Publication Search Results

ID: 159646
Type: article
Authors: Leisawitz, David; Amatucci, Edward; Allen, Lynn; Arenberg, Jonathan; Armus, Lee; Battersby, Cara; Bauer, James; Beaman, Bobby G.; Bell, Ray; Beltran, Porfirio; Benford, Dominic; Bergin, Edward; Bolognese, Jeffrey; Bradford, Charles M.; Bradley, Damon; Burgarella, Denis; Carey, Sean; Chi, J. D. (Danny); Cooray, Asantha; Corsetti, James; D'Asto, Thomas; De Beck, Elvire; Denis, Kevin; Derkacz, Christopher; Dewell, Larry; DiPirro, Michael; Earle, Cleland P.; East, Matthew; Edgington, Samantha; Ennico, Kimberly; Fantano, Louis; Feller, Greg; Folta, David; Fortney, Jonathan; Gavares, Benjamin J.; Generie, Joseph; Gerin, Maryvonne; Granger, Zachary; Greene, Thomas P.; Griffiths, Alex; Harpole, George; Harvey, Keith; Helmich, Frank; Hilliard, Lawrence; Howard, Joseph; Jacoby, Michael; Jamil, Anisa; Jamison, Tracee; Kaltenegger, Lisa; Kataria, Tiffany; Knight, John S.; Knollenberg, Perry; Lawrence, Charles; Lightsey, Paul; Lipscy, Sarah; Mamajek, Eric; Martins, Gregory; Mather, John C.; Meixner, Margaret; Melnick, Gary; Milam, Stefanie; Mooney, Ted; Moseley, Samuel H.; Narayanan, Desika; Neff, Susan; Nguyen, Thanh; Nordt, Alison; Olson, Jeffrey; Padgett, Deborah; Petach, Michael; Petro, Susanna; Pohner, John; Pontoppidan, Klaus; Pope, Alexandra; Ramspacker, Daniel; Rao, Alison; Roellig, Thomas; Sakon, Itsuki; Sandin, Carly; Sandstrom, Karin; Scott, Douglas; Seals, Len; Sheth, Kartik; Sokolsky, Lawrence M.; Staguhn, Johannes; Steeves, John; Stevenson, Kevin; Stoneking, Eric; Su, Kate; Tajdaran, Kiarash; Tompkins, Steven; Vieira, Joaquin; Webster, Cassandra; Wiedner, Martina C.; Wright, Edward L.; Wu, Chi; Zmuidzinas, Jonas
Abstract: The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20 μm wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250 μm. The Origins Survey Spectrometer will cover wavelengths from 25 to 588 μm, making wide-area and deep spectroscopic surveys with spectral resolving power R ∼ 300, and pointed observations at R ∼ 40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Origins' natural background-limited sensitivity.

ID: 159645
Type: article
Authors: Leisawitz, David; Amatucci, Edward; Allen, Lynn; Arenberg, Jonathan; Armus, Lee; Battersby, Cara; Bauer, James; Bell, Ray; Benford, Dominic; Bergin, Edward; Booth, Jeffrey T.; Bradford, Charles M.; Bradley, Damon; Carey, Sean; Carter, Ruth; Cooray, Asantha; Corsetti, James; Dewell, Larry; DiPirro, Michael; Drake, Bret G.; East, Matthew; Ennico, Kimberly; Feller, Greg; Flores, Angel; Fortney, Jonathan; Granger, Zachary; Greene, Thomas P.; Howard, Joseph; Kataria, Tiffany; Knight, John S.; Lawrence, Charles; Lightsey, Paul; Mather, John C.; Meixner, Margaret; Melnick, Gary; McMurtry, Craig; Milam, Stefanie; Moseley, Samuel H.; Narayanan, Desika; Nordt, Alison; Padgett, Deborah; Pontoppidan, Klaus; Pope, Alexandra; Rafanelli, Gerard; Redding, David C.; Rieke, George; Roellig, Thomas; Sakon, Itsuki; Sandin, Carly; Sandstrom, Karin; Sengupta, Anita; Sheth, Kartik; Sokolsky, Lawrence M.; Staguhn, Johannes; Steeves, John; Stevenson, Kevin; Su, Kate; Vieira, Joaquin; Webster, Cassandra; Wiedner, Martina; Wright, Edward L.; Wu, Chi; Yanatsis, David; Zmuidzinas, Jonas; Origins Space Telescope Mission Concept and Study Team
Abstract: The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the universe today? How do habitable planets form? How common are life-bearing worlds? We describe how Origins was designed to answer these alluring questions. We discuss the key decisions taken by the Origins mission concept study team, the rationale for those choices, and how they led through an exploratory design process to the Origins baseline mission concept. To understand the concept solution space, we studied two distinct mission concepts and descoped the second concept, aiming to maximize science per dollar and hit a self-imposed cost target. We report on the study approach and describe the concept evolution. The resulting baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. The chosen architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch. The cryo-thermal system design leverages James Webb Space Telescope technology and experience.

