- ID:
- ivo://CDS.VizieR/J/A+A/633/A126
- Title:
- Cha-MMS1 CO 3-2 and ^13^CO 3-2 datacubes
- Short Name:
- J/A+A/633/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of its low luminosity, its chemical composition, and the absence of a large-scale outflow, the dense core Cha-MMS1 located in the Chamaeleon I molecular cloud was proposed as a first hydrostatic core (FHSC) candidate a decade ago. Our goal is to test this hypothesis by searching for a slow, compact outflow driven by Cha-MMS1 that would match the predictions of MHD simulations for this short phase of star formation. We use the Atacama Large Millimeter/submillimeter Array (ALMA) to map Cha-MMS1 at high angular resolution in CO 3-2 and ^13^CO 3-2 as well as in continuum emission. We report the detection of a bipolar outflow emanating from the central core, along a (projected) direction roughly parallel to the filament in which Cha-MMS1 is embedded and perpendicular to the large-scale magnetic field. The morphology of the outflow indicates that its axis lies close to the plane of the sky. We measure velocities corrected for inclination of more than 90km/s which is clearly incompatible with the expected properties of a FHSC outflow. Several properties of the outflow are determined and compared to previous studies of Class 0 and Class I protostars. The outflow of Cha-MMS1 has a much smaller momentum force than the outflows of other Class0 protostars. In addition, we find a dynamical age of 200-3000yr indicating that Cha-MMS1 might be one of the youngest ever observed Class 0 protostars. While the existence of the outflow suggests the presence of a disk, no disk is detected in continuum emission and we derive an upper limit of 55au to its radius. We conclude that Cha-MMS1 has already gone through the FHSC phase and is a young Class 0 protostar, but it has not brought its outflow to full power yet.
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- ID:
- ivo://CDS.VizieR/J/A+A/640/A65
- Title:
- CLASH brightest cluster galaxies CO spectra
- Short Name:
- J/A+A/640/A65
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Brightest cluster galaxies (BCGs) are excellent laboratories to study galaxy evolution in dense Mpc-scale environments. We have observed in CO(1->0), CO(2->1), CO(3->2), or CO(4->3), with the IRAM-30m, 18 BCGs at z~0.2-0.9 that are drawn from the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Our sample includes RX1532, which is our primary target, being among the BCGs with the highest star formation rate (SFR>~100M_{sun}_/yr) in the CLASH sample. We unambiguously detected both CO(1->0) and CO(3->2) in RX1532, yielding a large reservoir of molecular gas, M_H2_=(8.7+/-1.1)10^10^M_{sun}_, and a high level of excitation r31=0.75+/-0.12. A morphological analysis of the Hubble Space Telescope I-band image of RX1532 reveals the presence of clumpy substructures both within and outside the half-light radius re=(11.6+/-0.3)kpc, similarly to those found independently both in ultraviolet and in H in previous work. We tentatively detected CO(1->0) or CO(2->1) in four other BCGs, with molecular gas reservoirs in the range M_H2_=2x10^10-11^M_{sun}_. For the remaining 13 BCGs we set robust upper limits of M_H2_/M*<~0.1, which are among the lowest molecular gas to stellar mass ratios found for distant ellipticals and BCGs. By comparison with distant cluster galaxies observed in CO our study shows that RX1532 (M_H2_/M*=0.40+/-0.05) belongs to the rare population of star forming and gas-rich BCGs in the distant universe. By using available X-ray based estimates of the central intra-cluster medium entropy, we show that the detection of large reservoirs of molecular gas M_H2_>~10^10^M_{sun}_ in distant BCGs is possible when the two conditions are met: i) high SFR and ii) low central entropy, which favors the condensation and the inflow of gas onto the BCGs themselves, similarly to what has been previously found for some local BCGs.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/109
- Title:
- Cloud decomposition & SFR measurements
- Short Name:
- J/ApJ/841/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galactic star formation scaling relations show increased scatter from kpc to sub-kpc scales. Investigating this scatter may hold important clues to how the star formation process evolves in time and space. Here, we combine different molecular gas tracers, different star formation indicators probing distinct populations of massive stars, and knowledge of the evolutionary state of each star-forming region to derive the star formation properties of ~150 star-forming complexes over the face of the Large Magellanic Cloud (LMC). We find that the rate of massive star formation ramps up when stellar clusters emerge and boost the formation of subsequent generations of massive stars. In addition, we reveal that the star formation efficiency of individual giant molecular clouds (GMCs) declines with increasing cloud gas mass (M_cloud_). This trend persists in Galactic star-forming regions and implies higher molecular gas depletion times for larger GMCs. We compare the star formation efficiency per freefall time ({epsilon}_ff_) with predictions from various widely used analytical star formation models. While these models can produce large dispersions in {epsilon}_ff_ similar to those in observations, the origin of the model-predicted scatter is inconsistent with observations. Moreover, all models fail to reproduce the observed decline of {epsilon}_ff_ with increasing M_cloud_ in the LMC and the Milky Way. We conclude that analytical star formation models idealizing global turbulence levels and cloud densities and assuming a stationary star formation rate (SFR) are inconsistent with observations from modern data sets tracing massive star formation on individual cloud scales. Instead, we reiterate the importance of local stellar feedback in shaping the properties of GMCs and setting their massive SFR.
