Person: Goodman, Alyssa
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Goodman
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Alyssa
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Goodman, Alyssa
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Publication A Galactic-scale gas wave in the solar neighbourhood(Springer Science and Business Media LLC, 2020-01-07) Alves, Joao; Zucker, Catherine; Goodman, Alyssa; Speagle, Joshua; Meingast, Stefan; Robitaille, Thomas; Finkbeiner, Douglas; Schlafly, Edward; Green, GregoryFor the past 150 years, the prevailing view of the local Interstellar Medium (ISM) was based on a peculiarity known as the Gould's Belt (Herschel 1847, Gould 1874, Bobylev 2014, Palous 2016), an expanding ring of young stars, gas, and dust, tilted about 20 deg to the Galactic plane. Still, the physical relation between local gas clouds has remained practically unknown because the distance accuracy to clouds is of the same order or larger than their sizes (Maddalena 1986, Lombardi 2008, Schlafly 2014). With the advent of large photometric surveys (Chambers 2016) and the Gaia satellite astrometric survey (Brown 2018) this situation has changed (Zucker 2019) Here we report the 3-D structure of all local cloud complexes. We find a narrow and coherent 2.7 kpc arrangement of dense gas in the Solar neighborhood that contains many of the clouds thought to be associated with the Gould Belt. This finding is inconsistent with the notion that these clouds are part of a ring, disputing the Gould Belt model. The new structure comprises the majority of nearby star-forming regions, has an aspect ratio of about 1:20, and contains about 3 million solar masses of gas. Remarkably, the new structure appears to be undulating and its 3-D distribution is well described by a damped sinusoidal wave on the plane of the Milky Way, with an average period of about 2 kpc and a maximum amplitude of about 160 pc. Our results represent a first step in the revision of the local gas distribution and Galactic structure and offer a new, broader context to studies on the transformation of molecular gas into stars.Publication Physical Properties of Large-scale Galactic Filaments(American Astronomical Society, 2018-09-11) Zucker, Catherine; Battersby, Cara; Goodman, AlyssaThe characterization of our Galaxy's longest filamentary gas features has been the subject of several studies in recent years, producing not only a sizable sample of large-scale filaments, but also confusion as to whether all these features (e.g., "Bones," "Giant Molecular Filaments") are the same. They are not. We undertake the first standardized analysis of the physical properties (H2 column densities, dust temperatures, morphologies, radial column density profiles) and kinematics of large-scale filaments in the literature. We expand and improve upon prior analyses by using the same data sets, techniques, and spiral arm models to disentangle the filaments' inherent properties from selection criteria and methodology. Our results suggest that the myriad filament-finding techniques are uncovering different physical structures, with length (11–269 pc), width (1–40 pc), mass ($3\times {10}^{3}\,{M}_{\odot }\mbox{--}1.1\times {10}^{6}\,{M}_{\odot }$), aspect ratio (3:1–117:1), and high column density fraction (0.2%–100%) varying by over an order of magnitude across the sample of 45 filaments. We develop a radial profile-fitting code, RadFil, which is publicly available. We also perform a position–position–velocity (p–p–v) analysis on a subsample and find that while 60%–70% lie spatially in the plane of the Galaxy, only 30%–45% concurrently exhibit spatial and kinematic proximity to spiral arms. In a parameter space defined by aspect ratio, dust temperature, and column density, we broadly distinguish three filament categories, which could indicate different formation mechanisms or histories. Highly elongated "Bone-like" filaments show the most potential for tracing gross spiral structure (e.g., arms, spurs), while other categories could be large concentrations of molecular gas (giant molecular clouds, core complexes).Publication Droplets. II. Internal Velocity Structures and Potential Rotational Motions in Pressure-dominated Coherent Structures(American Astronomical Society, 2019-11-27) Rosolowsky, Erik; Chen, Hope; Pineda, Jaime; Offner, Stella; Goodman, Alyssa; Burkert, Andreas; Friesen, Rachel; Scibelli, Samantha; Shirley, YancyWe present an analysis of the internal velocity structures of the newly identified sub-0.1 pc coherent structures, droplets, in L1688 and B18. By fitting 2D linear velocity fields to the observed maps of velocity centroids, we determine the magnitudes of linear velocity gradients and examine the potential rotational motions that could lead to the observed velocity gradients. The results show that the droplets follow the same power-law relation between the velocity gradient and size found for larger-scale dense cores. Assuming that rotational motion giving rise to the observed velocity gradient in each core is a solid-body rotation of a rotating body with a uniform density, we derive the "net rotational motions" of the droplets. We find a ratio between rotational and gravitational energies, β, of ∼0.046 for the droplets, and when including both droplets and larger-scale dense cores, we find β∼0.039. We then examine the alignment between the velocity gradient and the major axis of each droplet, using methods adapted from the histogram of relative orientations (HRO) introduced by Soler et al. (2013). We find no definitive correlation between the directions of velocity gradients and the elongations of the cores. Lastly, we discuss physical processes other than rotation that may give rise to the observed velocity field.