ID: 159432
Type: article
Authors: Lu, Xing; Li, Shanghuo; Ginsburg, Adam; Longmore, Steven N.; Kruijssen, J. M. Diederik; Walker, Daniel L.; Feng, Siyi; Zhang, Qizhou; Battersby, Cara; Pillai, Thushara; Mills, Elisabeth A. C.; Kauffmann, Jens; Cheng, Yu; Inutsuka, Shu-ichiro
Abstract: We observe 1.3 mm spectral lines at 2000 au resolution toward four massive molecular clouds in the Central Molecular Zone (CMZ) of the Galaxy to investigate their star formation activities. We focus on several potential shock tracers that are usually abundant in protostellar outflows, including SiO, SO, CH₃OH, H₂CO, HC₃N, and HNCO. We identify 43 protostellar outflows, including 37 highly likely ones and 6 candidates. The outflows are found toward both known high-mass star-forming cores and less massive, seemingly quiescent cores, while 791 out of the 834 cores identified based on the continuum do not have detected outflows. The outflow masses range from less than 1 M_⊙ to a few tens of M_⊙, with typical uncertainties of a factor of 70. We do not find evidence of disagreement between relative molecular abundances in these outflows and in nearby analogs such as the well-studied L1157 and NGC 7538S outflows. The results suggest that (i) protostellar accretion disks driving outflows ubiquitously exist in the CMZ environment, (ii) the large fraction of candidate starless cores is expected if these clouds are at very early evolutionary phases, with a caveat on the potential incompleteness of the outflows, (iii) high-mass and low-mass star formation is ongoing simultaneously in these clouds, and (iv) current data do not show evidence of a difference between the shock chemistry in the outflows that determines the molecular abundances in the CMZ environment and in nearby clouds.

ID: 159648
Type: article
Authors: Meixner, Margaret; Cooray, Asantha; Leisawitz, David T.; Staguhn, Johannes G.; Armus, Lee; Battersby, Cara; Bauer, James; Benford, Dominic; Bergin, Edwin; Bradford, Charles Matt; Burgarella, Denis; Carey, Sean; De Beck, Elvire; Ennico-Smith, Kimberly; Fortney, Jonathan J.; Gerin, Maryvonne; Helmich, Frank P.; Kataria, Tiffany; Mamajek, Eric E.; Melnick, Gary J.; Milam, Stefanie N.; Moseley, Samuel Harvey; Narayanan, Desika; Neff, Susan G.; Padgett, Deborah; Pontoppidan, Klaus; Pope, Alexandra; Roellig, Thomas L.; Sakon, Itsuki; Sandstrom, Karin; Scott, Douglas; Sheth, Kartik; Stevenson, Kevin B.; Su, Kate Y.; Vieira, Joaquin; Wiedner, Martina C.; Wright, Edward; Zmuidzinas, Jonas; Origins Study Team
Abstract: The Origins Space Telescope (Origins) concept is designed to investigate the creation and dispersal of elements essential to life, the formation of planetary systems, and the transport of water to habitable worlds and the atmospheres of exoplanets around nearby K- and M-dwarfs to identify potentially habitable-and even inhabited-worlds. These science priorities are aligned with NASA's three major astrophysics science goals: How does the Universe work? How did we get here? and Are we alone? We briefly describe the science case that arose from the astronomical community and the science traceability matrix for Origins. The science traceability matrix prescribes the design of Origins and demonstrates that it will address the key science questions motivated by the science case.

