- ID:
- ivo://CDS.VizieR/J/A+A/561/A148
- Title:
- Mass Distribution of Infrared Dark Clouds
- Short Name:
- J/A+A/561/A148
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the dust continuum emission at 870um in order to investigate the mass distribution of clumps within infrared dark clouds (IRDCs). We map six IRDCs with the Large APEX BOlometer CAmera (LABOCA) at APEX, reaching an rms noise level of 28-44mJy/beam. The dust continuum emission coming from these IRDCs was decomposed by using two automated algorithms, Gaussclumps and Clumpfind. We identify 510 and 352 sources with Gaussclumps and Clumpfind, respectively, and estimate masses and other physical properties assuming a uniform dust temperature. The mass ranges are 6-2692M_{sun}_(Gaussclumps) and 7-4254M_{sun} (Clumpfind) and the ranges in effective radius are around 0.10-0.74pc (Gaussclumps) and 0.16-0.99pc (Clumpfind). The mass distribution, independent of the decomposition method used, is fitted by a power law, dN/dM{prop.to}M^alpha^, with an index (alpha) of -1.60+/-0.06.
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- ID:
- ivo://CDS.VizieR/J/ApJ/780/173
- Title:
- Masses of giant molecular clouds in Milky Way
- Short Name:
- J/ApJ/780/173
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using ^13^CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') ^13^CO J=1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200M_{sun}_/pc^2^, which are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin ^13^CO J=1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11^+0.12^_-0.06__. The high column density subregions comprise 0.07^+0.13^_-0.05_ of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4km/s for various flow configurations.
- ID:
- ivo://CDS.VizieR/J/A+A/638/A105
- Title:
- 8 massive proto-cluster clumps NH2D & NH3 cubes
- Short Name:
- J/A+A/638/A105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The initial stage of star formation is very difficult to study because of its high density (n_H_2> 10^6^cm^-3^) and low temperature (T_dust_<18K). Under such conditions, many molecules become depleted from the gas phase by freezing out onto dust grains. However, the deuterated species could remain gaseous under these extreme conditions and are thus ideal tracers. We investigate the gas dynamics and NH_2_D chemistry in eight massive pre/protocluster clumps (G18.17, G18.21, G23.97N, G23.98, G23.44, G23.97S, G25.38, and G25.71). We present NH_2_D 1_11-1_01 (at 85.926GHz), NH_3_ (1,1) and (2,2) observations in the eight clumps using the PdBI and the VLA, respectively. We use 3D GAUSSCLUMPS to extract NH_2_D cores and provide a statistical view of their deuterium chemistry. We use NH_3_ (1,1) and (2,2) data to investigate the temperature and dynamics of dense and cold objects. We find that the distribution between deuterium fractionation and kinetic temperature shows a number density peak at around T_kin_=16.1K, and the NH_2_D cores are mainly located at a temperature range of 13.0 to 22.0K. The 3.5mm continuum cores have a kinetic temperature with the median width of 22.1+/-4.3K, which is obviously higher than the temperature in NH_2_D cores. We detect seven extremely high deuterium fractionation of 1.0<=D_frac_<=1.41. We find that the NH_2_D emission does not appear to coincide exactly with either dust continuum or NH3 peak positions, but often surrounds the star-formation active regions. This suggests that the NH_2_D has been destroyed by the central young stellar object (YSO) due to its heating. The detected NH_2_D lines are very narrow with a median width of 0.98+/-0.02km/s, which is dominated by non-thermal broadening. The extracted NH_2_D cores are gravitationally bound ({alpha}_vir_<1), are likely prestellar or starless, and can potentially form intermediate-mass or high-mass stars in future. Using NH3 (1,1) as a dynamical tracer, we find very complicated dynamical movement in all the eight clumps, which can be explained by a combined process with outflow, rotation, convergent flow, collision, large velocity gradient, and rotating toroids. High deuterium fractionation strongly depends on the temperature condition. NH_2_D is a poor evolutionary indicator of high-mass star formation in evolved stages, but a useful tracer in the starless and prestellar cores.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A85
- Title:
- 8 massive proto-cluster clumps observations
- Short Name:
- J/A+A/627/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive clumps tend to fragment into clusters of cores and condensations, some of which form high-mass stars. In this work, we study the structure of massive clumps at different scales, analyze the fragmentation process, and investigate the possibility that star formation is triggered by nearby HII regions. We present a high angular resolution study of a sample of 8 massive proto-cluster clumps. Combining infrared data, we use few-arcsecond resolution radio- and millimeter interferometric data to study their fragmentation and evolution. Our sample is unique in the sense that all the clumps have neighboring HII regions. Taking advantage of that, we test triggered star formation using a novel method where we study the alignment of the centres of mass traced by dust emission at multiple scales. The eight massive clumps have masses ranging from 228 to 