Browsing by Subject "MOLECULAR 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.
  • 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, 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.
  • 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.
  • Soam, Archana; Lee, Chang Won; Andersson, B-G; Maheswar, G.; Juvela, Mika; Liu, Tie; Kim, Gwanjeong; Rao, Ramprasad; Chung, Eun Jung; Kwon, Woojin; Ekta, S. (2019)
    L1521F is found to be forming multiple cores and it is cited as an example of the densest core with an embedded VeLLO in a highly dynamical environment. We present the core-scale magnetic fields (B-fields) in the near vicinity of the VeLLO L1521F-IRS using submillimeter polarization measurements at 850 mu m using JCMT POL-2. This is the first attempt to use high-sensitivity observations to map the sub-parsec-scale B-fields in a core with a VeLLO. The B-fields are ordered and very well connected to the parsec-scale field geometry seen in our earlier optical polarization observations and the large-scale structure seen in Planck dust polarization. The core-scale B-field strength estimated using the Davis-Chandrasekhar-Fermi relation is 330 +/- 100 mu G, which is more than 10 times the value we obtained in the envelope (the envelope in this paper is the "core envelope"). This indicates that B-fields are getting stronger on smaller scales. The magnetic energies are found to be 1 to 2 orders of magnitude higher than nonthermal kinetic energies in the envelope and core. This suggests that magnetic fields are more important than turbulence in the energy budget of L1521F. The mass-to-flux ratio of 2.3 +/- 0.7 suggests that the core is magnetically supercritical. The degree of polarization is steadily decreasing toward the denser part of the core with a power-law slope of -0.86.
  • 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.
  • 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.
  • Malinen, J.; Montier, L.; Montillaud, J.; Juvela, M.; Ristorcelli, I.; Clark, S. E.; Berne, O.; Bernard, J.-Ph.; Pelkonen, V.-M.; Collins, D. C. (2016)
    The nearby cloud L1642 is one of only two known very high latitude (b| > 30 deg) clouds actively forming stars. It is a rare example of star formation in isolated conditions, and can reveal important details of star formation in general, e.g. of the effect of magnetic fields. We compareHerschel dust emission structures and magnetic field orientation revealed byPlanck polarization maps in L1642. The high-resolution (similar to 20 arcsec)Herschel data reveal a complex structure including a dense, compressed central clump, and low-density striations. ThePlanck polarization data (at 10 arcmin resolution) reveal an ordered magnetic field pervading the cloud and aligned with the surrounding striations. There is a complex interplay between the cloud structure and large-scale magnetic field. This suggests that the magnetic field is closely linked to the formation and evolution of the cloud. CO rotational emission confirms that the striations are connected with the main clumps and likely to contain material either falling into or flowing out of the clumps. There is a clear transition from aligned to perpendicular structures approximately at a column density ofN(H) = 1.6 x 10(21) cm(-2). Comparing theHerschel maps with thePlanck polarization maps shows the close connection between the magnetic field and cloud structure even in the finest details of the cloud.
  • Redaelli, E.; Bizzocchi, L.; Caselli, P.; Harju, J.; Chacon-Tanarro, A.; Leonardo, E.; Dore, L. (2018)
    Context. The N-15 fractionation has been observed to show large variations among astrophysical sources, depending both on the type of target and on the molecular tracer used. These variations cannot be reproduced by the current chemical models. Aims. Until now, the N-14/N-15 ratio in N2H+ has been accurately measured in only one prestellar source, L1544, where strong levels of fractionation, with depletion in N-15, are found (N-14/N-15 approximate to 1000). In this paper, we extend the sample to three more bona fide prestellar cores, in order to understand if the antifractionation in N2H+ is a common feature of this kind of source. Methods. We observed N2H+, (NNH+)-N-15, and (NNH+)-N-15 in L183, L429, and L694-2 with the IRAM 30m telescope. We modelled the emission with a non-local radiative transfer code in order to obtain accurate estimates of the molecular column densities, including the one for the optically thick N2H+. We used the most recent collisional rate coefficients available, and with these we also re-analysed the L1544 spectra previously published. Results. The obtained isotopic ratios are in the range 580-770 and significantly differ with the value, predicted by the most recent chemical models, of approximate to 440, close to the protosolar value. Our prestellar core sample shows a high level of depletion of N-15 in diazenylium, as previously found in L1544. A revision of the N chemical networks is needed in order to explain these results.
  • Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J. J.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bridges, M.; Bucher, M.; Burigana, C.; Cardoso, J. -F.; Catalano, A.; Challinor, A.; Chamballu, A.; Chary, R. -R.; Chen, X.; Chiang, H. C.; Chiang, L. -Y; Christensen, P. R.; Church, S.; Clements, D. L.; Colombi, S.; Colombo, L. P. L.; Combet, C.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J. -M.; Desert, F. -X.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Ensslin, T. A.; Eriksen, H. K.; Falgarone, E.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Ciard, M.; Giraud-Heraud, Y.; Gonzadlez-Nuevo, J.; Gorski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Hanson, D.; Harrison, D.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hornstrup, A.; Hovest, W.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T. S.; Kneiss, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J. -M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leahy, J. P.; Leonardi, R.; Leroy, C.; Lesgourgues, J.; Liguori, M.; Lilje, P. B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P. M.; Macias-Perez, J. F.; Maffei, B.; Mandolesi, N.; Maris, M.; Marshall, D. J.; Martin, P. G.; Martinez-Gonzalez, E.; Masi, S.; Massardi, M.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M. -A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Norgaard-Nielsen, H. U.; North, C.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C. A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G. W.; Prezeau, G.; Prunet, S.; Puget, J. -L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Roudier, G.; Rusholme, B.; Santos, D.; Savini, G.; Scott, D.; Shellard, E. P. S.; Spencer, L. D.; Starck, J. -L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sureau, F.; Sutton, D.; Suur-Uski, A. -S.; Sygnet, J. -F.; Tauber, J. A.; Tavagnacco, D.; Terenzi, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Yvon, D.; Zacchei, A.; Zonca, A. (2014)
  • JCMT Large Program SCOPE Collabora; TRAO Key Sci Program TOP Collabora; Yi, Hee-Weon; Lee, Jeong-Eun; Liu, Tie; Kim, Kee-Tae; Choi, Minho; Eden, David; Evans, Neal J.; Di Francesco, James; Fuller, Gary; Hirano, N.; Juvela, Mika; Kang, Sung-ju; Kim, Gwanjeong; Koch, Patrick M.; Lee, Chang Won; Li, Di; Liu, H-Y B.; Liu, Hong-Li; Liu, Sheng-Yuan; Rawlings, Mark G.; Ristorcelli, I.; Sanhueza, Patrico; Soam, Archana; Tatematsu, Ken'ichi; Thompson, Mark; Toth, L.; Wang, Ke; White, Glenn J.; Wu, Yuefang; Yang, Yao-Lun (2018)
    Based on the 850 mu m dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the lambda Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well-known active star-forming regions, while the A Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant H-II region. PGCCs in the lambda Orionis cloud have higher dust temperatures (T-d = 16.13 +/- 0.15 K) and lower values of dust emissivity spectral index (beta = 1.65 +/- 0.02) than PGCCs in the Orion A (T-d = 13.79 +/- 0.21 K, beta = 2.07 +/- 0.03) and Orion B (T-d = 13.82 +/- 0.19 K, beta =1.96 +/- 0.02) clouds. We find 119 substructures within the 40 detected PGCCs and identify them as cores. Out of a total of 119 cores, 15 cores are discovered in the lambda Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the lambda Orionis cloud show much lower mean values of size R = 0.08 pc, column density N(H-2) (9.5 +/- 1.2) x 10(22)cm(-2) , number density n(H-2) - (2.9 +/- 0.4) x 10 5 CM -3 , and mass M-core = 1.0 +/- 0.3 M(circle dot)compared to the cores in the Orion A [R = 0.11 pc, N(H-2) = (2.3 +/- 0.3) x 10(23) cm(-2), n(H-2) = (3.8 +/- 0.5) x 10(5)cm(-3) , and M-core = 2.4 +/- 0.3 M-circle dot] and Orion B [R = 0.16 pc, N(H-2) (3.8 +/- 0.4) x 10(23) cm(-2), n(H-2) = (15.6 +/- 1.8) x 10(5) cm(-3) , and M-core = 2.7 +/- 0.3 M-circle dot] clouds. These core properties in the A Orionis cloud can be attributed to the photodissociation and external heating by the nearby H rr region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.
