Hamid ; Leroy, Adam K ; Schinnerer, Eva ; Ostriker, Eve C ; et al ( May 2024 , The Astrophysical Journal)

   We use 0.1″ observations from the Atacama Large Millimeter Array (ALMA), Hubble Space Telescope (HST), and JWST to study young massive clusters (YMCs) in their embedded “infant” phase across the central starburst ring in NGC 3351. Our new ALMA data reveal 18 bright and compact (sub-)millimeter continuum sources, of which 8 have counterparts in JWST images and only 6 have counterparts in HST images. Based on the ALMA continuum and molecular line data, as well as ancillary measurements for the HST and JWST counterparts, we identify 14 sources as infant star clusters with high stellar and/or gas masses (∼10⁵M_⊙), small radii (≲ 5 pc), large escape velocities (6–10 km s⁻¹), and short freefall times (0.5–1 Myr). Their multiwavelength properties motivate us to divide them into four categories, likely corresponding to four evolutionary stages from starless clumps to exposed Hiiregion–cluster complexes. Leveraging age estimates for HST-identified clusters in the same region, we infer an evolutionary timeline, ranging from ∼1–2 Myr before cluster formation as starless clumps, to ∼4–6 Myr after as exposed Hiiregion–cluster complexes. Finally, we show that the YMCs make up a substantial fraction of recent star formation across the ring, exhibit a nonuniform azimuthal distribution without a very coherent evolutionary trend along the ring, and are capable of driving large-scale gas outflows.

    

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3. A resolved, multiwavelength study of gas-rich dwarf galaxies in the Fornax cluster using MUSE, MeerKAT, and ALMA

   https://doi.org/10.1093/mnras/stae2495  

   Zabel, Nikki ; Loni, Alessandro ; Sarzi, Marc ; Serra, Paolo ; Chawla, Arjun ; Davis, Timothy_A ; Kleiner, Dane ; Loubser, S_Ilani ; Peletier, Reynier ( November 2024 , Monthly Notices of the Royal Astronomical Society)

   We combine new and archival Multi-unit spectroscopic explorer (MUSE) observations with data from the MeerKAT Fornax Survey and the ALMA Fornax Cluster Survey to study the ionized, atomic, and molecular gas in six gas-rich dwarf galaxies in the Fornax cluster in detail. We compare the distributions and velocity fields of the three gas phases with each other, with MUSE white-light images, and with the stellar velocity fields. Additionally, we derive the resolved molecular Kennicutt–Schmidt relation for each object, and compare these with existing relations for field galaxies and for the Fornax and Virgo clusters. Finally, we explore global measurements such as gas deficiencies and star formation rates to paint as complete a picture of their evolutionary state as possible. We find that all six gas-rich dwarf galaxies have very disturbed interstellar medium, with all three gas phases being irregular both in terms of spatial distribution and velocity field. Most objects lie well below the Kennicutt–Schmidt relations from the literature. Furthermore, they are quite deficient in H i (with def$_{{\rm{H}{\small I}}}$ between $\sim$1 and $\sim$2 dex), and moderately deficient in H$_2$ (with def$_{\mathrm{ H}_{2}}$ between $\sim$0 and $\sim$1), suggesting that, while both cold gas phases are affected simultaneously, H i is removed in significant quantities before H$_2$. We suggest that these dwarfs are on their first infall into the cluster, and are in the process of transitioning from star-forming to passive. A combination of tidal interactions, mergers/pre-processing, and ram pressure stripping is likely responsible for these transformations.

    

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4. Virial Clumps in Central Molecular Zone Clouds

   https://doi.org/10.3847/1538-4357/ac5906  

   Myers, Philip C. ; Hatchfield, H. Perry ; Battersby, Cara ( April 2022 , The Astrophysical Journal)

   CMZoom survey observations with the Submillimeter Array are analyzed to describe the virial equilibrium (VE) and star-forming potential of 755 clumps in 22 clouds in the Central Molecular Zone (CMZ) of the Milky Way. In each cloud, nearly all clumps follow the column density–mass trendN∝M^s, wheres= 0.38 ± 0.03 is near the pressure-bounded limits_p= 1/3. This trend is expected when gravitationally unbound clumps in VE have similar velocity dispersion and external pressure. Nine of these clouds also harbor one or two distinctly more massive clumps. These properties allow a VE model of bound and unbound clumps in each cloud, where the most massive clump has the VE critical mass. These models indicate that 213 clumps have velocity dispersion 1–2 km s⁻¹, mean external pressure (0.5–4) × 10⁸cm⁻³K, bound clump fraction 0.06, and typical virial parameterα= 4–15. These mostly unbound clumps may be in VE with their turbulent cloud pressure, possibly driven by inflow from the Galactic bar. In contrast, most Sgr B2 clumps are bound according to their associated sources andN–Mtrends. When the CMZ clumps are combined into mass distributions, their typical power-law slope is analyzed with a model of stopped accretion. It also indicates that most clumps are unbound and cannot grow significantly, due to their similar timescales of accretion and dispersal, ∼0.2 Myr. Thus, virial and dynamical analyses of the most extensive clump census available indicate that star formation in the CMZ may be suppressed by a significant deficit of gravitationally bound clumps.

    

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5. Sequential Star Formation in the Young SMC Region NGC 602: Insights from ALMA

   https://doi.org/10.3847/1538-4357/ac8d93  

   O’Neill, Theo J. ; Indebetouw, Rémy ; Sandstrom, Karin ; Bolatto, Alberto D. ; Jameson, Katherine E. ; Carlson, Lynn R. ; Finn, Molly K. ; Meixner, Margaret ; Sabbi, Elena ; Sewiło, Marta ( October 2022 , The Astrophysical Journal)

   Abstract NGC 602 is a young, low-metallicity star cluster in the “Wing” of the Small Magellanic Cloud. We reveal the recent evolutionary past of the cluster through analysis of high-resolution (∼0.4 pc) Atacama Large Millimeter/submillimeter Array observations of molecular gas in the associated H ii region N90. We identify 110 molecular clumps ( R < 0.8 pc) traced by CO emission, and study the relationship between the clumps and associated young stellar objects (YSOs) and pre-main-sequence (PMS) stars. The clumps have high virial parameters (typical α vir = 4–11) and may retain signatures of a collision in the last ≲8 Myr between H i components of the adjacent supergiant shell SMC-SGS 1. We obtain a CO-bright-to-H 2 gas conversion factor of X CO, B = (3.4 ± 0.2) × 10 20 cm −2 (K km s −1 ) −1 , and correct observed clump properties for CO-dark H 2 gas to derive a total molecular gas mass in N90 of 16,600 ± 2400 M ⊙ . We derive a recent (≲1 Myr) star formation rate of 130 ± 30 M ⊙ Myr −1 with an efficiency of 8% ± 3% assessed through comparing total YSO mass to total molecular gas mass. Very few significant radial trends exist between clump properties or PMS star ages and distance from NGC 602. We do not find evidence for a triggered star formation scenario among the youngest (≲2 Myr) stellar generations, and instead conclude that a sequential star formation process in which NGC 602 did not directly cause recent star formation in the region is likely. 

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