Publications by James Binney

Is there really a black hole at the center of NGC 4041? Constraints from gas kinematics

ASTROPHYSICAL JOURNAL 586 (2003) 868-890

A Marconi, DJ Axon, A Capetti, W Maciejewski, J Atkinson, D Batcheldor, J Binney, M Carollo, L Dressel, H Ford, J Gerssen, MA Hughes, D Macchetto, MR Merrifield, C Scarlata, W Sparks, M Stiavelli, Z Tsvetanov, RP van der Marel

Simple models of cooling flows

Monthly Notices of the Royal Astronomical Society 338 (2003) 837-845

JJ Binney, C.R. Kaiser

Is there really a black hole at the center of NGC 4041? Constraints from gas kinematics

Astrophysical Journal 586 (2003) 868-890

A Marconi, DJ Axon, A Capetti, W Maciejewski, J Atkinson, D Batcheldor, J Binney, M Carollo, L Dressel, H Ford, J Gerssen, MA Hughes, D Macchetto, MR Merrifield, C Scarlata, W Sparks, M Stiavelli, Z Tsvetanov, RP Van der Marel

We present Space Telescope Imaging Spectrograph spectra of the Sbc spiral galaxy NGC 4041, which were used to map the velocity field of the gas in its nuclear region. We detect the presence of a compact (r ≃ 0″.4 ≃ 40 pc), high surface brightness, rotating nuclear disk cospatial with a nuclear star cluster. The disk is characterized by a rotation curve with a peak-to-peak amplitude of ∼40 km s-1 and is systematically blueshifted by ∼10-20 km s-1 with respect to the galaxy systemic velocity. With the standard assumption of constant mass-to-light ratio and with the nuclear disk inclination taken from the outer disk, we find that a dark point mass of (1-0.7+0.6) × 107 M⊙ is needed to reproduce the observed rotation curve. However, the observed blueshift suggests the possibility that the nuclear disk could be dynamically decoupled. Following this line of reasoning, we relax the standard assumptions and find that the kinematical data can be accounted for by the stellar mass provided that either the central mass-to-light ratio is increased by a factor of ∼2 or the inclination is allowed to vary. This model results in a 3 σ upper limit of 6 × 106 M⊙ on the mass of any nuclear black hole (BH). Overall, our analysis only allows us to set an upper limit of 2 × 107 M⊙ on the mass of the nuclear BH. If this upper limit is taken in conjunction with an estimated bulge B magnitude of -17.7 and with a central stellar velocity dispersion of ≃95 km s-1, then these results are not inconsistent with both the MBH-Lsph and the MBH-σ* correlations. Constraints on BH masses in spiral galaxies of types as late as Sbc are still very scarce; therefore, the present result adds an important new data point to our understanding of BH demography.

Radial mixing in galactic discs

Monthly Notices of the Royal Astronomical Society 336 (2002) 785-796

JJ Binney, J.A. Sellwood

Two-body relaxation in cosmological simulations

Monthly Notices of the Royal Astronomical Society 333 (2002) 378-382

J Binney, A Knebe

It is logically possible that early two-body relaxation in simulations of cosmological clustering influences the final structure of massive clusters. Convergence studies in which mass and spatial resolution are simultaneously increased cannot eliminate this possibility. We test the importance of two-body relaxation in cosmological simulations with simulations in which there are two species of particles. The cases of two mass ratios, √2:1 and 4:1, are investigated. Simulations are run with both a spatially fixed softening length and adaptive softening using the publicly available codes GADGET and MLAPM, respectively. The effects of two-body relaxation are detected in both the density profiles of haloes and the mass function of haloes. The effects are more pronounced with a fixed softening length, but even in this case they are not so large as to suggest that results obtained with one mass species are significantly affected by two-body relaxation. The simulations that use adaptive softening are less affected by two-body relaxation and produce slightly higher central densities in the largest haloes. They run about three times faster than the simulations that use a fixed softening length.