ID: 159261
Type: article
Authors: Walker, Daniel L.; Longmore, Steven N.; Bally, John; Ginsburg, Adam; Kruijssen, J. M. Diederik; Zhang, Qizhou; Henshaw, Jonathan D.; Lu, Xing; Alves, João; Barnes, Ashley T.; Battersby, Cara; Beuther, Henrik; Contreras, Yanett A.; Gómez, Laura; Ho, Luis C.; Jackson, James M.; Kauffmann, Jens; Mills, Elisabeth A. C.; Pillai, Thushara
Abstract: G0.253+0.016, aka 'the Brick', is one of the most massive (>10⁵ M_⊙) and dense (>10⁴ cm^-3) molecular clouds in the Milky Way's Central Molecular Zone. Previous observations have detected tentative signs of active star formation, most notably a water maser that is associated with a dust continuum source. We present ALMA Band 6 observations with an angular resolution of 0.13 arcsec (1000 AU) towards this 'maser core' and report unambiguous evidence of active star formation within G0.253+0.016. We detect a population of eighteen continuum sources (median mass ∼2 M_⊙), nine of which are driving bi-polar molecular outflows as seen via SiO (5-4) emission. At the location of the water maser, we find evidence for a protostellar binary/multiple with multidirectional outflow emission. Despite the high density of G0.253+0.016, we find no evidence for high-mass protostars in our ALMA field. The observed sources are instead consistent with a cluster of low-to-intermediate-mass protostars. However, the measured outflow properties are consistent with those expected for intermediate-to-high-mass star formation. We conclude that the sources are young and rapidly accreting, and may potentially form intermediate- and high-mass stars in the future. The masses and projected spatial distribution of the cores are generally consistent with thermal fragmentation, suggesting that the large-scale turbulence and strong magnetic field in the cloud do not dominate on these scales, and that star formation on the scale of individual protostars is similar to that in Galactic disc environments.

ID: 159647
Type: article
Authors: Wiedner, Martina C.; Aalto, Susanne; Amatucci, Edward G.; Baryshev, Andrey; Battersby, Cara; Belitsky, Victor; Bergin, Edwin A.; Borgo, Bruno; Carter, Ruth C.; Caux, Emmanuel; Cooray, Asantha; Corsetti, James A.; De Beck, Elvire; Delorme, Yan; Desmaris, Vincent; Dipirro, Michael J.; Ellison, Brian; Di Giorgio, Anna M.; Eggens, Martin; Gallego, Juan-Daniel; Gerin, Maryvonne; Goldsmith, Paul F.; Goldstein, Christophe; Helmich, Frank; Herpin, Fabrice; Hills, Richard E.; Hogerheijde, Michiel R.; Hunt, Leslie K.; Jellema, Willem; Keizer, Geert; Krieg, Jean-Michel; Kroes, Gabby; Laporte, Philippe; Laurens, André; Leisawitz, David T.; Lis, Dariusz C.; Martins, Gregory E.; Mehdi, Imran; Meixner, Margaret; Melnick, Gary; Milam, Stefanie N.; Neufeld, David A.; Nguyen Tuong, Napoléon; Plume, René; Pontoppidan, Klaus M.; Quertier-Dagorn, Benjamin; Risacher, Christophe; Staguhn, Johannes G.; Tong, Edward; Viti, Serena; Wyrowski, Friedrich
Abstract: The Heterodyne Receiver for Origins (HERO) is the first detailed study of a heterodyne focal plane array receiver for space applications. HERO gives the Origins Space Telescope the capability to observe at very high spectral resolution (R = 10⁷) over an unprecedentedly large far-infrared (FIR) wavelengths range (111 to 617 μm) with high sensitivity, with simultaneous dual polarization and dual-frequency band operation. The design is based on prior successful heterodyne receivers, such as Heterodyne Instrument for the Far-Infrared /Herschel, but surpasses it by one to two orders of magnitude by exploiting the latest technological developments. Innovative components are used to keep the required satellite resources low and thus allowing for the first time a convincing design of a large format heterodyne array receiver for space. HERO on Origins is a unique tool to explore the FIR universe and extends the enormous potential of submillimeter astronomical spectroscopy into new areas of astronomical research.

