Browsing by Subject "stars: formation"

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  • Liu, Tie; Li, Pak Shing; Juvela, Mika; Kim, Kee-Tae; Evans, Neal J.; Di Francesco, James; Liu, Sheng-Yuan; Yuan, Jinghua; Tatematsu, Ken'ichi; Zhang, Qizhou; Ward-Thompson, Derek; Fuller, Gary; Goldsmith, Paul F.; Koch, P. M.; Sanhueza, Patricio; Ristorcelli, I.; Kang, Sung-ju; Chen, Huei-Ru; Hirano, N.; Wu, Yuefang; Sokolov, Vlas; Lee, Chang Won; White, Glenn J.; Wang, Ke; Eden, David; Li, Di; Thompson, Mark; Pattle, Kate M.; Soam, Archana; Nasedkin, Evert; Kim, Jongsoo; Kim, Gwanjeong; Lai, Shih-Ping; Park, Geumsook; Qiu, Keping; Zhang, Chuan-Peng; Alina, Dana; Eswaraiah, Chakali; Falgarone, Edith; Fich, Michel; Greaves, Jane; Gu, Q. -L.; Kwon, Woojin; Li, Hua-bai; Malinen, Johanna; Montier, Ludovic; Parsons, Harriet; Qin, Sheng-Li; Rawlings, Mark G.; Tang, Y. -W. (2018)
    Magnetic field plays a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained owing to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 mu m with SCUBA-2/POL-2 at JCMT for the first time. The magnetic field tends to be perpendicular to the densest part of the main filament (F-M), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of similar to 50 mu G for F-M is obtained using the Davis-Chandrasekhar-Fermi method. Based on (CO)-C-13 (1-0) line observations, we suggest a formation scenario of F-M due to large-scale (similar to 10 pc) cloud-cloud collision. Using additional NH3 line data, we estimate that F-M will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F-M, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F-M are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F-M may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive (similar to 200 M-circle dot, collapsing starless clump candidate, "c8," in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.
  • Tatematsu, Ken'ichi; Liu, Tie; Ohashi, Satoshi; Sanhueza, Patricio; Quang Nguyen Luong; Hirota, Tomoya; Liu, Sheng-Yuan; Hirano, Naomi; Choi, Minho; Kang, Miju; Thompson, Mark A.; Fuller, Gary; Wu, Yuefang; Li, Di; Di Francesco, James; Kim, Kee-Tae; Wang, Ke; Ristorcelli, Isabelle; Juvela, Mika; Shinnaga, Hiroko; Cunningham, Maria; Saito, Masao; Lee, Jeong-Eun; Toth, L. Viktor; He, Jinhua; Sakai, Takeshi; Kim, Jungha; JCMT Large Program SCOPE Collabora; TRAO Key Science Program TOP Colla (2017)
    We observed 13 Planck cold clumps with the James Clerk Maxwell Telescope/SCUBA-2 and with the Nobeyama 45 m radio telescope. The N2H+ distribution obtained with the Nobeyama telescope is quite similar to SCUBA-2 dust distribution. The 82 GHz HC3N, 82 GHz CCS, and 94 GHz CCS emission are often distributed differently with respect to the N2H+ emission. The CCS emission, which is known to be abundant in starless molecular cloud cores, is often very clumpy in the observed targets. We made deep single-pointing observations in DNC, (HNC)-C-13, N2D+, and cyclic-C3H2 toward nine clumps. The detection rate of N2D+ is 50%. Furthermore, we observed the NH3 emission toward 15 Planck cold clumps to estimate the kinetic temperature, and confirmed that most targets are cold (less than or similar to 20 K). In two of the starless clumps we observed, the CCS emission is distributed as it surrounds the N2H+ core (chemically evolved gas), which resembles the case of L1544, a prestellar core showing collapse. In addition, we detected both DNC and N2D+. These two clumps are most likely on the verge of star formation. We introduce the chemical evolution factor (CEF) for starless cores to describe the chemical evolutionary stage, and analyze the observed Planck cold clumps.
