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Start Over Subject molecular clouds Content Level Research
91. C^18^O cores in the S140 cloud
ID:
ivo://CDS.VizieR/J/ApJ/732/101
Title:
C^18^O cores in the S140 cloud
Short Name:
J/ApJ/732/101
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of C^18^O(J=1-0) mapping observations of a 20'x18' area in the Lynds 1204 molecular cloud associated with the Sharpless 2-140 (S140) HII region. The C^18^O cube ({alpha}-{delta}-{nu}_LSR_) data show that there are three clumps of sizes ~1pc in the region. Two of these have peculiar redshifted velocity components at their edges, which can be interpreted as the results of the interaction between the cloud and the Cepheus Bubble. From the C^18^O cube data, clumpfind identified 123 C^18^O cores, which have mean radius, velocity width in FWHM, and LTE mass of 0.36+/-0.07pc, 0.37+/-0.09km/s, and 41+/-29M_{sun}_, respectively. Considering the uncertainty in the C^18^O abundance, all the cores in S140 are most likely to be gravitationally bound. We derived a C^18^O core mass function (CMF), which shows a power-law-like behavior above a turnover at 30M_{sun}_.
92. ^13^CO cores in the Taurus molecular cloud
ID:
ivo://CDS.VizieR/J/ApJ/760/147
Title:
^13^CO cores in the Taurus molecular cloud
Short Name:
J/ApJ/760/147
Date:
21 Oct 2021
Publisher:
CDS
Description:
Young stars form in molecular cores, which are dense condensations within molecular clouds. We have searched for molecular cores traced by ^13^CO J=1-->0 emission in the Taurus molecular cloud and studied their properties. Our data set has a spatial dynamic range (the ratio of linear map size to the pixel size) of about 1000 and spectrally resolved velocity information, which together allow a systematic examination of the distribution and dynamic state of ^13^CO cores in a large contiguous region. We use empirical fit to the CO and CO_2_ ice to correct for depletion of gas-phase CO. The ^13^CO core mass function (^13^CO CMF) can be fitted better with a log-normal function than with a power-law function. We also extract cores and calculate the ^13^CO CMF based on the integrated intensity of ^13^CO and the CMF from Two Micron All Sky Survey. We demonstrate that core blending exists, i.e., combined structures that are incoherent in velocity but continuous in column density. The core velocity dispersion (CVD), which is the variance of the core velocity difference {delta}v, exhibits a power-law behavior as a function of the apparent separation L: CVD(km/s){prop.to}L(pc)^0.7^. This is similar to Larson's law for the velocity dispersion of the gas. The peak velocities of ^13^CO cores do not deviate from the centroid velocities of the ambient ^12^CO gas by more than half of the line width. The low velocity dispersion among cores, the close similarity between CVD and Larson's law, and the small separation between core centroid velocities and the ambient gas all suggest that molecular cores condense out of the diffuse gas without additional energy from star formation or significant impact from converging flows.
93. 13CO (1-0) data molecular cloud catalogue
ID:
ivo://CDS.VizieR/J/A+A/654/A144
Title:
13CO (1-0) data molecular cloud catalogue
Short Name:
J/A+A/654/A144
Date:
22 Feb 2022
Publisher:
CDS
Description:
New-generation spectroscopic surveys of the Milky Way plane have been revealing the structure of the interstellar medium, allowing the simultaneous study of dense structures from single star-forming objects or systems to entire spiral arms. The good sensitivity of the new surveys and the development of dedicated algorithms now enable building extensive catalogues of molecular clouds and deriving good estimates of their physical properties. This allows studying the behaviour of these properties across the Galaxy. We present the catalogue of molecular clouds extracted from the ^13^CO (1-0) data cubes of the Forgotten Quadrant Survey, which mapped the Galactic plane in the range 220{deg}<l<240{deg}, and -2.5{deg}<b<0{deg} in ^12^CO (1-0) and ^13^CO (1-0). We compared the properties of the clouds of our catalogue with those of other catalogues. The catalogue contains 87 molecular clouds for which the main physical parameters such as area, mass, distance, velocity dispersion, and virial parameter were derived. These structures are overall less extended and less massive than the molecular clouds identified in the ^12^CO (1-0) data-set because they trace the brightest and densest part of the ^12^CO (1-0) clouds. Conversely, the distribution of aspect ratio, equivalent spherical radius, velocity dispersion, and virial parameter in the two catalogues are similar. The mean value of the mass surface density of molecular clouds is 87+/-55M_{sun}_/pc^2^ and is almost constant across the galactocentric radius, indicating that this parameter, which is a proxy of star formation, is mostly affected by local conditions. In data of the Forgotten Quadrant Survey, we find a good agreement between the total mass and velocity dispersion of the clouds derived from ^12^CO (1-0) and ^13^CO (1-0). This is likely because in the surveyed portion of the Galactic plane, the H_2_ column density is not particularly high, leading to a CO emission with a not very high optical depth. This mitigates the effects of the different line opacities between the two tracers on the derived physical parameters. This is a common feature in the outer Galaxy, but our result cannot be readily generalised to the entire Milky Way because regions with higher particle density could show a different behaviour.
