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Start Over Subject molecular clouds Content Level Research Validation Level 2
1. A catalogue of Spitzer dark clouds
ID:
ivo://CDS.VizieR/J/A+A/505/405
Title:
A catalogue of Spitzer dark clouds
Short Name:
J/A+A/505/405
Date:
21 Oct 2021
Publisher:
CDS
Description:
The majority of stars form in clusters. Therefore a comprehensive view of star formation requires understanding the initial conditions for cluster formation. The goal of our study is to shed light on the physical properties of infrared dark clouds (IRDCs) and the role they play in the formation of stellar clusters. This article, the first of a series dedicated to the study of IRDCs, describes techniques developed to establish a complete catalogue of Spitzer IRDCs in the Galaxy. We have analysed Spitzer GLIMPSE and MIPSGAL data to identify a complete sample of IRDCs in the region of Galactic longitude and latitude 10{deg}<|l|<65{deg} and |b|<1{deg}. From the 8um observations we have constructed opacity maps and used a newly developed extraction algorithm to identify structures above a column density of N_H2_=1x10^22^cm^-2^. The 24um data are then used to characterize the star formation activity of each extracted cloud. A total of 11303 clouds have been extracted. A comparison with the existing MSX based catalogue of IRDCs shows that 80% of these Spitzer dark clouds were previously unknown. The algorithm also extracts ~20000 to 50000 fragments within these clouds, depending on detection threshold used.A first look at the MIPSGAL data indicates that between 20% and 68% of these IRDCs show 24um point-like association. This new database provides an important resource for future studies aiming to understand the initial conditions of star formation in the Galaxy.
2. Accretion history of massive stars
ID:
ivo://CDS.VizieR/J/MNRAS/496/3482
Title:
Accretion history of massive stars
Short Name:
J/MNRAS/496/3482
Date:
21 Oct 2021
Publisher:
CDS
Description:
The mass growth of protostars is a central element to the determination of fundamental stellar population properties such as the initial mass function. Constraining the accretion history of individual protostars is therefore an important aspect of star formation research. The goal of the study presented here is to determine whether high-mass (proto)stars gain their mass from a compact (<0.1pc) fixed-mass reservoir of gas, often referred to as dense cores, in which they are embedded, or whether the mass growth of high-mass stars is governed by the dynamical evolution of the parsec-scale clump that typically surrounds them. To achieve this goal, we performed a 350micron continuum mapping of 11 infrared dark clouds, along side some of their neighbouring clumps, with the ArTeMiS camera on APEX. By identifying about 200 compact ArTeMiS sources, and matching them with Herschel Hi-GAL 70micron sources, we have been able to produce mass vs. temperature diagrams. We compare the nature (i.e. starless or protostellar) and location of the ArTeMiS sources in these diagrams with modelled evolutionary tracks of both core-fed and clump-fed accretion scenarios. We argue that the latter provide a better agreement with the observed distribution of high-mass star-forming cores. However, a robust and definitive conclusion on the question of the accretion history of high-mass stars requires larger number statistics.
3. A Chandra X-ray observation of L1251B
ID:
ivo://CDS.VizieR/J/ApJ/694/425
Title:
A Chandra X-ray observation of L1251B
Short Name:
J/ApJ/694/425
Date:
21 Oct 2021
Publisher:
CDS
Description:
I report the results of a 60ks X-ray observation of the L1251 dark cloud in Cepheus, which was acquired with the ACIS-I camera on board the Chandra X-Ray Observatory. Forty-three compact X-ray sources were detected. The field of view was centered on the position of IRAS 22376+7455, an embedded Class 0/I protostar that is closely associated with the bright CO emission core, L1251B-Core E. A very intense impulsive X-ray flare was observed from a location within the formal error ellipse of the IRAS source and in close proximity (within <~1") to a thermal continuum radio source, VLA 3. Given their small spatial offsets, the radio, far-infrared, and X-ray objects appear to be identical and consequently the likely origin and driving source of high-velocity gas flows that are observed in L1251B.
4. ALMA CO observations of 30 Dor
ID:
ivo://CDS.VizieR/J/ApJ/774/73
Title:
ALMA CO observations of 30 Dor
Short Name:
J/ApJ/774/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Atacama Large (sub)Millimeter Array observations of 30 Doradus - the highest resolution view of molecular gas in an extragalactic star formation region to date (~0.4pcx0.6pc). The 30Dor-10 cloud north of R136 was mapped in ^12^CO 2-1, ^13^CO 2-1, C^18^O 2-1, 1.3mm continuum, the H30{alpha} recombination line, and two H_2_CO 3-2 transitions. Most ^12^CO emission is associated with small filaments and clumps (<~1pc, ~10^3^M_{sun}_ at the current resolution). Some clumps are associated with protostars, including "pillars of creation" photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to a higher surface density at a given size and linewidth compared to clouds studied at 10 pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the Large Magellanic Cloud mean, but the dust abundance may be reduced by ~2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend toward lower dense clump filling fraction deeper in the cloud.