2279M_{sun}_. The brightest compact structures within infrared bright clumps are typically associated with embedded compact radio continuum sources. The smaller scale structures of Reff~0.02pc observed within each clump are mostly gravitationally bound and massive enough to form at least a B3-B0 type star. Many condensations have masses larger than 8M_{sun}_ at small scale of Reff~0.02pc. Although the clumps are mostly infrared quiet, the dynamical movements are active at clump scale (~1pc). We studied the spatial distribution of the gas conditions detected at different scales. For some sources we find hints of external triggering, whereas for others we find no significant pattern that indicates triggering is dynamically unimportant. This probably indicates that the different clumps go through different evolutionary paths. In this respect, studies with larger samples are highly desired.
- ID:
- ivo://CDS.VizieR/J/ApJ/655/351
- Title:
- Massive quiescent cores in Orion. II.
- Short Name:
- J/ApJ/655/351
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have surveyed submillimeter continuum emission from relatively quiescent regions in the Orion molecular cloud to determine how the core mass function in a high-mass star-forming region compares to the stellar initial mass function. Such studies are important for understanding the evolution of cores to stars, and for comparison to formation processes in high- and low-mass star-forming regions. We used the SHARC II camera on the Caltech Submillimeter Observatory telescope to obtain 350um data having angular resolution of about 9", which corresponds to 0.02pc at the distance of Orion. Further data processing using a deconvolution routine enhances the resolution to about 3". Such high angular resolution allows a rare look into individually resolved dense structures in a massive star-forming region.
- ID:
- ivo://CDS.VizieR/J/ApJS/243/13
- Title:
- Massive star-forming clump from MALT90
- Short Name:
- J/ApJS/243/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We selected 90 massive star-forming clumps with strong N2H+(1-0), HCO+(1-0), HCN(1-0), and HNC(1-0) emission from the Millimetre Astronomy Legacy Team 90 GHz survey. We obtained Herschel data for all 90 sources and NRAO VLA Sky Survey data for 51 of them. We convolved and regridded all images to the same resolution and pixel size and derived the temperature, H2 column density, molecules' abundances and abundance, and ratios of each pixel. Our analysis yields three main conclusions. First, the abundances of N2H+, HCO+, HCN, and HNC increase when the column density decreases and the temperature increases, with spatial variations in their abundances dominated by changes in the H2 column density. Second, the abundance ratios between N2H+, HCO+, HCN, and HNC also display systemic variations as a function of the column density due to the chemical properties of these molecules. Third, the sources associated with the 20cm continuum emission can be classified into four types based on the behavior of the abundances of the four molecules considered here as a function of this emission. The variations of the first three types could also be attributed to the variation of the H2 column density.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A30
- Title:
- Massive star forming molecular clumps Tkin
- Short Name:
- J/A+A/598/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- For a general understanding of the physics involved in the star formation process, measurements of physical parameters such as temperature and density are indispensable. The chemical and physical properties of dense clumps of molecular clouds are strongly affected by the kinetic temperature. Therefore, this parameter is essential for a better understanding of the interstellar medium. Formaldehyde, a molecule which traces the entire dense molecular gas, appears to be the most reliable tracer to directly measure the gas kinetic temperature.We aim to determine the kinetic temperature with spectral lines from formaldehyde and to compare the results with those obtained from ammonia lines for a large number of massive clumps.Three 218 GHz transitions (J_KAKC_=3_03_-2_02_, 3_22_-2_21_, and 3_21_-2_20_) of para-H_2_CO were observed with the 15m James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic disk at various stages of high-mass star formation. Using the RADEX non-LTE model, we derive the gas kinetic temperature modeling the measured para-H_2_CO 3_22_-2_21_/3_03_-2_02_ and 3_21_-2_20_/3_03_-2_02_ ratios. The gas kinetic temperatures derived from the para-H2CO (3_21_-2_20_/3_03_-2_02_) line ratios range from 30 to 61K with an average of 46K. A comparison of kinetic temperature derived from para-H_2_CO, NH3, and the dust emission indicates that in many cases para-H_2_CO traces a similar kinetic temperature to the NH_3_ (2,2)/(1,1) transitions and the dust associated with the HII regions. Distinctly higher temperatures are probed by para-H_2_CO in the clumps associated with outflows/shocks. Kinetic temperatures obtained from para-H_2_CO trace turbulence to a higher degree than NH_3_ (2,2)/(1,1) in the massive clumps. The non-thermal velocity dispersions of para-H_2_CO lines are positively correlated with the gas kinetic temperature. The massive clumps are significantly influenced by supersonic non-thermal motions.