  • Liu, Tie; Zhang, Qizhou; Kim, Kee-Tae; Wu, Yuefang; Lee, Chang Won; Lee, Jeong-Eun; Tatematsu, Ken'ichi; Choi, Minho; Juvela, Mika; Thompson, Mark; Goldsmith, Paul F.; Liu, Sheng-yuan; Naomi, Hirano; Koch, Patrick; Henkel, Christian; Sanhueza, Patricio; He, JinHua; Rivera-Ingraham, Alana; Wang, Ke; Cunningham, Maria R.; Tang, Ya-Wen; Lai, Shih-Ping; Yuan, Jinghua; Li, Di; Fuller, Gary; Kang, Miju; Luong, Quang Nguyen; Liu, Hauyu Baobab; Ristorcelli, Isabelle; Yang, Ji; Xu, Ye; Hirota, Tomoya; Mardones, Diego; Qin, Sheng-Li; Chen, Huei-Ru; Kwon, Woojin; Meng, Fanyi; Zhang, Huawei; Kim, Mi-Ryang; Yi, Hee-Weon (2016)
    We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the lambda Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound brightrimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity (similar to 0.8 L-circle dot) and accretion rate (6.3 x 10(-7) M-circle dot yr(-1)) when compared with other young Class 0 sources (e.g., PACS Bright Red Sources) in the Orion complex. It has slightly larger internal luminosity (0.21 +/- 0.01 L-circle dot) and outflow velocity (similar to 14 km s(-1)) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than an FHSC. Considering its low internal luminosity (0.08 +/- 0.01 L-circle dot) and accretion rate (2.8 x 10(-8) M-circle dot yr(-1)), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency (similar to 0.3%-0.4%) and core formation efficiency (similar to 1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed owing to stellar feedback.
  • Ade, P. A. R.; Juvela, M.; Keihanen, E.; Kurki-Suonio, H.; Suur-Uski, A. -S.; Planck Collaboration (2014)
  • Ade, P. A. R.; Keihanen, E.; Kurki-Suonio, H.; Lähteenmäki, Anne; Suur-Uski, A-S; Valiviita, J.; Ysard, N.; Planck Collaboration (2014)
  • Ade, P. A. R.; Juvela, M.; Keihänen, E.; Kurki-Suonio, H.; Suur-Uski, A. -S.; Valiviita, J.; Planck Collaboration; Fermi LAT Collaboration (2015)
    The nearby Chamaeleon clouds have been observed in gamma rays by the Fermi Large Area Telescope (LAT) and in thermal dust emission by Planck and IRAS. Cosmic rays and large dust grains, if smoothly mixed with gas, can jointly serve with the Hi and (CO)-C-12 radio data to (i) map the hydrogen column densities, N-H, in the different gas phases, in particular at the dark neutral medium (DNM) transition between the H I-bright and CO-bright media; (ii) constrain the CO-to-H-2 conversion factor, X-CO; and (iii) probe the dust properties per gas nucleon in each phase and map their spatial variations across the clouds. We have separated clouds at local, intermediate, and Galactic velocities in H i and (1)2CO line emission to model in parallel the gamma-ray intensity recorded between 0.4 and 100 GeV; the dust optical depth at 353 GHz, tau(353); the thermal radiance of the large grains; and an estimate of the dust extinction, A(VQ), empirically corrected for the starlight intensity. The dust and gamma-models have been coupled to account for the DNM gas. The consistent gamma-emissivity spectra recorded in the different phases confirm that the GeV-TeV cosmic rays probed by the LAT uniformly permeate all gas phases up to the (CO)-C-12 cores. The dust and cosmic rays both reveal large amounts of DNM gas, with comparable spatial distributions and twice as much mass as in the CO-bright clouds. We give constraints on the H I-DNM-CO transitions for five separate clouds. CO-dark H-2 dominates the molecular columns up to A(V) similar or equal to 0.9 and its mass often exceeds the one-third of the molecular mass expected by theory. The corrected A(VQ) extinction largely provides the best fit to the total gas traced by the gamma rays. Nevertheless, we find evidence for a marked rise in A(VQ)/N-H with increasing N-H and molecular fraction, and with decreasing dust temperature. The rise in tau(353)/N-H is even steeper. We observe variations of lesser amplitude and orderliness for the specific power of the grains, except for a coherent decline by half in the CO cores. This combined information suggests grain evolution. We provide average values for the dust properties per gas nucleon in the different phases. The gamma rays and dust radiance yield consistent X-CO estimates near 0.7 x 10(20) cm(-2) K-1 km(-1) s. The A(VQ) and tau(353) tracers yield biased values because of the large rise in grain opacity in the CO clouds. These results clarify a recurrent disparity in the gamma-versus dust calibration of X-CO, but they confirm the factor of 2 difference found between the X-CO estimates in nearby clouds and in the neighbouring spiral arms.