5. ALMA cube and GMC catalog of J1023+1952
ID:
ivo://CDS.VizieR/J/A+A/645/A97
Title:
ALMA cube and GMC catalog of J1023+1952
Short Name:
J/A+A/645/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
Tidal dwarf galaxies (TDGs) are gravitationally bound condensations of gas and stars that formed during galaxy interactions. Here we present multi-configuration ALMA observations of J1023+1952, a TDG in the interacting system Arp 94, where we resolved CO(2-1) emission down to giant molecular clouds (GMCs) at 0.64" ~45pc resolution. We find a remarkably high fraction of extended molecular emission (~80-90%), which is filtered out by the interferometer and likely traces diffuse gas. We detect 111 GMCs that give a similar mass spectrum as those in the Milky Way and other nearby galaxies (a truncated power law with a slope of -1.76+/-0.13). We also study Larson's laws over the available dynamic range of GMC properties (~2dex in mass and ~1dex in size): GMCs follow the size-mass relation of the Milky Way, but their velocity dispersion is higher such that the size-linewidth and virial relations appear super-linear, deviating from the canonical values. The global molecular-to-atomic gas ratio is very high (~1) while the CO(2-1)/CO(1-0) ratio is quite low (~0.5), and both quantities vary from north to south. Star formation predominantly takes place in the south of the TDG, where we observe projected offsets between GMCs and young stellar clusters ranging from ~50pc to ~200pc; the largest offsets correspond to the oldest knots, as seen in other galaxies. In the quiescent north, we find more molecular clouds and a higher molecular-to-atomic gas ratio (~1.5); atomic and diffuse molecular gas also have a higher velocity dispersion there. Overall, the organisation of the molecular interstellar medium in this TDG is quite different from other types of galaxies on large scales, but the properties of GMCs seem fairly similar, pointing to near universality of the star-formation process on small scales.
6. ALMA 106GHz continuum observations in Chamaeleon I
ID:
ivo://CDS.VizieR/J/ApJ/823/160
Title:
ALMA 106GHz continuum observations in Chamaeleon I
Short Name:
J/ApJ/823/160
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an Atacama Large Millimeter/submillimeter Array (ALMA) 106 GHz (Band 3) continuum survey of the complete population of dense cores in the Chamaeleon I molecular cloud. We detect a total of 24 continuum sources in 19 different target fields. All previously known Class 0 and Class I protostars in Chamaeleon I are detected, whereas all of the 56 starless cores in our sample are undetected. We show that the Spitzer+Herschel census of protostars in Chamaeleon I is complete, with the rate at which protostellar cores have been misclassified as starless cores calculated as <1/56, or <2%. We use synthetic observations to show that starless cores collapsing following the turbulent fragmentation scenario are detectable by our ALMA observations when their central densities exceed ~10^8^/cm^3^, with the exact density dependent on the viewing geometry. Bonnor-Ebert spheres, on the other hand, remain undetected to central densities at least as high as 10^10^/cm^3^. Our starless core non-detections are used to infer that either the star-formation rate is declining in Chamaeleon I and most of the starless cores are not collapsing, matching the findings of previous studies, or that the evolution of starless cores are more accurately described by models that develop less substructure than predicted by the turbulent fragmentation scenario, such as Bonnor-Ebert spheres. We outline future work necessary to distinguish between these two possibilities.
7. ALMA images of the CND and SgrA*
ID:
ivo://CDS.VizieR/J/A+A/618/A35
Title:
ALMA images of the CND and SgrA*
Short Name:
J/A+A/618/A35
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present 1"-resolution ALMA observations of the circumnuclear disk (CND) and the environment around SgrA*. The images unveil the presence of small spatial scale CO (J=3-2) molecular "cloudlets" within the central pc of the Milky Way, moving at high speeds, up to 300km/s along the line-of-sight. The CO-emitting structures show intricate morphologies: extended and filamentary at high negative-velocities (v_LSR_<-150km/s), more localized and clumpy at extreme positive-velocities (v_LSR_>+200km/s). Based on the pencil-beam CO absorption spectrum toward SgrA* synchrotron emission, we also present evidence for a diffuse gas component producing absorption features at more extreme negative-velocities (v_LSR_<-200km/s). The CND shows a clumpy spatial distribution. Its motion requires a bundle of non-uniformly rotating streams of slightly different inclinations. The inferred gas density peaks are lower than the local Roche limit. This supports that CND molecular cores are transient. We apply the two standard orbit models, spirals vs. ellipses, invoked to explain the kinematics of the ionized gas streamers around SgrA*. The location and velocities of the CO cloudlets are inconsistent with the spiral model, and only two of them are consistent with the Keplerian ellipse model. Most cloudlets, however, show similar velocities that are incompatible with the motions of the ionized streamers or with gas bounded to the central gravity. We speculate that they are leftovers of more massive, tidally disrupted, clouds that fall into the cavity, or that they originate from instabilities in the inner rim of the CND and infall from there. Molecular cloudlets, all together with a mass of several 10M_{sun}_, exist around SgrA*. Most of them must be short-lived: photoevaporated by the intense stellar radiation field, blown away by winds from massive stars, or disrupted by strong gravitational shears.
