Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas.

Optical emission lines are used to categorize galaxies into three groups according to their dominant central radiation source: active galactic nuclei, star formation, or low-ionization (nuclear) emission regions [LI(N)ERs] that may trace ionizing radiation from older stellar populations. Using the Wisconsin H-Alpha Mapper, we detect optical line emission in low-extinction windows within eight degrees of Galactic Center. The emission is associated with the 1.5-kiloparsec-radius "Tilted Disk" of neutral gas. We modify a model of this disk and find that the hydrogen gas observed is at least 48% ionized. The ratio [NII] λ6584 angstroms/Hα λ6563 angstroms increases from 0.3 to 2.5 with Galactocentric radius; [OIII] λ5007 angstroms and Hß λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.

Synthesis of Plasmonic Group-4 Nitride Nanocrystals by Solid-State Metathesis.

Ceramic nanoparticles that exhibit a plasmonic response are promising next-generation photonic materials. In this contribution, a solid-state metathesis method has been reported for the synthesis of Group 4 nitride (TiN, ZrN, and HfN) nanocrystals. A high-temperature (1000 °C) reaction between Group 4 metal oxide (TiO2 , ZrO2 , and HfO2 ) nanoparticles and magnesium nitride powder yielded nitride nanocrystals that were dispersible in water. A localized surface plasmonic resonance was observed in the near-infrared region for TiN and in the visible region of light for ZrN and HfN nanocrystals. The frequency of the plasmon resonance was dependent on the refractive index of the solvent and the nanocrystal size.