Galaxy formation and evolution

Abstract:

We study the formation of stellar nuclear clusters (NC) with two types of N-body simulations: mergers of star clusters (SC) at the centre of disk galaxies and the accretion of a SC onto a previous NC. The merging of SCs produces systems consistent with observed scaling relations, they have shapes comparable with those observed and rotation consistent with that observed in the NCs of NGC 4244 and M 33. © 2010 American Institute of Physics.

Abstract:

We investigate the accuracy of mass determinations MBH of supermassive black holes in galaxies using dynamical models of the stellar kinematics. We compare 10 of our MBH measurements, using integral-field OASIS kinematics, to published values. For a sample of 25 galaxies we confront our new MBH derived using two modeling methods on the same OASIS data. © 2010 American Institute of Physics.

Abstract:

Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art observing methods and data processing, NICI typically achieves ~2 magnitudes better contrast compared to previous ground-based or space-based programs, at separations inside of ~2 arcsec. In preparation for the Campaign, we carried out efforts to identify previously unrecognized young stars, to rigorously construct our observing strategy, and to optimize the combination of angular and spectral differential imaging. The Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars. We describe the Campaign's goals, design, implementation, performance, and preliminary results. The NICI Campaign represents the largest and most sensitive imaging survey to date for massive (~1 Mjup) planets around other stars. Upon completion, the Campaign will establish the best measurements to date on the properties of young gas-giant planets at ~5-10 AU separations. Finally, Campaign discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with next-generation planet-finding instruments.

Abstract:

We report on two quantitative, morphological estimators of the filamentary structure of the Cosmic Web, the so-called global and local skeletons. The first, based on a global study of the matter density gradient flow, allows us to study the connectivity between a density peak and its surroundings, with direct relevance to the anisotropic accretion via cold flows on galactic halos. From the second, based on a local constraint equation involving the derivatives of the field, we can derive predictions for powerful statistics, such as the differential length and the relative saddle to extrema counts of the Cosmic web as a function of density threshold (with application to percolation of structures and connectivity), as well as a theoretical framework to study their cosmic evolution through the onset of gravity-induced non-linearities. © 2010 American Institute of Physics.

Abstract:

We present two-dimensional line-of-sight stellar kinematics of the lens galaxy in the Einstein Cross, obtained with the GEMINI 8 m telescope, using the GMOS integral-field spectrograph. The stellar kinematics extend to a radius of 4″ (with 0.″2 spaxels), covering about two-thirds of the effective (or half-light) radius Re - 6″ of this early-type spiral galaxy at redshift zl ≃ 0.04, of which the bulge is lensing a background quasar at redshift zs ≃ 1.7. The velocity map shows regular rotation up to ∼100 km s-1 around the minor axis of the bulge, consistent with axisymmetry. The velocity dispersion map shows a weak gradient increasing toward a central (R < 1″) value of σ0 = 170 ± 9 km s-1. We deproject the observed surface brightness from Hubble Space Telescope imaging to obtain a realistic luminosity density of the lens galaxy, which in turn is used to build axisymmetric dynamical models that fit the observed kinematic maps. We also construct a gravitational lens model that accurately fits the positions and relative fluxes of the four quasar images. We combine these independent constraints from stellar dynamics and gravitational lensing to study the total mass distribution in the inner parts of the lens galaxy. We find that the resulting luminous and total mass distribution are nearly identical around the Einstein radius Re = 0″.89, with a slope that is close to isothermal, but which becomes shallower toward the center if indeed mass follows light. The dynamical model fits to the observed kinematic maps result in a total mass-to-light ratio γdyn = 3.7 ± 0.5 γ⊙,I (in the I band). This is consistent with the Einstein mass Me = 1.54 × 1010 M⊙ divided by the (projected) luminosity within Re, which yields a total mass-to-light ratio of γE = 3.4 γ⊙,I, with an error of at most a few percent. We estimate from stellar population model fits to colors of the lens galaxy a stellar mass-to-light ratio γ* from 2.8 to 4.1 γ⊙,I. Although a constant dark matter fraction of 20% is not excluded, dark matter may play no significant role in the bulge of this ∼L* early-type spiral galaxy. © 2010. The American Astronomical Society.