Publication Search Results

ID: 157319
Type: article
Authors: Chen, Che-Yu; Behrens, Erica A.; Washington, Jasmin E.; Fissel, Laura M.; Friesen, Rachel K.; Li, Zhi-Yun; Pineda, Jaime E.; Ginsburg, Adam; Kirk, Helen; Scibelli, Samantha; Alves, Felipe; Redaelli, Elena; Caselli, Paola; Punanova, Anna; di Francesco, James; Rosolowsky, Erik; Offner, Stella S. R.; Martin, Peter G.; Chacón-Tanarro, Ana; Chen, Hope H. -H; Chen, Michael C. -Y; Keown, Jared; Seo, Youngmin; Shirley, Yancy; Arce, Hector G.; Goodman, Alyssa A.; Matzner, Christopher D.; Myers, Philip C.; Singh, Ayushi
Abstract: The role played by magnetic field during star formation is an important topic in astrophysics. We investigate the correlation between the orientation of star-forming cores (as defined by the core major axes) and ambient magnetic field directions in (I) a 3D magnetohydrodynamic simulation, (II) synthetic observations generated from the simulation at different viewing angles, and (III) observations of nearby molecular clouds. We find that the results on relative alignment between cores and background magnetic field in synthetic observations slightly disagree with those measured in fully 3D simulation data, which is partly because cores identified in projected 2D maps tend to coexist within filamentary structures, while 3D cores are generally more rounded. In addition, we examine the progression of magnetic field from pc to core scale in the simulation, which is consistent with the anisotropic core formation model that gas preferably flows along the magnetic field towards dense cores. When comparing the observed cores identified from the Green Bank Ammonia Survey and Planck polarization-inferred magnetic field orientations, we find that the relative core-field alignment has a regional dependence among different clouds. More specifically, we find that dense cores in the Taurus molecular cloud tend to align perpendicular to the background magnetic field, while those in Perseus and Ophiuchus tend to have random (Perseus) or slightly parallel (Ophiuchus) orientations with respect to the field. We argue that this feature of relative core-field orientation could be used to probe the relative significance of the magnetic field within the cloud.

ID: 157815
Type: article
Authors: Choudhury, Spandan; Pineda, Jaime E.; Caselli, Paola; Ginsburg, Adam; Offner, Stella S. R.; Rosolowsky, Erik; Friesen, Rachel K.; Alves, Felipe O.; Chacón-Tanarro, Ana; Punanova, Anna; Redaelli, Elena; Kirk, Helen; Myers, Philip C.; Martin, Peter G.; Shirley, Yancy; Chun-Yuan Chen, Michael; Goodman, Alyssa A.; di Francesco, James
Abstract: Context. Star formation takes place in cold dense cores in molecular clouds. Earlier observations have found that dense cores exhibit subsonic non-thermal velocity dispersions. In contrast, CO observations show that the ambient large-scale cloud is warmer and has supersonic velocity dispersions. Aims: We aim to study the ammonia (NH₃) molecular line profiles with exquisite sensitivity towards the coherent cores in L1688 in order to study their kinematical properties in unprecedented detail. Methods: We used NH₃ (1,1) and (2,2) data from the first data release (DR1) in the Green Bank Ammonia Survey (GAS). We first smoothed the data to a larger beam of 1' to obtain substantially more extended maps of velocity dispersion and kinetic temperature, compared to the DR1 maps. We then identified the coherent cores in the cloud and analysed the averaged line profiles towards the cores. Results: For the first time, we detected a faint (mean NH₃(1,1) peak brightness (1,1) peak brightness _MB), supersonic component towards all the coherent cores in L1688. We fitted two components, one broad and one narrow, and derived the kinetic temperature and velocity dispersion of each component. The broad components towards all cores have supersonic linewidths (ℳ_S ≥ 1). This component biases the estimate of the narrow dense core component's velocity dispersion by ≈28% and the kinetic temperature by ≈10%, on average, as compared to the results from single-component fits. Conclusions: Neglecting this ubiquitous presence of a broad component towards all coherent cores causes the typical single-component fit to overestimate the temperature and velocity dispersion. This affects the derived detailed physical structure and stability of the cores estimated from NH₃ observations.

