Martin Bureau

Abstract:

We examine a sample of 30 edge-on spiral and S0 galaxies that have boxy and peanut-shaped bulges.We compute model stellar kinematics by solving the Jeans equations for axisymmetric mass distributions derived from K-band images. These simple models have only one free parameter: the dynamical mass-to-light ratio, which we assume is independent of radius. Given the simplicity of the modelling procedure, the model second velocity moments are strikingly good fits to the observed stellar kinematics within the extent of our kinematic data, which typically reach ∼ 0.5-1 R25 (where R25 is the optical radius), or equivalently ∼ 2-3 Re (where Re is the effective or half-light radius).We therefore find no evidence for a dominant dark matter component within the optical disk of spiral galaxies. This is equally true of the S0s in our sample, which significantly extends previous observational constraints on dark matter in these galaxies. The predicted kinematics do deviate slightly but systematically from the observations in the bulge region of most galaxies, but we argue that this is consistent with the claim that boxy and peanut-shaped bulges are bars viewed edge-on.

Abstract:

The ATLAS3D project is a multiwavelength survey combined with a theoretical modelling effort. The observations span from the radio to the millimetre and optical, and provide multicolour imaging, two-dimensional kinematics of the atomic (Hi), molecular (CO) and ionized gas (Hβ, [Oiii] and [Ni]), together with the kinematics and population of the stars (Hβ, Fe5015 and Mg b), for a carefully selected, volume-limited (1.16 × 105Mpc3) sample of 260 early-type (elliptical E and lenticular S0) galaxies (ETGs). The models include semi-analytic, N-body binary mergers and cosmological simulations of galaxy formation. Here we present the science goals for the project and introduce the galaxy sample and the selection criteria. The sample consists of nearby (D < 42Mpc, |δ- 29°| < 35°, |b| > 15°) morphologically selected ETGs extracted from a parent sample of 871 galaxies (8 per cent E, 22 per cent S0 and 70 per cent spirals) brighter than MK < -21.5mag (stellar mass M{black star}≳ 6 ×109M⊙). We analyse possible selection biases and we conclude that the parent sample is essentially complete and statistically representative of the nearby galaxy population. We present the size-luminosity relation for the spirals and ETGs and show that the ETGs in the ATLAS3D sample define a tight red sequence in a colour-magnitude diagram, with few objects in the transition from the blue cloud. We describe the strategy of the SAURON integral field observations and the extraction of the stellar kinematics with the ppxf method. We find typical 1σ errors of ΔV≈ 6kms-1, Δσ≈ 7kms-1, Δh3≈Δh4≈ 0.03 in the mean velocity, the velocity dispersion and Gauss-Hermite (GH) moments for galaxies with effective dispersion σe≳ 120kms-1. For galaxies with lower σe (≈40 per cent of the sample) the GH moments are gradually penalized by ppxf towards zero to suppress the noise produced by the spectral undersampling and only V and σ can be measured. We give an overview of the characteristics of the other main data sets already available for our sample and of the ongoing modelling projects. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.