Browsing by Subject "ISM: clouds"

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  • Feher, O.; Juvela, M.; Lunttila, T.; Montillaud, J.; Ristorcelli, I.; Zahorecz, S.; Toth, L. V. (2017)
    Context. The physical state of cold cloud clumps has a great impact on the process and efficiency of star formation and the masses of the forming stars inside these objects. The sub-millimetre survey of the Planck space observatory and the far-infrared follow-up mapping of the Herschel space telescope provide an unbiased, large sample of these cold objects. Aims. We have observed (CO)-C-12(1-0) and (CO)-C-13(1-0) emission in 35 high-density clumps in 26 Herschel fields sampling different environments in the Galaxy. Here, we aim to derive the physical properties of the objects and estimate their gravitational stability. Methods. The densities and temperatures of the clumps were calculated from both the dust continuum and the molecular line data. Kinematic distances were derived using (CO)-C-13(1-0) line velocities to verify previous distance estimates and the sizes and masses of the objects were calculated by fitting 2D Gaussian functions to their optical depth distribution maps on 250 mu m. The masses and virial masses were estimated assuming an upper and lower limit on the kinetic temperatures and considering uncertainties due to distance limitations. Results. The derived excitation temperatures are between 8.5-19.5 K, and for most clumps between 10 15 K, while the Herschel-derived dust colour temperatures are more uniform, between 12 16 K. The sizes (0.1-3 pc), (CO)-C-13 column densities (0.5-44 x 10(15) cm(-2)) and masses (from less than 0.1 M-circle dot to more than 1500 M-circle dot) of the objects all span broad ranges. We provide new kinematic distance estimates, identify gravitationally bound or unbound structures and discuss their nature. Conclusions. The sample contains objects on a wide scale of temperatures, densities and sizes. Eleven gravitationally unbound clumps were found, many of them smaller than 0.3 pc, but large, parsec-scale clouds with a few hundred solar masses appear as well. Colder clumps have generally high column densities but warmer objects appear at both low and higher column densities. The clump column densities derived from the line and dust observations correlate well, but are heavily affected by uncertainties of the dust properties, varying molecular abundances and optical depth effects.
  • 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).
  • Saha, Anindya; Tej, Anandmayee; Liu, Hong-Li; Liu, Tie; Issac, Namitha; Lee, Chang Won; Garay, Guido; Goldsmith, Paul F.; Juvela, Mika; Qin, Sheng-Li; Stutz, Amelia; Li, Shanghuo; Wang, Ke; Baug, Tapas; Bronfman, Leonardo; Xu, Feng-Wei; Zhang, Yong; Eswaraiah, Chakali (2022)
    We present new continuum and molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey for the two protoclusters, G12.42+0.50 and G19.88-0.53. The 3 mm continuum maps reveal seven cores in each of the two globally contracting protoclusters. These cores satisfy the radius-mass relation and the surface mass density criteria for high-mass star formation. Similar to their natal clumps, the virial analysis of the cores suggests that they are undergoing gravitational collapse (alpha(vir) < < 2). The clump to core scale fragmentation is investigated and the derived core masses and separations are found to be consistent with thermal Jeans fragmentation. We detect large-scale filamentary structures with velocity gradients and multiple outflows in both regions. Dendrogram analysis of the (HCO+)-C-13 map identities several branch and leaf structures with sizes similar to 0.1 and 0.03 pc, respectively. The supersonic gas motion displayed by the branch structures is in agreement with the Larson power law indicating that the gas kinematics at this spatial scale is driven by turbulence. The transition to transonic/subsonic gas motion is seen to occur at spatial scales of similar to 0.1 pc indicating the dissipation of turbulence. In agreement with this, the leaf structures reveal gas motions that deviate from the slope of Larson's law. From the largescale converging filaments to the collapsing cores, the gas dynamics in G12.42+0.50 and G19.88-0.53 show scale-dependent dominance of turbulence and gravity and the combination of these two driving mechanisms needs to be invoked to explain massive star formation in the protoclusters.
