Person: Myers, Philip
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Myers
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Philip
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Myers, Philip
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Publication The Green Bank Ammonia Survey: Observations of Hierarchical Dense Gas Structures in Cepheus-L1251(American Astronomical Society, 2017) Keown, Jared; Di Francesco, James; Kirk, Helen; Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Ginsburg, Adam; Offner, Stella S. R.; Caselli, Paola; Alves, Felipe; Chacón-Tanarro, Ana; Punanova, Anna; Redaelli, Elena; Seo, Young Min; Matzner, Christopher D.; Chen, Michael Chun-Yuan; Goodman, Alyssa; Chen, Hope; Shirley, Yancy; Singh, Ayushi; Arce, Hector G.; Martin, Peter; Myers, PhilipWe use Green Bank Ammonia Survey observations of NH3 (1, 1) and (2, 2) emission with 32″ FWHM resolution from a ∼10 pc2 portion of the Cepheus-L1251 molecular cloud to identify hierarchical dense gas structures. Our dendrogram analysis of the NH3 data results in 22 top-level structures, which reside within 13 lower-level parent structures. The structures are compact (0.01 {pc}≲ {R}{eff}≲ 0.1 {pc}) and are spatially correlated with the highest H2 column density portions of the cloud. We also compare the ammonia data to a catalog of dense cores identified by higher-resolution (18.″2 FWHM) Herschel Space Observatory observations of dust continuum emission from Cepheus-L1251. Maps of kinetic gas temperature, velocity dispersion, and NH3 column density, derived from detailed modeling of the NH3 data, are used to investigate the stability and chemistry of the ammonia-identified and Herschel-identified structures. We show that the dust and dense gas in the structures have similar temperatures, with median T dust and T K measurements of 11.7 ± 1.1 K and 10.3 ± 2.0 K, respectively. Based on a virial analysis, we find that the ammonia-identified structures are gravitationally dominated, yet may be in or near a state of virial equilibrium. Meanwhile, the majority of the Herschel-identified dense cores appear to be not bound by their own gravity and instead confined by external pressure. CCS (20 − 10) and HC5N (9-8) emission from the region reveal broader line widths and centroid velocity offsets when compared to the NH3 (1, 1) emission in some cases, likely due to these carbon-based molecules tracing the turbulent outer layers of the dense cores.Publication The Green Bank Ammonia Survey: Dense Cores under Pressure in Orion A(American Astronomical Society, 2017) Kirk, Helen; Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Offner, Stella S. R.; Matzner, Christopher D.; Myers, Philip; Di Francesco, James; Caselli, Paola; Alves, Felipe O.; Chacón-Tanarro, Ana; Chen, Hope; Chen, Michael Chun-Yuan; Keown, Jared; Punanova, Anna; Seo, Young Min; Shirley, Yancy; Ginsburg, Adam; Hall, Christine; Singh, Ayushi; Arce, Héctor G.; Goodman, Alyssa; Martin, Peter; Redaelli, ElenaWe use data on gas temperature and velocity dispersion from the Green Bank Ammonia Survey and core masses and sizes from the James Clerk Maxwell Telescope Gould Belt Survey to estimate the virial states of dense cores within the Orion A molecular cloud. Surprisingly, we find that almost none of the dense cores are sufficiently massive to be bound when considering only the balance between self-gravity and the thermal and non-thermal motions present in the dense gas. Including the additional pressure binding imposed by the weight of the ambient molecular cloud material and additional smaller pressure terms, however, suggests that most of the dense cores are pressure-confined.Publication Alignment between Protostellar Outflows and Filamentary Structure(American Astronomical Society, 2017) Stephens, Ian; Dunham, Michael M.; Myers, Philip; Pokhrel, Riwaj; Sadavoy, Sarah; Vorobyov, Eduard I.; Tobin, John; Pineda, Jaime E.; Offner, Stella S. R.; Lee, Katherine I.; Kristensen, Lars E.; Jørgensen, Jes K.; Goodman, Alyssa; Bourke, Tyler; Arce, Héctor G.; Plunkett, Adele L.We present new Submillimeter Array (SMA) observations of CO(2-1) outflows toward young, embedded protostars in the Perseus molecular cloud as part of the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. For 57 Perseus protostars, we characterize the orientation of the outflow angles and compare them with the orientation of the local filaments as derived from Herschel observations. We find that the relative angles between outflows and filaments are inconsistent with purely parallel or purely perpendicular distributions. Instead, the observed distribution of outflow-filament angles are more consistent with either randomly aligned angles or a mix of projected parallel and perpendicular angles. A mix of parallel and perpendicular angles requires perpendicular alignment to be more common by a factor of ̃3. Our results show that the observed distributions probably hold regardless of the protostar’s multiplicity, age, or the host core’s opacity. These observations indicate that the angular momentum axis of a protostar may be independent of the large-scale structure. We discuss the significance of independent protostellar