- ID:
- ivo://CDS.VizieR/J/other/ApSS/361.191
- Title:
- High-mass star forming clumps from MALT90
- Short Name:
- J/other/ApSS/361
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A total of 197 relatively isolated high-mass star-forming clumps were selected from the Millimeter Astronomy Legacy Team 90GHz (MALT90) survey data and their global chemical evolution investigated using four molecular lines, N_2_H^+^(1-0), HCO^+^(1-0), HCN(1-0), and HNC(1-0). The results suggest that the global averaged integrated intensity ratios I(HCO^+^)/I(HNC), I(HCN)/I(HNC), I(N_2_H^+^)/I(HCO^+^), and I(N_2_H^+^)/ I(HCN) are promising tracers for evolution of high-mass star-forming clumps. The global averaged column densities and abundances of N_2_H^+^, HCO^+^, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCN)/X(HNC) could be used to trace evolution of high-mass star forming clumps, X(HCO^+^)/X(HNC) is more suitable for distinguishing high-mass star-forming clumps in prestellar (stage A) from those in protostellar (stage B) and HII/PDR region (stage C). These results suggest that the global averaged integrated intensity ratios between HCN(1-0), HNC(1-0), HCO^+^(1-0) and N_2_H^+^(1-0) are more suitable for tracing the evolution of high-mass star forming clumps. We also studied the chemical properties of the target high-mass star-forming clumps in each spiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-forming clumps in Sagittarius arm and Norma-Outer arm, comparing two groups located on one arm with different Galactocentric distances, the clumps near the Galactic Center appear to be younger than those far from the Galactic center, which may be due to more dense gas concentrated near the Galactic Center, and hence more massive stars being formed there.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/642/A87
- Title:
- Hub-filament candidates
- Short Name:
- J/A+A/642/A87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarves and massive O-type (50-100M_{sun}_) stars. To identify candidate hub-filament systems (HFS) in the Milky-Way and examine their role in the formation of the highest mass stars and star clusters. Filaments around ~35000 HiGAL clumps that are detected using the DisPerSE algorithm. Hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. ~3700~(11%) are candidate HFS of which, ~2150~(60%) are pre-stellar, ~1400~(40%) are proto-stellar. All clumps with L>10^4^L_{sun}_ and L>10^5^L_{sun}_ at distances respectively within 2kpc and 5kpc are located in the hubs of HFS. The column-densities of hubs are found to be enhanced by a factor of ~2 (pre-stellar sources) up to ~10 (proto-stellar sources). All high-mass stars preferentially form in the density enhanced hubs of HFS. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a 'filaments to clusters' unified paradigm for star formation, with the following salient features: a) low-intermediate mass stars form in the filaments slowly (10^6^yr) and massive stars quickly (10^5^yr) in the hub, b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, c) Feedback dissipation and mass segregation arise naturally due to HFS properties, and c) explain age spreads within bound clusters and formation of isolated OB associations.
- ID:
- ivo://CDS.VizieR/J/AJ/161/206
- Title:
- Infrared imaging of new born cluster H72.97-69.39
- Short Name:
- J/AJ/161/206
- Date:
- 20 Jan 2022
- Publisher:
- CDS
- Description:
- Young massive clusters and super star clusters (SSCs) represent an extreme mode of star formation. Far-infrared imaging of the Magellanic Clouds has identified one potential embedded SSC, HSO-BMHERICC-J72.971176-69.391112 (H72.97-69.39 in short), in the southwest outskirts of the Large Magellanic Cloud. We present Gemini Flamingos 2 and GSAOI near-infrared imaging of a 3'x3' region around H72.97-69.39 in order to characterize the stellar content of the cluster. The stellar content is probed down to 1.5M{sun}. We find substantial dust extinction across the cluster region, extending up to A_K_ of 3. Deeply embedded stars are associated with ALMA-detected molecular gas suggesting that star formation is ongoing. The high spatial resolution of the GSAOI data allows identification of the central massive object associated with the ^13^CO ALMA observations and detection of fainter low-mass stars around the H30{alpha} ALMA source. The morphology of the molecular gas and the nebulosity from adjacent star formation suggest they have interacted covering a region of several parsecs. The total stellar content in the cluster is estimated from the intermediate and high-mass stellar content to be at least 10000M{sun}, less than R136 with up to 100000M{sun} within 4.7pc radius, but places it in the regime of an SSC. Based on the extinction determination of individual stars we estimate a molecular gas mass in the vicinity of H72.97-69.39 of 6600M{sun}, suggesting more star formation can be expected.
