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Updated: Dec 9, 2025

Investigation of Early Plasma Evolution Induced by Ultrashort Laser Pulses
Published on: July 2, 2012
Discovery of diffuse optical emission lines from the inner Galaxy: Evidence for LI(N)ER-like gas
D Krishnarao1, R A Benjamin2, L M Haffner3,4,1
1Department of Astronomy, University of Wisconsin-Madison, 475 N Charter St., Madison, WI 53706, USA.
Abstract:
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 Hβ λ4861 angstroms are also sometimes detected. The line ratios for most Tilted Disk sightlines are characteristic of LI(N)ER galaxies.
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