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(Abridged) Objects with radii of 10 to 100 pc and masses in the range from 10^6 to 10^8 M_sun have been discovered during the past decade. These so-called ultra compact dwarf galaxies (UCDs) constitute a transition between classical star…
A constant stellar mass-to-light ratio $M_\star/L$ has been widely-used in studies of galaxy dynamics and strong lensing, which aim at disentangling the mass distributions of dark matter and baryons. However, systematic biases arising from…
High-resolution nuclear-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies show generally a steep nuclear rise and flat rotation from the disk to halo. The high-velocity central rotation indicates massive core within bulges. Since…
I show that three independent methods utilizing clusters of galaxies - cluster dynamics and mass-to-light ratio, baryon fraction in clusters, and cluster evolution - all indicate the same robust result: the mass-density of the universe is…
We present an analysis of the Fundamental Plane for a sample of 27 field early-type galaxies in the redshift range 0.6<z<1.15. The galaxies in this sample have high S/N spectra obtained at the VLT and high resolution imaging from the ACS.…
The dark matter content of early,- type galaxies (ETGs) is a hotly debated topic with contrasting results arguing in favour or against the presence of significant dark mass within the effective radius and the change with luminosity and…
We determine what aspects of the density field surrounding galaxies most affect their properties. For Sloan Digital Sky Survey galaxies, we measure the group environment, meaning the host group luminosity and the distance from the group…
With targeted imaging of groups in the local volume, the regions of collapse around bright galaxies can be clearly identified by the distribution of dwarfs and luminosity functions can be established to very faint levels. In the case of the…
We draw a quantitative comparison of the distribution of the galaxies and the intra-cluster gas in the Virgo cluster by extending the morphological analysis by Binggeli et al. (1987) to the intra-cluster gas. We use the Virgo Cluster…
We present a morphological study of galaxies in the A901/902 supercluster from the COMBO-17 survey. A total of 570 galaxies with photometric redshifts in the range 0.155 < z_phot < 0.185 are visually classified by three independent…
The MS1224+20 cluster of galaxies is a high luminosity X-ray source at z=0.325. To compare the lensing mass to the virial mass we have completed a uniform, high precision redshift survey over a field of $7\arcm\times9\arcm$, obtaining 75…
Galaxy clusters constitute powerful cosmological probes thanks to comparisons between observed and simulated clusters. As such Virgo constitutes a formidable source for detailed observations facilitated by its proximity. However, the…
We investigate the feasibility of carrying out likelihood analysis on the velocities of galaxy clusters to determine power spectrum parameters. Using N-body simulations of cosmological density fields we show that the velocity field traced…
The paper discusses the problem of the orientation of galaxies in groups in the Local Supercluster (LSC). The existence of the preferred orientation of galaxy group is shown. We found that the orientation of galaxy groups in the Local…
We study the stellar cluster population in two adjacent fields in the nearby, face-on spiral galaxy, M83, using WFC3/HST imaging. The clusters are selected through visual inspection to be centrally concentrated, symmetric, and resolved on…
We present internal velocity dispersion determinations from high-resolution spectroscopic observations of a sample of nine globular clusters in M31. Comprehensive numerical simulations are used to show that the typical uncertainty of our…
We have identified a large-scale structure at z~0.73 in the COSMOS field, coherently described by the distribution of galaxy photometric redshifts, an ACS weak-lensing convergence map and the distribution of extended X-ray sources in a…
Star clusters in 6 nearby spiral galaxies are examined using archive images from HST/WFPC2. The galaxies have previously been studied from the ground and some of them are known to possess rich populations of "young massive clusters" (YMCs).…
We use \sim 2000 galaxies belonging to different environments to show how the fractions of different galaxy morphological types vary with global environment and as function of galaxy stellar mass at low redshift. Considering mass limited…
We place constraints on the average density (Omega_m) and clustering amplitude (sigma_8) of matter using a combination of two measurements from the Sloan Digital Sky Survey: the galaxy two-point correlation function, w_p, and the…