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ALMA CN Zeeman Observations of AS 209: Limits on Magnetic Field Strength and Magnetically Driven Accretion RateHarrison, Rachel E.Looney, Leslie W.Stephens, Ian W.Li, Zhi-YunTeague, RichardCrutcher, Richard M.Yang, HaifengCox, Erin G.Fernández-López, ManuelShinnaga, HirokoDOI: info:10.3847/1538-4357/abd94ev. 908141
Harrison, Rachel E., Looney, Leslie W., Stephens, Ian W., Li, Zhi-Yun, Teague, Richard, Crutcher, Richard M., Yang, Haifeng, Cox, Erin G., Fernández-López, Manuel, and Shinnaga, Hiroko. 2021. "ALMA CN Zeeman Observations of AS 209: Limits on Magnetic Field Strength and Magnetically Driven Accretion Rate." The Astrophysical Journal 908:141. https://doi.org/10.3847/1538-4357/abd94e
ID: 159621
Type: article
Authors: Harrison, Rachel E.; Looney, Leslie W.; Stephens, Ian W.; Li, Zhi-Yun; Teague, Richard; Crutcher, Richard M.; Yang, Haifeng; Cox, Erin G.; Fernández-López, Manuel; Shinnaga, Hiroko
Abstract: While magnetic fields likely play an important role in driving the evolution of protoplanetary disks through angular momentum transport, observational evidence of magnetic fields has only been found in a small number of disks. Although dust continuum linear polarization has been detected in an increasing number of disks, its pattern is more consistent with that from dust scattering than from magnetically aligned grains in the vast majority of cases. Continuum linear polarization from dust grains aligned to a magnetic field can reveal information about the magnetic field's direction, but not its strength. On the other hand, observations of circular polarization in molecular lines produced by Zeeman splitting offer a direct measure of the line-of-sight magnetic field strength in disks. We present upper limits on the net toroidal and vertical magnetic field strengths in the protoplanetary disk AS 209 derived from Zeeman splitting observations of the CN 2-1 line. The 3σ upper limit on the net line-of-sight magnetic field strength in AS 209 is 5.0 mG on the redshifted side of the disk and 4.2 mG on the blueshifted side of the disk. Given the disk's inclination angle, we set a 3σ upper limit on the net toroidal magnetic field strength of 8.7 and 7.3 mG for the red and blue sides of the disk, respectively, and 6.2 and 5.2 mG on the net vertical magnetic field on the red and blue sides of the disk. If magnetic disk winds are a significant mechanism of angular momentum transport in the disk, magnetic fields of a strength close to the upper limits would be sufficient to drive accretion at the rate previously inferred for regions near the protostar.
Characterizing [C II] Line Emission in Massive Star-forming ClumpsJackson, James M.Allingham, DavidKillerby-Smith, NicholasWhitaker, J. ScottSmith, Howard A.Contreras, YanettGuzmán, Andrés E.Hogge, TaylorSanhueza, PatricioStephens, Ian W.DOI: info:10.3847/1538-4357/abba2ev. 90418
Jackson, James M., Allingham, David, Killerby-Smith, Nicholas, Whitaker, J. Scott, Smith, Howard A., Contreras, Yanett, Guzmán, Andrés E., Hogge, Taylor, Sanhueza, Patricio, and Stephens, Ian W. 2020. "Characterizing [C II] Line Emission in Massive Star-forming Clumps." The Astrophysical Journal 904:18. https://doi.org/10.3847/1538-4357/abba2e
ID: 158825
Type: article
Authors: Jackson, James M.; Allingham, David; Killerby-Smith, Nicholas; Whitaker, J. Scott; Smith, Howard A.; Contreras, Yanett; Guzmán, Andrés E.; Hogge, Taylor; Sanhueza, Patricio; Stephens, Ian W.
Abstract: Because the 157.74 µm [C II] line is the dominant coolant of star-forming regions, it is often used to infer the global star formation rates of galaxies. By characterizing the [C II] and far-infrared emission from nearby Galactic star-forming molecular clumps, it is possible to determine whether extragalactic [C II] emission arises from a large ensemble of such clumps, and whether [C II] is indeed a robust indicator of global star formation. We describe [C II] and far-infrared observations using the FIFI-LS instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA) airborne observatory toward four dense, high-mass, Milky Way clumps. Despite similar far-infrared luminosities, the [C II] to far-infrared luminosity ratio, ${L}_{[{\rm{C}}{\rm\small{II}}]}$ /LFIR, varies by a factor of at least 140 among these four clumps. In particular, for AGAL313.576+0.324, no [C II] line emission is detected despite a FIR luminosity of 24,000 ${L}_{\odot }$ . AGAL313.576+0.324 lies a factor of more than 100 below the empirical correlation curve between ${L}_{[{\rm{C}}{\rm\small{II}}]}$ /LFIR and ${S}_{\nu }(63\,\mu {\rm{m}})/{S}_{\nu }(158\,\mu {\rm{m}})$ found for galaxies. AGAL313.576+0.324 may be in an early evolutionary "protostellar" phase with insufficient ultraviolet flux to ionize carbon, or in a deeply embedded "'hypercompact" ${\rm{H}}\,{\rm\small{II}}$ region phase where dust attenuation of UV flux limits the region of ionized carbon to undetectably small volumes. Alternatively, its apparent lack of [C II] emission may arise from deep absorption of the [C II] line against the 158 µm continuum, or self-absorption of brighter line emission by foreground material, which might cancel or diminish any emission within the FIFI-LS instrument's broad spectral resolution element ( ${\rm{\Delta }}V\sim 250$ km s-1).
HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891Jones, Terry JayKim, Jin-AhDowell, C. DarrenMorris, Mark R.Pineda, Jorge L.Benford, Dominic J.Berthoud, MarcChuss, David T.Dale, Daniel A.Fissel, L. M.Goldsmith, Paul F.Hamilton, Ryan T.Hanany, ShaulHarper, Doyal A.Henning, Thomas K.Lazarian, AlexLooney, Leslie W.Michail, Joseph M.Novak, GilesSantos, Fabio P.Sheth, KartikSiah, JavadStacey, Gordon J.Staguhn, JohannesStephens, Ian W.Tassis, KonstantinosTrinh, Christopher Q.Vaillancourt, John E.Ward-Thompson, DerekWerner, MichaelWollack, Edward J.Zweibel, Ellen G.HAWC+ Science TeamDOI: info:10.3847/1538-3881/abada8v. 160167
Jones, Terry Jay, Kim, Jin-Ah, Dowell, C. Darren, Morris, Mark R., Pineda, Jorge L., Benford, Dominic J., Berthoud, Marc, Chuss, David T., Dale, Daniel A., Fissel, L. M., Goldsmith, Paul F., Hamilton, Ryan T., Hanany, Shaul, Harper, Doyal A., Henning, Thomas K., Lazarian, Alex, Looney, Leslie W., Michail, Joseph M., Novak, Giles, Santos, Fabio P., Sheth, Kartik, Siah, Javad, Stacey, Gordon J., Staguhn, Johannes, Stephens, Ian W. et al. 2020. "HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891." The Astronomical Journal 160:167. https://doi.org/10.3847/1538-3881/abada8
ID: 157604
Type: article
Authors: Jones, Terry Jay; Kim, Jin-Ah; Dowell, C. Darren; Morris, Mark R.; Pineda, Jorge L.; Benford, Dominic J.; Berthoud, Marc; Chuss, David T.; Dale, Daniel A.; Fissel, L. M.; Goldsmith, Paul F.; Hamilton, Ryan T.; Hanany, Shaul; Harper, Doyal A.; Henning, Thomas K.; Lazarian, Alex; Looney, Leslie W.; Michail, Joseph M.; Novak, Giles; Santos, Fabio P.; Sheth, Kartik; Siah, Javad; Stacey, Gordon J.; Staguhn, Johannes; Stephens, Ian W.; Tassis, Konstantinos; Trinh, Christopher Q.; Vaillancourt, John E.; Ward-Thompson, Derek; Werner, Michael; Wollack, Edward J.; Zweibel, Ellen G.; HAWC+ Science Team
Abstract: Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera Plus polarimetry at 154 μm is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 $\mathrm{MJy}\,{\mathrm{sr}}^{-1}$ are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891, the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.
Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?Karnath, N.Megeath, S. T.Tobin, J. J.Stutz, A.Li, Z. -YSheehan, P.Reynolds, N.Sadavoy, S.Stephens, Ian W.Osorio, M.Anglada, G.Díaz-Rodríguez, A. K.Cox, E.DOI: info:10.3847/1538-4357/ab659ev. 890129
Karnath, N., Megeath, S. T., Tobin, J. J., Stutz, A., Li, Z. -Y, Sheehan, P., Reynolds, N., Sadavoy, S., Stephens, Ian W., Osorio, M., Anglada, G., Díaz-Rodríguez, A. K., and Cox, E. 2020. "Detection of Irregular, Submillimeter Opaque Structures in the Orion Molecular Clouds: Protostars within 10,000 yr of Formation?." The Astrophysical Journal 890:129. https://doi.org/10.3847/1538-4357/ab659e
ID: 155822
Type: article
Authors: Karnath, N.; Megeath, S. T.; Tobin, J. J.; Stutz, A.; Li, Z. -Y; Sheehan, P.; Reynolds, N.; Sadavoy, S.; Stephens, Ian W.; Osorio, M.; Anglada, G.; Díaz-Rodríguez, A. K.; Cox, E.
Abstract: We report Atacama Large Millimeter/submillimeter Array and Very Large Array continuum observations that potentially identify the four youngest protostars in the Orion Molecular Clouds taken as part of the Orion VANDAM program. These are distinguished by bright, extended, irregular emission at 0.87 and 8 mm and are optically thick at 0.87 mm. These structures are distinct from the disk or point-like morphologies seen toward the other Orion protostars. The 0.87 mm emission implies temperatures of 41─170 K, requiring internal heating. The bright 8 mm emission implies masses of 0.5─1.2 M assuming standard dust opacity models. One source has a Class 0 companion, while another exhibits substructure indicating a companion candidate. Three compact outflows are detected, two of which may be driven by companions, with dynamical times of ∼300 to ∼1400 yr. The slowest outflow may be driven by a first hydrostatic core. These protostars appear to trace an early phase when the centers of collapsing fragments become optically thick to their own radiation and compression raises the gas temperature. This phase is thought to accompany the formation of hydrostatic cores. A key question is whether these structures are evolving on freefall times of ∼100 yr, or whether they are evolving on Kelvin─Helmholtz times of several thousand years. The number of these sources imply a lifetime of ∼6000 yr, in closer agreement with the Kelvin─Helmholtz time. In this case, rotational and/or magnetic support could be slowing the collapse.
Linear dust polarization during the embedded phase of protostar formation. Synthetic observations of bridge structuresKuffmeier, M.Reissl, S.Wolf, S.Stephens, IanCalcutt, H.DOI: info:10.1051/0004-6361/202038111v. 639A137
Kuffmeier, M., Reissl, S., Wolf, S., Stephens, Ian, and Calcutt, H. 2020. "Linear dust polarization during the embedded phase of protostar formation. Synthetic observations of bridge structures." Astronomy and Astrophysics 639:A137. https://doi.org/10.1051/0004-6361/202038111
ID: 157605
Type: article
Authors: Kuffmeier, M.; Reissl, S.; Wolf, S.; Stephens, Ian; Calcutt, H.
Abstract: Context. Measuring polarization from thermal dust emission can provide important constraints on the magnetic field structure around embedded protostars. However, interpreting the observations is challenging without models that consistently account for both the complexity of the turbulent protostellar birth environment and polarization mechanisms.
Aims: We aim to provide a better understanding of dust polarization maps of embedded protostars with a focus on bridge-like structures such as the structure observed toward the protostellar multiple system IRAS 16293-2422 by comparing synthetic polarization maps of thermal reemission with recent observations.
Methods: We analyzed the magnetic field morphology and properties associated with the formation of a protostellar multiple based on ideal magnetohydrodynamic 3D zoom-in simulations carried out with the RAMSES code. To compare the models with observations, we postprocessed a snapshot of a bridge-like structure that is associated with a forming triple star system with the radiative transfer code POLARIS and produced multiwavelength dust polarization maps.
