Mass–metallicity relation for local analogs of high-redshift galaxies: implicationsfor the evolution of the mass–metallicity relations

We revisit the evolution of the mass–metallicity relation of low- and high-redshift galaxies by using a sample oflocal analogs of high-redshift galaxies. These analogs share the same location of the UV-selected star-forminggalaxies at~z2on the[OIII]λ5007/Hβversus[NII]λ6584/Hαnebular emission-line diagnostic(or BPT)diagram. Their physical properties closely resemble those in~z2UV-selected star-forming galaxies beingcharacterized, in particular, by high ionization parameters(»qlog7.9)and high electron densities(»-n100 cme3). With the full set of well-detected rest-frame optical diagnostic lines, we measure the gas-phase oxygen abundance in the SDSS galaxies and these local analogs using the empirical relations and thephotoionization models. Wefind that the metallicity difference between the SDSS galaxies and our local analogs inthe*<<MM8.5 log9.0()☉stellar mass bin varies from−0.09 to 0.39 dex, depending on strong-line metallicitymeasurement methods. Due to this discrepancy, the evolution of mass–metallicity should be used to compare withthe cosmological simulations with caution. We use the[SII]/Hαand[OI]/HαBPT diagram to reduce thepotential AGN and shock contamination in our local analogs. Wefind that the AGN/shock influences arenegligible on the metallicity estimation

Cloud scale ISM structure and star formation in M51

We compare the structure of molecular gas at 40 pc resolution to the ability of gas to form stars across the disk of the spiral galaxy M51. We break the PAWS survey into 370 pc and 1.1 kpc resolution elements, and within each we estimate the molecular gas depletion time (tau(mol)(Dep)), the star-formation efficiency per free-fall time (epsilon(ff)), and the mass-weighted cloud-scale (40 pc) properties of the molecular gas: surface density, Sigma, line width, sigma, and b equivalent to Sigma/sigma(2) proportional to alpha(-1)(vir), a parameter that traces the boundedness of the gas. We show that the cloud-scale surface density appears to be a reasonable proxy for mean volume density. Applying this, we find a typical star-formation efficiency per free-fall time, epsilon(ff)() similar to 0.3%-0.36%, lower than adopted in many models and found for local clouds. Furthermore, the efficiency per free-fall time anti-correlates with both Sigma and sigma, in some tension with turbulent star-formation models. The best predictor of the rate of star formation per unit gas mass in our analysis is b equivalent to Sigma/sigma(2), tracing the strength of self-gravity, with tau(mol)(Dep) proportional to b(-0.9). The sense of the correlation is that gas with stronger self-gravity (higher b) forms stars at a higher rate (low tau(mol)(Dep)). The different regions of the galaxy mostly overlap in tau(mol)(Dep) as a function of b, so that low b explains the surprisingly high tau(mol)(Dep) found toward the inner spiral arms found by Meidt et al. (2013).INSU/CNRS (France) MPG (Germany) IGN (Spain) National Science Foundation 1615105 1615109 1653300 People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme under REA PITN-GA-2011-289313 European Research Council (ERC) under European Unions Horizon research and innovation programme 694343 Centre National d'Etudes Spatiales (CNES) Deutsche Forschungsgemeinschaft (DFG) KR4801/1-1 European Research Council (ERC) under European Union's Horizon research and innovation programme via ERC MUSTANG 714907 CONICYT/FONDECYT Programa de Iniciacion 11150220 Spanish MINECO AYA2012-32295 FIS2012-32096 DFG BI1546/1-1 AYA2016-76682-C3-2-P ESP2015-68964-

A Model for the Onset of Self-gravitation and Star Formation in Molecular Gas Governed by Galactic Forces. I. Cloud-scale Gas Motions