ID: 156879
Type: article
Authors: Harju, Jorma; Pineda, Jaime E.; Vasyunin, Anton I.; Caselli, Paola; Offner, Stella S. R.; Goodman, Alyssa A.; Juvela, Mika; Sipilä, Olli; Faure, Alexandre; Le Gal, Romane; Hily-Blant, Pierre; Alves, João; Bizzocchi, Luca; Burkert, Andreas; Chen, Hope; Friesen, Rachel K.; Güsten, Rolf; Myers, Philip C.; Punanova, Anna; Rist, Claire; Rosolowsky, Erik; Schlemmer, Stephan; Shirley, Yancy; Spezzano, Silvia; Vastel, Charlotte; Wiesenfeld, Laurent
Abstract: We present Atacama Large Millimeter/submillimeter Array maps of the starless molecular cloud core Ophiuchus/H-MM1 in the lines of deuterated ammonia (ortho- ${\mathrm{NH}}_{2}{\rm{D}}$ ), methanol ( ${\mathrm{CH}}_{3}\mathrm{OH}$ ), and sulfur monoxide (SO). The dense core is seen in ${\mathrm{NH}}_{2}{\rm{D}}$ emission, whereas the ${\mathrm{CH}}_{3}\mathrm{OH}$ and SO distributions form a halo surrounding the core. Because methanol is formed on grain surfaces, its emission highlights regions where desorption from grains is particularly efficient. Methanol and sulfur monoxide are most abundant in a narrow zone that follows the eastern side of the core. This side is sheltered from the stronger external radiation field coming from the west. We show that photodissociation on the illuminated side can give rise to an asymmetric methanol distribution but that the stark contrast observed in H-MM1 is hard to explain without assuming enhanced desorption on the shaded side. The region of the brightest emission has a wavy structure that rolls up at one end. This is the signature of Kelvin-Helmholtz instability occurring in sheared flows. We suggest that in this zone, methanol and sulfur are released as a result of grain-grain collisions induced by shear vorticity.

ID: 156371
Type: article
Authors: Kim, Shinyoung; Lee, Chang Won; Gopinathan, Maheswar; Tafalla, Mario; Sohn, Jungjoo; Kim, Gwanjeong; Kim, Mi-Ryang; Soam, Archana; Myers, Philip C.
Abstract: The CS molecule is known to be adsorbed onto dust in cold and dense conditions, causing it to be significantly depleted in the central region of cores. This study is aimed to investigate the depletion of the CS molecule using the optically thin {C}³⁴{S} molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197, using two molecular lines, {C}³⁴S (J = 2 - 1) and {N}₂{H}⁺ (J = 1 - 0) with the NRO 45 m telescope, doubling the number of cores where the CS depletion was probed using {C}³⁴S . In most of our targets, the distribution of {C}³⁴S emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to {H}₂ directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of ∼3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced, by an order of magnitude, when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line of sight is removed. Except for L1197-which is classified as relatively the least evolved core in our targets, based on its observed physical parameters-we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region, regardless of the relative difference in their evolutionary status.

ID: 158871
Type: article
Authors: Pillai, Thushara G. S.; Clemens, Dan P.; Reissl, Stefan; Myers, Philip C.; Kauffmann, Jens; Lopez-Rodriguez, Enrique; Alves, F. O.; Franco, G. A. P.; Henshaw, Jonathan; Menten, Karl M.; Nakamura, Fumitaka; Seifried, Daniel; Sugitani, Koji; Wiesemeyer, Helmut
Abstract: Observations indicate that molecular clouds are strongly magnetized, and that magnetic fields influence the formation of stars. A key observation supporting the conclusion that molecular clouds are significantly magnetized is that the orientation of their internal structure is closely related to that of the magnetic field. At low column densities, the structure aligns parallel with the field, whereas at higher column densities, the gas structure is typically oriented perpendicular to magnetic fields, with a transition at visual extinctions A_V ? 3 mag. Here we use far-infrared polarimetric observations from the HAWC+ polarimeter on SOFIA to report the discovery of a further transition in relative orientation, that is, a return to parallel alignment at A_V ? 21 mag in parts of the Serpens South cloud. This transition appears to be caused by gas flow and indicates that magnetic supercriticality sets in near A_V ? 21 mag, allowing gravitational collapse and star cluster formation to occur even in the presence of relatively strong magnetic fields.

