High Mass Star Formation: Properties of NH3 clumps in Southern Galactic Plane (original) (raw)
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Physical characterization of southern massive star-forming regions using Parkes NH3observations
Monthly Notices of The Royal Astronomical Society - MON NOTIC ROY ASTRON SOC, 2010
We have undertaken a Parkes ammonia spectral line study, in the lowest two inversion transitions, of southern massive star formation regions, including young massive candidate protostars, with the aim of characterizing the earliest stages of massive star formation. 138 sources from the submillimetre continuum emission studies of Hill et al. were found to have robust (1,1) detections, including two sources with two velocity components, and 102 in the (2,2) transition. We determine the ammonia line properties of the sources: linewidth, flux density, kinetic temperature, NH3column density and opacity, and revisit our spectral energy distribution modelling procedure to derive the mass for 52 of the sources. By combining the continuum emission information with ammonia observations we substantially constrain the physical properties of the high-mass clumps. There is clear complementarity between ammonia and continuum observations for derivations of physical parameters. The MM-only class, i...
arXiv: Astrophysics of Galaxies, 2016
We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment (ASTE) 10-m telescope. The star formation rates probed by total infrared luminosities (LTIR) are linearly correlated with clump masses (Mclump) for those clumps with LTIR larger than 10^3 Lsun, leading to a constant gas depletion time of ~107 Myr. The correlations between LTIR and molecular line luminosities (Lmol) of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with LTIR 10^3 Lsun. These correlations become linear when extended to external galaxies. A bimodal behavior in the LTIR-Lmol correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and sigma_line-to-sigma_vir ratio. Such bimodal behavior may be due to evolutionary effects. The slopes of LTIR-Lmol correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump ma...
Ammonia cores in high mass star formation regions
Astronomy and Astrophysics, 2006
We observed a sample of 35 water masers not coincident with known HII regions and/or low mass young stellar objects (YSOs) with the Effelsberg 100 m telescope in the NH 3 (J, K) = (1, 1), (2, 2), (3, 3) and (4, 4) transitions. Sixteen sources were detected in the NH 3 emission. The detection rate is 46%. All these sixteen sources have NH 3 (1, 1) and (2, 2) emission, among which four sources have NH 3 (3, 3) emission. Comparing with the IRAS and the 2MASS data, we analyzed the relationship between the detection rate and the infrared color, the dust temperature and the source distance. All the detected sources were mapped and 17 cores were obtained (one source IRAS 20215+3725 has two cores). From the detected sources five cores do not coincide with radio continuum or IRAS and MSX point sources. Excluding one core that has no MSX data available, the remaining eleven cores are coincident with IRAS or MSX point sources. The typical size and mass of the cores are 1.6 pc and 1.5 × 10 3 M ⊙ , respectively. The average line widths of the NH 3 (1, 1) and (2, 2) are 1.54 and 1.73 km s −1 . The average kinetic temperature of the gas is about 19 K. These values are much larger than those of low mass cores. The NH 3 cores that coincide with IRAS sources (referred to as Group I) have slightly larger line widths (1.65 and 1.75 km s −1 for the (1, 1) and (2, 2) lines, respectively) and larger masses (1.8 × 10 3 M ⊙ ) than the mean values of the sample. For this type of core the kinetic temperature correlates with the line width. The line width appears to correlate with the bolometric luminosity and the core size. Despite the average luminosity of 2.9 × 10 4 L ⊙ , there is no detectable 6 cm emission. These are candidates for high mass protostars or precursors of UC HII regions. The NH 3 cores with peaks offset from infrared sources (referred to as Group II) have an average size of 1.7 pc and an average line width of 1.50 km s −1 for the (1, 1) line. The line width of the (1, 1) emission is smaller than that of the group I. The average mass is 9.4 × 10 2 M ⊙ . One possible explanation for the deviation is that the NH 3 peak and the infrared source correspond to different clumps. These cores are potential high mass star formation sites and may be at an earlier evolutionary stage than those with IRAS point sources. This type of core is seen in mapping observations, and can be easily missed by single-spectrum observations toward the IRAS position.
