Neutral Hydrogen in the Local Group and around the Milky Way

Galaxies in our universe must acquire fresh gas to continue forming new stars. A likely source of this material may be the gas that resides between galaxies. We do not, however, have a clear understanding of the specifics, such as its distribution. The first claimed detection of this cosmic web of material directly in emission was published a decade ago using the Westerbork Synthesis Radio Telescope in the Netherlands while surveying neutral hydrogen in the Local Group of galaxies. Later evidence, in the form of stellar surveys and test particle simulations, showed that a tidal origin of the gas was another possibility.;More recent survey work of the Local Group, specifically between the galaxies M31 and M33, motivated us to map a section of the Westerbork emission using the Robert C . Byrd Green Bank Telescope (GBT). Our survey covers a 12 square degree area between M31 and M33, in which we reach 21 cm column density sensitivities of 1017.2 cm-2 after 400 hours of observations. These observations provide more than a factor of five better spatial resolution, and better than a factor of three in velocity resolution. Not only do we confirm the emission seen in the Westerbork data, we find that the hydrogen gas is composed of clouds a few kiloparsecs across, with properties suggesting they are a unique population to the Local Group. We conclude that the clouds are likely transient condensations from an intergalactic filament of gas, although a tidal feature cannot currently be ruled out. We also conducted GBT pointings to the northwest of M31 to search for the extended emission seen in the Westerbork data as well. What detections we find appear to be more related to the high velocity cloud population of M31. We are continuing to map other regions around M31 to search for more diffuse emission.;We also present southern sky maps of the high velocity and intermediate velocity clouds around our own Milky Way, using 21 cm survey data from the Parkes telescope in Australia. The existence of these objects have been known for over 50 years, yet there is no general consensus as to their origins. The maps we have produced are the most detailed to date, with high spatial and velocity resolution and good sensitivity. By using a model of Milky Way rotation, we more effectively filter out foreground emission from our own Galaxy to produce these maps. We also discuss the basic global properties of this gas and the features that are seen. Apart from the Magellanic system and Galactic warp, most of the emission is in the form of small clouds. Some of the emission seen in these data may be representative of the eventual fate of the M31-M33 clouds. Work with this survey is ongoing

Sensitive 21 cm observatios of neutral hydrogen in the local group near M31

Very sensitive 21 cm H i measurements have been made at several locations around the Local Group galaxy M31 using the Green Bank Telescope at an angular resolution of 9.′1, with a 5σ detection level of N{sub H} {sub i} = 3.9 × 10{sup 17} cm{sup −2} for a 30 km s{sup −1} line. Most of the H i in a 12 square-degree area almost equidistant between M31 and M33 is contained in nine discrete clouds that have a typical size of a few kpc and a H i mass of 10{sup 5}M{sub ⊙}. Their velocities in the Local Group Standard of Rest lie between −100 and +40 km s{sup −1}, comparable to the systemic velocities of M31 and M33. The clouds appear to be isolated kinematically and spatially from each other. The total H i mass of all nine clouds is 1.4 × 10{sup 6}M{sub ⊙} for an adopted distance of 800 kpc, with perhaps another 0.2 × 10{sup 6}M{sub ⊙} in smaller clouds or more diffuse emission. The H i mass of each cloud is typically three orders of magnitude less than the dynamical (virial) mass needed to bind the cloud gravitationally. Although they have the size and H i mass of dwarf galaxies, the cloudsmore » are unlikely to be part of the satellite system of the Local Group, as they lack stars. To the north of M31, sensitive H i measurements on a coarse grid find emission that may be associated with an extension of the M31 high-velocity cloud (HVC) population to projected distances of ∼100 kpc. An extension of the M31 HVC population at a similar distance to the southeast, toward M33, is not observed.« les

The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?

Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies characterized by high luminosity, blue color, and high surface brightness that sit at the critical juncture of galaxies evolving from the blue to the red sequence. As part of our multi-wavelength survey of local LCBGs, we have been studying the HI content of these galaxies using both single-dish telescopes and interferometers. Our goals are to determine if single-dish HI observations represent a true measure of the dynamical mass of LCBGs and to look for signatures of recent interactions that may be triggering star formation in LCBGs. Our data show that while some LCBGs are undergoing interactions, many appear isolated. While all LCBGs contain HI and show signatures of rotation, the population does not lie on the Tully-Fisher relation nor can it evolve onto it. Furthermore, the HI maps of many LCBGs show signatures of dynamically hot components, suggesting that we are seeing the formation of a thick disk or spheroid in at least some LCBGs. There is good agreement between the HI and H-alpha kinematics for LCBGs, and both are similar in appearance to the H-alpha kinematics of high redshift star-forming galaxies. Our combined data suggest that star formation in LCBGs is primarily quenched by virial heating, consistent with model predictions.Comment: 4 pages, 2 figures, to appear in the proceedings of IAU Symposium 277, "Tracing the Ancestry of Galaxies on the Land of our Ancestors", eds. C. Carignan, K.C. Freeman, and F. Combe

