Suchergebnisse

In Meidt et al., we showed that gas kinematics on the scale of individual molecular clouds are not entirely dominated by self-gravity but also track a component that originates with orbital motion in the potential of the host galaxy. This agrees with observed cloud line widths, which show systematic variations from virial motions with environment, pointing at the influence of the galaxy potential. In this paper, we hypothesize that these motions act to slow down the collapse of gas and so help regulate star formation. Extending the results of Meidt et al., we derive a dynamical collapse timescale that approaches the free-fall time only once the gas has fully decoupled from the galactic potential. Using this timescale, we make predictions for how the fraction of free-falling, strongly self-gravitating gas varies throughout the disks of star-forming galaxies. We also use this collapse timescale to predict variations in the molecular gas star formation efficiency, which is lowered from a maximum, feedback-regulated level in the presence of strong coupling to the galactic potential. Our model implies that gas can only decouple from the galaxy to collapse and efficiently form stars deep within clouds. We show that this naturally explains the observed drop in star formation rate per unit gas mass in the Milky Way's Central Molecular Zone and other galaxy centers. The model for a galactic bottleneck to star formation also agrees well with resolved observations of dense gas and star formation in galaxy disks and the properties of local clouds. ; German Research Foundation (DFG): SCHI 536/7-2, SPP 1573. German Research Foundation (DFG): 138713538-SFB 881. Heidelberg cluster of excellence - German Excellence Strategy: EXC 2181-390900948. German Research Foundation (DFG): KR4801/1-1. German Research Foundation (DFG): KR4801/2-1. European Research Council (ERC): 714907. National Science Foundation (NSF): 1615105, 1615109, 1653300. Natural Sciences and Engineering Research Council of Canada: RGPIN-2017-03987. European Research Council (ERC): 694343. Programme National "Physique et Chimie du Milieu Interstellaire" (PCMI) of CNRS/INSU. INC/INP - CEA. Centre National D'etudes Spatiales. Programme National Cosmology and Galaxies (PNCG) of CNRS/INSU. INP. IN2P3. French Atomic Energy Commission. Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU. European Union's Horizon 2020 research and innovation programme: 726384-EMPIRE. Spanish funding grants: AYA2016-79006-P, PGC2018-094671-B-I00.

Central molecular outflows in spiral galaxies are assumed to modulate their host galaxy's star formation rate (SFR) by removing gas from the inner region of the galaxy. Outflows consisting of different gas phases appear to be a common feature in local galaxies, yet, little is known about the frequency of molecular outflows in main sequence galaxies in the nearby universe. We develop a rigorous set of selection criteria, which allow the reliable identification of outflows in large samples of galaxies. Our criteria make use of central spectra, position-velocity diagrams and velocity-integrated intensity maps (line-wing maps). We use this method on high-angular resolution CO (2-1) observations from the PHANGS-ALMA survey, which provides observations of the molecular gas for a homogeneous sample of 90 nearby main sequence galaxies at a resolution of similar to 100 pc. We find correlations between the assigned outflow confidence and stellar mass or global SFR. We determine the frequency of central molecular outflows to be 25 +/- 2% considering all outflow candidates, or 20 +/- 2% for secure outflows only. Our resulting outflow candidate sample of 16-20 galaxies shows an overall enhanced fraction of active galactic nuclei (AGN) (50%) and bars (89%) compared to the full sample (galaxies with AGN: 24%, with bar: 61%). We extend the trend between mass outflow rates and SFR known for high outflow rates down to lower values (log(10) (M) over dot(out) [M-circle dot yr(-1)] < 0). Mass loading factors are of order unity, indicating that these outflows are not efficient in quenching the SFR in main sequence galaxies. ; European Research Council (ERC) 726384/Empire 694343 German Research Foundation (DFG) SFB 881 138713538 Heidelberg Cluster of Excellence "STRUCTURES" EXC-2181/1 390900948 European Research Council via the ERC Synergy Grant "ECOGAL" 855130 German Research Foundation (DFG) KR4801/1-1 KR4801/2-1 European Research Council (ERC) 714907 Instituto de Salud Carlos III Spanish Government PID2019-106027GA-C44 Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2017-03987 National Science Foundation (NSF) 1615105 1615109 1653300 Spanish funding grant (MINECO/FEDER) AYA2016-79006-P Spanish funding grant (MCIU/AEI/FEDER) PGC2018-094671-B-I00 Spanish funding grant (MICINN) PID2019-108765GB-I00 ; Versión publicada - versión final del editor