ID: 157803
Type: article
Authors: Pokhrel, Riwaj; Gutermuth, Robert A.; Betti, Sarah K.; Offner, Stella S. R.; Myers, Philip C.; Megeath, S. Thomas; Sokol, Alyssa D.; Ali, Babar; Allen, Lori; Allen, Thomas S.; Dunham, Michael M.; Fischer, William J.; Henning, Thomas; Heyer, Mark; Hora, Joseph L.; Pipher, Judith L.; Tobin, John J.; Wolk, Scott J.
Abstract: We explore the relation between the stellar mass surface density and the mass surface density of molecular hydrogen gas in 12 nearby molecular clouds that are located at <1.5 kpc distance. The sample clouds span an order-of-magnitude range in mass, size, and star formation rates. We use thermal dust emission from Herschel maps to probe the gas surface density and the young stellar objects from the most recent Spitzer Extended Solar Neighborhood Archive catalog to probe the stellar surface density. Using a star-sampled nearest neighbor technique to probe the star-gas surface density correlations at the scale of a few parsecs, we find that the stellar mass surface density varies as a power law of the gas mass surface density, with a power-law index of ∼2 in all the clouds. The consistent power-law index implies that star formation efficiency is directly correlated with gas column density, and no gas column density threshold for star formation is observed. We compare the observed correlations with the predictions from an analytical model of thermal fragmentation and with the synthetic observations of a recent hydrodynamic simulation of a turbulent star-forming molecular cloud. We find that the observed correlations are consistent for some clouds with the thermal fragmentation model and can be reproduced using the hydrodynamic simulations.

ID: 150899
Type: article
Authors: Andersen, Bridget C.; Stephens, Ian W.; Dunham, Michael M.; Pokhrel, Riwaj; Jørgensen, Jes K.; Frimann, Søren; Segura-Cox, Dominique; Myers, Philip C.; Bourke, Tyler L.; Tobin, John J.; Tychoniec, Łukasz
Abstract: In the standard picture for low-mass star formation, a dense molecular cloud undergoes gravitational collapse to form a protostellar system consisting of a new central star, a circumstellar disk, and a surrounding envelope of remaining material. The mass distribution of the system evolves as matter accretes from the large-scale envelope through the disk and onto the protostar. While this general picture is supported by simulations and indirect observational measurements, the specific timescales related to disk growth and envelope dissipation remain poorly constrained. In this paper we conduct a rigorous test of a method introduced by Jørgensen et al. to obtain mass measurements of disks and envelopes around embedded protostars with observations that do not resolve the disk (resolution of ˜1000 au). Using unresolved data from the recent Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, we derive disk and envelope mass estimates for 59 protostellar systems in the Perseus molecular cloud. We compare our results to independent disk mass measurements from the VLA Nascent Disk and Multiplicity survey and find a strong linear correlation, suggesting that accurate disk masses can be measured from unresolved observations. Then, leveraging the size of the MASSES sample, we find no significant trend in protostellar mass distribution as a function of age, as approximated from bolometric temperatures. These results may indicate that the disk mass of a protostar is set near the onset of the Class 0 protostellar stage and remains roughly constant throughout the Class I protostellar stage.

ID: 150487
Type: article
Authors: Auddy, Sayantan; Myers, Philip C.; Basu, Shantanu; Harju, Jorma; Pineda, Jaime E.; Friesen, Rachel K.
Abstract: 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.