94. CO emission towards Southern dark clouds
ID:
ivo://CDS.VizieR/J/other/PASA/17.92
Title:
CO emission towards Southern dark clouds
Short Name:
J/other/PASA/17.
Date:
21 Oct 2021
Publisher:
CDS
Description:
Using the 22-m 'Mopra' antenna (near Coonabarabran, NSW) of the Australia Telescope National Facility (ATNF), we have observed emission from the 115-GHz J=1-0 transition of CO towards the centre of each of the 1101 clouds listed in the Hartley et al. Catalogue of Southern Dark Clouds (SDC, Cat. <VII/191>). The velocity range covered was -96 to +70km/s, with a velocity resolution of 0.120km/s. CO was detected at 1049 of the positions, with 367 spectra showing emission at more than one radial velocity. Here we present the most comprehensive general survey of the SDC catalogue, with the intensity, velocity and half-width of the CO detection and a code describing the profile shape. The presence of blue- or red-shifted wings in many observations can provide a starting point in searches for star-forming regions.
95. CO-H2 and complex organic molecules in TMC-1C
ID:
ivo://CDS.VizieR/J/A+A/594/A117
Title:
CO-H2 and complex organic molecules in TMC-1C
Short Name:
J/A+A/594/A117
Date:
21 Oct 2021
Publisher:
CDS
Description:
Almost 200 different species have been detected in the interstellar medium (ISM) during the last decades, revealing not only simple species but complex molecules with more than 6 atoms. Other exotic compounds, like the weakly-bound dimer (H_2_)_2_, have also been detected in astronomical sources like Jupiter. We aim at detecting for the first time the CO-H_2_ van der Waals complex in the ISM, which if detected can be a sensitive indicator for low temperatures. We use the IRAM30m telescope, located in Pico Veleta (Spain), to search for the CO-H_2_ complex in a cold, dense core in TMC-1C (with a temperature of 10K). All the brightest CO-H_2_ transitions in the 3mm (80-110GHz) band have been observed with a spectral resolution of 0.5-0.7km/s, reaching a rms noise level of 2mK. The simultaneous observation of a broad frequency band, 16GHz, has allowed us to conduct a serendipitous spectral line survey. No lines belonging to the CO-H_2_ complex have been detected. We have set up a new, more stringent upper limit for its abundance to be [CO-H_2_]/[CO]=5x10^-6^, while we expect the abundance of the complex to be in the range 10^-8^-10^-3^. The spectral line survey has allowed us to detect 75 lines associated with 41 different species (including isotopologues). We detect a number of complex organic species, e.g. methyl cyanide (CH_3_CN), methanol (CH_3_OH), propyne (CH_3_CCH) and ketene (CH_2_CO), associated with cold gas (excitation temperatures about 7K), confirming the presence of these complex species not only in warm objects but also in cold regimes.
96. CO in extragalactic giant molecular clouds
ID:
ivo://CDS.VizieR/J/ApJ/686/948
Title:
CO in extragalactic giant molecular clouds
Short Name:
J/ApJ/686/948
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use high spatial resolution observations of CO to systematically measure the resolved size-line width, luminosity-line width, luminosity-size, and mass-luminosity relations of GMCs in a variety of extragalactic systems. Although the data are heterogeneous, we analyze them in a consistent manner to remove the biases introduced by limited sensitivity and resolution, thus obtaining reliable sizes, velocity dispersions, and luminosities. We compare the results obtained in dwarf galaxies with those from the Local Group spiral galaxies. We find that extragalactic GMC properties measured across a wide range of environments are very much compatible with those in the Galaxy. The property that shows the largest variability is their resolved brightness temperature, although even that is similar to the average Galactic value in most sources.
