Professor James Binney FRS

Abstract:

We have obtained integral-field spectroscopy for 23 spiral bulges using INTEGRAL on the William Herschel Telescope and SPIRAL on the Anglo-Australian Telescope. This is the first two-dimensional survey directed solely at the bulges of spiral galaxies. Eleven galaxies of the sample do not have previous measurements of the stellar velocity dispersion (σ*). These data are designed to complement our Space Telescope Imaging Spectrograph program for estimating black hole masses in the range 106-108 M ⊙ using gas kinematics from nucleated disks. These observations will serve to derive the stellar dynamical bulge properties using the traditional Mg b and Ca II triplets. We use both cross-correlation and maximum penalized likelihood to determine projected σ* in these systems and present radial velocity fields, major axis rotation curves, curves of growth, and σ* fields. Using cross-correlation to extract the low-order two-dimensional stellar dynamics we generally see coherent radial rotation and irregular velocity dispersion fields suggesting that is a nontrivial parameter to estimate. © 2005, The American Astronomical Society. All rights reserved.

Abstract:

Techniques for the construction of dynamical Galaxy models should be considered essential infrastructure that should be put in place before Gaia flies. Three possible modelling techniques are discussed. Although one of these seems to have significantly more potential than the other two, at this stage work should be done on all three. A major effort is needed to decide how to make a model consistent with a catalogue such as that which Gaia will produce. Given the complexity of the problem, it is argued that a hierarchy of models should be constructed, of ever increasing complexity and quality of fit to the data. The potential that resonances and tidal streams have to indicate how a model should be refined is briefly discussed.

Abstract:

We investigate the central regions of 23 spiral galaxies using Space Telescope Imaging Spectrograph (STIS) spectroscopy and archival Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging. The sample is taken from our program to determine the masses of central massive black holes (MBHs) in 54 nearby spiral galaxies. Stars are likely to contribute significantly to any dynamical central mass concentration that we find in our MBH program, and this paper is part of a series to investigate the nuclear properties of these galaxies. We use the Nuker law to fit surface brightness profiles, derived from the NICMOS images, to look for nuclear star clusters and find possible extended sources in three of the 23 galaxies studied (13%). The fact that this fraction is lower than that inferred from optical Bubble Space Telescope studies is probably due to the greater spatial resolution of those studies. Using R - H and J - H colors and equivalent widths of Hα emission (from the STIS spectra), we investigate the nature of the stellar population with evolutionary models. Under the assumption of hot stars ionizing the gas, as opposed to a weak active galactic nucleus (AGN), we find that there are young stellar populations (∼ 10-20 Myr); however, these data do not allow us to determine what percentage of the total nuclear stellar population they form. In addition, in an attempt to find any unknown AGN, we use [N II] and [S II] line flux ratios (relative to Hα) and find tentative evidence for weak AGNs in NGC 1300 and NGC 4536. © 2005. The American Astronomical Society. All rights reserved.

Abstract:

Both microlensing surveys and radio-frequency observations of gas flow imply that the inner Milky Way is completely dominated by baryons, contrary to the predictions of standard cold dark matter (CDM) cosmology. We investigate the predictions of the Modified Newtonian Dynamics (MOND) formula for the Galaxy given the measured baryon distribution. Satisfactory fits to the observationally determined terminal-velocity curve are obtained for different choices of the MOND's interpolating function mu(x). However, with simple analytical forms of mu(x), the local circular speed v_c(R_0) can be as large as 220 km/s only for values of the parameter a_0 that are excluded by observations of NGC 3198. Only a numerically specified interpolating function can produce v_c(R_0)=220 km/s, which is therefore an upper limit in MOND, while the asymptotic velocity is predicted to be v_c(infty)=170+-5 km/s. The data are probably not consistent with the functional form of mu(x) that has been explored as a toy model in the framework of Bekenstein's covariant theory of gravity.

Abstract:

The low-frequency power spectra of the X-ray and radio emission from four microquasars suggest that two distinct modes of energy output are at work: (i) the `coupled' mode in which the X-ray and radio luminosities are closely coupled and vary only weakly, and (ii) the `flaring' mode, which dramatically boosts the radio luminosity but makes no impact on the X-ray luminosity. The systems are in the flaring mode only a few percent of the time. However, flares completely dominate the power spectrum of radio emission, with the consequence that sources in which the flaring mode occurs, such as GRS 1915+105 and Cyg X-3, have radio power spectra that lie more than an order of magnitude above the corresponding X-ray power spectra. Of the four microquasars for which we have examined data, in only one, Cyg X-1, is the flaring mode seemingly inactive. While Cyg X-1 is a black-hole candidate, one of the three flaring sources, Sco X-1, is a neutron star. Consequently, it is likely that both modes are driven by the accretion disk rather than black-hole spin. Radio imaging strongly suggests that the flaring mode involves relativistic jets. A typical microquasar is in the flaring mode a few percent of the time, which is similar to the fraction of quasars that are radio loud. Thus there may be no essential difference between radio-loud and radio-quiet quasars; radio loudness may simply be a function of the epoch at which the source is observed.