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Register a new userAsymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global Collapse
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Using molecular line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90), we have searched the optically thick hcop, line for the blue asymmetry spectroscopic signature of infall motion in a large sample of high-mass, dense molecular clumps observed to be at different evolutionary stages of star cluster formation according to their mid-infrared appearance. To quantify the degree of the line asymmetry, we measure the asymmetry parameter $A = {{I_{blue}-I_{red}}over{I_{blue}+I_{red}}}$, the fraction of the integrated intensity that lies to the blueshifted side of the systemic velocity determined from the optically thin tracer thp. For a sample of 1,093 sources, both the mean and median of $A$ are positive ($A = 0.083pm0.010$ and $0.065pm0.009$, respectively) with high statistical significance, and a majority of sources (a fraction of $0.607 pm 0.015$ of the sample) show positive values of A, indicating a preponderance of blue-asymmetric profiles over red-asymmetric profiles. Two other measures, the local slope of the line at the systemic velocity and the $delta v$ parameter of citet{Mardones1997}, also show an overall blue asymmetry for the sample, but with smaller statistical significance. This blue asymmetry indicates that these high-mass clumps are predominantly undergoing gravitational collapse. The blue asymmetry is larger ($A sim 0.12$) for the earliest evolutionary stages (quiescent, protostellar and compact H II region) than for the later H II region ($A sim 0.06$) and PDR ($A sim 0$) classifications.
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We present interferometric observations of the CN(1-0) line emission in Mrk231 and combine them with previous observations of CO and other H$_2$ gas tracers to study the physical properties of the massive molecular outflow. We find a strong boost of the CN/CO(1-0) line luminosity ratio in the outflow, which is unprecedented compared to any other known Galactic or extragalactic source. For the dense gas phase in the outflow traced by the HCN and CN emissions, we infer $rm X_{rm CN}equiv [CN]/[H_2] > X_{rm HCN}$ by at least a factor of three, with H$_2$ gas densities of $n_{rm H_2}sim10^{5-6}$ cm$^{-3}$. In addition, for the first time, we resolve narrow spectral features in the HCN(1-0) and HCO$^+$(1-0) high-velocity line wings tracing the dense phase of the outflow. The velocity dispersions of these spectral features, $sigma_vsim7-20$ km s$^{-1}$, are consistent with those of massive extragalactic giant molecular clouds detected in nearby starburst nuclei. The H$_2$ gas masses inferred from the HCN data are quite high, $M_{mol}sim0.3-5times10^8$ $M_{odot}$. Our results suggest that massive, denser molecular gas complexes survive embedded into the more diffuse H$_2$ phase of the outflow, and that the chemistry of such outflowing dense clouds is affected by enhanced UV radiation.
An inverse P-Cygni profile of H13CO+ (1-0) in G31.41+0.31 was recently observed, which indicates the presence of an infalling gas envelope. Also, an outflow tracer, SiO, was observed. Here, exclusive radiative transfer modelings have been implemented to generate synthetic spectra of some key species (H13 CO+, HCN, SiO, NH3, CH3 CN, CH3OH, CH3SH, and CH3NCO) and extract the physical features to infer the excitation conditions of the surroundings where they observed. The gas envelope is assumed to be accreting in a spherically symmetric system towards the central hot core region. Our principal intention was to reproduce the observed line profiles toward G31.41+0.31 and extract various physical parameters. The LTE calculation with CASSIS and non-LTE analysis with the RATRAN radiative transfer codes are considered for the modeling purpose. The best-fitted line parameters are derived, which represents the prevailing physical condition of the gas envelope. Our results suggest that an infalling gas could explain the observed line profiles of all the species mentioned above except SiO. An additional outflow component is required to confer the SiO line profile. Additionally, an astrochemical model is implemented to explain the observed abundancests various species in this source.
