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- ID:
- ivo://CDS.VizieR/J/ApJ/833/229
- Title:
- Star forming cloud-giant molecular cloud complexes
- Short Name:
- J/ApJ/833/229
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Star formation on galactic scales is known to be a slow process, but whether it is slow on smaller scales is uncertain. We cross-correlate 5469 giant molecular clouds (GMCs) from a new all-sky catalog with 256 star-forming complexes (SFCs) to build a sample of 191 SFC-GMC complexes-collections of multiple clouds each matched to 191 SFCs. The total mass in stars harbored by these clouds is inferred from WMAP free-free fluxes. We measure the GMC mass, the virial parameter, the star formation efficiency {epsilon} and the star formation rate per freefall time {epsilon}_ff_. Both {epsilon} and {epsilon}_ff_ range over 3-4 orders of magnitude. We find that 68.3% of the clouds fall within {sigma}_log{epsilon}_=0.79+/-0.22dex and {sigma}_log{epsilon}_ff__=0.91+/-0.22dex about the median. Compared to these observed scatters, a simple model with a time-independent {epsilon}_ff_ that depends on the host GMC properties predicts {sigma}_log{epsilon}_ff__=0.12-0.24. Allowing for a time-variable {epsilon}_ff_, we can recover the large dispersion in the rate of star formation. This strongly suggests that star formation in the Milky Way is a dynamic process on GMC scales. We also show that the surface star formation rate profile of the Milky Way correlates well with the molecular gas surface density profile.
- ID:
- ivo://CDS.VizieR/J/AJ/153/214
- Title:
- Star-forming potential in the Perseus complex
- Short Name:
- J/AJ/153/214
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our investigation of the star-forming potential in the Perseus star-forming complex. We build on previous starless core, protostellar core, and young stellar object (YSO) catalogs from Spitzer (3.6-70 {mu}m), Herschel (70-500 {mu}m), and SCUBA (850 {mu}m) observations in the literature. We place the cores and YSOs within seven star-forming clumps based on column densities greater than 5x10^21^/cm^2^. We calculate the mean density and free-fall time for 69 starless cores as ~5.55x10^-19^ g/cm^3^ and ~0.1 Myr, respectively, and we estimate the star formation rate for the near future as ~150 M_{sun}_/Myr. According to Bonnor-Ebert stability analysis, we find that majority of starless cores in Perseus are unstable. Broadly, these cores can collapse to form the next generation of stars. We found a relation between starless cores and YSOs, where the numbers of young protostars (Class 0 + Class I) are similar to the numbers of starless cores. This similarity, which shows a one-to-one relation, suggests that these starless cores may form the next generation of stars with approximately the same formation rate as the current generation, as identified by the Class 0 and Class I protostars. It follows that if such a relation between starless cores and any YSO stage exists, the SFR values of these two populations must be nearly constant. In brief, we propose that this one-to-one relation is an important factor in better understanding the star formation process within a cloud.
- ID:
- ivo://CDS.VizieR/J/A+A/579/A80
- Title:
- Star-forming regions deuteration
- Short Name:
- J/A+A/579/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical evolution in high-mass star-forming regions is still poorly constrained. Studying the evolution of deuterated molecules allows distinguishing between subsequent stages of high-mass star formation regions based on the strong temperature dependence of deuterium isotopic fractionation. We observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass protostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO^+^, and N_2_D^+^ as well as their non-deuterated counterparts. The overall detection fraction of DCN, DNC, and DCO^+^ is high and exceeds 50% for most of the stages. N_2_D^+^ was only detected in a few infrared dark clouds and high-mass protostellar objects. This may be related to problems in the bandpass at the transition frequency and to low abundances in the more evolved, warmer stages. We find median D/H ratios of 0.02 for DCN, 0.005 for DNC, 0.0025 for DCO^+^, and 0.02 for N_2_D^+^. While the D/H ratios of DNC, DCO^+^, and N_2_D^+^ decrease with time, DCN/HCN peaks at the hot molecular core stage. We only found weak correlations of the D/H ratios for N_2_D^+^ with the luminosity of the central source and the FWHM of the line, and no correlation with the H_2_ column density. In combination with a previously observed set of 14 other molecules (Paper I), we fitted the calculated column densities with an elaborate 1D physico-chemical model with time-dependent D-chemistry including ortho- and para-H_2_ states. Good overall fits to the observed data were obtained with the model. This is one of the first times that observations and modeling were combined to derive chemically based best-fit models for the evolution of high-mass star formation including deuteration.
