Observations of the Extended Distribution of Ionized Hydrogen in the Plane of M31

Abstract

We have used the Wisconsin H-Alpha Mapper (WHAM) 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 HI disk. Beyond the bright stellar disk, but within the HI disk, weak H-alpha is detected with an intensity I(H-alpha) = 0.05 (+0.01 / -0.02) Rayleighs. Since M31 is inclined 77 degrees with respect to the line of sight, this implies that the ambient intergalactic ionizing flux onto each side of M31 is Phi_0 <= 1.6 x 10^4 photons cm^-2 s^-1. Just beyond the outer boundary of the HI disk we find no significant detection of H-alpha and place an upper limit I(H-alpha) <= 0.019 Rayleighs.

To appear in ApJ Letters; 12 pages, 4 figures

References in corpus (2)

• Star Formation Thresholds in Galactic Disks
• Gas, Dust, and Young Stars in the Outer Disk of M 31

Cited by in corpus (16)

• A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy
• Atomic Hydrogen Gas in Dark-Matter Minihalos and the Compact High Velocity Clouds
• Fossil imprint of a powerful flare at the Galactic Centre along the Magellanic Stream
• Intergalactic Lyman continuum photon budget in the past 5 billion years
• A measurement of the z = 0 UV background from H$\alpha$ fluorescence
• WHAM Observations of H-alpha from High-Velocity Clouds: Are They Galactic or Extragalactic?
• A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies
• Are Compact High-Velocity Clouds Extragalactic Objects?
• An Investigation of Diffuse Interstellar Gas toward a Large, Low Extinction Window into the Inner Galaxy
• A new z=0 metagalactic UV background limit
• In search of cool flow accretion onto galaxies $-$ where does the disk gas end?
• The effects of an ionizing background on the HI column density distribution in the local Universe
• A Spectroscopic Study of the H-alpha Surface Brightness Profiles in the Outer Disks of Galaxies
• The Circumgalactic H$\alpha$ Spectrograph (CH$\alpha$S) I. Design, Engineering, and Early Commissioning
• MCMC determination of the cosmic UV background at $z\simeq 0$ from H$\alpha$ fluorescence
• The WHAM Northern Sky Survey and the Nature of the Warm Ionized Medium in the Galaxy