ID: 152918
Type: article
Authors: Chen, Hope How-Huan; Pineda, Jaime E.; Goodman, Alyssa A.; Burkert, Andreas; Offner, Stella S. R.; Friesen, Rachel K.; Myers, Philip C.; Alves, Felipe; Arce, Héctor G.; Caselli, Paola; Chacón-Tanarro, Ana; Chen, Michael Chun-Yuan; di Francesco, James; Ginsburg, Adam; Keown, Jared; Kirk, Helen; Martin, Peter G.; Matzner, Christopher; Punanova, Anna; Redaelli, Elena; Rosolowsky, Erik; Scibelli, Samantha; Seo, Youngmin; Shirley, Yancy; Singh, Ayushi; The GAS Collaboration
Abstract: We present the observation and analysis of newly discovered coherent structures in the L1688 region of Ophiuchus and the B18 region of Taurus. Using data from the Green Bank Ammonia Survey, we identify regions of high density and near-constant, almost-thermal velocity dispersion. We reveal 18 coherent structures are revealed, 12 in L1688 and 6 in B18, each of which shows a sharp “transition to coherence” in velocity dispersion around its periphery. The identification of these structures provides a chance to statistically study the coherent structures in molecular clouds. The identified coherent structures have a typical radius of 0.04 pc and a typical mass of 0.4 M _⊙, generally smaller than previously known coherent cores identified by Goodman et al., Caselli et al., and Pineda et al. We call these structures “droplets.” We find that, unlike previously known coherent cores, these structures are not virially bound by self-gravity and are instead predominantly confined by ambient pressure. The droplets have density profiles shallower than a critical Bonnor–Ebert sphere, and they have a velocity (V _LSR) distribution consistent with the dense gas motions traced by NH₃ emission. These results point to a potential formation mechanism through pressure compression and turbulent processes in the dense gas. We present a comparison with a magnetohydrodynamic simulation of a star-forming region, and we speculate on the relationship of droplets with larger, gravitationally bound coherent cores, as well as on the role that droplets and other coherent structures play in the star formation process.

ID: 152916
Type: article
Authors: Chung, Eun Jung; Lee, Chang Won; Kim, Shinyoung; Kim, Gwanjeong; Caselli, Paola; Tafalla, Mario; Myers, Philip C.; Soam, Archana; Liu, Tie; Gopinathan, Maheswar; Kim, Miryang; Kim, Kyoung Hee; Kwon, Woojin; Kang, Hyunwoo; Lee, Changhoon
Abstract: “TRAO FUNS” is a project to survey the Gould Belt’s clouds in molecular lines. This paper presents its first results on the central region of the California molecular cloud, L1478. We performed on-the-fly mapping observations using the Taeduk Radio Astronomy Observatory 14 m single-dish telescope equipped with a 16 multibeam array covering a ∼1.0 square degree area of this region using {{{C}}}¹⁸{{O}}(1{--}0), mainly tracing low-density clouds, and a ∼460 square arcminute area using {{{N}}}₂{{{H}}}⁺(1{--}0), mainly tracing dense cores. {CS}(2{--}1) and {SO}({3}₂{--}{2}₁) were also used simultaneously to map a ∼440 square arcminute area of this region. We identified 10 filaments by applying the dendrogram technique to the {{{C}}}¹⁸{{O}} data cube and 8 dense {{{N}}}₂{{{H}}}⁺ cores using FELLWALKER. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that L1478 consists of several filaments with slightly different velocities. Particularly, the filaments that are supercritical are found to contain dense cores detected in {{{N}}}₂{{{H}}}⁺. A comparison of nonthermal velocity dispersions derived from {{{C}}}¹⁸{{O}} and {{{N}}}₂{{{H}}}⁺ for the filaments and dense cores indicates that some of the dense cores share kinematics similar to those of the surrounding filaments, while several dense cores have different kinematics from those of their filaments. This suggests that the formation mechanism of dense cores and filaments can be different in individual filaments depending on their morphologies and environments.