rotation axes in the general picture of filament-based star formation.Publication The Green Bank Ammonia Survey: First Results of NH3 Mapping of the Gould Belt(American Astronomical Society, 2017) Friesen, Rachel K.; Pineda, Jaime E.; Rosolowsky, Erik; Alves, Felipe; Chacón-Tanarro, Ana; Chen, Hope; Chen, Michael Chun-Yuan; Di Francesco, James; Keown, Jared; Kirk, Helen; Punanova, Anna; Seo, Youngmin; Shirley, Yancy; Ginsburg, Adam; Hall, Christine; Offner, Stella S. R.; Singh, Ayushi; Arce, Héctor G.; Caselli, Paola; Goodman, Alyssa; Martin, Peter G.; Matzner, Christopher; Myers, Philip; Redaelli, Elena; undefined, undefinedWe present an overview of the first data release (DR1) and first-look science from the Green Bank Ammonia Survey (GAS). GAS is a Large Program at the Green Bank Telescope to map all Gould Belt star-forming regions with {A}{{V}}≳ 7 mag visible from the northern hemisphere in emission from NH3 and other key molecular tracers. This first release includes the data for four regions in the Gould Belt clouds: B18 in Taurus, NGC 1333 in Perseus, L1688 in Ophiuchus, and Orion A North in Orion. We compare the NH3 emission to dust continuum emission from Herschel and find that the two tracers correspond closely. We find that NH3 is present in over 60% of the lines of sight with {A}{{V}}≳ 7 mag in three of the four DR1 regions, in agreement with expectations from previous observations. The sole exception is B18, where NH3 is detected toward ̃40% of the lines of sight with {A}{{V}}≳ 7 mag. Moreover, we find that the NH3 emission is generally extended beyond the typical 0.1 pc length scales of dense cores. We produce maps of the gas kinematics, temperature, and NH3 column densities through forward modeling of the hyperfine structure of the NH3 (1, 1) and (2, 2) lines. We show that the NH3 velocity dispersion, {σ }v, and gas kinetic temperature, T K, vary systematically between the regions included in this release, with an increase in both the mean value and the spread of {σ }v and T K with increasing star formation activity. The data presented in this paper are publicly available (https://dataverse.harvard.edu/dataverse/GAS_DR1).Publication Misalignment of Outflow Axes in the Proto-Multiple Systems in Perseus(American Astronomical Society, 2016) Lee, Katherine I.; Dunham, Michael M.; Myers, Philip; Arce, Héctor G.; Bourke, Tyler; Goodman, Alyssa; Jørgensen, Jes K.; Kristensen, Lars E.; Offner, Stella S. R.; Pineda, Jaime; Tobin, John J.; Vorobyov, Eduard I.We investigate the alignment between outflow axes in nine of the youngest binary/multiple systems in the Perseus Molecular Cloud. These systems have typical member spacing larger than 1000 au. For outflow identification, we use 12CO(2-1) and 12CO(3-2) data from a large survey with the Submillimeter Array: Mass Assembly of Stellar Systems and their Evolution with the SMA. The distribution of outflow orientations in the binary pairs is consistent with random or preferentially anti-aligned distributions, demonstrating that these outflows are misaligned. This result suggests that these systems are possibly formed in environments where the distribution of angular momentum is complex and disordered, and these systems do not come from the same co-rotating structures or from an initial cloud with aligned vectors of angular momentum.Publication Mass Assembly of Stellar Systems and Their Evolution With the Sma (Masses). Multiplicity and the Physical Environment in L1448n(IOP Publishing, 2015) Lee, Katherine I.; Dunham, Michael; Myers, Philip; Tobin, John J.; Kristensen, Lars E.; Pineda, Jaime E.; Vorobyov, Eduard I.; Offner, Stella S. R.; Arce, Héctor G.; Li, Zhi-Yun; Bourke, Tyler L.; Jørgensen, Jes K.; Goodman, Alyssa; Sadavoy, Sarah I.; Chandler, Claire J.; Harris, Robert J.; Kratter, Kaitlin; Looney, Leslie W.; Melis, Carl; Perez, Laura M.; Segura-Cox, DominiqueWe present continuum and molecular line observations at 230 and 345 GHz from the Submillimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project "Mass Assembly of Stellar Systems and their Evolution with the SMA." Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C18O ($J=2\to 1$), 13CO ($J=2\to 1$), and HCO+ ($J=4\to 3$), and have offsets with N2D+ ($J=3\to 2$) peaks. High angular resolution data from a complementary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to <100 AU. Velocity gradients in each source obtained from two-dimensional fits to the SMA C18O emission are found to be perpendicular to within 20° of the outflow directions as revealed by 12CO ($J=2\to 1$). We have observed that Sources B and NW with multiplicity have higher densities than Source A without multiplicity. This suggests that thermal Jeans fragmentation can be relevant in the fragmentation process. However, we have not observed a difference in the ratio between rotational and gravitational energy between sources with and without multiplicity. We also have not observed a trend between non-thermal velocity dispersions and the level of fragmentation. Our study has provided the first direct and comprehensive comparison between multiplicity and core properties in low-mass protostars, although based on small number statistics.