  • Liu, Tie; Evans, Neal J.; Kim, Kee-Tae; Goldsmith, Paul F.; Liu, Sheng-Yuan; Zhang, Qizhou; Tatematsu, Ken'ichi; Wang, Ke; Juvela, Mika; Bronfman, Leonardo; Cunningham, Maria R.; Garay, Guido; Hirota, Tomoya; Lee, Jeong-Eun; Kang, Sung-Ju; Li, Di; Li, Pak-Shing; Mardones, Diego; Qin, Sheng-Li; Ristorcelli, Isabelle; Tej, Anandmayee; Toth, L. Viktor; Wu, Jing-Wen; Wu, Yue-Fang; Yi, Hee-weon; Yun, Hyeong-Sik; Liu, Hong-Li; Peng, Ya-Ping; Li, Juan; Li, Shang-Huo; Lee, Chang Won; Shen, Zhi-Qiang; Baug, Tapas; Wang, Jun-Zhi; Zhang, Yong; Issac, Namitha; Zhu, Feng-Yao; Luo, Qiu-Yi; Soam, Archana; Liu, Xun-Chuan; Xu, Feng-Wei; Wang, Yu; Zhang, Chao; Ren, Zhiyuan; Zhang, Chao (2020)
    The ATOMS, standing for ALMA Three-millimeter Observations of Massive Star-forming regions, survey has observed 146 active star-forming regions with ALMA band 3, aiming to systematically investigate the spatial distribution of various dense gas tracers in a large sample of Galactic massive clumps, to study the roles of stellar feedback in star formation, and to characterize filamentary structures inside massive clumps. In this work, the observations, data analysis, and example science of the ATOMS survey are presented, using a case study for the G9.62+0.19 complex. Toward this source, some transitions, commonly assumed to trace dense gas, including CS J = 2-1, HCO+ J = 1-0, and HCN J = 1-0, are found to show extended gas emission in low-density regions within the clump; less than 25 per cent of their emission is from dense cores. SO, CH3OH, (HCN)-C-13, and HC3N show similar morphologies in their spatial distributions and reveal well the dense cores. Widespread narrow SiO emission is present (over similar to 1 pc), which may be caused by slow shocks from large-scale colliding flows or HII regions. Stellar feedback from an expanding HII region has greatly reshaped the natal clump, significantly changed the spatial distribution of gas, and may also account for the sequential high-mass star formation in the G9.62+0.19 complex. The ATOMS survey data can be jointly analysed with other survey data, e.g. MALT90, Orion B, EMPIRE, ALMA IMF, and ALMAGAL, to deepen our understandings of 'dense gas' star formation scaling relations and massive protocluster formation.
  • Liu, Tie; Evans, Neal J.; Kim, Kee-Tae; Goldsmith, Paul F.; Liu, Sheng-Yuan; Zhang, Qizhou; Tatematsu, Ken'ichi; Wang, Ke; Juvela, Mika; Bronfman, Leonardo; Cunningham, Maria R.; Garay, Guido; Hirota, Tomoya; Lee, Jeong-Eun; Kang, Sung-Ju; Li, Di; Li, Pak-Shing; Mardones, Diego; Qin, Sheng-Li; Ristorcelli, Isabelle; Tej, Anandmayee; Toth, L. Viktor; Wu, Jing-Wen; Wu, Yue-Fang; Yi, Hee-weon; Yun, Hyeong-Sik; Liu, Hong-Li; Peng, Ya-Ping; Li, Juan; Li, Shang Huo; Lee, Chang Won; Shen, Zhi-Qiang; Baug, Tapas; Wang, Jun-Zhi; Zhang, Yong; Issac, Namitha; Zhu, Feng-Yao; Luo, Qiu-Yi; Liu, Xun-Chuan; Xu, Feng-Wei; Wang, Yu; Zhang, Chao; Ren, Zhiyuan; Zhang, Chao (2020)
    We report studies of the relationships between the total bolometric luminosity (L-bol or L-TIR) and the molecular line luminosities of J = 1 - 0 transitions of (HCN)-C-13, (HCO+)-C-13, HCN, and HCO+ with data obtained from ACA observations in the 'ATOMS' survey of 146 active Galactic star-forming regions. The correlations between L-bol and molecular line luminosities L-mol' of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in L-bol-L-mol' relations as their main line emission. The log(L-bol/L-mol') for different molecular line tracers have similar distributions. The L-bol-to-L-mol' ratios do not change with galactocentric distances (R-GC) and clump masses (M-clump). The molecular line luminosity ratios (HCN-to-HCO+, (HCN)-C-13-to-(HCO+)-C-13, HCN-to-(HCN)-C-13, and HCO+-to-(HCO+)-C-13) all appear constant against L-bol, dust temperature (T-d), M-clump, and R-GC. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the 'ATOMS' survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.
  • Liu, Hong-Li; Tej, Anandmayee; Liu, Tie; Goldsmith, Paul F.; Stutz, Amelia; Juvela, Mika; Qin, Sheng-Li; Xu, Feng-Wei; Bronfman, Leonardo; Evans, Neal J.; Saha, Anindya; Issac, Namitha; Tatematsu, Ken'ichi; Wang, Ke; Li, Shanghuo; Zhang, Siju; Baug, Tapas; Dewangan, Lokesh; Wu, Yue-Fang; Zhang, Yong; Lee, Chang Won; Liu, Xun-Chuan; Zhou, Jianwen; Soam, Archana (2022)
    We present a comprehensive study of the gas kinematics associated with density structures at different spatial scales in the filamentary infrared dark cloud, G034.43+00.24 (G34). This study makes use of the (HCO+)-C-13 (1-0) molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey, which has spatial and velocity resolution of similar to 0.04 pc and 0.2 km s(-1), respectively. Several tens of dendrogram structures have been extracted in the position-position-velocity space of (HCO+)-C-13, which include 21 small-scale leaves and 20 larger-scale branches. Overall, their gas motions are supersonic but they exhibit the interesting behaviour where leaves tend to be less dynamically supersonic than the branches. For the larger scale, branch structures, the observed velocity-size relation (i.e. velocity variation/dispersion versus size) are seen to follow the Larson scaling exponent while the smaller-scale, leaf structures show a systematic deviation and display a steeper slope. We argue that the origin of the observed kinematics of the branch structures is likely to be a combination of turbulence and gravity-driven ordered gas flows. In comparison, gravity-driven chaotic gas motion is likely at the level of small-scale leaf structures. The results presented in our previous paper and this current follow-up study suggest that the main driving mechanism for mass accretion/inflow observed in G34 varies at different spatial scales. We therefore conclude that a scale-dependent combined effect of turbulence and gravity is essential to explain the star-formation processes in G34.