Results: The typical density in the most prominent bridge of our sample is about 10-16 g cm-3, and the magnetic field strength in the bridge is about 1 to 2 mG. Inside the bridge, the magnetic field structure has an elongated toroidal morphology, and the dust polarization maps trace the complex morphology. In contrast, the magnetic field strength associated with the launching of asymmetric bipolar outflows is significantly more magnetized (~100 mG). At λ = 1.3 mm, and the orientation of the grains in the bridge is very similar for the case accounting for radiative alignment torques (RATs) compared to perfect alignment with magnetic field lines. However, the polarization fraction in the bridge is three times smaller for the RAT scenario than when perfect alignment is assumed. At shorter wavelength (λ ≲ 200 μm), however, dust polarization does not trace the magnetic field because other effects such as self-scattering and dichroic extinction dominate the orientation of the polarization.
Conclusions: Compared to the launching region of protostellar outflows, the magnetic field in bridge-like structures is weak. Synthetic dust polarization maps of ALMA Bands 6 and 7 (1.3 mm and 870 μm, respectively) can be used as a tracer of the complex morphology of elongated toroidal magnetic fields associated with bridges.
Probing the temperature structure of optically thick discs using polarized emission of aligned grainsLin, Zhe-Yu DanielLi, Zhi-YunYang, HaifengLooney, LeslieLee, Chin-FeiStephens, IanLai, Shih-PingDOI: info:10.1093/mnras/staa542v. 4934868–4883
Lin, Zhe-Yu Daniel, Li, Zhi-Yun, Yang, Haifeng, Looney, Leslie, Lee, Chin-Fei, Stephens, Ian, and Lai, Shih-Ping. 2020. "Probing the temperature structure of optically thick discs using polarized emission of aligned grains." Monthly Notices of the Royal Astronomical Society 493:4868– 4883. https://doi.org/10.1093/mnras/staa542
ID: 156326
Type: article
Authors: Lin, Zhe-Yu Daniel; Li, Zhi-Yun; Yang, Haifeng; Looney, Leslie; Lee, Chin-Fei; Stephens, Ian; Lai, Shih-Ping
Abstract: Polarized continuum emission from aligned grains in discs around young stellar objects can be used to probe the magnetic field, radiation anisotropy, or drift between dust and gas, depending on whether the non- spherical grains are aligned magnetically, radiatively, or mechanically. We show that it can also be used to probe another key disc property - the temperature gradient - along sightlines that are optically thick, independent of the grain alignment mechanism. We first illustrate the technique analytically using a simple 1D slab model, which yields an approximate formula that relates the polarization fraction to the temperature gradient with respect to the optical depth τ at the τ = 1 surface. The formula is then validated using models of stellar irradiated discs with and without accretion heating. The promises and challenges of the technique are illustrated with a number of Class 0 and I discs with ALMA dust polarization data, including NGC 1333 IRAS4A1, IRAS 16293B, BHB 07-11, L1527, HH 212, and HH 111. We find, in particular, that the sightlines passing through the near-side of a highly inclined disc trace different temperature gradient directions than those through the far-side, which can lead to a polarization orientation on the near-side that is orthogonal to that on the far-side, and that the HH 111 disc may be such a case. Our technique for probing the disc temperature gradient through dust polarization can complement other methods, particularly those using molecular lines.
Validating scattering-induced (sub)millimetre disc polarization through the spectral index, wavelength-dependent polarization pattern, and polarization spectrum: the case of HD 163296Lin, Zhe-Yu DanielLi, Zhi-YunYang, HaifengLooney, LeslieStephens, IanHull, Charles L. H.DOI: info:10.1093/mnras/staa1499v. 496169–181
Lin, Zhe-Yu Daniel, Li, Zhi-Yun, Yang, Haifeng, Looney, Leslie, Stephens, Ian, and Hull, Charles L. H. 2020. "Validating scattering-induced (sub)millimetre disc polarization through the spectral index, wavelength-dependent polarization pattern, and polarization spectrum: the case of HD 163296." Monthly Notices of the Royal Astronomical Society 496:169– 181. https://doi.org/10.1093/mnras/staa1499
ID: 157606
Type: article
Authors: Lin, Zhe-Yu Daniel; Li, Zhi-Yun; Yang, Haifeng; Looney, Leslie; Stephens, Ian; Hull, Charles L. H.
Abstract: A number of young circumstellar discs show strikingly ordered (sub)millimetre polarization orientations along the minor axis, which is strong evidence for polarization due to scattering by ∼0.1 mm-sized grains. To test this mechanism further, we model the ALMA dust continuum and polarization data of HD 163296 using radmc-3d. We find that scattering by grains with a maximum size of 90 μm simultaneously reproduces the polarization observed at Band 7 and the unusually low spectral index (α ∼ 1.5) between Bands 7 and 6 in the optically thick inner disc as a result of more efficient scattering at the shorter wavelength. The low spectral index of ∼2.5 inferred for the optically thin gaps is reproduced by the same grains, as a result of telescope beam averaging of the gaps (with an intrinsic α ∼ 4) and their adjacent optically thick rings (where α ≲ 2). The tension between the grain sizes inferred from polarization and spectral index disappears because the low α values do not require large mm-sized grains. In addition, the polarization fraction has a unique azimuthal variation: higher along the major axis than the minor axis in the gaps, but vice versa in the rings. We find a rapidly declining polarization spectrum (with p ∝ λ-3 approximately) in the gaps, which becomes flattened or even inverted towards short wavelengths in the optically thick rings. These contrasting behaviours in the rings and gaps provide further tests for scattering-induced polarization via resolved multiwavelength observations.
SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068Lopez-Rodriguez, EnriqueDowell, C. DarrenJones, Terry J.Harper, Doyal A.Berthoud, MarcChuss, DavidDale, Daniel A.Guerra, Jordan A.Hamilton, Ryan T.Looney, Leslie W.Michail, Joseph M.Nikutta, RobertNovak, GilesSantos, Fabio P.Sheth, KartikSiah, JavadStaguhn, JohannesStephens, Ian W.Tassis, KonstantinosTrinh, Christopher Q.Ward-Thompson, DerekWerner, MichaelWollack, Edward J.Zweibel, Ellen G.HAWC+Science TeamDOI: info:10.3847/1538-4357/ab5849v. 88866
Lopez-Rodriguez, Enrique, Dowell, C. Darren, Jones, Terry J., Harper, Doyal A., Berthoud, Marc, Chuss, David, Dale, Daniel A., Guerra, Jordan A., Hamilton, Ryan T., Looney, Leslie W., Michail, Joseph M., Nikutta, Robert, Novak, Giles, Santos, Fabio P., Sheth, Kartik, Siah, Javad, Staguhn, Johannes, Stephens, Ian W., Tassis, Konstantinos, Trinh, Christopher Q., Ward-Thompson, Derek, Werner, Michael, Wollack, Edward J., Zweibel, Ellen G., and HAWC+Science Team. 2020. "SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068." The Astrophysical Journal 888:66. https://doi.org/10.3847/1538-4357/ab5849
ID: 155689
Type: article
Authors: Lopez-Rodriguez, Enrique; Dowell, C. Darren; Jones, Terry J.; Harper, Doyal A.; Berthoud, Marc; Chuss, David; Dale, Daniel A.; Guerra, Jordan A.; Hamilton, Ryan T.; Looney, Leslie W.; Michail, Joseph M.; Nikutta, Robert; Novak, Giles; Santos, Fabio P.; Sheth, Kartik; Siah, Javad; Staguhn, Johannes; Stephens, Ian W.; Tassis, Konstantinos; Trinh, Christopher Q.; Ward-Thompson, Derek; Werner, Michael; Wollack, Edward J.; Zweibel, Ellen G.; HAWC+Science Team
Abstract: We report the first detection of galactic spiral structure by means of thermal emission from magnetically aligned dust grains. Our 89 μm polarimetric imaging of NGC 1068 with the High-resolution Airborne Wideband Camera/Polarimeter (HAWC+) on NASAs Stratospheric Observatory for Infrared Astronomy (SOFIA) also sheds light on magnetic field structure in the vicinity of the galaxy's inner-bar and active galactic nucleus (AGN). We find correlations between the 89 μm magnetic field vectors and other tracers of spiral arms, and a symmetric polarization pattern as a function of the azimuthal angle arising from the projection and inclination of the disk field component in the plane of the sky. The observations can be fit with a logarithmic spiral model with pitch angle of {16.9}-2.8+2.7\circ and a disk inclination of 48° ± 2°. We infer that the bulk of the interstellar medium from which the polarized dust emission originates is threaded by a magnetic field that closely follows the spiral arms. Inside the central starburst disk (<1.6 kpc), the degree of polarization is found to be lower than for far-infrared sources in the Milky Way, and has minima at the locations of most intense star formation near the outer ends of the inner-bar. Inside the starburst ring, the field direction deviates from the model, becoming more radial along the leading edges of the inner-bar. The polarized flux and dust temperature peak ∼3″─6″ NE of the AGN at the location of a bow shock between the AGN outflow and the surrounding interstellar medium, but the AGN itself is weakly polarized (<1%) at both 53 and 89 μm.
Four annular structures in a protostellar disk less than 500,000 years oldSegura-Cox, DominiqueSchmiedeke, AnikaPineda, Jaime E.Stephens, Ian W.Fernández-López, ManuelLooney, Leslie W.Caselli, PaolaLi, Zhi-YunMundy, Lee G.Kwon, WoojinHarris, Robert J.DOI: info:10.1038/s41586-020-2779-6v. 586No. 7828228–231
Segura-Cox, Dominique, Schmiedeke, Anika, Pineda, Jaime E., Stephens, Ian W., Fernández-López, Manuel, Looney, Leslie W., Caselli, Paola, Li, Zhi-Yun, Mundy, Lee G., Kwon, Woojin, and Harris, Robert J. 2020. "Four annular structures in a protostellar disk less than 500,000 years old." Nature 586 (7828):228– 231. https://doi.org/10.1038/s41586-020-2779-6
ID: 157178
Type: article
Authors: Segura-Cox, Dominique; Schmiedeke, Anika; Pineda, Jaime E.; Stephens, Ian W.; Fernández-López, Manuel; Looney, Leslie W.; Caselli, Paola; Li, Zhi-Yun; Mundy, Lee G.; Kwon, Woojin; Harris, Robert J.
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar DisksTobin, John J.Sheehan, Patrick D.Megeath, S. ThomasDíaz-Rodríguez, Ana KarlaOffner, Stella S. R.Murillo, Nadia M.van 't Hoff, Merel L. R.van Dishoeck, Ewine F.Osorio, MayraAnglada, GuillemFurlan, EliseStutz, Amelia M.Reynolds, NickalasKarnath, NicoleFischer, William J.Persson, MagnusLooney, Leslie W.Li, Zhi-YunStephens, IanChandler, Claire J.Cox, ErinDunham, Michael M.Tychoniec, ŁukaszKama, MihkelKratter, KaitlinKounkel, MarinaMazur, BrianMaud, LukePatel, LisaPerez, LauraSadavoy, Sarah I.Segura-Cox, DominiqueSharma, RajeebStephenson, BrianWatson, Dan M.Wyrowski, FriedrichDOI: info:10.3847/1538-4357/ab6f64v. 890130
Tobin, John J., Sheehan, Patrick D., Megeath, S. Thomas, Díaz-Rodríguez, Ana Karla, Offner, Stella S. R., Murillo, Nadia M., van 't Hoff, Merel L. R., van Dishoeck, Ewine F., Osorio, Mayra, Anglada, Guillem, Furlan, Elise, Stutz, Amelia M., Reynolds, Nickalas, Karnath, Nicole, Fischer, William J., Persson, Magnus, Looney, Leslie W., Li, Zhi-Yun, Stephens, Ian, Chandler, Claire J., Cox, Erin, Dunham, Michael M., Tychoniec, Łukasz, Kama, Mihkel, Kratter, Kaitlin et al. 2020. "The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. II. A Statistical Characterization of Class 0 and Class I Protostellar Disks." The Astrophysical Journal 890:130. https://doi.org/10.3847/1538-4357/ab6f64
ID: 156217
