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[en] We present molecular line and 1.4 mm continuum observations toward five massive star-forming regions at arcsecond resolution using the Submillimeter Array. We find that the warm molecular gas surrounding each H II region (as traced by SO2 and OCS) appears to be undergoing bulk rotation. From the molecular line emission and thermal component of the continuum emission, we independently derived gas masses for each region which are consistent with each other. From the free-free component of the continuum emission, we estimate the minimum stellar mass required to power the H II region and find that this mass, when added to the derived gas mass, is a significant fraction of the dynamical mass for that region.
[en] Accretion flows onto massive stars must transfer mass so quickly that they are themselves gravitationally unstable, forming dense clumps and filaments. These density perturbations interact with young massive stars, emitting ionizing radiation, alternately exposing and confining their H II regions. As a result, the H II regions are predicted to flicker in flux density over periods of decades to centuries rather than increase monotonically in size as predicted by simple Spitzer solutions. We have recently observed the Sgr B2 region at 1.3 cm with the Very Large Array in its three hybrid configurations (DnC, CnB, and BnA) at a resolution of ∼0.''25. These observations were made to compare in detail with matched continuum observations from 1989. At 0.''25 resolution, Sgr B2 contains 41 ultracompact (UC) H II regions, 6 of which are hypercompact. The new observations of Sgr B2 allow comparison of relative peak flux densities for the H II regions in Sgr B2 over a 23 year time baseline (1989-2012) in one of the most source-rich massive star forming regions in the Milky Way. The new 1.3 cm continuum images indicate that four of the 41 UC H II regions exhibit significant changes in their peak flux density, with one source (K3) dropping in peak flux density, and the other three sources (F10.303, F1, and F3) increasing in peak flux density. The results are consistent with statistical predictions from simulations of high mass star formation, suggesting that they offer a solution to the lifetime problem for UC H II regions
[en] The Multi-scale Continuum and Line Exploration of W49 is a comprehensive gas and dust survey of the giant molecular cloud (GMC) of W49A, the most luminous star-formation region in the Milky Way. The project covers, for the first time, the entire GMC at different scales and angular resolutions. In this paper, we present (1) an all-configuration Submillimeter Array mosaic in the 230 GHz (1.3 mm) band covering the central ∼3' × 3' (∼10 pc, known as W49N), where most of the embedded massive stars reside and (2) Purple Mountain Observatory 14 m telescope observations in the 90 GHz band, covering the entire GMC with maps of up to ∼35' × 35' in size, or ∼113 pc. We also make use of archival data from the Very Large Array, JCMT-SCUBA, the IRAM 30 m telescope, and the Caltech Submillimeter Observatory BOLOCAM Galactic Plane Survey. We derive the basic physical parameters of the GMC at all scales. Our main findings are as follows. (1) The W49 GMC is one of the most massive in the Galaxy, with a total mass M gas ∼ 1.1 × 106 M ☉ within a radius of 60 pc. Within a radius of 6 pc, the total gas mass is M gas ∼ 2 × 105 M ☉. At these scales, only ∼1% of the material is photoionized. The mass reservoir is sufficient to form several young massive clusters (YMCs) as massive as a globular cluster. (2) The mass of the GMC is distributed in a hierarchical network of filaments. At scales <10 pc, a triple, centrally condensed structure peaks toward the ring of HC H II regions in W49N. This structure extends to scales from ∼10 to 100 pc through filaments that radially converge toward W49N and its less-prominent neighbor W49S. The W49A starburst most likely formed from global gravitational contraction with localized collapse in a 'hub-filament' geometry. (3) Currently, feedback from the central YMCs (with a present mass M cl ≳ 5 × 104 M ☉) is still not enough to entirely disrupt the GMC, but further stellar mass growth could be enough to allow radiation pressure to clear the cloud and halt star formation. (4) The resulting stellar content will probably remain as a gravitationally bound massive star cluster or a small system of bound clusters.
[en] We present single-dish observations of the L1689-SMM16 core in the Ophiuchus molecular cloud in NH3 (1, 1) and (2, 2) emission using the Green Bank Telescope, in N2H+ (1-0) emission using the Nobeyama Radio Observatory, and in NH2D (11,1a(--)10,1s), HCN (1-0), HNC (1-0), H13CO+ (1-0), and HCO+ (1-0) emission using the Mopra telescope. The morphologies of the integrated NH3 (1, 1) and N2H+ (1-0) emission well match that of 250 μm continuum emission. Line widths of NH3 (1, 1) and N2H+ (1-0) show the presence of transonic turbulence across the core. Jeans and virial analyses made using updated measurements of core mass and size confirm that L1689-SMM16 is prestellar, i.e., gravitationally bound. It also has accumulated more mass compared to its corresponding Jeans mass in the absence of magnetic fields and therefore is a 'super-Jeans' core. The high levels of X(NH3)/X(N2H+) and deuterium fractionation reinforce the idea that the core has not yet formed a protostar. Comparing the physical parameters of the core with those of a Bonnor-Ebert sphere reveals the advanced evolutionary stage of L1689-SMM16 and shows that it might be unstable to collapse. We do not detect any evidence of infall motions toward the core. Instead, red asymmetry in the line profiles of HCN (1-0) and HNC (1-0) indicates the expansion of the outer layers of the core at a speed of ∼0.2 km s–1 to 0.3 km s–1. For a gravitationally bound core, expansion in the outer layers might indicate that the core is experiencing oscillations.