  • Liu, Rong; Liu, Tie; Chen, Gang; Liu, Hong-Li; Wang, Ke; Li, Jin-Zeng; Lee, Chang Won; Liu, Xunchuan; Juvela, Mika; Garay, Guido; Dewangan, Lokesh; Soam, Archana; Bronfman, Leonardo; He, Jinhua; Eswaraiah, Chakali; Zhang, Si-Ju; Zhang, Yong; Xu, Feng-Wei; Toth, L. Viktor; Shen, Zhi-Qiang; Li, Shanghuo; Wu, Yue-Fang; Qin, Sheng-Li; Ren, Zhiyuan; Zhang, Guoyin; Tej, Anandmayee; Goldsmith, Paul F.; Baug, Tapas; Luo, Qiuyi; Zhou, Jianwen; Zhang, Chang (2022)
    To understand the nature of SiO emission, we conducted ACA observations of the SiO (2-1) lines toward 146 massive star-forming regions, as part of the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey. We detected SiO emission in 128 (87.7 per cent) sources and identified 171 SiO clumps, 105 of which are spatially separated from 3 mm continuum emission. A large amount of the SiO line profiles (60 per cent) are non-Gaussian. The velocity dispersion of the SiO lines ranges from 0.3 to 5.43 km s(-1). In 63 sources the SiO clumps are associated with H II regions characterized by H40 alpha emission. We find that 68 per cent (116) of the SiO clumps are associated with strong outflows. The median velocity dispersion of the SiO line for outflow sources and non-outflow sources is 1.91 km s(-1) and 0.99 km s(-1), respectively. These results indicate that outflow activities could be connected to strongly shocked gas. The velocity dispersion and [SiO]/[(HCO+)-C-13] intensity ratio do not show any correlation with the dust temperature and particle number density of clumps. We find a positive correlation between the SiO line luminosity and the bolometric luminosity, implying stronger shock activities are associated with more luminous protoclusters. The SiO clumps in associations with HII regions were found to show a steeper feature in Lsio/Lbol. The SiO line luminosity and the fraction of shocked gas have no apparent evidence of correlation with the evolutionary stages traced by luminosity to mass ratio (L-bol/M).
  • Qin, Sheng-Li; Liu, Tie; Liu, Xunchuan; Goldsmith, Paul F.; Li, Di; Zhang, Qizhou; Liu, Hong-Li; Wu, Yuefang; Bronfman, Leonardo; Juvela, Mika; Lee, Chang Won; Garay, Guido; Zhang, Yong; He, Jinhua; Hsu, Shih-Ying; Shen, Zhi-Qiang; Lee, Jeong-Eun; Wang, Ke; Tang, Ningyu; Tang, Mengyao; Zhang, Chao; Yue, Yinghua; Xue, Qiaowei; Li, Shanghuo; Peng, Yaping; Dutta, Somnath; Ge, Jixing; Xu, Fengwei; Chen, Long-Fei; Baug, Tapas; Dewangan, Lokesh; Tej, Anandmayee (2022)
    Hot cores characterized by rich lines of complex organic molecules are considered as ideal sites for investigating the physical and chemical environments of massive star formation. We present a search for hot cores by using typical nitrogen- and oxygen-bearing complex organic molecules (C2H5CN, CH3OCHO, and CH3OH), based on ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS). The angular resolutions and line sensitivities of the ALMA observations are better than 2 arcsec and 10 mJy beam(-1), respectively. A total of 60 hot cores are identified with 45 being newly detected, in which the complex organic molecules have high gas temperatures (> 100 K) and hot cores have small source sizes (< 0.1 pc). So far, this is the largest sample of hot cores observed with similar angular resolution and spectral coverage. The observations have also shown nitrogen and oxygen differentiation in both line emission and gas distribution in 29 hot cores. Column densities of CH3OH and CH3OCHO increase as rotation temperatures rise. The column density of CH3OCHO correlates tightly with that of CH3OH. The pathways for production of different species are discussed. Based on the spatial position difference between hot cores and ultracompact H ii (UC H ii) regions, we conclude that 24 hot cores are externally heated, while the other hot cores are internally heated. The observations presented here will potentially help establish a hot core template for studying massive star formation and astrochemistry.