  • 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.
  • Saajasto, Mika; Harju, Jorma; Juvela, Mika; Tie, Liu; Zhang, Qizhou; Liu, Sheng-Yuan; Hirano, Naomi; Wu, Yuefang; Kim, Kee-Tae; Tatematsu, Kenichi; Wang, Ke; Thompson, Mark (2019)
    Context. We present molecular line and dust continuum observations of a Planck-detected cold cloud, G074.11+00.11. The cloud consists of a system of curved filaments and a central star-forming clump. The clump is associated with several infrared sources and H2O maser emission. Aims. We aim to determine the mass distribution and gas dynamics within the clump to investigate if the filamentary structure seen around the clump repeats itself on a smaller scale, and to estimate the fractions of mass contained in dense cores and filaments. The velocity distribution of pristine dense gas can be used to investigate the global dynamical state of the clump, the role of filamentary inflows, filament fragmentation, and core accretion. Methods. We used molecular line and continuum observations from single dish observatories and interferometric facilities to study the kinematics of the region. Results. The molecular line observations show that the central clump may have formed as a result of a large-scale filament collision. The central clump contains three compact cores. Assuming a distance of 2.3 kpc, based on Gaia observations and a three-dimensional extinction method of background stars, the mass of the central clump exceeds 700 M-circle dot, which is roughly similar to 25% of the total mass of the cloud. Our virial analysis suggests that the central clump and all identified substructures are collapsing. We find no evidence for small-scale filaments associated with the cores. Conclusions. Our observations indicate that the clump is fragmented into three cores with masses in the range [10, 50] M-circle dot and that all three are collapsing. The presence of an H2O maser emission suggests active star formation. However, the CO lines show only weak signs of outflows. We suggest that the region is young and any processes leading to star formation have just recently begun.
  • Saajasto, M.; Juvela, M.; Dobashi, K.; Shimoikura, T.; Ristorcelli, I.; Montillaud, J.; Marshall, D. J.; Malinen, J.; Pelkonen, V. -M.; Feher, O.; Rivera-Ingraham, A.; Toth, L. V.; Montier, L.; Bernard, J. -Ph.; Onishi, T. (2017)
    Context. The combination of line and continuum observations can provide vital insight into the formation and fragmentation of filaments and the initial conditions for star formation. We have carried out line observations to map the kinematics of an evolved, actively star forming filament G82.65-2.00. The filament was first identified from the Planck data as a region of particularly cold dust emission and was mapped at 100-500 mu m as a part of the Herschel key program Galactic Cold Cores. The Herschel observations cover the central part of the filament, corresponding to a filament length of similar to 12 pc at the assumed distance of 620 pc.& para;& para;Aims. CO observations show that the filament has an intriguing velocity field with several velocity components around the filament. In this paper, we study the velocity structure in detail, to quantify possible mass accretion rate onto the filament, and study the masses of the cold cores located in the filament.& para;& para;Methods. We have carried out line observations of several molecules, including CO isotopologues, HCO+, HCN, and CS with the Osaka 1.85 m telescope and the Nobeyama 45 m telescope. The spectral line data are used to derive velocity and column density information.& para;& para;Results. The observations reveal several velocity components in the field, with strongest line emission concentrated to velocity range similar to[3,5] km s(-1). The column density of molecular hydrogen along the filament varies from 1.0 to 2.3 x 10(22) cm(2). We have examined six cold clumps from the central part of the filament. The clumps have masses in the range 10-20 M circle dot (similar to 70 M circle dot in total) and are close to or above the virial mass. Furthermore, the main filament is heavily fragmented and most of the substructures have a mass lower than or close to the virial mass, suggesting that the filament is dispersing as a whole. Position-velocity maps of (CO)-C-12 and (CO)-C-13 lines indicate that at least one of the striations is kinematically connected to two of the clumps, potentially indicating mass accretion from the striation onto the main filament. We tentatively estimate the accretion rate to be M = 2.23 x 10(-6) M circle dot/yr.& para;& para;Conclusions. Our line observations have revealed two or possibly three velocity components connected to the filament G82.65-2.00 and putative signs of mass accretion onto the filament. The line observations combined with Herschel and WISE maps suggest a possible collision between two cloud components.