Physical and chemical structure of high-mass star-forming regions
Astronomy & Astrophysics, 2021
Aims. Current star formation research centers the characterization of the physical and chemical properties of massive stars, which are in the process of formation, at the spatial resolution of individual high-mass cores. Methods. We use sub-arcsecond resolution (~0.′′4) observations with the NOrthern Extended Millimeter Array at 1.37 mm to study the dust emission and molecular gas of 18 high-mass star-forming regions. With distances in the range of 0.7−5.5 kpc, this corresponds to spatial scales down to 300−2300 au that are resolved by our observations. We combined the derived physical and chemical properties of individual cores in these regions to estimate their ages. The temperature structures of these regions are determined by fitting the H2CO and CH3CN line emission. The density profiles are inferred from the 1.37 mm continuum visibilities. The column densities of 11 different species are determined by fitting the emission lines with XCLASS. Results. Within the 18 observed regio...
Astrophysical Journal Supplement Series, 2011
We present observations of HCO + and H 13 CO + , N 2 H + , HCS + , HNC and HN 13 C, SO and 34 SO, CCH, SO 2 , and CH 3 OH-E towards a sample of 27 highmass clumps coincident with water maser emission. All transitions are observed with or convolved to nearly identical resolution (30 ′′ ), allowing for intercomparison of the clump properties derived from the mapped transitions. We find N 2 H + emission is spatially differentiated compared to the dust and the other molecules towards a few very luminous cores (10 of 27) and the N 2 H + integrated
NH3 observations of the S235 star-forming region: Dense gas in inter-core bridges
Publications of the Astronomical Society of Japan, 2019
Star formation is thought to be driven by two groups of mechanisms; spontaneous collapse and triggered collapse. Triggered star formation mechanisms further diverge into cloud–cloud collision (CCC), “collect and collapse” (C&C) and shock-induced collapse of pre-existing, gravitationally stable cores, or “radiation driven implosion” (RDI). To evaluate the contributions of these mechanisms and establish whether these processes can occur together within the same star-forming region, we performed mapping observations of radio-frequency ammonia and water maser emission lines in the S235 massive star-forming region. Via spectral analyses of main, hyperfine, and multi-transitional ammonia lines we explored the distribution of temperature and column density in the dense gas in the S235 and S235AB star-forming region. The most remarkable result of the mapping observations is the discovery of high-density gas in inter-core bridges which physically link dense molecular cores that house young p...
The Astrophysical Journal
We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z>1) star forming galaxies (SFGs), indicating a constant gas depletion time of ∼100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L TIR ) and molecular line luminosities ¢ L mol ( ) of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L TIR ∼10 3 L ☉ . These correlations become linear when extended to external galaxies. A bimodal behavior in the L TIR -¢ L mol correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and σ line /σ vir . Such bimodal behavior may be due to evolutionary effects. The slopes of L TIR -L′ mol correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in . The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L TIR larger than L TIR ∼10 4.5 L ☉ . High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M clump -L′ mol and L TIR -L′ mol relations.
Evidence for Inflow in High-mass Star-forming Clumps
Astrophysical Journal, 2011
We analyze the HCO+ 3-2 and H13CO+ 3-2 line profiles of 27 high-mass star-forming regions to identify asymmetries that are suggestive of mass inflow. Three quantitative measures of line asymmetry are used to indicate whether a line profile is blue, red or neither - the ratio of the temperature of the blue and red peaks, the line skew and the dimensionless parameter delta_v. We find nine HCO+ 3-2 line profiles with a significant blue asymmetry and four with significant red asymmetric profiles. Comparing our HCO+ 3-2 results to HCN 3-2 observations from Wu et al. (2003, 2010), we find that eight of the blue and three of red have profiles with the same asymmetry in HCN. The eight sources with blue asymmetries in both tracers are considered strong candidates for inflow. Quantitative measures of the asymmetry (e.g. delta_v) tend to be larger for HCN. This, combined with possible HCO+ abundance enhancements in outflows, suggests that HCN may be a better tracer of inflow. Understanding the behavior of common molecular tracers like HCO+ in clumps of different masses is important for properly analyzing the line profiles seen in a sample of sources representing a broad range of clump masses. Such studies will soon be possible with the large number of sources with possible self-absorption seen in spectroscopic follow-up observations of clumps identified in the Bolocam Galactic Plane Survey.