- ID:
- ivo://CDS.VizieR/J/A+A/540/A113
- Title:
- Starless clumps in ATLASGAL
- Short Name:
- J/A+A/540/A113
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding massive star formation requires comprehensive knowledge about the initial conditions of this process. The cradles of massive stars are believed to be located in dense and massive molecular clumps. In this study, we present an unbiased sample of the earliest stages of massive star formation across 20deg^2^ of the sky. Within the region 10{deg}<l<20{deg} and |b|<1{deg}, we search the ATLASGAL survey at 870um for dense gas condensations. These clumps are carefully examined for indications of ongoing star formation using YSOs from the GLIMPSE source catalog as well as sources in the 24um MIPSGAL images, to search for starless clumps. We calculate the column densities as well as the kinematic distances and masses for sources where the v_lsr_ is known from spectroscopic observations. Within the given region, we identify 210 starless clumps with peak column densities >10^23^cm^-2^. In particular, we identify potential starless clumps on the other side of the Galaxy. The sizes of the clumps range between 0.1pc and 3pc with masses between a few tens of M_{sun}_ up to several ten thousands of M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A136
- Title:
- Starless core L1521E chemical structure
- Short Name:
- J/A+A/630/A136
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained ~2.5x2.5 arcminute maps toward L1521E using the IRAM-30m telescope in transitions of various species, including C^17^O, CH_3_OH c-C_3_H_2_, CN, SO, H_2_CS, and CH_3_CCH. We derived abundances for the observed species and compared them to those obtained toward L1544. We estimated CO depletion factors using the C^17^O IRAM-30m map, an N(H2) map derived from Herschel/ SPIRE data and a 1.2 mm dust continuum emission map obtained with the IRAM-30m telescope. Similarly to L1544, c-C_3_H_2_ and CH_3_OH peak at different positions. Most species peak toward the c-C_3_H_2_ peak: C_2_S, C_3_S, HCS^+^, HC_3_N, H_2_CS, CH_3_CCH, C^34^S. C^17^O and SO peak close to both the c-C_3_H_2_ and the CH_3_OH peaks. CN and N_2_H^+^ peak close to the Herschel dust peak. We found evidence of CO depletion toward L1521E. The lower limit of the CO depletion factor derived toward the Herschel dust peak is 4.3+/-1.6, which is about a factor of three lower than toward L1544. We derived abundances for several species toward the dust peaks of L1521E and L1544. The abundances of most sulfur-bearing molecules such as C_2_S, HCS^+^, C^34^S, C^33^S, and HCS^+^ are higher toward L1521E than toward L1544 by factors of ~2-20, compared to the abundance of A-CH_3_OH. The abundance of methanol is very similar toward the two cores.