- ID:
- ivo://CDS.VizieR/J/ApJ/860/172
- Title:
- Cloud-scale molecular gas properties in 15 galaxies
- Short Name:
- J/ApJ/860/172
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We measure the velocity dispersion, {sigma}, and surface density, {Sigma}, of the molecular gas in nearby galaxies from CO spectral line cubes with spatial resolution 45-120pc, matched to the size of individual giant molecular clouds. Combining 11 galaxies from the PHANGS-ALMA survey with four targets from the literature, we characterize ~30000 independent sightlines where CO is detected at good significance. {Sigma} and {sigma} show a strong positive correlation, with the best-fit power-law slope close to the expected value for resolved, self-gravitating clouds. This indicates only a weak variation in the virial parameter {alpha}_vir_{propto}{sigma}^2^/{Sigma}, which is ~1.5-3.0 for most galaxies. We do, however, observe enormous variation in the internal turbulent pressure P_turb_{propto}{Sigma}{sigma}^2^, which spans ~5dex across our sample. We find {Sigma}, {sigma}, and P_turb_ to be systematically larger in more massive galaxies. The same quantities appear enhanced in the central kiloparsec of strongly barred galaxies relative to their disks. Based on sensitive maps of M31 and M33, the slope of the {sigma}-{Sigma} relation flattens at {Sigma}<~10M_{sun}_/pc^2^, leading to high {sigma} for a given {Sigma} and high apparent {alpha}_vir_. This echoes results found in the Milky Way and likely originates from a combination of lower beam-filling factors and a stronger influence of local environment on the dynamical state of molecular gas in the low-density regime.
- ID:
- ivo://CDS.VizieR/J/ApJ/703/736
- Title:
- Clump properties in the LMC 30 Dor region
- Short Name:
- J/ApJ/703/736
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a complete ^12^CO(J=1-0) map of the prominent molecular ridge in the Large Magellanic Cloud (LMC) obtained with the 22m ATNF Mopra Telescope. The region stretches southward by ~2{deg} (or 1.7kpc) from 30 Doradus, the most vigorous star-forming region in the Local Group. The location of this molecular ridge is unique insofar as it allows us to study the properties of molecular gas as a function of the ambient radiation field in a low-metallicity environment. The mass spectrum and the scaling relations between the properties of the CO clumps in the molecular ridge are similar, but not identical, to those that have been established for Galactic molecular clouds.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A12
- Title:
- Clustering the Orion B giant molecular cloud
- Short Name:
- J/A+A/610/A12
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/ chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional probability density function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. A clustering analysis based only on the J=1-0 lines of three isotopologues of CO proves sufficient to reveal distinct density/column density regimes (n_H_~100cm^-3^, ~500cm^-3^, and >1000cm^-3^), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J=1-0 line of HCO^+^ and the N=1-0 line of CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO^+^ and CN emission, which we relate to a photochemical enrichment effect. We also find a tail of high CN/HCO^+^ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (n_H_~710^3^cm^-3^, ~410^4^cm^-3^) for the densest regions are also identified, likely related to the higher critical density of the CN and HCO^+^ (1-0) lines. These distinctions are only possible because the high-density regions are spatially resolved. Molecules are versatile tracers of GMCs because their line intensities bear the signature of the physics and chemistry at play in the gas. The association of simultaneous multi-line, wide-field mapping and powerful machine learning methods such as the Meanshift clustering algorithm reveals how to decode the complex information available in these molecular tracers.