ID: 157805
Type: article
Authors: Battersby, Cara; Keto, Eric; Walker, Daniel; Barnes, Ashley; Callanan, Daniel; Ginsburg, Adam; Hatchfield, H. Perry; Henshaw, Jonathan; Kauffmann, Jens; Kruijssen, J. M. Diederik; Longmore, Steven N.; Lu, Xing; Mills, Elisabeth A. C.; Pillai, Thushara; Zhang, Qizhou; Bally, John; Butterfield, Natalie; Contreras, Yanett A.; Ho, Luis C.; Ott, Jürgen; Patel, Nimesh; Tolls, Volker
Abstract: We present an overview of the CMZoom survey and its first data release. CMZoom is the first blind, high-resolution survey of the Central Molecular Zone (CMZ; the inner 500 pc of the Milky Way) at wavelengths sensitive to the pre-cursors of high-mass stars. CMZoom is a 550 hr Large Program on the Submillimeter Array that mapped at 1.3 mm all of the gas and dust in the CMZ above a molecular hydrogen column density of 10²³ cm^-2 at a resolution of ∼3″ (0.1 pc). In this paper, we focus on the 1.3 mm dust continuum and its data release, but also describe CMZoom spectral line data which will be released in a forthcoming publication. While CMZoom detected many regions with rich and complex substructure, its key result is an overall deficit in compact substructures on 0.1-2 pc scales (the compact dense gas fraction: CDGF). In comparison with clouds in the Galactic disk, the CDGF in the CMZ is substantially lower, despite having much higher average column densities. CMZ clouds with high CDGFs are well-known sites of active star formation. The inability of most gas in the CMZ to form compact substructures is likely responsible for the dearth of star formation in the CMZ, surprising considering its high density. The factors responsible for the low CDGF are not yet understood but are plausibly due to the extreme environment of the CMZ, having far-reaching ramifications for our understanding of the star formation process across the cosmos.

ID: 158746
Type: article
Authors: Hatchfield, H. Perry; Battersby, Cara; Keto, Eric; Walker, Daniel; Barnes, Ashley; Callanan, Daniel; Ginsburg, Adam; Henshaw, Jonathan D.; Kauffmann, Jens; Kruijssen, J. M. Diederik; Longmore, Steve N.; Lu, Xing; Mills, Elisabeth A. C.; Pillai, Thushara; Zhang, Qizhou; Bally, John; Butterfield, Natalie; Contreras, Yanett A.; Ho, Luis C.; Ott, Jürgen; Patel, Nimesh; Tolls, Volker
Abstract: In this paper we present the CMZoom survey's catalog of compact sources (₂) = 10²³ cm^-2) of the innermost 500 pc of the Galaxy in the 1.3 mm dust continuum. We generate both a robust catalog designed to reduce spurious source detections, and a second catalog with higher completeness, both generated using a pruned dendrogram. In the robust catalog, we report 285 compact sources, or 816 in the high-completeness catalog. These sources have effective radii between 0.04 and 0.4 pc, and are the potential progenitors of star clusters. The masses for both catalogs are dominated by the Sagittarius B2 cloud complex, where masses are likely unreliable due to free-free contamination, uncertain dust temperatures, and line-of-sight confusion. Given the survey selection and completeness, we predict that our robust catalog accounts for more than ˜99% of compact substructure capable of forming high-mass stars in the CMZ. This catalog provides a crucial foundation for future studies of high-mass star formation in the Galactic Center.

ID: 156957
Type: article
Authors: Lu, Xing; Cheng, Yu; Ginsburg, Adam; Longmore, Steven N.; Kruijssen, J. M. Diederik; Battersby, Cara; Zhang, Qizhou; Walker, Daniel L.
Abstract: We report Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 continuum observations of 2000 au resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy. To study gas fragmentation, we use the dendrogram method to identify cores as traced by the dust continuum emission. The four clouds exhibit different fragmentation states at the observed resolution despite having similar masses at the cloud scale (∼1-5 pc). Assuming a constant dust temperature of 20 K, we construct core mass functions of the clouds and find a slightly top-heavy shape as compared to the canonical initial mass function, but we note several significant uncertainties that may affect this result. The characteristic spatial separation between the cores as identified by the minimum spanning tree method, ∼10⁴ au, and the characteristic core mass, 1-7 ${M}_{\odot }$ , are consistent with predictions of thermal Jeans fragmentation. The three clouds showing fragmentation may be forming OB associations (stellar mass ∼10³ ${M}_{\odot }$ ). None of the four clouds under investigation seem to be currently able to form massive star clusters like the Arches and the Quintuplet (≳10⁴ ${M}_{\odot }$ ), but they may form such clusters by further gas accretion onto the cores.