- ID:
- ivo://CDS.VizieR/J/A+A/643/A60
- Title:
- Starless cores CH_3_OH and c-C_3_H_2_ maps
- Short Name:
- J/A+A/643/A60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The spatial distribution of molecules around starless cores is a powerful tool for studying the physics and chemistry governing the earliest stages of star formation. Our aim is to study the chemical differentiation in starless cores to determine the influence of large-scale effects on the spatial distribution of molecules within the cores. Furthermore, we want to put observational constraints on the mechanisms responsible in starless cores for the desorption of methanol from the surface of dust grains where it is efficiently produced. We mapped methanol, CH_3_OH, and cyclopropenylidene, c-C_3_H_2_, with the IRAM 30m telescope in the 3mm band towards six starless cores embedded in different environments, and in different evolutionary stages. Furthermore, we searched for correlations among physical properties of the cores and the methanol distribution. From our maps we can infer that the chemical segregation between CH_3_OH and c-C_3_H_2_ is driven by uneven illumination from the interstellar radiation field (ISRF). The side of the core that is more illuminated has more C atoms in the gas-phase and the formation of carbon-chain molecules like c-C3H2 is enhanced. Instead, on the side that is less exposed to the ISRF the C atoms are mostly locked in carbon monoxide, CO, the precursor of methanol. We conclude that large-scale effects have a direct impact on the chemical segregation that we can observe at core scale. However, the non-thermal mechanisms responsible for the desorption of methanol in starless cores do not show any dependency on the H_2_ column density at the methanol peak.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A119
- Title:
- Starless gas clump IRDC 18310-4 images
- Short Name:
- J/A+A/581/A119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the fragmentation and collapse properties of the dense gas during the onset of high-mass star formation. We observed the massive (800M_{sun}) starless gas clump IRDC 18310-4 with the Plateau de Bure Interferometer (PdBI) at subarcsecond resolution in the 1.07 mm continuum and N_2_H^+^(3-2) line emission.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A99
- Title:
- Starless MDCs of NGC6334 molecular spectra
- Short Name:
- J/A+A/622/A99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The formation of high-mass stars remains unknown in many aspects. Two families of models compete to explain the formation of high-mass stars. On the one hand, quasi-static models predict the existence of high-mass pre-stellar cores sustained by a high degree of turbulence. On the other hand competitive accretion models predict that high-mass proto-stellar cores evolve from low/intermediate mass proto-stellar cores in dynamic environments. The aim of the present work is to bring observational constraints at the scale of high-mass cores (~0.03pc). We targeted with ALMA and MOPRA a sample of 9 starless massive dense cores (MDCs) discovered in a recent Herschel/HOBYS study. Their mass and size (~110M_{sun}_ and r=0.1pc, respectively) are similar to the initial conditions used in the quasi-static family of models explaining for the formation of high-mass stars.We present ALMA 1.4mm continuum observations that resolve the Jeans length ({lambda}_Jeans_~0.03pc) and that are sensitive to the Jeans mass (M_Jeans_~0.65M_{sun}_) in the 9 starless MDCs, together with ALMA-^12^CO(2-1) emission line observations. We also present HCO^+^(1-0), H^13^CO+(1-0) and N_2_H^+^(1-0) molecular lines from the MOPRA telescope for 8 of the 9 MDCs. The 9 starless MDCs have the mass reservoir to form high-mass stars according to the criteria by Baldeschi et al. (2017MNRAS.466.3682B). Three of the starless MDCs are subvirialized with {alpha}_vir_~0.35, and 4 MDCs show sign of collapse from their molecular emission lines. ALMA observations show very little fragmentation within the MDCs. Only two of the starless MDCs host compact continuum sources, whose fluxes correspond to <3M_{sun}_ fragments. Therefore the mass reservoir of the MDCs has not yet been accreted onto compact objects, and most of the emission is filtered out by the interferometer. These observations do not support the quasi-static models for high-mass star formation since no high-mass pre-stellar core is found in NGC6334. The competitive accretion models, on the other hand, predict a level of fragmentation much higher than what we observe
- ID:
- ivo://CDS.VizieR/J/AJ/138/227
- Title:
- Stellar clusters in NGC 6334 complex
- Short Name:
- J/AJ/138/227
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, has not been well sampled in past studies. We analyze here a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95% of these are expected to be cluster members, most lower mass pre-main-sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20,000-30,000 pre-main-sequence stars.