97. CO large-field observations around l=150{deg}
ID:
ivo://CDS.VizieR/J/ApJ/838/49
Title:
CO large-field observations around l=150{deg}
Short Name:
J/ApJ/838/49
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present large-field (4.25x3.75deg^2^) mapping observations toward the Galactic region centered at l=150{deg},b=3.5{deg} in the J=1-0 emission line of CO isotopologues (^12^CO, ^13^CO, and C^18^O), using the 13.7m millimeter-wavelength telescope of the Purple Mountain Observatory. Based on the ^13^CO observations, we reveal a filamentary cloud in the Local Arm at a velocity range of -0.5 to 6.5km/s. This molecular cloud contains 1 main filament and 11 sub-filaments, showing the so-called "ridge-nest" structure. The main filament and three sub-filaments are also detected in the C^18^O line. The velocity structures of most identified filaments display continuous distribution with slight velocity gradients. The measured median excitation temperature, line width, length, width, and linear mass of the filaments are ~9.28K, 0.85km/s, 7.30pc, 0.79pc, and 17.92M_{sun}_/pc, respectively, assuming a distance of 400pc. We find that the four filaments detected in the C^18^O line are thermally supercritical, and two of them are in the virialized state, and thus tend to be gravitationally bound. We identify in total 146 ^13^CO clumps in the cloud, about 77% of the clumps are distributed along the filaments. About 56% of the virialized clumps are found to be associated with the supercritical filaments. Three young stellar object candidates are also identified in the supercritical filaments, based on the complementary infrared data. These results indicate that the supercritical filaments, especially the virialized filaments, may contain star-forming activities.
98. Cold & molecular clumps and YSOs within G15.684-0.29
ID:
ivo://CDS.VizieR/J/ApJ/897/74
Title:
Cold & molecular clumps and YSOs within G15.684-0.29
Short Name:
J/ApJ/897/74
Date:
11 Mar 2022
Publisher:
CDS
Description:
The bubble G15.684-0.29 has a radius of 15.7pc. Its large size indicates that it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from the HI-GAL survey. All of them satisfy the criteria for forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from the 12CO(3-2) survey, all of which are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs, and 12 transition disks (TDs) around the bubble. For those young stellar objects (YSOs) located within the bubble boundary, 6 of 7 Class I YSOs lie in the shell, 15 of 22 Class II YSOs lie inside the bubble, and 3 of 5 TDs lie inside the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is ~4Myr, which is much greater than the shell fragmentation time, ~0.82-1.74Myr. We suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect and collapse model may work here. However, we cannot rule out the possibility that the radiation-driven implosion model may work on the formation of some YSOs. As we expected, the larger bubble has a much longer dynamical age, but we failed to find a clear age gradient for YSOs around the bubble.
99. Collisional excitation of sulfur dioxide
ID:
ivo://CDS.VizieR/J/A+A/531/A103
Title:
Collisional excitation of sulfur dioxide
Short Name:
J/A+A/531/A103
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present collisional rate coefficients for SO_2_ with ortho and para molecular hydrogen for the physical conditions prevailing in dark molecular clouds. Rate coefficients for the first 31 rotational levels of this species (energies up to 55K) and for temperatures between 5 and 30K are provided. We have found that these rate coefficients are about ten times more than those previously computed for SO_2_ with helium. We calculated the expected emission of the centimeter wavelength lines of SO_2_. We find that the transition connecting the metastable 2_02_ level with the 111 one is in absorption against the cosmic background for a wide range of densities. The 4_04_-3_13_ line is found to be inverted for densities below a few 10^4^cm^-3^. We observed the 1_11_-2_02_ transition with the 100m Green Bank Telescope towards some dark clouds. The line is observed, as expected, in absorption and provides an abundance of SO_2_ in these objects of a few 10^-10^. The potential use of millimeter lines of SO_2_ as tracers of the physical conditions of dark clouds is discussed.
100. Column density maps in 4 IRDCs
ID:
ivo://CDS.VizieR/J/A+A/578/A29
Title:
Column density maps in 4 IRDCs
Short Name:
J/A+A/578/A29
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of prominent, massive infrared dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using ^13^CO 1->0 and ^12^CO 3->2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds (GMCs) and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near and/or mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile of three of our clouds, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre- and protostellar cores for the highest column densities. A significant impact on the cloud properties from radiative feedback is unlikely because the clouds are mostly devoid of star formation. Independent from the PDF analysis, we find infall signatures in the spectral profiles of ^12^CO for G28.37+0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. Our results are in line with earlier interpretations that see massive IRDCs as the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N>10^23^cm^-2^ over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated) cloud regions, the PDF constructed from this kind of a clipped image does not represent the (turbulence dominated) low column density regime of the cloud.

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