  • Harju, J.; Daniel, F.; Sipilä, O.; Caselli, P.; Pineda, J. E.; Friesen, R. K.; Punanova, A.; Guesten, R.; Wiesenfeld, L.; Myers, P. C.; Faure, A.; Hily-Blant, P.; Rist, C.; Rosolowsky, E.; Schlemmer, S.; Shirley, Y. L. (2017)
    Context. Ammonia and its deuterated isotopologues probe physical conditions in dense molecular cloud cores. The time-dependence of deuterium fractionation and the relative abundances of different nuclear spin modifications are supposed to provide a means of determining the evolutionary stages of these objects. Aims. We aim to test the current understanding of spin-state chemistry of deuterated species by determining the abundances and spin ratios of NH2D, NHD2 and ND3 in a quiescent, dense cloud. Methods. Spectral lines of NH3, NH2D, NHD2, ND3 and N2D+ were observed towards a dense, starless core in Ophiuchus with the APEX, GBT and IRAM 30-m telescopes. The observations were interpreted using a gas-grain chemistry model combined with radiative transfer calculations. The chemistry model distinguishes between the different nuclear spin states of light hydrogen molecules, ammonia and their deuterated forms. Different desorption schemes can be considered. Results. High deuterium fractionation ratios with NH2D = NH3 similar to 0 : 4, NHD2 = NH2D similar to 0 : 2 and ND3 = NHD2 similar to 0 : 06 are found in the core. The observed ortho/para ratios of NH2D and NHD2 are close to the corresponding nuclear spin statistical weights. The chemistry model can approximately reproduce the observed abundances, but consistently predicts too low ortho/para-NH2D, and too large ortho/para-NHD2 ratios. The longevity of N2H+ and NH3 in dense gas, which is prerequisite to their strong deuteration, can be attributed to the chemical inertia of N-2 on grain surfaces. Conclusions. The discrepancies between the chemistry model and the observations are likely to be caused by the fact that the model assumes complete scrambling in principal gas-phase deuteration reactions of ammonia, which means that all the nuclei are mixed in reactive collisions. If, instead, these reactions occur through proton hop/hydrogen abstraction processes, statistical spin ratios are to be expected. The present results suggest that while the deuteration of ammonia changes with physical conditions and time, the nuclear spin ratios of ammonia isotopologues do not probe the evolutionary stage of a cloud.
  • 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.
  • Bulut, N.; Roncero, O.; Aguado, A.; Loison, J-C; Navarro-Almaida, D.; Wakelam, V.; Fuente, A.; Roueff, E.; Le Gal, R.; Caselli, P.; Gerin, M.; Hickson, K. M.; Spezzano, S.; Riviere-Marichalar, P.; Alonso-Albi, T.; Bachiller, R.; Jimenez-Serra, Izaskun; Kramer, C.; Tercero, B.; Rodriguez-Baras, M.; Garcia-Burillo, S.; Goicoechea, J. R.; Trevino-Morales, S. P.; Esplugues, G.; Cazaux, S.; Commercon, B.; Laas, J.; Kirk, J.; Lattanzi, M.; Martin-Domenech, R.; Munoz-Caro, G.; Pineda, J.; Ward-Thompson, D.; Tafalla, M.; Marcelino, N.; Malinen, J.; Friesen, R.; Giuliano, B. M.; Agundez, M.; Hacar, A. (2021)
    Context. Carbon monosulphide (CS) is among the most abundant gas-phase S-bearing molecules in cold dark molecular clouds. It is easily observable with several transitions in the millimeter wavelength range, and has been widely used as a tracer of the gas density in the interstellar medium in our Galaxy and external galaxies. However, chemical models fail to account for the observed CS abundances when assuming the cosmic value for the elemental abundance of sulfur. Aims. The CS+O -> CO + S reaction has been proposed as a relevant CS destruction mechanism at low temperatures, and could explain the discrepancy between models and observations. Its reaction rate has been