Scaling relations of star-forming regions: from kpc-sized clumps to H ii regions
Monthly Notices of the Royal Astronomical Society, 2012
We present the properties of eight star-forming regions, or 'clumps,' in three galaxies at z ∼ 1.3 from the WiggleZ Dark Energy Survey, which are resolved with the OH Suppressing InfraRed Imaging Spectrograph (OSIRIS) integral field spectrograph. Within turbulent discs, σ ∼ 90 km s −1 , clumps are measured with average sizes of 1.5 kpc and average Jeans masses of 4.2 × 10 9 M , in total accounting for 40-60 per cent of the stellar mass of the discs. These findings lend observational support to models that predict larger clumps will form as a result of higher disc velocity dispersions driven-up by cosmological gas accretion. As a consequence of the changes in global environment, it may be predicted that star-forming regions at high redshift should not resemble star-forming regions locally. Yet despite the increased sizes and dispersions, clumps and H II regions are found to follow tight scaling relations over the range z = 0-2 for Hα size, velocity dispersion, luminosity and mass when comparing >2000 H II regions locally and 30 clumps at z > 1 (σ ∝ r 0.42 ±0.03 , L Hα ∝ r 2.72 ±0.04 , L Hα ∝ σ 4.18 ±0.21 and L Hα ∝ M 1.24±0.05 Jeans). We discuss these results in the context of the existing simulations of clump formation and evolution, with an emphasis on the processes that drive-up the turbulent motions in the interstellar medium. Our results indicate that while the turbulence of discs may have important implications for the size and luminosity of regions which form within them, the same processes govern their formation from high redshift to the current epoch.
Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey
Astronomy & Astrophysics, 2012
Context. The APEX Telescope Large Area Survey: the GALaxy (ATLASGAL) is an unbiased continuum survey of the inner Galactic disk at 870 μm. It covers ±60 • in Galactic longitude and aims to find all massive clumps at various stages of high-mass star formation in the inner Galaxy, particularly the earliest evolutionary phases. Aims. We aim to determine properties such as the gas kinetic temperature and dynamics of new massive cold clumps found by ATLASGAL. Most importantly, we derived their kinematical distances from the measured line velocities. Methods. We observed the ammonia (J, K) = (1, 1) to (3, 3) inversion transitions toward 862 clumps of a flux-limited sample of submm clumps detected by ATLASGAL and extracted 13 CO (1−0) spectra from the Galactic Ring Survey (GRS). We determined distances for a subsample located at the tangential points (71 sources) and for 277 clumps whose near/far distance ambiguity is resolved. Results. Most ATLASGAL clumps are cold with rotational temperatures from 10−30 K with a median of 17 K. They have a wide range of NH 3 linewidths (1−7 km s −1 ) with 1.9 km s −1 as median, which by far exceeds the thermal linewidth, as well as a broad distribution of high column densities from 10 14 to 10 16 cm −2 (median of 2 × 10 15 cm −2 ) with an NH 3 abundance in the range of 5 to 30 × 10 −8 . ATLASGAL sources are massive, > ∼ 100 M , and a fraction of clumps with a broad linewidth is in virial equilibrium. We found an enhancement of clumps at Galactocentric radii of 4.5 and 6 kpc. The comparison of the NH 3 lines as high-density probes with the GRS 13 CO emission as low-density envelope tracer yields broader linewidths for 13 CO than for NH 3 . The small differences in derived clump velocities between NH 3 (representing dense core material) and 13 CO (representing more diffuse molecular cloud gas) suggests that the cores are essentially at rest relative to the surrounding giant molecular cloud. Conclusions. The high detection rate (87%) confirms ammonia as an excellent probe of the molecular content of the massive, cold clumps revealed by ATLASGAL. A clear trend of increasing rotational temperatures and linewidths with evolutionary stage is seen for source samples ranging from 24 μm dark clumps to clumps with embedded HII regions. The survey provides the largest ammonia sample of high-mass star forming clumps and thus presents an important repository for the characterization of statistical properties of the clumps and the selection of subsamples for detailed, high-resolution follow-up studies.