Extremely Large Telescope

Abstract:

We combine VLT/ISAAC NIR spectroscopy with archival HST/WFPC2 and HST/NICMOS imaging to study the central 20"x20" of M83. Our NIR indices for clusters in the circumnuclear star-burst region are inconsistent with simple instantaneous burst models. However, models of a single burst dispersed over a duration of 6 Myrs fit the data well and provide the clearest evidence yet of an age gradient along the star forming arc, with the youngest clusters nearest the north-east dust lane. The long slit kinematics show no evidence to support previous claims of a second hidden mass concentration, although we do observe changes in molecular gas velocity consistent with the presence of a shock at the edge of the dust lane.

Abstract:

We present spatially-resolved, rest-frame optical spectroscopy of a Lyman-break galaxy (LBG), Q0347-383 C5, obtained with SINFONI on the VLT. This galaxy, among the % brightest LBGs, is only the second LBG observed with an integral-field spectrograph. It was first described by Pettini et al. (2001, ApJ, 554, 981), who obtained WFPC2 F702W imaging and longslit spectroscopy in the -band. We find that the emission line morphology is dominated by two unresolved blobs at a projected distance of 5 kpc with a velocity offset of km s. Velocity dispersions suggest that each blob has a mass of. Unlike Pettini et al. (2001), our spectra are deep enough to detect H, and we derive star-formation rates of yr, and use the H/[OIII] ratio to crudely estimate an oxygen abundance , which is in the range typically observed for LBGs. We compare the properties of Q0347-383 C5 with what is found for other LBGs, including the gravitationally lensed "arc+core" galaxy (Nesvadba et al. 2006, ApJ, 650, 661), and discuss possible scenarios for the nature of the source, namely disk rotation, a starburst-driven wind, disk fragmentation, and merging of two LBGs. We favor the merging interpretation for bright, extended LBGs like Q0347-383 C5, in broad agreement with predicted merger rates from hierarchical models. © 2008 ESO.

Abstract:

We present a simple and efficient anisotropic generalization of the semi-isotropic (two-integral) axisymmetric Jeans formalism, which is used to model the stellar kinematics of galaxies. The following is assumed: (i) a constant mass-to-light ratio (M/L) and (ii) a velocity ellipsoid that is aligned with cylindrical coordinates (R, z) and characterized by the classic anisotropy parameter. Our simple models are fit to SAURON integral-field observations of the stellar kinematics for a set of fast-rotator early-type galaxies. With only two free parameters (βz and the inclination), the models generally provide remarkably good descriptions of the shape of the first (V) and second () velocity moments, once a detailed description of the surface brightness is given. This is consistent with previous findings on the dynamical structure of these objects. With the observationally motivated assumption that βz ≳ 0, the method is able to recover the inclination. The technique can be used to determine the dynamical M/L and angular momenta of early-type fast-rotators and spiral galaxies, especially when the quality of the data does not justify more sophisticated modelling approaches. This formalism allows for the inclusion of dark matter, supermassive black holes, spatially varying anisotropy and multiple kinematic components. © 2008 RAS.

Abstract:

We analysed two-dimensional maps of 48 early-type galaxies obtained with the SAURON and OASIS integral-field spectrographs using kinemetry, a generalization of surface photometry to the higher order moments of the line-of-sight velocity distribution (LOSVD). The maps analysed include: reconstructed image, mean velocity, velocity dispersion, h3 and h4 Gauss-Hermite moments. Kinemetry is a good method to recognize structures otherwise missed by using surface photometry, such as embedded discs and kinematic subcomponents. In the SAURON sample, we find that 31 per cent of early-type galaxies are single component systems. 91 per cent of the multicomponents systems have two kinematic subcomponents, the rest having three. In addition, 29 per cent of galaxies have kinematically decoupled components, nuclear components with significant kinematic twists. We differentiate between slow and fast rotators using velocity maps only and find that fast-rotating galaxies contain discs with a large range in mass fractions to the main body. Specifically, we find that the velocity maps of fast rotators closely resemble those of inclined discs, except in the transition regions between kinematic subcomponents. This deviation is measured with the kinemetric k 5/k1 ratio, which is large and noisy in slow rotators and about 2 per cent in fast rotators. In terms of E/S0 classification, this means that 74 per cent of Es and 92 per cent of S0s have components with disc-like kinematics. We suggest that differences in k5/k1 values for the fast and slow rotators arise from their different intrinsic structure which is reflected on the velocity maps. For the majority of fast rotators, the kinematic axial ratios are equal to or less than their photometric axial ratios, contrary to what is predicted with isotropic Jeans models viewed at different inclinations. The position angles of fast rotators are constant, while they vary abruptly in slow rotators. Velocity dispersion maps of face-on galaxies have shapes similar to the distribution of light. Velocity dispersion maps of the edge-on fast rotators and all slow rotators show differences which can only be partially explained with isotropic models and, in the case of fast rotators, often require additional cold components. We constructed local (bin-by-bin) h3-V/σ and h4-V/σ diagrams from SAURON observations. We confirm the classical anticorrelation of h3 and V/σ, but we also find that h3 is almost zero in some objects or even weakly correlated with V/σ. The distribution of h4 for fast and slow rotators is mildly positive on average. In general, fast rotators contain flattened components characterized by a disc-like rotation. The difference between slow and fast rotators is traceable throughout all moments of the LOSVD, with evidence for different intrinsic shapes and orbital contents and, hence, likely different evolutionary paths. © 2008 RAS.