- ID:
- ivo://CDS.VizieR/J/ApJ/869/72
- Title:
- IN-SYNC. VIII. YSOs in NGC 1333, IC 348 and Orion A
- Short Name:
- J/ApJ/869/72
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we address two issues related to primordial disk evolution in three clusters (NGC1333, IC348, and OrionA) observed by the INfrared Spectra of Young Nebulous Clusters (IN-SYNC) project. First, in each cluster, averaged over the spread of age, we investigate how disk lifetime is dependent on stellar mass. The general relation in IC348 and OrionA is that primordial disks around intermediate-mass stars (2-5M_{sun}_) evolve faster than those around loss-mass stars (0.1-1M_{sun}_), which is consistent with previous results. However, considering only low-mass stars, we do not find a significant dependence of disk frequency on stellar mass. These results can help to better constrain theories on gas giant planet formation timescales. Second, in the OrionA molecular cloud, in the mass range of 0.35-0.7M_{sun}_, we provide the most robust evidence to date for disk evolution within a single cluster exhibiting modest age spread. By using surface gravity as an age indicator and employing 4.5{mu}m excess as a primordial disk diagnostic, we observe a trend of decreasing disk frequency for older stars. The detection of intra-cluster disk evolution in NGC1333 and IC348 is tentative, since the slight decrease of disk frequency for older stars is a less than 1{sigma} effect.
- ID:
- ivo://CDS.VizieR/J/AJ/160/37
- Title:
- Intergalac. medium opacity from Lyman-break galaxies
- Short Name:
- J/AJ/160/37
- Date:
- 08 Dec 2021
- Publisher:
- CDS
- Description:
- We measure the effective opacity ({tau}_eff_) of the intergalactic medium from the composite spectra of 281 Lyman-break galaxies in the redshift range 2<~z<~3. Our spectra are taken from the COSMOS Ly{alpha} Mapping And Tomographic Observations survey derived from the Low Resolution Imaging Spectrometer on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Ly{alpha} forest, we measure the effective Ly{alpha} opacity ({tau}_eff_) in the 2.02<~z<~2.44 range. At z=2.22, we estimate {tau}_eff_=0.159{+/-}0.001 from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at z<2.5 indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian processes model of our results and previous {tau}_eff_ measurements that describes the steep redshift evolution in {tau}_eff_ from z=1.5-4.
- ID:
- ivo://CDS.VizieR/J/ApJ/849/139
- Title:
- Interstellar acetone (CH_3_COCH_3_) in 3 regions
- Short Name:
- J/ApJ/849/139
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of interstellar acetone (CH_3_COCH_3_) detected in broadband line surveys in the 1.3mm band from the Caltech Submillimeter Observatory (CSO). The observations were conducted toward three massive star-forming regions: GAL31.41+0.31, GAL034.3+00.2, and GAL10.47+00.03. Numerous acetone lines were detected in these three sources. The results were analyzed using the assumption of local thermodynamic equilibrium. These results rigorously confirm the previous reports of acetone detections in GAL31.41+0.31 and GAL10.47+00.03, and add a new acetone detection in GAL034.3+00.2. Source-averaged column densities for acetone were determined to be 1.1(6)x10^16^cm^-2^ for GAL31.41+0.31, 6.4(3)x10^16^cm^-2^ for GAL10.47+00.03, and 1.3(3)x10^15^cm^-2^ for GAL034.3+00.2. The rotational temperatures of acetone in these three sources range from 49 to 132K, which suggests a complicated formation mechanism for interstellar acetone.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/53
- Title:
- IR dark clouds parameters in molecular clouds
- Short Name:
- J/ApJ/897/53
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- Ever since their discovery, infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbor HM young stellar objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to readdress the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated with a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The cataloged positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319M{odot}/pc^2^, mean mass of 1062M{odot}, and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to HM young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often-used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty-five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100M{odot}.
