The Origin of the Diffuse Hα in Spirals

Zurita, A.; Rozas, M.; Beckman, J. E.
Bibliographical reference

Astrophysics and Space Science, v. 276, Issue 2/4, p. 1015-1022 (2001).

Advertised on:
3
2001
Number of authors
3
IAC number of authors
3
Citations
3
Refereed citations
3
Description
Using high-quality H_α images of five spiral galaxies, we have studied the luminosity and distribution of the emission from diffuse ionized gas (DIG). The estimated DIG luminosities account for 25-60% of the total H_α emission in each galaxy and analysis of the distribution has shown that the DIG is highly correlated geometrically with the most luminous HII regions of the galaxies. The power required to ionize the DIG is very high. The mean ionization rates per unit surface area of a galaxy disc are of the order of 10^7 cm^-2 s^-1. Lyman continuum photons (Lyc) from OB asociations are the most probable sources of this ionization. Here we propose a specific model for these sources: we show that the Lyman photon flux that leaks out of the density-bounded HII regions of the galaxies is more than enough to ionize the measured DIG in the five galaxies analysed.