A&A 370, 868-874 (2001)
Search for the [CII] 158 micron emission toward the blue compact dwarf galaxy I Zw 36K. Mochizuki and T. Onaka
Department of Astronomy, University of Tokyo, Japan
(Received 2 August 2000 / Accepted 15 February 2001 )
We observed the blue compact dwarf galaxy I Zw 36 in the [CII] line with the Infrared Space Observatory obtaining an upper limit for the line flux, (). A comparison with previous CO observations yields an upper limit for the [CII]/CO J = 1-0 line flux ratio, (). This limit indicates that the [CII]/CO J = 1-0 line ratio in I Zw 36 is not higher than those in our Galactic plane ( ) and is at least one order of magnitude lower than those in irregular galaxies ( ) with low metallicities, in spite of the lower metallicity in I Zw 36 ( ) than in the irregulars. The observed difference in the line ratio between I Zw 36 and the irregulars can be accounted for by a higher gas density ( ) in I Zw 36, because the higher CO-formation rate at the higher density enables CO molecules to survive even against the photodissociation enhanced by the low dust abundance. The expected higher gas density in I Zw 36 may be related to change in large-scale gravitational potential with galactic evolution, if blue compact dwarfs and irregulars have evolutionary links.
Key words: ISM: clouds -- dust, extinction -- galaxies: abundances -- galaxies: dwarf -- galaxies: individual: I Zw 36 -- infrared: galaxies
Offprint request: K. Mochizuki, firstname.lastname@example.org
© ESO 2001