We present kinematic orientations and high-resolution (150 pc) rotation curves for 67 main-sequence star-forming galaxies surveyed in CO (2-1) emission by PHANGS-ALMA. Our measurements are based on the application of a new fitting method tailored to CO velocity fields. Our approach identifies an optimal global orientation as a way to reduce the impact of nonaxisymmetric (bar and spiral) features and the uneven spatial sampling characteristic of CO emission in the inner regions of nearby galaxies. The method performs especially well when applied to the large number of independent lines of sight contained in the PHANGS CO velocity fields mapped at 1 '' resolution. The high-resolution rotation curves fitted to these data are sensitive probes of mass distribution in the inner regions of these galaxies. We use the inner slope as well as the amplitude of our fitted rotation curves to demonstrate that CO is a reliable global dynamical mass tracer. From the consistency between photometric orientations from the literature and kinematic orientations determined with our method, we infer that the shapes of stellar disks in the mass range of log(M-star (M-circle dot)) = 9.0-10.9 probed by our sample are very close to circular and have uniform thickness. ; European Research Council (ERC) 694343 Natural Sciences and Engineering Research Council of Canada RGPIN-201703987 German Research Foundation (DFG) KR4801/1-1 German Research Foundation (DFG) KR4801/2-1 European Research Council (ERC) 714907 German Research Foundation (DFG) SFB 881 138713538 EXC 2181/1-390900948 Programme National "Physique et Chimie du Milieu Interstellaire" (PCMI) of CNRS/INSU INC/INP - CEA Centre National D'etudes Spatiales Programme National Cosmology and Galaxies (PNCG) of CNRS/INSU INP IN2P3 French Atomic Energy Commission European Union's Horizon 2020 research and innovation program 726384

Statistical analysis of velocity fluctuations in the interstellar medium (ISM) of the Milky Way and NGC 4321 show that the motion of molecular gas over scales ranging from 0.1 to 1,000 pc is similar, and consistent with that generated by a combination of gravity and turbulence. ISM structure at one scale is therefore linked to structure at other scales. The density structure of the interstellar medium determines where stars form and release energy, momentum and heavy elements, driving galaxy evolution(1-4). Density variations are seeded and amplified by gas motion, but the exact nature of this motion is unknown across spatial scales and galactic environments(5). Although dense star-forming gas probably emerges from a combination of instabilities(6,7), convergent flows(8)and turbulence(9), establishing the precise origin is challenging because it requires gas motion to be quantified over many orders of magnitude in spatial scale. Here we measure(10-12)the motion of molecular gas in the Milky Way and in nearby galaxy NGC 4321, assembling observations that span a spatial dynamic range 10(-1)-10(3) pc. We detect ubiquitous velocity fluctuations across all spatial scales and galactic environments. Statistical analysis of these fluctuations indicates how star-forming gas is assembled. We discover oscillatory gas flows with wavelengths ranging from 0.3-400 pc. These flows are coupled to regularly spaced density enhancements that probably form via gravitational instabilities(13,14). We also identify stochastic and scale-free velocity and density fluctuations, consistent with the structure generated in turbulent flows(9). Our results demonstrate that the structure of the interstellar medium cannot be considered in isolation. Instead, its formation and evolution are controlled by nested, interdependent flows of matter covering many orders of magnitude in spatial scale. ; German Research Foundation (DFG) KR4801/1-1 KR4801/2-1 European Research Council (ERC) 714907 European Union's Horizon 2020 research and innovation program 639459 National Science Foundation (NSF) 1615105 1615109 1653300 NASA under ADAP NNX16AF48G NNX17AF39G Natural Sciences and Engineering Research Council of Canada RGPIN-2017-03987 National Science Foundation (NSF) 1816715 AST-9800334 AST-0098562 AST-0100793 AST-0228993 AST-0507657 German Research Foundation (DFG) SFB 881 Heidelberg Cluster of Excellence STRUCTURES of Germany's Excellence Strategy EXC-2181/1-390900948 ERC under the European Union's Horizon 2020 research and innovation programme 694343 European Union's Horizon 2020 research and innovation programme 726384 Programme National 'Physique et Chimie du Milieu Interstellaire' (PCMI) of CNRS/INSU INC/INP French Atomic Energy Commission Centre National D'etudes Spatiales Australian Government Australian Research Council UNSW, Sydney Monash Universities Commonwealth Scientific & Industrial Research Organisation (CSIRO)