ID: 154699
Type: article
Authors: Keown, Jared; di Francesco, James; Rosolowsky, Erik; Singh, Ayushi; Figura, Charles; Kirk, Helen; Anderson, L. D.; Chen, Michael Chun-Yuan; Elia, Davide; Friesen, Rachel; Ginsburg, Adam; Marston, A.; Pezzuto, Stefano; Schisano, Eugenio; Bontemps, Sylvain; Caselli, Paola; Liu, Hong-Li; Longmore, Steven; Motte, Frédérique; Myers, Philip C.; Offner, Stella S. R.; Sanhueza, Patricio; Schneider, Nicola; Stephens, Ian; Urquhart, James
Abstract: We present initial results from the K-band Focal Plane Array Examinations of Young STellar Object Natal Environments survey, a large project on the 100 m Green Bank Telescope mapping ammonia emission across 11 giant molecular clouds at distances of 0.9-3.0 kpc (Cygnus X North, Cygnus X South, M16, M17, Mon R1, Mon R2, NGC 2264, NGC 7538, Rosette, W3, and W48). This data release includes the NH₃ (1,1) and (2,2) maps for each cloud, which are modeled to produce maps of kinetic temperature, centroid velocity, velocity dispersion, and ammonia column density. Median cloud kinetic temperatures range from 11.4 ± 2.2 K in the coldest cloud (Mon R1) to 23.0 ± 6.5 K in the warmest cloud (M17). Using dendrograms on the NH₃ (1,1) integrated intensity maps, we identify 856 dense gas clumps across the 11 clouds. Depending on the cloud observed, 40%-100% of the clumps are aligned spatially with filaments identified in H₂ column density maps derived from spectral energy distribution fitting of dust continuum emission. A virial analysis reveals that 523 of the 835 clumps (̃63%) with mass estimates are bound by gravity alone. We find no significant difference between the virial parameter distributions for clumps aligned with the dust-continuum filaments and those unaligned with filaments. In some clouds, however, hubs or ridges of dense gas with unusually high mass and low virial parameters are located within a single filament or at the intersection of multiple filaments. These hubs and ridges tend to host water maser emission, multiple 70 μm detected protostars, and have masses and radii above an empirical threshold for forming massive stars.

ID: 150506
Type: article
Authors: Li, Juan; Myers, Philip C.; Kirk, Helen; Gutermuth, Robert A.; Dunham, Michael M.; Pokhrel, Riwaj
Abstract: We analyze high-quality stellar catalogs for 24 young and nearby (within 1 kpc) embedded clusters and present a catalog of 32 groups which have a high concentration of protostars. The median effective radius of these groups is 0.17 pc. The median protostellar and pre-main-sequence star surface densities are 46 M _⊙ pc^‑2 and 11 M _⊙ pc^‑2, respectively. We estimate the age of these groups using a model of constant birthrate and random accretion stopping and find a median value of 0.25 Myr. Some groups in Aquila, Serpens, Corona Australia, and Ophichus L1688 show high protostellar surface density and high molecular gas surface density, and seem to be undergoing vigorous star formation. These groups provide an excellent opportunity to study the initial conditions of clustered star formation. Comparisons of protostellar and pre-main-sequence stellar surface densities reveal continuous low-mass star formation of these groups over several Myr in some clouds. For groups with typical protostellar separations of less than 0.4 pc, we find that these separations agree well with the thermal Jeans fragmentation scale. On the other hand, for groups with typical protostellar separations larger than 0.4 pc, these separations are always larger than the associated Jeans length.

