Tim de Zeeuw

The SAURON project – VIII. OASIS/CFHT integral‐field spectroscopy of elliptical and lenticular galaxy centres

We present high spatial resolution integral-field spectros copy of 28 elliptical (E) and lenticular (S0) galaxies from the SAURON representative survey obtained with the OASIS spectrograph during its operation at the CFHT. These seeing-limited observations explore the central 8 ′′ ×10 ′′ (typically one kiloparsec diameter) regions of these galax ies using a spatial sampling four times higher than SAURON (0. 27 vs. 0. 94 spatial elements), resulting in almost a factor of two improvement in the median PSF. These data allow accurate study of the central regions to complement the large-scale view provided by SAURON. Here we present the stellar and gas kinematics, stellar absorption-line strengths and neb ular emission-line strengths for this sample. We also characterise the stellar velocity maps using the ‘kinemetry’ technique, and derive maps of the luminosity-weighted stellar age, metallicity and abundance ratio via stellar population models. We give a brief review of the structures found in our maps, linking also to larger-scale structures measured with SAURON. We present two previously unreported kinematically-decoupled components (KDCs) in the centres of NGC 3032 and NGC 4382. We compare the intrinsic size and luminosity-weighted stellar age of all the visible KDCs in the full SAURON sample, and find two types of components: kiloparsec-scale K DCs, which are older than 8 Gyr, and are found in galaxies with little net rot ation; and compact KDCs, which have intrinsic diameters of less than a few hundred parsec, show a range of stellar ages from 0.5 - 15 Gyr (with 5/6 younger than 5 Gyr), are found exclusively in fast-rotating galaxies, and are close to counter-rotating around the same axis as their host. Of the 7 galaxies in the SAURON sample with integrated luminosity-weighted ages less than 5 Gyr, 5 show such compact KDCs, suggesting a link between counter-rotation and recent star-formation. We show that this may be due to a combination of small sample size at young ages, and an observational bias, since young KDCs are easier to detect than their older and/or co-rotating counterparts.

The SAURON project - XIII. SAURON-GALEX study of early-type galaxies: the ultraviolet colour-magnitude relations and Fundamental Planes

We present Galaxy Evolution Explorer (GALEX) far (FUV) and near (NUV) ultraviolet imaging of 34 nearby early-type galaxies from the SAURON representative sample of 48 E/S0 galaxies, all of which have ground-based optical imaging from the MDM Observatory. The surface brightness profiles of nine galaxies (≈ 26 per cent) show regions with blue UV−optical colours sug

Early‐type galaxies in different environments: an H i view

Original article can be found at: http://onlinelibrary.wiley.com/ Copyright Royal Astronomical Society

The black hole in NGC 3379: a comparison of gas and stellar dynamical mass measurements with HST and integral‐field data★

We combine Hubble Space Telescope spectroscopy and ground-based integral-field data from the SAURON and OASIS instruments to study the central black hole in the nearby elliptical galaxy NGC 3379. From these data, we obtain kinematics of both the stars and the nuclear gaseous component. Axisymmetric three-integral models of the stellar kinematics find a black hole of mass 1.4 +2.6 -1.0 x 10 8 M ⊙ (3σ errors). These models also probe the velocity distribution in the immediate vicinity of the black hole and reveal a nearly isotropic velocity distribution throughout the galaxy and down to the black hole sphere of influence R BH . The morphology of the nuclear gas disc suggests that it is not in the equatorial plane; however the core of NGC 3379 is nearly spherical. Inclined thin-disc models of the gas find a nominal black hole of mass (2.0 ± 0.1) x 10 8 M ⊙ (3a errors), but the model is a poor fit to the kinematics. The data are better fit by introducing a twist in the gas kinematics (with the black hole mass assumed to be 2.0 x 10 8 M ⊙ ), although the constraints on the nature and shape of this perturbation are insufficient for more detailed modelling. Given the apparent regularity of the gas disc appearance, the presence of such strong non-circular motion indicates that caution must be used when measuring black hole masses with gas dynamical methods alone.

Formation and evolution of S0 galaxies: a SAURON case study of NGC 7332

ABSTRACT We present SAURONintegral-field observations of the S0 galaxy NGC7332. Existing broad-band ground-based and HST photometry reveals a double disk structure and a boxy bulgeinterpreted as a bar viewed close to edge-on. TheSAURONtwo-dimensional stellar kinematicmaps confirm the existence of the bar and inner disk but also un cover the presence of a coldcounter-rotating stellar component within the central250 pc. The Hβ and [O III ] emissionline maps show that the ionised gas has a complex morphology and kinematics, includingboth a component counter-rotating with respect to the starsand a fainter co-rotating one.Analysis of the absorption line-strength maps show that NGC7332 is young everywhere. Thepresence of a large-scale bar can explain most of those properties, but the fact that we see asignificant amount of unsettled gas, together with a few pecu liar features in the maps, suggestthat NGC7332 is still evolving. Interactions as well as bar-driven processes must thus haveplayed an important role in the formation and evolution of NGC7332, and presumably of S0galaxies in general.Key words: galaxies: abundances – galaxies: elliptical and lenticular, cD – galaxies: evo-lution – galaxies: formation – galaxies: individual (NGC73 32) – galaxies: kinematics anddynamics – galaxies: stellar content

A bar signature and central disc in the gaseous and stellar velocity fields of NGC 5448

We analyse SAURON kinematic maps of the inner kpc of the early-type (Sa) barred spiral galaxy NGC 5448. The observed morphology and kinematics of the emissionline gas is patchy and perturbed, indicating clear departures from circular motion. The kinematics of the stars is more regular, and display a small inner disk-like system embedded in a large-scale rotating structure. We focus on the [O iii] gas, and use a harmonic decomposition formalism to analyse the gas velocity field. The higher-order harmonic terms and the main kinematic features of the observed data are consistent with an analytically constructed simple bar model. The bar model is derived using linear theory, considering an m = 2 perturbation mode, and with bar parameters which are consistent with the large-scale bar detected via imaging. We also study optical and near infra-red images to reveal the asymmetric extinction in NGC 5448, and we recognise that some of the deviations between the data and the analytical bar model may be due to these complex dust features. Our study illustrates how the harmonic decomposition formalism can be used as a powerful tool to quantify non-circular motions in observed gas velocity fields.