  • Ade, P. A. R.; Aghanim, N.; Alina, D.; Alves, M. I. R.; Aniano, G.; Annitage-Caplan, C.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Battaner, E.; Benabed, K.; Benoit-Levy, A.; Bernard, J. -P.; Bersanelli, M.; Bielewicz, P.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Cardoso, J. -F.; Catalano, A.; Chamballu, A.; Chiang, H. C.; Christensen, P. R.; Colombi, S.; Colombo, L. P. E.; Combet, C.; Couchot, F.; Coulais, A.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; Juvela, M.; Keihanen, E.; Kurki-Suonio, H.; Pelkonen, V. -M.; Suur-Uski, A. -S.; Valiviita, J. (2015)
    Polarized emission observed by Planck HFI at 353GHz towards a sample of nearby fields is presented, focusing on the statistics of polarization fractions p and angles psi. The polarization fractions and column densities in these nearby fields are representative of the range of values obtained over the whole sky. We find that: (i) the largest polarization fractions are reached in the most diffuse fields; (ii) the maximum polarization fraction p(max) decreases with column density N-H in the more opaque fields with N-H > 10(21) cm(-2); and (iii) the polarization fraction along a given line of sight is correlated with the local spatial coherence of the polarization angle. These observations are compared to polarized emission maps computed in simulations of anisotropic magnetohydrodynamical turbulence in which we assume a uniform intrinsic polarization fraction of the dust grains. We find that an estimate of this parameter may be recovered from the maximum polarization fraction p(max) in diffuse regions where the magnetic field is ordered on large scales and perpendicular to the line of sight. This emphasizes the impact of anisotropies of the magnetic field on the emerging polarization signal. The decrease of the maximum polarization fraction with column density in nearby molecular clouds is well reproduced in the simulations, indicating that it is essentially due to the turbulent structure of the magnetic field: an accumulation of variously polarized structures along the line of sight leads to such an anti-correlation. In the simulations, polarization fractions are also found to anti-correlate with the angle dispersion function S. However, the dispersion of the polarization angle for a given polarization fraction is found to be larger in the simulations than in the observations, suggesting a shortcoming in the physical content of these numerical models. In summary, we find that the turbulent structure of the magnetic field is able to reproduce the main statistical properties of the dust polarization as observed in a variety of nearby clouds, dense cores excluded, and that the large-scale field orientation with respect to the line of sight plays a major role in the quantitative analysis of these statistical properties.