  • Peng, Yaping; Liu, Tie; Qin, Sheng-Li; Baug, Tapas; Liu, Hong-Li; Wang, Ke; Garay, Guido; Zhang, Chao; Chen, Long-Fei; Lee, Chang Won; Juvela, Mika; Li, Dalei; Tatematsu, Ken'ichi; Liu, Xun-Chuan; Lee, Jeong-Eun; Luo, Gan; Dewangan, Lokesh; Wu, Yue-Fang; Zhang, Li; Bronfman, Leonardo; Ge, Jixing; Tang, Mengyao; Zhang, Yong; Xu, Feng-Wei; Wang, Yao; Zhou, Bing (2022)
    Investigating the physical and chemical structure of massive star-forming regions is critical for understanding the formation and early evolution of massive stars. We performed a detailed line survey toward six dense cores, named MM1, MM4, MM6, MM7, MM8, and MM11, in the G9.62+0.19 star-forming region resolved in Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species, including organic oxygen-, nitrogen-, and sulphur-bearing molecules and their isotopologues. Four dense cores, MM7, MM8, MM4, and MM11, are line-rich sources. Modelling of these spectral lines reveals that the rotational temperature lies in the range 72-115, 100-163, 102-204, and 84-123 K for MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 x 10(15) -9.2 x 10(17) cm(-2) toward the four cores. The cores MM8 and MM4 show a chemical difference between oxygenand nitrogen-bearing species, i.e. MM4 is rich in oxygen-bearing molecules, while nitrogen-bearing molecules, especially vibrationally excited HC3N lines, are mainly observed in MM8. The distinct initial temperatures at the accretion phase may lead to this N/O differentiation. Through analysing column densities and spatial distributions of O-bearing complex organic molecules (COMB), we found that C2H5OH and CH3OCH3 might have a common precursor, CH3OH. CH3OCHO and CH3OCH3 are likely chemically linked. In addition, the observed variation in HC3N and HC5N emission may indicate their different formation mechanisms in hot and cold regions.
  • Liu, Hong-Li; Tej, Anandmayee; Liu, Tie; Issac, Namitha; Saha, Anindya; Goldsmith, Paul F.; Wang, Jun-Zhi; Zhang, Qizhou; Qin, Sheng-Li; Wang, Ke; Li, Shanghuo; Soam, Archana; Dewangan, Lokesh; Lee, Chang Won; Li, Pak-Shing; Liu, Xun-Chuan; Zhang, Yong; Ren, Zhiyuan; Juvela, Mika; Bronfman, Leonardo; Wu, Yue-Fang; Tatematsu, Ken'ichi; Chen, Xi; Li, Di; Stutz, Amelia; Zhang, Siju; Tóth, L. Viktor; Luo, Qiu-Yi; Xu, Feng-Wei; Li, Jinzeng; Liu, Rong; Zhou, Jianwen; Zhang, Chao; Tang, Mengyao; Zhang, Chao; Baug, Tapas; Mannfors, Emma Elisa; Chakali, Eswaraiah; Dutta, Somnath (2022)
    We present new 3-mm continuum and molecular lines observations from the ATOMS survey towards the massive protostellar clump, MM1, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observed are the tracers of either dense gas (e.g. HCO+/(HCO+)-C-13 J= 1-0) or outflows (e.g. CS J = 2-1). The most complete picture to date of seven cores in MM1 is revealed by dust continuum emission. These cores are found to be gravitationally bound, with virial parameter, alpha(vir) < 2. At least four outflows are identified in MM1 with a total outflowing mass of similar to 45 M-circle dot, and a total energy of 1 x 10(47) erg, typical of outflows from a B0-type star. Evidence of hierarchical fragmentation, where turbulence dominates over thermal pressure, is observed at both the cloud and the clump scales. This could be linked to the scale-dependent, dynamical mass inflow/accretion on clump and core scales. We therefore suggest that the G34 cloud could be undergoing a dynamical mass inflow/accretion process linked to the multiscale fragmentation, which leads to the sequential formation of fragments of the initial cloud, clumps, and ultimately dense cores, the sites of star formation.
  • Mannfors, E.; Juvela, M.; Bronfman, L.; Eden, D. J.; He, J.; Kim, G.; Kim, K-T; Kirppu, H.; Liu, T.; Montillaud, J.; Parsons, H.; Sanhueza, P.; Shang, H.; Soam, A.; Tatematsu, K.; Traficante, A.; Vaisala, M. S.; Lee, C. W. (2021)
    Context. Although the basic processes of star formation (SF) are known, more research is needed on SF across multiple scales and environments. The Planck all-sky survey provided a large catalog of Galactic cold clouds and clumps that have been the target of several follow-up surveys. Aims. We aim to characterize a diverse selection of dense, potentially star-forming cores, clumps, and clouds within the Milky Way in terms of their dust emission and SF activity. Methods. We studied 53 fields that have been observed in the JCMT SCUBA-2 continuum survey SCOPE and have been mapped with Herschel. We estimated dust properties by fitting Herschel observations with modified blackbody functions, studied the relationship between dust temperature and dust opacity spectral index beta, and estimated column densities. We extracted clumps from the SCUBA-2 850 mu m maps with the FellWalker algorithm and examined their masses and sizes. Clumps are associated with young stellar objects found in several catalogs. We estimated the gravitational stability of the clumps with virial analysis. The clumps are categorized as unbound starless, prestellar, or protostellar. Results. We find 529 dense clumps, typically with high column densities from (0.3-4.8) x 10(22) cm(-2), with a mean of (1.5 +/- 0.04) x10(22) cm(-2), low temperatures (T similar to 10-20 K), and estimated submillimeter beta = 1.7 +/- 0.1. We detect a slight increase in opacity spectral index toward millimeter wavelengths. Masses of the sources range from 0.04 M-circle dot to 4259 M-circle dot. Mass, linear size, and temperature are correlated with distance. Furthermore, the estimated gravitational stability is dependent on distance, and more distant clumps appear more virially bound. Finally, we present a catalog of properties of the clumps. Conclusions. Our sources present a large array of SF regions, from high-latitude, nearby diffuse clouds to large SF complexes near the Galactic center. Analysis of these regions will continue with the addition of molecular line data, which will allow us to study the densest regions of the clumps in more detail.
