2001/09/06 by G. J. Madsen, R. J. Reynolds, L. M. Haffner +2 · 1 citation
Physics and Astronomy · #Andromeda Galaxy #Astronomy #Astrophysics #Astrophysics and Star Formation Studies #Flux (metallurgy) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Intergalactic medium #Intergalactic travel #Ionization #Line-of-sight #Lyman limit #Physics #Redshift #Scale height #Spiral galaxy #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/324313
To appear in ApJ Letters; 12 pages, 4 figures
arxiv created 2001/09/06 · openalex publication_date 2001/10/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We have used the Wisconsin H-Alpha Mapper to observe the spatially extended distribution of ionized hydrogen in M31 beyond the stellar disk. We obtained five sets of observations, centered near the photometric major axis of M31, that extend from the center of the galaxy to just off the edge of the southwestern H I disk. Beyond the bright stellar disk, but within the H I disk, weak Hα is detected with an intensity I Hα = 0.05 R. Since M31 is inclined 77° with respect to the line of sight, this implies that the ambient intergalactic ionizing flux on each side of M31 is Φ 0 ≤ 1.6 × 10 4 photons cm -2 s -1 . Just beyond the outer boundary of the H I disk, we find no significant detection of Hα and place an upper limit I Hα ≤ 0.019 R.