  • Haikala, L. K.; Gahm, G. F.; Grenman, T.; Mäkelä, M. M.; Persson, C. M. (2017)
    Context. The Carina nebula hosts a large number of globulettes. An optical study of these tiny molecular clouds shows that the majority are of planetary mass, but there are also those with masses of several tens up to a few hundred Jupiter masses. Aims. We seek to search for, and hopefully detect, molecular line emission from some of the more massive objects; in case of successful detection we aim to map their motion in the Carina nebula complex and derive certain physical properties. Methods. We carried out radio observations of molecular line emission in (CO)-C-12 and (CO)-C-13 (2-1) and (3-2) of 12 globulettes in addition to positions in adjacent shell structures using APEX. Results. All selected objects were detected with radial velocities shifted relative to the emission from related shell structures and background molecular clouds. Globulettes along the western part of an extended dust shell show a small spread in velocity with small velocity shifts relative to the shell. This system of globulettes and shell structures in the foreground of the bright nebulosity surrounding the cluster Trumpler 14 is expanding with a few km s(-1) relative to the cluster. A couple of isolated globulettes in the area move at similar speed. Compared to similar studies of the molecular line emission from globulettes in the Rosette nebula, we find that the integrated line intensity ratios and line widths are very different. The results show that the Carina objects have a different density/temperature structure than those in the Rosette nebula. In comparison the apparent size of the Carina globulettes is smaller, owing to the larger distance, and the corresponding beam filling factors are small. For this reason we were unable to carry out a more detailed modelling of the structure of the Carina objects in the way as performed for the Rosette objects. Conclusions. The Carina globulettes observed are compact and denser than objects of similar mass in the Rosette nebula. The distribution and velocities of these globulettes suggest that they have originated from eroding shells and elephant trunks. Some globulettes in the Trumpler 14 region are quite isolated and located far from any shell structures. These objects move at a similar speed as the globulettes along the shell, suggesting that they once formed from cloud fragments related to the same foreground shell.
  • Liu, Tie; Kim, Kee-Tae; Yoo, Hyunju; Liu, Sheng-Yuan; Tatematsu, Ken'ichi; Qin, Sheng-Li; Zhang, Qizhou; Wu, Yuefang; Wang, Ke; Goldsmith, Paul F.; Juvela, Mika; Lee, Jeong-Eun; Toth, L. Viktor; Mardones, Diego; Garay, Guido; Bronfman, Leonardo; Cunningham, Maria R.; Li, Di; Lo, Nadia; Ristorcelli, Isabelle; Schnee, Scott (2016)
    We observed 146 Galactic clumps in HCN (4-3) and CS (7-6) with the Atacama Submillimeter Telescope Experiment 10 m telescope. A tight linear relationship between star formation rate and gas mass traced by dust continuum emission was found for both Galactic clumps and the high redshift (z > 1) star forming galaxies (SFGs), indicating a constant gas depletion time of similar to 100 Myr for molecular gas in both Galactic clumps and high z SFGs. However, low z galaxies do not follow this relation and seem to have a longer global gas depletion time. The correlations between total infrared luminosities (L-TIR) and molecular line luminosities (L-mol') of HCN (4-3) and CS (7-6) are tight and sublinear extending down to clumps with L-TIR similar to 10(3) L-circle dot. These correlations become linear when extended to external galaxies. A bimodal behavior in the L-TIR-L-mol' correlations was found for clumps with different dust temperature, luminosity-to-mass ratio, and sigma(line)/sigma(vir). Such bimodal behavior may be due to evolutionary effects. The slopes of L-TIR-L-mol' correlations become more shallow as clumps evolve. We compared our results with lower J transition lines in Wu et al. (2010). The correlations between clump masses and line luminosities are close to linear for low effective excitation density tracers but become sublinear for high effective excitation density tracers for clumps with L-TIR larger than L-TIR similar to 10(4.5) L-circle dot. High effective excitation density tracers cannot linearly trace the total clump masses, leading to a sublinear correlations for both M-clump-L-mol' and L-TIR-L-mol' relations.