  • Harju, Jorma; Sipilä, Olli; Brunken, Sandra; Schlemmer, Stephan; Caselli, Paola; Juvela, Mika; Menten, Karl M.; Stutzki, Juergen; Asvany, Oskar; Kaminski, Tomasz; Okada, Yoko; Higgins, Ronan (2017)
    We report on the detection of the ground-state rotational line of ortho-D2H+ at 1.477 THz (203 mu m) using the German REceiver for Astronomy at Terahertz frequencies (GREAT) on. board the Stratospheric Observatory For Infrared Astronomy (SOFIA). The line is seen in absorption against. far-infrared continuum from the protostellar binary IRAS 16293-2422 in Ophiuchus. The para-D2H+ line at 691.7 GHz was not detected with the APEX telescope toward this position. These D2H+ observations complement our previous detections of para-H2D+ and ortho-H2D+ using SOFIA and APEX. By modeling chemistry and radiative transfer in the dense core surrounding the protostars, we find that the ortho-D2H+ and para-H2D+ absorption features mainly originate in the cool (T <18 K) outer envelope of the core. In contrast, the ortho-H2D+ emission from the core is significantly absorbed by the ambient molecular cloud. Analyses of the combined D2H+ and H2D+ data result in an age estimate of similar to 5. x. 10(5) yr for the core, with an uncertainty of similar to 2. x. 10(5) yr. The core material has probably been pre-processed for another 5. x. 10(5) years in conditions corresponding to those in the ambient molecular cloud. The inferred timescale is more than 10 times the age of the embedded protobinary. The D2H+ and H2D+ ions have large and nearly equal total (ortho+ para) fractional abundances of similar to 10(-9) in the outer envelope. This confirms the central role of H-3 + in the deuterium chemistry in cool, dense gas, and adds support to the prediction of chemistry models that also D-3(+) should be abundant in these conditions.
  • Juvela, Mika; Neha, Sharma; Mannfors, Emma; Saajasto, Mika; Ysard, Nathalie; Pelkonen, Veli-Matti (2020)
    Context. LDN 1642 is a rare example of a star-forming, high-latitude molecular cloud. The dust emission of LDN 1642 has already been studied extensively in the past, but its location also makes it a good target for studies of light scattering.Aims. We wish to study the near-infrared (NIR) light scattering in LDN 1642, its correlation with the cloud structure, and the ability of dust models to simultaneously explain observations of sub-millimetre dust emission, NIR extinction, and NIR scattering.Methods. We used observations made with the HAWK-I instrument to measure the NIR surface brightness and extinction in LDN 1642. These data were compared with Herschel observations of dust emission and, with the help of radiative transfer modelling, with the predictions calculated for different dust models.Results. We find, for LDN 1642, an optical depth ratio tau (250 mu m)/tau (J) approximate to 10(-3), confirming earlier findings of enhanced sub-millimetre emissivity. The relationships between the column density derived from dust emission and the NIR colour excesses are linear and consistent with the shape of the standard NIR extinction curve. The extinction peaks at A(J) = 2.6 mag, and the NIR surface brightness remains correlated with N(H-2) without saturation. Radiative transfer models are able to fit the sub-millimetre data with any of the tested dust models. However, these predict an NIR extinction that is higher and an NIR surface brightness that is lower than based on NIR observations. If the dust sub-millimetre emissivity is rescaled to the observed value of tau (250 mu m)/tau (J), dust models with high NIR albedo can reach the observed level of NIR surface brightness. The NIR extinction of the models tends to be higher than in the direct extinction measurements, which is also reflected in the shape of the NIR surface brightness spectra.Conclusions. The combination of emission, extinction, and scattering measurements provides strong constraints on dust models. The observations of LDN 1642 indicate clear dust evolution, including a strong increase in the sub-millimetre emissivity, which has not been fully explained by the current dust models yet.
  • Chacon-Tanarro, A.; Pineda, J. E.; Caselli, P.; Bizzocchi, L.; Gutermuth, R. A.; Mason, B. S.; Gomez-Ruiz, A.; Harju, J.; Devlin, M.; Dicker, S. R.; Mroczkowski, T.; Romero, C. E.; Sievers, J.; Stanchfield, S.; Offner, S.; Sanchez-Argueelles, D. (2019)
    Context. The study of dust emission at millimeter wavelengths is important to shed light on the dust properties and physical structure of pre-stellar cores, the initial conditions in the process of star and planet formation. Aims. Using two new continuum facilities, AzTEC at the Large Millimeter Telescope Alfonso Serrano and MUSTANG-2 at the Green Bank Observatory, we aim to detect changes in the optical properties of dust grains as a function of radius for the well-known pre-stellar core L1544. Methods. We determined the emission profiles at 1.1 and 3.3 mm and examine whether they can be reproduced in terms of the current best physical models for L1544. We also made use of various tools to determine the radial distributions of the density, temperature, and dust opacity in a self-consistent manner. Results. We find that our observations cannot be reproduced without invoking opacity variations. New temperature and density profiles, as well as opacity variations across the core, have been derived with the new data. The opacity changes are consistent with the expected variations between uncoagulated bare grains, toward the outer regions of the core, and grains with thick ice mantles, toward the core center. A simple analytical grain growth model predicts the presence of grains of similar to 3-4 mu m within the central 2000 au for the new density profile.