ID: 158025
Type: article
Authors: Wang, Y.; Beuther, H.; Schneider, N.; Meidt, S. E.; Linz, H.; Ragan, S.; Zucker, Catherine; Battersby, C.; Soler, J. D.; Schinnerer, E.; Bigiel, F.; Colombo, D.; Henning, Th
Abstract: Context. Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large (≳50 pc) and massive (≳10⁵ M_☉) filaments, know as giant molecular filaments (GMFs), may be linked to Galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. Yet our physical understanding of GMFs is still poor.
Aims: We investigate the dense gas properties of one GMF, with the ultimate goal of connecting these dense gas tracers with star formation processes in the GMF.
Methods: We imaged one entire GMF located at l ~ 52-54° longitude, GMF54 (~68 pc long), in the empirical dense gas tracers using the HCN(1-0), HNC(1-0), and HCO⁺(1-0) lines, and their ¹³C isotopologue transitions, as well as the N₂H⁺(1-0) line. We studied the dense gas distribution, the column density probability density functions (N-PDFs), and the line ratios within the GMF.
Results: The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to ¹³CO(1-0). We constructed the N-PDFs of H₂ for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log-log representation, and the HCO⁺ N-PDF has the flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star-forming and photon-dominated regions have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N₂H⁺/¹³CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except Ultraluminous Infrared Galaxies.
Conclusions: As the largest coherent cold gaseous structure in our Milky Way, GMFs, are outstanding candidates for connecting studies of star formation on Galactic and extragalactic scales. By analyzing a complete map of the dense gas in a GMF we have found that: (1) the dense gas N-PDFs appear flatter in more evolved regions and steeper in younger regions, and (2) its integrated dense gas intensity ratios are similar to those of nearby galaxies.
Datacubes and integrated intensity maps are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/641/A53

ID: 151872
Type: article
Authors: Henshaw, J. D.; Ginsburg, A.; Haworth, T. J.; Longmore, S. N.; Kruijssen, J. M. D.; Mills, E. A. C.; Sokolov, V.; Walker, D. L.; Barnes, A. T.; Contreras, Y.; Bally, J.; Battersby, C.; Beuther, H.; Butterfield, N.; Dale, J. E.; Henning, T.; Jackson, J. M.; Kauffmann, J.; Pillai, T.; Ragan, S.; Riener, M.; Zhang, Qizhou
Abstract: In this paper we provide a comprehensive description of the internal dynamics of G0.253+0.016 (a.k.a. `the Brick'); one of the most massive and dense molecular clouds in the Galaxy to lack signatures of widespread star formation. As a potential host to a future generation of high-mass stars, understanding largely quiescent molecular clouds like G0.253+0.016 is of critical importance. In this paper, we reanalyse Atacama Large Millimeter Array cycle 0 HNCO J = 4(0, 4) - 3(0, 3) data at 3 mm, using two new pieces of software that we make available to the community. First, SCOUSEPY, a Python implementation of the spectral line fitting algorithm SCOUSE. Secondly, ACORNS (Agglomerative Clustering for ORganising Nested Structures), a hierarchical n-dimensional clustering algorithm designed for use with discrete spectroscopic data. Together, these tools provide an unbiased measurement of the line-of-sight velocity dispersion in this cloud, σ _{v_{ los}, 1D}=4.4± 2.1 km s<sup>-1</sup>, which is somewhat larger than predicted by velocity dispersion-size relations for the central molecular zone (CMZ). The dispersion of centroid velocities in the plane of the sky are comparable, yielding σ _{v_{ los}, 1D}/σ _{v_{ pos}, 1D}˜ 1.2± 0.3. This isotropy may indicate that the line-of-sight extent of the cloud is approximately equivalent to that in the plane of the sky. Combining our kinematic decomposition with radiative transfer modelling, we conclude that G0.253+0.016 is not a single, coherent, and centrally condensed molecular cloud; `the Brick' is not a brick. Instead, G0.253+0.016 is a dynamically complex and hierarchically structured molecular cloud whose morphology is consistent with the influence of the orbital dynamics and shear in the CMZ.