  • Miettinen, O. (2018)
    Context. Filamentary molecular clouds, such as many of the infrared dark clouds (IRDCs), can undergo hierarchical fragmentation into substructures (clumps and cores) that can eventually collapse to form stars. Aims. We aim to determine the occurrence of fragmentation into cores in the clumps of the filamentary IRDC G304.74 + 01.32 (hereafter, G304.74). We also aim to determine the basic physical characteristics (e.g. mass, density, and young stellar object (YSO) content) of the clumps and cores in G304.74. Methods. We mapped the G304.74 filament at 350 mu m using the Submillimetre APEX Bolometer Camera (SABOCA) bolometer. The new SABOCA data have a factor of 2.2 times higher resolution than our previous Large APEX BOlometer CAmera (LABOCA) 870 mu m map of the cloud (9 '' vs. 19 ''.86). We also employed the Herschel far-infrared (IR) and submillimetre, andWide-field Infrared Survey Explorer (WISE) IR imaging data available for G304.74. The WISE data allowed us to trace the IR emission of the YSOs associated with the cloud. Results. The SABOCA 350 mu m data show that G304.74 is composed of a dense filamentary structure with a mean width of only 0.18 +/- 0.05 pc. The percentage of LABOCA clumps that are found to be fragmented into SABOCA cores is 36% +/- 16%, but the irregular morphology of some of the cores suggests that this multiplicity fraction could be higher. The WISE data suggest that 65% +/- 18% of the SABOCA cores host YSOs. The mean dust temperature of the clumps, derived by comparing the Herschel 250, 350, and 500 mu m flux densities, was found to be 15.0 +/- 0.8 K. The mean mass, beam-averaged H-2 column density, and H2 number density of the LABOCA clumps are estimated to be 55 +/- 10 M-circle dot, (2.0 +/- 0.2) x 10(22) cm(-2), and (3.1 +/- 0.2) x 10(4) cm(-3). The corresponding values for the SABOCA cores are 29 +/- 3 M-circle dot, (2.9 +/- 0.3) x 10(22) cm(-2), and (7.9 +/- 1.2) x 10(4) cm(-3). The G304.74 filament is estimated to be thermally supercritical by a factor of greater than or similar to 3.5 on the scale probed by LABOCA, and by a factor of greater than or similar to 1.5 for the SABOCA filament. Conclusions. Our data strongly suggest that the IRDC G304.74 has undergone hierarchical fragmentation. On the scale where the clumps have fragmented into cores, the process can be explained in terms of gravitational Jeans instability. Besides the filament being fragmented, the finding of embedded YSOs in G304.74 indicates its thermally supercritical state, although the potential non-thermal (turbulent) motions can render the cloud a virial equilibrium system on scale traced by LABOCA. The IRDC G304.74 has a seahorse-like morphology in the Herschel images, and the filament appears to be attached by elongated, perpendicular striations. This is potentially evidence that G304.74 is still accreting mass from the surrounding medium, and the accretion process can contribute to the dynamical evolution of the main filament. One of the clumps in G304.74, IRAS 13039-6108, is already known to be associated with high-mass star formation, but the remaining clumps and cores in this filament might preferentially form low and intermediate-mass stars owing to their mass reservoirs and sizes. Besides the presence of perpendicularly oriented, dusty striations and potential embedded intermediate-mass YSOs, G304.74 is a relatively nearby (d similar to 2.5 kpc) IRDC, which makes it a useful target for future star formation studies. Owing to its observed morphology, we propose that G304.74 could be nicknamed the Seahorse Nebula.
  • Väisälä, M. S.; Gent, F. A.; Juvela, M.; Käpylä, M. J. (2018)
    Context. Efforts to compare polarization measurements with synthetic observations from magnetohydrodynamics (MHD) models have previously concentrated on the scale of molecular clouds. Aims. We extend the model comparisons to kiloparsec scales, taking into account hot shocked gas generated by supernovae and a non-uniform dynamo-generated magnetic field at both large and small scales down to 4 pc spatial resolution. Methods. We used radiative transfer calculations to model dust emission and polarization on top of MHD simulations. We computed synthetic maps of column density N-H, polarization fraction p, and polarization angle dispersion S, and studied their dependencies on important properties of MHD simulations. These include the large-scale magnetic field and its orientation, the small-scale magnetic field, and supernova-driven shocks. Results. Similar filament-like structures of S as seen in the Planck all-sky maps are visible in our synthetic results, although the smallest scale structures are absent from our maps. Supernova-driven shock fronts and S do not show significant correlation. Instead, S can clearly be attributed to the distribution of the small-scale magnetic field. We also find that the large-scale magnetic field influences the polarization properties, such that, for a given strength of magnetic fluctuation, a strong plane of the sky mean field weakens the observed S, while strengthening p. The anticorrelation of p and S, and decreasing p as a function of NH are consistent across all synthetic observations. The magnetic fluctuations follow an exponential distribution, rather than Gaussian characteristic of flows with intermittent repetitive shocks. Conclusions. The observed polarization properties and column densities are sensitive to the line-of-sight distance over which the emission is integrated. Studying synthetic maps as the function of maximum integration length will further help with the interpretation of observations. The effects of the large-scale magnetic field orientation on the polarization properties are difficult to be quantified from observations solely, but MHD models might turn out to be useful for separating the effect of the large-scale mean field.