Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics

A sample of 197 X-ray emitting clusters of galaxies is considered in the context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the gas mass, extrapolated via an assumed $\beta$ model to a fixed radius of 3 Mpc, is correlated with the gas temperature as predicted by MOND ($M_g \propto T^2$). The observed temperatures are generally consistent with the inferred mass of hot gas; no substantial quantity of additional unseen matter is required in the context of MOND. However, modified dynamics cannot resolve the strong lensing discrepancy in those clusters where this phenomenon occurs. The prediction is that additional baryonic matter may be detected in the central regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro

Stripes on a 6-Leg Hubbard Ladder

While DMRG calculations find stripes on doped n-leg t-J ladders, little is known about the possible formation of stripes on n-leg Hubbard ladders. Here we report results for a 7x6 Hubbard model with 4 holes. We find that a stripe forms for values of U/t ranging from 6 to 20. For U/t ~ 3-4, the system exhibits the domain wall feature of a stripe, but the hole density is very broadened.Comment: 4 pages, 5 figure

Observing the sky at extremely high energies with the Cherenkov Telescope Array: Status of the GCT project

The Cherenkov Telescope Array is the main global project of ground-based gamma-ray astronomy for the coming decades. Performance will be significantly improved relative to present instruments, allowing a new insight into the high-energy Universe [1]. The nominal CTA southern array will include a sub-array of seventy 4 m telescopes spread over a few square kilometers to study the sky at extremely high energies, with the opening of a new window in the multi-TeV energy range. The Gamma-ray Cherenkov Telescope (GCT) is one of the proposed telescope designs for that sub-array. The GCT prototype recorded its first Cherenkov light on sky in 2015. After an assessment phase in 2016, new observations have been performed successfully in 2017. The GCT collaboration plans to install its first telescopes and cameras on the CTA site in Chile in 2018-2019 and to contribute a number of telescopes to the subsequent CTA production phase.Comment: 8 pages, 7 figures, ICRC201

A simplified PERT system

Modified PERT technique processes the input data and arranges it in familiar graphic form in a booklet which is issued at periodic intervals. The tabulated data provides readily available information to management personnel concerned with monitoring the progress of a program

Star-Formation in Low Radio Luminosity AGN from the Sloan Digital Sky Survey

We investigate faint radio emission from low- to high-luminosity Active Galactic Nuclei (AGN) selected from the Sloan Digital Sky Survey (SDSS). Their radio properties are inferred by co-adding large ensembles of radio image cut-outs from the FIRST survey, as almost all of the sources are individually undetected. We correlate the median radio flux densities against a range of other sample properties, including median values for redshift, [OIII] luminosity, emission line ratios, and the strength of the 4000A break. We detect a strong trend for sources that are actively undergoing star-formation to have excess radio emission beyond the ~10^28 ergs/s/Hz level found for sources without any discernible star-formation. Furthermore, this additional radio emission correlates well with the strength of the 4000A break in the optical spectrum, and may be used to assess the age of the star-forming component. We examine two subsamples, one containing the systems with emission line ratios most like star-forming systems, and one with the sources that have characteristic AGN ratios. This division also separates the mechanism responsible for the radio emission (star-formation vs. AGN). For both cases we find a strong, almost identical, correlation between [OIII] and radio luminosity, with the AGN sample extending toward lower, and the star-formation sample toward higher luminosities. A clearer separation between the two subsamples is seen as function of the central velocity dispersion of the host galaxy. For systems with similar redshifts and velocity dispersions, the star-formation subsample is brighter than the AGN in the radio by an order of magnitude. This underlines the notion that the radio emission in star-forming systems can dominate the emission associated with the AGN.Comment: Accepted for publication in Astronomical Journal; 15 pages, 8 color figure