- ID:
- ivo://CDS.VizieR/J/A+A/421/1087
- Title:
- CO abundance of 3 globules
- Short Name:
- J/A+A/421/1087
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied the ratio of carbon monoxide column density to the extinction A_J_ of background field stars in the direction of three globules: B133, B335, L466. The N(CO) to A_J_ ratios were found to vary from cloud to cloud so that they are larger in B335 than in B133 and L466. These variations are thought to primarily arise from variations of the ratio N(CO)/N(H_2_).
- ID:
- ivo://CDS.VizieR/J/A+AS/99/291
- Title:
- CO and HCN observations of circumstellar envelopes
- Short Name:
- J/A+AS/99/291
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have searched the literature for all observations of the ^12^CO(1-0), ^12^CO(2-1), and HCN(1-0) lines in circumstellar envelopes of late type stars published between January 1985 and September 1992. We report data for 1361 observations (stellar velocity, expansion velocity, peak intensity, integrated area, noise level). This CO-HCN sample now contains 444 sources. 184 are identified as oxygen-rich, 205 as carbon-rich, and there are 9 S stars. About 85% of the sources are AGB stars. There are 32 planetary nebulae and about thirty post-AGB stars candidates. Besides results of millimeter observations, we also list identifications, coordinates, IRAS data, chemical and spectral types for every source. For AGB stars, we have estimated (or compiled) bolometric fluxes and distances for 349 sources, and mass loss rates deduced from CO results for 324 sources, taking into account the influence of the CO photodissociation radius. We also list mass loss rates derived from detailed models of CO emission which we could find in the literature.
- ID:
- ivo://CDS.VizieR/J/A+A/554/A55
- Title:
- C^18^O(1-0) and N_2_H^+^(1-0) in L1495/B213
- Short Name:
- J/A+A/554/A55
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Core condensation is a critical step in the star-formation process, but it is still poorly characterized observationally. We have studied the 10pc-long L1495/B213 complex in Taurus to investigate how dense cores have condensed out of the lower density cloud material. We observed L1495/B213 in C^18^O(1-0), N_2_H^+^(1-0), and SO(J_N_=3_2_-2_1_) with the 14m FCRAO telescope, and complemented the data with dust continuum observations using APEX (870um) and IRAM 30m (1200um).
- ID:
- ivo://CDS.VizieR/J/ApJS/236/49
- Title:
- CO and 850um obs. of Planck Galactic cold clumps
- Short Name:
- J/ApJS/236/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to understand the initial conditions and early evolution of star formation in a wide range of Galactic environments, we carried out an investigation of 64 Planck Galactic cold clumps (PGCCs) in the second quadrant of the Milky Way. Using the ^13^CO and C^18^O J=1-0 lines and 850{mu}m continuum observations, we investigated cloud fragmentation and evolution associated with star formation. We extracted 468 clumps and 117 cores from the ^13^CO line and 850{mu}m continuum maps, respectively. We made use of the Bayesian distance calculator and derived the distances of all 64 PGCCs. We found that in general, the mass-size plane follows a relation of m~r^1.67^. At a given scale, the masses of our objects are around 1/10 of that of typical Galactic massive star-forming regions. Analysis of the clump and core masses, virial parameters, densities, and mass-size relation suggests that the PGCCs in our sample have a low core formation efficiency (~3.0%), and most PGCCs are likely low-mass star-forming candidates. Statistical study indicates that the 850{mu}m cores are more turbulent, more optically thick, and denser than the ^13^CO clumps for star formation candidates, suggesting that the 850{mu}m cores are likely more appropriate future star formation candidates than the ^13^CO clumps.
