Photoionisation and Heating of a Supernova Driven, Turbulent, Interstellar Medium

The Diffuse Ionised Gas (DIG) in galaxies traces photoionisation feedback from massive stars. Through three dimensional photoionisation simulations, we study the propagation of ionising photons, photoionisation heating and the resulting distribution of ionised and neutral gas within snapshots of magnetohydrodynamic simulations of a supernova driven turbulent interstellar medium. We also investigate the impact of non-photoionisation heating on observed optical emission line ratios. Inclusion of a heating term which scales less steeply with electron density than photoionisation is required to produce diagnostic emission line ratios similar to those observed with the Wisconsin H{\alpha} Mapper. Once such heating terms have been included, we are also able to produce temperatures similar to those inferred from observations of the DIG, with temperatures increasing to above 15000 K at heights |z| > 1 kpc. We find that ionising photons travel through low density regions close to the midplane of the simulations, while travelling through diffuse low density regions at large heights. The majority of photons travel small distances (< 100pc); however some travel kiloparsecs and ionise the DIG.Comment: 10 pages, 13 figures, accepted to MNRA

Interstellar H-Alpha Line Profiles toward HD 93521 and the Lockman Window

We have used the Wisconsin H-Alpha Mapper (WHAM) facility to measure the interstellar H-Alpha emission toward the high Galactic latitude O star HD 93521 (l = 183.1, b = +62.2). Three emission components were detected having radial velocities of -10 km s^{-1}, -51 km s^{-1}, and -90 km s^{-1} with respect to the local standard of rest (LSR) and H-Alpha intensities of 0.20 R, 0.15 R, and 0.023 R, respectively, corresponding to emission measures of 0.55 cm^{-6} pc, 0.42 cm^{-6} pc, and 0.06 cm^{-6} pc. We have also detected an H-Alpha emission component at -1 km s^{-1} (LSR) with an intensity of 0.20 R (0.55 cm^{-6} pc) toward the direction l = 148.5, b = +53.0, which lies in the region of exceptionally low H I column density known as the Lockman Window. In addition, we studied the direction l = 163.5, b = +53.5. Upper limits on the possible intensity of Galactic emission toward this direction are 0.11 R at the LSR and 0.06 R at -50 km s^{-1}. We also detected and characterized twelve faint (~0.03-0.15 R), unidentified atmospheric lines present in WHAM H-Alpha spectra. Lastly, we have used WHAM to obtain [O I] 6300 spectra along the line of sight toward HD 93521. We place an upper limit of 0.060 R on the [O I] intensity of the -51 km s^{-1} component. If the temperature of the gas is 10,000 K within the H-Alpha emitting region, the hydrogen ionization fraction n(H+)/n(H_total) > 0.6.Comment: 23 pages, 4 figures. Acccepted for publication in the 1 Feb issue of The Astronomical Journa

No well-defined remnant Fermi surface in Sr2CuO2Cl2

In angle-resolved photoelectron spectra of the antiferromagnetic insulators Ca2CuO2Cl2 and Sr2CuO2Cl2 a sharp drop of the spectral intensity of the lowest-lying band is observed along a line in k space equivalent to the Fermi surface of the optimally doped high-temperature superconductors. This was interpreted as a signature of the existence of a remnant Fermi surface in the insulating phase of the high-temperature superconductors. In this paper it is shown that the drop of the spectral intensity is not related to the spectral function but is a consequence of the electron-photon matrix elementComment: 4 pages, 3 figure