The quest for hot gas in the halo of NGC 1511

XMM-Newton observations of the starburst galaxy NGC 1511 reveal the presence of a previously unknown extended hot gaseous phase of its ISM, which partly extends out of the disk plane. The emission distribution is asymmetric, being brightest in the eastern half of the galaxy, where also radio continuum observations suggest the highest level of star formation. Spectral analysis of the integral 0.2-12 keV X-ray emission from NGC 1511 indicates a complex emission composition. A model comprising a power law plus thermal plasma component, both absorbed by foreground gas, cannot explain all details of the observed spectrum, requiring a third spectral component to be added. This component can be a second thermal plasma, but other spectral models can be fitted as well. Its X-ray properties characterize NGC 1511 as a starburst galaxy. The X-ray-to-infrared luminosity ratio is consistent with this result. Together with the X-ray data, XMM-Newton obtained UV images of NGC 1511, tracing massive stars heating the ambient gas, which is then seen in H\alpha emission. UV, H\alpha and near-infrared imagery suggest that NGC 1511 is disturbed, most likely by its two small companions, NGC 1511a and NGC 1511b.Comment: 7 pages, 7 figures, accepted for publication in A&

Innovative Composite Cold Formed Steel Floor System

Presented in this paper is a new, unique and innovative composite cold formed steel floor system developed by iSPAN Technologies, called the “iSPAN Composite Floor System”. The joist sections are fabricated by fastening two cold-rolled flange chord elements with cold-driven rivets to a flat web element. This makes it possible to create a section where the flange chord elements can be of a different steel thickness with respect to the web element, resulting in a most efficient structural cross section and numerous design alternatives. The joist sections have lip-reinforced web openings spaced at 4 ft o.c. along the joist length to accommodate the usual service items. The joists are typically spaced 4 ft o.c. with a 7/8 in. corrugated steel deck spanning between the joists to support the concrete during casting. Featured in this paper are the results from push-out tests that have been carried out to establish the interlocking capacity of the concrete with the top chord of the joist section. The results of a full-scale laboratory structural test are also presented to substantiate the calculated strength and stiffness characteristics. Finally, the results of a field test during construction are presented

On the Physical Origin of OVI Absorption-Line Systems

We present a unified analysis of the O{\sc vi} absorption-lines seen in the disk and halo of the Milky Way, high velocity clouds, the Magellanic Clouds, starburst galaxies, and the intergalactic medium. We show that these disparate systems define a simple relationship between the O{\sc vi} column density and absorption-line width that is independent of the Oxygen abundance over the range O/H $\sim$ 10% to twice solar. We show that this relation is exactly that predicted theoretically as a radiatively cooling flow of hot gas passes through the coronal temperature regime - independent of its density or metallicity (for O/H $\gtrsim$ 0.1 solar). Since most of the intregalactic O{\sc vi} clouds obey this relation, we infer that they can not have metallicities less than a few percent solar. In order to be able to cool radiatively in less than a Hubble time, the intergalactic clouds must be smaller than $\sim$1 Mpc in size. We show that the cooling column densities for the O{\sc iv}, O{\sc v}, Ne{\sc v}, and Ne{\sc vi} ions are comparable to those seen in O{\sc vi}. This is also true for the Li-like ions Ne{\sc viii}, Mg{\sc x}, and Si{\sc xii} (if the gas is cooling from $T \gtrsim 10^6$ K). All these ions have strong resonance lines in the extreme-ultraviolet spectral range, and would be accessible to $FUSE$ at $z \gtrsim$ 0.2 to 0.8. We also show that the Li-like ions can be used to probe radiatively cooling gas at temperatures an order-of-magnitude higher than where their ionic fraction peaks. We calculate that the H-like (He-like) O, Ne, Mg, Si, and S ions have cooling columns of $\sim10^{17}$ cm$^{-2}$. The O{\sc vii}, O{\sc viii}, and Ne{\sc ix} X-ray absorption-lines towards PKS 2155-304 may arise in radiatively cooling gas in the Galactic disk or halo.Comment: 25 pages, 5 figure

FUSE Observations of Outflowing OVI in the Dwarf Starburst Galaxy NGC1705

We report FUSE far-UV spectroscopy of the prototypical dwarf starburst galaxy NGC 1705. These data allow us for the first time to probe the coronal-phase gas (T = 10E5 to 10E6 K) that may dominate the radiative cooling of the supernova-heated ISM and thereby determine the dynamical evolution of starburst-driven outflows. We detect a broad (100 km/s) and blueshifted (by 80 km/s) OVI absorption-line arising in the previously-known galactic outflow. The properties of the OVI absorption are inconsistent with the standard superbubble model in which this gas arises in a conductive interface inside the outer shell. We show that the superbubble in NGC 1705 is blowing out of the galaxy ISM. During blow-out, coronal-phase gas can be created by hydrodynamical mixing as hot gas rushes out through fissures in the fragmenting shell of cool gas. As the coronal gas cools radiatively, it can naturally produce the observed OVI column density and outflow speed. The OVI data show that the cooling rate in the coronal-phase gas is less than about 10% of the supernova heating rate. Since the X-ray luminosity from hotter gas is even smaller, we conclude that radiative losses are insignificant. The outflow should be able to vent its metals and kinetic energy out of the galaxy. This process has potentially important implications for the evolution of dwarf galaxies and the IGM.Comment: ApJ (in press