- ID:
- ivo://CDS.VizieR/J/ApJ/566/945
- Title:
- Massive star forming regions at 1.2mm
- Short Name:
- J/ApJ/566/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed 1.2mm continuum and CS spectral line study of a large sample of 69 massive star forming regions in very early stages of evolution, most of them prior to building up an ultracompact H II region.
- ID:
- ivo://CDS.VizieR/J/A+A/569/A20
- Title:
- Massive stars in two giant molecular clouds
- Short Name:
- J/A+A/569/A20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young massive stars and stellar clusters continuously form in the Galactic disk, generating new HII regions within their natal giant molecular clouds and subsequently enriching the interstellar medium via their winds and supernovae. Massive stars are among the brightest infrared stars in such regions; their identification permits the characterisation of the star formation history of the associated cloud as well as constraining the location of stellar aggregates and hence their occurrence as a function of global environment. We present a stellar spectroscopic survey in the direction of the giant molecular cloud G23.3-0.3. This complex is located at a distance of ~4-5kpc, and consists of several HII regions and supernova remnants. We discovered 11 Of_K_^+^ stars, one candidate luminous blue variable, several OB stars, and candidate red supergiants. Stars with K-band extinction from ~1.3-1.9mag appear to be associated with the GMC G23.3-0.3; O and B-types satisfying this criterion have spectrophotometric distances consistent with that of the giant molecular cloud. Combining near-IR spectroscopic and photometric data allowed us to characterize the multiple sites of star formation within it. The O-type stars have masses from ~25-45M_{sun}_, and ages of 5-8Myr. Two new red supergiants were detected with interstellar extinction typical of the cloud; along with the two RSGs within the cluster GLIMPSE9, they trace an older burst with an age of 20-30Myr. Massive stars were also detected in the core of three supernova remnants - W41, G22.7-0.2, and G22.7583-0.4917. A large population of massive stars appears associated with the GMC G23.3-0.3, with the properties inferred for them indicative of an extended history of stars formation.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/70
- Title:
- Massive YSOs in the IR dark cloud G79.3+0.3
- Short Name:
- J/ApJ/876/70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- G79.3+0.3 is an infrared dark cloud in the Cygnus-X complex that is home to massive deeply embedded young stellar objects (YSOs). We have produced a Submillimeter Array (SMA) 1.3mm continuum image and ^12^CO line maps of the eastern section of G79.3+0.3 in which we detect five separate YSOs. We have estimated physical parameters for these five YSOs and others in the vicinity of G79.3+0.3 by fitting existing photometry from Spitzer, Herschel, and ground-based telescopes to spectral energy distribution models. Through these model fits we find that the most massive YSOs seen in the SMA 1.3mm continuum emission have masses in the 5-6M_{sun}_ range. One of the SMA sources was observed to power a massive collimated ^12^CO outflow extending at least 0.94pc in both directions from the protostar, with a total mass of 0.83M_{sun}_ and a dynamical timescale of 23kyr.