  • Juvela, Mika; Guillet, Vincent; Liu, Tie; Ristorcelli, Isabelle; Pelkonen, Veli-Matti; Alina, Dana; Bronfman, Leonardo; Eden, David J.; Kim, Kee Tae; Koch, Patrick M.; Kwon, Woojin; Lee, Chang Won; Malinen, Johanna; Micelotta, Elisabetta; Montillaud, Julien; Rawlings, Mark G.; Sanhueza, Patricio; Soam, Archana; Traficante, Alessio; Ysard, Nathalie; Zhang, Chuan-Peng (2018)
    Context. The sub-millimetre polarisation of dust emission from star-forming clouds carries information on grain properties and on the effects that magnetic fields have on cloud evolution. Aims. Using observations of a dense filamentary cloud G035.39-00.33, we aim to characterise the dust emission properties and the variations of the polarisation fraction. Methods. JCMT SCUBA-2/POL-2 observations at 850 mu m were combined with Planck 850 mu m (353 GHz) data to map polarisation fraction at small and large scales. With previous total intensity SCUBA-2 observations (450 and 850 mu m) and Herschel data, the column densities were determined via modified black-body fits and via radiative transfer modelling. Models were constructed to examine how the observed polarisation angles and fractions depend on potential magnetic field geometries and grain alignment processes. Results. POL-2 data show clear changes in the magnetic field orientation. These are not in contradiction with the uniform orientation and almost constant polarisation fraction seen by Planck, because of the difference in the beam sizes and the POL-2 data being affected by spatial filtering. The filament has a peak column density of N(H-2) similar to 7 x 10(22) cm(-2), a minimum dust temperature of T similar to 12 K, and a mass of similar to 4300 M-circle dot for the area N(H-2) > 5 x 10(21) cm(-2). The estimated average value of the dust opacity spectral index is beta similar to 1.9. The ratio of sub-millimetre and J-band optical depths is tau (250 mu m)/tau(J) similar to 2.5 x 10(-3), more than four times the typical values for diffuse medium. The polarisation fraction decreases as a function of column density to p similar to 1% in the central filament. Because of noise, the observed decrease of p(N) is significant only at N(H-2) > 2 x 10(22) cm(-2). The observations suggest that the grain alignment is not constant. Although the data can be explained with a complete loss of alignment at densities above similar to 10(4) cm(-3) or using the predictions of radiative torques alignment, the uncertainty of the field geometry and the spatial filtering of the SCUBA-2 data prevent strong conclusions. Conclusions. The G035.39-00.33 filament shows strong signs of dust evolution and the low polarisation fraction is suggestive of a loss of polarised emission from its densest parts.
  • Juvela, M.; Malinen, J.; Montillaud, J.; Pelkonen, V.-M.; Ristorcelli, I.; Tóth, L. V. (2018)
    Context. The Galactic Cold Cores (GCC) project has made Herschel photometric observations of interstellar clouds where Planck detected compact sources of cold dust emission. The fields are in different environments and stages of star formation. Aims. Our aim is to characterise the structure of the clumps and their parent clouds, and to study the connections between the environment and the formation of gravitationally bound objects. We also examine the accuracy to which the structure of dense clumps can be determined from sub-millimetre data. Methods. We use standard statistical methods to characterise the GCC fields. Individual clumps are extracted using column density thresholding. Based on sub-millimetre measurements, we construct a three-dimensional radiative transfer (RT) model for each field. These are used to estimate the relative radiation field intensities, to probe the clump stability, and to examine the uncertainty of column density estimates. We examine the structural parameters of the clumps, including their radial column density profiles. Results. In the GCC fields, the structure noise follows the relations previously established at larger scales and in lower-density clouds. The fractal dimension has no significant dependence on column density and the values D-p = 1.25 +/- 0.07 are only slightly lower than in typical molecular clouds. The column density probability density functions (PDFs) exhibit large variations, for example, in the case of externally compressed clouds. At scales r > 0.1 pc, the radial column density distributions of the clouds follow an average relation of N similar to r(-1). In spite of a great variety of clump morphologies (and a typical aspect ratio of 1.5), clumps tend to follow a similar N similar to r(-1) relation below r similar to 0.1 pc. RT calculations indicate only factor 2.5 variation in the local radiation field intensity. The fraction of gravitationally bound clumps increases significantly in regions with A v > 5 mag but most bound objects appear to be pressure-confined. Conclusions. The host clouds of the cold clumps in the GCC sample have statistical properties similar to general molecular clouds. The gravitational stability, peak column density, and clump orientation are connected to the cloud background while most other statistical clump properties (e.g. D-p and radial profiles) are insensitive to the environment. The study of clump morphology should be continued with a comparison with numerical simulations.
