Abstract by Rodrigo Herrera Camus
The blue compact dwarf galaxy I Zw18 is one of the most metal poor systems in the local Universe, with a nebular metallicity of 12 + log(O/H) = 7.2. Because of this, I Zw18 can provide crucial information about the relation between dust-to-gas mass ratio and metallicity in galaxies. In this work we use Spitzer MIPS observations at 70 and 160 micrometer combined with empirical fits from Muñoz-Mateos et al. (2009) to Draine et al. (2007) dust emission models to derive a dust mass upper limit for I Zw 18 of M_Dust = 3 * 10^4 solar masses and a upper limit to the dust-to-gas mass ratio of M_Dust / M_gas = 9.1 * 10^{-4} (3 sigma limits). This upper limit for the dust-to-gas mass ratio is similar to the Milky Way value after scaling by their respective metallicities, and suggests that a linear scaling law could be compatible with metal-poor systems. The upper limit to the dust mass is driven by the confusion limit of Spitzer at 160 micrometer, and we expect it to be significantly improved by future Herschel observations.
Relevant papers
"Dust in I Zw 18 from Hubble Space Telescope Narrowband Imaging" Cannon et al. 2002
"Dust in the Extremely Metal-Poor Blue Compact Dwarf Galaxy I Zw 18: The Spitzer Mid-infrared View" Wu et al. 2007
Talk slides
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What is the expected flux level at 160 microns? You have detections at shorter wavelengths and should be able to predict the 160 micron flux assuming a reasonable SED for the dust.
ReplyDeleteIs the upper limit of the dust mass consistent with the mass of the dust produced by the AGB stars and giants? Since the SF history has been determined, you know the number of these stars, and if you believe stellar evolution and wind models, you can calculate the mass of the released dust.
ReplyDeleteDear Claus,
ReplyDeleteif we assume that the dust mass of I Zw 18 is the one estimated by Cannon et al. 2002 using Ha/Hb as a dust tracer, Mdust ~ 7e3 and based on the fits to the Draine & Li models, we would expect a flux of about 25mJy @ 160 microns. This flux is about half the value of our upper limit.