- ID:
- ivo://CDS.VizieR/J/AJ/155/99
- Title:
- IR variability among YSOs in the Serpens South cluster
- Short Name:
- J/AJ/155/99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a time-variability study of young stellar objects (YSOs) in the Serpens South cluster performed at 3.6 and 4.5 {mu}m with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability project. We have collected light curves for more than 1500 sources, including 85 cluster members, over 38 days. This includes 44 class I sources, 19 sources with flat spectral energy distributions (SEDs), 17 class II sources, and five diskless YSO candidates. We find a high variability fraction among embedded cluster members of ~70%, whereas young stars without a detectable disk display no variability. We detect periodic variability for 32 sources with periods primarily in the range of 0.2-14 days and a subset of fast rotators thought to be field binaries. The timescale for brightness changes are shortest for stars with the most photospheric SEDs and longest for those with flat or rising SEDs. While most variable YSOs become redder when fainter, as would be expected from variable extinction, about 10% get bluer as they get fainter. One source, SSTYSV J183006.13-020108.0, exhibits "cyclical" color changes.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A113
- Title:
- ISOSS22478 and ISOSS23053 images
- Short Name:
- J/A+A/649/A113
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research. We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation. Employing the NOrthern Extended Millimeter Array (NOEMA) and the IRAM 30m telescope, we observe two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3mm continuum and spectral line emission at high angular resolution (~0.8''). Resolving altogether 29 cores that are largely located along filament-like structures, we find that these cores follow a mass-size relation of approximately M~r^3^, corresponding to a constant mean density of roughly 10^6cm^-3^. The correlation of the core masses with their nearest neighbor separations is consistent with thermal Jeans fragmentation. Although the kinematics of the two regions appear very different at first sight -- multiple velocity components along filaments in ISOSS22478 versus a steep velocity gradient of more than 50km/s/pc in ISOSS23053 -- the findings can all be explained in the framework of a dynamical cloud collapse scenario. While our data are consistent with a dynamical cloud collapse scenario and subsequent thermal Jeans fragmentation, the importance of additional environmental properties -- e.g., the magnetization of the gas or external shocks triggering converging gas flows -- is still less well constrained and requires future investigation.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A48
- Title:
- Linking ice and gas. Serpens SVS4
- Short Name:
- J/A+A/643/A48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The interaction between dust, ice, and gas during the formation of stars produces complex organic molecules. While observations indicate that several species are formed on ice-covered dust grains and are released into the gas phase, the exact chemical interplay between solid and gas phases and their relative importance remain unclear. Our goal is to study the interplay between dust, ice, and gas in regions of low-mass star formation through ice- and gas- mapping and by directly measuring gas-to-ice ratios. This provides constraints on the routes that lead to the chemical complexity that is observed in solid and gas phases. We present observations of gas-phase methanol (CH_3_OH) and carbon monoxide (^13^CO and C^18^O) at 1.3mm towards ten low-mass young protostars in the Serpens SVS4 cluster from the SubMillimeter Array (SMA) and the Atacama Pathfinder EXperiment (APEX) telescope. We used archival data from the Very Large Telescope (VLT) to derive abundances of ice H_2_O, CO, and CH_3_OH towards the same region. Finally, we constructed gas-ice maps of SVS4 and directly measured CO and CH_3_OH gas-to-ice ratios. The SVS4 cluster is characterised by a global temperature of 15+/-5K. At this temperature, the chemical behaviours of CH_3_OH and CO are anti-correlated: larger variations are observed for CH_3_OH gas than for CH_3_OH ice, whereas the opposite is seen for CO. The gas-to-ice ratios (N_gas_/N_ice_) range from 1-6 for CO and 1.4x10^-4^-3.7x10^-3^for CH_3_OH. The CO gas-maps trace an extended gaseous component that is not sensitive to the effect of freeze-out. Because of temperature variations and dust heating around 20K, the frozen CO is efficiently desorbed. The CH_3_OH gas-maps, in contrast, probe regions where methanol is predominantly formed and present in ices and is released into the gas phase through non-thermal desorption mechanisms. Combining gas- and ice-mapping techniques, we measure gas-to-ice ratios of CO and CH_3_OH in the SVS4 cluster. The CH_3_OH gas-to-ice ratio agrees with values that were previously reported for embedded Class 0/I low-mass protostars. We find that there is no straightforward correlation between CO and CH_3_OH gas with their ice counterparts in the cluster. This is likely related to the complex morphology of SVS4: the Class 0 protostar SMM4 and its envelope lie in the vicinity, and the outflow associated with SMM4 intersects the cluster. This study serves as a pathfinder for future observations with ALMA and the James Webb Space Telescope (JWST) that will provide high-sensitivity gas-ice maps of molecules more complex than methanol. Such comparative maps will be essential to constrain the chemical routes that regulate the chemical complexity in star-forming regions.
