H{alpha} AND FREE-FREE EMISSION FROM THE WARM IONIZED MEDIUM

Journal Article · Thu Jan 20 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/727/1/35· OSTI ID:21567611

Ruobing, Dong; Draine, B T ^[1]

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1. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)

Recent observations have found the ratio of H{alpha} to free-free radio continuum to be surprisingly high in the diffuse ionized interstellar medium (the so-called warm ionized medium), corresponding to an electron temperature of only {approx}3000 K. Such low temperatures were unexpected in gas that was presumed to be photoionized. We consider a three-component model for the observed diffuse emission, consisting of a mix of (1) photoionized gas, (2) gas that is recombining and cooling, and (3) cool H I gas. This model can successfully reproduce the observed intensities of free-free continuum, H{alpha}, and collisionally excited lines such as [N II]6583. To reproduce the low observed value of free-free to H{alpha}, the polycyclic aromatic hydrocarbon abundance in the photoionized regions must be lowered by a factor {approx}3, and {approx}20% of the diffuse H{alpha} must be reflected from dust grains, as suggested by Wood and Reynolds.

• OSTI ID: 21567611
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 727; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
AROMATICS
BALMER LINES
ELECTRON TEMPERATURE
EMISSION
HYDROCARBONS
INTERSTELLAR SPACE
IONIZATION
MATTER
ORGANIC COMPOUNDS
PHOTOIONIZATION
POLYCYCLIC AROMATIC HYDROCARBONS
SPACE