We present a unified description of the scenario of Global Hierarchical Collapse and fragmentation (GHC) in molecular clouds (MCs), owing to the continuous decrease of the average Jeans mass in the contracting cloud. GHC constitutes a regime of collapses within collapses, in which small-scale collapses begin at later times, but occur on shorter timescales than large-scale ones. The difference in timescales allows for most of the clouds mass to be dispersed by feedback from the first massive stars, maintaining the global star formation rate low. All scales accrete from their parent structures. The main features of GHC are: star-forming MCs are in an essentially pressureless regime, which produces filaments that accrete onto clumps and cores (hubs). The filaments constitute the collapse flow from cloud to hub scales and may approach a quasi-stationary state; the molecular and dense mass fractions of the clouds increase over time; the first (low-mass) stars appear several Myr after global contraction began; more massive stars appear after a few Myr in massive hubs resulting from the collapse of larger scales; the minimum fragment mass may extend well into the brown-dwarf regime; Bondi-Hoyle-Lyttleton accretion occurs at the protostellar and core scales, accounting for a near-Salpeter IMF; the extreme anisotropy of the filamentary network explains the difficulty in detecting large-scale infall signatures; the balance between inertial and gravitationally-driven motions in clumps evolves during the contraction; prestellar cores adopt Bonnor-Ebert-like profiles, but are contracting ever since early times when they may appear to be unbound and to require pressure confinement; stellar clusters develop radial age and mass segregation gradients. Finally, we discuss the incompatibility between supersonic turbulence and the observed scalings in the molecular hierarchy.
We aim to characterize a diverse selection of dense, potentially star-forming cores, clumps, and clouds within the Milky Way in terms of their dust emission and SF activity. We studied 53 fields that have been observed in the JCMT SCUBA-2 continuum survey SCOPE and have been mapped with Herschel. We estimated dust properties by fitting Herschel observations with modified blackbody functions, studied the relationship between dust temperature and dust opacity spectral index $beta$, and estimated column densities. We extracted clumps from the SCUBA-2 850 $mu$m maps with the FellWalker algorithm and examined their masses and sizes. Clumps are associated with young stellar objects found in several catalogs. We estimated the gravitational stability of the clumps with virial analysis. The clumps are categorized as unbound starless, prestellar, or protostellar. We find 529 dense clumps, typically with high column densities from (0.3-4.8)$times 10^{22}$ cm$^{-2}$, with a mean of (1.5$pm$0.04)$times10^{22}$ cm$^{-2}$, low temperatures ($Tsim $10-20 K), and estimated submillimeter $beta$ =1.7$pm$0.1. We detect a slight increase in opacity spectral index toward millimeter wavelengths. Masses of the sources range from 0.04 $M_odot$ to 4259 $M_odot$. Mass, linear size, and temperature are correlated with distance. Furthermore, the estimated gravitational stability is dependent on distance, and more distant clumps appear more virially bound. Finally, we present a catalog of properties of the clumps.Our sources present a large array of SF regions, from high-latitude, nearby diffuse clouds to large SF complexes near the Galactic center. Analysis of these regions will continue with the addition of molecular line data, which will allow us to study the densest regions of the clumps in more detail.
The article deals with observations of star-forming regions S231-S235 in quasi-thermal lines of ammonia (NH$_3$), cyanoacetylene (HC$_3$N) and maser lines of methanol (CH$_3$OH) and water vapor (H$_2$O). S231-S235 regions is situated in the giant molecular cloud G174+2.5. We selected all massive molecular clumps in G174+2.5 using archive CO data. For the each clump we determined mass, size and CO column density. After that we performed observations of these clumps. We report about first detections of NH$_3$ and HC$_3$N lines toward the molecular clumps WB89 673 and WB89 668. This means that high-density gas is present there. Physical parameters of molecular gas in the clumps were estimated using the data on ammonia emission. We found that the gas temperature and the hydrogen number density are in the ranges 16-30 K and 2.8-7.2$times10^3$ cm$^{-3}$, respectively. The shock-tracing line of CH$_3$OH molecule at 36.2 GHz is newly detected toward WB89 673.
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