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Register a new userStudying star-forming processes towards G29.862-0.044
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Mar\\'ia Bel\\'en Areal
Publication date
2019
fields
Physics
and research's language is
English
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We present a multiwavelength study towards the young stellar object (YSO) G29.862-0.044 (hereafter G29), which is embedded in the massive star-forming region G29.96-0.02, located at a distance of about 6.5 kpc. The surrounding interstellar medium of G29 is studied using molecular lines data (angular resolution about 15) obtained from the databases of the James Clerk Maxwell Telescope. The physical conditions of G29 molecular outflows and the clump where the YSO is embedded are characterized. Near-IR data is also analyzed (spatial resolution of about 0.5) obtained with NIRI at Gemini North to have a detailed view of the circumstellar ambient of G29. The Ks emission towards G29 exhibits a cone-like feature pointing to the red molecular outflow. The aim of this work is to obtain a complete picture of this YSO, the related star-forming processes, and the interstellar medium around it. Studies like this are important because they contribute to a comprehensive understanding of star formation.
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Massive molecular clumps fragment into cores where star formation takes place, hence star-forming studies should be done at different spatial scales. Using near-IR data obtained with Gemini, data of CH3OCHO and CH3CN from the ALMA database, observations of HCN, HNC, HCO+, and C2H carried out with ASTE, and CO data from public surveys, we perform a deep study of the YSO G29.86-0.004 at core and clump spatial scales. The near-IR emission shows two nebulosities separated by a dark lane, suggesting a typical disk-jets system, but highly asymmetric. They are likely produced by scattered light in cavities carved out by jets on an infalling envelope of material, which also present line emission of H2 and [FeII]. The presence of the complex molecular species observed with ALMA confirms that we are mapping a hot molecular core. The CH3CN emission concentrates at the position of the dark lane and it appears slightly elongated from southwest to northeast in agreement with the inclination of the system as observed at near-IR. The morphology of the CH3OCHO emission is more complex and extends along some filaments and concentrates in knots and clumps, mainly southwards the dark-lane, suggesting that the southern jet is encountering a dense region. The northern jet flows more freely, generating more extended features. This is in agreement with the red-shifted molecular outflow traced by the 12CO J=3-2 line extending towards the northwest and the lack of a blue-shifted outflow. This configuration can be explained by considering that the YSO is located at the furthest edge of the molecular clump along the line of sight, which is consistent with the position of the source in the cloud mapped in the C18O J=3-2 line. The detection of HCN, HNC, HCO+, and C2H allowed us to characterize the dense gas at clump scales, yielding results that are in agreement with the presence of a high-mass protostellar object.
We present the study of deuteration of cyanoacetylene (HC$_3$N) towards a sample of 28 high-mass star-forming cores divided into different evolutionary stages, from starless to evolved protostellar cores. We report for the first time the detection of DC$_3$N towards 15 high-mass cores. The abundance ratios of DC$_3$N with respect HC$_3$N range in the interval 0.003$-$0.022, lower than those found in low-mas protostars and dark clouds. No significant trend with the evolutionary stage, or with the kinetic temperature of the region, has been found. We compare the level of deuteration of HC$_3$N with those of other molecules towards the same sample, finding weak correlation with species formed only or predominantly in gas phase (N$_2$H$^+$ and HNC, respectively), and no correlation with species formed only or predominantly on dust grains (CH$_3$OH and NH$_3$, respectively). We also present a single-dish map of DC$_3$N towards the protocluster IRAS 05358+3543, which shows that DC$_3$N traces an extended envelope ($sim$0.37 pc) and peaks towards two cold condensations separated from the positions of the protostars and the dust continuum. The observations presented in this work suggest that deuteration of HC$_3$N is produced in the gas of the cold outer parts of massive star-forming clumps, giving us an estimate of the deuteration factor prior to the formation of denser gas.
We have conducted a search for ionized gas at 3.6 cm, using the Very Large Array, towards 31 Galactic intermediate- and high-mass clumps detected in previous millimeter continuum observations. In the 10 observed fields, 35 HII regions are identified, of which 20 are newly discovered. Many of the HII regions are multiply peaked indicating the presence of a cluster of massive stars. We find that the ionized gas tends to be associated towards the millimeter clumps; of the 31 millimeter clumps observed, 9 of these appear to be physically related to ionized gas, and a further 6 have ionized gas emission within 1. For clumps with associated ionized gas, the combined mass of the ionizing massive stars is compared to the clump masses to provide an estimate of the instantaneous star formation efficiency. These values range from a few percent to 25%, and have an average of 7 +/- 8%. We also find a correlation between the clump mass and the mass of the ionizing massive stars within it, which is consistent with a power law. This result is comparable to the prediction of star formation by competitive accretion that a power law relationship exists between the mass of the most massive star in a cluster and the total mass of the remaining stars.
From targeted observations of ground-state OH masers towards 702 Multibeam (MMB) survey 6.7-GHz methanol masers, between Galactic longitudes 186$^{circ}$ through the Galactic centre to 20$^{circ}$, made as part of the `MAGMO project, we present the physical and polarisation properties of the 1720-MHz OH maser transition, including the identification of Zeeman pairs. We present 10 new and 23 previously catalogued 1720-MHz OH maser sources detected towards star formation regions. In addition, we also detected 16 1720-MHz OH masers associated with supernova remnants and two sites of diffuse OH emission. Towards the 33 star formation masers, we identify 44 Zeeman pairs, implying magnetic field strengths ranging from $-$11.4 to $+$13.2 mG, and a median magnetic field strength of $|B_{LOS}|$ $sim$ 6 mG. With limited statistics, we present the in-situ magnetic field orientation of the masers and the Galactic magnetic field distribution revealed by the 1720-MHz transition. We also examine the association statistics of 1720-MHz OH SFR masers with other ground-state OH masers, excited-state OH masers, class I and class II methanol masers and water masers, and compare maser positions with mid-infrared images of the parent star forming regions. Of the 33 1720-MHz star formation masers, ten are offset from their central exciting sources, and appear to be associated with outflow activity.
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