Publications by James Binney


A centrally heated dark halo for our Galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press 465 (2016) 798-810

D Cole, J Binney

We construct a new family of models of our Galaxy in which dark matter and disc stars are both represented by distribution functions that are analytic functions of the action integrals of motion. The potential that is self-consistently generated by the dark matter, stars and gas is determined, and parameters in the distribution functions are adjusted until the model is compatible with observational constraints on the circularspeed curve, the vertical density profile of the stellar disc near the Sun, the kinematics of nearly 200 000 giant stars within 2 kpc of the Sun, and estimates of the optical depth to microlensing of bulge stars. We find that the data require a dark halo in which the phase-space density is approximately constant for actions |J| ≲ 140 kpc km s−1 . In real space these haloes have core radii ≃ 2 kpc.


The Radial Velocity Experiment (RAVE): Fifth data release

Astronomical Journal Institute of Physics 153 (2017) 75-

P Jofre, T Antoja, G Gilmore, A Siebert, B Famaey, O Bienaymé, BK Gibson, KC Freeman, JF Navarro, U Munari, G Seabroke, B Anguiano, M Žerjal, I Minchev, W Reid, J Bland-Hawthorn, J Kos, S Sharma, F Watson, QA Parker, R-D Scholz, D Burton, P Cass, M Hartley, K Fiegert

<p>Data Release 5 (DR5) of the Radial Velocity Experiment (RAVE) is the fifth data release from a magnitude-limited (9 &lt; I &lt; 12) survey of stars randomly selected in the Southern Hemisphere. The RAVE medium-resolution spectra (R ~ 7500) covering the Ca-triplet region (8410–8795 Å) span the complete time frame from the start of RAVE observations in 2003 to their completion in 2013. Radial velocities from 520,781 spectra of 457,588 unique stars are presented, of which 255,922 stellar observations have parallaxes and proper motions from the Tycho-Gaia astrometric solution in Gaia DR1. For our main DR5 catalog, stellar parameters (effective temperature, surface gravity, and overall metallicity) are computed using the RAVE DR4 stellar pipeline, but calibrated using recent K2 Campaign 1 seismic gravities and Gaia benchmark stars, as well as results obtained from high-resolution studies. Also included are temperatures from the Infrared Flux Method, and we provide a catalog of red giant stars in the dereddened color - J Ks0 ( ) interval (0.50, 0.85) for which the gravities were calibrated based only on seismology. Further data products for subsamples of the RAVE stars include individual abundances for Mg, Al, Si, Ca, Ti, Fe, and Ni, and distances found using isochrones. Each RAVE spectrum is complemented by an error spectrum, which has been used to determine uncertainties on the parameters. The data can be accessed via the RAVE Web site or the VizieR database.</p>


The angular momentum of cosmological coronae and the inside-out growth of spiral galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press 467 (2017) 311-329

G Pezzulli, F Fraternali, J Binney

Massive and diffuse haloes of hot gas (coronae) are important intermediaries between cosmology and galaxy evolution, storing mass and angular momentum acquired from the cosmic web until eventual accretion on to star-forming discs. We introduce a method to reconstruct the rotation of a galactic corona, based on its angular momentum distribution (AMD). This allows us to investigate in what conditions the angular momentum acquired from tidal torques can be transferred to star-forming discs and explain observed galaxy-scale processes, such as inside-out growth and the build-up of abundance gradients. We find that a simple model of an isothermal corona with a temperature slightly smaller than virial and a cosmologically motivated AMD is in good agreement with galaxy evolution requirements, supporting hot-mode accretion as a viable driver for the evolution of spiral galaxies in a cosmological context. We predict moderately sub-centrifugal rotation close to the disc and slow rotation close to the virial radius. Motivated by the observation that the Milky Way has a relatively hot corona (T ≃ 2 × 10^6 K), we also explore models with a temperature larger than virial. To be able to drive inside-out growth, these models must be significantly affected by feedback, either mechanical (ejection of low angular momentum material) or thermal (heating of the central regions). However, the agreement with galaxy evolution constraints becomes, in these cases, only marginal, suggesting that our first and simpler model may apply to a larger fraction of galaxy evolution history.