Antioxidant activities and phenolic contents of the methanol extracts of the stems of Acokanthera oppositifolia and Adenia gummifera

Abstract Background Acokanthera oppositifolia Lam (family: Apocynaceae) is a shrub or small tree with white latex, and the leaves of this plant are used in the form of a snuff to treat headaches and in infusions for abdominal pains and convulsions and septicaemia. Adenia gummifera Harv of the family Passifloraceae is a distinctive woody climber whose infusions are used as emetics and are said to help with some forms of depression. Lipid peroxidation has gained more importance today because of its involvement in pathogenesis of many diseases. Free radicals are the main agents in lipid peroxidation. Antioxidants thus play an important role of protecting the human body against damage by the free radicals. Plants containing phenolic compounds have been reported to possess strong antioxidant properties. Methods The antioxidant activities and phenolic contents of the methanol extracts of the stems of Acokanthera oppositifolia and Adenia gummifera were evaluated using in vitro standard procedures. Spectrophotometry was the basis for the determinations of total phenol, total flavonoids, flavonols, and proanthocyanidins. Tannins, quercetin and catechin equivalents were used for these parameters. The antioxidant activities of the stem extract of Acokanthera oppositifolia were determined by the 2,2'-azinobis-3- ethylbenzothiazoline-6-sulfonic acid (ABTS), 1,1-Diphenyl-2-picrylhydrazyl (DPPH), and ferrous reducing antioxidant property (FRAP) methods. Results The results from this study showed that the antioxidant activities of the stem extract of Acokanthera oppositifolia as determined by the 1,1-Diphenyl-2-picrylhydrazyl (DPPH), and ferrous reducing antioxidant property (FRAP) methods, were higher than that of Adenia gummifera. The levels of total phenols and flavonols for A. oppositifolia were also higher. On the other hand, the stem extract of Adenia gummifera had higher level of total flavonoids and proanthocyanidins than that of Acokanthera oppositifolia. The 2, 2'-azinobis-3- ethylbenzothiazoline-6-sulfonic acid (ABTS) activities of the 2 plant extracts were similar and comparable to that of BHT. Conclusion Thus, the present results indicate clearly that the extracts of Acokanthera oppositifolia and Adenia gummifera possess antioxidant properties and could serve as free radical inhibitors or scavengers, acting possibly as primary antioxidants. This study has to some extent validated the medicinal potential of the stems of Acokanthera oppositifolia and Adenia gummifera.</p

Testing a dynamic field account of interactions between spatial attention and spatial working memory

Studies examining the relationship between spatial attention and spatial working memory (SWM) have shown that discrimination responses are faster for targets appearing at locations that are being maintained in SWM, and that location memory is impaired when attention is withdrawn during the delay. These observations support the proposal that sustained attention is required for successful retention in SWM: if attention is withdrawn, memory representations are likely to fail, increasing errors. In the present study, this proposal is reexamined in light of a neural process model of SWM. On the basis of the model’s functioning, we propose an alternative explanation for the observed decline in SWM performance when a secondary task is performed during retention: SWM representations drift systematically toward the location of targets appearing during the delay. To test this explanation, participants completed a color-discrimination task during the delay interval of a spatial recall task. In the critical shifting attention condition, the color stimulus could appear either toward or away from the memorized location relative to a midline reference axis. We hypothesized that if shifting attention during the delay leads to the failure of SWM representations, there should be an increase in the variance of recall errors but no change in directional error, regardless of the direction of the shift. Conversely, if shifting attention induces drift of SWM representations—as predicted by the model—there should be systematic changes in the pattern of spatial recall errors depending on the direction of the shift. Results were consistent with the latter possibility—recall errors were biased toward the location of discrimination targets appearing during the delay

Can an Infectious Disease Genomics Project Predict and Prevent the Next Pandemic?

Infectious diseases need a globally coordinated genomic-based movement linking sequencing efforts to development of response tools to mitigate the impact of existing and emerging threats

Effect of three‐dimensional slab geometry on deformation in the mantle wedge: Implications for shear wave anisotropy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94690/1/ggge1124.pd