Search For Companions Of Nearby Isolated Galaxies

The radial velocities are measured for 45 galaxies located in the neighborhoods of 29 likely isolated galaxies in a new catalog. We find that about 85% of these galaxies actually are well isolated objects. 4% of nearby galaxies with V_LG<3500 km/s are this kind of cosmic "orphan".Comment: 7 pages, 2 figure

Towards a realistic population of simulated galaxy groups and clusters

We present a new suite of large-volume cosmological hydrodynamical simulations called cosmo-OWLS. They form an extension to the OverWhelmingly Large Simulations (OWLS) project, and have been designed to help improve our understanding of cluster astrophysics and non-linear structure formation, which are now the limiting systematic errors when using clusters as cosmological probes. Starting from identical initial conditions in either the Planck or WMAP7 cosmologies, we systematically vary the most important ‘sub-grid’ physics, including feedback from supernovae and active galactic nuclei (AGN). We compare the properties of the simulated galaxy groups and clusters to a wide range of observational data, such as X-ray luminosity and temperature, gas mass fractions, entropy and density profiles, Sunyaev–Zel'dovich flux, I-band mass-to-light ratio, dominance of the brightest cluster galaxy and central massive black hole (BH) masses, by producing synthetic observations and mimicking observational analysis techniques. These comparisons demonstrate that some AGN feedback models can produce a realistic population of galaxy groups and clusters, broadly reproducing both the median trend and, for the first time, the scatter in physical properties over approximately two decades in mass (1013 M⊙ ≲ M500 ≲ 1015 M⊙) and 1.5 decades in radius (0.05 ≲ r/r500 ≲ 1.5). However, in other models, the AGN feedback is too violent (even though they reproduce the observed BH scaling relations), implying that calibration of the models is required. The production of realistic populations of simulated groups and clusters, as well as models that bracket the observations, opens the door to the creation of synthetic surveys for assisting the astrophysical and cosmological interpretation of cluster surveys, as well as quantifying the impact of selection effects

Implications for the origin of early-type dwarf galaxies: A detailed look at the isolated rotating early-type dwarf galaxy LEDA 2108986 (CG 611), ramifications for the fundamental plane's S-K(2) kinematic scaling, and the spin-ellipticity diagram

Selected from a sample of nine, isolated, dwarf early-type galaxies (ETGs) with the same range of kinematic properties as dwarf ETGs in clusters, we use LEDA 2108986 (CG 611) to address the nature versus nurture debate regarding the formation of dwarf ETGs. The presence of faint disk structures and rotation within some cluster dwarf ETGs has often been heralded as evidence that they were once late-type spiral or dwarf irregular galaxies prior to experiencing a cluster-induced transformation into an ETG. However, CG 611 also contains significant stellar rotation (≈20 km s-1) over its inner half-light radius (Re,maj= 0.71 kpc), and its stellar structure and kinematics resemble those of cluster ETGs. In addition to hosting a faint young nuclear spiral within a possible intermediate-scale stellar disk, CG 611 has accreted an intermediate-scale, counter-rotating gas disk. It is therefore apparent that dwarf ETGs can be built by accretion events, as opposed to disk-stripping scenarios. We go on to discuss how both dwarf and ordinary ETGs with intermediate-scale disks, whether under (de)construction or not, are not fully represented by the kinematic scaling S0.5= √0.5 V2rot+ σ2, and we also introduce a modified spin-ellipticity diagram λ (R)-ϵ (R) with the potential to track galaxies with such disks