Managing resonant-trapped orbits in our Galaxy

Monthly Notices of the Royal Astronomical Society Oxford University Press (OUP) 462 (2016) 2792-2803

J Binney


Age velocity dispersion relations and heating histories in disc galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press (2016)

M Aumer, JJ Binney, RA Schönrich

We analyse the heating of stellar discs by non axisymmetric structures and giant molecular clouds (GMCs) in N-body simulations of growing disc galaxies. The analysis resolves long-standing discrepancies between models and data by demonstrating the importance of distinguishing between measured age-velocity dispersion relations (AVRs) and the heating histories of the stars that make up the AVR. We fit both AVRs and heating histories with formulae ∝ tβ and determine the exponents β bar R and β bar z derived from in-plane and vertical AVRs and βR and βz from heating histories. Values of βz are in almost all simulations larger than values of βbarz , wheras values of βR are similar to or mildly larger than values of β bar R. Moreover, values of βz (β bar z) are generally larger than values of βR (β bar R). The dominant cause of these relations is the decline over the life of the disc in importance of GMCs as heating agents relative to spiral structure and the bar. We examine how age errors and biases in solar neighbourhood surveys in uence the measured AVR: they tend to decrease β values by smearing out ages and thus measured dispersions. We compare AVRs and velocity ellipsoid shapes σz/σR from simulations to Solar-neighbourhood data. We conclude that for the expected disc mass and dark halo structure, combined GMC and spiral/bar heating can explain the AVR of the Galactic thin disc. Strong departures of the disc mass or the dark halo structure from expectation spoil fits to the data.


Chemical separation of disc components using RAVE

Monthly Notices of the Royal Astronomical Society Oxford University Press 461 (2016) 4246-4255

J Wojno, G Kordopatis, M Steinmetz, P McMillan, G Matijevič, J Binney, RFG Wyse, C Boeche, A Just, EK Grebel, A Siebert, O Bienaymé, BK Gibson, T Zwitter, J Bland-Hawthorn, JF Navarro, QA Parker, W Reid, G Seabroke, F Watson

We present evidence from the RAdial Velocity Experiment (RAVE) survey of chemically separated, kinematically distinct disc components in the solar neighbourhood.We apply probabilistic chemical selection criteria to separate our sample into α-low (‘thin disc’) and α-high (‘thick disc’) sequences. Using newly derived distances,which will be utilized in the upcoming RAVE DR5, we explore the kinematic trends as a function of metallicity for each of the disc components. For our α-low disc, we find a negative trend in the mean rotational velocity (Vφ) as a function of iron abundance ([Fe/H]). We measure a positive gradient ∂Vφ/∂[Fe/H] for the α-high disc, consistent with results from high-resolution surveys.We also find differences between the α-low and α-high discs in all three components of velocity dispersion.We discuss the implications of an α-low, metal-rich population originating from the inner Galaxy, where the orbits of these stars have been significantly altered by radial mixing mechanisms in order to bring them into the solar neighbourhood. The probabilistic separation we propose can be extended to other data sets for which the accuracy in [α/Fe] is not sufficient to disentangle the chemical disc components a priori. For such data sets which will also have significant overlap with Gaia DR1, we can therefore make full use of the improved parallax and proper motion data as it becomes available to investigate kinematic trends in these chemical disc components.


Chemodynamical modelling of the Milky Way

Astronomische Nachrichten Wiley 337 (2016) 939-943

J Binney, JL Sanders


Characterizing stellar halo populations – I. An extended distribution function for halo K giants

Monthly Notices of the Royal Astronomical Society Oxford University Press 460 (2016) 1725-1738

P Das, J Binney

We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ∼80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ∼−2 to ∼−4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ∼−0.001 dex kpc−1, a small gradient in the dispersion in [Fe/H] of ∼0.001 dex kpc−1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ∼−1.5 and ∼−2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.


The quiescent phase of galactic disc growth

Monthly Notices of the Royal Astronomical Society Oxford University Press (2015)

M Aumer, J Binney, R Schönrich

We perform a series of controlled N-body simulations of growing disc galaxies within non-growing, live dark matter haloes of varying mass and concentration. Our initial conditions include either a low-mass disc or a compact bulge. New stellar particles are continuously added on near-circular orbits to the existing disc, so spiral structure is continuously excited. To study the effect of combined spiral and giant molecular cloud (GMC) heating on the discs, we introduce massive, short-lived particles that sample a GMC mass function. An isothermal gas component is introduced for a subset of the models. We perform a resolution study and vary parameters governing the GMC population, the histories of star formation and radial scale growth. Models with GMCs and standard values for the disc mass and halo density provide the right level of self-gravity to explain the age–velocity dispersion relation of the solar neighbourhood (Snhd). GMC heating generates remarkably exponential vertical profiles with scaleheights that are radially constant and agree with observations of galactic thin discs. GMCs are also capable of significantly delaying bar formation. The amount of spiral-induced radial migration agrees with what is required for the metallicity distribution of the Snhd. However, in our standard models, the outward-migrating populations are not hot enough vertically to create thick discs. Thick discs can form in models with high baryon fractions, but the corresponding bars are too long, the young stellar populations too hot and the discs flare considerably.