ID: 154425
Type: article
Authors: Pineda, Jaime E.; Zhao, Bo; Schmiedeke, Anika; Segura-Cox, Dominique M.; Caselli, Paola; Myers, Philip C.; Tobin, John J.; Dunham, Michael
Abstract: The determination of the specific angular momentum radial profile, j(r), in the early stages of star formation is crucial to constrain star and circumstellar disk formation theories. The specific angular momentum is directly related to the largest Keplerian disk possible, and it could constrain the angular momentum removal mechanism. We determine j(r) toward two Class 0 objects and a first hydrostatic core candidate in the Perseus cloud, which is consistent across all three sources and well fit with a single power-law relation between 800 and 10,000 au: {j}_fit}(r)={10}^{-3.60+/- 0.15}{≤ft(r/1000{au}\right)}^{1.80+/- 0.04} {km} {{{s}}}^-1 {pc}. This power-law relation is in between solid body rotation (∝r ²) and pure turbulence (∝r ^1.5). This strongly suggests that even at 1000 au, the influence of the dense core's initial level of turbulence or the connection between core and the molecular cloud is still present. The specific angular momentum at 10,000 au is ≈3× higher than previously estimated, while at 1000 au, it is lower by 2×. We do not find a region of conserved specific angular momentum, although it could still be present at a smaller radius. We estimate an upper limit to the largest Keplerian disk radius of 60 au, which is small but consistent with published upper limits. Finally, these results suggest that more realistic initial conditions for numerical simulations of disk formation are needed. Some possible solutions include: (a) using a larger simulation box to include some level of driven turbulence or connection to the parental cloud or (b) incorporating the observed j(r) to set up the dense core kinematics initial conditions.

ID: 154596
Type: article
Authors: Sadavoy, Sarah I.; Stephens, Ian W.; Myers, Philip C.; Looney, Leslie; Tobin, John; Kwon, Woojin; Commerçon, Benoît; Segura-Cox, Dominique; Henning, Thomas; Hennebelle, Patrick
Abstract: We present 0.″25 resolution (35 au) ALMA 1.3 mm dust polarization observations for 37 young stellar objects (YSOs) in the Ophiuchus molecular cloud. These data encompass all the embedded protostars in the cloud and several flat-spectrum and Class II objects to produce the largest, homogeneous study of dust polarization on disk scales to date. The goal of this study is to study dust polarization morphologies down to disk scales. We find that 14/37 (38%) of the observed YSOs are detected in polarization at our sensitivity. Nine of these sources have uniform polarization angles, and four sources have azimuthal polarization structure. We find that the sources with uniform polarization tend to have steeper inclinations (>60°) than those with azimuthal polarization (60° are the best candidates for future polarization studies of dust self-scattering, as these systems will generally show uniform polarization vectors that do not require very high resolution to resolve. We release the continuum and polarization images for all the sources with this publication. Data from the entire survey can be obtained from Dataverse.

ID: 154516
Type: article
Authors: Stephens, Ian W.; Bourke, Tyler L.; Dunham, Michael M.; Myers, Philip C.; Pokhrel, Riwaj; Tobin, John J.; Arce, Héctor G.; Sadavoy, Sarah I.; Vorobyov, Eduard I.; Pineda, Jaime E.; Offner, Stella S. R.; Lee, Katherine I.; Kristensen, Lars E.; Jørgensen, Jes K.; Gurwell, Mark A.; Goodman, Alyssa A.
Abstract: We present and release the full data set for the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. This survey used the Submillimeter Array (SMA) to image the 74 known protostars within the Perseus molecular cloud. The SMA was used in two array configurations to capture outflows for scales >30″ (>9000 au) and to probe scales down to ∼1″ (∼300 au). The protostars were observed with the 1.3 mm and 850 μm receivers simultaneously to detect continuum at both wavelengths and molecular line emission from CO(2─1), ¹³CO(2─1), C¹⁸O(2─1), N₂D⁺(3─2), CO(3─2), HCO⁺(4─3), and H¹³CO⁺(4─3). Some of the observations also used the SMA's recently upgraded correlator, SWARM, whose broader bandwidth allowed for several more spectral lines to be observed (e.g., SO, H₂CO, DCO⁺, DCN, CS, CN). Of the main continuum and spectral tracers observed, 84% of the images and cubes had emission detected. The median C¹⁸O(2─1) line width is ∼1.0 km s⁻¹, which is slightly higher than those measured with single-dish telescopes at scales of 3000─20,000 au. Of the 74 targets, six are suggested to be first hydrostatic core candidates, and we suggest that L1451-mm is the best candidate. We question a previous continuum detection toward L1448 IRS2E. In the SVS 13 system, SVS 13A certainly appears to be the most evolved source, while SVS 13C appears to be hotter and more evolved than SVS 13B. The MASSES survey is the largest publicly available interferometric continuum and spectral line protostellar survey to date, and is largely unbiased as it only targets protostars in Perseus. All visibility (uv) data and imaged data are publicly available at https://dataverse.harvard.edu/dataverse/full_MASSES/.

