We study the volume-limited and nearly mass selected (stellar mass M stars > ∼ 6 × 10 9 M ) ATLAS 3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). We construct detailed axisymmetric dynamical models (JAM), which allow for orbital anisotropy, include a dark matter halo, and reproduce in detail both the galaxy images and the highquality integral-field stellar kinematics out to about 1R e , the projected half-light radius. We derive accurate total mass-to-light ratios (M/L) e and dark matter fractions f DM , within a sphere of radius r = R e centred on the galaxies. We also measure the stellar (M/L) stars and derive a median dark matter fraction f DM = 13% in our sample. We infer masses M JAM ≡ L × (M/L) e ≈ 2 × M 1/2 , where M 1/2 is the total mass within a sphere enclosing half of the galaxy light. We find that the thin two-dimensional subset spanned by galaxies in the (M JAM , σ e , R maj e ) coordinates system, which we call the Mass Plane (MP) has an observed rms scatter of 19%, which implies an intrinsic one of 11%. Here R maj e is the major axis of an isophote enclosing half of the observed galaxy light, while σ e is measured within that isophote. The MP satisfies the scalar virial relation M JAM ∝ σ 2 e R maj e within our tight errors. This show that the larger scatter in the Fundamental Plane (FP) (L, σ e , R e ) is due to stellar population effects (including trends in the stellar Initial Mass Function [IMF]). It confirms that the FP deviation from the virial exponents is due to a genuine (M/L) e variation. However, the details of how both R e and σ e are determined are critical in defining the precise deviation from the virial exponents. The main uncertainty in masses or M/L estimates using the scalar virial relation is in the measurement of R e . This problem is already relevant for nearby galaxies and may cause significant biases in virial mass and size determinations at high-redshift. Dynamical models can eliminate these problems. We revisit the (M/L) e − σ e relation, which describes most of the deviations between the MP and the FP. The best-fitting relation is (M/L) e ∝ σ 0.72 e (r-band). It provides an upper limit to any systematic increase of the IMF mass normalization with σ e . The correlation is more shallow and has smaller scatter for slow rotating systems or for galaxies in Virgo. For the latter, when using the best distance estimates, we observe a scatter in (M/L) e of 11%, and infer an intrinsic one of 8%. We perform an accurate empirical study of the link between σ e and the galaxies circular velocity V circ within 1R e (where stars dominate) and find the relation max(V circ ) ≈ 1.76 × σ e , which has an observed scatter of 7%. The accurate parameters described in this paper are used in the companion Paper XX of this series to explore the variation of global galaxy properties, including the IMF, on the projections of the MP.

Much of our knowledge of galaxies comes from analysing the radiation emitted by their stars, which depends on the present number of each type of star in the galaxy. The present number depends on the stellar initial mass function (IMF), which describes the distribution of stellar masses when the population formed, and knowledge of it is critical to almost every aspect of galaxy evolution. More than 50 years after the first IMF determination, no consensus has emerged on whether it is universal among different types of galaxies. Previous studies indicated that the IMF and the dark matter fraction in galaxy centres cannot both be universal, but they could not convincingly discriminate between the two possibilities. Only recently were indications found that massive elliptical galaxies may not have the same IMF as the Milky Way. Here we report a study of the two-dimensional stellar kinematics for the large representative ATLAS(3D) sample of nearby early-type galaxies spanning two orders of magnitude in stellar mass, using detailed dynamical models. We find a strong systematic variation in IMF in early-type galaxies as a function of their stellar mass-to-light ratios, producing differences of a factor of up to three in galactic stellar mass. This implies that a galaxy's IMF depends intimately on the galaxy's formation history.

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 (H i), molecular (CO) and ionized gas (Hβ, [O iii] and [N i]), together with the kinematics and population of the stars (Hβ, Fe5015 and Mg b), for a carefully selected, volume‐limited (1.16 × 105 Mpc3) 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 < 42 Mpc, |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 < −21.5 mag (stellar mass M★≳ 6 ×109 M⊙). 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≈ 6 km s−1, Δσ≈ 7 km s−1, Δh3≈Δh4≈ 0.03 in the mean velocity, the velocity dispersion and Gauss–Hermite (GH) moments for galaxies with effective dispersion σe≳ 120 km s−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.

We present the stellar population content of early-type galaxies from the ATLAS 3D survey. Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive nonparametric star-formation histories, mass-weighted average values of age, metallicity, and half-mass formation timescales. Using homogeneously derived effective radii and dynamically-determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (M JAM , σ e , R maj e ), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alphaenhanced than their larger counterparts.From non-parametric star-formation histories, we find that the duration of star formation is systematically more extended in lower mass objects. Assuming that our sample represents most of the stellar content of today's local Universe, approximately 50% of all stars formed within the first 2 Gyr following the big bang. Most of these stars reside today in the most massive galaxies (> 10 10.5 M ), which themselves formed 90% of their stars by z ∼2. The lower-mass objects, in contrast, have formed barely half their stars in this time interval. Stellar population properties are independent of environment over two orders of magnitude in local density, varying only with galaxy mass. In the highest-density regions of our volume (dominated by the Virgo cluster), galaxies are older, alpha-enhanced and have shorter star-formation histories with respect to lower density regions.This paper proceeds as follows: Section 2 describes the observations and analysis methods; Sections 3 and 4 present our population parameters on the mass-size plane, and against velocity dispersion and mass, respectively; Section 5 presents trends from our empirical star formation histories, and Section 6 concludes. OBSERVATIONS, LINE-STRENGTHS AND ANALYSISHere we describe the optical spectroscopy used in our analysis. The same spectral data cubes were used for deriving the line strengths and for the spectral fitting, so calibration and removal of emission applies to both techniques. SAURON observations and basic calibrationThe SAURON spectrograph and basic data reduction is described in detail in Bacon et al. (2001). Further details of the ATLAS 3D SAURON observations are given in Cappellari et al. (2011a). The details of our calibrations and line-strength measurements follow closely the techniques developed and described by Kuntschner et al. (2006). Most of the 260 ATLAS 3D SAURON spectra were obtained after the spectrograph was upgraded with a volume-phase holographic (VPH) grating in 2004, except for 64 objects observed as part of the SAURON Survey (de Zeeuw et al. 2002) and other related projects. The pre-and post-VPH data are reduced and analysed self-consistently to respect th...