A review of action estimation methods for galactic dynamics

Monthly Notices of the Royal Astronomical Society Oxford University Press 457 (2016) 2107-2121

JL Sanders, J Binney

We review the available methods for estimating actions, angles and frequencies of orbits in both axisymmetric and triaxial potentials. The methods are separated into two classes. Unless an orbit has been trapped by a resonance, convergent, or iterative, methods are able to recover the actions to arbitrarily high accuracy given sufficient computing time. Faster non-convergent methods rely on the potential being sufficiently close to a separable potential, and the accuracy of the action estimate cannot be improved through further computation. We critically compare the accuracy of the methods and the required computation time for a range of orbits in an axisymmetric multicomponent Galactic potential. We introduce a new method for estimating actions that builds on the adiabatic approximation of Schönrich and Binney and discuss the accuracy required for the actions, angles and frequencies using suitable distribution functions for the thin and thick discs, the stellar halo and a star stream. We conclude that for studies of the disc and smooth halo component of the Milky Way, the most suitable compromise between speed and accuracy is the Stäckel Fudge, whilst when studying streams the non-convergent methods do not offer sufficient accuracy and the most suitable method is computing the actions from an orbit integration via a generating function. All the software used in this study can be downloaded from https://github.com/jls713/tact.


Torus mapper: a code for dynamical models of galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 456 (2016) 1982-1998

J Binney, PJ McMillan


The distribution function of the Galaxy's dark halo

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 454 (2015) 3653-3663

J Binney, T Piffl


Gas flow in barred potentials - III. Effects of varying the quadrupole

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 454 (2015) 1818-1839

MC Sormani, J Binney, J Magorrian


Gas flow in barred potentials - II. Bar-driven spiral arms

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 451 (2015) 3437-3452

MC Sormani, J Binney, J Magorrian


Identification of globular cluster stars in RAVE data - I. Application to stellar parameter calibration

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 451 (2015) 1229-1246

B Anguiano, DB Zucker, R-D Scholz, EK Grebel, G Seabroke, A Kunder, J Binney, PJ McMillan, T Zwitter, RFG Wyse, G Kordopatis, O Bienayme, J Bland-Hawthorn, C Boeche, KC Freeman, BK Gibson, G Gilmore, U Munari, J Navarro, Q Parker, W Reid, A Siebert, A Siviero, M Steinmetz, F Watson


The Gaia-ESO Survey: Empirical determination of the precision of stellar radial velocities and projected rotation velocities

ASTRONOMY & ASTROPHYSICS 580 (2015) ARTN A75

RJ Jackson, RD Jeffries, J Lewis, SE Koposov, GG Sacco, S Randich, G Gilmore, M Asplund, J Binney, P Bonifacio, JE Drew, S Feltzing, AMN Ferguson, G Micela, I Neguerela, T Prusti, H-W Rix, A Vallenari, EJ Alfaro, CA Prieto, C Babusiaux, T Bensby, R Blomme, A Bragaglia, E Flaccomio, P Francois, N Hambly, M Irwin, AJ Korn, AC Lanzafame, E Pancino, A Recio-Blanco, R Smiljanic, S Van Eck, N Walton, A Bayo, M Bergemann, G Carraro, MT Costado, F Damiani, B Edvardsson, E Franciosini, A Frasca, U Heiter, V Hill, A Hourihane, P Jofre, C Lardo, P de Laverny, K Lind, L Magrini, G Marconi, C Martayan, T Masseron, L Monaco, L Morbidelli, L Prisinzano, L Sbordone, SG Sousa, CC Worley, S Zaggia


Bringing the Galaxy's dark halo to life

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 451 (2015) 639-650

T Piffl, Z Penoyre, J Binney


SELF-GRAVITY, RESONANCES AND ORBITAL DIFFUSION IN STELLAR DISKS

ASTROPHYSICAL JOURNAL 806 (2015) ARTN 117

J-B Fouvry, J Binney, C Pichon


Extended distribution functions for our Galaxy

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 449 (2015) 3479-3502

JL Sanders, J Binney


Gas flow in barred potentials

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 449 (2015) 2421-2435

MC Sormani, J Binney, J Magorrian

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