Observable consequences of cold clouds as dark matter

Monthly Notices of the Royal Astronomical Society 332 (2002)

E Kerins, J Binney, J Silk

Cold, dense clouds of gas have been proposed to explain the dark matter in Galactic haloes, and have also been invoked in the Galactic disc as an explanation for the excess faint submillimetre sources detected by SCUBA. Even if their dust-to-gas ratio is only a small percentage of that in conventional gas clouds, these dense systems would be opaque to visible radiation. We examine the possibility that the data sets of microlensing experiments searching for massive compact halo objects can also be used to search for occultation signatures by such clouds. We compute the rate and time-scale distribution of stellar transits by clouds in the Galactic disc and halo. We find that, for cloud parameters typically advocated by theoretical models, thousands of transit events should already exist within microlensing survey data sets. We examine the seasonal modulation in the rate caused by the Earth's orbital motion and find it provides an excellent probe of whether detected clouds are of disc or halo origin.

AGN and cooling flows

ASTR SOC P 250 (2002) 481-486

J Binney

For two decades the steady-state cooling-flow model has dominated-the literature of cluster and elliptical-galaxy X-ray sources. For ten years this model has been in severe difficulty from a theoretical point of view, and it is now coming under increasing pressure observationally A small number of enthusiasts have argued for a radically different interpretation of the data, but had little impacton prevailing opinion be-causeAhe unsteady heating picture that they-advocate is extremely hard to work out in detail. Here I explain why it is difficult to extract robust observational predictions from the heating picture. Major problems include the variability of the sources, the different ways in which a bi-polar flow can impact on X-ray emission, the weakness of synchrotron emission from sub-relativistic flows, and the sensitivity of synchrotron emission to a magnetic field that is probably highly localized.

Cuspy dark matter haloes and the Galaxy

Monthly Notices of the Royal Astronomical Society 327 (2001) L27-L31

JJ Binney, N.W. Evans

Multi-level adaptive particle mesh (MLAPM): A c code for cosmological simulations

Monthly Notices of the Royal Astronomical Society 325 (2001) 845-864

A Knebe, A Green, J Binney

We present a computer code written in c that is designed to simulate structure formation from collisionless matter. The code is purely grid-based and uses a recursively refined Cartesian grid to solve Poisson's equation for the potential, rather than obtaining the potential from a Green's function. Refinements can have arbitrary shapes and in practice closely follow the complex morphology of the density field that evolves. The time-step shortens by a factor of 2 with each successive refinement. Competing approaches to N-body simulation are discussed from the point of view of the basic theory of N-body simulation. It is argued that an appropriate choice of softening length ∈ is of great importance and that ∈ should be at all points an appropriate multiple of the local interparticle separation. Unlike tree and P3M codes, multigrid codes automatically satisfy this requirement. We show that at early times and low densities in cosmological simulations, ∈ needs to be significantly smaller relative to the interparticle separation than in virialized regions. Tests of the ability of the code's Poisson solver to recover the gravitational fields of both virialized haloes and Zel'dovich waves are presented, as are tests of the code's ability to reproduce analytic solutions for plane-wave evolution. The times required to conduct a ACDM cosmological simulation for various configurations are compared with the times required to complete the same simulation with the ART, AP3M and GADGET codes. The power spectra, halo mass functions and halo-halo correlation functions of simulations conducted with different codes are compared. The code is available from

Kinematics from spectroscopy with a wide slit: Detecting black holes in galaxy centres

Monthly Notices of the Royal Astronomical Society 323 (2001) 831-838

W Maciejewski, J Binney

We consider long-slit emission-line spectra of galactic nuclei when the slit is wider than the instrumental point spread function, and the target has large velocity gradients. The finite width of the slit generates complex distributions of brightness at a given spatial point in the measured spectrum, which can be misinterpreted as coming from additional physically distinct nuclear components. We illustrate this phenomenon for the case of a thin disc in circular motion around a nuclear black hole (BH). We develop a new method for estimating the mass of the BH that exploits a feature in the spectrum at the outer edge of the BH's sphere of influence, and therefore gives higher sensitivity to BH detection than traditional methods. Moreover, with this method we can determine the BH mass and the inclination of the surrounding disc separately, whereas the traditional approach to BH estimation requires two long-slit spectra to be taken. We show that, with a given spectrograph, the detectability of a BH depends on the sense of rotation of the nuclear disc. We apply our method to estimate the BH mass in M84 from a publicly available spectrum, and recover a value four times lower than that published previously from the same data.