Observing nearby galaxies with submillimeter telescopes on the ground has two major challenges. First, the brightness is significantly reduced at long submillimeter wavelengths compared to the brightness at the peak of the dust emission. Second, it is necessary to use a high-pass spatial filter to remove atmospheric noise on large angular scales, which has the unwelcome side effect of also removing the galaxy's large-scale structure. We have developed a technique for producing high-resolution submillimeter images of galaxies of large angular size by using the telescope on the ground to determine the small-scale structure (the large Fourier components) and a space telescope (Herschel or Planck) to determine the large-scale structure (the small Fourier components). Using this technique, we are carrying out the HARP and SCUBA-2 High Resolution Terahertz Andromeda Galaxy Survey (HASHTAG), an international Large Program on the James Clerk Maxwell Telescope, with one aim being to produce the first high-fidelity high-resolution submillimeter images of Andromeda. In this paper, we describe the survey, the method we have developed for combining the space-based and ground-based data, and we present the first HASHTAG images of Andromeda at 450 and 850 mu m. We also have created a method to predict the CO(J = 3-2) line flux across M31, which contaminates the 850 mu m band. We find that while normally the contamination is below our sensitivity limit, it can be significant (up to 28%) in a few of the brightest regions of the 10 kpc ring. We therefore also provide images with the predicted line emission removed. ; National Key R&D Program of China 2017YFA0402700 UK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC) Canada Foundation for Innovation CGIAR European Regional Development Fund (ERDF) via the Welsh Government UK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC) ST/K000926/1 European Research Council (ERC) European Commission ERC-2014-CoG-647939 National Research Foundation 2018R1D1A1B07048314 National Natural Science Foundation of China (NSFC) 12073002 11721303 11991052 STFC consolidated grant "Astrophysics at Oxford" ST/H002456/1 ST/K00106X/1 UK Research & Innovation (UKRI) Science & Technology Facilities Council (STFC) ST/S00033X/1 National Natural Science Foundation of China (NSFC) 11873086 U1631237 11873028 Yunnan Province of China 2017HC018 Chinese Academy of Sciences National Basic Research Program of China 2017YFA0402704 2016YFA0400702 National Natural Science Foundation of China (NSFC) 11861131007 12033004 Chinese Academy of Sciences Key Research Program of Frontier Sciences QYZDJ-SSW-SLH008 National Commission for Scientific and Technological Research of Chile (CONICYT) through a CAS-CONICYT Joint Postdoctoral Fellowship Academia Sinica - Taiwan AS-IA-106-M03 Ministry of Science and Technology, Taiwan MOST107-2119-M-001-031-MY3 European Research Council (ERC) European Commission SNDUST ERC-2015-AdG-694520 National Key Research and Development Program of China 2017YFA0402703 National Science Centre, Poland through the POLONEZ 2015/19/P/ST9/04010 SONATA BIS grant 2018/30/E/ST9/00208 Natural Sciences and Engineering Research Council of Canada (NSERC) CGIAR Canada Research Chairs European Research Council (ERC) 694343 ; Versión publicada - versión final del editor

The PHANGS program is building the first data set to enable the multiphase, multiscale study of star formation across the nearby spiral galaxy population. This effort is enabled by large survey programs with the Atacama Large Millimeter/submillimeter Array (ALMA), MUSE on the Very Large Telescope, and the Hubble Space Telescope (HST), with which we have obtained CO(2–1) imaging, optical spectroscopic mapping, and high-resolution UV– optical imaging, respectively. Here, we present PHANGS-HST, which has obtained NUV–U–B–V–I imaging of the disks of 38 spiral galaxies at distances of 4–23 Mpc, and parallel V- and I-band imaging of their halos, to provide a census of tens of thousands of compact star clusters and multiscale stellar associations. The combination of HST, ALMA, and VLT/MUSE observations will yield an unprecedented joint catalog of the observed and physical properties of ∼100,000 star clusters, associations, H II regions, and molecular clouds. With these basic units of star formation, PHANGS will systematically chart the evolutionary cycling between gas and stars across a diversity of galactic environments found in nearby galaxies. We discuss the design of the PHANGS-HST survey and provide an overview of the HST data processing pipeline and first results. We highlight new methods for selecting star cluster candidates, morphological classification of candidates with convolutional neural networks, and identification of stellar associations over a range of physical scales with a watershed algorithm. We describe the cross-observatory imaging, catalogs, and software products to be released. The PHANGS high-level science products will seed a broad range of investigations, in particular, the study of embedded stellar populations and dust with the James Webb Space Telescope, for which a PHANGS Cycle 1 Treasury program to obtain eight-band 2–21 μm imaging has been approved. ; National Aeronautics & Space Administration (NASA) NAS 5-26555 Aparece en contenido como:NASA 15654 German Research Foundation (DFG) KR4801/1-1 KR4801/2-1 European Research Council (ERC) 714907 Aparece en contenido como:European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program via the ERC Starting Grant MUSTANG 726384/Empire 694343 Aparece en contenido como:European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program German Research Foundation (DFG) SFB 881 138713538 Aparece en contenido como:DFG via the collaborative research center Heidelberg Cluster of Excellence STRUCTURES EXC-2181/1-390900948 ERC via the ERC Synergy Grant ECOGAL 855130 German Research Foundation (DFG) SFB 881 138713538 KR4598/2-1 Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2017-03987 ; Versión publicada - versión final del editor