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 Galactic supernova remnant candidates discovered by THOR(EDP Sciences, 2017) Anderson, L. D.; Wang, Y.; Bihr, S.; Rugel, M.; Beuther, H.; Bigiel, F.; Churchwell, E.; Glover, S. C. O.; Goodman, Alyssa; Henning, Th.; Heyer, M.; Klessen, R. S.; Linz, H.; Longmore, Steven; Menten, K. M.; Ott, J.; Roy, N.; Soler, J. D.; Stil, J. M.; Urquhart, J. S.Context. There is a considerable deficiency in the number of known supernova remnants (SNRs) in the Galaxy compared to that expected. This deficiency is thought to be caused by a lack of sensitive radio continuum data. Searches for extended low-surface brightness radio sources may find new Galactic SNRs, but confusion with the much larger population of H II regions makes identifying such features challenging. SNRs can, however, be separated from H II regions using their significantly lower mid-infrared (MIR) to radio continuum intensity ratios. Aims: Our goal is to find missing SNR candidates in the Galactic disk by locating extended radio continuum sources that lack MIR counterparts. Methods: We use the combination of high-resolution 1-2 GHz continuum data from The HI, OH, Recombination line survey of the Milky Way (THOR) and lower-resolution VLA 1.4 GHz Galactic Plane Survey (VGPS) continuum data, together with MIR data from the Spitzer GLIMPSE, Spitzer MIPSGAL, and WISE surveys to identify SNR candidates. To ensure that the candidates are not being confused with H II regions, we exclude radio continuum sources from the WISE Catalog of Galactic H II Regions, which contains all known and candidate H II regions in the Galaxy. Results: We locate 76 new Galactic SNR candidates in the THOR and VGPS combined survey area of 67.4° > ℓ > 17.5°, | b | ≤ 1.25° and measure the radio flux density for 52 previously-known SNRs. The candidate SNRs have a similar spatial distribution to the known SNRs, although we note a large number of new candidates near ℓ ≃ 30°, the tangent point of the Scutum spiral arm. The candidates are on average smaller in angle compared to the known regions, 6.4' ± 4.7' versus 11.0' ± 7.8', and have lower integrated flux densities. Conclusions: The THOR survey shows that sensitive radio continuum data can discover a large number of SNR candidates, and that these candidates can be efficiently identified using the combination of radio and MIR data. If the 76 candidates are confirmed as true SNRs, for example using radio polarization measurements or by deriving radio spectral indices, this would more than double the number of known Galactic SNRs in the survey area. This large increase would still, however, leave a discrepancy between the known and expected SNR populations of about a factor of two.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 Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation(American Astronomical Society, 2017) Hull, Charles L. H.; Mocz, Philip; Burkhart, Blakesley; Goodman, Alyssa; Girart, Josep M.; Cortés, Paulo C.; Hernquist, Lars; Springel, Volker; Li, Zhi-Yun; Lai, Shih-PingWe report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140 au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (̃80,000 au) to disk (̃100 au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvénic (weakly magnetized) to sub-Alfvénic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ̃100 au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000 au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence—not the magnetic field—that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.Publication Star and Planet Formation through the WorldWide Telescope(Protostars and Planets VI, 2013) Goodman, AlyssaThe WorldWide Telescope is a Universe Information System that can display and access nearly all astronomical images and literature available online. In the five years since its initial release, the program has been downloaded more than 10 million times, but only a very tiny fraction of those downloads, so far, are by professional research astronomers. While WorldWide Telescope (WWT) is a fantastic tool for education and outreach (see wwtambassadors.org), it is also a tremendously valuable research tool, especially for putting results into their astronomical context. In this poster, we demonstrate how the WWT can be used to: 1) put surveys into context, on top of more than 40 different all-sky images, spanning the electromagnetic spectrum; 2) perform literature searches from the sky; 3) compare images and catalogs at different wavelenghts, on-the-fly in seconds; 4) show your own online data to the world, in an API that allows users to see it on the sky in their browsers; and 5) communicate to colleagues and learners about the sky using interactive Tours of your data and ideas. Examples of data distribution can be found at http://www.worldwidetelescope.org/COMPLETE/WWTCoverageTool.htm and a star-formation-related educational tour sample is at wwtambassadors.org/wwt/tours/dust-and-us.