The dark matter problem in disc galaxies

Monthly Notices of the Royal Astronomical Society 321 (2001) 471-474

J Binney, O Gerhard, J Silk

In the generic CDM cosmogony, dark-matter haloes emerge too lumpy and centrally concentrated to host observed galactic discs. Moreover, discs are predicted to be smaller than those observed. We argue that the resolution of these problems may lie with a combination of the effects of protogalactic discs, which would have had a mass comparable to that of the inner dark halo and be plausibly non-axisymmetric, and of massive galactic winds, which at early times may have carried off as many baryons as a galaxy now contains. A host of observational phenomena, from quasar absorption lines and intracluster gas through the G-dwarf problem, point to the existence of such winds. Dynamical interactions will homogenize and smooth the inner halo, and the observed disc will be the relic of a massive outflow. The inner halo expanded after absorbing energy and angular momentum from the ejected material. Observed discs formed at the very end of the galaxy formation process, after the halo had been reduced to a minor contributor to the central mass budget and strong radial streaming of the gas had died down.

Secular evolution of tile galactic disk


J Binney

Supernovae and the intergalactic medium


J Binney

Dynamics of the Galaxy's satellites


J Binney

Microlensing and galactic structure


J Binney

Gas kinematics from Spectroscopy with a wide slit: Detecting nuclear black holes


W Maciejewski, J Binney

The black hole mass vs bulge mass relationship in spiral galaxies


A Marconi, D Axon, J Atkinson, J Binney, A Capetti, M Carollo, L Dressel, H Ford, J Gerssen, M Hughes, D Macchetto, W Maciejewski, M Merrifield, C Scarlata, W Sparks, M Stiavelli, Z Tsvetanov, R van der Marel

The age of the solar neighbourhood

Monthly Notices of the Royal Astronomical Society 318 (2000) 658-664

J Binney, W Dehnen, G Bertelli

High-quality Hipparcos data for a complete sample of nearly 12 000 main-sequence and subgiant stars, together with Padua isochrones, are used to constrain the star formation history of the solar neigbourhood and the processes that stochastically accelerate disc stars. The velocity dispersion of a coeval group of stars is found to increase with time from ∼8 km s-1 at birth as t0.33. In the fits, the slope of the initial mass function (IMF) near 1 M⊙ proves to be degenerate with the rate at which the star formation rate declines. If the slope of the IMF is to lie near Salpeter's value, -2.35, the star formation rate has to be very nearly constant. The age of the solar neighbourhood is found to be 11.2 ± 0.75 Gyr with remarkably little sensitivity to variations in the assumed metallicity distribution of old disc stars. This age is only a gigayear younger than the age of the oldest globular clusters when the same isochrones and distance scale are employed. It is compatible with current indications of the redshift of luminous galaxy formation only if there is a large cosmological constant. A younger age is formally excluded because it provides a poor fit to the number density of red stars. Since this density is subject to a significantly uncertain selection function, ages as low as 9 Gyr are plausible even though they lie outside our formal error bars.

Is galactic structure compatible with microlensing data?


J Binney, N Bissantz, O Gerhard

Is galactic structure compatible with microlensing data?

Astrophysical Journal 537 (2000)

J Binney, N Bissantz, O Gerhard

We generalize to elliptical models an argument introduced by Gould, which connects the microlensing optical depth toward the Galactic bulge to the Galactic rotation curve. When applied to the latest value from the MACHO collaboration for the optical depth for microlensing of bulge sources, the argument implies that even a barred Galactic model cannot plausibly reconcile the measured values of the optical depth, the rotation curve, and the local mass density. Either there is a problem with the interpretation of the microlensing data or our line of sight to the Galactic center is highly atypical in that it passes through a massive structure with small solid angle as seen from the Galactic center.