  • Rivera-Ingraham, A.; Ristorcelli, I.; Juvela, M.; Montillaud, J.; Men'shchikov, A.; Malinen, J.; Pelkonen, V. -M.; Marston, A.; Martin, P. G.; Pagani, L.; Paladini, R.; Paradis, D.; Ysard, N.; Ward-Thompson, D.; Bernard, J. -P.; Marshall, D. J.; Montier, L.; Toth, L. V. (2017)
    Context. The onset of star formation is intimately linked with the presence of massive unstable filamentary structures. These filaments are therefore key for theoretical models that aim to reproduce the observed characteristics of the star formation process in the Galaxy. Aims. As part of the filament study carried out by the Herschel Galactic Cold Cores Key Programme, here we study and discuss the filament properties presented in GCC VII (Paper I) in context with theoretical models of filament formation and evolution. Methods. A conservatively selected sample of filaments located at a distance D <500 pc was extracted from the GCC fields with the getfilaments algorithm. The physical structure of the filaments was quantified according to two main components: the central (Gaussian) region of the filament (core component), and the power-law-like region dominating the filament column density profile at larger radii (wing component). The properties and behaviour of these components relative to the total linear mass density of the filament and the column density of its environment were compared with the predictions from theoretical models describing the evolution of filaments under gravity-dominated conditions. Results. The feasibility of a transition from a subcritical to supercritical state by accretion at any given time is dependent on the combined effect of filament intrinsic properties and environmental conditions. Reasonably self-gravitating (high M-line,M-core) filaments in dense environments (Av greater than or similar to 3 mag) can become supercritical on timescales of t similar to 1 Myr by accreting mass at constant or decreasing width. The trend of increasing M-line,M-tot (M-line,M-core and M-line,M-wing) and ridge A(v) with background for the filament population also indicates that the precursors of star-forming filaments evolve coevally with their environment. The simultaneous increase of environment and filament Av explains the observed association between dense environments and high Mlille,co values, and it argues against filaments remaining in constant single-pressure equilibrium states. The simultaneous growth of filament and background in locations with efficient mass assembly, predicted in numerical models of filaments in collapsing clouds, presents a suitable scenario for the fulfillment of the combined filament mass-environment criterium that is in quantitative agreement with Herschel observations.
  • Navarro-Almaida, D.; Le Gal, R.; Fuente, A.; Riviere-Marichalar, P.; Wakelam; Cazaux, S.; Caselli, P.; Laas, J. C.; Alonso-Albi, T.; Loison, J. C.; Gerin, M.; Kramer, C.; Roueff, E.; Bachillerl, R.; Commercon, B.; Friesen, R.; Garcia-Burillo, S.; Goicoechea, J. R.; Giuliano, B. M.; Jimenez-Serram; Kirk, J. M.; Lattanzi, M.; Malinen, J.; Marcelino, N.; Martin-Domenech, R.; Caro, G. M. Munoz; Pineda, J.; Tercero, B.; Trevino-Morales, S. P.; Roncero, O.; Hacar, A.; Tafalla, M.; Ward-Thompson, D. (2020)
    Context. Sulphur is one of the most abundant elements in the Universe. Surprisingly, sulphuretted molecules are not as abundant as expected in the interstellar medium and the identity of the main sulphur reservoir is still an open question.Aims. Our goal is to investigate the H2S chemistry in dark clouds, as this stable molecule is a potential sulphur reservoir.Methods. Using millimeter observations of CS, SO, H2S, and their isotopologues, we determine the physical conditions and H2S abundances along the cores TMC 1-C, TMC 1-CP, and Barnard 1b. The gas-grain model NAUTILUS is used to model the sulphur chemistry and explore the impact of photo-desorption and chemical desorption on the H2S abundance.Results. Our modeling shows that chemical desorption is the main source of gas-phase H2S in dark cores. The measured H2S abundance can only be fitted if we assume that the chemical desorption rate decreases by more than a factor of 10 when n(H) > 2 x 10(4). This change in the desorption rate is consistent with the formation of thick H2O and CO ice mantles on grain surfaces. The observed SO and H2S abundances are in good agreement with our predictions adopting an undepleted value of the sulphur abundance. However, the CS abundance is overestimated by a factor of 5-10. Along the three cores, atomic S is predicted to be the main sulphur reservoir.Conclusions. The gaseous H2S abundance is well reproduced, assuming undepleted sulphur abundance and chemical desorption as the main source of H2S. The behavior of the observed H2S abundance suggests a changing desorption efficiency, which would probe the snowline in these cold cores. Our model, however, highly overestimates the observed gas-phase CS abundance. Given the uncertainty in the sulphur chemistry, we can only conclude that our data are consistent with a cosmic elemental S abundance with an uncertainty of a factor of 10.