ID: 151198
Type: article
Authors: Kruijssen, J. M. D.; Dale, J. E.; Longmore, S. N.; Walker, D. L.; Henshaw, J. D.; Jeffreson, S. M. R.; Petkova, M. A.; Ginsburg, A.; Barnes, A. T.; Battersby, C. D.; Immer, K.; Jackson, J. M.; Keto, Eric R.; Krieger, N.; Mills, E. A. C.; Sánchez-Monge, Á.; Schmiedeke, A.; Suri, S. T.; Zhang, Qizhou
Abstract: The evolution of molecular clouds in galactic centres is thought to differ from that in galactic discs due to a significant influence of the external gravitational potential. We present a set of numerical simulations of molecular clouds orbiting on the 100-pc stream of the Central Molecular Zone (the central {˜ }500 {pc} of the Galaxy) and characterize their morphological and kinematic evolution in response to the background potential and eccentric orbital motion. We find that the clouds are shaped by strong shear and torques, by tidal and geometric deformation, and by their passage through the orbital pericentre. Within our simulations, these mechanisms control cloud sizes, aspect ratios, position angles, filamentary structure, column densities, velocity dispersions, line-of-sight velocity gradients, spin angular momenta, and kinematic complexity. By comparing these predictions to observations of clouds on the Galactic Centre `dust ridge', we find that our simulations naturally reproduce a broad range of key observed morphological and kinematic features, which can be explained in terms of well-understood physical mechanisms. We argue that the accretion of gas clouds on to the central regions of galaxies, where the rotation curve turns over and the tidal field is fully compressive, is accompanied by transformative dynamical changes to the clouds, leading to collapse and star formation. This can generate an evolutionary progression of cloud collapse with a common starting point, which either marks the time of accretion on to the tidally compressive region or of the most recent pericentre passage. Together, these processes may naturally produce the synchronized starbursts observed in numerous (extra)galactic nuclei.

ID: 154700
Type: article
Authors: Lu, Xing; Mills, Elisabeth A. C.; Ginsburg, Adam; Walker, Daniel L.; Barnes, Ashley T.; Butterfield, Natalie; Henshaw, Jonathan D.; Battersby, Cara; Kruijssen, J. M. Diederik; Longmore, Steven N.; Zhang, Qizhou; Bally, John; Kauffmann, Jens; Ott, Jürgen; Rickert, Matthew; Wang, Ke
Abstract: We present new observations of the C-band continuum emission and masers to assess high-mass (>8 {M}_☉ ) star formation at early evolutionary phases in the inner 200 pc of the Central Molecular Zone (CMZ) of the Galaxy. The continuum observation is complete to free-free emission from stars above 10-11 {M}_☉ in 91% of the covered area. We identify 104 compact sources in the continuum emission, among which five are confirmed ultracompact H II regions, 12 are candidates of ultracompact H II regions, and the remaining 87 sources are mostly massive stars in clusters, field stars, evolved stars, pulsars, extragalactic sources, or of unknown nature that is to be investigated. We detect class II CH₃OH masers at 23 positions, among which six are new detections. We confirm six known H₂CO masers in two high-mass star-forming regions and detect two new H₂CO masers toward the Sgr C cloud, making it the ninth region in the Galaxy that contains masers of this type. In spite of these detections, we find that current high-mass star formation in the inner CMZ is only taking place in seven isolated clouds. The results suggest that star formation at early evolutionary phases in the CMZ is about 10 times less efficient than expected from the dense gas star formation relation, which is in line with previous studies that focus on more evolved phases of star formation. This means that if there will be any impending, next burst of star formation in the CMZ, it has not yet begun.

ID: 150510
Type: article
Authors: Lu, Xing; Zhang, Qizhou; Kauffmann, Jens; Pillai, Thushara; Ginsburg, Adam; Mills, Elisabeth A. C.; Kruijssen, J. M. Diederik; Longmore, Steven N.; Battersby, Cara; Liu, Hauyu Baobab; Gu, Qiusheng
Abstract: We investigate star formation at very early evolutionary phases in five massive clouds in the inner 500 pc of the Galaxy, the Central Molecular Zone (CMZ). Using interferometer observations of H₂O masers and ultra-compact H II regions, we find evidence of ongoing star formation embedded in cores of 0.2 pc scales and ≳10⁵ cm^‑3 densities. Among the five clouds, Sgr C possesses a high (9%) fraction of gas mass in gravitationally bound and/or protostellar cores, and follows the dense (≳10⁴ cm^‑3) gas star formation relation that is extrapolated from nearby clouds. The other four clouds have less than 1% of their cloud masses in gravitationally bound and/or protostellar cores, and star formation rates 10 times lower than predicted by the dense gas star formation relation. At the spatial scale of these cores, the star formation efficiency is comparable to that in Galactic disk sources. We suggest that the overall inactive star formation in these CMZ clouds could be because there is much less gas confined in gravitationally bound cores, which may be a result of the strong turbulence in this region and/or the very early evolutionary stage of the clouds when collapse has only recently started.