Modern extragalactic molecular gas surveys now reach the scales of star-forming giant molecular clouds (GMCs; 20–50 pc). Systematic variations in GMC properties with galaxy environment imply that clouds are not universally self-gravitating objects, decoupled from their surroundings. Here we re-examine the coupling of clouds to their environment and develop a model for 3D gas motions generated by forces arising with the galaxy gravitational potential defined by the background disk of stars and dark matter. We show that these motions can resemble or even exceed the motions needed to support gas against its own self-gravity throughout typical galactic disks. The importance of the galactic potential in spiral arms and galactic centers suggests that the response to self-gravity does not always dominate the motions of gas at GMC scales, with implications for observed gas kinematics, virial equilibrium, and cloud morphology. We describe how a uniform treatment of gas motions in the plane and in the vertical direction synthesizes the two main mechanisms proposed to regulate star formation: vertical pressure equilibrium and shear/Coriolis forces as parameterized by Toomre Q ≈ 1. As the modeled motions are coherent and continually driven by the external potential, they represent support for the gas that is distinct from that conventionally attributed to turbulence, which decays rapidly and thus requires maintenance, e.g., via feedback from star formation. Thus, our model suggests that the galaxy itself can impose an important limit on star formation, as we explore in a second paper in this series

Demand system rank Direct utility GARP tests, and portfolio separation

SIGLEAvailable from British Library Document Supply Centre-DSC:4363.343505(IFS-WP-W--96/19) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

HST emission line galaxies at z similar to 2: comparing physical properties oflyman alpha and optical emission line selected galaxies

Artículo de publicación ISIWe compare the physical and morphological properties of z similar to 2 Ly alpha emitting galaxies (LAEs) identified in the HETDEX Pilot Survey and narrow band studies with those of z similar to 2 optical emission line selected galaxies (oELGs) identified via HST WFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same range in stellar mass (7.5 < log M/M-circle dot < 10.5), size (0.5 < R < 3.0 kpc), and star formation rate (similar to 1 < SFR < 100 M-circle dot yr(-1)). Remarkably, a comparison of the most commonly used physical and morphological parameters-stellar mass, half-light radius, UV slope, SFR, ellipticity, nearest neighbor distance, star formation surface density, specific SFR, [O III] luminosity, and [O III] equivalent width-reveals no statistically significant differences between the populations. This suggests that the processes and conditions which regulate the escape of Ly alpha from a z similar to 2 star-forming galaxy do not depend on these quantities. In particular, the lack of dependence on the UV slope suggests that Ly alpha emission is not being significantly modulated by diffuse dust in the interstellar medium. We develop a simple model of Ly alpha emission that connects LAEs to all high-redshift starforming galaxies where the escape of Ly alpha depends on the sightline through the galaxy. Using this model, we find that mean solid angle for Ly alpha escape is Omega(Ly alpha) = 2.4 +/- 0.8 steradians; this value is consistent with those calculated from other studies.NSF, German Research Council (DFG), NASA/JPL SURP Program, NAS

Ubiquitous velocity fluctuations throughout the molecular interstellar medium

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

The lifecycle of molecular clouds in nearby star-forming disc galaxies

German Research Foundation (DFG) KR4801/1-1 German Research Foundation (DFG) KR4801/2-1 European Research Council (ERC) 714907 Australia-Germany Joint Research Cooperation Scheme (UA-DAAD) 57387355 Australian Research Council FT140101202 Programme National 'Physique et Chimie du Milieu Interstellaire' (PCMI) of the Centre national de la recherche scientifique/Institut national des sciences de l'Univers (CNRS/INSU) Institut de Chimie/Institut de Physique (INC/INP) French Atomic Energy Commission Centre National D'etudes Spatiales Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU INP Institut national de physique nucleaire et de physique des particules (IN2P3) French Atomic Energy Commission Centre National D'etudes Spatiales European Research Council (ERC) 694343 726384 National Science Foundation (NSF) 1615105 1615109 1653300 National Aeronautics and Space Administration (NASA) Astrophysics Data Analysis Program (ADAP) NNX16AF48G NNX17AF39G Natural Sciences and Engineering Research Council of Canada RGPIN-2017-03987 Fondo de Fomento al Desarrollo Cientifico y Tecnologico of the Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT/FONDECYT), Programa de Iniciacion, Folio 11150220 German Research Foundation (DFG) SFB 881 Germany's Excellence Strategy (Heidelberg STRUCTURES Excellence Cluster) EXC-2181/1-390900948 German Research Foundation (DFG) KR4598/2-1 MINECO/FEDER AYA2016-79006-P MCIU/AEI/FEDER PGC2018-094671-B-I00 Centre National de la Recherche Scientifique (CNRS) Max Planck Society IGN (Spain