Adam Leroy et al. 2007 ApJ 663 990 doi:10.1086/518501
Adam Leroy1, John Cannon1,2, Fabian Walter1, Alberto Bolatto3 and Axel Weiss4
Show affiliationsWe present sensitive molecular line observations of the metal-poor blue compact dwarf I Zw 18 obtained with the IRAM Plateau de Bure interferometer. These data constrain the CO J = 1 → 0 luminosity within our 300 pc (FWHM) beam to be LCO < 1 × 105 K km s-1 pc2 (ICO < 1 K km s-1), an order of magnitude lower than previous limits. Although I Zw 18 is starbursting, it has a CO luminosity similar to or less than nearby low-mass irregulars (e.g., NGC 1569, the SMC, and NGC 6822). There is less CO in I Zw 18 relative to its B-band luminosity, H I mass, or star formation rate than in spiral or dwarf starburst galaxies (including the nearby dwarf starburst IC 10). Comparing the star formation rate to our CO upper limit reveals that unless molecular gas forms stars much more efficiently in I Zw 18 than in our own Galaxy, it must have a very low CO to H2 ratio, ~10-2 times the Galactic value. We detect 3 mm continuum emission, presumably due to thermal dust and free-free emission, toward the radio peak.
galaxies: dwarf; galaxies: individual (I Zw 18); galaxies: ISM; radio lines: ISM
Issue 2 (2007 July 10)
Received 2007 January 29, accepted for publication 2007 March 23
Adam Leroy et al. 2007 ApJ 663 990
D. A. Dale et al. 2007 ApJ 655 863
John M. Cannon and Evan D. Skillman 2004 ApJ 610 772
Henry Lee et al. 2006 ApJ 647 970
John M. Cannon et al. 2002 ApJ 565 931
Daniel R. Weisz et al 2009 ApJ 691 L59
John M. Cannon et al. 2004 ApJ 607 274
John M. Cannon et al 2005 ApJ 630 L37
Fabian Walter et al. 2007 ApJ 661 102
Dale C. Jackson et al. 2006 ApJ 646 192