In the companion Paper XV of this series we derive accurate total mass-to-light ratios (M/L) JAM ≈ (M/L)(r = R e ) within a sphere of radius r = R e centred on the galaxy, as well as stellar (M/L) stars (with the dark matter removed) for the volume-limited and nearly mass selected (stellar mass M > ∼ 6 × 10 9 M ) ATLAS 3D sample of 260 early-type galaxies (ETGs, ellipticals Es and lenticulars S0s). Here we use those parameters to study the two orthogonal projections (M JAM , σ e ) and (M JAM , R maj e ) of the thin Mass Plane (MP) (M JAM , σ e , R maj e ) which describes the distribution of the galaxy population, where M JAM ≡ L × (M/L) JAM ≈ M . The distribution of galaxy properties on both projections of the MP is characterized by: (i) the same zone of exclusion (ZOE), which can be transformed from one projection to the other using the scalar virial equation. The ZOE is roughly described by two power-laws, joined by a break at a characteristic mass M JAM ≈ 3 × 10 10 M , which corresponds to the minimum R e and maximum stellar density. This results in a break in the mean M JAM − σ e relation with trends M JAM ∝ σ 2.3

We present a detailed two-dimensional stellar dynamical analysis of a sample of 44 cosmological hydrodynamical simulations of individual central galaxies with stellar masses of 2 × 10 10 M M * 6 × 10 11 M . Kinematic maps of the stellar line-of-sight velocity, velocity dispersion, and higher-order Gauss-Hermite moments h 3 and h 4 are constructed for each central galaxy and for the most massive satellites. The amount of rotation is quantified using the λ R -parameter. The velocity, velocity dispersion, h 3 , and h 4 fields of the simulated galaxies show a diversity similar to observed kinematic maps of early-type galaxies in the ATLAS 3D survey. This includes fast (regular), slow, and misaligned rotation, hot spheroids with embedded cold disk components as well as galaxies with counter-rotating cores or central depressions in the velocity dispersion. We link the present day kinematic properties to the individual cosmological formation histories of the galaxies. In general, major galaxy mergers have a significant influence on the rotation properties resulting in both a spin-down as well as a spin-up of the merger remnant. Lower mass galaxies with significant ( 18 per cent) in-situ formation of stars since z ≈ 2, or with additional gas-rich major mergers -resulting in a spin-up -in their formation history, form elongated ( ∼ 0.45) fast rotators (λ R ∼ 0.46) with a clear anti-correlation of h 3 and v/σ. An additional formation path for fast rotators includes gas poor major mergers leading to a spin-up of the remnants (λ R ∼ 0.43). This formation path does not result in anti-correlated h 3 and v/σ. The formation histories of slow rotators can include late major mergers. If the merger is gas-rich the remnant typically is a less flattened slow rotator with a central dip in the velocity dispersion. If the merger is gas poor the remnant is very elongated ( ∼ 0.43) and slowly rotating (λ R ∼ 0.11). The galaxies most consistent with the rare class of nonrotating round early-type galaxies grow by gas-poor minor mergers alone. In general, more massive galaxies have less in-situ star formation since z ∼ 2, rotate slower and have older stellar populations. We discuss general implications for the formation of fast and slowly rotating galaxies as well as the weaknesses and strengths of the underlying models.

The Next Generation Virgo Cluster Survey (NGVS) is a program that uses the 1 deg 2 MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical imaging survey of the Virgo cluster, from its core to its virial radius-covering a total area of 104 deg 2-in the u * griz bandpasses. Thanks to a dedicated data acquisition strategy and processing pipeline, the NGVS reaches a point-source depth of g ≈ 25.9 mag (10σ) and a surface brightness limit of μ g ∼ 29 mag arcsec −2 (2σ above the mean sky level), thus superseding all previous optical studies of this benchmark galaxy cluster. In this paper, we give an overview of the technical aspects of the survey, such as areal coverage, field placement, choice of filters, limiting magnitudes, observing strategies, data processing and calibration pipelines, survey timeline, and data products. We also describe the primary scientific topics of the NGVS, which include: the galaxy luminosity and mass functions; the color-magnitude relation; galaxy scaling relations; compact stellar systems; galactic nuclei; the extragalactic distance scale; the large-scale environment of the cluster and its relationship to the Local Supercluster; diffuse light and the intracluster medium; galaxy interactions and evolutionary processes; and extragalactic star clusters. In addition, we describe a number of ancillary programs dealing with "foreground" and "background" science topics, including the study of highinclination trans-Neptunian objects; the structure of the Galactic halo in the direction of the Virgo Overdensity and Sagittarius Stream; the measurement of cosmic shear, galaxy-galaxy, and cluster lensing; and the identification of distant galaxy clusters, and strong-lensing events.

Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (≤ 50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈ 300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7 pc resolution AMR simulations of high-redshift disks including photo-ionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (≤ 200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can re-accrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. Our simulations produce gaseous outflows with velocities, densities and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of highredshift galaxies, without rapid dispersion and reformation of clumps. These long-lived clumps can be involved in inside-out evolution and thickening of the disk, spheroid growth and fueling of the central black hole.