Type: article
Authors: Tobin, John J.; Sheehan, Patrick D.; Megeath, S. Thomas; Díaz-Rodríguez, Ana Karla; Offner, Stella S. R.; Murillo, Nadia M.; van 't Hoff, Merel L. R.; van Dishoeck, Ewine F.; Osorio, Mayra; Anglada, Guillem; Furlan, Elise; Stutz, Amelia M.; Reynolds, Nickalas; Karnath, Nicole; Fischer, William J.; Persson, Magnus; Looney, Leslie W.; Li, Zhi-Yun; Stephens, Ian; Chandler, Claire J.; Cox, Erin; Dunham, Michael M.; Tychoniec, Łukasz; Kama, Mihkel; Kratter, Kaitlin; Kounkel, Marina; Mazur, Brian; Maud, Luke; Patel, Lisa; Perez, Laura; Sadavoy, Sarah I.; Segura-Cox, Dominique; Sharma, Rajeeb; Stephenson, Brian; Watson, Dan M.; Wyrowski, Friedrich
Abstract: We have conducted a survey of 328 protostars in the Orion molecular clouds with the Atacama Large Millimeter/submillimeter Array at 0.87 mm at a resolution of ∼0"1 (40 au), including observations with the Very Large Array at 9 mm toward 148 protostars at a resolution of ∼0"08 (32 au). This is the largest multiwavelength survey of protostars at this resolution by an order of magnitude. We use the dust continuum emission at 0.87 and 9 mm to measure the dust disk radii and masses toward the Class 0, Class I, and flat-spectrum protostars, characterizing the evolution of these disk properties in the protostellar phase. The mean dust disk radii for the Class 0, Class I, and flat-spectrum protostars are ${44.9}_{-3.4}^{+5.8}$ , ${37.0}_{-3.0}^{+4.9}$ , and ${28.5}_{-2.3}^{+3.7}$ au, respectively, and the mean protostellar dust disk masses are 25.9 ${}_{-4.0}^{+7.7}$ , ${14.9}_{-2.2}^{+3.8}$ , ${11.6}_{-1.9}^{+3.5}$ ${M}_{\oplus }$ , respectively. The decrease in dust disk masses is expected from disk evolution and accretion, but the decrease in disk radii may point to the initial conditions of star formation not leading to the systematic growth of disk radii or that radial drift is keeping the dust disk sizes small. At least 146 protostellar disks (35% of 379 detected 0.87 mm continuum sources plus 42 nondetections) have disk radii greater than 50 au in our sample. These properties are not found to vary significantly between different regions within Orion. The protostellar dust disk mass distributions are systematically larger than those of Class II disks by a factor of >4, providing evidence that the cores of giant planets may need to at least begin their formation during the protostellar phase.
Revealing the dust grain size in the inner envelope of the Class I protostar Per-emb-50Agurto-Gangas, C.Pineda, J. E.Szűcs, L.Testi, L.Tazzari, M.Miotello, A.Caselli, P.Dunham, M.Stephens, Ian W.Bourke, T. L.DOI: info:10.1051/0004-6361/201833666v. 623A147
Agurto-Gangas, C., Pineda, J. E., Szűcs, L., Testi, L., Tazzari, M., Miotello, A., Caselli, P., Dunham, M., Stephens, Ian W., and Bourke, T. L. 2019. "Revealing the dust grain size in the inner envelope of the Class I protostar Per-emb-50." Astronomy and Astrophysics 623:A147. https://doi.org/10.1051/0004-6361/201833666
ID: 155421
Type: article
Authors: Agurto-Gangas, C.; Pineda, J. E.; Szűcs, L.; Testi, L.; Tazzari, M.; Miotello, A.; Caselli, P.; Dunham, M.; Stephens, Ian W.; Bourke, T. L.
Abstract: Context. A good constraint of when the growth of dust grains from sub-micrometer to millimeter sizes occurs, is crucial for planet formation models. This provides the first step towards the production of pebbles and planetesimals in protoplanetary disks. Currently, it is well established that Class II objects have large dust grains. However, it is not clear when in the star formation process this grain growth occurs. Aims: We use multi-wavelength millimeter observations of a Class I protostar to obtain the spectral index of the observed flux densities αmm of the unresolved disk and the surrounding envelope. Our goal is to compare our observational results with visibility modeling at both, 1.3 and 2.7 mm simultaneously. Methods: We present data from NOEMA at 2.7 mm and SMA at 1.3 mm of the Class I protostar, Per- emb-50. We model the dust emission with a variety of parametric and radiative-transfer models to deduce the grain size from the observed emission spectral index. Results: We find a spectral index in the envelope of Per-emb-50 of αenv = 3.3 ± 0.3, similar to the typical ISM values. The radiative-transfer modeling of the source confirms this value of αenv with the presence of dust with a amax ≤ 100 μm. Additionally, we explore the backwarming effect, where we find that the envelope structure affects the millimeter emission of the disk. Conclusions: Our results reveal grains with a maximum size no larger than 100 μm in the inner envelope of the Class I protostar Per-emb-50, providing an interesting case to test the universality of millimeter grain growth expected in these sources. Based on observations carried out under project number S16AT with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).
The Mass Evolution of Protostellar Disks and Envelopes in the Perseus Molecular CloudAndersen, Bridget C.Stephens, Ian W.Dunham, Michael M.Pokhrel, RiwajJørgensen, Jes K.Frimann, SørenSegura-Cox, DominiqueMyers, Philip C.Bourke, Tyler L.Tobin, John J.Tychoniec, ŁukaszDOI: info:10.3847/1538-4357/ab05c7v. 87354
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., and Tychoniec, Łukasz. 2019. "The Mass Evolution of Protostellar Disks and Envelopes in the Perseus Molecular Cloud." The Astrophysical Journal 873:54. https://doi.org/10.3847/1538-4357/ab05c7
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.
HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1Chuss, David T.Andersson, B. -GBally, JohnDotson, Jessie L.Dowell, C. DarrenGuerra, Jordan A.Harper, Doyal A.Houde, MartinJones, Terry JayLazarian, A.Lopez Rodriguez, EnriqueMichail, Joseph M.Morris, Mark R.Novak, GilesSiah, JavadStaguhn, JohannesVaillancourt, John E.Volpert, C. G.Werner, MichaelWollack, Edward J.Benford, Dominic J.Berthoud, MarcCox, Erin G.Crutcher, RichardDale, Daniel A.Fissel, L. M.Goldsmith, Paul F.Hamilton, Ryan T.Hanany, ShaulHenning, Thomas K.Looney, Leslie W.Moseley, S. HarveySantos, Fabio P.Stephens, IanTassis, KonstantinosTrinh, Christopher Q.Van Camp, EricWard-Thompson, DerekHAWC + Science TeamDOI: info:10.3847/1538-4357/aafd37v. 872187
Chuss, David T., Andersson, B. -G, Bally, John, Dotson, Jessie L., Dowell, C. Darren, Guerra, Jordan A., Harper, Doyal A., Houde, Martin, Jones, Terry Jay, Lazarian, A., Lopez Rodriguez, Enrique, Michail, Joseph M., Morris, Mark R., Novak, Giles, Siah, Javad, Staguhn, Johannes, Vaillancourt, John E., Volpert, C. G., Werner, Michael, Wollack, Edward J., Benford, Dominic J., Berthoud, Marc, Cox, Erin G., Crutcher, Richard, Dale, Daniel A. et al. 2019. "HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1." The Astrophysical Journal 872:187. https://doi.org/10.3847/1538-4357/aafd37
ID: 155451
Type: article
Authors: Chuss, David T.; Andersson, B. -G; Bally, John; Dotson, Jessie L.; Dowell, C. Darren; Guerra, Jordan A.; Harper, Doyal A.; Houde, Martin; Jones, Terry Jay; Lazarian, A.; Lopez Rodriguez, Enrique; Michail, Joseph M.; Morris, Mark R.; Novak, Giles; Siah, Javad; Staguhn, Johannes; Vaillancourt, John E.; Volpert, C. G.; Werner, Michael; Wollack, Edward J.; Benford, Dominic J.; Berthoud, Marc; Cox, Erin G.; Crutcher, Richard; Dale, Daniel A.; Fissel, L. M.; Goldsmith, Paul F.; Hamilton, Ryan T.; Hanany, Shaul; Henning, Thomas K.; Looney, Leslie W.; Moseley, S. Harvey; Santos, Fabio P.; Stephens, Ian; Tassis, Konstantinos; Trinh, Christopher Q.; Van Camp, Eric; Ward-Thompson, Derek; HAWC + Science Team
Abstract: We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 μm at angular resolutions of 5″, 8″, 14″, and 19″ for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the "hourglass" configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin- Neugebauer/Kleinman-Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.
Formation of high-mass stars in an isolated environment in the Large Magellanic CloudHarada, RyoheiOnishi, ToshikazuTokuda, KazukiZahorecz, SaroltaHughes, AnnieMeixner, MargaretSewiło, MartaIndebetouw, RemyNayak, OmnarayaniFukui, YasuoTachihara, KengoTsuge, KisetstuKawamura, AkikoSaigo, KazuyaWong, TonyBernard, Jean-PhilippeStephens, Ian W.DOI: info:10.1093/pasj/psz011v. 7144
Harada, Ryohei, Onishi, Toshikazu, Tokuda, Kazuki, Zahorecz, Sarolta, Hughes, Annie, Meixner, Margaret, Sewiło, Marta, Indebetouw, Remy, Nayak, Omnarayani, Fukui, Yasuo, Tachihara, Kengo, Tsuge, Kisetstu, Kawamura, Akiko, Saigo, Kazuya, Wong, Tony, Bernard, Jean-Philippe, and Stephens, Ian W. 2019. "Formation of high-mass stars in an isolated environment in the Large Magellanic Cloud." Publications of the Astronomical Society of Japan 71:44. https://doi.org/10.1093/pasj/psz011
ID: 155236
Type: article
Authors: Harada, Ryohei; Onishi, Toshikazu; Tokuda, Kazuki; Zahorecz, Sarolta; Hughes, Annie; Meixner, Margaret; Sewiło, Marta; Indebetouw, Remy; Nayak, Omnarayani; Fukui, Yasuo; Tachihara, Kengo; Tsuge, Kisetstu; Kawamura, Akiko; Saigo, Kazuya; Wong, Tony; Bernard, Jean-Philippe; Stephens, Ian W.
Abstract: The aim of this study is to characterize the distribution and basic properties of the natal gas associated with high-mass young stellar objects (YSOs) in isolated environments in the Large Magellanic Cloud. High-mass stars usually form in giant molecular clouds (GMCs) as part of a young stellar cluster, but some OB stars are observed far from GMCs. By examining the spatial coincidence between the high-mass YSOs and 12CO (J = 1-0) emission detected by NANTEN and Mopra observations, we selected ten high-mass YSOs that are located away from any of the NANTEN clouds but are detected by the Mopra pointed observations. The ALMA observations revealed that a compact molecular cloud whose mass is a few thousand solar masses or smaller is associated with the high-mass YSOs, which indicates that these compact clouds are the sites of high-mass star formation. The high density and high temperature throughout the clouds are explained by the severe photodissociation of CO due to the lower metallicity than in the Galaxy. The star formation efficiency ranges from several to as high as ∼40%, indicating efficient star formation in these environments. The enhanced turbulence may be a cause of the efficient star formation therein, as judged from the gas velocity information and the association with the lower density gas.
Dust Polarization in Four Protoplanetary Disks at 3 mm: Further Evidence of Multiple OriginsHarrison, Rachel E.Looney, Leslie W.Stephens, Ian W.Li, Zhi-YunYang, HaifengKataoka, AkimasaHarris, Robert J.Kwon, WoojinMuto, TakayukiMomose, MunetakeDOI: info:10.3847/2041-8213/ab1e46v. 877L2
Harrison, Rachel E., Looney, Leslie W., Stephens, Ian W., Li, Zhi-Yun, Yang, Haifeng, Kataoka, Akimasa, Harris, Robert J., Kwon, Woojin, Muto, Takayuki, and Momose, Munetake. 2019. "Dust Polarization in Four Protoplanetary Disks at 3 mm: Further Evidence of Multiple Origins." The Astrophysical Journal 877:L2. https://doi.org/10.3847/2041-8213/ab1e46
ID: 155152
Type: article
Authors: Harrison, Rachel E.; Looney, Leslie W.; Stephens, Ian W.; Li, Zhi-Yun; Yang, Haifeng; Kataoka, Akimasa; Harris, Robert J.; Kwon, Woojin; Muto, Takayuki; Momose, Munetake
Abstract: We present polarimetric observations of four Class II protoplanetary disks (DG Tau, Haro 6-13, RY Tau, and MWC 480) taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at 3 mm. The polarization morphologies observed fall into two distinct categories: azimuthal polarization (DG Tau and Haro 6-13) and polarization parallel to the disk minor axis (RY Tau and MWC 480). The mechanisms responsible for disk polarization at millimeter and submillimeter wavelengths are currently under debate. In this Letter, we investigate two mechanisms capable of producing polarized dust emission in disks: self-scattering and grain alignment to the radiation anisotropy. The polarization morphologies of DG Tau and Haro 6-13 are broadly consistent with that expected from radiation alignment (though radiative alignment still does not account for all of the features seen in these disks), while RY Tau and MWC 480 are more consistent with self-scattering. Such a variation in the polarized morphology may provide evidence of dust grain size differences between the sources.