ID: 149396
Type: article
Authors: Lee, Chang Won; Kim, Gwanjeong; Myers, Philip C.; Saito, Masao; Kim, Shinyoung; Kwon, Woojin; Lyo, A. -Ran; Soam, Archana; Kim, Mi-Ryang
Abstract: This paper presents our observational attempts to precisely measure the central mass of a proto-brown dwarf candidate, L328-IRS, in order to investigate whether L328-IRS is in the substellar mass regime. Observations were made for the central region of L328-IRS with the dust continuum and CO isotopologue line emission at Atacama Large Millimeter/submillimeter Array (ALMA) band 6, discovering the detailed outflow activities and a deconvolved disk structure of a size of ∼87 × 37 au. We investigated the rotational velocities as a function of the disk radius, finding that its motions between 130 and 60 au are partially fitted with a Keplerian orbit by a stellar object of ∼0.30 M_⊙, while the motions within 60 au do not follow any Keplerian orbit at all. This makes it difficult to lead a reliable estimation of the mass of L328-IRS. Nonetheless, our ALMA observations were useful enough to well constrain the inclination angle of the outflow cavity of L328-IRS as ∼66°, enabling us to better determine the mass accretion rate of ∼8.9 × 10^‑7 M_⊙ yr^‑1. From assumptions that the internal luminosity of L328-IRS is mostly due to this mass accretion process in the disk, or that L328-IRS has mostly accumulated the mass through this constant accretion rate during its outflow activity, its mass was estimated to be ∼0.012–0.023 M_⊙, suggesting L328-IRS to be a substellar object. However, we leave our identification of L328-IRS as a proto-brown dwarf to be tentative because of various uncertainties, especially regarding the mass accretion rate.

ID: 146160
Type: article
Authors: Lu, Xing; Zhang, Qizhou; Liu, Hauyu Baobab; Sanhueza, Patricio; Tatematsu, Ken'ichi; Feng, Siyi; Smith, Howard A.; Myers, Philip C.; Sridharan, T. K.; Gu, Qiusheng
Abstract: Filamentary structures are ubiquitous in high-mass star-forming molecular clouds. Their relation with high-mass star formation is still to be understood. Here we report interferometric observations toward eight filamentary high-mass star-forming clouds. A total of 50 dense cores are identified in these clouds, most of which present signatures of high-mass star formation. Five of them are not associated with any star formation indicators and hence are prestellar core candidates. Evolutionary phases of these cores and their line widths, temperatures, {NH}}₃ abundances, and virial parameters are found to be correlated. In a subsample of four morphologically well-defined filaments, we find that their fragmentation cannot be solely explained by thermal or turbulence pressure support. We also investigate distributions of gas temperatures and nonthermal motions along the filaments and find a spatial correlation between nonthermal line widths and star formation activities. We find evidence of gas flows along these filaments and derive an accretion rate along filaments of ∼10^‑4 {M}_ȯ {yr}}^-1. These results suggest a strong relationship between massive filaments and high-mass star formation, through (i) filamentary fragmentation in very early evolutionary phases to form dense cores, (ii) accretion flows along filaments that are important for the growth of dense cores and protostars, and (iii) enhancement of nonthermal motion in the filaments by the feedback or accretion during star formation.