Quantifying Resonant Structure in NGC 6946 from Two-dimensional Kinematics

We study the two-dimensional kinematics of the Hα-emitting gas in the nearby barred Scd galaxy NGC 6946, in order to determine the pattern speed of the primary m = 2 perturbation mode. The pattern speed is a crucial parameter for constraining the internal dynamics, estimating the impact velocities of the gravitational perturbation at the resonance radii, and setting up an evolutionary scenario for NGC 6946. Our data allow us to derive the best-fitting kinematic position angle and the geometry of the underlying gaseous disk, which we use to derive the pattern speed using the Tremaine-Weinberg method. We find a main pattern speed Ω = 22 km s-1 kpc-1, but our data clearly reveal the presence of an additional pattern speed Ω = 47 km s-1 kpc-1 in a zone within 1.25 kpc of the nucleus. Using the epicyclic approximation, we deduce the location of the resonance radii and confirm that inside the outer inner Lindblad resonance radius of the main oval, a primary bar has formed rotating at more than twice the outer pattern speed. We further confirm that a nuclear bar has formed inside the inner Lindblad resonance radius of the primary bar, coinciding with the inner inner Lindblad resonance radius of the large-scale m = 2 mode oval.

Re-evaluation of the central velocity-dispersion profile in NGC 6388

Context. The globular cluster NGC 6388 is one of the most massive clusters in our Milky Way and has been the subject of many studies. Recently, two independent groups found very different results when measuring its central velocity-dispersion profile with different methods. While we found a rising profile and a high central velocity dispersion (23.3s-1), measurements obtained by Lanzoni et al. (2013, ApJ, 769, 107) showed a value lower by 40%. The value of the central velocity dispersion has a serious effect on the mass and possible presence of an intermediate-mass black hole at the center of NGC 6388. Aims. The goal of this paper is to quantify the biases arising from measuring velocity dispersions from individual extracted stellar velocities versus the line broadening measurements of the integrated light using new tools to simulate realistic observations made with integral field units (IFU). Methods. We used a photometric catalog of NGC 6388 to extract the positions and magnitudes from the brightest stars in the central three arcseconds of NGC 6388 and created a simulated SINFONI and ARGUS dataset. The IFU data cube was constructed with different observing conditions (i.e., Strehl ratios and seeing) reproducing the conditions reported for the original observations as closely as possible. In addition, we produced an N-body realization of a ∼106 M stellar cluster with the same photometric properties as NGC 6388 to account for unresolved stars. Results. We find that the individual radial velocities, that is, the measurements from the simulated SINFONI data, are systematically biased towards lower velocity dispersions. The reason is that the velocities become biased toward the mean cluster velocity as a result of the wings in the point spread function of adaptive optics (AO) corrected data sets. This study shows that even with AO supported observations, individual radial velocities in crowded fields do not reproduce the true velocity distribution. The ARGUS observations do not show this kind of bias, but they were found to have larger uncertainties than previously obtained. We find a bias toward higher velocity dispersions in the ARGUS pointing when fixing the extreme velocities of the three brightest stars, but these variations are within the determined uncertainties. We reran Jeans models and fit them to the kinematic profile with the new uncertainties. This yielded a black-hole mass of M • = (2.8 ± 0.4) × 104 M and M/L ratio M/L = (1.6 ± 0.1) M/L, consistent with our previous results.

On the origin and fate of ionised-gas in early-type galaxies: The SAURON perspective

By detecting ionised-gas emission in 75% of the cases, the SAURON integral-field spectroscopic survey has further demonstrated that early-type galaxies often display nebular emission. Furthermore, the SAURON data have shown that such emission comes with an intriguing variety of morphologies, kinematic behaviours and line ratios. Perhaps most puzzling was the finding that round and slowly rotating objects generally display uncorrelated stellar and gaseous angular momenta, consistent with an external origin for the gas, whereas flatter and fast rotating galaxies host preferentially co-rotating gas and stars, suggesting internal production of gas. Alternatively, a bias against the internal production of ionised gas and against the acquisition of retrograde material may be present in these two kinds of objects, respectively. In light of the different content of hot gas in these systems, with slowly rotating objects being the only systems capable of hosting massive X-ray halos, we suggest that a varying importance of evaporation of warm gas in the hot interstellar medium can contribute to explain the difference in the relative behaviour of gas and stars in these two kinds of objects. Namely, whereas in X-ray bright and slowly rotating galaxies stellar-loss material would quickly evaporate in the hot medium, in X-ray faint and fast rotating objects such material would be allowed to lose angular momentum and settle in a disk, which could also obstruct the subsequent acquisition of retrograde gas. Evidence for a connection between warm and hot gas phases, presumably driven by heat conduction, is presented for four slowly rotating galaxies with Chandra observations.

Integral-field kinematics and stellar populations of early-type galaxies out to three half-light radii

Funding: STFC grant ST/K502339/1 during the course of this work (NFB), Leverhulme Trust Early Career Fellowship (AW).