  • Fuente, A.; Navarro, D. G.; Caselli, P.; Gerin, M.; Kramer, C.; Roueff, E.; Alonso-Albi, T.; Bachiller, R.; Cazaux, S.; Commercon, B.; Friesen, R.; Garcia-Burillo, S.; Giuliano, B. M.; Goicoechea, J. R.; Gratier, P.; Hacar, A.; Jimenez-Serra, Izaskun; Kirk, J.; Lattanzi, Fernando Alfredo; Loison, J. C.; Malinen, J.; Marcelino, N.; Martin-Domenech, R.; Munoz-Caro, G.; Pineda, J.; Tafalla, M.; Tercero, B.; Ward-Thompson, D.; Trevino-Morales, S. P.; Riviere-Marichalar, P.; Roncero, O.; Vidal, T.; Ballester, M. Y. (2019)
    GEMS is an IRAM 30 m Large Program whose aim is determining the elemental depletions and the ionization fraction in a set of prototypical star-forming regions. This paper presents the first results from the prototypical dark cloud Taurus molecular cloud (TMC) 1. Extensive millimeter observations have been carried out with the IRAM 30 m telescope (3 and 2mm) and the 40 m Yebes telescope (1.3 cm and 7 mm) to determine the fractional abundances of CO, HCO+, HCN, CS, SO, HCS+, and N2H+ in three cuts which intersect the dense filament at the well-known positions TMC 1-CP, TMC 1-NH3, and TMC 1-C, covering a visual extinction range from A(v) similar to 3 to similar to 20 mag. Two phases with differentiated chemistry can be distinguished: (i) the translucent envelope with molecular hydrogen densities of 1-5 x 10(3) cm(-3); and (ii) the dense phase, located at A(v) > 10 mag, with molecular hydrogen densities >10(4) cm(-3). Observations and modeling show that the gas phase abundances of C and O progressively decrease along the C+/C/CO transition zone (A(v) similar to 3 mag) where C/H similar to 8 x 10(-5) and C/O similar to 0.8-1, until the beginning of the dense phase at A(v) similar to 10 mag. This is consistent with the grain temperatures being below the CO evaporation temperature in this region. In the case of sulfur, a strong depletion should occur before the translucent phase where we estimate an S/H similar to (0.4-2.2) x 10(-6), an abundance similar to 7-40 times lower than the solar value. A second strong depletion must be present during the formation of the thick icy mantles to achieve the values of S/H measured in the dense cold cores (S/H similar to 8 x 10(-8)). Based on our chemical modeling, we constrain the value of zeta(H2) to similar to(0.5-1.8) x 10(-16) s(-1) in the translucent cloud.
  • Auddy, Sayantan; Myers, Philip C.; Basu, Shantanu; Harju, Jorma; Pineda, Jaime E.; Friesen, Rachel K. (2019)
    We develop a new "core field structure" (CFS) model to predict the magnetic field strength and magnetic field fluctuation profile of dense cores using gas kinematics. We use spatially resolved observations of the nonthermal velocity dispersion from the Green Bank Ammonia survey along with column density maps from SCUBA-2 to estimate the magnetic field strength across seven dense cores located in the L1688 region of Ophiuchus. The CFS model predicts the profile of the relative field fluctuation, which is related to the observable dispersion in the direction of the polarization vectors. Within the context of our model, we find that all of the cores have a transcritical mass-to-flux ratio.
  • Montillaud, Julien; Juvela, Mika; Vastel, Charlotte; He, JinHua; Liu, Tie; Ristorcelli, Isabelle; Eden, David; Kang, Sung-ju; Kim, Kee-Tae; Koch, Patrick M.; Lee, Chang Won; Rawlings, Mark G.; Saajasto, Mika; Sanhueza, Patricio; Soam, Archana; Zahorecz, Sarolta; Alina, Dana; Bogner, Rebeka; Cornu, David; Doi, Yasuo; Malinen, Johanna; Marshall, Douglas J.; Micelotta, Elisabetta R.; Pelkonen, V.-M.; Tóth, L. Viktor; Traficante, Alessio; Wang, Ke (2019)
    Context. Current theories and models attempt to explain star formation globally, from core scales to giant molecular cloud scales. A multi-scale observational characterisation of an entire molecular complex is necessary to constrain them. We investigate star formation in G202.3+2.5, a similar to 10 x 3 pc sub-region of the Monoceros OB1 cloud with a complex morphology that harbours interconnected filamentary structures. Aims. We aim to connect the evolution of cores and filaments in G202.3+2.5 with the global evolution of the cloud and to identify the engines of the cloud dynamics. Methods. In this first paper, the star formation activity is evaluated by surveying the distributions of dense cores and protostars and their evolutionary state, as characterised using both infrared observations from the Herschel and WISE telescopes and molecular line observations with the IRAM 30 m telescope. Results. We find ongoing star formation in the whole cloud, with a local peak in star formation activity around the centre of G202.3+2.5, where a chain of massive cores (10 50 M-circle dot) forms a massive ridge (greater than or similar to 150 M-circle dot). All evolutionary stages from starless cores to Class II protostars are found in G202.3+2.5, including a possibly starless and massive (52 M-circle dot) core, which presents a high column density (8 x 10(22) cm(-2)). Conclusions. All the core-scale observables we examined point to an enhanced star formation activity that is centred on the junction between the three main branches of the ramified structure of G202.3+2.5. This suggests that the increased star formation activity results from the convergence of these branches. To further investigate the origin of this enhancement, it is now necessary to extend the analysis to larger scales in order to examine the relationship between cores, filaments, and their environment. We address these points through the analysis of the dynamics of G202.3+2.5 in a joint paper.