ID: 154600
Type: article
Authors: Svoboda, Brian E.; Shirley, Yancy L.; Traficante, Alessio; Battersby, Cara; Fuller, Gary A.; Zhang, Qizhou; Beuther, Henrik; Peretto, Nicolas; Brogan, Crystal; Hunter, Todd
Abstract: The initial physical conditions of high-mass stars and protoclusters remain poorly characterized. To this end, we present the first targeted ALMA Band 6 1.3 mm continuum and spectral line survey toward high-mass starless clump candidates, selecting a sample of 12 of the most massive candidates (4× {10}² {M}_ȯ ≲ {M}_cl}≲ 4× {10}³ {M}_ȯ ) within {d}_{ȯ syn} ≈ 0.″8) and have high point-source mass-completeness down to M≈ 0.3 {M}_ȯ at 6{σ }_rms} (or 1{σ }_rms} column density sensitivity of N=1.1× {10}²² {cm}}^-2). We discover previously undetected signposts of low-luminosity star formation from {CO} J=2\to 1 and {SiO} J=5\to 4 bipolar outflows and other signatures toward 11 out of 12 clumps, showing that current MIR/FIR Galactic plane surveys are incomplete to low- and intermediate-mass protostars ({L}_bol}≲ 50 {L}_ȯ ), and emphasizing the necessity of high-resolution follow-up. We compare a subset of the observed cores with a suite of radiative transfer models of starless cores. We find a high-mass starless core candidate with a model-derived mass consistent with {29}₁₅⁵² {M}_ȯ when integrated over size scales of R when integrated over size scales of R⁴ {au}. Unresolved cores are poorly fit by radiative transfer models of externally heated Plummer density profiles, supporting the interpretation that they are protostellar even without detection of outflows. A high degree of fragmentation with rich substructure is observed toward 10 out of 12 clumps. We extract sources from the maps using a dendrogram to study the characteristic fragmentation length scale. Nearest neighbor separations, when corrected for projection with Monte Carlo random sampling, are consistent with being equal to the clump average thermal Jeans length ({λ }_{{j},{th}}; i.e., separations equal to 0.4{--}1.6× {λ }_{{j},{th}}). In the context of previous observations that, on larger scales, see separations consistent with the turbulent Jeans length or the cylindrical thermal Jeans scale (≈ 3{--}4× {λ }_{{j},{th}}), our findings support a hierarchical fragmentation process, where the highest-density regions are not strongly supported against thermal gravitational fragmentation by turbulence or magnetic fields.

ID: 145802
Type: article
Authors: Ginsburg, Adam; Bally, John; Barnes, Ashley; Bastian, Nate; Battersby, Cara; Beuther, Henrik; Brogan, Crystal; Contreras, Yanett; Corby, Joanna; Darling, Jeremy; De Pree, Chris; Galván-Madrid, Roberto; Garay, Guido; Henshaw, Jonathan; Hunter, Todd; Kruijssen, J. M. Diederik; Longmore, Steven; Lu, Xing; Meng, FanYi; Mills, Elisabeth A. C.; Ott, Juergen; Pineda, Jaime E.; Sánchez-Monge, Álvaro; Schilke, Peter; Schmiedeke, Anika; Walker, Daniel; Wilner, David
Abstract: We report ALMA observations with resolution ?0.´´5 at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 au. By ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact H II regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses {M}_* ? 8 {M}_o . Their spatial distribution spread over a ~12 × 3 pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated "starburst" within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density (N({{{H}}}₂)? 2× {10}²³ {{cm}}^-2), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear {{{? }}}_* {--}{{{? }}}_{gas} relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.

ID: 145785
Type: article
Authors: Walker, D. L.; Longmore, S. N.; Zhang, Qizhou; Battersby, C.; Keto, E.; Kruijssen, J. M. D.; Ginsburg, A.; Lu, X.; Henshaw, J. D.; Kauffmann, J.; Pillai, T.; Mills, E. A. C.; Walsh, A. J.; Bally, J.; Ho, L. C.; Immer, K.; Johnston, K. G.
Abstract: The star formation rate in the Central Molecular Zone (CMZ) is an order of magnitude lower than predicted according to star formation relations that have been calibrated in the disc of our own and nearby galaxies. Understanding how and why star formation appears to be different in this region is crucial if we are to understand the environmental dependence of the star formation process. Here, we present the detection of a sample of high-mass cores in the CMZ's `dust ridge' that have been discovered with the Submillimeter Array. These cores range in mass from ˜50-2150 M<sub>⊙</sub> within radii of 0.1-0.25 pc. All appear to be young (pre-UCHII), meaning that they are prime candidates for representing the initial conditions of high-mass stars and sub-clusters. We report that at least two of these cores (`c1' and `e1') contain young, high-mass protostars. We compare all of the detected cores with high-mass cores and clouds in the Galactic disc and find that they are broadly similar in terms of their masses and sizes, despite being subjected to external pressures that are several orders of magnitude greater, ˜10⁸ K cm^-3, as opposed to ˜10⁵ K cm^-3. The fact that >80 per cent of these cores do not show any signs of star-forming activity in such a high-pressure environment leads us to conclude that this is further evidence for an increased critical density threshold for star formation in the CMZ due to turbulence.