8. ALMA massive protocluster gas clumps maps
ID:
ivo://CDS.VizieR/J/A+A/615/A94
Title:
ALMA massive protocluster gas clumps maps
Short Name:
J/A+A/615/A94
Date:
21 Oct 2021
Publisher:
CDS
Description:
Fragmentation of massive dense molecular clouds is the starting point in the formation of rich clusters and massive stars. Theory and numerical simulations indicate that the population of the fragments (number, mass, diameter, separation) resulting from the gravitational collapse of such clumps is probably regulated by the balance between the magnetic field and the other competitors of self-gravity, in particular turbulence and protostellar feedback. We have observed 11 massive, dense and young star-forming clumps with the Atacama Large Millimeter Array (ALMA) in the thermal dust continuum emission at 1mm with an angular resolution of 0.25 arcseconds with the aim of determining their population of fragments.
9. ALMA obs. of giant molecular clouds in Hen 2-10
ID:
ivo://CDS.VizieR/J/ApJ/876/141
Title:
ALMA obs. of giant molecular clouds in Hen 2-10
Short Name:
J/ApJ/876/141
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new ^12^CO (J=1-0) observations of He 2-10, a blue compact dwarf galaxy about 8.7Mpc away, taken with the Atacama Large Millimeter Array. These are the highest spatial and spectral resolution observations, to date, of the molecular gas in this starburst galaxy. We measure a molecular mass of (1.2+/-0.4)x10^8^M_{sun}_ in He 2-10, and 75% of the molecular gas mass is contained within the northern region of the galaxy near the previously identified young super star clusters, which has a projected size of about 300pc. We use the CPROPS algorithm to identify 119 resolved giant molecular clouds distributed throughout the galaxy, and the molecular gas contained within these clouds makes up between 45% and 70% of the total molecular mass. The molecular clouds in He 2-10 have similar median sizes (~26pc), luminous masses (~4x10^5^M_{sun}_), and surface densities (~180M_{sun}_/pc^2^) to Milky Way clouds. However, He 2-10 clouds have velocity dispersions (~3km/s) about 50% higher than those in the Milky Way. We provide evidence that He 2-10 clouds tend to be in virial equilibrium, with the virial and luminous masses scaling according to M_vir_{propto}M_lum_^1.2+/-0.1^, similar to clouds in the Milky Way. However, we measure a scaling relationship between luminous mass and size, M_lum_{propto}R^3.0+/-0.3^, that is steeper than what is observed in Milky Way clouds. Assuming that He 2-10 molecular clouds are virialized, we infer values of the CO-to-H_2_ conversion factor ranging from 0.5 to 13 times the standard value in the solar neighborhood. Given star formation efficiencies as low as 5%, the most massive molecular clouds in He 2-10 currently have enough mass to form the next generation of super star clusters in the galaxy.
10. ALMA obs. of massive clouds in the CMZ
ID:
ivo://CDS.VizieR/J/ApJ/894/L14
Title:
ALMA obs. of massive clouds in the CMZ
Short Name:
J/ApJ/894/L14
Date:
19 Jan 2022 13:10:58
Publisher:
CDS
Description:
We report Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 continuum observations of 2000au resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy. To study gas fragmentation, we use the dendrogram method to identify cores as traced by the dust continuum emission. The four clouds exhibit different fragmentation states at the observed resolution despite having similar masses at the cloud scale (~1-5pc). Assuming a constant dust temperature of 20K, we construct core mass functions of the clouds and find a slightly top-heavy shape as compared to the canonical initial mass function, but we note several significant uncertainties that may affect this result. The characteristic spatial separation between the cores as identified by the minimum spanning tree method, ~10^4^au, and the characteristic core mass, 1-7M_{sun}_, are consistent with predictions of thermal Jeans fragmentation. The three clouds showing fragmentation may be forming OB associations (stellar mass ~10^3^M_{sun}_). None of the four clouds under investigation seem to be currently able to form massive star clusters like the Arches and the Quintuplet (>~10^4^M_{sun}_), but they may form such clusters by further gas accretion onto the cores.

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