experimentally measured at temperatures of 150-400 K, but the extrapolation to lower temperatures is doubtful. Our goal is to calculate the CS+O reaction rate at temperatures Methods. We performed ab initio calculations to obtain the three lowest potential energy surfaces (PES) of the CS+O system. These PESs are used to study the reaction dynamics, using several methods (classical, quantum, and semiclassical) to eventually calculate the CS + O thermal reaction rates. In order to check the accuracy of our calculations, we compare the results of our theoretical calculations for T similar to 150-400 K with those obtained in the laboratory. Results. Our detailed theoretical study on the CS+O reaction, which is in agreement with the experimental data obtained at 150-400 K, demonstrates the reliability of our approach. After a careful analysis at lower temperatures, we find that the rate constant at 10 K is negligible, below 10(-15) cm(3) s(-1), which is consistent with the extrapolation of experimental data using the Arrhenius expression. Conclusions. We use the updated chemical network to model the sulfur chemistry in Taurus Molecular Cloud 1 (TMC 1) based on molecular abundances determined from Gas phase Elemental abundances in Molecular CloudS (GEMS) project observations. In our model, we take into account the expected decrease of the cosmic ray ionization rate, zeta(H2), along the cloud. The abundance of CS is still overestimated when assuming the cosmic value for the sulfur abundance.
  • Juvela, Mika; He, Jinhua; Pattle, Katherine; Liu, Tie; Bendo, George; Eden, David J.; Feher, Orsolya; Fich, Michel; Fuller, Gary; Hirano, Naomi; Kim, Kee-Tae; Li, Di; Liu, Sheng-Yuan; Malinen, Johanna; Marshall, Douglas J.; Paradis, Deborah; Parsons, Harriet; Pelkonen, Veli-Matti; Rawlings, Mark G.; Ristorcelli, Isabelle; Samal, Manash R.; Tatematsu, Ken'ichi; Thompson, Mark; Traficante, Alessio; Wang, Ke; Ward-Thompson, Derek; Wu, Yuefang; Yi, Hee-Weon; Yoo, Hyunju (2018)
    Context. Analysis of all-sky Planck submillimetre observations and the IRAS 100 mu m data has led to the detection of a population of Galactic cold clumps. The clumps can be used to study star formation and dust properties in a wide range of Galactic environments. Aims. Our aim is to measure dust spectral energy distribution ( SED) variations as a function of the spatial scale and the wavelength. Methods. We examined the SEDs at large scales using IRAS, Planck, and Herschel data. At smaller scales, we compared JCMT/SCUBA-2 850 mu m maps with Herschel data that were filtered using the SCUBA-2 pipeline. Clumps were extracted using the Fellwalker method, and their spectra were modelled as modified blackbody functions. Results. According to IRAS and Planck data, most fields have dust colour temperatures T-C similar to 14-18K and opacity spectral index values of beta = 1.5-1.9. The clumps and cores identified in SCUBA-2 maps have T similar to 13K and similar beta values. There are some indications of the dust emission spectrum becoming flatter at wavelengths longer than 500 mu m. In fits involving Planck data, the significance is limited by the uncertainty of the corrections for CO line contamination. The fits to the SPIRE data give a median beta value that is slightly above 1.8. In the joint SPIRE and SCUBA-2 850 mu m fits, the value decreases to beta similar to 1.6. Most of the observed T-beta anticorrelation can be explained by noise. Conclusions. The typical submillimetre opacity spectral index fi of cold clumps is found to be similar to 1.7. This is above the values of diffuse clouds, but lower than in some previous studies of dense clumps. There is only tentative evidence of a T-beta anticorrelation and beta decreasing at millimetre wavelengths.