ID: 143851
Type: article
Authors: Barnes, A. T.; Longmore, S. N.; Battersby, C.; Bally, J.; Kruijssen, J. M. D.; Henshaw, J. D.; Walker, D. L.
Abstract: The inner few hundred parsecs of the Milky Way harbours gas densities, pressures, velocity dispersions, an interstellar radiation field and a cosmic ray ionization rate orders of magnitude higher than the disc; akin to the environment found in star-forming galaxies at high redshift. Previous studies have shown that this region is forming stars at a rate per unit mass of dense gas which is at least an order of magnitude lower than in the disc, potentially violating theoretical predictions. We show that all observational star formation rate diagnostics - both direct counting of young stellar objects and integrated light measurements - are in agreement within a factor two, hence the low star formation rate (SFR) is not the result of the systematic uncertainties that affect any one method. As these methods trace the star formation over different time-scales, from 0.1 to 5 Myr, we conclude that the SFR has been constant to within a factor of a few within this time period. We investigate the progression of star formation within gravitationally bound clouds on ∼parsec scales and find 1-4 per cent of the cloud masses are converted into stars per free-fall time, consistent with a subset of the considered 'volumetric' star formation models. However, discriminating between these models is obstructed by the current uncertainties on the input observables and, most importantly and urgently, by their dependence on ill-constrained free parameters. The lack of empirical constraints on these parameters therefore represents a key challenge in the further verification or falsification of current star formation theories.

ID: 142810
Type: article
Authors: Battersby, Cara; Bally, John; Svoboda, Brian
Abstract: High-mass stars form within star clusters from dense, molecular regions (DMRs), but is the process of cluster formation slow and hydrostatic or quick and dynamic? We link the physical properties of high-mass star-forming regions with their evolutionary stage in a systematic way, using Herschel and Spitzer data. In order to produce a robust estimate of the relative lifetimes of these regions, we compare the fraction of DMRs above a column density associated with high-mass star formation, N(H₂) > 0.4-2.5 × 10²² cm^-2, in the "starless" (no signature of stars ?10 {M}_? forming) and star-forming phases in a 2° × 2° region of the Galactic Plane centered at l = 30°. Of regions capable of forming high-mass stars on ~1 pc scales, the starless (or embedded beyond detection) phase occupies about 60%-70% of the DMR lifetime, and the star-forming phase occupies about 30%-40%. These relative lifetimes are robust over a wide range of thresholds. We outline a method by which relative lifetimes can be anchored to absolute lifetimes from large-scale surveys of methanol masers and UCHII regions. A simplistic application of this method estimates the absolute lifetime of the starless phase to be 0.2-1.7 Myr (about 0.6-4.1 fiducial cloud free-fall times) and the star-forming phase to be 0.1-0.7 Myr (about 0.4-2.4 free-fall times), but these are highly uncertain. This work uniquely investigates the star-forming nature of high column density gas pixel by pixel, and our results demonstrate that the majority of high column density gas is in a starless or embedded phase.

ID: 143284
Type: article
Authors: Lu, Xing; Zhang, Qizhou; Kauffmann, Jens; Pillai, Thushara; Longmore, Steven N.; Kruijssen, J. M. Diederik; Battersby, Cara; Liu, Hauyu Baobab; Ginsburg, Adam; Mills, Elisabeth A. C.; Zhang, Zhi-Yu; Gu, Qiusheng
Abstract: We recently reported a population of protostellar candidates in the 20 km s^-1 cloud in the Central Molecular Zone of the Milky Way, traced by H₂O masers in gravitationally bound dense cores. In this paper, we report molecular line studies with high angular resolution (~3´´) of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH₃ inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations are complemented with single-dish data. We find that the CH₃OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of ?100 K at 0.1 pc scales based on RADEX modeling of the H₂CO and NH₃ lines. Although no strong correlations between temperatures and linewidths/H₂O maser luminosities are found, in high-angular-resolution maps we note several candidate shock-heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1 pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.