The Interaction between the Supernova Remnant W41 and the Filamentary Infrared Dark Cloud G23.33-0.30Hogge, Taylor G.Jackson, James M.Allingham, DavidGuzman, Andres E.Killerby-Smith, NicholasKraemer, Kathleen E.Sanhueza, PatricioStephens, Ian W.Whitaker, J. ScottDOI: info:10.3847/1538-4357/ab5180v. 88779
Hogge, Taylor G., Jackson, James M., Allingham, David, Guzman, Andres E., Killerby-Smith, Nicholas, Kraemer, Kathleen E., Sanhueza, Patricio, Stephens, Ian W., and Whitaker, J. Scott. 2019. "The Interaction between the Supernova Remnant W41 and the Filamentary Infrared Dark Cloud G23.33-0.30." The Astrophysical Journal 887:79. https://doi.org/10.3847/1538-4357/ab5180
ID: 154525
Type: article
Authors: Hogge, Taylor G.; Jackson, James M.; Allingham, David; Guzman, Andres E.; Killerby-Smith, Nicholas; Kraemer, Kathleen E.; Sanhueza, Patricio; Stephens, Ian W.; Whitaker, J. Scott
Abstract: G23.33-0.30 is a 600 M infrared dark molecular filament that exhibits large NH3 velocity dispersions (σ ∼ 8 km s−1) and bright, narrow NH3(3, 3) line emission. We have probed G23.33-0.30 at the (3, 3) line emission. We have probed G23.33-0.30 at the 3(3, 3) line is emitted by four rare NH3(3, 3) masers, which are excited by a large-scale shock impacting the filament. G23.33-0.30 also displays a velocity gradient along its length, a velocity discontinuity across its width, shock- tracing SiO(5─4) emission extended throughout the filament, and broad turbulent line widths in NH3(1, 1) through (6, 6), CS(5─4), and SiO(5─4), as well as an increased NH3 rotational temperature (T rot) and velocity dispersion (σ) associated with the shocked, blueshifted component. The correlations among T rot, σ, and V LSR imply that the shock is accelerating, heating, and adding turbulent energy to the filament gas. Given G23.33-0.30's location within the giant molecular cloud G23.0-0.4, we speculate that the shock and NH3(3, 3) masers originated from the supernova remnant (SNR) W41, which exhibits additional evidence of an interaction with G23.0-0.4. We have also detected the 1.3 mm dust continuum emission from at least three embedded molecular cores associated with G23.33-0.30. Although the cores have moderate gas masses (M = 7─10 M ), their large virial parameters (α = 4─9) suggest that they will not collapse to form stars. The turbulent line widths of the (α > 1) cores may indicate negative feedback due to the SNR shock.
Asymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global CollapseJackson, James M.Whitaker, J. ScottRathborne, J. M.Foster, J. B.Contreras, Y.Sanhueza, PatricioStephens, Ian W.Longmore, S. N.Allingham, DavidDOI: info:10.3847/1538-4357/aaef84v. 8705
Jackson, James M., Whitaker, J. Scott, Rathborne, J. M., Foster, J. B., Contreras, Y., Sanhueza, Patricio, Stephens, Ian W., Longmore, S. N., and Allingham, David. 2019. "Asymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global Collapse." The Astrophysical Journal 870:5. https://doi.org/10.3847/1538-4357/aaef84
ID: 155463
Type: article
Authors: Jackson, James M.; Whitaker, J. Scott; Rathborne, J. M.; Foster, J. B.; Contreras, Y.; Sanhueza, Patricio; Stephens, Ian W.; Longmore, S. N.; Allingham, David
Abstract: Using molecular line data from the Millimetre Astronomy Legacy Team 90 GHz Survey, we have searched the optically thick HCO+ (1-0) line for the "blue asymmetry" spectroscopic signature of infall motion in a large sample of high-mass, dense molecular clumps observed to be at different evolutionary stages of star cluster formation according to their mid-infrared appearance. To quantify the degree of the line asymmetry, we measure the asymmetry parameter A=\displaystyle \frac{{I}blue}-{I}red}}{{I}blue}+{I}red}}, the fraction of the integrated intensity that lies to the blueshifted side of the systemic velocity determined from the optically thin tracer N2H+ (1-0). For a sample of 1093 sources, both the mean and median of A are positive (A=0.083+/- 0.010 and 0.065 ± 0.009, respectively) with high statistical significance, and a majority of sources (a fraction of 0.607 ± 0.015 of the sample) show positive values of A, indicating a preponderance of blue asymmetric profiles over red asymmetric profiles. Two other measures, the local slope of the line at the systemic velocity and the δv parameter of Mardones et al. (1997), also show an overall blue asymmetry for the sample, but with smaller statistical significance. This blue asymmetry indicates that these high-mass clumps are predominantly undergoing gravitational collapse. The blue asymmetry is larger (A∼ 0.12) for the earliest evolutionary stages (quiescent, protostellar, and compact H II region) than for the later H II region (A∼ 0.06) and photodissociation region (A∼ 0) classifications.
SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic WindJones, Terry JayDowell, C. DarrenLopez Rodriguez, EnriqueZweibel, Ellen G.Berthoud, MarcChuss, David T.Goldsmith, Paul F.Hamilton, Ryan T.Hanany, ShaulHarper, Doyal A.Lazarian, AlexLooney, Leslie W.Michail, Joseph M.Morris, Mark R.Novak, GilesSantos, Fabio P.Sheth, KartikStacey, Gordon J.Staguhn, JohannesStephens, Ian W.Tassis, KonstantinosTrinh, Christopher Q.Volpert, C. G.Werner, MichaelWollack, Edward J.HAWC+ Science TeamDOI: info:10.3847/2041-8213/aaf8b9v. 870L9
Jones, Terry Jay, Dowell, C. Darren, Lopez Rodriguez, Enrique, Zweibel, Ellen G., Berthoud, Marc, Chuss, David T., Goldsmith, Paul F., Hamilton, Ryan T., Hanany, Shaul, Harper, Doyal A., Lazarian, Alex, Looney, Leslie W., Michail, Joseph M., Morris, Mark R., Novak, Giles, Santos, Fabio P., Sheth, Kartik, Stacey, Gordon J., Staguhn, Johannes, Stephens, Ian W., Tassis, Konstantinos, Trinh, Christopher Q., Volpert, C. G., Werner, Michael, Wollack, Edward J. et al. 2019. "SOFIA Far-infrared Imaging Polarimetry of M82 and NGC 253: Exploring the Supergalactic Wind." The Astrophysical Journal 870:L9. https://doi.org/10.3847/2041-8213/aaf8b9
ID: 155460
Type: article
Authors: Jones, Terry Jay; Dowell, C. Darren; Lopez Rodriguez, Enrique; Zweibel, Ellen G.; Berthoud, Marc; Chuss, David T.; Goldsmith, Paul F.; Hamilton, Ryan T.; Hanany, Shaul; Harper, Doyal A.; Lazarian, Alex; Looney, Leslie W.; Michail, Joseph M.; Morris, Mark R.; Novak, Giles; Santos, Fabio P.; Sheth, Kartik; Stacey, Gordon J.; Staguhn, Johannes; Stephens, Ian W.; Tassis, Konstantinos; Trinh, Christopher Q.; Volpert, C. G.; Werner, Michael; Wollack, Edward J.; HAWC+ Science Team
Abstract: We present far-infrared polarimetry observations of M82 at 53 and 154 μm and NGC 253 at 89 μm, which were taken with High-resolution Airborne Wideband Camera-plus (HAWC+) in polarimetry mode on the Stratospheric Observatory for Infrared Astronomy. The polarization of M82 at 53 μm clearly shows a magnetic field geometry perpendicular to the disk in the hot dust emission. For M82 the polarization at 154 μm shows a combination of field geometry perpendicular to the disk in the nuclear region, but closer to parallel to the disk away from the nucleus. The fractional polarization at 53 μm (154 μm) ranges from 7% (3%) off nucleus to 0.5% (0.3%) near the nucleus. A simple interpretation of the observations of M82 invokes a massive polar outflow, dragging the field along, from a region ∼700 pc in diameter that has entrained some of the gas and dust, creating a vertical field geometry seen mostly in the hotter (53 μm) dust emission. This outflow sits within a larger disk with a more typical planar geometry that more strongly contributes to the cooler (154 μm) dust emission. For NGC 253, the polarization at 89 μm is dominated by a planar geometry in the tilted disk, with weak indication of a vertical geometry above and below the plane from the nucleus. The polarization observations of NGC 253 at 53 μm were of a insufficient signal-to-noise ratio for a detailed analysis.
KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular CloudsKeown, Jareddi Francesco, JamesRosolowsky, ErikSingh, AyushiFigura, CharlesKirk, HelenAnderson, L. D.Chen, Michael Chun-YuanElia, DavideFriesen, RachelGinsburg, AdamMarston, A.Pezzuto, StefanoSchisano, EugenioBontemps, SylvainCaselli, PaolaLiu, Hong-LiLongmore, StevenMotte, FrédériqueMyers, Philip C.Offner, Stella S. R.Sanhueza, PatricioSchneider, NicolaStephens, IanUrquhart, JamesDOI: info:10.3847/1538-4357/ab3e76v. 8844
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, and Urquhart, James. 2019. "KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds." The Astrophysical Journal 884:4. https://doi.org/10.3847/1538-4357/ab3e76
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.
Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2Kwon, WoojinStephens, Ian W.Tobin, John J.Looney, Leslie W.Li, Zhi-Yunvan der Tak, Floris F. S.Crutcher, Richard M.DOI: info:10.3847/1538-4357/ab24c8v. 87925
Kwon, Woojin, Stephens, Ian W., Tobin, John J., Looney, Leslie W., Li, Zhi-Yun, van der Tak, Floris F. S., and Crutcher, Richard M. 2019. "Highly Ordered and Pinched Magnetic Fields in the Class 0 Protobinary System L1448 IRS 2." The Astrophysical Journal 879:25. https://doi.org/10.3847/1538-4357/ab24c8
ID: 155123
Type: article
Authors: Kwon, Woojin; Stephens, Ian W.; Tobin, John J.; Looney, Leslie W.; Li, Zhi-Yun; van der Tak, Floris F. S.; Crutcher, Richard M.
Abstract: We have carried out polarimetric observations with the Atacama Large Millimeter/submillimeter Array toward the Class 0 protostellar system L1448 IRS 2, which is a protobinary embedded within a flattened, rotating structure, and for which a hint of a central disk has been suggested, but whose magnetic fields are aligned with the bipolar outflow on the cloud core scale. Our high-sensitivity and high- resolution (∼100 au) observations show a clear hourglass magnetic field morphology centered on the protostellar system, but the central pattern is consistent with a toroidal field indicative of a circumstellar disk; though, other interpretations are also possible, including field lines dragged by an equatorial accretion flow into a configuration parallel to the midplane. If a relatively large disk does exist, it would suggest that the magnetic braking catastrophe is averted in this system, not through a large misalignment between the magnetic and rotation axes, but rather through some other mechanisms, such as nonideal magnetohydrodynamic effects and/or turbulence. We have also found a relationship of decreasing polarization fractions with intensities and the various slopes of this relationship can be understood as multiple polarization mechanisms and/or depolarization from a changing field morphology. In addition, we found a prominent clumpy depolarization strip crossing the center perpendicular to the bipolar outflow. Moreover, a rough estimate of the magnetic field strength indicates that the field is strong enough to hinder formation of a rotationally supported disk, which is inconsistent with the feature of a central toroidal field. This also suggests that early disk formation can happen even in young stellar objects with a strong primordial magnetic field.