ID: 145756
Type: article
Authors: Pokhrel, Riwaj; Myers, Philip C.; Dunham, Michael M.; Stephens, Ian W.; Sadavoy, Sarah I.; Zhang, Qizhou; Bourke, Tyler L.; Tobin, John J.; Lee, Katherine I.; Gutermuth, Robert A.; Offner, Stella S. R.
Abstract: We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud (&gsim; 10 pc) to smaller clumps (~1 pc), cores (~0.05--0.1 pc), envelopes (~300--3000 au), and protostellar objects (~15 au). We use new observations from the Submillimeter Array (SMA) large project ``Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)'' to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

ID: 145763
Type: article
Authors: Sadavoy, Sarah I.; Keto, Eric; Bourke, Tyler L.; Dunham, Michael M.; Myers, Philip C.; Stephens, Ian W.; di Francesco, James; Webb, Kristi; Stutz, Amelia M.; Launhardt, Ralf; Tobin, John J.
Abstract: We present intensity-corrected Herschel maps at 100, 160, 250, 350, and 500 mum for 56 isolated low-mass clouds. We determine the zero-point corrections for Herschel Photodetector Array Camera and Spectrometer (PACS) and Spectral Photometric Imaging Receiver (SPIRE) maps from the Herschel Science Archive (HSA) using Planck data. Since these HSA maps are small, we cannot correct them using typical methods. Here we introduce a technique to measure the zero-point corrections for small Herschel maps. We use radial profiles to identify offsets between the observed HSA intensities and the expected intensities from Planck. Most clouds have reliable offset measurements with this technique. In addition, we find that roughly half of the clouds have underestimated HSA-SPIRE intensities in their outer envelopes relative to Planck, even though the HSA-SPIRE maps were previously zero-point corrected. Using our technique, we produce corrected Herschel intensity maps for all 56 clouds and determine their line-of-sight average dust temperatures and optical depths from modified blackbody fits. The clouds have typical temperatures of ~14--20 K and optical depths of ~10^-5--10^-3. Across the whole sample, we find an anticorrelation between temperature and optical depth. We also find lower temperatures than what was measured in previous Herschel studies, which subtracted out a background level from their intensity maps to circumvent the zero-point correction. Accurate Herschel observations of clouds are key to obtaining accurate density and temperature profiles. To make such future analyses possible, intensity-corrected maps for all 56 clouds are publicly available in the electronic version. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

ID: 150217
Type: article
Authors: Sadavoy, Sarah I.; Myers, Philip C.; Stephens, Ian W.; Tobin, John; Kwon, Woojin; Segura-Cox, Dominique; Henning, Thomas; Commerçon, Benoît; Looney, Leslie
Abstract: We present high-resolution (∼35 au) ALMA Band 6 1.3 mm dust polarization observations of IRAS 16293. These observations spatially resolve the dust polarization across the two protostellar sources and toward the filamentary structures between them. The dust polarization and inferred magnetic field have complicated structures throughout the region. In particular, we find that the magnetic field is aligned parallel to three filamentary structures. We characterize the physical properties of the filamentary structure that bridges IRAS 16293A and IRAS 16293B and estimate a magnetic field strength of 23–78 mG using the Davis-Chandrasekhar-Fermi method. We construct a toy model for the bridge material assuming that the young stars dominate the mass and gravitational potential of the system. We find that the expected gas flow to each star is of comparable order to the Alfvén speed, which suggests that the field may be regulating the gas flow. We also find that the bridging material should be depleted in ∼10³ yr. If the bridge is part of the natal filament that formed the stars, then it must have accreted new material. Alternatively, the bridge could be a transient structure. Finally, we show that the 1.3 mm polarization morphology of the optically thick IRAS 16293B system is qualitatively similar to dust self-scattering. Based on similar polarization measurements at 6.9 mm, we propose that IRAS 16293B has produced a substantial population of large dust grains with sizes between 200 and 2000 μm.